Growth patterns of Phragmites karka under saline conditions depend on the bulk elastic modulus *

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1 CSIRO PUBLISHING Crop & Psture Science, 218, 69, Growth ptterns of Phrgmites krk under sline conditions depend on the ulk elstic modulus * Erum Shoukt A, Irfn Aziz A, Muhmmd Zheer Ahmed A,B, Zinul Aideen A, nd Muhmmd Ajml Khn A A Institute of Sustinle Hlophyte Utiliztion, University of Krchi, Krchi 7527, Pkistn. B Corresponding uthor. Emil: mzhmed@uok.edu.pk Astrct. Slt stress is known to hmper stedy-stte wter flow, which my reduce plnt growth. This reserch ws imed to study the roles of lef turgor, osmotic djustment nd cell wll elsticity under sline conditions which my reduce iomss production in Phrgmites krk (Retz.) Trin, ex. Steud. ( mrsh grss). Plnts were grown in, 1 nd 3 mm NCl nd hrvested on 3, 7, 15 nd 3 dys to oserve periodic chnges in growth nd wter reltions. Lef numer, reltive growth rte, nd reltive elongtion rtes were higher in the non-sline control thn in the plnts grown under sline conditions. Plnts showed rpid decline in lef growth rte (7 15 dys) in 3 mm NCl compred with delyed response (15 3 dys) in 1 mm NCl. Lef wter potentil decresed with increses in slinity fter the third dy of exposure wheres osmotic potentil decresed fter the fifteenth dy. Low lef turgor (Y p ) on the third dy indicted n initil phse of osmotic stress under sline conditions. Plnts mintined higher Y p in nd 1 mm thn in 3 mm NCl. Differences etween mid-dy nd pre-dwn wter potentil nd wter sturtion deficit were higher in 3 mm NCl thn with other tretments. Wter potentil nd hydrulic cpcitnce t turgor loss point decresed wheres ulk elstic modulus incresed in 3 mm NCl. Mintennce of turgor nd growth t 1 mm NCl could e relted to efficient osmotic djustment (use of K + nd Cl ), higher WUE i, nd lower ulk elsticity wheres poor growth t 3 mm NCl my hve een consequence of low turgor, decresed cell hydrulic cpcitnce nd higher ulk elstic modulus. Additionl keywords: cell wll rigidity, diurnl wter reltion, lef turgor, mrshy grss, memrne rigidity, pressure volume curve. Received 25 My 217, ccepted 8 Ferury 218, pulished online 17 April 218 Introduction Low wter vilility cused y drought, slinity, or other iotic fctors usully limits plnt growth nd development (Mhjn nd Tutej 25; Munns nd Tester 28; Álvrez et l. 212). Among these iotic stresses, slinity hs ecome n incresingly serious prolem, which restricts yield on lmost 5% of irrigted lnd glolly (Run et l. 21). Depleting fresh wter resources nd incresing slt-ffected res re mjor hurdles for crop cultivtion (Run et l. 21). Hence, growing crop plnts s lternte sources of energy (e.g. iofuel) would further increse pressure on cultivted lnds (Aideen et l. 212). In view of the ovementioned prolems, domestiction of non-conventionl crops on sline wste lnds seems vile lterntive (Reddy et l. 28; Rozem nd Flowers 28; Aideen et l. 212). Hlophytes re cple of mintining high wter-use efficiency levels (Chves et l. 29; Riccrdi et l. 214) nd etter yields when grown in sline hitts thn non-hlophytes Arevitions: Y W, Lef wter potentil; Y p, Lef osmotic potentil; Y p, Lef turgor potentil; YW, Wter potentil t full turgor; YS, Osmotic potentil t full turgor; YP, Turgor potentil (PVC derived); YW TLP, Wter potentil t turgor loss point; RWC, Reltive wter content t full turgor; RWC TLP, Reltive wter content t turgor loss point; C FT, Hydrulic cpcitnce t full turgor; C TLP, Hydrulic cpcitnce t turgor loss point; e, Bulk elstic modulus; LTD, Lef tissue density; PVC, Pressure volume curve; OA t, Totl osmotic djustment; AOA, Active osmotic djustment; POA, Pssive osmotic djustment; FW, Fresh weight; RGR lef, Reltive growth rte of lef; RER lef, Reltive elongtion rte of lef; SUC, Succulence; WSD, Wter sturtion deficit; WUE i, Instntneous wter-use efficiency. * Erum Shoukt, Irfn Aziz, Muhmmd Zheer Ahmed contriuted to the experimentl design nd executed ll reserch work. Muhmmd Zheer Ahmed rrnged the funds for this study. All uthors helped in finlising the mnuscript. Journl compiltion CSIRO 218

