Changes in leaf water potential and photosynthesis of Bauhinia forficata Link under water deficit and after rehydration

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1 Hoehne 4(1): , 7 fig., 213 Chnges in lef wter potentil nd photosynthesis of Buhini forfict Link under wter deficit nd fter rehydrtion Rodrigo Fzni Esteves Snches 1 nd Emerson Alves d Silv 2,3 Received: ; ccepted: ABSTRACT - (Chnges in lef wter potentil nd photosynthesis of Buhini forfict Link under wter deficit nd fter rehydrtion). To evlute the influence of different intensities of wter deficit nd rehydrtion on wter reltions nd gs exchnges of Buhini forfict Link, plnts were grown in greenhouse for three months under the following wter regimes: dily wtered (control) nd wtered every 7 (7D) nd 15 dys (15D) returning to dily wtering on 7D nd 15D tretments t 75 dys of the experiment. Aiming to evlute short term responses to re hydrtion, plnts of 7D nd 15D tretments were re wtered 2 dys efore mesurements nd smpling ws crried out t the 45 th dy of experiment. At fortnightly intervls (15, 3, 45, 6, 75, nd 9 dys) soil moisture (Usoil), lef wter potentil (Ψwf), photosynthesis in response to photosyntheticlly ctive rdition (A PPFD) to otin the mximum net photosynthesis (Amx), nd light sturtion point (PARst) were evluted. The wter deficit hs ffected wter reltions nd photosynthesis with the lowest vlues oserved in the tretments Usoil 7D, nd 15D respectively, coinciding with the lowest Ψwf nd Amx. Chnges in PARst in response to wter deficit were oserved showing men vlues of 665, 275 nd 254 µmol photons m -2 s -1 in control, 7D nd 15D respectively. The return of dily wtering fter 75 dys of experiment, promoted the recovery of Amx (7.8 nd 9.6 µmol CO 2 m -2 s -1 ) nd PARst (588 nd 643 µmol photons m -2 s -1 ) in 7D nd 15D respectively with vlues higher thn control plnts (4.7 µmol CO 2 m -2 s -1 nd 631 µmol photons m -2 s -1 ), suggesting strong dependence of photosynthesis of Buhini forfict to the soil wter vilility. Key words: Brzilin Orchid-tree, drought tolernce, plsticity RESUMO - (Alterções no potencil hídrico folir e fotossíntese de Buhini forfict Link so déficit hídrico e pós reidrtção). Pr vlir influênci de déficits hídricos de diferentes intensiddes e d reidrtção ns relções hídrics e trocs gsoss, plnts de Buhini forfict Link form cultivds em cs de vegetção durnte três meses e sumetids os regimes de regs diáris (controle) e regs cd 7 (7D) e 15 dis (15D) retornndo s regs diáris nos regimes 7D e 15D os 75 dis de experimento. Com o ojetivo de vlir resposts de curto przo à re hidrtção, plnts dos trtmentos 7D e 15D form re irrigds 2 dis ntes ds medids relizds no 45º de experimento. Em intervlos quinzenis (15, 3, 45, 6, 75 e 9 dis) form vlids umidde do solo (Usolo), potencil hídrico folir (Ψwf), fotossíntese em respost rdição fotossinteticmente tiv (A PPFD) pr otenção d fotossíntese máxim (Amx) e d rdição fotossinteticmente tiv n sturção (PARst). O déficit hídrico fetou s relções hídrics e fotossíntese, sendo que os menores vlores de Usolo oservdos nos trtmentos 7D e 15D respectivmente, coincidirm com os menores Ψwf e Amx. Alterções nos PARst em respost o déficit hídrico form oservds presentndo vlores médios de 665, 275 e 254 µmol fótons m -2 s -1 no controle, 7D e 15D, respectivmente. O retorno ds regs diáris pós 75 dis de experimento promoveu recuperção de Amx (7,8 e 9,6 µmol CO 2 m -2 s -1 ) e dos PARst (588 e 643 µmol fótons m -2 s -1 ) ds plnts 7D e 15D, respectivmente, os 9 dis, com vlores miores dqueles oservdos ns plnts controle (4,7 µmol CO 2 m -2 s -1 e 631 µmol fótons m -2 s -1 ), sugerindo forte dependênci d fotossíntese de Buhini forfict à disponiilidde hídric no solo. Plvrs-chve: pt-de-vc, plsticidde, tolerânci sec INTRODUCTION The distriution of plnts on Erth's surfce is controlled siclly y two iotic fctors, ir temperture nd wter vilility in soil. Since ir temperture llows, the mount nd distriution of rin ecomes the mjor limiting fctor to plnt development (Krmer & Boyer 1995). This ecologicl importnce of wter is result of its physiologicl importnce, eing the only wy y which n environmentl fctor 1. Progrm de Pós-grdução em Fisiologi e Bioquímic de Plnts, Universidde de São Pulo, ESALQ, Av. Pádu Dis, 11, Pircic, SP, Brsil 2. Instituto de Botânic, Núcleo de Pesquis em Fisiologi e Bioquímic, Av. Miguel Stéfno 3687, São Pulo, SP, Brsil 3. Corresponding uthor: esilv@iot.sp.gov.r

