SILVA FENNICA. Comparison of Growth and Physiological Responses to Severe Drought between Two Altitudinal Hippophae rhamnoides Populations

Transcription

1 SILVA FENNICA Silv Fennic 44(4) reserch rticles ISSN The Finnish Society of Forest Science The Finnish Forest Reserch Institute Comprison of Growth nd Physiologicl Responses to Severe etween Two Altitudinl Hippophe rhmnoides Popultions Yongqing Yng, Yinn Yo nd Xuejing Zhng Yng, Y., Yo, Y. & Zhng, X. 21. Comprison of growth nd physiologicl responses to severe drought etween two ltitudinl Hippophe rhmnoides popultions. Silv Fennic 44(4): Growth nd physiologicl differences in response to drought were compred etween two se uckthorn (Hippophe rhmnoides L.) popultions inhited in the southest of the Qinghi- Tietn Plteu of Chin. The experimentl design included two wter regimes (1% nd 25% of field cpcity) nd two popultions from the low nd high ltitude zone. Our experiments were conducted in nturlly lit greenhouse under semi-controlled environmentl conditions for whole growing seson in dry vlley (18 m ove the se level). We found tht drought tolernce is highly relted to the plnt ntioxidnt cpcity nd wter use efficiency s well s lef nutrient sttus in H. rhmnoides. The highlnd popultion (HP) experienced greter inhiition in plnt growth nd lef enlrgement, lower lef nitrogen nd phosphorus content, lower root nodule iomss nd root mss/folige re rtio, nd higher lef wter content loss prlleling with higher enhncement of scisic cid level in response to drought, s compred with lowlnd popultion (LP). Additionlly, reduction of lef lignin content in HP further reduced its drought tolernce. On the contrry, LP showed effective dpttion strtegies such s improvement of wter economy nd mintining high scoric cid content. Therefore, we conclude tht LP ws more tolernt to drought thn HP, nd could e selected for reforesttion in the dry vlleys of upper Minjing River regions in Chin. Keywords se uckthorn (Hippophe rhmnoides L.), physiologicl response, scisic cid (ABA), cron isotope composition Addresses Yng, Xinjing Institute of Ecology nd Geogrphy, Chinese Acdemy of Sciences, Urumqi, 8311, Chin & College of Life Sciences, Chongqing Norml University, Chongqing, 447, Chin; Yo, Xinjing Institute of Ecology nd Geogrphy, Chinese Acdemy of Sciences, Urumqi, 8311, Chin; Zhng, Institute for Plnt Protection nd Soil sciences, Huei Acdemy of Agriculturl Sciences, Wuhn, 4364, Chin E-mil yoy@ms.xj.c.cn Received 2 Septemer 29 Revised 6 My 21 Accepted 24 Septemer 21 Aville t 63

2 Silv Fennic 44(4), 21 reserch rticles 1 Introduction The incresed frequency nd severity of drought cused y climte chnges will ffect forest primry productivity directly through wter depletion nd indirectly y reduced nutrient uptke (Sxe et l. 1998). In generl, plnts possess numerous mechnisms for responding to drought stress, such s chnges in plnt structure, growth rte nd tissue osmotic potentil (Lrcher 1995). Differences in drought tolernce of species, lines, clones, cultivrs or provennces hve een ttriuted to the effects of drought on proline (Heuer 1994, Hre et l. 1999) nd scisic cid (ABA) (Volire et l. 1998, Li nd Wng 23), since proline is thought of s the most frequent osmoprotectnt, nd ABA is well-known stress-inducile plnt hormone. On the other hnd, the cron isotope composition (δ 13 C) hs een developed s tool to mesure wter use efficiency (WUE), since strong correltion hs een found etween the cron isotope rtio (δ 13 C) nd WUE (Frquhr et l. 1989), therefore, mesuring δ 13 C of plnt tissue could provide n integrted mesurement of internl plnt physiology nd externl environmentl properties influencing photosynthetic gs exchnge over the time when the cron ws fixed (Brodri nd Hill 1998). Studies exmining the effects