2 536 Crop & Psture Science E. Shoukt et l. (Khn nd Ansri 28; Glenn et l. 213; Ventur nd Sgi 213). In view of n incresing world food demnd, the growth dynmics of conventionl crops with chnging soil wter potentil hve een extensively discussed in some species (Romero-Arnd et l. 21; Fernández-Grcí et l. 24; Netondo et l. 24) ut limited informtion exists on wter reltion of gint hlophytic grsses. Plnts living in slt-stressed environments respond differently to soil wter potentil thn those growing under non-sline conditions. One of the importnt mechnisms is osmotic djustment, the ccumultion of solutes tht could help in chieving osmotic lnce nd wter uptke for mintining growth (Flowers nd Colmer 28). In some plnts, prticulrly grsses, synthesising orgnic osmolytes my compromise growth (Roy nd Chkrorty 214). Chnges in growth re not only relted to physiologicl ttriutes ut, they re lso linked with morphologicl nd ntomicl chrcters (Bose et l. 215; Flowers et l. 215). Chnges in turgor due to cell wll elsticity, incresed succulence nd tissue density represent growth modultion (Hoffmnn nd Poorter 22). Some plnts lter ulk elstic modulus, increse lef thickness nd tissue density wheres others chnge their reltive wter content to mintin turgor (Gullo nd Slleo 1988; Villr-Slvdor 24). Plnts with highly elstic tissues mintin higher mounts of wter t full sturtion, nd hence t the turgor loss point they my hve lrger hydrulic cpcitnce with respect to the cell volume (Lmers et l. 28; Brtlett et l. 212). However, rigid wlls would decrese wter potentil with smll wter loss (Nvrro et l. 27). Prmeters such s osmotic potentil t full turgor (YS ), wter potentil t turgor loss point (YW TLP ) nd ulk elstic modulus (e) derived from Pressure volume curve (PVC) re commonly used to understnd the dynmics of lef wter reltions to osmotic djustment s well s plnt growth (Brtlett et l. 212). In ddition, the concentrtions of clcium, which is importnt s signlling molecule nd structurl component of the cell wll (Hepler nd Winship 21; Bickerton nd Pittmn 212; Prvin et l. 216), my increse in plnt tissues under sline conditions, nd therefore it is importnt to understnd the link etween clcium content nd cell wll elsticity. Phrgmites krk (Retz.) Trin, ex. Steud, is perennil hlophytic grss distriuted on sline mrshy hitts round Krchi (Zehr nd Khn 27). This species is lso present in the ntive flor of Austrli ( rowse/profile/556, ccessed 23 Mrch 218). P. krk produces lrge mounts of iomss nd, like other grsses such s Arundo donx, Phrgmites ustrlis, nd Miscnthus gignteus is considered to e potentil cndidte for iofuels ecuse of its suitle ligno-cellulosic composition (Sims et l. 26; Brney nd DiTomso 28; Aideen et l. 212; Cotn et l. 215). It ws reported tht P. krk mintined growth nd wter reltions under moderte slinity (1 mm), wheres t 3 mm NCl low lef hydrtion nd turgor loss reduced plnt growth (Aideen et l. 214). However, it remins uncler whether wter deprivtion or incresing slt lods in the roots of P. krk is the mjor cuse of turgor loss, nd little informtion is ville out the impct of slinity on plnt wter reltions, nd prticulrly regrding structurl modifiction in this species. The present work is sed on the hypothesis tht the growth response of P. krk under slinity depends on the ulk elstic modulus. This study ws crried out to determine how the durtion of slt exposure nd diurnl chnges in wter reltions interct with ulk elstic modulus (e) for controlling growth. The present study lso descries link mong growth, wter reltion ttriutes nd cell wll rigidity of P. krk in sline condition tht hs not een descried in previous reserch on gint grsses. Mterils nd methods Seeds of Phrgmites krk were collected from mrshy hitts of Krchi University, Pkistn ( N nd E) in Ferury 214. Seeds were sown in plstic trys contining sndy soil plus mnure nd irrigted with wter for germintion. Fiveweek-old seedlings of similr size (length 6 8 cm, three-lef stge) were trnsplnted into plstic pots (6 cuic litres; three individuls per pot) contining snd nd lom (2 : 1) nd suirrigted with 1/2 strength Hoglnd nutrient solution (modified fter Epstein 1972). Plnts were grown in netted greenhouse under mient environmentl conditions (temperture: 37 18C; reltive humidity: 5 5%; light intensity: 45 1 mmol m 2 s 1 ). Slinity tretments were strted fter 3 dys of seedling cclimtistion. Plnts were divided into three slt tretment groups (, 1, 3 mm NCl) nd five su-groups (, 3, 7, 15, 3 dys). In order to void osmotic shock, NCl ws pplied grdully with n increse of 5 mm per dy in the nutrient solution. Tretment solution ws completely replced t weekly intervls until the end of the experiment. Growth prmeters Growth prmeters [fresh weight (FW) nd lef numer] were determined t, 3, 7, 15, 3 dys of slt tretment. Reltive growth rte of lef (RGR lef ) ws estimted y using the formul of Hoffmnn nd Poorter (22): RGR lef ðgg 1 dy 1 Þ¼lnW 2 lnw 1 =t 2 t 1 where, W 1 nd W 2 re the initil nd finl dry weight (g), wheres t 1 nd t 2 re the initil nd finl time (dy) from the strt of slinity tretments. Reltive lef elongtion rte ws clculted using the formul (Muller et l. 21): Reltive lef elongtion rte ðcm cm 1 dy 1 Þ ¼ lnl 2 lnl 1 =t 2 t 1 where L 1 nd L 2 re the initil nd finl length (cm), wheres t 1 nd t 2 re the initil nd finl time (dy) from the strt of slinity tretments. Lef re ws clculted using ImgeJ softwre version 1.45 ( ccessed 23 Mrch 218). Lef sclerophylly indices [succulence (SUC), lef tissue density (LTD), nd wter sturtion deficit (WSD)] were clculted using the following formule (Pujol et l. 21; Denx et l. 212): WSDð%Þ ¼ðTW FWÞ=ðTW DWÞ1 SUCðg H 2 Og 1 DWÞ ¼FW DW=DW LTDðg g 1 Þ¼ðDW=FWÞ1