2 182 Hoehne 4(1): , 213 such s wter cn ffect the plnt growth is influencing physiologicl processes (Koslowski & Pllrdy 1997). Due to the increse of cron dioxide in tmosphere, which leds to n increse in ir temperture, it is considered tht there will rise the tmospheric demnd for wter nd, on mny regions, with higher occurrence, frequency, intensity nd distriution of droughts. The climte chnge models show n high frequency of rinfll seprted y long dry periods (Dore 25). In this scenrio, the projected climte chnges for the coming yers due to glol wrming, mke studies on wter use y ntive species criticl, not only to preserve ecosystems, ut lso to define strtegies for recovery of degrded res, since the estlishment of the species is criticl step to the recovery of these res. Thus, mong the environmentl fctors, wter deficiency stnds out s n dverse fctor to the growth nd crop production mking it essentil for studies to ddress the issue. Wter deficiency hs een considered s one of the min fctors limiting the productivity, oth griculturl nd nturl ecosystems. In nture, the intensity nd distriution of rinfll determine the wter regime, from influencing the growth nd productivity of individuls, to the distriution of popultions nd the iodiversity of ecosystems. The wter deficit cused y drought is estlished when the wter sorption from root system cnnot meet the demnds of the plnt (Fn et l. 26). Among the min demnds re photosynthesis nd trnspirtion, two essentil processes for plnt growth. Before the wter deficit hs een estlished, roots hve to sense the dry soil nd trnsmit this informtion to shoot, which cretes n integrted response of the plnt llowing its survivl until the wter vilility increses. This communiction is done y severl mens in ddition to the reduction of the upwrd flow of wter (Dvies & Zhng 1991). The min physiologicl processes tht ffectes plnts under wter deficit, re stomtl conductnce, mesophyll photosynthesis nd, y extension, their growth. However, such effects depend of the species studied s well s the intensity nd durtion of the wter deficit rte (Chves & Pereir 1992). Stomtl closure is in fct one of the first lines of defense ginst wter deficits, since it is fst nd flexile process on reltion to other lterntives, such s chnges in the life cycle, root growth or lef re, which constitute long term responses. The stomtl closure reduces wter loss y the plnt, ut t the sme time decreses the entry of CO 2 from the tmosphere to the sustomtl cvity, influencing the cron ssimiltion (Chves 1991). The species Buhini forfict Link presents rod neotropicl distriution eing found in Argentin, Bolivi, Prguy, Uruguy nd Brzil (Fortunto 1986), thus occurring in different iomes. Moreover, it is recommended for projects of recovery of degrded res, eing good model for studies on plnt responses to environmentl stresses such s wter deficit. Due to the wide distriution, we hypothesized tht of B. forfict presents high tolernce to drought llowing their occurrence nd survivl under different environments, minly under wter deficit conditions. Furthermore, since photosynthetic cpcity plys n importnt role on plnt estlishment nd growth, little is known out the effects of wter stress in the photosynthesis of this species, considering tht it is widely recommended for recovery of degrded res. This work imed t evlutes chnges in photosynthesis of Buhini forfict in response to different intensities of wter deficits nd fter recovery y hydrttion. Mteril nd methods Plnt mteril nd growing conditions - plnts of B. forfict with 6 months of ge were otined in the nursery BioFlor Forest Restortion in the city of Pircic, São Pulo Stte, Brzil nd trnsplnted into individul pots of 2 L, contining orgnic soil sustrte (Tropstrto, HT ). Plnts were dily wtered nd received Clrk nutrient solution (Clrk 1975), once week until eginning of the experiment. After, nutrient solution ws pplied in fortnightly intervls. The pot plnt sets were mintined in greenhouse t the Núcleo de Pesquis em Fisiologi e Bioquímic do Instituto de Botânic (IBt/SMA/SP) throughout the experimentl period. After three mouths the different wter regimes were imposed on plnts in the following tretments: dily wtered plnts (control), wtered every 7 dys (7D) nd every 15 dys (15D) returning to dily wter regimes t 75 th dys of the experiment. Aiming to evlute short term responses to re hydrtion, plnts of 7D nd 15D tretments were re wtered 2 dys efore mesurements nd smpling crried t 45 th dys of the experiment. In ech tretment of wtering regimes wter ws provided until pot sturtion iming to elevte soil moisture close to the field cpcity in pots.

