applications of free living plant growth-promoting rhizobacteria

Applications of free living plant growth-promoting rhizobacteria

M.Lucy,E.Reed and Bernard R.Glick *

Department of Biology,University of Waterloo,Waterloo,Ontario,Canada,N2L 3G1;*Author for

correspondence (e-mail:glick@sciborg.uwaterloo.ca;phone:(519)888-4567ext.5208;fax:(519)746-0614)

Received 4June 2003;accepted in revised form 30October 2003

teria

Abstract

Free-living plant growth-promoting rhizobacteria ?PGPR ?can be used in a variety of ways when plant growth enhancements are required.The most intensively researched use of PGPR has been in agriculture and horticul-ture.Several PGPR formulations are currently available as commercial products for agricultural production.Re-cently developing areas of PGPR usage include forest regeneration and phytoremediation of contaminated soils.As the mechanisms of plant growth promotion by these bacteria are unravelled,the possibility of more efficient plant-bacteria pairings for novel and practical uses will follow.The progress to date in using PGPR in a variety of applications with different plants is summarized and discussed here.

Introduction

New and novel solutions for plant growth enhance-ments are required to ease the burden imposed on our environment and other resources.Here we look at potential solutions to these issues by examining some of the research conducted regarding the biological applications of free-living plant growth promoting rhizobacteria ?PGPR ?.The major applications of bac-teria for improved plant growth include agriculture,horticulture,forestry and environmental restoration.This review presents an overview of information available on these various applications.

Indirect mechanisms used by PGPR include antibi-otic protection against pathogenic bacteria,reduction of iron available to phytopathogens in the rhizo-sphere,synthesis of fungal cell wall-lysing enzymes,and competition with detrimental microorganisms for sites on plant roots.Direct mechanisms of plant growth by PGPR include the provision of bioavail-able phosphorus for plant uptake,nitrogen ?xation for plant use,sequestration of iron for plants by sidero-phores,production of plant hormones like auxins,cy-

tokinins and gibberellins,and lowering of plant ethylene levels ?Glick 1995;Glick et al.1999?.Applications of PGPR in Agriculture

The most intensively studied application for free liv-ing PGPR is agriculture.Researchers in the former Soviet Union and India conducted widespread tests in the early to the mid part of the 20th century studying the effects of PGPR on different crops.Though results from different experiments were not harmonized and were often inconsistent,up to 50to 70%yield increases were reported.Inconsistency of results was due to a lack of quality in experimental design and analysis of results ?Brown 1974;Cooper 1959?.Moreover,during this time an understanding of the detailed mechanisms of plant growth promotion by rhizobacteria was largely unknown.Nevertheless,these ?eld experiments provided clues concerning the optimal conditions for bacterial colonization and growth promotion of target crops ?Brown 1974?.The results of many studies of the effect of free-living rhizobacteria on various crop plants,

conducted

Antonie van Leeuwenhoek 86: 1–25, 2004.

?2004Kluwer Academic Publishers.Printed in the Netherlands.

1

Key Review article

words:Agriculture,Forestry,Horticulture,Inoculants,Phytoremediation,Plant growth promoting rhizobac-

over approximately the last twenty-?ve years,are

summarized in Table1.Plant growth bene?ts due to

the addition of PGPR include increases in germina-

tion rates,root growth,yield?including grain?,leaf

area,chlorophyll content,magnesium content,nitro-

gen content,protein content,hydraulic activity,toler-

ance to drought,shoot and root weights,and delayed

leaf senescence.Another major bene?t of PGPR use

is disease resistance conferred to the plant,sometimes

known as‘biocontrol’.

The use of PGPR to increase crop yield has been

limited due to the variability and inconsistency of re-

sults between laboratory,greenhouse and?eld stud-

ies?Mishustin and Naumova1962?.Soil is an

unpredictable environment and an intended result is

sometimes difficult to obtain?Bashan1998?.For ex-

ample,in a study by Frommel et al.?1993?,poor col-

onization of the PGPR on plant roots occurred at one

site due to adverse conditions,including high Verti-

cillum infection of the soil,low soil pH,high mean temperature and low rainfall during the growing sea-

son.These undesirable growing conditions most

likely contributed to the low root colonization?Dob-

belaere et al.2001;Klein et al.1990;Parke1991;

Suslow and Schroth1982?.Climatic variability also

has a large impact on the effectiveness of PGPR ?Okon and Labandera-Gonzalez1994?but sometimes unfavourable growth conditions in the?eld are to be

expected as a normal functioning of agriculture.In-

creased yields obtained with wheat inoculated by

Pseudomonas species in the growth chamber have also been observed in the?eld?Weller and Cook 1986?.Even though there is a possibility of great variability in?eld results,if a positive effect of a PGPR is seen on a speci?c crop in greenhouse stud-ies,there is a strong likelihood that those bene?ts will carry through to?eld conditions.

There is a great deal of contradictory information

on the effectiveness of PGPR on plants in soils under

various conditions of fertilization,especially with

Azospirillum species.In the past,the main mechanism of plant growth promotion by Azospirillum was thought to occur by providing the plant with?xed ni-trogen.In fact,it has been reported that the plant growth promotion effect of Azospirillum only occurs in nitrogen-limited conditions?Dobbelaere et al. 2001;Fallik and Okon1996?.However,in other cases,much greater increases in plant growth promo-tion have been observed after the addition of fertiliz-ers?Okon and Labandera-Gonzalez1994?.Another way in which Azospirillum species improve plant growth is through the production of indole acetic acid ?IAA?,a plant hormone?Dobbelaere et al.1999; Okon and Labandera-Gonzalez1994?.

Different soil types can in?uence the effectiveness of PGPR?e.g.,Kloepper et al.1980?.In a study with wheat and a pseudomonad,results suggested that the less fertile the soil,the greater the plant growth stim-ulation by the PGPR?De Freitas and Germida1990?. This is similar to observations in studies conducted with Azospirillum species,despite the fact that pseudomonads?x little or no nitrogen.On the other hand,growth promotion of maize with a strain of Azospirillum lipoferum has been reported to be inde-pendent of cultivar or soil type in the?eld?Fages 1994?.When choosing an effective PGPR for a plant at a speci?c site,it is imperative to consider the nu-trient level in the soil and how the intended PGPR would perform at that location.

Soil moisture content affects the colonization of the plant rhizosphere by the PGPR after inoculation?Burr et al.1978?.Studies in the Soviet Union suggested that optimum results were obtained when the soil moisture was40%?Brown1974;Cooper1959?. However,this may be a function of the type of bac-terium utilized since high moisture content may de-crease the oxygen content of the soil.

In some instances,speci?c strains of bacteria may promote bacterial growth only in certain crops.In one example,it was found that out of four Pseudomonas strains that promoted the growth of radish,only one was effective in promoting the growth of potato ?Kloepper et al.1980?.It has also been observed that maximum increases in germination and yield often occur in crops inoculated with PGPR strains isolated from the plants native rhizosphere?Fages and Arsac 1991;Favilli et al.1987?.

During the initial stages of testing in the laboratory, PGPR survival in a microcosm of the?eld environ-ment should be determined.This is to ensure that any manipulations conducted on the bacteria are not det-rimental to their growth promotion effect and their competitiveness in the?eld?Tang et al.1995?.In the ?eld,the number of PGPR cells applied to the plant is often vital for proper growth promotion?Boddey and Dobereiner1988?.Many researchers?Table1?have applied up to108colony forming units?CFU?per seed?De Freitas and Germida1991;Di Ciocco and Rodriguez-Caceres1994;Fages1994;Okon et al. 1988;Tran Van et al.2000;Weller and Cook1986?or up to109CFU/g of inoculant?Barrios et al.1984; De Freitas and Germida1990a,1990b;Fallik and

2

T a b l e 1.E x a m p l e s o f f r e e -l i v i n g p l a n t g r o w t h p r o m o t i n g r h i z o b a c t e r i a t e s t e d o n v a r i o u s c r o p t y p e s

B a c t e r i a P l a n t

C o n d i t i o n s

R e s u l t s o f a d d i t i o n o f b a c t e r i a t o p l a n t R e f e r e n c e

A z o s p i r i l l u m ?l o c a l i s o l a t e s f r o m A r g e n t i n a ?W h e a t ,M a i z e

F i e l d

–i n w h e a t c u l t i v a r s o v e r s e v e n s e a s o n s ,i n c r e a s e s o f y i e l d f r o m 15t o 30%,a n d i n c r e a s e s i n y i e l d o f 50-60%w h e n f e r t i l i z e d –o v e r s i x s e a s o n s ,i n c r e a s e s o f m a i z e y i e l d f r o m 15t o 25%o b s e r v e d ,a n d w i t h f e r t i l i z a t i o n ,y i e l d i n c r e a s e d u p t o 40%

O k o n a n d L a b a n d e r a -G o n z a -l e z 1994A z o s p i r i l l u m b r a s i l e n s e

G u i n e a g r a s s P e a r l m i l l e t ,D i g i t a r i a d e c u m b e n s

F i e l d

–g r e a t e r d r y m a t t e r y i e l d c o m p a r e d t o u n i n o c u l a t e d c o n -t r o l s –a p p r o x i m a t e l y 40k g /h a p e r y e a r o f n i t r o g e n e s t i m a t e d a s s a v e d d u e t o i n o c u l a t i o n

S m i t h e t a l .1978

A z o s p i r i l l u m b r a s i l e n s e

F i n g e r m i l l e t ,S o r g h u m ,P e a r l m i l l e t

F i e l d

–a v e r a g e o f u p t o 15%y i e l d i n c r e a s e f o r ?n g e r m i l l e t –f o r s o r g h u m ,a v e r a g e i n c r e a s e i s 19%–i n t e n y e a r s o f s t u d y ,A z o s p i r i l l u m s u c c e s s f u l i n s i g n i ?-c a n t l y i n c r e a s i n g y i e l d i n 60%o f t r i a l s R a o 1986

A z o s p i r i l l u m b r a s i l e n s e S o r g h u m

H y d r o p o n i c s y s t e m i n g r e e n -h o u s e –s i g n i ?c a n t i n c r e a s e s i n d r y m a t t e r ,l e a f a r e a a n d g r a i n y i e l d a f t e r f o u r w e e k s –l e a f s e n e s c e n c e d e l a y e d

S a r i g e t a l .1990

A z o s p i r i l l u m b r a s i l e n s e S o r g h u m G r e e n h o u s e –i n c r e a s e d t o t a l n u m b e r a n d l e n g t h o f a d v e n t i t i o u s r o o t s b y 33t o 40%a n d i n c r e a s e d h y d r a u l i c c o n d u c t i v i t y b y 25-40%

S a r i g e t a l .1992

A z o s p i r i l l u m b r a s i l e n s e

B e a n H y d r o p o n i c g r o w t h c h a m b e r –i n c r e a s e d f r e s h r o o t a n d s h o o t w e i g h t s

V e d d e r -W e i s s e t a l .1999

A z o s p i r i l l u m b r a s i l e n s e

S o r g h u m ,W h e a t ,B a r l e y

F i e l d ?t e s t e d o n o v e r 200,000h a ?

–c o n s i s t e n t p o s i t i v e e f f e c t s w i t h u p t o 26%i n c r e a s e o f y i e l d –b e s t r e s u l t s s e e n i n l i g h t s a n d y s o i l s w i t h i n t e r m e d i a t e a m o u n t s o f f e r t i l i z e r s

D o b b e l a e r e e t a l .2001

A z o s p i r i l l u m b r a s i l e n s e C d

F o u n t a i n g r a s s S o r g h u m S u d a n g r a s s

F i e l d –i n c r e a s e s i n y i e l d o f 11t o 24%a t o n e l o c a t i o n

S m i t h e t a l .1984

A z o s p i r i l l u m b r a s i l e n s e C d

M a i z e ,M i l l e t S o r g h u m ,W h e a t

F i e l d

–s u m m e r c r o p s s h o w s i g n i ?c a n t y i e l d i n c r e a s e s i n 75%o f t r i a l p l o t s ,w h i l e w i n t e r c r o p s o n l y h a v e s i g n i ?c a n t y i e l d i n c r e a s e s i n 5-12%o f t r i a l s

O k o n e t a l .19883

T a b l e 1.C o n t i n u e d .

B a c t e r i a P l a n t

C o n d i t i o n s

R e s u l t s o f a d d i t i o n o f b a c t e r i a t o p l a n t R e f e r e n c e

A z o s p i r i l l u m b r a s i l e n s e C d A z o s p i r i l l u m l i p o r f e r u m

B r -17

M a i z e

F i e l d –c o n s i s t e n t i n c r e a s e s o f y i e l d a t i n t e r m e d i a t e s o i l f e r t i l i t y –r e p l a c e s 35-40%o f n i t r o g e n f e r t i l i z e r s O k o n a n d L a b a n d e r a -

G o n z a -l e z 1994A z o s p i r i l l u m b r a s i l e n s e C d M a i z e

F i e l d –s i g n i ?c a n t i n c r e a s e i n t h e n u m b e r o f a d v e n t i t i o u s r o o t s ,r o o t l e n g t h ,r o o t a n d s h o o t d r y w e i g h t i n t h r e e d i f f e r e n t r e g i o n s

D o b b e l a e r e e t a l .2001

A z o s p i r i l l u m b r a s i l e n s e C d

C h i c k p e a s ,F a b a b e a n s

G r e e n h o u s e a n d ?e l d

–s i g n i ?c a n t i n c r e a s e s i n r o o t n o d u l a t i o n b y n a t i v e r h i z o -b i a a n d i m p r o v e d r o o t a n d s h o o t d e v e l o p m e n t –w h e n i r r i g a t e d b y s a l i n e w a t e r ,i n o c u l a t e d p l a n t s a r e n o t a s n e g a t i v e l y a f f e c t e d c o m p a r e d t o c o n t r o l –?e l d r e s u l t s s h o w a s i g n i ?c a n t i n c r e a s e i n s h o o t g r o w t h a n d c r o p y i e l d H a m a o u i e t a l .2001

A z o s p i r i l l u m b r a s i l e n s e C d ,245

O a t ,M a i z e ,S o r g h u m

G r e e n h o u s e a n d ?e l d

–p o s i t i v e i n c r e a s e s i n m a i z e a n d s o r g h u m b i o m a s s i n b o t h ?e l d a n d g r e e n h o u s e ,b u t n o t s t a t i s t i c a l l y s i g n i ?c a n t –s i g n i ?c a n t i n c r e a s e o f b i o m a s s o f o a t f o r o n e y e a r ’s ?e l d t e s t b u t n o t f o r t h e s e c o n d y e a r

D o b b e l a e r e e t a l .2001A z o s p i r i l l u m b r a s i l e n s e C d ,A z -39A z o s p i r i l l u m l i p o f e r u m A z -30

M i l l e t F i e l d

–i n c r e a s e d y i e l d u p t o 30%a n d 21%i n t w o y e a r s o f p l a n t g r o w t h D i C i o c c o a n d R o d r i g u e z -C a c e r e s 1994

A z o s p i r i l l u m b r a s i l e n s e C d ,A z -39

W h e a t F i e l d

–p l a n t y i e l d i n c r e a s e d ,e s p e c i a l l y w i t h A z -29C a c e r e s e t a l .1996

A z o s p i r i l l u m b r a s i l e n s e N O 40

R i c e F i e l d –i n c r e a s e d y i e l d b y 15-20%i n t w o l o c a t i o n s O m a r e t a l .1989

A z o s p i r i l l u m b r a s i l e n s e S p 245A z o s p i r i l l u m i r a k e n s e K

B

C l

W i n t e r w h e a t ,M a i z e

F i e l d

–p l a n t g r o w t h p r o m o t i o n e f f e c t d i s a p p e a r e d w h e n p l a n t s o v e r f e r t i l i z e d w i t h n i t r o g e n –i n p l o t s w i t h l o w n i t r o g e n ,h i g h e r y i e l d s n o t o b t a i n e d ,l i k e l y d u e t o a d v e r s e w e a t h e r c o n d i t i o n s a t t e s t p l o t s

D o b b e l a e r e e t a l .2001

A z o s p i r i l l u m b r a s i l e n s e S p -111

W h e a t F i e l d

–y i e l d i n c r e a s e s o f 1.3t o 2f o l d o v e r t h e ?v e y e a r s t u d y –v a r i a b l e r e s u l t s d u e t o c l i m a c t i c c o n d i t i o n s

O k o n a n d L a b a n d e r a -G o n z a -l e z 1994

4

T a b l e 1.C o n t i n u e d .

