Relationship between stable carbon isotope discrimination and water use

Relationship between stable carbon isotope discrimination and water use ef?ciency under regulated de?cit irrigation of pear-jujube tree

Ningbo Cui a ,c ,Taisheng Du b ,*,Shaozhong Kang b ,*,Fusheng Li d ,Xiaotao Hu a ,Mixia Wang a ,Zhijun Li a

a

Key Laboratory of Agricultural Soil and Water Engineering in Arid and Semiarid Areas,Ministry of Education,Northwest A&F University,Yangling,Shaanxi,712100,China b

Center for Agricultural Water Research in China,China Agricultural University,Beijing,100083,China c

College of Hydropower Engineering,Sichuan University,Chengdu,Sichuan,610065,China d

Agricultural College,Guangxi University,Nanning,Guangxi,530005,China

1.Introduction

Shortage of water resource is a problem in the fruit production in the arid and semi-arid region of northwest China,where many fruit trees need to supply irrigation water during the growing season.Because regulated de?cit irrigation (RDI)can save irrigation water and improve crop water use ef?ciency (WUE)of pear-jujube tree greatly (Cui et al.,2008),it may alleviate the contradiction of water need and supply in this region.

Water use ef?ciency is an important index in indicating the ability of plant adapted to the arid environment,and it is divided into WUE i (photosynthesis rate/transpiration rate,P n /T r )and WUE n (photosynthesis rate/stomatal conductance of CO 2,P n /g s )

at leaf level (Erice et al.,2007),and WUE y (yield/crop water consumption,Y /ET c )at yield level.WUE n can express leaf WUE better than WUE i (Cabrera-Bosquet et al.,2007).The WUE i and WUE n measured by gas exchange method are the instantaneous values and can only explain short-term response to the environ-mental factors,but they have the limitations in expressing plant productivity and the physiological process during longer growth stage.

Carbon isotope discrimination resolution (D 13C)and carbon isotope ratio (d 13C)are two commonly used indexes in the stable carbon isotope discrimination.D 13C can re?ect the change of C i /C a [the ratio of leaf intercellular CO 2concentration (C i )to the ambient atmosphere CO 2concentration (C a )]in a time interval,and it can indirectly express the deviation of the leaf intercellular 13C/12C relative to the ambient atmosphere 13C/12C on the basis of plant dry mass,such carbon isotope discrimination can directly re?ect the impendent difference in carboxylation reaction of ribulose dipho-sphate carboxylase (RUBPC)and phosphoenolpruvate carboxylase

Agricultural Water Management 96(2009)1615–1622

A R T I C L E I N F O Article history:

Received 4January 2009

Received in revised form 27May 2009Accepted 14June 2009

Available online 18July 2009Keywords:

Carbon isotope discrimination Pear-jujube (Zizyphus jujube Mill.)Regulated de?cit irrigation Water use ef?ciency

A B S T R A C T

To investigate the relationship between stable carbon isotope discrimination (D )of different organs and water use ef?ciency (WUE)under different water de?cit levels,severe,moderate and low water de?cit levels were treated at bud burst to lea?ng,?owering to fruit set,fruit growth and fruit maturation stages of ?eld grown pear-jujube tree,and leaf stable carbon isotope discrimination (D L )at different growth stages and fruit stable carbon isotope discrimination (D F )at fruit maturation stage were measured.The results indicated that water de?cit had signi?cant effect on D L at different growth stages and D F at fruit maturation stage.As compared with full irrigation,the average D L at different growth stages and D F at fruit maturation stage were decreased by 1.23%and 2.67%for different water de?cit levels,respectively.D L and D F among different water de?cit treatments had signi?cant difference at the same growth stage (P <0.05).Under different water de?cit conditions,signi?cant relationships between the D L and WUE i (photosynthesis rate/transpiration rate,P n /T r ),WUE n (photosynthesis rate/stomatal conductance of CO 2,P n /g s ),WUE y (yield/crop water consumption,Y /ET c )and yield,or between the D F and WUE y and yield were found,respectively.There were signi?cantly negative correlations of D L with WUE i ,WUE n ,WUE y and yield (P <0.01)at the fruit maturation stage,or D L with WUE i and WUE n (P <0.01)over whole growth stage,respectively.D F was negatively correlated with WUE y ,WUE n and yield (P <0.05),but positively correlated with ET c (P <0.01)over the whole growth stage.Thus D L or D F can compare WUE n and WUE y ,so the stable carbon isotope discrimination method can be applied to evaluate the water use ef?ciency of pear-jujube tree under the regulated de?cit irrigation.