3 Snches & Silv: Chnges in lef wter potentil nd photosynthesis of Buhini forfict 183 The wtering frequencies of 7 nd 15 dys were defined previously on n pilot experiment where wter supply to 1 potted plnts distinct from tht used in the min experiment. ws totlly suspended nd lef wter potentil ws mesured iming to ensure the estlishment of wter deficit nd void plnt deth during the min experiment. At fortnightly intervls (15, 3, 45, 6, 75 nd, 9 dys) soil moisture (Usoil), lef wter potentil (Ψwf) t predwn, photosynthesis in response to photosynthetic photon flux density (A PPFD) to otin the mximum net photosynthesis (Amx) nd light sturtion point (PARst) were evluted. During the experiment, the temperture ( C), reltive humidity (RH, %) nd the photosynthetic photon flux density (PPFD, µmol photons m -2 s -1 ) were monitored inside the greenhouse using temperture/humidity sensor (Li 14 14, Li Cor - Nersk, USA) nd quntum sensor (Li- 19SA, Li Cor - Nersk, USA) respectively. The sensors were connected to dtlogger (Li 14, Li Cor - Nersk, USA), which ws configured to perform the mesurements t intervls of 1 minutes, clculting dily mens for ech prmeter evluted. Ecophysiologicl Evlutions - Soil moisture (Usoil, %) ws mesured y time domin reflectometry, using sensor model ML2 Delt X T Devices (ThetProe, Cmridge, UK). In order to quntify the intensity of wter deficit imposed to the plnts in the different tretments, lef wter potentil (Ψwf, MP) t predw (5 nd 6 h) were mesured in the 2 nd fully expnded lef from the pex of ech plnt using pressure pump type Scholnder, Model 1 (PMS Instrument Co., UTAH, USA). We performed instntneous mesurements of net cron ssimiltion rtes (A, µmol CO 2 m -2 s -1 ), stomtl conductnce (gs, mol m -2 s -1 ) nd trnspirtion (E, nmol m -2 s -1 ) in response to photosyntheticlly ctive rdition (PAR, µmol photons m -2 s -1 ), curves A PPFD. From these curves we defined the light point sturtion (PARSt, µmol photons m -2 s -1 ) nd mximum net photosynthesis (Amx, µmol photons m -2 s -1 ) ccording to model proposed y Long & Hällgren (1993). Mesurements were crried using n infrred gs nlyzer (IRGA) model Li 64 (Li Cor - Nersk, USA) in open system, etween 8 to 11 h. Curves A PPFD were performed in the 3 rd fully expnd lef from the pex of ech plnt, with concentrtion of 38 ppm of CO 2 nd photosynthetic photon flux density (PPFD) of, 5, 1, 3, 5, 7, 1, nd, 1,2 µmol m -2 s -1 in order to verify possile chnges in prmeters of gs exchnge in response to wter deficit. Ech point in the A PPFD curve represents men of five replictes for ech PPDF. Experimentl design nd sttisticl nlysis - The experiment ws conducted etween Septemer nd Novemer 21 rrnged on completely rndomized design with five replictes per tretment in ech point of nlyses. Six points of nlyses were crried over these 3 months with totl of 3 plnts per tretment. Dt of ecophysiologicl prmeters were sujected to vrince nlysis (ANOVA), nd ny contrst etween mens ws evluted y Tukey test t 5% level of proility, using the sttisticl pckge BioEstt 3. (Ayres et l. 2). Normlity tests were previously performed. The dt were lso sujected to Person correltion nlyses etween the prmeters evluted. Correltions were tested y t Student test. Results nd discussion The men ir temperture during the experiment ws 25.8 ºC with minimum nd mximum mens of 21 nd 31 C, respectively (Figure 1). Under nturl nd greenhouse conditions, with incresing rdition, the temperture rises nd the reltive humidity decreses (Medin et l. 1999) incresing the tmospheric demnd for wter. So, s expected, we oserved significnt inverse correltion etween the PAR nd RH (r = -.75; p =.229), with the lowest men vlues of PAR (345.9 µmol m -2 s -1 ) coinciding with the highest men vlues of RH (57%), reflecting the influence of high clouds