3 Wter reltions of Phrgmites krk tll reed grss Crop & Psture Science 537 where, FW, DW nd TW re: lef fresh weight, dry weight nd turgid weight, respectively. Wter reltion prmeters Wter potentil nd the osmotic potentil of leves were determined on 3, 7, 15 nd 3 dys fter the highest slinity (3 mm NCl) hd een reched. Wter potentil of 5-mm disks of fully expnded young leves ws determined using C-52 smple chmer connected to Wescor HR-33T, thermocouple psychrometer (Wescor, Inc., Logn, UT, USA). Sp osmollity of the sme lef ws determined using Vpor pressure Osmometer (Vpro-552, Wescor, Inc.). The osmotic contriution of ions (N +,K +, nd Cl ) nd solule sugr were clculted using the vn t Hoff eqution (Guerrier 1996). Trnspirtion rte nd instntneous wter-use efficiency (WUE i ; net photosynthesis to trnspirtion rtio) were clculted using Li-COR 64 instrument (64XT, Li-Cor Inc., Lincoln, NE, USA). Clcium content Clcium (C +2 ) ws determined ccording to Aogdllh (21). A hot-wter extrct ws prepred from finely ground dried plnt mteril in distilled wter t 18C for 2 h. This filtrte ws used to determine lef C +2 y tomic sorption spectrometry (AA-7; Perkin Elmer, Snt Clr, CA, USA). Diurnl wter reltions Lef wter nd osmotic potentils were determined t pre-dwn nd noon to oserve chnges in diurnl wter reltions of plnt fter 15 dys of slinity tretments. Pressure volume curves (PVC) Fully expnded young leves were selected on the fifteenth dy of slinity tretments for PVC mesurements, s lef hydrulic properties chieve stedy-stte fter out 2 weeks of slt tretment (Serrno et l. 25). Leves from the second node were hydrted overnight y covering with plstic gs. PVC were otined using Wescor HR-33T, thermocouple psychrometer (Wescor, Inc.) with C-52 smple chmer (Ogurn nd Edwrds 29). The entire smple (lef nd their excised 5-mm Ø disc) ws weighed immeditely fter the lef ws detched from the mother plnt. The lef disc ws quickly seled inside the smple chmer (C-52) to minimise ir exposure of the cut surfce to void ny discrepncies in wter potentil (Wlker et l. 1984). Smples were llowed to equilirte t room temperture (298C). Between mesurements, lef disc ws removed from the smple chmer nd llowed to dry for 1 2 min (depending on the hydrtion stte of the lef tissue). Smples were re-weighed nd trnsferred to smple chmer for the susequent wter potentil reding. This process ws repeted 8 1 times per lef smple to determine the PVC. The inverse of wter potentil (1/ Y w ) ws plotted ginst reltive wter content to generte the PVC. A line ws drwn s n inflection point in the liner portion of the curve, to determine the turgor loss point (where wter nd osmotic potentils ecomes equl) (Tyree nd Hmmel 1972). The following wter reltion prmeters were derived from the PVC: osmotic potentil t full turgor (YS ), wter potentil t turgor loss point (YW TLP ), reltive wter content t full sturtion (RWC ) nd turgor loss point (RWC TLP ), ulk elstic modulus (e), cpcitnce t full turgor (C FT ) nd cpcitnce t turgor loss point (C TLP ) (Tyree nd Hmmel 1972; Lenz et l. 26; Brtlett et l. 212). Totl osmotic djustment (OA t ) ws clculted y sutrcting middy Y p in control ( mm) from those of the sline tretments (1 nd 3 mm NCl) (Boussdi et l. 213). Active osmotic djustment (AOA) ws clculted s the difference in YS etween control nd sline tretments (Girm nd Krieg 1992). The contriution of pssive osmotic djustment (POA) to OA t ws clculted using the following formul (Boussdi et l. 213): POA ¼ OA AOA Sttisticl nlyses Sttisticl nlysis ws conducted using SPSS version 16. for windows (SPSS Inc., Chicgo, IL, USA). Anlysis of vrince (ANOVA) ws used to identify significnt effects of NCl concentrtion nd durtion of slinity tretment on growth nd wter reltion prmeters t P <.5. Bonferroni nd pired smple t-test were used to compre individul mens. Dt in the form of mens nd stndrd errors were used to construct grphs using Sigmplot for Windows version 11. (Systt Softwre, Sn Jose, CA, USA). Results A two-wy ANOVA showed significnt effect for slinity (S) (P <.1, F = 23.3), time of exposure (T) to slinity (P <.1, F = 36.57) s well s their interctions (S T) (P <.1, F = 14.2) on lef fresh weight of P. krk (Fig. 1). Similr results were oserved with slinity (S) (P <.1, F = 64.34), time (T) (P <.1, F = 65.31) nd their interctions (S T) (P <.1, F = 2.86) on totl plnt fresh weight (Fig. 1). During the initil (15) dys of slt exposure oth plnt nd lef tissue mintined higher fresh