B a c t e r i a P l a n t

C o n d i t i o n s

R e s u l t s o f a d d i t i o n o f b a c t e r i a t o p l a n t R e f e r e n c e

A z o s p i r i l l u m b r a s i l e n s e S p -245,S p -107s t

W h e a t

F i e l d –s i g n i ?c a n t i n c r e a s e s o f g r a i n y i e l d a n d p l a n t n i t r o g e n c o n t e n t –s t r a i n S p -245m o s t e f f e c t i v e o n w h e a t

B o d d e y a n d D o b e r e i n e r 1988A z o s p i r i l l u m l i p o f e r u m S u n ?o w e r G r e e n h o u s e

–s t r a i n s o r i g i n a l l y s e l e c t e d f r o m p l a n t r h i z o s p h e r e –p o s i t i v e g r o w t h r e s p o n s e s w i t h r e s p e c t t o g e r m i n a t i o n

F a g e s a n d A r s a c 1991

A z o s p i r i l l u m l i p o f e r u m C R T 1M a i z e F i e l d

–g r o w t h p r o m o t i o n e f f e c t o c c u r r e d e a r l y ,d e s p i t e r a p i d d e c r e a s e o f b a c t e r i a l d e n s i t y o f i n t r o d u c e d b a c t e r i a –p l a n t h e i g h t ,p r i m a r y r o o t l e n g t h a n d r o o t f r e s h w e i g h t a l l e n h a n c e d b y t h e a d d i t i o n o f t h e b a c t e r i a

J a c o u d e t a l .1998

A z o s p i r i l l u m l i p o f e r u m C R T 1M a i z e F i e l d –a v e r a g e g r a i n y i e l d s a n d N c o n t e n t h i g h e r f o r t h e i n o c u -l a t e d p l a n t s ,b u t n o t s t a t i s t i c a l l y s i g n i ?c a n t –l a r g e r r o o t s y s t e m s ,a n d l o w e r g r a i n m o i s t u r e m e a s u r e d

D o b b e l a e r e e t a l .2001

A z o s p i r i l l u m l i p o f e r u m C R T -1

M a i z e F i e l d –p o s i t i v e r e s p o n s e o f y i e l d t o i n o c u l a t i o n r e g a r d l e s s o f c u l t i v a r o r s o i l t y p e

F a g e s 1994

A z o s p i r i l l u m s p .M a i z e F i e l d

–i n c r e a s e d y i e l d o f 6.7t o 75.1%

K a p u l n i k e t a l .1981

A z o s p i r i l l u m s p .W h e a t

F i e l d

–c h a n g e s i n y i e l d o f ?9.6t o 14.8%

R e y n d e r s a n d V l a s s a k 1982

A z o s p i r i l l u m s p .W h e a t

F i e l d

–c h a n g e s i n y i e l d o f ?15.8t o 31%

B a l d a n i e t a l .1987

A z o s p i r i l l u m s p .M i l l e t

F i e l d

–c h a n g e s i n y i e l d o f ?12.1t o 31.7%

K l o e p p e r e t a l .1989

A z o s p i r i l l u m s p .M u s t a r d

F i e l d

–i n c r e a s e d y i e l d o f 16t o 128%

K l o e p p e r e t a l .1989

A z o s p i r i l l u m s p .R i c e

F i e l d

–i n c r e a s e d y i e l d o f 4.9t o 15.5%

K l o e p p e r e t a l .1989

A z o s p i r i l l u m s p .M a i z e

F i e l d

–s i g n i ?c a n t i n c r e a s e s i n y i e l d i n l i g h t s o i l s a n d a t i n t e r -m e d i a t e n i t r o g e n f e r t i l i z a t i o n –i n ?e l d s w i t h n o n i t r o g e n f e r t i l i z a t i o n ,a d e ?n i t e y i e l d i n c r e a s e o v e r u n i n o c u l a t e d p l a n t s ,b u t n o t s t a t i s t i c a l l y s i g -n i ?c a n t –i n ?e l d s w i t h h i g h n i t r o g e n f e r t i l i z a t i o n ,n o g r o w t h e n -h a n c e m e n t e f f e c t

O k o n a n d L a b a n d e r a -G o n z a -l e z 1994

5

T a b l e 1.C o n t i n u e d .

B a c t e r i a P l a n t

C o n d i t i o n s

R e s u l t s o f a d d i t i o n o f b a c t e r i a t o p l a n t R e f e r e n c e

A z o s p i r i l l u m s p .M a i z e

F i e l d –n o e f f e c t o f i n o c u l a t i o n o n p l a n t y i e l d s w h e n s o i l s a r e h e a v y a n d h i g h i n n i t r o g e n c o n t e n t –i n l i g h t s o i l s l o w i n n i t r o g e n f e r t i l i z a t i o n ,y i e l d i n c r e a s e o f 11-14%

F a l l i k a n d O k o n 1996A z o s p i r i l l u m s p .

S o r g h u m F i e l d

–i n c r e a s e d y i e l d o f 20.5t o 30.5%

K a p u l n i k e t a l .1997

A z o s p i r i l l u m s p .M a i z e

F i e l d

–s i g n i ?c a n t i n c r e a s e i n d r y m a t t e r y i e l d –i n c r e a s e d m a g n e s i u m p e r c e n t a g e

H e r n a n d e z e t a l .1997A z o s p i r i l l u m s p .

S o r g h u m F i e l d –i n c r e a s e d y i e l d o f 12t o 18.5%

S a r i g e t a l .1998

A z o s p i r i l l u m s p .M a i z e

G r e e n h o u s e

–i n c r e a s e d a c t i v i t y o f g l u t a m a t e d e h y d r o g e n a s e a n d g l u t a m i n e s y n t h e t a s e –i n c r e a s e d N c o n t e n t i n l e a v e s a n d r o o t s

R i b a u d o e t a l .2001

A z o s p i r i l l u m s p .W h e a t G r e e n h o u s e –h i g h e r b i o m a s s ,g r a i n y i e l d ,p r o t e i n c o n t e n t a n d p l a n t n i t r o g e n c o n t e n t –c o n c l u d e d t h a t n i t r o g e n u p t a k e i s t h e m e c h a n i s m o f p l a n t g r o w t h p r o m o t i o n i n t h i s c a s e

S a u b i d e t e t a l .2002

A z o t o b a c t e r c h r o o c o c c u m

B a r l e y G r o w t h c h a m b e r a s s a y s

–i n c r e a s e o f s e e d g e r m i n a t i o n a n d s e e d l i n g d e v e l o p m e n t –n o c h a n g e i n t h e n u m b e r o f s e e d s g e r m i n a t e d ,b u t i n -c r e a s e s e e n i n t h e e x t e n s i o n o f t h e g r o w i n g r o o t –a d d i t i o n o f n i t r a t e d e c r e a s e s p l a n t s t i m u l a t i o n e f f e c t –s o m e i n c o n s i s t e n t r e s u l t s s e e n ,a n d a u t h o r s c o n c l u d e t h a t A z o t o b a c t e r i s n o t a r e l i a b l e i n o c u l a n t

H a r p e r a n d L y n c h 1979A z o t o b a c t e r s p .B a c i l l u s s p .E n t e r o b a c t e r s p .X a n t h o b a c t e r s p .

R i c e F i e l d

–i n c r e a s e s o f t o t a l d r y m a t t e r y i e l d ,g r a i n y i e l d ,a n d n i t r o -g e n a c c u m u l a t i o n b y 6t o 24%o v e r t w o y e a r s o f s t u d y –h y p o t h e s i s e d t h a t y i e l d i n c r e a s e s d u e t o i n c r e a s e i n r o o t l e n g t h ,l e a f a r e a a n d c h l o r o p h y l l c o n t e n t

A l a m e t a l .2001

B a c i l l u s a m y l i q u e f a c i e n s

I N 937B a c i l l u s p u m i l i s I N R 7,S E 34B a c i l l u s s u b t i l i s G B 03B a c i l l u s

c e r e u s C 4

T o m a t o ,P e p p e r

F i e l d

–s t a t i s t i c a l l y s i g n i ?c a n t i n c r e a s e s o f p l a n t g r o w t h i n t w o g r o w i n g y e a r s i n s t e m d i a m e t e r ,s t e m a r e a ,l e a f s u r f a c e a r e a ,w e i g h t s o f r o o t s a n d s h o o t s a n d n u m b e r o f l e a v e s –t r a n s p l a n t v i g o u r a n d f r u i t y i e l d i m p r o v e d –p a t h o g e n n u m b e r s a n d d i s e a s e n o t r e d u c e d i n t o m a t o e s o r p e p p e r w i t h t h e e x c e p t i o n o f r e d u c t i o n o f g a l l i n g i n p e p p e r b y r o o t -k n o t n e m a t o d e

K o k a l i s -B u r e l l e e t a l .2002

6

T a b l e 1.C o n t i n u e d .

B a c t e r i a P l a n t

C o n d i t i o n s

R e s u l t s o f a d d i t i o n o f b a c t e r i a t o p l a n t R e f e r e n c e

B a c i l l u s p o l y m y x a W h e a t

F i e l d

–i n c r e a s e s i n p l a n t y i e l d C a c e r e s e t a l .1996B a c i l l u s p o l y m y x a B u r k h o l d e r i a s p .P s e u d o m o n a s s p .

S u g a r b e e t

F i e l d –s i g n i ?c a n t i n c r e a s e s i n r o o t y i e l d ?6.1t o 13.0%?,s u g a r y i e l d ?2.3t o 7.8%?–y i e l d s f u r t h e r e n h a n c e d b y N ,P a n d N P a p p l i c a t i o n s

C a k m a k c i e t a l .2001B a c i l l u s s p .S o r g h u m

F i e l d

–i n c r e a s e d y i e l d o f 15.3t o 33%

B r o a d b e n t e t a l .1977

B a c i l l u s s p .W h e a t

F i e l d

–c h a n g e s i n y i e l d o f 0t o 114%

K l o e p p e r e t a l .1977

B a c i l l u s s u b t i l i s A -13P e a n u t

F i e l d

–y i e l d i n c r e a s e s u p t o 37%;o n l y t w o o f 24t e s t s i t e s p r o -d u c e d n e g a t i v e r e s u l t s –p l a n t r e s p o n s e s m o s t p o s i t i v e w h e n s u b j e c t e d t o s t r e s s l i k e l i m i t e d w a t e r ,p o o r n u t r i t i o n ,c o l d t e m p e r a t u r e s –p l a n t d i s e a s e r e d u c e d

T u r n e r a n d B a c k m a n 1991

B a c i l l u s s u b t i l i s B 2O n i o n G r o w t h c h a m b e r –s i g n i ?c a n t i n c r e a s e s i n s h o o t d r y w e i g h t ?12-94%?,d r y r o o t w e i g h t ?13-100%?a n d s h o o t h e i g h t ?12-40%?o v e r c o n t r o l s –r h i z o s p h e r e p o p u l a t i o n s o f i n o c u l a t e d b a c t e r i a d e c r e a s e d t h r o u g h o u t s t u d y ,b u t g r o w t h p r o m o t i o n e f f e c t s t i l l o b -s e r v e d

R e d d y a n d R a h e 1989

B e i j e r i n c k i a m o b i l i s

C l o s t r i d i u m s p .

B e e t ,B a r l e y ,W h e a t ,R e d r a d i s h ,

C u c u m b e r

L a b e x p e r i m e n t s a n d g r e e n -h o u s e

–i n c o m b i n a t i o n w i t h m i n e r a l f e r t i l i z e r s ,i n c r e a s e o f p l a n t p r o d u c t i o n b y 1.5t o 2.5t i m e s –p o s i t i v e i n c r e a s e s s e e n w i t h s e e d g e r m i n a t i o n r a t e ,m e a n p l a n t l e n g t h a n d p l a n t w e i g h t –d i f f e r e n t c u c u m b e r c u l t i v a r s d e m o n s t r a t e d v a r i a b i l i t y i n s e e d g e r m i n a t i o n r e s p o n s e

P o l y a n s k a y a e t a l .2000B u r k h o l d e r i a v i e t n a m i e n s i s T V V 75

R i c e O u t d o o r p o t a n d ?e l d t r i a l s

–w h e n p l a n t s i n o c u l a t e d a n d t r a n s p l a n t e d a t d a y 24,i n -c r e a s e s o f s h o o t w e i g h t ?u p t o 33%?,r o o t w e i g h t ?u p t o 55%?a n d l e a f s u r f a c e ?u p t o 30%?o b s e r v e d –e n d g r a i n y i e l d i n c r e a s e o f 13-22%–g r a i n w e i g h t ?a l a t e -s e a s o n y i e l d c o m p o n e n t ?s i g n i ?-c a n t l y i n c r e a s e d d u e t o i n o c u l a t i o n ,b u t n o t d u e t o t h e a d -d i t i o n o f n i t r o g e n

T r a n V a n e t a l .2000

E n t e r o b a c t e r c l o a c a e C A L 3

T o m a t o ,P e p p e r ,M u n g b e a n

G r e e n h o u s e –p o s i t i v e s e e d l i n g g r o w t h r e s p o n s e b y a l l t h r e e p l a n t s p e -c i e s t o P G P R t r e a t m e n t ,e s p e c i a l l y t o m a t o ,w h e r e n o e x o -g e n o u s m i n e r a l n u t r i e n t s a d d e d –e a r l y s t i m u l a t i o n e f f e c t o n s e e d l i n g s o b s e r v e d

M a y a k e t a l .2001

7

T a b l e 1.C o n t i n u e d .