chrcteristic of this time of yer in these meteorologicl prmeters. Soil moisture (Usoil) presented low chnges in the pots of control plnts with vlues etween 22 to 26% (Figure 2). However, for pots of plnts sujected to 7D nd 15D tretments, vlues rnged etween 2 to 12%, nd 1 to 8% respectively, showing sttisticl differences etween these tretments only on the 15 th dy of the experiment. Notwithstnding the lowest vlues of Usoil oserved coincided with low vlues of RH (57%) nd high vlues of PAR (45 µmol m -2 s -1 ) on the 6 th dy (figure 1). With the returning of dily wtering fter the 75 th dy of experiment, in the tretments 7D nd 15D until the end of the experiment, the vlues of Usoil reched 18% showing no sttisticl differences when compred to control. The wter tretments of 7D nd 15D were sufficient to generte wter deficits in plnts leding

4 184 Hoehne 4(1): , 213 to significnt decresing on lef wter potentil (Ψwf, MP) (Figure 3), net cron ssimiltion rtes (A) (Figure 4), stomtl conductnce (gs) (Figure 5) nd, trnspirtion (E) (Figure 6) if compred to control plnts. Controls plnts did not chnge significntly in Ψwf, remining lwys ove 1. MP, showing tht dily wtering ws sufficient to mintin high vlues of Usoil (Figure 2) nd low vlues of Ψwf (Figure 3) throughout the whole experiment. On the other hnd, the plnts in 7D nd 15D tretments showed tht the Ψwf vlues close to 1. to 1.45 MP t the eginning of the experiment nd 2. nd 3. MP fter 3 dys respectively. However, only plnts in the 15D tretment showed sttisticl differences when compred to control in these dys. Aiming to evlute short therm responses to re hydrtion, the plnts of 7D nd 15D tretments were re wtered 2 dys efore mesurements nd smpling t 45 th dy. Two dys fter re wtering, plnts of 7D nd 15D tretments presented n incresing in Ψwf Air temp., C RH, % Dys Figure 1. Air temperture ( ), photosyntheticlly ctive rdition (PPFD) ( ), nd ir reltive humidity (RH) ( ) inside the greenhouse during the experimentl period. The symols indicte the dys of ecophysiologicl evlutions PPFD, µmol photons m -2 s -1 reching vlues of 1. nd 1.12 MP respectively, showing rpid lef rehydrtion. However, t 6 th dys, tretments 7D nd 15D showed fst decrese in Ψwf with men vlues of 3.3 nd 4.3 MP respectively, with visile effects in gs (Figure 5) nd in E (Figure 6), ut keeping positive A vlues (Figure 4). As expected, there ws positive correltion etween vritions in Usoil nd in Ψwf in plnts of 7D (r =.916; p =.1) nd 15D (r =.828; p =.42) tretments, i.e. s soil wter vilility decresed, the Ψwf lso decresed. As oserved for Usoil, the return of dily wtering fter 75 dys of the experiment, llowed the increse in Ψwf from plnts under wter deficit to vlues similr to the control plnts. The wter deficit imposed to the plnts in this study ws sufficient to generte chnges in content nd free energy of wter in soils nd plnts, respectively, which in turn ffected the photosynthesis of B. forfict. In fct, the decrese in wter content is ccompnied y loss of turgor nd wilting, disruption in cell expnsion, stomtl closure, reduced photosynthesis, ffecting plnt growth nd productivity (Hu & Schmidhlter 1998, Kumr & Sing 1998, Krmer & Boyer 1995). Associted to mesurements of wter potentil (Figure 3), net cron ssimiltion rtes (A) (Figure 4) in response to photosyntheticlly ctive rdition (PAR) showed positive reltion of dependency of plnts B. forfict to soil wter vilility. U soil, % c Dys Figure 2. Soil Moisture (U soil ) in the pot of plnts of Buhini forfict Link under dily wtered (Control - ) nd wtered every 7-(7D - ) nd 15-dy (15D - ) conditions. The rrow indictes the return of dily wtering in 7D nd 15D tretments. Brs indicte the stndrd error (n = 5). Mens followed y sme letter in ech smple do not differ significntly y Tukey s test (P =.5).