of environmentl fctors on stle isotope composition (δ 13 C) hve een widely used in plnt tissues exposed to chnge of eril CO 2 content (Polley et l. 1993), nutrient deficit (Livingston et l. 1999) nd wter stress (Li et l. 2, Li nd Wng 23). Some previous studies report tht drought my lso ffect the nutritionl sttus in plnts t the level of nutrient uptke nd long distnce trnsport in xylem nd phloem (Hsio 1973), ut the effects of drought on the nutritionl sttus of plnts re less well known until now compred with other drought effects on wter reltions, cron ssimiltion nd iomss lloction (Peuke nd Rennenerg 24). Additionlly, s mjor polymer of plnt cell wlls tht confers hydrophoicity nd mechnicl strength to withstnd the negtive pressure generted y trnspirtion, lignin might ply n importnt role in response to wter deficit, ut its response nd dpttion mechnism under severe drought need to e clrified. In the sulpine res of southest of the Qinghi-Tietn Plteu of Chin, the dry vlleys re widely distriuted long upper Minjing River nd its triutries, which re chrcterized y comintion of high mountins nd low rinfll, prlleled with high solr rdition nd high potentil evportion. The environment condition in dry vlleys is very frgile nd highly prone to desertifiction (Tng et l. 24). Vrious efforts hve een conducted on the rehilittion of degrded ecosystems in these vlleys. However, the reforesttion ojective is still fr from eing reched. Hippophe rhmnoides L. is thorny, nitrogen-fixing, deciduous perennil shru, widely distriuted in vrious climte regions, dpted to very diverse ecologicl conditions (Lu 1995), nd plys very importnt role in preventing soil wter loss, in regulting microclimte nd in retining ecologicl stility. It hs een used s n idel pioneer species in reforesttion of rid nd semi-rid regions (Lu 1992), nd it ws lso selected s one of plnt species for reforesttion of dry vlleys in Mingjing River. Under the contrst environmentl condition in the sulpine res of the Qinghi-Tietn Plteu, pronounced popultion differences occurred in this species on their tolernce for environmentl stresses such s drought, cold, UV-B, et l. Here we hypothesized whether highlnd H. rhmnoides. popultion grown nd evolved under higher UV rdition nd lower tempeture hve evolved etter tolernce to drought stress, due to cross tolernce to different environmentl stresses. In this study, pot-grown seedlings of two ltitudinl H. rhmnoides. popultions were employed to compre their responses in terms of plnt growth nd physiology to long-term drought. The ojectives were to 1) ssess vrition in growth trits, lef nutrients nd lignin, cron isotope composition, proline nd ABA ccumultion of two selected ltitudinl popultions s response to drought, nd 2) test whether popultions of different drought sensitivity could e identified etween the different provennces. These differences in drought responses my e used s criteri of genotype selection for reforesttion in the dry vlleys of upper Minjing River regions. 64

3 Yng, Yo nd Zhng Comprison of Growth nd Physiologicl Responses to Severe 2 Mterils nd Methods 2.1 Plnt Mteril nd Experimentl Design A lowlnd popultion (LP) (33 16 N, E, 18 m, ove the se level) nd highlnd popultion (HP) (3 59 N, 11 7 E, 33 m, ove the se level) of Hippophe rhmnoides L. were selected for this study. The men nnul precipittion is out 52 mm nd 65 mm, nd the men nnul temperture is 12 C nd 7.5 C for LP nd HP, respectively. The seeds in ech popultion were collected from 2 fruit-riping plnts whose pirwise distnce ws more thn 2 metres. In the utumn of 25, the seeds from 2 plnts in ech popultion were seprtely sowed in 2 pots nd grown in growth chmer (kept 22 C in the dy nd 18 C in the night, 14/1 h light drk cycle, nd 22 μmol m 2 s 1 PPFD). In Mrch of 