weights in nd 1 mm NCl thn in 3 mm NCl (Fig. 1, ). However, t the end of the experiment (thirtieth dy), FW ws 2-fold lower in 1 nd 4-fold lower in 3 mm NCl compred with control (Fig. 1, ). The numer of leves per plnt ws lso similr during 15 dys of slinity tretments fter which considerle increse in lef numer t nd 1 mm NCl ws oserved (Fig. 2). Lef senescence ws initited on the seventh dy in 3 mm NCl nd the fifteenth dy in nd 1 mm NCl tretments. By the end of the experiment, ~85% of leves were dry (yellow) in 3 mm nd only 5% in 1 mm NCl (Fig. 2). Higher slinity (3 mm NCl) significntly (P <.1) decresed RGR lef nd RER lef compred with nd 1 mm NCl (Fig. 3, ). RER lef ws higher wheres RGR lef ws lower during the erly phse (15 dys) of the experiment in ll tretments compred with the lter (3 dys) phse (Fig. 3, ). Lef sclerophylly indices indicted tht there ws no chnge in LTD nd SUC under sline conditions, ut lef re decresed nd WSD incresed in 3 mm NCl in comprison to other tretments (Tle 1). Clculted WUE i significntly incresed (P <.5) in P. krk under slinity tretments wheres trnspirtion decresed more in 3 mm NCl thn 1 mm NCl (Tle 1). Lef clcium ws unchnged in 1 mm NCl wheres significnt (P <.5) increse ws

4 538 Crop & Psture Science E. Shoukt et l. 8 () 6 S = 23.3 T = S T = 14.2 mm 1 mm 3 mm () S = 7.48 T = S T = 4.58 mm 1 mm 3 mm 4 45 FW (g plnt 1 ) () S = T = S T = 2.86 c Numer of leves per plnt () S = T = 62.9 S T = c Time (dys) c c Time (dys) Fig. 1. () Fresh weight (FW) of Phrgmites krk leves nd () totl plnt fter NCl tretment (, 1 nd 3 mm) for different time periods (3, 7, 15 nd 3 dys). F nd P-vlues were otined from ANOVA, where S (NCl tretment), T (Time period) nd Symols represent significnt levels (*P <.5; **P <.1; ***P <.1). Vlues mong slinity tretments with similr Bonferroni letters were not significntly different t P <.5. Fig. 2. () Numer of Phrgmites krk totl leves nd () dry leves fter NCl tretment (, 1 nd 3 mm) for different time periods (3, 7, 15 nd 3 dys). F nd P-vlues were otined from ANOVA, where S (NCl tretment), T (Time period), nd Symols represent significnt levels (*P <.5; **P <.1; ***P <.1). Vlues mong slinity tretments with similr Bonferroni letters were not significntly different t P <.5. found in 3 mm NCl s compred with the non-sline control (Tle 1). Lef Y W decresed with increses in NCl concentrtion nd ws more prominent fter 7 dys of slinity tretment (Fig. 4). Lef Y p strted to decrese from the seventh dy in 3 mm nd fifteenth dy in 1 mm NCl, wheres no further reduction ws oserved etween 15 nd 3 dys of slinity tretment (Fig. 4). Slinity tretments reduced Y p on the third dy; however, no difference in Y p ws found etween nd 1 mm NCl fter 1 week. Moreover, Y p of 3 mm NCl treted plnts significntly incresed (P <.1, F = 26.13) fter the third dy, lthough it ws still lower thn the control nd 1 mm NCl tretments (Fig. 4c). Little vrition occurred in wter reltions etween 15 nd 3 dys, so dt on the diurnl pttern with detiled PVC nlysis were tken on the fifteenth dy only. Pre-dwn lef Y W nd Y p were sustntilly higher thn mid-dy vlues nd this difference ws more pronounced in 3 mm NCl (Fig. 5, ). A pired smple t-test indicted tht mid-dy lef Y p dropped more significntly (P <.1) in 3 mm NCl thn in ny other tretment (Fig. 5c). Lef YW progressively decresed with increses in slinity wheres YS decresed under sline conditions with similr vlues in 1 nd 3 mm NCl (Tle 2). Lef YP ws higher in 1 mm NCl thn other tretments (Tle 2). A decrese in YW TLP ws oserved with increses in slinity (Fig. 6, Tle 2). Lef RWC ws similr t nd 1 mm nd decresed t 3 mm NCl, wheres RWC TLP in non-sline condition ws comprle with tht t 3 mm NCl ut ws incresed in 1 mm NCl. Differences in reltive wter content (DRWC) etween RWC nd RWC TLP were higher in nd 1 mm NCl (~5% nd 32% respectively) nd lower in 3 mm NCl (~26%) (Fig. 6, Tle 2). Hydrulic cpcitnce decresed t full turgor (C FT ) in 1 mm, while t turgor loss point (C TLP ) in 3 mm NCl. There ws difference of ~2.5 mol m 2 MP 1 etween C FT nd C TLP in nd 1 mm NCl, wheres this difference ws.13 mol m 2 MP 1 in 3 mm NCl (Tle 2). Bulk elstic modulus (e) ws similr t nd 1 mm nd incresed in 3 mm NCl (Tle 2). The contriution of ions (K + nd Cl ) to osmotic djustment ws 55% in sline-treted plnts wheres the rest ws ttriuted to orgnic osmolytes (Tle 3). No difference ws found in OA t etween 1 nd 3 mm NCl. Plnts showed ctive osmotic djustment (AOA) in oth NCl tretment wheres pssive osmotic djustment (POA) only t 3 mm NCl (Tle 3). Person nlysis showed significnt negtive correltion of e with YW TLP, lef FW nd plnt FW (Tle 4). In ddition, YS ws positively correlted with YW TLP, wheres YW TLP ws positively correlted with lef nd plnt FW (Tle 4).