5 Snches & Silv: Chnges in lef wter potentil nd photosynthesis of Buhini forfict 185 As oserved in figure 4, A in 7D nd 15D tretments ws lredy ffected t 15 th dys of the experiment with vlues lwys lower thn the control, including negtive rtes oserved on the 3 th dy of experiment. The re wtering of plnts in 7D nd 15D tretments two dys efore the 45 th dys fvored the recovering of positive photosynthetic rtes returning to zero nd negtive vlues t 6 th nd 75 th dys of experiment. During the experiment the higher vlue of Amx in B. forfict ws oserved in control plnts (12 µmol CO 2 m -2 s -1 ) tht showed vlues lwys higher thn plnts of 7D nd 15D tretments until the 75 th dy. However, with the return of dily wtering, Amx of plnts in the 7D nd 15D tretments showed vlues of 7.8 nd 9.6 µmol CO 2 m -2 s -1 respectively t the 9 th dy, which were significntly higher thn control plnts (4.7 µmol CO 2 m -2 s -1 ). Light nd wter vilility is one of the most importnt fctors tht ffect the productivity of plnts, minly y reducing stomtl conductnce nd photosynthesis (Blum 1997). In this work we re showing tht the mximum photosynthetic rtes (Amx) of plnts under wter deficit (Figure 7A) presented high nd significnt correltion with Usoil (r =.86; p =.5 nd r =.846; p =.34) nd Ψwf (r =.887; p =.18 nd r =.941; p =.5) on the 7D nd 15D Ψ wf, MP Dys Figure 3. Lef wter potentil (Ψ wf ) of plnts of Buhini forfict Link grown under dily wtered (Control - ) nd wtered every 7 (7D - ) nd 15 dy (15D - ) conditions. The rrow indictes the return of dily wtering in 7D nd 15D tretments. Brs indicte the stndrd error (n = 5). Mens followed y sme letter in ech smple do not differ significntly y Tukey s test (P =.5). c tretments respectively. Such correltions ssocited with the fct tht photosynthesis on 7D nd 15D plnts were higher thn control fter the return of dily wtering reinforces the reltion of dependence of photosynthesis of B. forfict to wter vilility, suggesting high plsticity of its photosynthetic pprtus. Also with respect to gs exchnge, is oserved in Figure 4 tht the influence of wter deficit decresing A ws prtly due to reductions in gs preventing, tht plnts from oth 7D nd 15D tretments chieved their photosynthetic compenstion points. On the other hnd, the recovery of positive vlues of A rtes t 9 th dys in the plnts 7D nd 15D with higher vlues thn the control, ssocited with the gs dt (Figure 5) nd E (Figure 6) suggest rpid cclimtion of the photosynthetic pprtus of plnts 7D nd 15D to the low vilility of wter in the soil nd fter wter recovery. The process of stomtl perture nd closure is minly relted to light intensity nd stte of lef hydrtion. Thus, in situtions of low wter vilility in soil, plnts reduce their stomtl conductnce in order to decrese wter loss through trnspirtion, fvoring the mintennce of cell turgor in drought conditions (Silv et l. 24). However, when the stomt closes preventing wter loss, simultneously they restrict the diffusion of tmospheric CO 2 for sustomtl chmers (Chves 1991) ffecting ruisco croxyltion nd the rtes of riulose 1,5 isphosphte regenertion (Bjorkmn 1981), two importnt fctors tht define the minimum vlues of A (Frquhr et l. 198). Figure 5 shows the stomtl conductnce (gs) of B. forfict plnts sumitted to wter deficit, where the plnts of 7D nd 15D tretments kept their stomt constntly closed when soil wter vilility ws less thn 1%. Figure 7B lso shows tht the photosynthetic sturtion point (PARst) ws ltered in response to wter deficit imposed on plnts in 7D nd 15D tretments. Under optiml conditions of wter vilility, the PARst showed men vlues of 665 µmol photons m -2 s -1 in control while the 7D nd 15D tretments showed minimum vlues of 43 nd 18 µmol photons m -2 s -1 respectively. In ddition, s oserved in Amx, the PARst of plnts 7D nd 15D correlted significntly with Usoil (r =.775; p =.5 nd r =.881; p =.2) nd Ψwf (r =.868; p =.25 e r =.929; p =.7) respectively.