26, helthy seedlings of uniform height (35 4 cm) were trnsplnted to 5. L plstic pots filled with homogenized soil, one seedling per one pot. In ech popultion, one replicte were set up y 5 pots, totlly 8 replictes for ech popultion. The soils in ll the pots were rown soil, which were sieved from topsoil nd homogenized, with 9.5% orgnic mtter, 2.8g kg 1 ville N,.9 g kg 1 ville P nd.36 g kg 1 ville K, with ph 6.7. A totl of 2.5g slow relese fertilizer (13% N, 1% P nd 14% K) ws dded to ech pot t the trnsplnting time. Those pots were grown in nturlly lit greenhouse under semi-controlled environmentl conditions in Moxin ecologicl sttion (31 41 N, E, 18 m ove the se level) locted in dry vlley of upper Mingjing River. During the growing sesons, the seedling were grown in dy temperture rnge of C, night temperture rnge of 9 15 C nd the reltive humidity rnge of 35 85%. Experimentl tretments strted 3 d fter the seedlings were trnsplnted. A completely rndomized design with two fctors (two popultions nd two wtering regimes) ws employed. For drought tretment, hlf of replictes in ech popultion were mintined t 25% of field cpcity (generlly severe drought condition in the summer in the dry vlleys) y wtering every four dys, four replictes in ech popultion. For the well-wtered tretment (s control), nother hlf of replictes in ech popultion were wtered to 1% of field cpcity y supplying n mount of tp wter equl to trnspirtion losses every four dys. Evportion from the soil surfce ws prevented y enclosing the pots in plstic gs, which were tied to the stems of the plnts. Trnspirtion wter loss ws mesured grvimetriclly y weighing ll pots every four dys. The experiment tretment lsted for 1 dys. At the end of experiment, fully expnded leves in the middle prt of plnts of ech replicte were rndomly smpled to mke physiologicl ssys. 2.2 Mesurements of Growth Trits nd Lef Wter Content Ten seedlings of ech tretment were rndomly tgged nd chosen to mesure seedlings height every ten dys during the experimentl period (totlly 1 dys). At the end of the experiment, ten plnts in ech tretment were hrvested for plnt growth chrcteristic mesurements. After lef re for ech seedling ws determined y CI-22-scnning plnimeter (CID Inc., Cms, WA), plnts were divided into lef, stem, root nd root nodule, dried (8 C, 48 h) to constnt mss nd weighed for iomss determintion. Averge lef size, iomss prtition, specific lef mss (lef dry mss divided y lef re, SLM), root mss/folige re rtio nd root/totl iomss rtio were then clculted. Lef wter content ws lso determined y formul s follows: lef wter content (%) = (1 dry mss / fresh mss) 1. The reltive growth rte (RGR, g g 1 dy 1 ) ws clculted s: RGR = (lnw 2 / lnw 1 ) / t, where W 1 nd W 2 re the initil nd finl totl dry mss nd t is experiment durtion (dys). WUE (wter use efficiency) ws clculted for ech plnt s the rtio of iomss production to wter trnspired during the experiment. 2.3 Lef Pigments Anlyses Totl photosynthetic pigments were extrcted with dimethyl sulfoxide (DMSO). Fresh lef tissue (.1 g, rndomly selected from the middle prts of plnts in ech replicte s mentioned ove) ws plced in test tue contining 1 ml 65

4 Silv Fennic 44(4), 21 reserch rticles DMSO nd left in the drk for 48 h. The sornce of the extrct ws mesured spectrophotometriclly t 48, 665, 649 nm, nd the turidity of the extrct ws checked t 75 nm to e sure tht it ws lwys less thn.1. The mounts of chlorophyll nd crotenoids were clculted using the equtions s descried y Wellurn (1994) nd expressed upon per unit dry mss (DM) sis. 2.4 Proline Content nd Ascoric Acid Content Determintion.5 g leves ws extrcted for determintion of free proline content ccording to the method of Btes et l. (1973). The rection mixture consisted of 2 ml lef tissue extrct, 2 ml