?2009Elsevier B.V.All rights reserved.

*Corresponding authors.Fax:+861062737611.

E-mail addresses:dutaisheng@https://www.360docs.net/doc/ef3956177.html, (T.Du),kangshaozhong@https://www.360docs.net/doc/ef3956177.html, (S.Kang).

Contents lists available at ScienceDirect

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j o u r n a l h o m e p a g e :w w w.e l se v i e r.c o m /l o c a t e /a g w a t

(PEPC)as well as the diffusion of CO2in the interior of leaf(Dawson

et al.,2002).Simultaneously,D13C can express the WUE y and may infer WUE i and WUE n(Pate,2001).The d13C of plant samples by isotope mass spectrometer can integrate the carbon absorption of all

organs and the change of photosynthetic characteristic and

physiological indices in the plant growth cycle,which can quantify

water stress effect.Thus it can evaluate the accuracy of mean leaf

WUE determined by the gas exchange(Su et al.,2005).

The D13C of different plant organs can express the WUE at different levels.Farquhar et al.(1989)found the negative

correlation of leaf D13C(D L)with WUE n in C3plants,and it can also express WUE i.Souza et al.(2005)found a negative correlation

of D L with WUE n in grape under water de?cit condition.When soil water levels were40%,70%and100%of?eld capacity in potted

durum wheat,the D L was negatively correlated with WUE i (R2=0.58)and WUE n(R2=0.78),respectively(Cabrera-Bosquet

et al.,2007).El-sharkawy and Tafur(2007)indicated signi?cantly

negative relationship between D L and WUE n in cassava under the naturally water de?cit environment,and Cabuslay et al.(2002)

obtained similar result in rice.Under the water de?cit condition,

the D L had signi?cantly negative correlation with WUE(biomass/ water consumption)in the poplar(Yin et al.,2005),or the D L and D F had signi?cantly negative correlation with WUE(biomass/ water consumption)in rice,respectively(Impa et al.,2005;Zhao

et al.,2004a),or D F had strong negative correlation with WUE y in barley both in greenhouse(R=0.79)and?eld conditions(R=0.94) (Anyia et al.,2007).However,some studies con?rmed that the D F was positively correlated with WUE y under different water de?cit conditions(Andrea et al.,2006;Philippe et al.,2005,2007).

The relationship between organ D13C and yield is affected by the environmental condition,growth stage and experimental organ(Araus et al.,2003),and it may be positive(Dorit et al.,2006; Monneveux et al.,2004),negative(Andrea et al.,2006;Philippe et al.,2005,2007),even no correlation(El-Hendawy et al.,2005;Xu et al.,2007).In addition,Grattan et al.(2006)showed that the D13C recorded under different water conditions during the growth stage might provide the important information for the effective irrigation.

The D13C was a simple,direct and effective method in evaluating the plant WUE under different water conditions. Now there are many studies on the relationship between the D13C and WUE of?eld crops,e.g.,wheat,rice and maize etc.,but few studies on fruit trees.The measurement of fruit tree WUE at leaf and yield levels is quite complex and time-consuming,but the accurate and fast measurements of fruit tree WUE at different levels can improve the orchard water management,therefore,it is important to study on the reliability of various organ D13C in indicating the WUE of fruit tree under different growth stages and water de?cit levels.