6 186 Hoehne 4(1): , A, μmol CO 2 m -2 s PPFD, μmol photons m -2 s -1 Figure 4. Curves of net cron ssimiltion rtes in response to photosyntheticlly ctive rdition (A PPFD) of plnts of Buhini forfict Link under dily wtered (Control - ) nd wtered every 7-(7D - Δ) nd 15-dy (15D - ) conditions. The rrow indictes the return of dily wtering in 7D nd 15D tretments (n = 5).

7 Snches & Silv: Chnges in lef wter potentil nd photosynthesis of Buhini forfict g s, mol m -2 s PPFD, μmol photons m -2 s -1 Figure 5. Curves of stomtl conductnce (g s ) in response to photosyntheticlly ctive rdition (g s xpar) of plnts of Buhini forfict Link under dily wtered (Control - ) nd wtered every 7-(7D - Δ) nd 15-dy (15D - ) conditions. The rrow indictes the return of dily wtering in 7D nd 15D tretments (n = 5).

8 188 Hoehne 4(1): , E, nmol m -2 s PPFD, μmol photons m -2 s -1 Figure 6. Curves of trnspirtion (E) in response to photosyntheticlly ctive rdition (ExPAR) of plnts of Buhini forfict Link under dily wtered (Control - ) nd wtered every 7-(7D - Δ) nd 15-dy (15D - ) conditions. The rrow indictes the return of dily wtering in 7D nd 15D tretments (n = 5).

9 Snches & Silv: Chnges in lef wter potentil nd photosynthesis of Buhini forfict 189 The photosynthetic ehvior of plnts response to wter deficit in our experiment re similr to those oserved y Portes et l. (26), who lso evluted under field conditions, the effect of wter deficit on photosynthesis of B. forfict present in regions of clering nd understory. These uthors showed tht vlues of Ψwf etween 2.47 nd 3.3 MP oserved in clering t the end of the dry seson nd fter 45 dys without rin, respectively, chrcterized wter deficit condition tht reduced the photosynthetic rtes of plnts indicting tht this environmentl stress significntly ffected the use of photosynthetic ctive rdition y B. forfict. In sme wy our results showed tht photosynthesis of B. forfict, species tht present rod neotropicl distriution is highly dependent of soil wter vilility. If not otherwise we lso confirmed our hypothesis tht the species B. forfict present high A mx, µmol CO 2 m -2 s -1 PAR st, µmol fótons m -2 s Figure 7 Mximum net photosynthesis (A mx ) nd light sturtion point (PAR st ) of plnts of Buhini forfict Link under dily wtered (Control - ) nd wtered every 7-(7D - ) nd 15-dy (15D - ) conditions. The rrow indictes the dy of dily wtering return in 7D nd 15D tretments. Brs indicte the stndrd error (n = 5). Mens followed y sme letter in ech smple do not differ significntly y Tukey s test (P =.5) Dys c A B cpcity to tolerte drought imposed y wter deficits of different intensities during erly development stge, rpidly recovering photosynthetic rtes fter the reestlishment of soil wter vilility. Such spects should explin the wide territoril occurrence of the species nd justify its ppliction in restortion projects of degrded res. Additionl nlyses out internl nd externl control of photosynthesys of B. forfict re necessry to elucidte the physiologicl nd iochemicl mechnisms involved in its drought tolernce. Acknoweledgments This work ws supported y FAPESP (9/157 ); R.F.E.S. held scholrship grnted y CAPES (Brzil); mny thnks re lso due to Guto Pereir for their kindly English revision. Literture