cid ninhydrin nd 2 ml of glcil cetic cid, nd ws oiled t 1 C for 1 h. After termintion of rection in ice th, the rection mixture ws extrcted with 4 ml of toluene nd the sornce ws red t 52 nm, the free proline content ws expressed s μg g 1 DM..4 g leves ws extrcted to estimte the totl scoric cid content (As) using the method s descried y Jin et l. (23), nd the As concentrtion ws expressed s mg g 1 DM. 2.6 Chemicl Anlyses At lst, the remining leves in the middle prts of plnts in ech replicte were pooled nd dried to constnt mss. Dried leves were milled to pss through 1 mm sieve nd.4 g susmple ws ssyed for totl P (molydenum lue colorimetry) nd N (Kjeldhl digestion nd titrtion). Lef cron (C) content ws nlyzed y the wet oxidtion method (Moore nd Chpmn 1986). The nlysis procedure for cetyl romide lignin determintion ws ccording to Iiym nd Wllis (199) nd Htfield et l. (1999). Individul smples were plced in 15-ml glss rection tue with solution of 25% (w/w) AcBr in cetic cid (2.5 ml), nd the tues were cpped immeditely nd heted in dry locks set t 7 C for 3 min. The tues were shken t 1-min intervls to promote dissolution of the smples. After heting, the smples were quntittively trnsferred, with the id of cetic cid, to 5 ml volumetric flsks tht contined 1 ml of 2 M NOH nd 12 ml of cetic cid. Hydroxylmine (1.75 ml,.5 M) ws dded to ech flsk, nd smples were diluted to 5 ml with cetic cid. The sorption t 28 nm ws determined. All mesurements were run in five times for ech tretment. 2.5 Mesurements of ABA Content nd Cron Isotope Composition Fully expnded leves were used to mesure ABA content. The smples were weighed immeditely fter hrvest in the morning, then frozen in liquid nitrogen nd stored t 8 C until nlyzed. ABA ws nlyzed s descried y Li et l. (22) nd expressed s ng g 1 DM. The undnces of stle isotopes of cron in lef smples were determined, s descried y Li et l. (2). The smples were oven-dried for 48 h t 8 C nd homogenized y grinding in ll mill, nd the reltive undnce of 13 C nd 12 C ws determined with n isotope rtioning mss spectrometer (Finnegn MAT Delt-E). The overll precision in δ-vlues ws higher thn.1, s determined from repeted smples. 2.7 Sttisticl Anlysis Anlyses were performed with the softwre Sttisticl Pckge for the Socil Science (SPSS) version 11. (SPSS Inc., Chicgo, IL, USA). Dt were log-trnsformed if necessry to ensure ssumptions of normlity nd homogeneity of vrinces. Min fctor effects (Popultion nd Wter regimes) nd their interction were tested using two-wy ANOVA. Among the ll tretments, the mens were compred using the LSD (lest significnce difference) test. For height growth nlysis, three-wy ANOVA ws used to test the effects of popultion, wter regime nd durtion. Person s correltion coefficients were clculted to determine the reltionships etween vriles for different popultions. 66

5 Yng, Yo nd Zhng Comprison of Growth nd Physiologicl Responses to Severe 3 Results 3.1 Effects of on Plnt Morphologicl Trits The drought significntly depressed height growth of H. rhmnoides throughout the whole experiment in oth popultions (Fig. 1). The min effects nlysis show tht wter regimes, popultion nd durtion hd significnt impcts on height increment of oth popultions, nd interctions etween these three fctors were lso significnt. LP hd higher height increment in oth well wtered nd drought conditions. lso significntly decresed reltive growth rte (RGR), nodule iomss (Fig. 2c), nd lef size (Tle 1), while significntly incresed root/totl iomss rtio (Fig. 2), specific lef mss (SLM) nd root mss/folige re rtio in oth popultions (Tle 1). On the other hnd, LP hd higher vlues in RGR (Fig. 2) nd lef size t the control Fig. 1. Height growth in H. rhmnoides L. seedlings (, denote the lowlnd nd highlnd popultion, respectively) in response to drought stress (open, control, lck, drought, respectively). Vlues re mens ± SE of 8 replictes. Symols (*, ** nd ***) indicte significnt P-vlues t.5,.1 nd.1 levels, respectively. W, wter regime, P, popultion, T, time. Tle 1. The effects of drought on morphologicl nd physiologicl properties in two ltitudinl H. rhmnoides L. popultions. Morphologicl nd physiologicl properties Lowlnd popultion Highlnd popultion F-vlues Control (1%) (25%) Control (1%) (25%) W P W P Lef size (cm 2 ) 2.41±.1 2.3± ±.1.78±.3c *** *** *** SLM (g m 2 ) 46.43±1.29d 61.59± ±.7c 79.72± *** *** 9.93 ** Root mss/folige re (g m 2 ) 15.88±1.16d 64.5± ±1.44c 77.38± *** 14.3 ***.8 NS Lef wter content (%) 67.13± ±.36c 69.78± ±.39c *** *** 7.27 * Chlorophyll content (μgg 1 dm) 847.± ±13.43c ± ± ** 27.4 ***.44 NS Totl crotenoids (μgg 1 dm) ± ± ± ±.35.2 NS ***.32 NS Crotenoids / Chlorophyll.175±.1c.189±.6.175±.1c.186± *** 4.71 * 2.25 NS Proline content (μg g 1 dm) 64.95± ± ± ± ** 3.36 NS 1.95 NS ABA content (ng g 1 dm) ±149.33c ± ±36.32c ± *** 1.8 * ** As content (mg g 1 dm) ± ± ± ±9.43c ***.32 NS *** WUE(g kg 1 ) 3.46± ± ± ± *** 3.2 NS 11.76* δ 13 C 28.6± ± ± ± *** NS.198 NS Vlues shown re men ±SE of t lest six replictes. Vlues within row followed y the sme letter do not differ significntly t P <.5 y LSD pirwise comprisons. dm, dry mtter; SLM, specific lef mss; W, wtering effect; P, popultion effect; W P, wtering popultion interction.*,**,*** indicte significnt tretment min effects t P <.5, P <.1, P <.1, respectively. 67

6 Silv Fennic 44(4), 21 reserch rticles Reltive growth rte (g g -1 d -1 ) C ontrol c d Root : Totl iomss rtio C ontrol Lowlnd popultion Highlnd popultion Lowlnd popultion Highlnd popultion Nodule iomss (g dm) c C ontrol Fig. 2. Reltive growth rte (), root / totl iomss rtio () nd nodule iomss (c) in H. rhmnoides L. seedlings in response to drought stress. Vlues re mens ± SE of 8 replictes. Vlues followed y the sme letter do not differ significntly t P <.5 y LSD pirwise comprisons. Lowlnd popultion c Highlnd popultion Tle 2. Sttisticl significnce of the F vlues (ANOVA) for the effects of wter regime (W), popultion (P) nd their interction (W P) on different prmeters in two contrsting H. rhmnoides popultions. RGR R/TB NB Cron Nitrogen Phosphorus Lignin W *** *** *** *** NS *** *** P *** NS.425 NS 1.66 NS *** 2.29 NS *** W P ***.269 NS.714 NS 7.643*.484 NS 25.83*** NS RGR, reltive growth rte; R/TB, root/totl iomss rtio; NB, nodule iomss. NS, not significnt. *, **, *** indicte significnt tretment min effects t P <.5, P <.1, P <.1, respectively. condition thn those of HP (Tle 1). In ddition, significnt drought popultion interctions were oserved in RGR (Tle 2, Fig. 2), lef size nd SLM (Tle 1), which mde chnges of these prmeters cused y wter stress in HP much higher thn the other popultion. 3.2 Effects of on Physiologicl Trits significntly decresed lef wter content, totl chlorophyll content, nd As content, ut incresed crotenoids/chlorophyll rtio, pro- 68

7 Yng, Yo nd Zhng Comprison of Growth nd Physiologicl Responses to Severe line content, ABA content nd δ 13 C vlue in oth popultions. Furthermore, popultion differences were lso detected. HP hd higher vlues in lef wter content, totl chlorophyll content, totl crotenoids content, crotenoids/chlorophyll nd As content in the control condition, ut hd lower ABA content. Significnt increse of WUE vlue ws only seen in LP under drought condition. In ddition, interctions of drought popultion demonstrted tht HP experienced greter reductions in wter content nd As content, nd higher increment of ABA content response to drought compred with LP. The ccumultion of ABA content under drought ws s high s eightfold compred with the control in HP (Tle 1). 3.3 Effects of on Lef Cron, Nitrogen, Phosphorus nd Lignin significntly decresed lef cron (C), phosphorus (P) nd lignin content, ut hd little effect on nitrogen in oth popultions (Fig. 3 c). However, LP hd higher nitrogen vlue thn HP (P <.1, Fig. 3). The drought popultion interction showed tht drought-cused decrese in phosphorus nd lignin were much higher in HP (Tle 2, Fig. 3cd). Nitrogen content (mg g -1 ) c Control c Cron content (mg g -1 ) c C ontrol c Lowlnd popultion Highlnd popultion Lowlnd popultion Highlnd popultion Phosphorus content (mg g -1 ) c C ontrol c Lignin content (mg g -1 ) d Control Lowlnd popultion Highlnd popultion Lowlnd popultion Highlnd popultion Fig. 3 Cron content (), Nitrogen content (), Phosphorus content(c) nd Lignin content(d)) in H. rhmnoides L. leves in response to drought stress. Vlues re mens ± SE of t lest 4 replictes. Vlues followed y the sme letter do not differ significntly t P <.5 y LSD pirwise comprisons. 69

8 Silv Fennic 44(4), 21 reserch rticles Tle 3. Correltion coefficients for some morphologicl nd physiologicl properties of the contrsting H. rhmnoides popultions. LP (upper tringle) nd HP (lower tringle). SLW R/TB RGR WUE ABA δ 13 C C P lignin Chl proline SLW.932**.937**.949*** **.88*.811*.812*.816*.597 R/TB.972***.995***.995*** ***.944***.866**.922**.872**.752* RGR.98***.999***.997*** ***.92***.852**.918**.863**.765* WUE ***.917**.85**.918**.868**.771* ABA.959***.997***.994*** δ 13 C.963***.987***.99*** ***.952***.91**.954***.94**.734* C *.88**.88**.759* P.947***.953***.953*** ***.949*** **.779*.465 lignin.936**.964***.955*** ***.938** ***.764*.769* Chl.81*.91**.892** **.875** **.932**.614 proline.928**.92**.927** **.926** **.914**.854** SLW, specific lef mss; R/TB, root/totl iomss rtio; RGR, reltive growth rte; WUE, wter use efficiency; ABA, scisic cid; δ 13 C, cron isotope composition; C, lef cron content; P, lef phosphorus content; Chl, totl lef chlorophyll content. *, P <.5; **, P <.1; ***, P < Reltionships mong the Morphologicl nd Physiologicl Responses of Leves The reltionships mong SLW, R/TB, RGR, WUE, ABA, δ 13 C, C, P, lignin, Chl nd proline re shown in Tle 3. In oth popultions, RGR were positively correlted with P, lignin nd Chl, ut negtively correlted with δ 13 C nd proline, while some morphologicl trits such s SLW nd R/TB were positively correlted with δ 13 C, negtively correlted with P, lignin nd Chl. For physiologicl trits, δ 13 C, lignin nd proline were significntly correlted with most of the tested indices. However, popultion differences could lso e oserved, WUE nd C were significntly correlted with most physiologicl prmeters in LP, while correltions etween ABA nd other prmeters ws found mostly in HP popultion. 4 Discussion significntly decresed plnt height, RGR nd lef size, while incresed root/totl iomss rtio, SLM nd root mss/folige re rtio in oth tested se uckthorn popultions. All these responses in plnt structure nd growth pttern re often considered s n importnt cclimtion strtegy to severe wter deficit over long time scles (Lrcher 1995, Li et l 2). Furthermore, in greement with recent reserch conducted y Mrino et l (27), which reported tht drought stress ffected rhizoil growth, formtion, longevity nd nodule functions, in our study, the nodule production of se uckthorn popultions ws lso mrkedly decresed y drought. On the other hnd, much greter reductions in RGR nd lef enlrgement (lef size) prlleled with thicker leves (indicted y higher SLM) were detected in HP in comprison with LP. As iomss ccumultion (indicted y RGR) is the integrted consequence of morphologicl, physiologicl nd iochemicl responses to environmentl condition, the greter reduction of RGR in HP implies tht this popultion is more sensitive to drought. Additionlly, compred with LP, smller