B a c t e r i a P l a n t

C o n d i t i o n s

R e s u l t s o f a d d i t i o n o f b a c t e r i a t o p l a n t R e f e r e n c e

N o n -?u o r e s c e n t p s e u d o m o n a d i s o l a t e d f r o m o n i o n r h i z o s h p e r e

P o t a t o

G r o w t h c h a m b e r –p l a n t l e t s s h o w e d s i g n i ?c a n t i n c r e a s e s i n r o o t d r y w e i g h t o f 44t o 201%,s t e m l e n g t h 26t o 28%,l i g n i n u p t o 43%,a n d e n h a n c e d s t e m h a i r f o r m a t i o n 55t o 110%F r o m m e l e t a l .1991

O T H E R S p e c i e s a n d M i x -t u r e s

P s e u d o m o n a d s s p p .??u o r e s -c e n t s t r a i n s ?

W i n t e r w h e a t

F i e l d –b i o c o n t r o l e f f e c t s s e e n a g a i n s t t a k e a l l ?

G a e u m a n n o m y -c e s g r a m i n i s ?,27%y i e l d i n c r e a s e d u e t o i n o c u l a t i o n D e F r e i t a s a n d G e r m i d a 1990

P s e u d o m o n a s c e p a c i a P s e u d o m o n a s ?u o r e s c e n s P s e u d o m o n a s p u t i d a

W i n t e r w h e a t

P o t t e d p l a n t s i n g r o w t h c h a m b e r

–s t r a i n s d e m o n s t r a t e b i o c o n t r o l a g a i n s t R h i z o c t o n i a s o l a n i a n d L e p t o s p h a e r a m a c u l a n s –d i f f e r e n t s t r a i n s s t i m u l a t e d i f f e r e n t p l a n t p a r t s –g r o w t h o f p l a n t s i n l e s s f e r t i l e s o i l s t i m u l a t e d

D e F r e i t a s a n d G e r m i d a 1990P s e u d o m o n a s c e p a c i a M R 85,R 85P s e u d o m o n a s p u t i d a M R 111,R 105

W i n t e r w h e a t F i e l d

–b a c t e r i a i n o c u l a t e d o n p l a n t s a b l e t o o v e r w i n t e r o n r o o t s a n d s u r v i v e ;w i t h l e v e l s r e a c h i n g 104t o 108C F U /g –w h e a t g r a i n y i e l d s i n c r e a s e d s i g n i ?c a n t l y a t s e v e r a l s i t e s w i t h t h e s e s t r a i n s ,h o w e v e r o v e r a l l r e s u l t s w e r e n o t s i g n i f -i c a n t d u e t o v a r i a b i l i t y o f r e s u l t s b e t w e e n s o m e t r i a l s

D e F r e i t a s a n d G e r m i d a 1992b P s e u d o m o n a s c e p a c i a R 55,R 85P s e u d o m o n a s p u t i d a R 104

W i n t e r w h e a t G r o w t h c h a m b e r

–a n t a g o n i s m d e m o n s t r a t e d a g a i n s t R h i z o c t o n i a s o l a n i –i n c r e a s e o f d r y w e i g h t o f i n o c u l a t e d p l a n t s ?62-78%?g r o w n i n R .s o l a n i i n f e c t e d s o i l –d r y r o o t w e i g h t i n c r e a s e d b y 92-128%a n d s h o o t d r y w e i g h t i n c r e a s e d b y 28-48%

D e F r e i t a s a n d G e r m i d a 1991

P s e u d o m o n a s c e p a c i a R 85P s e u d o m o n a s ?u o r e s c e n s R 104,R 105P s e u d o m o n a s p u t i d a R 111

W i n t e r w h e a t

P o t t e d p l a n t s i n g r o w t h c h a m b e r –t w o s o i l t y p e s t e s t e d u n d e r s i m u l a t e d f a l l c o n d i t i o n s ?5oC ?–r e s p o n s e o f w h e a t n u t r i e n t u p t a k e t o i n o c u l a t i o n d e p e n -d a n t o n s o i l c o m p o s i t i o n –g r a i n y i e l d e n h a n c e d 46-75%i n m o r e f e r t i l e s o i l

D e F r e i t a s a n d G e r m i d a 1992a

P s e u d o m o n a s c h l o r o r a p h i s 2E 3,O 6

S p r i n g w h e a t F i e l d a n d l a b o r a t o r y –i n c r e a s e d e m e r g e n c e a t t w o d i f f e r e n t s i t e s b y 8t o 6%–s t r o n g i n h i b i t i o n o f F u s a r i u m c u l m o r u m –n o p r o m o t i o n e f f e c t o f i n o c u l a t e d p l a n t s e v i d e n t i n s o i l s f r e e o f F u s a r i u m i n f e c t i o n

K r o p p e t a l .1996

P s e u d o m o n a s c o r r u g a t a A z o t o b a c t e r c h r o o c o c c u m A m a r a n t h u s p a n i c u l a t u s E l e u s i n e c o r a c a n a

–p l a n t g r o w t h a n d n i t r o g e n c o n t e n t i n c r e a s e d –h y p o t h e s i s e d t h a t t h e g r o w t h p r o m o t i o n e f f e c t i s d u e t o t h e s t i m u l a t i o n o f n a t i v e b a c t e r i a l c o m m u n i t i e s

P a n d e y e t a l .1999

8

T a b l e 1.C o n t i n u e d .

B a c t e r i a P l a n t

C o n d i t i o n s

R e s u l t s o f a d d i t i o n o f b a c t e r i a t o p l a n t R e f e r e n c e

P s e u d o m o n a s ?u o r e s c e n s P s e u d o m o n a s p u t i d a T L 3,B K 1

P o t a t o

F i e l d –l a c k o f g r o w t h p r o m o t i o n e f f e c t a n d b a c t e r i a l s u r v i v a l i n d r y s o i l s –i n n o r m a l c o n d i t i o n s s t a t i s t i c a l l y s i g n i ?c a n t i n c r e a s e s o f y i e l d o f 14-33%i n 5o f 9p l o t s

B u r r e t a l .1978P s e u d o m o n a s ?u o r e s c e n s W i n t e r w h e a t F i e l d a n d g r o w t h c h a m b e r

–i n g r o w t h c h a m b e r ,s e e d l i n g h e i g h t p r o m o t i o n s e e n –i n P y t h i u m -c o n t a m i n a t e d s i t e s ,s i g n i ?c a n t i n c r e a s e s i n s t a n d ,p l a n t h e i g h t ,n u m b e r o f h e a d s ,a n d g r a i n y i e l d

W e l l e r a n d C o o k 1986

P s e u d o m o n a s ?u o r e s c e n s 63-28,R 17-F P 2,Q P 5,R 15-A 4

T o m a t o

G r e e n h o u s e w i t h n a t u r a l l i g h t i n g

–i n f a v o u r a b l e l i g h t c o n d i t i o n s ,f r u i t y i e l d s i n c r e a s e d b y 5.6t o 9.4%–i n u n f a v o u r a b l e l i g h t c o n d i t i o n s ,y i e l d s i n c r e a s e d u p t o 18.2%

G a g n ée t a l .1993

P s e u d o m o n a s ?u o r e s c e n s 63-49,63-28,15P s e u d o m o n a s c o r r u g a t e 13S e r r a t i a p l y m t h i c a R 1G C 4

C u c u m b e r F i e l d –s t r a i n 63-49s i g n i ?c a n t l y i n c r e a s e s f r u i t n u m b e r s b y 12%a n d f r u i t w e i g h t b y 18%–s t r a i n s 13,15,R 1G C 4s l i g h t l y i n c r e a s e y i e l d s –i n P y t h i u m i n f e c t e d s o i l s ,y i e l d i n c r e a s e d u p t o 18%w i t h a d d i t i o n o f s t r a i n s 63-49a n d 63-28

M c C u l l a u g h e t a l .2001

P s e u d o m o n a s ?u o r e s c e n s P f 5B a c i l l u s p u m i l u s

H i g h b u s h b l u e b e r r y –l e a f a r e a a n d s t e m d i a m e t e r i n c r e a s e s

d e S i l v a e t a l .2000

P s e u d o m o n a s p u t i d a P s e u d o m o n a s p u t i d a b i o v a r B P s e u d o m o n a s ?u o r e s c e n s A r t h r o b a c t e r c i t r e u s S e r r a t i a l i q u e f a c i e n s

C a n o l a ?B r a s s i c a c a m p e s t r i s L .a n d B r a s s i c a n a p u s L .?

F i e l d a n d g r e e n h o u s e

–i n g r e e n h o u s e ,s e l e c t e d s t r a i n s p r o d u c e 57%i n c r e a s e i n y i e l d –i n ?e l d c o n d i t i o n s ,s e l e c t s t r a i n s i n c r e a s e s e e d l i n g e m e r -g e n c e a n d v i g o u r –y i e l d i n c r e a s e f r o m 6t o 13%o v e r a t w o y e a r t e s t p e -r i o d

K l o e p p e r e t a l .1988

P s e u d o m o n a s p u t i d a B a c i l l u s s u b t i l i s E n t e r o b a c t e r a e r o g e n e s E n t e r o b a c t e r a g g l o m e r a n s B a c i l l u s c e r e u s

C u c u m b e r I n v i t r o a n d g r e e n h o u s e

–m o s t s t r a i n s i n c r e a s e d r o o t l e n g t h i n P y t h i u m -i n f e c t e d p l a n t s i n v i t r o –i n g r e e n h o u s e ,i n c r e a s e s o f t h e w e i g h t o f c u c u m b e r p l a n t s b y 29%,f r u i t y i e l d b y 14%a n d f r u i t n u m b e r b y 50%b y B .s u b t i l i s

U t h e d e e t a l .1999

P s e u d o m o n a s p u t i d a G R 12-2C a n o l a G r e e n h o u s e

–n o n -n i t r o g e n ?x i n g m u t a n t s p r o v i d e g r e a t e r r o o t e l o n g a -t i o n e f f e c t s a n d g r e a t e r p h o s p h a t e u p t a k e

L i f s h i t z e t a l .1987

9

T a b l e 1.C o n t i n u e d .

B a c t e r i a

P l a n t C o n d i t i o n s R e s u l t s o f a d d i t i o n o f b a c t e r i a t o p l a n t R e f e r e n c e

P s e u d o m o n a s p u t i d a G R 12-2C a n o l a ,L e t t u c e ,T o m a t o ,B a r l e y ,W h e a t ,O a t

G r o w t h c h a m b e r

–i n d i c o t p l a n t s ,r o o t e l o n g a t i o n s t i m u l a t e d b y t h e b a c t e -r i a ,b u t i n m o n o c o t p l a n t s ,l i t t l e t o n o g r o w t h p r o m o t i o n s e e n –d i f f e r e n c e d u e t o s e n s i t i v i t y d i f f e r e n c e s t o e t h y l e n e ,t h i s b a c t e r i a l s t r a i n c o n t a i n s g e n e t o r e d u c e e t h y l e n e s y n t h e s i s ?i .e .A C C d e a m i n a s e ?

H a l l e t a l .1996

P s e u d o m o n a s p u t i d a W 4P 63P o t a t o F i e l d

–i n c r e a s e d y i e l d o f 10.2t o 11.7%–p o t a t o s o f t r o t ?E r w i n i a c a r o t o v o r a ?s u p p r e s s e d

X u a n d G r o s s ,1986

P s e u d o m o n a s s p .V a r i o -v o v a x s p .A g r o b a c t e r i u m s p .P h y l l o b a c t e r i u m s p .

C a n o l a G r o w t h c h a m b e r –s i g n i ?c a n t i n c r e a s e i n r o o t d r y w e i g h t f r o m 11t o 52%–m o s t i m p o r t a n t p r o m o t i o n e f f e c t b y P h y l l o b a c t e r i u m s p .

B e r t r a n d e t a l .2001

P s e u d o m o n a s s p .P s J N P o t a t o

G r e e n h o u s e a n d ?e l d t r i a l s

–i n g r e e n h o u s e ,i n c r e a s e o f w h o l e p l a n t d r y w e i g h t ;r e s u l t n o t i n ?u e n c e d b y s o i l s t e r i l i t y –i n ?e l d ,e a r l y e m e r g e n c e s t i m u l a t e d a n d s i g n i ?c a n t t u b e r y i e l d i n c r e a s e s i n 3o f 4t r i a l s

F r o m m e l e t a l .1983P s e u d o m o n a s s p p .??u o r e s c e n t s t r a i n s ?A 1,B 10,T L 3,B K 1,E 6

P o t a t o G r e e n h o u s e a n d ?e l d

–t r e a t e d s e e d p i e c e s p r o d u c e l a r g e r r o o t s y s t e m s i n g r e e n -h o u s e –s i g n i ?c a n t y i e l d i n c r e a s e s o c c u r r e d i n a l l t e s t ?e l d s ,b u t d i f f e r e n t s t r a i n s p r o m o t e p l a n t g r o w t h d i f f e r e n t l y i n d i f f e r -e n t s o i l t y p e s –e a r l y p l a n t r e s p o n s e s c o r r e l a t e d t o i n c r e a s e d y i e l d s

K l o e p p e r e t a l .1980P s e u d o m o n a s s p p .??u o r e s c e n t s t r a i n s ?A 1,B 2,B 4,E 6,R V 3,S H 5

S u g a r b e e t G r e e n h o u s e a n d ?e l d t r i a l s

–i n c r e a s e s o f s e e d l i n g m a s s b y a l l s t r a i n s i n g r e e n h o u s e –e f f e c t s o f i n o c u l a t i o n p o s i t i v e o n y i e l d i n ?e l d t r i a l s ,b u t r e s u l t s v a r i a b l e f r o m s i t e t o s i t e –s t u d y a u t h o r s c o n c l u d e t h a t p r o m o t i o n e f f e c t d u e t o a n -t a g o n i s m o f p l a n t d i s e a s e

S u s l o w a n d S c h r o t h 1982P s e u d o m o n a s s p p .

P o t a t o F i e l d

–c h a n g e s i n y i e l d o f ?10t o 37%

H o w i e a n d E c h a n d i 1983

P s e u d o m o n a s s p p .P o t a t o

F i e l d

–c h a n g e s i n y i e l d o f ?9t o 20%

G e e l s e t a l .1986

P s e u d o m o n a s s p p .P o t a t o

F i e l d

–c h a n g e s i n y i e l d o f ?14t o 33%

K l o e p p e r e t a l .1989

P s e u d o m o n a s s p p .R i c e

F i e l d

–i n c r e a s e d y i e l d o f 3t o 160%

K l o e p p e r e t a l .1989

10

T a b l e 1.C o n t i n u e d .

B a c t e r i a P l a n t

C o n d i t i o n s

R e s u l t s o f a d d i t i o n o f b a c t e r i a t o p l a n t R e f e r e n c e

P s e u d o m o n a s s p p .

L e t t u c e ,C u c u m b e r ,T o m a t o ,C a n o l a

H y d r o p o n i c g r o w t h c h a m b e r –i n c r e a s e s o f r o o t a n d s h o o t w e i g h t s f o r a l l p l a n t s t e s t e d –m o s t s i g n i ?c a n t p o s i t i v e g r o w t h r e s p o n s e s i n l e t t u c e ,t o m a t o a n d c u c u m b e r

V a n P e e r a n d S c h i p p e r s 1998P s e u d o m o n a s s p p .7N S K 2

M a i z e ,B a r l e y ,W h e a t

F i e l d

–i n c r e a s e d y i e l d o f 15t o 25%I s w a n d i e t a l .1987

P s e u d o m o n a s s y r i n g a e p v .P h a s e o l i c o l a

B e a n

G r e e n h o u s e –p o o r e s t a b l i s h m e n t o f t e s t p a t h o g e n i n p l a n t s i n o c u l a t e d w i t h P .s y r i n g a e –i n c r e a s e d a m o u n t s o f p r o t e i n i n i n o c u l a t e d p l a n t s

A l s t r o m 1995

P s e u d o m o n a s W 34B a c i l l u s c e r e u s S 18

L e t t u c e ,T o m a t o P o t e x p e r i m e n t

–s i g n i ?c a n t r e d u c t i o n i n g a l l i n g a n d e n h a n c e d s e e d l i n g b i o m a s s i n s o i l s i n f e s t e d w i t h M e l o i d o g y n e i n c o g n i t a –B .c e r e u s S 18c a u s e s u p t o a 9%y i e l d i n c r e a s e c o m -p a r e d t o t h e c o n t r o l

H o f f m a n n -H e r g a r t e n e t a l .1998

S e r r a t i a l i q u f a c i e n s P s e u d o m o n a s s p .B a c i l l u s s p .

M a i z e G r e e n h o u s e –i n c r e a s e d o f y i e l d o f 8t o 14%–S .l i q u e f a c i e n s a n d P s e u d o m o n a s s p .g i v e s t h e h i g h e s t s t i m u l a t i o n e f f e c t i n d i f f e r e n t s o i l s

L a l a n d e e t a l .1989

S e r r a t i a p r o t e a m a c u l a n s 102S e r r a t i a l i q u e f a c i e n s 2-68

S o y b e a n F i e l d

–t r e a t m e n t e f f e c t s o f b o t h b a c t e r i a l s t r a i n s n o t s i g n i ?c a n t o v e r t w o s t u d y y e a r s

P a n e t a l .2002

X a n h o m o n a s m a l t o p h i l a S u n ?o w e r L a b a n d g r e e n h o u s e

–i n c r e a s e d g e r m i n a t i o n r a t e

F a g e s a n d A r s a c 1991

‘Y i e l d I n c r e a s i n g B a c t e r i a ’?Y I B ??S p e c i e s U n k n o w n ?

R i c e ,W h e a t ,C o r n ,M i l l e t ,S w e e t P o t a t o ,C o t t o n ,B e e t ,R a p e s e e d ,W a t e r m e l o n

F i e l d ?T o t a l a r e a o f t e s t c r o p s i s 3.46m i l l i o n h a ?

–m a j o r s t u d y c o n d u c t e d i n C h i n a i n v a r i o u s p r o v i n c e s –a v e r a g e y i e l d i n c r e a s e s o f 10.0t o 22.5%a f t e r a p p l i c a -t i o n o f Y I B o n c r o p s

M e i e t a l .1990

11

Okon1996;Lalande et al.2002;Paredes-Cardona 1988?.While there may be a threshold number of bacteria that should be inoculated on a given plant, excessively large numbers of bacteria could be detri-mental to the germination and growth of seeds or plants?Chanway1997?.However,growth promotion effects can still occur even with lower bacterial popu-lations?Jacoud et al.1998?.It has been shown under controlled experimental conditions,that initial bacte-rial binding to seed,not necessarily the roots after germination,is most important for enhanced plant root elongation?Hong et al.1991?.

The over-wintering ability of PGPR is fundamen-tal when considering uses in colder climates.There is evidence that Pseudomonas species are able to over-winter in sufficient quantities on the roots of winter wheat?De Freitas and Germida1990b?.It has also been argued that antifreeze protein activity of many bacterial species may contribute to their survival in colder climates?Sun et al.1995;Xu et al.1998?.On the other hand,strains of Azospirillum often have low survival rates in soils that are colder?Lifshitz et al. 1986?.

There are a few other points of interest that relate to agricultural uses of PGPR.For example,it has been shown that some PGPR strains are able to counteract irrigation problems by reducing the negative effect of irrigation of crops with highly saline water?Hamaoui et al.1996?.This may re?ect the lowering of plant ethylene levels elevated by salt stress by means of 1-amino-cyclopropane-1-carboxylate?ACC?deami-nase-containing PGPR?S.Mayak,T.Tirosh,B.R. Glick,unpublished results?.Also,it has been ob-served that PGPR numbers decline rapidly in the rhizosphere after inoculation?Jacoud et al.1998?,al-though their effects last throughout the growing sea-son.Several studies show that growth promotion effects are seen early in plant development,and these subsequently translate into higher yields?Glick et al. 1997;Hoffmann-Hergarten et al.1998;Kloepper et al.1988;Polyanskaya et al.2000?.Evidence of late-season grain weight increases have also been reported in studies with PGPR and rice?Tran Van et al.2000?. Free living PGPRs can be administered to crops in some formulations that are available commercially ?Table2?.The majority of these products are biocon-trol agents which contribute indirectly to the growth promotion of crops?Chet and Chernin2002;Glick et al.1999?.Commercial free living PGPR inoculants provide a possible alternative to the use of pesticides and fertilizers on various crops,though they are not used widely at present?Glick et al.1999?.

A broad array of methods and materials exist for the delivery of bacteria to crops in the?eld.Presently the non-free living symbiotic Rhizobium spp.are most commonly incorporated into peat as inoculant carri-ers.Peat carriers,although cheap and easily used, have many disadvantages.Peat is generally used as a non-sterile medium and holds a large contaminant load.Also,peat quality can be variable and peat itself is not necessarily readily available worldwide.Heat sterilization of peat can release substances toxic to the chosen bacteria.Some peat is known to inhibit plant growth,probably a reason for some of the negative effects of inoculation by PGPR seen in Table1.Fi-nally,bacteria in peat formulations are vulnerable to temperature?uctuations and have a limited shelf life ?Bashan1998?.

Understanding the mechanisms of plant growth promotion is important when deciding what type of bacteria to use with a plant in a given situation.For example,Pseudomonas putida GR12-12contains the gene for ACC deaminase,which inhibits ethylene synthesis,ethylene being a product of stress.This mechanism is most effective on plants that are more susceptible to the effects of ethylene,such as dicoty-ledonous plants?Hall et al.1996?especially under such stress conditions as?ooding?Grichko and Glick, 2001?drought?S.Mayak,T.Tirosh,B.R.Glick,un-published results?and phytopathogens?Wang et al. 2000?.

More recent knowledge of indirect mechanisms of plant growth promotion by soil bacteria may aid the agricultural production of certain legume crops.The hydrogen gas that is produced as a by-product of ni-trogen?xation by rhizobia within legume nodules may be recaptured and recycled by those rhizobial strains that contain a hydrogen uptake system?Evans et al.1987?.It is clearly bene?cial to the plant to ob-tain its nitrogen from a symbiotic diazotroph that has a hydrogen uptake system;however,this trait is not common in naturally occurring rhizobial strains ?Evans et al.1987?.The lack of an endogenous hy-drogen uptake system notwithstanding,many soils contain large numbers of free living microorganisms that can capture some of the hydrogen gas produced during nitrogen?xation and thereby indirectly pro-mote the growth of the rhizobia-treated plants?Dong and Layzell2001;McLearn and Dong2002?.In these instances,the organisms responsible for this plant growth promotion effect have not been characterized.

12

T a b l e 2.E x a m p l e s o f c o m m e r c i a l p r o d u c t s u s i n g f r e e -l i v i n g p l a n t g r o w t h p r o m o t i n g r h i z o b a c t e r i a ?C h e t a n d C h e r n i n 2002,G l i c k e t a l .1999?

B a c t e r i a l

C o n t e n t

P r o d u c t

I n t e n d e d C r o p

A g r o b a c t e r i u m r a d i o b a c t e r

D i e g a l l G a l l t r o l -A N o g a l l N o r b a c 84C

F r u i t ,n u t ,o r n a m e n t a l n u r s e r y s t o c k a n d t r e e s

A z o s p i r i l l u m b r a s i l e n s e

A z o -G r e e n

T u r f a n d f o r a g e c r o p s

A z o s p i r i l l u m b r a s i l e n s e C d A z o s p i r i l l u m l i p o f e r u m

B r -17

Z e a -N i t M a i z e A z o s p i r i l l u m l i p o f e r u m C R T 1

A Z O G R E E N -m

M a i z e

B a c i l l u s a m y l o l i q u e f a c i e n s G B 99B a c i l l u s s u b t i l i s

C B 122Q u a n t u m 4000B i o Y i e l d T M

B r o c c o l i ,c a b b a g e ,c a n t a l o u p e ,c a u l i ?o w e r ,c e l e r y ,c u c u m b e r ,l e t t u c e ,o r n a m e n t a l s ,p e p -p e r s ,t o m a t o ,a n d w a t e r m e l o n

B a c i l l u s s u b t i l i s

E p i c H i S t i c k N /T K o d i a k R h i z o -P l u s S e r e n a d e S u b t i l e x S y s t e m 3

B a r l e y ,b e a n s ,c o t t o n ,l e g u m e s p e a n u t ,p e a ,r i c e ,a n d s o y b e a n

B u l k h o l d e r i a c e p a c i a B l u e

C i r c l e

D e n y I n t e r c e p t

A l f a l f a ,b a r l e y ,b e a n s ,c l o v e r ,c o t t o n ,m a i z e ,p e a s ,s o r g h u m ,v e g e t a b l e s a n d w h e a t

P s e u d o m o n a s ?u o r e s c e n s B l i g h t B a n A 506C o n q u e r V i c t u s

A l m o n d ,a p p l e ,c h e r r y ,m u s h r o o m ,p e a c h ,p e a r ,p o t a t o ,s t r a w b e r r y a n d t o m a t o

P s e u d o m o n a s s y r i n g a e B i o -s a v e 10

C i t r u s a n d p o m e f r u i t

S t r e p t o m y c e s g r i s e o v i r d i s K 61

M y c o s t o p

F i e l d ,o r n a m e n t a l a n d v e g e t a b l e c r o p s

13

In other cases,free living bacteria that promote the rhizobial-legume symbiosis have been identi?ed and characterized?e.g.,Andrade et al.1998;Marek-Kozaczuk et al.2000;Xu et al.1994?.In these cases, the free living bacteria are thought to act by decreas-ing the interference in the nodulation process by other soil microorganisms.

What is currently missing from the research of PGPR in agriculture is a lack of comparative studies between crop types and different species or strains of rhizobacteria.For example,when Pseudomonas putida GR12-2is inoculated on various crops,there are dissimilarities in the plant stimulation between monocot and dicot plants?Hall et al.1996?.There are also signi?cant differences in yield between summer versus winter crops following inoculation with Azospirillum brasilense Cd?Okon et al.1988?.Nev-ertheless,as noted by Okon et al.?1994?,the positive effects of PGPR shown for several rhizobacterial types on many economically important crops is a valid phenomenon,and these results can act as a ba-sis for the effective utilization of PGPR in a variety of applications.

Applications of PGPR in Forestry

Research on the use of PGPR in forestry is much less widespread than for agricultural applications.PGPR and their effect on angiosperms were the initial research focus through the1980s,however from the 1990s to the present there has been more research of PGPR on gymnosperms?Chanway1997?.A wider scope of studies of both of these tree types and PGPR could bene?t the commercial forestry sector,as well as reforestation efforts worldwide.Table3summa-rizes many of the studies that have been conducted with different PGPR and tree species.

There are different considerations that must be taken into account when evaluating the performance of the inoculation of PGPR on tree species,in con-trast to agricultural crops.Fruit and grain yield increases are obviously not an imperative aspect of tree growth but biomass increases due to inoculation are quite important.Aspects such as seedling emer-gence and reduction in seedling transplant injury dur-ing the transfer from nursery to?eld are also signi?cant?Shishido and Chanway2000?.While some tree types are very good at rapid and effective germination,without inoculation,many have diffi-culty in getting established to grow into an adult tree ?Zaady and Perevoltsky1995?.Soil type may also be a major consideration when testing PGPR in a forest

environment.Many forest soils are acidic,especially

those of conifer forests,and some PGPR are sensitive

to low pH conditions?Brown1974?.

Winter survival of PGPR is imperative,especially

with trees intended for the colder regions of the world ?e.g.,Canada,Scandinavia,Russia?and also particu-larly since trees are perennial plants in contrast to

most agricultural crops.Chanway et al.?2000?has

shown that there is promise for many PGPR,such as

strains of Bacillus polymyxa and Pseudomonas?uo-

rescens to over-winter on the roots of?eld-planted trees.In that study,from one year to the next,there was a decrease of approximately two orders of mag-nitude in the inoculated bacterial populations;how-ever,the bene?ts of inoculation were seen the next year?Chanway et al.2000?.

The medium in which a bacterial strain is prepared

preceding inoculation may affect the root colonization

pattern of the inoculated bacteria?Zaady et al.1993?.

This study showed that malate-grown bacteria were

better able to promote the growth of oak,than bacte-

rial cells of the same strain grown in fructose-based

media.It was found that malate-grown cells have a

tendency to aggregate,while the fructose cells

disperse through the soil substrate.Fructose-grown

cells may be adequate for growth promotion of sur-

face-rooted plants like maize,however,they were not

sufficient for the growth promotion of trees such as

oak with deep tap roots?Zaady et al.1993?.