cited Ayres, M., Ayres J.R., Ayres, D.L.M. & Sntos, A.S. 23. BioEstt 3.: plicções esttístics ns áres de ciêncis iológics e médics. Sociedde Civil Mmiruá, Belém, CNPq, Brsíli. Bjorkmn, O. Responses to different quntum flux densities. In: O.L. Lnge, P.S. Noel, C.B. Osmond & H. Ziegler (eds.). Encyclopedi of Plnt Physiology: Physiologicl Plnt Ecology I. Springer-Verlg, New York, pp Blum, A Crop responses to drought nd the interprettion of dpttion. In: I. Belhssen (ed.). Drought tolernce in higher plnts: geneticl, physiologicl nd moleculr iologicl nlysis. Kluwer Acdemic Plulishers, Dordrecht, pp Chves, M.M. & Pereir, J.S Wter stress, CO 2 nd climte chnge. Journl of Experimentl Botny 43: Chves, M.M Effects of wter deficits on cron ssimiltion. Journl of Experimentl Botny 42: Chves, M.M., Flexs, J. & Pinheiro, C. 29. Photosynthesis under drought nd slt stress: regultion mechnisms from whole plnt to cell. Annls of Botny 13: Clrk, R.B. Chrcteriztion of phosphtse of intct mize roots. Journl of Agriculture nd Food Chemistry 23: Dvies, W.J. & Zhng, J Root signls nd the regultion of growth nd development of plnts in drying soil. Annul Review of Plnt Physiology nd Moleculr Biology 42:

10 19 Hoehne 4(1): , 213 Dore, M.H.I. 25. Climte chnge nd chnges in glol precipittion ptterns: Wht do we know? Environmentl Interntionl 31: Fn, L., Linker, R., Gepstein, S., Tnimoto, E., Ymmoto, R. & Neumnn, P.M. 26. Progressive inhiition y wter deficit of cell wll extensiility nd growth long the elongtion zone of mize roots is relted to increse lignin metolism nd progressive stellr ccumultion of wll phenolics. Plnt Physiology 14: Frquhr, G.D., von Cemmerer, S., Berry, J.A A iochemicl model of photosynthetic CO 2 ssimiltion in leves of C3 species. Plnt 149: Fortunto, R.H Revision del genero Buhini (Cercidee, Ceslpinioide, Fcee) pr L Argentin. Drwinin 27: Hu, Y. & Schmidhlter, U Sptil distriutions of inorgnic ions nd crohydrtes contriuting to osmotic djustment in the elongting whet lef under sline conditions. Austrlin Journl of Plnt Physiology 25: Koslowski, T.T. & Pllrdy, S.G Physiology of woody plnts. 2 nd ed. Acdemic Press, Sn Diego. Krmer, P.J. & Boyer, J.S Wter reltions of plnts nd soils. Acdemic Press, Sn Diego. Kumr, A. & Singh, D.P Use of physiologicl indices s screening technique for drought to tolernce in oilseed Brssic species. Annls of Botny 81: Long, S.P. & Hällgren, J.E Mesurements of CO 2 ssimiltion y plnts in the field nd lortory. In: D.O. Hll, J.M.O. Scurlock, H.R. Bolhr-Nordenkmpf, R.C. Leegood & S.P. Long (eds.). Photosynthesis nd productivity in chnging environment: field nd lortory mnul. Chpmn nd Hll, London, pp Medin, C.L., Mchdo, E.C. & Gomes, M.M.A Condutânci estomátic, trnspirção e fotossíntese em lrnjeir "Vlênci" so deficiênci hídric. Revist Brsileir de Fisiologi Vegetl 11: Portes, M.T., Alves, T.H. & Souz, G.M. 26. Wter deficit ffects photosynthetic induction in Buhini forfict Link (Fcee) nd Esenecki leiocrp Engl. (Rutcee) growing in understorey nd gp conditions. Brzilin Journl of Plnt Physiology 18: Silv, E.C., Nogueir, R.J.M.C., Neto, A.D.A., Brito, J.Z. & Crl, E.L. 24. Aspectos ecofisiológicos de dez espécies em um áre de cting no município de Cceirs, Prí, Brsil. Iheringi, Série Botânic 59: