J[ Agronomy + Crop Science 073\ 02*05 "1999#Þ 1999 Blackwell Wissenschafts!Verlag\ BerlinISSN 9820!1149

Indian Grassland and Fodder Research Institute\ Jhansi\ India

Effect of Secondary Salinization on Photosynthesis in Fodder Oat "Avena sativaL[# Genotypes

A[ Chatrath\ P[ K[ Mandal and M[ Anuradha

Authors| address] Dr Anjali Chatrath "corresponding author#\ Dr P[ K[ Mandal and Dr M[ Anuradha\ Division of CropImprovement\ Indian Grassland and Fodder Research Institute\ Jhansi!173992\ India

With 0 _gure and 1 tables

Received May 19\ 0887^ accepted October 5\ 0887

Abstract

The e}ect of secondary salinization on photosynthesiswas studied in fodder oat genotypes Kent\ JHO!718\JHO!770\ UPO!83 and OS!5 at the ~ower initiation stage[With an increase in the electrical conductivity "EC# ofirrigation water\ the net photosynthesis rate "PN# and thetranspiration rate "E# of all the genotypes decreased[ Theintercellular CO1 concentration "Ci# increased in all geno!types at 09 dS m−0[ Stomatal resistance "Rs# had a strongnegative correlation with PN and E[ The increase in Citogether with the increase in the Rs shows that at higherEC non!stomatal factors also start contributing to thelimitation of photosynthesis[ This study suggests thatsecondary salinization e}ects are strongly under stomatalcontrol at lower saline water irrigation levels\ but athigher levels non!stomatal factors may come intoplay[

Key words] carbon exchange rate * electrical con!ductivity * internal carbon dioxide con!centration * oat * salinity * stomatal resist!ance * transpiration

Abbreviations]Ci\ internal CO1 concentration * E\ transpirationrate * EC\ electrical conductivity * PN\ net pho!tosynthetic rate * RS\ stomatal resistance

Introduction

Salinity is one of the most important abiotic stresseslimiting agricultural production[ In arid and semi!arid areas where agricultural activity is dependenton irrigation\ the coincidence of salinization andirrigation is a constant threat to agriculture[

Reduction in photosynthetic capacity is usuallyassociated with a decline in growth caused by sal!inity "Longstreth et al[ 0873^ Munns and Termatt0875#[ The limitation of photosynthesis can be sep!arated into two categories] "0# limitation due to

U[S[ Copyright Clearance Center Code Statement] 9820Ð1149:99:7390Ð9902 ,04[99:9

reduced stomatal conductance\ and "1# reduction inthe biochemical photosynthetic capacity of the leaf[In many studies\ di}erences have been found in therelative predominance of stomatal "De Jong 0867\Guy and Reid 0875 Wang et al[ 0877\ Everard etal[ 0883# and non!stomatal "Longstreth et al[ 0873\Pearcy and Ustin 0873\ Myers et al[ 0889# factorsassociated with lower photosynthetic capacity[ Inthis study\ the gas exchange characteristics of oatgenotypes were measured with the aim of ascer!taining the e}ect of salinity on the extent of limi!tation of photosynthesis by the component pro!cesses of photosynthetic capacity and stomatalconductance[

Materials and Methods

Seeds of the _ve fodder oat genotypes\ Kent and OS!5 "salt tolerant#\ and JHO!718\ JHO!770 and UPO!83"susceptible#\ were raised in pots _lled with 09 kg of 2 ] 0sandy loam soil to farm yard manure mixture and a basaldose of 59 kg ha−0 N and 39 kg ha−0 P1O4[ The pots wereirrigated regularly with saline water[ Irrigation water wasprepared by adding equivalent amounts of NaCl\ CaCl1\MgCl1 and Na1SO3 to tap water having an EC of 9[7 dSm−0 so as to increase the EC to 1\ 3\ 5\ 7 and 09 dS m−0

for di}erent treatments[ The 9[7 dS m−0 water served asthe non!saline control[ There were _ve pots per treatmentand three plants per pot[ Measurements were carried outat several growth stages on the last fully expanded leaf[However\ only measurements carried out at ~owerinitiation stage are presented[ The gas exchange measure!ments were made on the potted plants using a portableIRGA "Model LI 5199\ LICOR\ USA#[

Carboxylation e.ciency "PN:Ci# was calculated fromthe data on net photosynthetic rate "PN# and internal CO1

concentration "Ci#[ The data were statistically analysedfollowing standard statistical methods "Gomez andGomez 0873#[

03 Chatrath et al[

Fig[ 0] E}ect of saline water irrigation on "a# photosynthetic rate\ "b# stomatal resistance\ "c# internal CO1 concentrationand "d# transpiration rate

Results and Discussion

In the absence of salinity in the root environment\the leaf PN showed variability among the genotypes"Fig[ 0a#[ The genotypes OS!5 and JHO!718 showedsimilar PN\ while Kent\ JHO!770 and UPO!83 hadsimilar PN values which were signi_cantly lower thanthose of OS!5 and JHO!718[ Di}erences were alsoobserved in genotypes irrigated with 1 dS m−0 salinewater\ with Kent showing a signi_cant increase"41[4 )# and JHO!718 and UPO!83 signi_cantdecreases of 08[3 and 37[5 )\ respectively\ whencompared to the control plants[ In sugarbeets\photosynthesis was enhanced under low salinity lev!

els "Heuer and Plaut 0870#[ This shows that photo!synthesis is not limited as long as the salinity isbelow a critical level[ Salinity adaptation of leaf cellsand minimal inhibition of photosynthetic activitytook place up to a salinity level which caused dam!age to cells[ This could also explain an increase inthe PN of salt!tolerant Kent at 1 dS m−0[ All thegenotypes showed a decline as the salinity of theirrigation water was increased[ At maximum salinitylevels of 09 dS m−0\ all the genotypes had more orless the same PN[

Stomatal resistance was observed to be similar inall the genotypes irrigated with non!saline water"Fig[ 0b#[ The genotype UPO!83 showed a increase

04E}ect of Salinization on Photosynthesis in Oat

Table 0] Correlation matrix for net photosynthetic rate"PN#\ internal CO1 concentration "Ci#\ transpiration rate"E# and stomatal resistance "Rs# in oat genotypes

Ci E Rs

0[ PN 9[246� 9[854�� −9[781��1[ Ci 9[229� −9[0592[ E −9[785��

�\ �� Signi_cant at 9[94 and 9[90 probability levels\respectively[

Table 1] Carboxylation e.ciency "PN:Ci# of oat genotypesat di}erent levels of irrigation with saline water

EC of saline water "dS m−0#

Genotype 9[7 1 3 5 7 09

Kent 9[952 9[987 9[962 9[970 9[961 9[905JHO!718 9[978 9[968 9[958 9[949 9[953 9[906JHO!770 9[966 9[985 9[938 9[962 9[943 9[922UPO!83 9[967 9[933 9[943 9[935 9[920 9[908OS!5 9[982 9[975 9[954 9[934 9[927 9[906

LSD at 4)^ C 9[997^ T 9[998^ G×T 9[919[

at 3 dS m−0 followed by a decline at 5 dS m−0 anda gradual increase thereafter[ A steep increase wasobserved in all the genotypes at 09 dS m−0\ except inJHO!718[ Stomatal resistance and PN have a strongnegative correlation "−9[781#\ as shown in Table 0\which indicates that as salinity increases stomatalfactors have a more signi_cant e}ect on photo!synthesis[ This was also reported in spinach "Down!town et al[ 0874#\ plantago "Flanagan and Je}eries0877#\ rice "Wang et al[ 0877# and celery "Everardet al[ 0883#[

The intercellular CO1 concentration "Ci# showeda steep decline in all the genotypes compared tocontrol "Fig[ 0c#[ Ci also had a positive correlation"r � 9[246# with PN "Table 0#\ which suggests thatthe availability of CO1 at the carboxylating sitein~uences PN[ There was a signi_cant increase in Ci

after 7 dS m−0 except in JHO!770[ At 09 dS m−0\when both stomatal resistance and Ci were high\a signi_cant reduction in carboxylation e.ciency"PN:Ci# was observed "Table 1#[ At the highest sal!inity levels "09 dS m−0#\ carboxylation e.ciencywas signi_cantly reduced in all the genotypes[ Thisobservation is in accordance with that reported inC2 halophytes "Myers et al[ 0889# and glycophytes

Dunn and Neales 0882#[ This indicates that non!stomatal factors are more limiting to PN than stoma!tal factors at high EC levels[

The transpiration rate was higher in OS!5 whenit was irrigated with tap water[ A gradual decline intranspiration rate occurred as the EC of the irri!gation water increased "Fig[ 0d#[ Onkware "0889#also found that salt stress signi_cantly reduced theleaf transpiration rates in _ngermillet[ With theexceptions of JHO!770 and Kent\ which showedan increase in transpiration rate at 1 EC\ all thegenotypes showed an insigni_cant di}erences intranspiration rate[ Stomatal resistance also had astrong correlation "r � 9[785# with transpirationrate\ and thus stomatal conductance is also respon!sible for regulating the transpiration rate[

Hence\ the e}ect of secondary salinization onphotosynthesis is strongly under stomatal control atlow salinity levels\ and non!stomatal factors maycontribute at higher salinities[

Acknowledgements

The authors thank the Head of Division and Director ofthe Institute for providing facilities during this study[

Zusammenfassung

Ein~u) einer sekunda�ren Versalzung auf die Photo!synthese von Futterhafer "Avena sativa L[#!Geno!typen

Der Ein~u) einer sekunda�ren Versalzung auf die Photo!synthese bei den Futterhafer!Genotypen Kent\ JHO!718\JHO!770\ UPO!83\ OS!5 zum Stadium der Blu�tenanlagewurde untersucht[ Mit der Zunahme in der elektrischenKonduktivita�t "EC# des Bewa�sserungswassers nahm dieNetto!Photosyntheserate "PN# und die Transpirationsrate"E# bei allen Genotypen ab[ Interzellula�re CO1!Kon!zentration "Ci# nahm bei allen Genotypen um 09 dS−0

zu[ Stomata�re Resistenz "Rs# hatte eine stra}e negativeKorrelation mit PN und E[ Die Zunahme in Ci zusammenmit der Zunahme in Rs zeigt\ da) bei hoher EC die nicht!stomata�ren Faktoren beginnen\ auch einen Beitrag zurLimitierung der Fotosynthese zu geben[ Diese Untersu!chung weist daraufhin\ da) sekunda�re Versalzungse}ektestark unter stomata�rer Kontrolle bei gering versalztemBewa�sserungswasser stehen\ wa�hrend danach nicht!sto!mata�re Faktoren Bedeutung bekommen ko�nnen[

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05 Chatrath et al[

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