Similar to the speci?city observed in agricultural

crops,a speci?c bacterial strain may promote growth

only in certain tree species.?Enebak et al.1998;Sh-

ishido and Chanway2000?.Sometimes even the tree

ecovar is important.For example,while a strain of

bacteria was effective at promoting growth in one

type of pine species it was not effective with another

pine species?Chanway1995?.Ecotypes,or trees of

the same species from different regions or altitudes,

also show differential responses to bacterial inocula-

tion?Chanway1995?.For example in one case,Hy-

drogenophaga pseudo?ava consistently promoted the growth of only one of two spruce ecovars?Chanway and Holl1993?.However,there are also some broad-range bacterial strains,such Bacillus polymxa L6, which consistently promote the growth of many pine varieties and other tree species?Chanway1995;Holl and Chanway1992?.It is interesting to note that this strain of bacteria was originally isolated from the rhizosphere of perennial ryegrass,and not a tree spe-cies?Holl and Chanway1992?.

14

T a b l e 3.E x a m p l e s o f f r e e -l i v i n g p l a n t g r o w t h p r o m o t i n g r h i z o b a c t e r i a t e s t e d o n v a r i o u s t r e e s p e c i e s .

B a c t e r i a P l a n t

C o n d i t i o n s

R e s u l t s o f a d d i t i o n o f b a c t e r i a t o p l a n t R e f e r e n c e

A g r o b a c t e r i u m r a d i o b a c t e r

B e e c h ,S c o t c h p i n e

G r e e n h o u s e –b e e c h b i o m a s s i n c r e a s e s o f u p t o 235%–p i n e b i o m a s s i n c r e a s e s o f u p t o 15%

L e y v a l a n d B e r t h e l i n 1989

A r t h r o b a c t e r c i t r e u s P s e u d o m o n a s ?u o r e s c e n s P s e u d o m o n a s p u t i d a

B l a c k s p r u c e ,J a c k p i n e ,W h i t e s p r u c e

G r e e n h o u s e

–h e i g h t a n d b i o m a s s i n c r e a s e s d e m o n s t r a t e d B e a l l a n d T i p p i n g 1989

A r t h r o b a c t e r o x y d a n s P s e u d o m o n a s a u r e o f a c i e n s

D o u g l a s F i r

G r e e n h o u s e a n d ?e l d –h e i g h t a n d b i o m a s s i n c r e a s e s o f u p t o 68%–a l s o i n c r e a s e d b r a n c h a n d r o o t w e i g h t s –s o m e v a r i a b i l i t y i n r e s p o n s e o f ?r e c o t y p e s t o i n o c u l a -t i o n

C h a n w a y a n d H o l l 1994

A r t h r o b a c t e r s p .

P i n e L a b a s s a y –s h o o t l e n g t h i n c r e a s e s u p t o 69%

P o k o j s k a -B u r d z i e j e t a l .1982

A z o s p i r i l l u m b r a s i l e n s e R i v e r O a k

G r e e n h o u s e

–b i o m a s s i n c r e a s e o f 90%

R o d r i g u e z -B a r r u e c o e t a l .1991

A z o s p i r i l l u m b r a s i l e n s e C d O a k G r e e n h o u s e

–r o o t g r o w t h i n c r e a s e s o f u p t o 70%–t h e s e g r o w t h p r o m o t i o n o b s e r v e d o n l y w i t h c e l l s c u l -t u r e d i n m a l a t e a n d n o t f r u c t o s e

Z a a d y e t a l .1993,Z a a d y a n d P e r e v o l t s k y 1995

A z o t o b a c t e r c h r o o c o c c u m O a k ,a s h G r o w t h c h a m b e r

–b i o m a s s i n c r e a s e s o f 13t o 26%

A k h r o m e i k o a n d S h e s t a k o v a 1958

A z o t o b a c t e r c h r o o c o c c u m Q u e r c u s s e r r a t a

P o t t e d p l a n t e x p e r i m e n t o u t d o o r s

–b i o m a s s i n c r e a s e s o f u p t o 38%

P a n d e y e t a l .1986

A z o t o b a c t e r c h r o o c o c c u m

B a c i l l u s m e g a t e r i u m

E u c a l y p t u s P o t t e d p l a n t e x p e r i m e n t o u t d o o r s

–b i o m a s s i n c r e a s e s o f u p t o 44%M o h a m m e d a n d P r a s a d 1998

B a c i l l u s l i c h e n i f o r m i s

C E C T 5105B a c i l l u s p u m i l i s C E C T 5106

S i l v e r s p r u c e

G r e e n h o u s e

–s t a t i s t i c a l l y s i g n i ?c a n t i n c r e a s e i n a e r i a l p l a n t g r o w t h –r o o t s y s t e m d e v e l o p m e n t n o t a f f e c t e d –i n c r e a s e d p l a n t n i t r o g e n c o n t e n t

P r o b a n z a e t a l .2002

B a c i l l u s l i c h e n i f o r m i s P h y l o -b a c t e r i u m s p .M a n g r o v e G r e e n h o u s e

–d o u b l i n g o f n i t r o g e n i n c o r p o r a t i o n i n t o p l a n t –i n c r e a s e d l e a f d e v e l o p m e n t

B a s h a n a n d H o l g u i n 2002,R o j a s e t a l .2001

15

T a b l e 3.C o n t i n u e d .

B a c t e r i a

P l a n t C o n d i t i o n s R e s u l t s o f a d d i t i o n o f b a c t e r i a t o p l a n t R e f e r e n c e

B a c i l l u s p o l y m y x a

D o u g l a s F i r ,L o d g e p o l e P i n e ,W h i t e s p r u c e G r o w t h c h a m b e r a n d g r e e n -h o u s e

–f o r l o d g e p o l e p i n e ,s i g n i ?c a n t i n c r e a s e s i n r o o t d r y w e i g h t ?1.35-f o l d ?a n d t h e n u m b e r a n d l e n g t h o f s e c o n d -a r y r o o t s ?1.44-f o l d a n d 1.92-f o l d ,r e s p e c t i v e l y ?–i n p i n e ,r o o t g r o w t h ,e m e r g e n c e ,h e i g h t a n d w e i g h t ,r o o t c o l l a r d i a m e t e r i n c r e a s e s p r e s e n t f o r p l a n t s g r o w n i n s t e r -i l e v e r s u s n o n -s t e r i l e m e d i a –s e e d l i n g e m e r g e n c e i n c r e a s e s f o r w h i t e s p r u c e

C h a n w a y e t a l .1991B a c i l l u s p o l y m y x a W e s t e r n h e m l o c k G r e e n h o u s e

–i n c r e a s e d s e e d l i n g h e i g h t a n d b i o m a s s u p t o 30%,d u e t o p l a n t h e i g h t a n d w e i g h t i n c r e a s e s o f 1.19a n d 1.30-f o l d r e s p e c t i v e l y –d e g r e e o f h e m o l o c k g r o w t h p r o m o t i o n d i f f e r e n t f o r b i o -v a r s f r o m d i f f e r e n t a l t i t u d e s

C h a n w a y 1995B a c i l l u s p o l y m y x a

P s e u d o m o n a s ?u o r e s c e n s L o b l o l l y p i n e ,s l a s h p i n e

G r e e n h o u s e

–s i g n i ?c a n t i n c r e a s e s i n t h e s p e e d o f s e e d l i n g e m e r g e n c e a n d t o t a l b i o m a s s –p o s t -e m e r g e n c e d a m p i n g o f f r e d u c e d i n l o b l o l l y p i n e –t w o b a c t e r i a l s t r a i n s s h o w r e d u c t i o n o f b i o m a s s o f b o t h p i n e s p e c i e s –l o b l o l l y p i n e h a s i n c r e a s e d r o o t l e n g t h w i t h s o m e s t r a i n s

E n e b a k e t a l .1998B a c i l l u s p o l y m y x a P s e u d o m o n a s ?u o r e s c e n s

H y b r i d s p r u c e F i e l d

–i n c r e a s e o f s p r u c e s e e d l i n g d r y w e i g h t u p t o 57%a b o v e u n i n o c u l a t e d s p r u c e p l a n t s a t ?v e o f n i n e t e s t s i t e s –a l l t e s t s t r a i n s i n c r e a s e d r y w e i g h t o f s p r u c e a t f o u r o f t h e n i n e s i t e s –s o m e p l a n t g r o w t h i n h i b i t i o n d e t e c t e d d u e t o i n o c u l a t i o n a t s o m e s i t e s

C h a n w a y e t a l .2000B a c i l l u s p o l y m y x a S t a p h y l o c o c c u s h o m i n i s

H y b r i d s p r u c e G r e e n h o u s e ?u s i n g ?e l d s o i l ?

–s i g n i ?c a n t g r o w t h i n c r e a s e u p t o 59%O ’N e i l l e t a l .1992

B a c i l l u s p o l y m y x a L 6L o d g e p o l e P i n e

G r e e n h o u s e

–s o m e s e e d l i n g s c o -i n o c u l a t e d w i t h m y c o r r h i z a e –n o e f f e c t w i t h B a c i l l u s a l o n e –s h o o t a n d r o o t b i o m a s s i n c r e a s e s

C h a n w a y a n d H o l l 1991

B a c i l l u s p o l y m y x a L 6L o d g e p o l e P i n e G r o w t h c h a m b e r

–s t a t i s t i c a l l y s i g n i ?c a n t i n c r e a s e s i n s e e d l i n g b i o m a s s a t 6w e e k s o f p l a n t g r o w t h –m e a n s h o o t a n d r o o t w e i g h t s i n c r e a s e d u p t o 35%

H o l l a n d C h a n w a y 199216

T a b l e 3.C o n t i n u e d .

B a c t e r i a

P l a n t

C o n d i t i o n s

R e s u l t s o f a d d i t i o n o f b a c t e r i a t o p l a n t

R e f e r e n c e

B a c i l l u s s u b t i l i s P s e u d o m o n a s s p p .

H y b r i d s p r u c e

G r e e n h o u s e p l a n t s o u t p l a n t e d t o ?e l d –s i g n i ?c a n t i n c r e a s e s o f p l a n t b i o m a s s b y i n o c u l a t i o n w i t h P s e u d o m o n a s s t r a i n o f 10t o 234%a t a l l s i t e s w i t h t y p i c a l i n c r e a s e s o f 28t o 70%–r e d u c t i o n i n s e e d l i n g s h o o t i n j u r y a f t e r t r a n s p l a n t –B a c i l l u s s t r a i n i n e f f e c t i v e

S h i s h i d o a n d C h a n w a y 2000

H y d r o g e n o p h a g a p s e u d o ?a v a P s e u d o m o n a s p u t i d a H y b r i d s p r u c e F i e l d

–H .p s e u d o ?a v a i n c r e a s e d s e e d l i n g b i o m a s s a n d r o o t b r a n c h n u m b e r s u p t o 49%i n t w o s p r u c e e c o t y p e s t e s t e d –o n e e c o t y p e s h o w s r o o t g r o w t h p r o m o t i o n –P .p u t i d a i n c r e a s e s s e e d l i n g b i o m a s s i n t w o t r i a l s a n d h a s i n h i b i t o r y e f f e c t i n o t h e r t r i a l s C h a n w a y a n d H o l l 1993

P s e u d o m o n a s s p p .

A p p l e

G r e e n h o u s e a n d ?e l d

–g r o w t h i n c r e a s e s o f s e e d l i n g s u p t o 65%a n d o f r o o t -s t o c k s 179%–s o m e b i o c o n t r o l s e e n a g a i n s t p a t h o g e n i c f u n g i

C a e s a r a n d B u r r 1987

17

Sterility of the bacterial inoculant carrier can have an impact on the amount of plant growth promotion.Chanway et al.?1991?demonstrated that pine trees inoculated with PGPR in sterilized peat-vermiculite carrier material promoted growth to a greater extent compared to when they were inoculated with PGPR in non-sterilized material ?Chanway et al.1991?.Also,many researchers tend to inoculate seedlings or older plants.This is in contrast to the agricultural use of PGPR,where there is a tendency to inoculate seeds,or the substrate surrounding the seed.This may have to do with differential practices in these two disciplines,since many trees in the forestry industry have their beginnings in a nursery and are long lived,while crop plants are usually started in the ?eld and are relatively short lived.

There are currently very few research groups working in the area of forestry PGPR research.As a consequence,there is currently no ?eld data for de-ciduous trees and still comparatively little ?eld data for coniferous trees ?Chanway 1997?.Applications of PGPR for Environmental Remediation

An extension of PGPR technology is the emerging use of the bacteria with plants for environmental ap-plications.Recent studies in this area include many different uses:for growth promotion of soil stabiliz-ing plants ?Bashan et al.1999?;to counteract ?ood-ing stress of plants ?Grichko and Glick 2001?;to aid plant growth in acidic conditions ?Belimov et al.1998a ?;to counter high temperature stress ?Bensalim et al.1998?;and the use of PGPR in phytoremedia-tion technologies ?Burd et al.1998;Burd et al.2000;Huang et al.2000;Huang et al.2003a,b ?.Besides environmental uses,some of the outcomes of these studies may also have an impact on agricultural or forestry applications.

Phytoremediation is the use of plants to extract,degrade or stabilize hazardous substances present in the environment.?Cunningham and Berti 1993;Cun-ningham et al.1995;Cunningham and Ow 1996?.Plants used for phytoremediation should be able to accumulate high amounts of the contaminant,and also be able to produce a large biomass.However,very often plants can be compromised by growing on contaminated sites due to the inherent toxicity,so adding PGPR can aid plant growth ?Burd et al.2000?.Clearly,when plants used for phytoremediation are

able to grow well,the site detoxi?cation will be greatly enhanced.

Table4shows examples of research that has been conducted using free-living rhizosphere bacteria with plants and contaminants,to study their potential for use in phytoremediation technologies.The bacteria listed in this Table include both bacteria with estab-lished plant growth promoting properties as well as bacteria with previously unknown credentials as plant growth promoters.Table4includes examples of rhizobacteria which are bene?cial to plants by mobi-lization of soil contaminants as well as those which promote plant growth.There also exist rhizosphere bacteria that degrade contaminants but are not neces-sarily PGPR.In this case,plant roots serve only as a site for contaminant breakdown by the rhizobacteria ?Anderson et al.1993?and these examples have not been included in Table4.

The plant properties that are improved by PGPR during phytoremediation include biomass,contami-nant uptake,and plant nutrition and health.Grain yield was measured by Belimov et al.?1998b?as an indication of plant health and growth,however this attribute is obviously not important in plants used for phytoremediation.

Some plants like barley,tomato,canola?Brassica campestris)and Indian mustard?Brassica juncea?do not accumulate more contaminants?namely metal?per gram of plant material with the addition of PGPR, even though the total biomass increases?Belimov et al.1998c;Burd et al.2002;Burd et al.1998;Nie et al.2002?.However,Ho?ich and Metz?1997?and Whiting et al.?2001?have shown that bacterial inoculation of maize and Thlaspi caerulescens in-creases the uptake of heavy metals by these plants.In addition,de Souza et al.?1999?found increased sele-nium accumulation by Brassica juncea after inocula-tion.Upon closer examination,it appears that the very low level of contaminants used in some studies have probably in?uenced the amount of uptake so that in-creased contaminant accumulation in the presence of PGPR occurs only at low contaminant concentrations and not at the higher levels that inhibit plant growth. When choosing a PGPR to increase metal uptake by plants,it is important to ensure that the bacteria used do not cause a reduction in metal uptake.With barley,the addition of Azospirillum lipoferum137 signi?cantly reduced the amount of radiolabelled ce-sium uptake per gram of plant dry weight?Belimov et al.1998c?.

Survival and PGPR success is essential for use in phytoremediation.It has been shown that high con-taminant levels can have inhibitory effects on the growth of PGPR.For example,Enterobacter cloacae CAL2growth was inhibited by50%in20mM arsen-ate contaminated soils,but was only inhibited by2% in2mM arsenate contamination?Nie et al.2002?. Also,some bacteria are sensitive to one contaminant, but not another.In a study by Belimov et al.?1998b?, it was shown that Flavobacterium sp.is very sensi-tive to cadmium,but not to lead.In practice,it is es-sential that the bacteria used are at least somewhat resistant to the levels of contaminants endogenous to the environment to be cleaned up.Thus,preliminary selection of resistant strains,as performed by Burd et al.?1998?for nickel on Kluyvera ascorbata,is imperative for the practical use of these organisms. Pairing of PGPR with transgenic plants may be a good way of increasing the efficacy of phytoremedia-tion.In the presence of arsenate,fresh root and shoot weights of canola plants were greatly increased due to the concerted action of the PGPR Enterobacter cloacae CAL2and the canola plants which express the stress tolerance gene ACC deaminase?Nie et al. 2002?.

Plant exudates are essential for the association of bacteria with the rhizosphere of the plant as shown by Belimov and Dietz?2000?who demonstrated that the addition of an alternate carbon source to the soil caused an abolition of plant growth promotion in a contaminated site.

PGPRs in association with plants have an impor-tant role in the phytoremediation of soils but the re-search in this area has been limited.As seen in Table 4,there have been no?eld studies of this work and only controlled studies in greenhouses and/or growth chambers have been conducted.Also,only rudimen-tary inoculation procedures have been used.In addi-tion,only a few known PGPR and plants types have been tested.Despite the lack of extensive data,PGPR inoculation technology has a great deal of potential in the area of phytoremediation.

Conclusions

PGPR present an alternative to the use of chemicals for plant growth enhancement in many different ap-plications.Extensive research has demonstrated that PGPRs could have an important role in agriculture and horticulture in improving crop productivity.In

18

T a b l e 4.E x a m p l e s o f f r e e -l i v i n g p l a n t g r o w t h p r o m o t i n g r h i z o b a c t e r i a t e s t e d f o r p h y t o r e m e d i a t i o n t e c h n o l o g i e s .

B a c t e r i a P l a n t

C o n t a m i n a n t

C o n d i t i o n s R e s u l t s o f p a i r i n g o f b a c t e r i a a n d p l a n t R e f e r e n c e

A g r o b a c t e r i u m r a d i o b a c t e r 10A r t h r o b a c t e r m y s o r e n s 7A z o s p i r i l l u m l i p o f e r u m 137F l a v o b a c t e r i u m s p .L 30

B a r l e y

C a d m i u m ,L e a d P o t e x p e r i m e n t s i n g r e e n h o u s e

–F l a v o b a c t e r i u m s p .L 30v e r y n e g a t i v e l y s e n -s i t i v e t o c a d m i u m –F l a v o b a c t e r i u m s p .L 30a n d A .m y s o r e n s 7g i v e i n c r e a s e s o f g r a i n y i e l d –e n h a n c e d l e a d a c c u m u l a t i o n b y p l a n t s i n o c u -l a t e d w i t h A .r a d i o b a c t e r 10a n d A .m y s o r e n s 7–s i g n i ?c a n t g r o w t h i m p r o v e m e n t s s e e n i n p l a n t s i n o c u l a t e d b y a l l s t r a i n s a t h i g h e r c a d -m i u m c o n c e n t r a t i o n s

B e l i m o v e t a l .1998b A g r o b a c t e r i u m r a d i o b a c t e r 10A r t h r o b a c t e r m y s o r e n s 7A z o s p i r i l l u m l i p o f e r u m 137F l a v o b a c t e r i u m s p .L 30

B a r l e y

134

C e s i u m

P o t e x p e r i m e n t s i n g r e e n h o u s e

–F l a v o b a c t e r i u m s p .L 30i n c r e a s e s 134C s u p -t a k e b y b a r l e y ,b u t n o t s i g n i ?c a n t l y ,d u e t o i n c r e a s e d p l a n t b i o m a s s –A .l i p o f e r u m 137s i g n i ?c a n t l y d e c r e a s e s t h e t o t a l a c c u m u l a t i o n o f 134C s

B e l i m o v e t a l .1998c

A g r o b a c t e r i u m r a d i o b a c t e r 10A r t h r o b a c t e r m y s o r e n s 7A z o s p i r i l l u m l i p o f e r u m 137F l a v o b a c t e r i u m s p .L 30

B a r l e y

C a d m i u m

P o t e x p e r i m e n t s i n g r o w t h c h a m b e r –i n c r e a s e d a b s o r p t i o n o f e s s e n t i a l n u t r i e n t s f r o m c o n t a m i n a t e d g r o w t h m e d i u m –s l i g h t s t i m u l a t i o n o f r o o t l e n g t h a n d b i o m a s s i n c o n t a m i n a t e d g r o w t h m e d i u m –A .l i p o f e r u m 137i n c r e a s e d c o n c e n t r a t i o n o f c a d m i u m i n r o o t s ,b u t n o c h a n g e i n c a d m i u m u p t a k e b y p l a n t s i n o c u l a t e d w i t h o t h e r s t r a i n s

B e l i m o v a n d D i e t z 2000

A g r o b a c t e r i u m s p .P s e u d o m o n a s s p .S t e n o t r o p h o m a s s p .M a i z e ,R y e ,P e a ,L u p i n C a d m i u m ,C o p p e r ,L e a d ,N i c k e l ,Z i n c ,C h r o m i u m

P o t e x p e r i m e n t s i n g r o w t h c h a m b e r

–b a c t e r i a s t i m u l a t e s g r o w t h o f m a i z e a n d i n -c r e a s e s m e t a l u p t a k e b y m a i z e ;t h i s e f f e c t m o r e p r o n o u n c e d o n m o r e w e a k l y p o l l u t e d s o i l s c o m p a r e d t o h e a v i l y -p o l l u t e d s o i l s –g r o w t h a n d m e t a l u p t a k e o f l u p i n ,p e a a n d r y e n o t a f f e c t e d b y b a c t e r i a a d d i t i o n

H o ?i c h a n d M e t z 1997A z o s p i r i l l u m b r a s i l e n s e C d E n t e r o b a c t e r c l o a c a e C A L 2P s e u d o m o n a s p u t i d a U W 3

T a l l f e s c u e

P o l y c y c l i c a r o m a t i c h y d r o c a r b o n s ?P A H s ?P o t e x p e r i m e n t s i n g r o w t h c h a m b e r

–a c c e l e r a t e d a n d m o r e c o m p l e t e P A H r e m o v a l f r o m t h e s o i l w i t h i n o c u l a t i o n –e f f e c t i v e n e s s o f P A H r e m o v a l f u r t h e r e n -h a n c e d i n c o m b i n a t i o n w i t h t h e u s e o f l a n d -f a r m e d s o i l a n d i n o c u l a t i o n w i t h P A H -d e g r a d i n g b a c t e r i a

H u a n g e t a l .2003a ,I n p r e s s 19

T a b l e 4.C o n t i n u e d .

B a c t e r i a

P l a n t C o n t a m i n a n t C o n d i t i o n s R e s u l t s o f p a i r i n g o f b a c t e r i a a n d p l a n t R e f e r e n c e

A z o s p i r i l l u m b r a s i l e n s e C d E n t e r o b a c t e r c l o a c a e C A L 2P s e u d o m o n a s p u t i d a U W 3

K e n t u c k y b l u e g r a s s ,T a l l f e s c u e ,W i l d r y e

P A H s P o t e x p e r i m e n t s i n g r o w t h c h a m b e r

–i n c r e a s e d P A H r e m o v a l f r o m s o i l –g e r m i n a t i o n o f a l l t h r e e p l a n t t y p e s i n c r e a s e d d r a m a t i c a l l y i n P A H -s p i k r d s o i l w i t h i n o c u l a -t i o n –r o o t b i o m a s s s i g n i ?c a n t l y i n c r e a s e d i n a l l p l a n t t y p e s

H u a n g e t a l .2003b ,I n p r e s s E n t e r o b a c t e r c a n c e r o g e n e s M i -c r o b a c t e r i u m s a p e r d a e P s e u d o m o n a s m o n t e i l i i

T h l a s p i c a e r u l e s c e n s T h l a s p i a r v e n s e

Z i n c

P o t e x p e r i m e n t s i n g r o w t h c h a m b e r

–T .c a e r u l e s c e n s h a s t w o -f o l d i n c r e a s e o f z i n c c o n c e n t r a t i o n i n r o o t s a f t e r i n o c u l a t i o n a n d f o u r f o l d i n c r e a s e o f z i n c a c c u m u l a t i o n i n s h o o t s –T .c a e r c u l e s c e n s h a s h i g h e r s h o o t b i o m a s s w i t h i n o c u l a t i o n –T .a r v e n s e h a s n o i n c r e a s e d g r o w t h o r m e t a l a c c u m u l a t i o n w i t h i n o c u l a t i o n

W h i t i n g e t a l .2001E n t e r o b a c t e r c l o a c a e C A L 2C a n o l a A r s e n a t e

P o t e x p e r i m e n t s i n g r o w t h c h a m b e r

–s l i g h t i n h i b i t o r y e f f e c t o f C A L 2o n g e r m i n a -t i o n o f c a n o l a i n p r e s e n c e o f a r s e n a t e –p a r t n e r e d w i t h t r a n s g e n i c p l a n t s ,b a c t e r i a i n d u c e d s i g n i ?c a n t l y h i g h e r r o o t a n d s h o o t w e i g h t s i n p l a n t s –n o i n c r e a s e o f a r s e n a t e c o n c e n t r a t i o n b y r o o t s o f p l a n t s N i e e t a l .2002

K l u y v e r a a s c o r b a t a S U D 165C a n o l a ,T o m a t o N i c k e l

P o t e x p e r i m e n t s i n g r o w t h c h a m b e r

–f o r t o m a t o a n d c a n o l a ,b o t h r o o t s a n d s h o o t s p r o t e c t e d f r o m t o x i c i t y w i t h i n o c u l a t i o n –s i g n i ?c a n t d e c e a s e i n e t h y l e n e p r o d u c t i o n b y p l a n t s –n o i n c r e a s e o r c h a n g e i n n i c k e l u p t a k e i n p l a n t m a t e r i a l w i t h i n o c u l a t i o n

B u r d e t a l .1998K l u y v e r a a s c o r b a t a S U D 165/26,S U D 165I n d i a n m u s t a r d ,

C a n o l a ,T o m a t o ,

N i c k e l ,L e a d ,Z i n c

P o t e x p e r i m e n t s i n g r o w t h c h a m b e r

–b o t h s t r a i n s d e c r e a s e s o m e p l a n t g r o w t h i n h i -b i t i o n b y t h e m e t a l s ,b u t n o t a l w a y s s i g n i ?-c a n t l y –S U D 165/26d e c r e a s e s p l a n t g r o w t h i n h i b i t i o n b e s t –n o i n c r e a s e o f m e t a l u p t a k e w i t h e i t h e r s t r a i n o v e r n o n i n o c u l a t e d p l a n t s

B u r d e t a l .200020

c语言中函数malloc的用法

c语言中函数malloc的用法 c语言中函数malloc的用法的用法如下：一、malloc()和free()的基本概念以及基本用法：1、函数原型及说明：void *malloc(long NumBytes)：该函数分配了NumBytes个字节，并返回了指向这块内存的指针。 如果分配失败，则返回一个空指针（NULL）。 关于分配失败的原因，应该有多种，比如说空间不足就是一种。 void free(void *FirstByte)：该函数是将之前用malloc分配的空间还给程序或者是操作系统，也就是释放了这块内存，让它重新得到自由。 2、函数的用法：其实这两个函数用起来倒不是很难，也就是malloc()之后觉得用够了就甩了它把它给free()了，举个简单例子：// Code...char *Ptr = NULL;Ptr = (char *)malloc(100 * sizeof(char));if (NULL == Ptr){exit (1);}gets(Ptr);// code...free(Ptr);Ptr = NULL;// code...就是这样！当然，具体情况要具体分析以及具体解决。 比如说，你定义了一个指针，在一个函数里申请了一块内存然后通过函数返回传递给这个指针，那么也许释放这块内存这项工作就应该留给其他函数了。 3、关于函数使用需要注意的一些地方：A、申请了内存空间后，必须检查是否分配成功。 B、当不需要再使用申请的内存时，记得释放；释放后应该把指向这块内存的指针指向NULL，防止程序后面不小心使用了它。

C、这两个函数应该是配对。 如果申请后不释放就是内存泄露；如果无故释放那就是什么也没有做。 释放只能一次，如果释放两次及两次以上会 D、虽然malloc()函数的类型是(void *),任何类型的指针都可以转换成(void *),但是最好还是在前面进行强制类型转换，因为这样可以躲过一些编译器的检查。 二、malloc()到底从哪里得来了内存空间：1、malloc()到底从哪里得到了内存空间？答案是从堆里面获得空间。 也就是说函数返回的指针是指向堆里面的一块内存。 操作系统中有一个记录空闲内存地址的链表。 当操作系统收到程序的申请时，就会遍历该链表，然后就寻找第一个空间大于所申请空间的堆结点，然后就将该结点从空闲结点链表中删除，并将该结点的空间分配给程序。 就是这样！说到这里，不得不另外插入一个小话题，相信大家也知道是什么话题了。 什么是堆？说到堆，又忍不住说到了栈！什么是栈？下面就另外开个小部分专门而又简单地说一下这个题外话：2、什么是堆：堆是大家共有的空间，分全局堆和局部堆。 全局堆就是所有没有分配的空间，局部堆就是用户分配的空间。 堆在操作系统对进程初始化的时候分配，运行过程中也可以向系