Pear-jujube(Zizyphus jujube Mill.)is an important export fruit

of China and is mainly distributed in the arid and semi-arid region

of north China.At present,irrational irrigation method results in

waste of water resources and poor water use ef?ciency in this

region and insuf?cient water supply has already become an

important limiting factor affecting the production of local pear-

jujube.How to combine the carbon stable isotope technology and

photosynthesis index of pear-jujube tree in providing the fast and

simple technical guidance for the water-saving,production-

increasing,and high-quality fruit production has become an

urgent problem.The objectives of our study are to(1)investigate

the effect of different water de?cit at different growth stages on D L and D F of pear-jujube tree over whole growth stage,(2)investigate the relationship between leaf D L,fruit pulp D F and WUE i,WUE n, WUE y,yield and water consumption of pear-jujube tree under WUE and related indices of pear-jujube tree under the regulated de?cit irrigation condition in the arid and semi-arid region and determine the proper sampling date and organ of D13C in indicating the WUE.

2.Materials and methods

2.1.Experimental site,plant and design

The?eld experiment was located at Dengzhuang,Dali,Shannxi, China(latitude348520N,longitude1098560E,1340m altitude).The site situation was described in Cui et al.(2008).Twenty-eight7-year-old pear-jujube trees(Zizyphus jujuba Mill.cv.Lizao)were selected as experimental trees.The selected trees were healthy and uniform.Trees were planted in3m within-row spacing and2m between the rows.The whole growing season of pear-jujube tree can be divided into?ve growth stages,i.e.,bud burst to lea?ng stage(stage I,early April–early May),?owering to fruit set stage (stage II,mid May–late June),fruit growth stage(stage III,late June–late July),fruit maturation stage(stage IV,early August–early September)and dormancy stage(stage V,this October–next March).

Treatments included full irrigation(FI,control),low(LD,2/3of full irrigation),moderate(MD,1/2of irrigation)and severe(SD,no irrigation)water de?cit treatments at the growth stages I–IV. Totally,13treatments were designed and applied.FI treatment received irrigation water of900m3/ha(90mm)at each growth stage.LD,MD and SD treatments,respectively received irrigation water of600,450and0m3/ha during the water de?cit treatment stage while they got irrigation water of900m3/ha at other three stages.Each treatment was applied to one tree in a plot with the area of3m2(2m?1.5m).Four plots were labeled for repetition of FI,two plots for repetition of the other treatments.One irrigation ditch of20cm in width and80cm in depth between different treatments was built and covered with double layers of plastic?lm in order to prevent water from lateral movement.And one20cm high ridge between different treatments was also built and covered with double layers of plastic?lm.Pear-jujube trees is highly resistant to water stress,by the irrigation experience of the local fruit grower,soil water content in the FI treatment was kept about 55%of?eld capacity(170.6mm in the upper1.0m soil layer),and irrigation date was determined when the FI treatment needed to be irrigated,i.e.,soil water content in the FI treatment was lower than 55%of?eld capacity.All treatments were irrigated by border irrigation method and randomly distributed,and with the same cultivation,fertilization and diseases and insect control etc.The irrigation schedule was shown in Table1.

2.2.Measurements

Physiological indices such as leaf photosynthesis rate(P n), transpiration rate(T r),stomatal conductance(g s),intercellular CO2 concentration(C i)and ambient atmosphere CO2concentration(C a) were measured with a LI-6400portable photosynthesis system(LI-COR,Nebrasaka USA.)at9:30–10:30in the morning of2–3 cloudless clear days at each growth stage.Each treatment selected a tree in which three sunlit healthy leaves were randomly labeled in different directions,each leaf was measured three times in every measurement,and the same living leaves were measured at each growth stage.The average value of each index in different days was computed,and then leaf WUE i(P n/T r),WUE n(P n/g s)and C i/C a(the ratio of C i to C a(the ambient atmosphere CO2concentration))were calculated at each growth stage,respectively.