increment of root mss/folige re rtio in HP my further reduce its cpcity to uptke soil wter nd nutrients under drought condition. It is well documented tht ABA is sensitive indictor of lef wter deficit nd the chnge of soil wter vilility (Peuke et l. 22, Li et l. 22). In the well wtered condition, HP possessed higher lef wter content nd lower ABA content thn LP, ut drought tretment cused greter reduction in lef wter content nd pronouncedly higher increment of ABA content in HP. The two prmeters showed tht HP ws physiologiclly more ffected y drought. Also, the free proline, well-known indictor for physiologicl dryness (Ptel nd Vor 1985), 61

9 Yng, Yo nd Zhng Comprison of Growth nd Physiologicl Responses to Severe ws significntly enhnced in HP ut not in LP. The different physiologicl dryness my led to popultion-specific responses in scoric cid synthesis. In our result, As content ws significntly decresed in HP ut remined unffected in LP under drought condition. It ws reported in previous studies tht scorte synthesis could e decresed due to limittion of cron fixtion under severe drought condition (Smirnoff 1996, Brtoli et l. 1999), s is detected in HP in our study, which would significntly limit plnt protective cpcity ginst high levels of oxidtive pressure under severe drought conditions. In ddition, the different physiologicl dryness would cuse popultion-specific chnges in plnt wter use efficiency (WUE). In the present study, WUE ws incresed only in LP under drought condition, nd this result demonstrted tht LP could ccumulte more ssimilted sustnce nd survive severe drought etter thn HP in the wter-limited conditions. As tool to mesure long-term WUE (Frquhr et l. 1989), cron isotope composition (δ 13 C) in our present study ws incresed y drought, however, there existed little difference etween the two popultions nd tht ws not consistent with WUE. Mny previous studies lso vlidted tht δ 13 C does not lwys correlted with WUE (Edon et l. 1998). As fr s photosynthetic pigments re concerned, similr chnges occurred in the two tested popultions under drought condition. The chlorophyll content ws significntly decresed s oserved in other studies (Morn et l. 1994, Dun et l. 25), which could e due to either slow synthesis or fst rekdown of chlorophyll pigments (Ashrf 23). Since the crotenoid content remined t high level, the significnt increse of crotenoids/chlorophyll rtio could help protect chloroplst from photooxidtive destruction under drought condition. Lef qulity ws lso ffected y drought in oth popultions in our study. Higher lef nitrogen content in LP would e eneficil for photosynthesis nd therefore mintining higher RGR, in prticulr under severe drought condition. hd little effect on lef nitrogen content in oth popultions, nd it would e result of plnt structure djustment (i.e. significntly enhnced root mss/folige re rtio nd root/totl iomss), which compensted the nitrogen soring insufficiency due to destroying of nodules. And this thus helps mintin the functioning of the photosynthetic system nd improve wter economy (Li et l 26). On the other hnd, drought stress cused greter reduction of nodule iomss in HP, which proly lowered this popultion s ility for nitrogen uptke nd consequently led to lower lef nitrogen content compred with LP under drought condition. The reduction of cron ccumultion y drought is well reported (e.g. Peuke et l. 22, Peuke nd Rennenerg 24) nd consistent with our results. Compred with HP, there existed more ctive growing sink in LP for the pronouncedly higher RGR nd lower ABA content under drought condition. So the lef cron ssimiltes in the mture leves were llocted more to other growing orgns such s root, shoot nd expnding leves, which resulted in lower level of lef cron content in