5 Wter reltions of Phrgmites krk tll reed grss Crop & Psture Science 539 RER lef (cm cm 1 dy 1 ) RGR lef (g g 1 dy 1 ).4 () S = T = S T = () S = T = S T = dys 15 3 dys.5 c. 1 3 NCI (mm) Fig. 3. Reltive lef elongtion rte (RER lef ) nd reltive growth rte (RGR lef )ofphrgmites krk leves fter different durtion ( 15 nd 15 3 dys) of NCl tretment (, 1 nd 3 mm). F nd P-vlues were otined from ANOVA, where S (NCl tretment), T (Time period), nd Symols represent significnt levels (*P <.5; **P <.1; ***P <.1). Vlues mong slinity tretments with similr Bonferroni letters were not significntly different t P <.5. Tle 1. Chnges in clcium content, sclerophylly indices nd wter reltion prmeters of leves under slinity Lef re (LA), clcium content (C +2 ), lef tissue density (LTD), succulence (SUC), wter sturtion deficit (WSD), instntneous wter-use efficiency (WUE i ) nd trnspirtion (E) of Phrgmites krk treted with, 1 nd 3 mm NCl for 15 dys. Vlues mong slinity tretments followed y similr Bonferroni letter re not significntly different t P <.5 Prmeters Discussion Slinity lowers soil wter potentil, which my restrict wter supply to the plnts (Duli et l. 211). Morpho-metric chnges such s lef elongtion rte, lef development, reduced trnspirtion, nd stomtl closure disrupt plnt wter lnce nd growth under stress (Rsheed et l. 216). In this study the response in growth of Phrgmites krk to periodic chnges in wter reltions under NCl tretments ws determined. NCl (mm) 1 3 LA (cm 2 plnt 1 ) 67.4 ± ± ±.6 C +2 (mg g 1 DW) 2.8 ± ± ±.1 LTD (g g 1 ).3 ±..3 ±..3 ±. SUC (g g 1 DW) 2.6 ± ±. 2.8 ±.1 WSD (%) 3.4 ± ± ± 2.8 WUE i (mmol CO 2 mmol 1 H 2 O) 36.1 ± ± ± 1.3 E (mmol m 2 s 1 ) 5.9 ± ± ±.4c Ψ W (MP) Ψ p (MP) Ψ π (MP) () () (c) A A A B A A A A A B C S = T = S T = S = T = S T = 12.7 S = T = 1.74 S T = NS Cc A A B A Time (dys) Growth responses nd iomss production of Phrgmites krk were similr t nd 1 mm until the fifteenth dy compred with 3 mm NCl. However, y the end of the experiment (3 dys) optimum plnt growth (fresh weight nd lef numer) occurred in the non-sline control, which is common feture in some mrsh grsses such s Aeluropus lgopoides, Sporoolus iocldos, nd Urochondr setulos (Gulzr nd Khn 28). Aideen et l. (214) reported etter plnt growth of P. krk t 1 mm NCl (moderte slinity) compred with growth under non-sline conditions in quick check system (light intensity: 25 mmol m 2 s 1 ; temperture: 258C), which is similr to other species such s, Sprtin lternifolr nd Sprtin mritim (M et l. 211; B B A A B B A C Bc B A mm 1 mm 3 mm Fig. 4. Wter potentil (Y w ; ), osmotic potentil (Y p ; ) nd turgor potentil (Y p ; c) ofphrgmites krk fter NCl tretment (, 1 nd 3 mm) for different time periods (3, 7, 15 nd 3 dys). F nd P-vlues were otined from ANOVA, where S (NCl tretment), T (Time period), nd Symols represent significnt levels (*P <.5; **P <.1; ***P <.1; NS, non-significnt). Similr cpitl letters mong slinity tretments nd smll letters within ech slinity tretment re not significntly different (P <.5) from ech other, Bonferroni test. C A A B B A 3 Cc Bc B

6 54 Crop & Psture Science E. Shoukt et l. Ψ W (MP) Ψ p (MP) Ψ π (MP) P < P < P <.1 () - P < P < P <.1 () (c) - NS 1 - NS 3 - P <.1 Nidoo et l. 212). In this experiment, the reduced growth t 1 mm NCl could e ttriuted to high light intensity (~5 mmol m 2 s 1 ) nd mient temperture (378C). In the erly vegettive phse (15 dys), P. krk ppered to invest in lef elongtion rther thn in new lef development, (which demnds high energy consumption) nd hence mintined fresh weights t 1 mm NCl tht were similr to the nonsline control. However, with dvncing ge (3 dys), plnts ppered to invest in new lef development irrespective of the slinity tretments. Moreover, iomss reduction in modertely sline condition could lso e linked with energy requiring Pre-dwn Mid-dy 1 3 NCI (mm) Fig. 5. Pre-dwn nd mid-dy wter potentil (Y w ; ), osmotic potentil (Y p ; ) nd turgor potentil (Y p ; c) of Phrgmites krk treted with different concentrtions of NCl (, 1 nd 3 mm) for 15 dys. P-vlues represent the degree of significnce in t-test nlysis. Vlues within ech slinity tretments with similr letters re not significntly different ccording to the t-test. Tle 2. Chnges in lef prmeters relted to pressure volume curve Wter potentil t full turgor (YW ), osmotic potentil t full turgor (YS ), turgor potentil (YP ), wter potentil t turgor loss point (YW TLP ), reltive wter content t full turgor (RWC ), reltive wter content t turgor loss point (RWC TLP ), hydrulic cpcitnce t full turgor (C FT ), hydrulic cpcitnce t turgor loss point (C TLP ) nd ulk elstic modulus (e)] of Phrgmites krk treted with, 1 nd 3 mm NCl for 15 dys. Vlues mong slinity tretments followed y similr Bonferroni letters re not significntly different t P <.5 Prmeters NCl (mm) 1 3 YW ( MP).6 ±. 1.1 ±. 1.5 ±.c YS ( MP) 1.2 ±. 2. ±.1 2. ±. YP (MP).6 ±.1.9 ±..5 ±.1 YW TLP ( MP) 1.3 ±. 2.1 ± ±.c RWC (%) 96.5 ± ± ± 3. RWC TLP (%) 44.9 ± ± ± 3.5 C FT (mol m 2 MP 1 ).4 ±.1.2 ±..2 ±. C TLP (mol m 2 MP 1 ) 3. ± ±.5.3 ±. e (MP) 2.4 ± ± ±.5 processes such s nutrient homeostsis, ROS quenching, nd osmotic djustment (Asrr et l. 217). Phrgmites krk displyed clssicl time- nd dosedependent slinity response in growth nd wter reltions, which is similr to those oserved in other hlophytic grsses (Liu et l. 211; Ahmed et l. 213). Plnts regulte their iomss (plnt FW, lef FW, RGR lef ) t 1 mm NCl with the help of higher reltive wter content nd etter WUE i (Nerd nd Psternk 1992; Riccrdi et l. 214). Growth reduction of P. krk in 3 mm NCl within 3 7 dys seems to e due to osmotic rther thn ionic effects of slinity, which my e relted to lef turgor loss nd tissue dehydrtion (Aideen et l. 214). However, growth reduction (RGR lef, RER lef ) with incresed numer of ded leves during longterm exposure (3 dys) of 3 mm NCl is proly due to oth osmotic nd ionic effects of slinity (Munns nd Termt 1986; Wng nd Nii 2; Munns nd Tester 28). Clcium plys n importnt role in plnt growth under sline conditions ecuse of its involvement in signlling cscdes nd structurl modifictions (Hepler nd Winship 21; Bickerton nd Pittmn 212; Prvin et l. 216). In the present study, considerle increse in C +2 content t 3 mm NCl my e linked with high cell wll rigidity of P. krk. It ppers tht C +2 ws involved in the hrdening of cell wlls vi complexes of C-pectte (Cosgrove 25; Hepler nd Winship 21), which my result in n inhiition of cell elongtion nd lef re. Clcium content t 1 mm NCl ws similr to the non-sline control, which is concomitnt with unltered ulk elstic modulus. However, the involvement of C +2 signlling in stomtl opening (We et l. 1996) nd quporin function (Cñero et l. 26) in moderte slinity requires further investigtion. Lef osmotic potentil (Y p ) ws similr mong slinity tretments on the third dy resulting in lower lef turgor, which indictes tht plnts fced difficulty in otining wter due to the osmotic effect of slinity (Munns nd Tester 28). However, prominent decrese in Y p t 1 mm NCl fter 15 dys indictes etter osmotic djustment. A rpid decrese

7 Wter reltions of Phrgmites krk tll reed grss Crop & Psture Science Ψ W mm Ψ π.5 y =.27x R 2 =.99 W TLP = 1.33 Tle 3. Chnges in lef osmotic djustment under slinity Osmotic djustment (totl osmotic djustment: OA t, ctive osmotic djustment: AOA, pssive osmotic djustment: POA) nd percent contriution of sodium (N + ), potssium (K + ), chloride (Cl ), solule sugr to lef osmotic potentil of Phrgmites krk treted with 1 nd 3 mm NCl for 15 dys Prmeters NCl 1 mm 3 mm Ψ (MP) mm y =.42x.49 R 2 =.91 W TLP = mm y =.43x.49 R 2 =.96 Inorgnic N ± ±.5 K ± ±.6 Cl 29.8 ± ± 2. P (N+ K+ Cl) 55.7 ± ± 3.5 Orgnic Solule sugr 9.1 ± ±.9 Others 25.2 ± ± 6.2 Osmotic djustment OA t.8 ±.1 1. ±.1 AOA.8 ±.1.8 ±. POA. ±.2.2 ±.1 Tle 4. Person correltion mong different prmeters of the pressure volume curve Bulk elstic modulus (e), osmotic potentil t full turgor (YS ), osmotic potentil t turgor loss point (YW TLP )] nd growth ttriutes [leves fresh weight (LFW) nd plnt fresh weight (PFW)]. *P <.5; **P <.1; ***P <.1; n.s., non-significnt Prmeters YS YW TLP LFW PFW e.4n.s..7*.8**.7* YS.9***.5n.s..5n.s. YS TLP.8*.7* LFW.9** RWC W TLP = Fig. 6. Pressure volume curve of Phrgmites krk treted with