At harvest,fresh yield per tree was weighted,and WUE y was

N.Cui et al./Agricultural Water Management96(2009)1615–1622 1616

The stable carbon isotope ratio (d 13C)of different organs in pear-jujube was measured with the MAT-251mass analyzer (Finnigan Mat Corp.,USA,the sensitivity is 1000mol/ion,the ion source vacuum <3.1?10à6Pa,the analysis room vacuum <5.1?10à6Pa).After the measurement of physiological index had been completed,the leaves in different water de?cit treatments were sampled at different growth stages,and after the air-drying leaves were grinded and sieved,1g sample was taken for the measurement of d 13C.Eight healthy and relatively identical colour and lustre fruits were selected in each treatment at the relatively identical position in different directions at the fruit maturation stage.1g fruit pulp was taken for the measurement of d 13C after oven-dried.The d 13C values of leaf and fruit were respectively,measured as described in Farquhar et al.(1989)in detail.Take PDB (Pee Dee Belemnite)as the standard,d 13C (%)was calculated according to the equation of Farquhar et al.(1989).

d 13C e%T?

ee13C =12C Tsample àe13C =12C Tstandard T

eC =12C Tstandard

!?1000(1)

where (13C/12C)sample and (13C/12C)standard are the 13C/12C ratios of the sample and standard PDB,respectively.When the analysis error 0.2%,carbon isotope discrimination (D 13C,%)was calculated as:

D 13

C e%T?

d air àd plant 1td plant

?1000(2)

where d air is the d 13C of air CO 2(à7%),D 13C is plant 13C discrimination resolution.When the D 13C is greater,the dis-crimination is higher,but its corresponding abundance of 13C in plant and d 13C were lower.Leaf D 13C at different growth stages and fruit D 13C at fruit maturation stage can be denoted as D L and D F ,respectively.2.3.Data analysis

Correlation analysis,regression analysis,analysis of variance (ANOVA)were performed using SPSS 13.0(Chicago,USA),and all treatment means were compared for signi?cant differences using the Duncan’s multiple range test at level of P =0.05.3.Results and discussion

3.1.Carbon isotope discrimination of leaf and fruit in pear-jujube tree under different water de?cit levels

Fig.1shows that leaf D 13C (D L )and fruit D 13C (D F )ranged 19.33–21.03%and 18.06–19.43%under different water de?cit treatments,with average D L and D F of 19.95%and 18.87%,https://www.360docs.net/doc/ef3956177.html,pared to full irrigation (FI),D L values in severe (SD),moderate (MD)and low (LD)water de?cit treatments were decreased by 0.77–2.52%,0.72–1.98%and 0.10–0.87%,the D F values in corresponding treatments 3.03–6.91%,1.21–4.95%and decreased by 1.23%and 2.67%for different water de?cit levels,respectively.

Fig.1also shows that the both D L and D F had signi?cant difference among different treatments at the same growth stage (P <0.05),and the D L was signi?cantly higher than D F (P <0.01),which was similar to the results of sun?ower (Lambrides et al.,2004),grapevine (Souza et al.,2005)and barley (Anyia et al.,2007).The difference between the D L and D F may result from (1)the fractionation during the export,phloem loading and unloading and transport of carbohydrate from photosynthetic to storage organs (Dorit et al.,2006),(2)different chemical composition of different organs,for example,higher contents of lipid and lignin may lead to a relative depletion in 13C while higher cellulose contents lead to a relative enrichment (Brugnoli and Farquhar,2000),(3)the difference of D value in fruits and leaves.Fruits that are the products of secondary metabolism usually have lower D value than the leaves,which are the primary products of photosynthesis (Zhao et al.,2004b ).In addition,the D L value at early growth stage (stages I and II)was signi?cantly lower than that at later growth stage (stages

Table 1

Irrigation schedule for regulated de?cit irrigation of ?eld grown pear-jujube tree (mm).Growth stage T 1(CK)T 2(SD)T 3(MD)T 4(LD)T 5(SD)T 6(MD)T 7(LD)T 8(SD)T 9(MD)T 10(LD)T 11(SD)T 12(MD)T 13(LD)Bud burst to lea?ng 9004560909090909090909090Flowering to fruit set 9090909004560909090909090Fruit growth 9090909090909004560909090Fruit maturation

90

90

90

90

90

90

90

90

90

90

45

60

Fig.1.Change of 13C discrimination (D 13C)in leaves (D L )and fruit (D F )of pear-jujube tree under different water de?cit.FI (full irrigation,control),LD (low,2/3of full irrigation),MD (moderate,1/2of irrigation)and SD (severe,no irrigation).N.Cui et al./Agricultural Water Management 96(2009)1615–1622

1617

III and IV),which was consistent with the result of desert plant in central Hexi corridor region (Su et al.,2003).Such difference may result in the difference of environmental factors,e.g.,temperature and solar radiation between the early and later growth stages of pear-jujube tree,and its own physiological characteristic.

Comparing to FI,the D L and D F decreased with the increase of water de?cit at the same growth stage.Under normal water environment,when the photosynthesis absorbs CO 2,the plant repels heavy isotope 13C,and then the 13C/12C ratio in the photosynthesis product was lower than that of atmospheric CO 2,thus the accumulated 13C and d 13C were relatively lower,i.e.,higher D 13C value.However,under the water de?cit condition,the heavy isotope 13C repelled by the plant is signi?cantly reduced,thus the accumulated 13C and d 13C were relatively higher,i.e.,lower D 13C value.In addition,the D 13C had signi?cant difference between different organs of pear-jujube tree under different water de?cit treatments,which was similar to the results of beet (Andrea et al.,2006;Dorit et al.,2006),grapevine (Souza et al.,2005)and rice (Murasea et al.,2006).

Table 2shows that D L and D F values had signi?cant difference among different water de?cit growth stages and water de?cit treatments (P <0.001).And the orders of D L and D F value at different growth stages were IV >III >II >I and III >I >II >IV,respectively.

3.2.Change of C i /C a ,WUE,ET c and yield of pear-jujube tree under different water de?cit levels

As shown in Table 3,compared to the FI,the C i /C a [the ratio of leaf intercellular CO 2concentration (C i )to the ambient atmosphere CO 2concentration (C a )]in the other growth stages except the stage II had signi?cant difference (P <0.01)among different water de?cit treatments.The WUE i (photosynthesis rate/transpiration rate,P n /T r )in the other growth stages except stage III had signi?cant difference (P <0.01)among different water de?cit treatments.Meanwhile,WUE i in different water de?cit treatments was reduced at stage I,but increased slightly at stages III and IV.The WUE n (photosynthesis rate/stomatal conductance of CO 2,P n /g s )at different growth stages also had signi?cant difference (P <0.05)among different water de?cit treatments (P <0.05).There are signi?cant differences of WUE y ,ET c and yield (P <0.05)among different water de?cit treatments at the same growth stage.

As compared with FI,LD and MD treatments at stages II and all water de?cit treatments at stages III and IV signi?cantly increased the WUE i ,furthermore,MD and SD treatments at different growth stages increased WUE n ,which was also supported by the results on poplar (Yin et al.,2005),spruce (Warren and Adams,2006),loquat (Yang et al.,2007)and apple (Li et al.,2007).Under the water de?cit condition,g s and T r were greatly reduced but the P n was

Table 2

Two-way variance analyses of the D L and D F between water de?cit and growth stage.Variance source

D L

D F

DF

SS MS F value Signi?cance

DF SS MS F value Signi?cance

Water de?cit 0.385430.128513.6** 1.202430.40089.881**Growth stage 4.77453 1.5915168.5

***

0.550630.1835 4.525

*

Error

0.08590.0094

0.365190.0406

Corrected total

5.2449

15

2.118

15

*Signi?cant differences for P <0.05.**

Signi?cant differences for P <0.01.***

Signi?cant differences for P <0.001.

Table 3

Change of C i /C a (the ratio of C i (intercellular CO 2concentration)to C a (the ambient atmosphere CO 2concentration),WUE i (photosynthesis rate/transpiration rate,P n /T r ),WUE n (photosynthesis rate/stomatal conductance of CO 2,P n /g s ),WUE y (yield/crop water consumption,Y/ET c ),ET c (water consumption)and yield under different water de?cit treatments and growth stages.Growth stages

Treatment

C i /C a

(m mol mol à1)WUE i

(m mol CO 2mol à1H 2O)WUE n

(m mol CO 2mol à1H 2O)WUE y

(kg m à3)ET c (mm)Yield

(kg h m à2)Bud burst to lea?ng

CK

0.76b 10.94a 0.16b 6.78b 537.88a 36465.00c T 2(SD)0.65c 9.31c 0.18a 10.88a 442.25c 48097.50a T 3(MD)0.73b 9.85c 0.17ab 7.10b 489.46b 41332.50b T 4(LD)0.82a 10.05b 0.16b 5.98c 506.04ab 30227.50d F value 20.77** 4.12* 3.24*16.12**7.83*7.74*

Flowering to fruit set

CK 0.58a 5.65bc 0.15b 6.85b 552.78a 36878.50a T 5(SD)0.54ab 5.35c 0.18a 7.86a 446.6c 35103.75b T 6(MD)0.51b 6.21a 0.16ab 6.03c 489.88c 29535.00d T 7(LD)0.56a 6.04b 0.17a 6.31c 505.23b 31886.25c F value 2.53ns 18.08** 5.12*7.73* 6.98*8.15*

Fruit growth

CK 0.61a 6.04b 0.10c 6.65b 534.21a 37546.30a T 8(SD)0.52c 6.88a 0.12b 7.26a 441.37c 32051.25b T 9(MD)0.55c 6.42ab 0.13a 5.91c 491.3b 29040.00c T 10(LD)0.58b 6.74a 0.12b 7.28a 504.32b 36712.50a F value 15.24** 5.44ns 6.74* 6.14* 4.87*9.24*

Fruit maturation

CK

0.76a 5.30d 0.14ab 6.95d 528.75a 36248.30b T 11(SD)0.65b 5.68a 0.14ab 8.97a 449.89c 40342.50a T 12(MD)0.63b 5.52c 0.15a 7.88b 490.7b 40012.50a T 13(LD)0.72a 5.58b 0.13b 7.36c 505.7a 37207.50b F value

7.42*

14.45**

3.82*

8.73*

5.74*

6.75*

C i /C a ,WUE i ,WUE n represent average of more than eight measurements.Field measurements on April 25th,26th,27th,June 11th,13th,July 13th,15th,and August 19th,21st,22nd,2006;WUE y,ET c and yield represent average of two replicates.Within each treatment,means followed by different letters are signi?cantly different by Duncan’s multiple range test at P =0.05.N.Cui et al./Agricultural Water Management 96(2009)1615–1622

1618

slightly decreased with increasing water stress,then leaf WUE was increased.In addition,leaf cells have stronger enduring ability with water de?cit by the osmotic adjustment.

High WUE y[the ratio of fruit yield per tree(Y)to its water consumption(ET c)]was often regarded as an important index in improving crop performance under water de?cit condition(Araus et al.,2003).The enhanced WUE can reduce crop water requirement under certain yield level and increase crop yield signi?cantly under certain water condition(Impa et al.,2005).It indicated that water de?cit treatments at different growth stages increased WUE y when compared to the FI(Table3),which agreed with the results on sugar beet(Dorit et al.,2006).Because water de?cit increased the secretion of hormones,e.g.,gibberellin(GA), abscisic acid(ABA)and indole acetic acid(IAA),the transport of photosynthetic product from the leaves and branches to the fruits was increased,which may counteract the negative effect of water de?cit on fruit growth to some extent,thus the WUE y was enhanced while irrigation water was reduced without reduction in crop yield.