浅析淘宝网的发展现状和未来发展模式

浅析淘宝网的发展现状和未来发展模式 摘要：2008年以来，受到全球金融危机蔓延深化的影响，我国多数行业都受到了不同程度的冲击。但包括网络零售的电子商务行业发展却一路繁荣，成为危机背景下经济增长的一个亮点。本文以淘宝网为例，运用SWOT分析法，浅析目前淘宝网的发展面临的优势，劣势，机会和威胁，而后提出我们对于淘宝未来发展的应对之策。 关键词：淘宝网，网络购物，C2C模式， 一．引言 在国内C2C网络购物网站中，以淘宝网发展最为迅猛，《2009年上半年中国网络购物市场发展报告》显示，2009年上半年网络购物交易规模达到1034.6亿元，其 中，淘宝网交易额达到827.6亿元，占据整体市场份额的80％，位居第二的是拍拍网，市场份额占整体市场份额的8．1％。可以看出，淘宝网的运营模式可以代表国内C2C网购市场的一个重要发展方向，因此研究淘宝网的运营模式对准确把C2C电子商务现状和走势，解决C2C电子商务今后发展急需解决的突出问题，具有现实意义。 二．电子商务的内涵 电子商务：从广义上说，是指以电子设备为媒介进行的商务活动；从狭义上说，是指以计算机网络为基础所进行的各种商务活动，包括商品和服务的提供者、广告、消费者、中介商等有关各方行为的总和。报告中的电子商务是指狭义上的。 三．网络购物概念 网络购物：借助网络实现商品或服务从商家/卖家转移到个人用户（消费者）的过程在整个过程中的资金流，物流和信息流，其中任何一个环节有网络的参与，都称之为网络购物。 网络购物分类见下图： 四．淘宝的市 场份额 目前，我国网 民的大部分网购 商品网络购物交易 集中于平台式购物 网站，，而其首选购物网站则是淘宝网。淘宝网用户市场份额达84.6，处于绝对领先地位。

C语言高级编程及实例剖析

C语言高级编程及实例分析 第一章：内存管理 c语言对程序精心编译时，将函数中命令、语句编译成相应序列的机器指令代码，放在代码段；将已初始化的数据，如已赋值的全局变量、静态局部变量等，放在数据段；将未初始化的数据放在BBS段内；将临时数据，如函数调用时传递的参数、局部变量、返回调用时的地址等放在栈段内；而对一些动态变化的数据，如在程序执行中建立的一些数据结构，如链表，动态数组等，则放在堆结构中。 内存管理系统是操作系统的重要部分。C语言中使用malloc（）函数和free（）函数来分配和释放内存。再次释放已经释放的内存和释放未被分配的内存都会造成系统的崩溃。 1.1.1PC存储器结构 PC机存储器结构分为主存储器、外存储器和高速缓存几个部分。 1.1.4 内存编译模式 编译模式是指如何在内存中放置程序代码及数据，如何分配堆栈，并确认占用的内存大小及如何存取它们，当指定内存模式以后，语言编译程序将按事先选择好的内存模式编译组织程序。C语言提供了6种编译模式，分别是：微模式，小模式，紧凑模式，中模式，大模式和巨模式。 1.1.5 堆概念和结构 堆是一种动态的存储结构（存储链表，动态数组等），实际上就是数据段的自由存储区。 1.1.6 堆管理函数 1.malloc（）函数 用来分配内存。函数原型为void *malloc（unsigned size） 如：int *p；

P= （int*）malloc（sizeof（int））； 如果要分配100个int型的空间时，表示为：int *p=（int*）malloc （sizeof（int））； 2.free（）函数 用来释放内存。函数原型为void *free（指针变量） 如：int *p=（int *）malloc（4）； *p=100； free（p）； 3.realloc（）函数 用来重调空间的大小，函数声明为：void *realloc（void *block，int size）； block是指向要扩张或缩小的内存空间的指针。Size指定新的大小。 4.calloc（）函数 用来分配一个能容纳n个元素，每个元素长度为size的内存空间。函数声明为void *calloc （size_t nelem，size_t elsize）。该函数将分配一个容量为nelem *size大小的空间，并用0初始化该内存区域，即每个地址装入0.该函数将返回一个指向分配空间的指针。如果没有空间可用，则返回NULL指针。若在大数据模式下建立远堆，则可用farmalloc函数。 1.2.2 函数剖析 1 函数init_Heap（） 实现了初始化内存分配程序的功能 2函数My_Free（） 完成函数释放内存的功能 3函数Allocate（）

中国路灯现状与未来发展分析

中国路灯现状与未来发展分析 一、目前全国公路的分布与建设 据“中华人民共和国交通运输部《09年公路水路交通运输行业发展统计公报》”数据统计，2009年底，全国公路总里程达386.08万公里，按公路技术等级分，各等级公路里程分别为：高速公路6.51万公里，一级公路5.95万公里，二级公路30.07万公里，三级公路37.90万公里，四级公路225.20万公里，等外公路80.46万公里。 公路桥梁、隧道总量继续增加。2009年底，全国公路桥梁达62.19万座、2726.06万米，全国公路隧道为6139处、394.20万米，是世界上公路隧道最多的国家。 二、我国公路未来5年的发展 1、公路公路建设方面 我国现在在二级以上的公路建设（不包括高速公路）投入发展规划，每年约以12万公里的速度递增，未来5年将增加60万公里的公路交通枢纽。 2、高速公路建设方面 关于高速公路的网点建设方面，《国家高速公路网规划》已经国务院审议通过，规划的出台标志着中国高速公路发展进入了新的历史阶段。据中国交通部部长张春贤表示，中国国家高速公路规划网络是一项庞大的工程，未来30年静态

投资两万亿元人民币，这个投资的力度随计划建设的进度而变化。2010年前，每年的年均投资大约在1400到1500亿元人民币，每年增加3000公里左右。2010年以后到2020年之间，年均投资大约在1000亿元人民币，每年增加2000公里左右。至2015年，我国高速公路将增加1万公里，总长度预计达到7.51万公里。 3、隧道建设方面 随着公路网点的建设，我国未来五年在隧道建设方面预计将会增加300公里。 三、我国路灯的分布与发展 中国在2006年具有1500万盏路灯，并以每年20％的速度增长，也就是每年新增的路灯数也有300万盏。至2010年，中国路灯的现存数量已经达到2700万盏。 在桥梁、隧道灯方面，按照《公路隧道设计规范》的设计标准，隧道照明每10米按装一盏照明灯具（两边共2盏），目前我国现存隧道灯数量达到624万盏。 在未来5年的道路建设发展规划和发展速度计算，我国将新增道路照明灯具共1500万盏（按照年增加300万盏计算），隧道灯将增加6万盏（按照总长增加300公里计算）。 四、关于路灯方面节能减排的发展思路 近年来，随着我国城市建设规模的不断扩大和建设水平的不断提高，作为城市建设的一项重要内容，城市道路照明、

我去过的地方英语作文4篇

[标签:标题] 篇一：英语比较作文范文4篇 英语比较作文范文4篇 City Life and Suburban Life 1．最近几年越来越多的人迁往近郊居住 2．城市生活和近郊生活各有特点 3．比较起来，我喜欢的是… (1)In recent years more and more homes are being pushed outwards as the activities of business, government and pleasure tend to be concentrated in the centers of the cities. (2)Although most people are reluctant to move to the outskirts of the cities, I feel like living in the suburbs. (3)It is true that the city can provide much convenience and entertainment, the very reason people can’t bear to part with city life. (4)But the cost for the privilege of living in the city is also high. (5)Just think of the places where we live, full of petrol fumes and toxic gases, torn by the roar of buses and lorries day and night, and thronged ceaselessly by great crowds. (6)Besides, as the housing problem in the central city gets more serious, people have to pay high rents for very tiny flats which I would certainly disdain to live in. (7)In contrast, living near the countryside one can enjoy the clean atmosphere, the closeness to nature and the quiet, peaceful surroundings—the essentials of a healthy life. (8)Nothing can be compared, as the pace of modern life is getting quicker, with the first cock crow, the twittering of birds at dawn, and sight of the rising sun glinting on the trees and green fields. (9)Although living in the suburbs you may suffer a little discomfort brought about by the necessity of traveling miles to work every day, the situation will change soon as many highways and subways are being constructed. (10)The new suburban life is fast becoming a predominant pattern of living in most cities; and with the development of traffic and the perfection of services, it will prove to hold great superiority over city life. Newspaper as a Better Source of News 1．现在许多人都从电视上得知天下事 2．但我认为报纸是获取消息的更好来源 3．其理由是… (1)For most of us today, television has become our main source of daily news. (2)This is unfortunate, however, because for several reasons newspapers should be regarded as a better source. (3)It is true that television news can vividly bring into our living rooms dramatic events of singular importance, such as space launchings, natural disasters, wars and so on, but it can not cover important stories in the depth they may deserve because of its time limitation. (4)On the contrary, print news excels in its ability to devote as much space to a story as it sees fit, though it can not compete with television visually. (5)Besides, television is essentially a passive medium. (6)Whether we like a particular piece of news or not, all we have to do is sit in front of the tube and “let it happen”. (7)But a newspaper reader can select what he is interested in, skip what he

中国中小企业发展现状与未来前景分析

中国中小企业发展现状与未来前景分析 中国的民营中小企业差不多都是由个体户、夫妻店和家庭作坊演变而来。由于失业和再就业的压力，总会有大量下岗和失业人员寻求创业的途径和机会，因此个人和家庭创业然后形成小企业将是中国长期而普遍的现象，研究小企业生存和发展的模式，以及政府需要为之提供的政策环境，对中国经济发展和社会稳定具有十分重要的现实意义。下岗和失业人员本身处于弱势地位，我们不可能对其专业素质期望太高，也不能指望在比较短的时间内能通过培训使其成为具有竞争力的企业家。因此，小企业成长需要政策和体制上的帮助。在小企业的发展中有必要克服当前流行的一个错误观点，即小企业做大了就是成功。报告认为，小企业是一种企业形态，有其自身的特性和生存规律，从国内外历史上看，家庭作坊也有百年老店，证明小企业有自己的成功之路。 小企业变成大企业只是一种变化，不能作为成功的标志，大企业也有倒闭的，企业的规模与其成功与否没有直接关系。 另外，小企业的管理模式并不复杂，往往是由经营者直接面对员工、面对客户，所以经营者的素质就等于是企业的素质。小企业主未必都有作大的志向(尽管这种志向并不重要)，但一定都有多盈利的愿望，政府的一切政策法规和支持措施应以帮助小企业盈利为出发点，抓住这个要 点，并以此为中心展开促进小企业发展的各项工作，就会形成小企业繁荣和成长的良好局面。政府不需要设定某种企业模式，也不需要设定企业成长的某种指标，政府的政策法规就是企业自我设计的重要参考因素。有时可以听到抱怨说小企业不注重品牌，不讲求信誉，报告认为不在乎自己形象的企业只能是少数，从一般经济理论分析可以看出，企业

的短期行为通常是由政府政策的短期行为引致，所以克服企业短期行为的最好办法是政府政策的长期稳定和前后一致。 应该说，从中央政府到地方政府的方向性政策中，不管是提供市场准入和提供资金扶持方面，都有很好的法律和法规环境。现在的问题是在个体实施这些法律法规的过程中，尚有一些体制上的不配套、程序设置上的不到位以及更重要的一点即政府工作人员观念转变未完成。以体制 为例，中国的金融体系原来完全服务于国有特别是大型国有企业，在银行自身的商业化改造中，也是注重于银行自身风险的防范和提高盈利能力，还没有来的及改革银行乃至整个金融体系使之能够服务于各类企业特别是中小企业。尽管在中央政府的指示下，各大银行均表示要为中小企业融资提供帮助，但完成整个面对小企业服务体系的设计和安排肯定要花费很长的时间。前任中国人民银行行长戴相龙先生在十六大之前的一次讲话中明确了中国金融系统目前的重要工作之一是完成针对中小企业的金融服务体系改革，预示着中小企业的融资状况在不远的将来会有所改善，但在现行体制下中小企业的资金紧张状况还会再持续一段时间。 另外一个重要问题是中小企业如何面对政府政策的变化和政府部门的管理。中小企业是中国新生的经济门类，政府的政策、法规和体制必然是随着小企业的成长壮大而不断地制定、修改、完善和调整，换句话说就是存在边制定边修改的情况，这就会给小企业带来很大的压力。如上 述，小企业的特点就是人数比较少，不能象大企业那样可以设立专门的部门或人员负责政府相应部门的联系和协调工作。因此，小企业在忙于自己生意的同时，就难于拿出许多时间奔波于政府的各个职能部门之中，而且即使这样，也未必跟得上一些政策法规的变化。这种情况一方面增加了小企

2019年最喜欢的国家英语作文-范文word版 (3页)

本文部分内容来自网络整理，本司不为其真实性负责，如有异议或侵权请及时联系，本司将立即删除！ == 本文为word格式，下载后可方便编辑和修改！ == 最喜欢的国家英语作文 导语：你最喜欢哪个国家呢?每个人的答案都不一样。下面是小编为大家整理的英语作文，希望对大家有所帮助。更多相关的知识，请关注CNFLA学习网! 1最喜欢的国家英语作文 Besides the China my favorite country is Korea. I like Korean pop songs I like Korean stars and I can speak a little Korean. My favorite starts are Super Junior what the thirteen pretty boys they are! And I also like their songs for example sorry sorry and no other .I think their voice is sounds of nature! Their behave like Gentlemen. I like An Zhaoxi(安昭熙) too! She is very cute! She is one of Wonder Girlsfrom Korea their songs are nicetoo like Nobody and Tell me! My friends call me“Ha Hanzu”! Besides the China which country's cultural do you like best?除了中国，我最喜欢的国家是韩国。我喜欢韩国流行歌曲，我喜欢韩国明星，我会说一点韩语。我最喜欢的开始是Super Junior，他们是十三个漂亮男孩!我也 喜欢他们的歌，比如说对不起，对不起，我想他们的声音是天籁!他们的举止像绅士。 我喜欢安朝熙(安昭熙)，太!她很可爱!她是一个奇迹girlsfrom韩国，他们的歌曲是好的，也没人告诉我! 我的朋友叫我“哈汉祖”! 除了中国，哪个国家的文化你最喜欢? 2最喜欢的国家英语作文

c语言中free的用法如何工作.doc

c语言中free的用法如何工作c语言中free的用法：malloc()和free() 1、函数原型及说明： void *malloc(long NumBytes)：该函数分配了NumBytes个字节，并返回了指向这块内存的指针。如果分配失败，则返回一个空指针（NULL）。 关于分配失败的原因，应该有多种，比如说空间不足就是一种。 void free(void *FirstByte)：该函数是将之前用malloc分配的空间还给程序或者是操作系统，也就是释放了这块内存，让它重新得到自由。 2、函数的用法： 其实这两个函数用起来倒不是很难，也就是malloc()之后觉得用够了就甩了它把它给free()了，举个简单例子： 程序代码： // Code... char *Ptr = NULL; Ptr = (char *)malloc(100 * sizeof(char)); if (NULL == Ptr) { exit (1); } gets(Ptr);