different concentrtions of NCl (, 1 nd 3 mm) for 15 dys. The sign of Y represents potentil of wter (Y w ), solute (Y p ) nd wter potentil t the turgor loss point (W TLP ), nd reltive wter content (RWC). in lef Y p t 1 mm NCl indictes tht the osmo-regultor strtegy of Phrgmites krk my e similr to P. ustrlis (Vsquez et l. 26; Gori et l. 211) nd severl other grsses such s Sporoolus tremulus: Moinuddin et l. (214); Andropogon greenwyi: Hmilton et l. (21). This strtegy enles osmotic djustment in plnts where frequent chnges in soil slinity re not common (Adm 1993). Most of the hlophytic species use N + nd Cl s chep osmoticum ecuse the synthesis of orgnic osmolytes requires high energy (Wng et l. 24). The osmotic contriution of inorgnic content ws ~5% in P. krk under slinity. Among orgnic osmolytes the contriution of solule sugrs ws 1%, wheres the proline nd glycine etine contriution ws <1% in osmotic djustment (dt not shown). Similr results were lso reported in P. ustrlis (Gori et l. 211; Mimiti et l. 216). However, there is possiility tht polyols (especilly mnnitol) my contriute to osmotic djustment in P. krk s lso reported in Phrgmites ustrlis (Mimiti et l. 216) nd Phrgmites communis (Briens nd Lrher 1982). Although smll chnges in lef Y p were found t 3 mm NCl, there ws significnt loss in turgor potentil (Y p ), which suggests tht incresing cell wll rigidity my result in poor plnt growth (Mrtìnez et l. 24; Verslues et l. 26). Some plnts show significnt chnges in diurnl lef wter reltions (Nidoo et l. 28) compred with others with little vritions (Turner nd Long 1975; Wenkert et l. 1978; Hinckley et l. 198). These chnges could e result of oth higher tissue rigidity nd decreses in osmotic potentil (Touchette 26; Rozem nd Scht 213). Plnts hving less elstic cell wlls ut with greter fluctutions in diurnl Y W, my e termed s drought voiders with wter spending strtegy wheres those showing little vritions in diurnl wter reltions tend to hve wter conserving strtegy nd re known s drought tolernt (Slleo 1983; Gullo et l. 1986; Gullo nd Slleo 1988). A rpid chnge in diurnl Y W (decrese in mid-dy Y W ) indictes tht P. krk ws le to quickly pull wter from the soil, which suggests wter spending strtegy (Slleo 1983). The differences etween pre-dwn nd mid-dy lef Y W nd Y p were even higher in 3 mm NCl, which indictes poor drought resistnce in P. krk (Bolños nd Longstreth 1984;

8 542 Crop & Psture Science E. Shoukt et l. Moderte slinity (1 nm NCI) High slinity (3 nm NCI) Low ulk elstic modulus High hydrulic cpcitnce High turgidity Incresed lef re Better growth WUE WUE High ulk elstic modulus Low hydrulic cpcitnce Low turgidity Decresed lef re Poor growth Trnspirtion Trnspirtion Wter content Wter content Low WSD High wter uptke High WSD Low wter uptke Fig. 7. Model representing the chnges in different prmeters of Phrgmites krk fter tretment with 1 nd 3 mm NCl. The direction of the rrows shows the chnge in comprison with the non-sline tretment nd the numer of rrows indicte significnt difference (P <.5) etween slinity tretments. Prdossi et l. 1998; Touchette 26). However, to confirm this ssumption, further reserch would e required under drought nd flooding conditions coupled with slinity. In our experiment, the PVC dt showed higher YP t 1 mm NCl, which is in greement with higher solute ccumultion (more negtive YS ) tht contriuted to lower YW (Touchette et l. 29). Moreover, the lck of difference in e nd WSD t 1 mm NCl compred with the non-sline control indictes non-disruptive wter lnce (Touchette 27). Plnts lso incresed WUE i to strictly regulte wter loss from eril tissues in order to mintin wter lnce. A 5% reduction in YP in 3 mm NCl is linked to 3-fold increse in e of cell wll nd lower YW TLP (Zheng et l. 21; Surez 211), which indictes plnt sensitivity to wter stress (Bolños nd Longstreth 1984; Prdossi et l. 1998; Lenz et l. 26; Touchette 27; Touchette et l. 29). Differences etween YW TLP nd lef Y p were lower in 3 mm NCl compred with 1 mm NCl, suggesting tht plnts re unle to pull wter from the soil, which is well supported y increses in WSD nd reduced lef growth, trnspirtion rte nd hydrulic conductnce (Brtlett et l. 212). Phrgmites krk ws lso unle to further decrese lef Y p t 3 mm compred with 1 mm NCl (s indicted y unchnged OA t etween 1 nd 3 mm NCl). Most of the modertely slttolernt grsses of slt mrshes disply similr response (for exmple, Andropogon greenwyi: Hmilton et l. 21; Sporoolus tremulus: Moinuddin et l. 214), wheres highly slt-tolernt grsses grdully decrese Y p with increses in slinity (Urochondr setulos: Gulzr nd Khn 28; Aeluropus lgopoides: Moinuddin et l. 214). Brtlett et l. (212) lso reported tht different responses in lef Y p depend on the type of species nd hitt in which plnts nturlly grow. Phrgmites krk incresed solute ccumultion (decrese in YS ) t 1 mm NCl (Aideen et l. 214) indicting high dependency on ctive osmotic djustment (AOA) (Slpeter et l. 212). However, t 3 mm NCl plnts mintined OA t y incresing cell wll rigidity thus restricting the entry of oth wter nd solutes, which could result in incresed poplstic wter frction (Touchette et l. 29; Slpeter et l. 212; Flowers et l. 215; Hessini et l. 215). Incresing poplstic wter represents pssive osmotic djustment (POA), which is considered useful strtegy ginst the negtive effects of slinity in generl (Nvrro et l. 27) nd for voiding oxidtive stress in prticulr (Miller et l. 21). However, POA in plnts could e t the cost of cellulr dehydrtion (Flowers nd Yeo 1986), which is in ccordnce with high WSD. Increse in WSD t 3 mm NCl pper to e linked with e ut not with sclerophylly indices like LTD nd SUC, s oserved in other monocots (Prid nd Ds 25; Gori et l. 21; Rozem nd Scht 213). In ddition, incresed e is the possile reson for the decline in hydrulic cpcitnce of lef tissues under 3 mm NCl, i.e. the difference etween C FT nd C TLP in 3 mm (.13 mol m 2 Mp 1 ) compred with nd 1 mm NCl (2.5 mol m 2 MP 1 ). A strong negtive correltion of e with YW TLP, LFW nd PFW indictes greter role of cell wll rigidity in P. krk under physiologicl drought. Our findings re in greement to the ove mentioned hypothesis tht growth response of P. krk under slinity depends on the ulk elstic modulus. Conclusion This study provides detiled explntion of wter reltions of P. krk under slinity. Plnts mintined turgor under moderte slinity (1 mm NCl) y low tissue rigidity, incresed hydrulic cpcitnce nd ctive osmotic djustment, which

9 Wter reltions of Phrgmites krk tll reed grss Crop & Psture Science 543 ultimtely fcilitted in mintennce of wter lnce nd growth (Fig. 7). However, lef wilting nd poor plnt growth t 3 mm NCl is the consequence of greter diurnl fluctutions in wter potentil, low trnspirtion, high wter sturtion deficit nd tissue rigidity (Fig. 7). Wter deprivtion t 3 mm NCl indicted poor drought tolernce compred with non-sline control nd 1 mm NCl. In conclusion, it is recommended tht P. krk could e grown on mrginlly sline lnds prticulrly for producing iomss for iofuels. This study lso provides new dimension for future reserch to understnd the role of cell wll rigidity on growth, with the help of modern moleculr tools, which my e useful to enhnce the slt tolernce of gint grsses. Conflicts of Interest The uthors declre no conflicts of interest. Acknowledgements The uthors would like to thnk Dr Rzi-uddin Ansri, Dr Brent L. Nielsen nd nonymous reviewers for their input in revising nd improving the qulity of this mnuscript. The provision of funds for the current reserch y the Fculty of Science, University of Krchi is lso gretly cknowledged. References Aideen Z, Ansri R, Gul B, Khn MA (212) The plce of hlophytes in Pkistn s iofuel industry. Biofuels 3, doi:1.4155/fs Aideen Z, Koyro HW, Huchzermeyer B, Ahmed MZ, Gul B, Khn MA (214) Moderte slinity stimultes growth nd photosynthesis of Phrgmites krk y wter reltions nd tissue specific ion regultion. Environmentl nd Experimentl Botny 15, doi:1.116/ j.envexpot Aogdllh GM (21) Sensitivity of Trifolium lexndrinum L. to slt stress is relted to the lck of long-term stress-induced gene expression. Plnt Science 178, doi:1.116/j.plntsci Adm P (1993) Sltmrsh ecology. 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