3.3.Relationship between D L,D F and WUE,ET c and yield of pear-jujube under different water de?cit levels and growth stages Table4shows that there were signi?cant correlations between the D L,D F and WUE,ET c,yield at different growth stages.Under different water de?cit conditions,the D L was positively correlated with the D F(P<0.05or0.01)in the other growth stages except stage II,and D L had signi?cantly negative correlation with the WUE y at stage IV(R=à0.982,P<0.01)but no signi?cant correlation at stages I,II and III(P>0.05).There was signi?cantly negative correlation between the D L and WUE i,WUE n at stages III and IV(P<0.05),but not signi?cant(P>0.05)at stages I and II, which was consistent with the result of Zhao et al.(2005).The WUE i and WUE n in different growth stages were different due to plant physiological characteristics and the effect of light, temperature and other environmental factors.Moreover,the D L revealed WUE n better than WUE i,because the WUE n can directly express the effect of stomatal activity on the C i/C a.

It also shows that D L was positively correlated with ET c in other growth stages(P<0.05)except stage I and D F was positively correlated with ET c(P<0.01)in other growth stages except stage II (Table4).D L and D F were positively correlated with fruit yield under different water de?cit at stages II and III,but negatively correlated with fruit yield at stages I and IV.And D L had signi?cantly correlation with fruit yield only at stage IV(P<0.05). However,D F was weak negatively correlated with WUE y at stages I,II and IV,with signi?cant difference only at stage IV(P<0.05).

Under water de?cit treatments at stage IV,the relationship between D L and WUE i(R2=0.5121,P<0.05)was weaker than that of D L and WUE n(R2=0.5378,P<0.05),indicating that D L compared leaf WUE at stage IV.Meanwhile,the correlations were evident between D L and WUE y(R2=0.9640,P<0.01)or D L and yield(Y)(R2=0.8458,P<0.05)at stage IV.And there have signi?cant correlations between D F and WUE y(R2=0.9220, P<0.05)or D F and fruit yield(R2=0.9420,P<0.05)at stage IV. Thus D F and D L had some token of WUE y at fruit maturation stage under water de?cit treatments,and they both suggested the change of WUE y and yield.Furthermore,D L is better than D F in implying WUE y,because leaf D L at fruit maturation stage has integrated the information of water use and photosynthetic characteristic over the whole growth stage of pear-jujube,but D F has only recorded the information at the fruit growth stage.But D F is better than D L in suggesting yield,because D F can directly record the information about the transport of photosynthetic product from the leaves and branches to the fruits at the fruit growth stage.Many previous studies also showed that D L had strong negative correlation with WUE y(Jaggi et al.,2002;Rytter, 2005;Zhao et al.,2004a)and it was an ideal indication of crop yield under limited irrigation(Anyia et al.,2007;Xu et al.,2007).The D F was negatively correlated with WUE y(Bloch et al.,2006)and it re?ected the change of crop yield under water de?cit environment (Philippe et al.,2005,2007).

Table4

Relationship between D L,D F and WUE,ET c,yield under different water de?cit treatments and growth stages.

Growth stage Parameter D L D F WUE y WUE i WUE n ET c Bud burst to lea?ng D F0.934*