// code... free(Ptr); Ptr = NULL; // code... 就是这样！当然，具体情况要具体分析以及具体解决。比如说，你定义了一个指针，在一个函数里申请了一块内存然后通过函数返回传递给这个指针，那么也许释放这块内存这项工作就应该留给其他函数了。 3、关于函数使用需要注意的一些地方： A、申请了内存空间后，必须检查是否分配成功。 B、当不需要再使用申请的内存时，记得释放；释放后应该把指向这块内存的指针指向NULL，防止程序后面不小心使用了它。 C、这两个函数应该是配对。如果申请后不释放就是内存泄露；如果无故释放那就是什么也没有做。释放只能一次，如果释放两次及两次以上会 出现错误（释放空指针例外，释放空指针其实也等于啥也没做，所以释放空指针释放多少次都没有问题）。 D、虽然malloc()函数的类型是(void *),任何类型的指针都可以转换成(void *),但是最好还是在前面进行强制类型转换，因为这样可以躲过一 些编译器的检查。 好了！最基础的东西大概这么说！现在进入第二部分： c语言中free的用法：malloc()到底从哪里得来了内存空间 1、malloc()到底从哪里得到了内存空间？答案是从堆里面获得空间。也就是说函数返回的指针是指向堆里面的一块内存。

市场分析一体机市场现状及未来发展方向分析

（市场分析）一体机市场现状及未来发展方向分析

标题：壹体机市场现状及未来发展方向分析 资料信息： 壹体机是什么呢？它就是集成了打印、复印、扫描、传真里俩种或俩种之上功能的办公设备。因为壹体机除了于速度、分辨率等性能上和单壹设备不相上下之外，最主要的是于功能集成、外观体积等品质上要优于单壹功能的办公设备，它倡导了符合当今集成化，简约化的办公潮流。简言之，壹体机就是壹个“N”(N≥2)，N的结果将是“远远大于1”！ 信息化时代产品的更新换代之快可用“壹日千里”来形容，技术进步和市场需求互为动力，为我们平凡的生活谱写了美丽的乐章。近年来大规模出现的“壹体机”就是这些乐章的壹个重要音符。随着办公设备向自动化、数字化、集成化方向发展，用户们为了进壹步完善办公环境，开始使用代表这种发展方向的壹体机设备。由于其具有操作简捷、工作效率高等优势，很快便赢得了我们办公者的青睐，赢得了部分办公设备市场。 从技术方式上来见，壹体机能够分为碳带热转印壹体机、喷墨壹体机和激光壹体机。从它们的市场地位而言，壹体机可分成激光型、喷墨型俩大类。喷墨壹体机凭借色彩处理和价格优势占据了相当的市场份额。激光壹体机则凭借其优秀的输出质量和数码技术，于壹体机市场中占据主流地位。随着人们消费能力的提高，办公需求的增加以及激光打印技术的进壹步发展，激光壹体机很大程度上将成为未来壹体机市场的主导产品。 1998～2001年中国多功能壹体机市场功能组合方式构成 传真、打印和复印的功能组合是目前市场的主流组合形式，而全方位集成的产品也有壹定的规模。 实际上，不管是喷墨壹体机仍是激光壹体机，它们且不是多个设备的简单叠加，而是采用了完善的集成技术，将复印、打印、扫描、传真等众多功能有机集于壹身，既节省空间，又经济高效。虽说这些功能能够同时工作，但每款壹体机仍是有不同的主导功能，有的以打印为主，有的以扫描为主，有的以复印为主，有的以传真为主等，这样就形成了不同导向的壹体机市场环境。 而当下不论于办公室仍是家庭，最常用的仍是打印和复印功能。不少厂商推出的壹体机大多是由传真机或打印机脱胎换骨而成，此种机型于传真或打印方面功能突出，而于复印方面表现平平。多功能壹体机的复印功能是数码复印，同普通复印机相比有许多优势。它利用缓冲技术，可实现壹次扫描、多次拷贝，使复印速度和打印速度相当；有些复印导向壹体机仍具有数码编辑能力，能实现去除复印件边框、预留装订区等功能；重要壹点是数码复印的质量比普通复印有质的飞跃，多数喷墨打印类的壹体机仍能轻松实现高品质的彩色复印。由于复印导向壹体机技术复杂，所以于这个领域仍有待进壹步发展。 1998～2001年中国多功能壹体机市场功能输出方式构成 激光输出以其优秀的输出质量和真正的数码技术，于多功能壹体机市场中占据主流地位，而喷墨输出凭借色彩处理和价格上的优势也占据着相当的份额。 从发展趋势来见，喷墨输出方式于最近俩年有不断上升的趋势，这正是喷墨输出的多功能壹体机的相对较高的性价比和适合中国经济情况以及用户购买力的表现。

英语作文 --- 为什么你想去国外参加交换

Write in 300 words why you would like to participate in the student exchange programme in these countries. French – Belgium, france, swizerland German- Austria, germany, Switzerland Broaden vision Gain independence Experience different culture and ways of life International experience Asthetics of the cities I would like to participate in the student exchange programme because I want to take a step out of my home country, Singapore, to gain international exposure of different cultures and way of learning and doing things. Venturing beyond our local shores will allow me to step out of my comfort zone, develop my own opinions and build up my character. It will also improve my self-confidence and communication skills. Furthermore, the participation in the exchange programme will enable me to widen my social circle by making more international friends. As a business student, establishing a wider social network may be helpful when I enter the workforce, particularly into fields such as finance and banking. In addition, studying abroad will broaden my vision and expose me to new things and methods employed by people from a vastly different society. I believe that with these experiences gained, it will allow me to contribute to the future organizations I would be working for by sharing the other possible perspectives locally and internationally. In conclusion, with the opportunity to experience different culture and sharpen my interpersonal skills as well as widen my social circle, I wish to not only have a fun-filled and interesting university life but also to acquire skills for life that will allow me to contribute and give back to the society that has nurtured me.

支付宝现状与未来发展趋势研究分析

支付宝现状与未来发展趋势分析

————————————————————————————————作者：————————————————————————————————日期： 2

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我想去北京英语作文

三一文库（https://www.docsj.com/doc/d616625743.html,） 〔我想去北京英语作文〕 我想去北京的英语作文如何写？那么，下面是小编给大家整理收集的我想去北京英语作文，供大家阅读参考。 我想去北京英语作文1 I’d like to go to a beautiful place. I think it would be Beijing. Beijing is not only our capital city, but also a famous city with long history and wonderful culture. Beijing is also China’s political and cultural center. There’re many old places of great interest, such as the Great Wall, the Summer Palace, the Forbidden City, the Temple of Heaven, and Tiananmen Square. Once you see Tiananmen Square, you will think of Beijing. It has been the symbol of Beijing since 1949. 我想去北京英语作文2 I went to Beijing more than eight times. Beijing is the capital of China. It’s a big city. I am very familiar with Beijing. It takes an hour and forty minutes from Nantong to Beijing by plane. There are many tall buildings in Beijing. It’s a modern city. My family visited the Great Wall, the Summer

free函数和malloc函数

malloc 原型：extern void *malloc(unsigned int num_bytes); 用法：#include 或#include 功能：分配长度为num_bytes字节的内存块 说明：如果分配成功则返回指向被分配内存的指针，否则返回空指针NULL。 当内存不再使用时，应使用free()函数将内存块释放。 malloc的语法是：指针名=（数据类型*）malloc（长度）,（数据类型*）表示指针. 举例： // malloc.c #include #include main() { char *p; clrscr(); // clear screen p=(char *)malloc(100); if(p) printf("Memory Allocated at: %x",p); else printf("Not Enough Memory!\n"); if(p) free(p); getchar(); return 0; } malloc（）函数的工作机制 malloc函数的实质体现在，它有一个将可用的内存块连接为一个长长的列表的所谓空闲链表。调用malloc函数时，它沿连接表寻找一个大到足以满足用户请求所需要的内存块。然后，将该内存块一分为二（一块的大小与用户请求的大小相等，另一块的大小就是剩下的字节）。接下来，将分配给用户的那块内存传给用户，并将剩下的那块（如果有的话）返回到连接表上。调用free函数时，它将用户释放的内存块连接到空闲链上。到最后，空闲链会被切成很多的小内存片段，如果这时用户申请一个

globalalloc、malloc和new的区别

GlobalAlloc是为了与Win16兼容才保留的，在Win32下不要使用。全局内存对象使用GlobalAlloc函数分配,在Windows 3.X 的时代，分配的内存可以有两种，全局的和局部的，例如GlobalAlloc和LocalAlloc。但在Win32的时代这些函数已经被废弃了，现在的内存只有一种就是虚存。在Win32中所有的进程所使用的内存区域是相互隔离的，每个进程都拥有自己的地址空间。而且系统使用了页面交换功能，就是利用磁盘空间来模拟RAM，在RAM中数据不使用时将会被交换到磁盘，在需要时将会被重新装入RAM。 两者都是在堆上分配内存区。 malloc()是C运行库中的动态内存分配函数，WINDOWS程序基本不使用了，因为它比WINDOWS内存分配函数少了一些特性，如，整理内存。 GlobalAlloc()是16位WINDOWS程序使用的API，返回一个内存句柄，在实际需要使用时，用GlobalLock()来实际得到内存区。但，32位WINDOWS系统中，应使用新的内存分配函数HeapAlloc()以得到更好的支持，GlobalAlloc()还可以用，主要是为了兼容。 HeapAlloc apply memory from kernel32.dll GlobalAlloc obsolete malloc apply memory form C runtime memory ,and C r untime applys from kernel32.dll new a wrapper of malloc but it is NOT a must for new to implement based on malloc. CoMemAlloc apply memory from kernel32.dll all are heap memory. recommend HeapAlloc for big block memory allocation recommend stack memory space. recommend HeapAlloc for big block memory allocation recommend stack memory space. malloc与free是C++/C语言的标准库函数，new/delete是C++的运算符。它们都可用于申请动态内存和释放内存。 对于非内部数据类型的对象而言，光用maloc/free无法满足动态对象的要求。对象在创建的同时要自动执行构造函数，对象在消亡之前要自动执行析构函数。由于malloc/free是库函数而不是运算符，不在编译器控制权限之内，不能够把执行构造函数和析构函数的任务强加于malloc/free。 因此C++语言需要一个能完成动态内存分配和初始化工作的运算符new，以及一个能完成清理与释放内存工作的运算符delete。注意new/delete不是库函数。 我们先看一看malloc/free和new/delete如何实现对象的动态内存管理，见示例7-8。 class Obj{ public : Obj(){ cout << “Initialization” << endl; } ~Obj(){ cout << “Destroy” << endl; } void Initialize(){ cout << “Initialization” << endl; } void Destroy(){ cout << “Destroy” << endl; } }; void UseMallocFree(){ Obj *a = (obj *)malloc(sizeof(obj)); // 申请动态内存

动态存储分配

动态存储分配在此之前，我们用于存储数据的变量和数组都必须在说明部分进行定义。C编译程序通过定义语句了解他们所需存储空间的大小，并预先为其分配适当的空间。这些空间一经分配，在变量或数组的生存期内是固定不变的。故称这种分配方式为“静态存储分配”。C语言中还有一种称作“动态存储分配”的内存空间分配方式：在程序执行期间需要空间来存储数据时，通过“申请”分配指定的内存空间；当有闲置不用的空间时，可以随时将其释放，由系统另作它用。用户可通过调用C语言提供的标准库函数来实现动态分配，从而得到指定数目的内存空间或释放指定的内存空间。ANSI C标准为动态分配系统定义了四个函数，它们是：malloc、calloc、free和realloc。使用这些函数时，必须在程序开头包含文件stdib.h。本节只介绍malloc、calloc和free函数的使用。1、malloc函数和free函数（1）malloc函数ANSI C标准规定malloc函数返回值的类型为void *,函数的调用形式为：malloc （size）。要求size的类型为unsigned int。malloc函数用来分配size个字节的存储区，返回一个指向存储区首地址的基类型为void的地址。若没有足够的内存单元供分配，函数返回空（NULL）。假设int型数据占2字节，float型数据占4字节存储单元，以下程序段将使pi指向一个int类型的存储单元，使pf指向一个float类型的存储单元。int *pi;float *pf;pi=(int *)malloc(2);pf=(float *)malloc(4);由于在ANSI C中malloc函数返回的地址为void *（无值型），故在调用函数时，必须利用强制类型转换将其转换成所需的类型。此处括号中的*号不可少，否则就转换成普通变量类型而不是指针类型了。若有以下语句段：if(pi!=NULL) *pi=6;if(pf!=NULL) *pf=3.8;赋值后数据的存储单元情况如图7.2所示。 pi pf图7.2由动态分配得到的存储单元没有名字，只能靠指针变量来引用它。一旦指针改变指向，原存储单元及所存储数据都将无法再引用。通过调用malloc函数所分配的动态存储单元中没有确定的初值。若不能确定数据类型所占字节数，可以使用sizeof运算符来求得。例如：pi=(int *) malloc（sizeof（int））；pf=(float *) malloc（sizeof（float））；这是一种常用的形式。它由系统来计算指定类型的字节数。（2）free函数函数的调用形式为：free（p）；这里指针变量p必须指向由动态分配函数malloc分配的地址。free函数将指针p所指的存储空间释放，使这部分空间可以由系统重新支配。此函数没有返回值。2、calloc函数ANSI C 标准规定calloc函数返回值的类型为void *，函数的调用形式为：calloc（n，size）;要求n和size的类型都为unsigned int。calloc函数用来给n个同一类型的数据项分配连续的存储空间。每个数据项的长度为size个字节。若分配成功，函数返回存储空间的首地址；否则返回空。由调用calloc函数所分配的存储单元，系统自动置初值0。例如：char *ps;ps=（char *）calloc（10，sizeof（char））；以上函数调用语句开辟了10个连续的char类型的存储单元，由ps指向存储单元的首地址。每个存储单元可以存放一个字符。显然，使用calloc函数动态开辟的存储单元相当于开辟了一个一维数组。函数的第一个参数决定了一维数组的大小；第二个参数决定了数组元素的类型。函数的返回值就是数组的首地址。使用calloc函数开辟的动态存储单元，同样用free函数释放。