WUE yà0.551à0.766ns

WUE i0.7470.918*à0.732

WUE nà0.818à0.920*0.926*à0.787

ET c0.8530.983**à0.854à0.947*à0.941*

Yà0.660à0.7410.908*à0.5410.941*à0.772 Flowering to fruit set D F0.717

WUE yà0.180à0.461

WUE ià0.0270.282à0.977*

WUE nà0.703à0.997**0.530à0.357

ET c0.934*0.890à0.4610.261à0.893

Y0.4610.0710.787à0.8990.0010.180 Fruit growth D F0.994**

WUE y0.1270.060

WUE ià0.549*à0.6340.597

WUE nà0.649*à0699à0.2520.610

ET c0.901*0.932*à0.306à0.823à0.577

Y0.8680.8530.549à0.292à0.8070.614 Fruit maturity D F0.948*

WUE yà0.982**à0.960*

WUE ià0.716*à0.8540.825

WUE n0.733*à06670.6000.187

ET c0.692*0.967*à0.995**à0.875à0.547

Yà0.920*à0.971*0.8920.7260.809à0.888

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3.4.Relationship between D L and D F and WUE and related indices under different water de?cit levels over whole growth stage As shown in Fig.2,the correlation of D L with WUE i and WUE n under all water de?cit treatments had signi?cantly difference over the whole growth stage.D L had signi?cantly negative correlation with WUE i (R 2=0.2777,P <0.05),which was similar to the results of wheat (Cabrera-Bosquet et al.,2007),soybean (Raeini-Sarjaz et al.,1998)and barley (Anyia et al.,2007)under water de?cit condition.D L had also signi?cantly negative correlation with the WUE n (R 2=0.3556,P <0.01),which agreed with the results of Stylosanthes (Chandra et al.,2004;Amaresh and Bhatt,2008),grape (Souza et al.,2005),wheat (Farquhar et al.,1989)and rice (Zhao et al.,2004a,b )under water de?cit condition.Thus the D L can indicate WUE i and WUE n under different water de?cit effectively re?ect the effect of stomatal resistance on leaf water use when compared to the WUE i .

There was a weak negative correlation between D F and yield,but a weak positive correlation between D L and ET c .The correlation equations between D F and WUE y or D F and ET c under all treatments during whole growth stages were WUE y =à1.7832D F +40.909(R 2=0.2861,P <0.05)and ET c =64.695D F à726.31(R 2=0.4819,P <0.01),respectively.Thus D F can be a comparison of WUE y and ET c ,which was in line with the conclusion of Cabrera-Bosquet et al.(2007).Because more than 70%of crop yield is depended on environmental factors (Jaggi et al.,2002),D F can record the effect of environmental information such as temperature,water,humidity,atmospheric pressure on fruit over the whole growth stage,and it has the signi?cant response to water change,thus it can compare WUE y .Our study suggests that D F compare ET c of pear-jujube tree

Fig.2.Relationship between leaf carbon isotope discrimination (D L )and WUE i (P n /T r ),WUE n (P n /g s )and ET c ,or between carbon isotope discrimination (D F )and yield,WUE y (yield/crop water consumption,Y /ET c )and ET c under different water de?cit treatments and growth stages.

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4.Conclusions

The correlations between carbon stable isotope resolution of leaf(D L)or fruit(D F)and WUE i,WUE n,WUE y,yield and ET c were studied,the main conclusions are as follows:

(1)The D L and D F decreased with the increasing water de?cit,

signi?cant difference of D L or D F was found among different water treatments(P<0.01),and the D L was signi?cantly greater than D F.Moreover,D L had signi?cant difference during different growth stages,indicating that the effect of water de?cit on carbon stable isotope varied with crop organs and growth stages.

(2)After water de?cit treated in different growth stages,sig-

ni?cant correlations between D L and WUE i or D L and WUE n were found at both fruit maturation and fruit growth stages (P<0.05),and the D L was negatively correlated with WUE i (P<0.05)and WUE n(P<0.01)over the whole growth stage.

D F was negatively correlated with WU

E y(P<0.05),but

positively correlated with ET c(P<0.01)over the whole growth stage,so D F can compare WUE y and ET c over the whole growth stage.Therefore,the stable carbon isotope discrimination is a proper method in evaluating the WUE and providing effective and simple index for irrigation management of pear-jujube tree.

To sum up,the stable carbon isotope resolution(D13C)of different organs can compare plant response to water de?cit and then leaf WUE.However,there are still some arguments about whether the correlation of WUE and yield with D13C of different plants organs under different water de?cit treatment is reliable. Because the D13C cannot directly provide the rate of gas exchange, plant WUE can be distinguished by comparing the carbon isotope ratio under different growing environments.And there existed inter-annual change of WUE correlation with D L and D F.Since inter-annual comparison is not involved in our study,it still needs further study to reveal such relationship between the D13C of different organs and WUE,so as to provide a simple,rapid and accurate index of WUE and irrigation management for different fruit tree.

Acknowledgments

We are grateful for the research grants from the National Key Basic Research Program of China(973Program,2006CB403406), Chinese National Natural Science Fund(50709038,50869001)and Program for Changjiang Scholars and Innovative Research Team in University in China(IRT0657).

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