LP in our study. Consistent with previous studies (e.g. Peuke nd Rennenerg 24, Srdns et l. 28), the lef P content of se uckthorn popultions ws lso significntly reduced y drought ecuse of the decreses of soil phosphorus vilility (Pssiour 22). In the present study, the mrked reduction of lef phosphorus content in HP my ffect mny physiologicl processes relted to phosphorus, in prticulr the conversion nd trnsporttion of plnt metolites. Recently, Fernndez et l. (26) oserved tht decrese of lef P content led to incresed stomtl conductnce nd hence lower WUE, nd we lso oserved tht HP with lower lef P content hve low level of WUE under drought condition. Vincent et l. (25) reported tht lignin content in mize leves ws decresed y drought, which lso occurred in HP popultion in our study. Lignin ply n importnt role in preventing lef wter dissiption, nd the reduction of lignin content in HP would further ggrvte the dmging effect of drought stress. Until now, very little is known out the effects of drought on lef lignin iosynthesis (Mour et l. 21). In n erly study, Hrrk et l (1999) oserved the decreses of lignin concentrtion nd trnscript of one reltive gene (PTGRP) under drought condition. Recently, Alvrez et l. (28) oserved reductions of ferulic cid nd nionic peroxidse ctivity, increses of p-coumric, cffeic cids nd ctionic peroxidse ctivity in the 611

10 Silv Fennic 44(4), 21 reserch rticles xylem sp of mize under drought condition, nd they suggested this s n indiction tht drought decresed the iosynthesis of lignin in mize. Hu et l (29) lso oserved the decreses in lef lignin concentrtion nd expressions of two key enzymes for lignin synthesis when withholding wter vilility in drought-sensitive mize cultivrs, nd concluded tht lef lignin could serve s useful index for evlution of drought tolernce. In our results, different chnges of lef lignin in two H. rhmnoides popultions might e importnt reson for different tolernce to drought. In conclusion, HP hd much lower rtes of iomss ccumultion, plnt growth nd lef enlrgement thn LP under drought condition, nd it lso experienced higher loss of lef wter content prlleling with greter enhncement of ABA level. The higher vulnerility of HP to drought ws relted to its lower ility for uptke of plnt nutrition such s nitrogen nd phosphorus under drought condition. Just contrry to our previous hypothesis, the present resusts demonstrte tht drought tolernce of HP ws not necessrily improved y cclimtion to low temperture nd high UV-B rdition. However, LP exhiited effective dpttion strtegies such s improvement of wter economy nd mintining high level of As content. We suggest tht mny fctors should e tken into ccount in the genotype selection of H. rhmnoides for reforesttion of upper Minjing River regions in Chin. Not only the plnt ntioxidnt cpcity nd WUE ffect plnt drought tolernce, ut lso nutrient vilility does. Acknowledgments The reserch ws supported y the Ntionl Science Foundtion of Chin (Nos nd 38127) nd the Progrm of 1 Distinguished Young Scientists in Chinese Acdemy of Sciences. References Alvrez, S., Mrsh, E.L., Schroeder, S.G. & Schchtmn, D.P. 28. Metolomic nd proteomic chnges in the xylem sp of mize under drought. Plnt, Cell nd Environment 31: Ashrf, M. 23. Reltionships etween lef gs exchnge chrcteristics nd growth of differently dpted popultions of lue pnicgrss (Pnicum ntidotle Retz.) under slinity or wterlogging. Trends in Plnt Science 165: Brtoli, C.G., Simontcchi, M., Tmussi, E., Beltrno, J., Montldi, E. & Puntrulo, S nd wtering-dependent oxidtive stress: effect on ntioxidnt content in Triticum estivum L. leves. Journl of Experimentl Botny 5: Btes, L.S, Wldren, R.P. & Ter, I.D Rpid determintion of free proline for wter-stress studies. Plnt nd Soil 39: Brodri, T. & Hill, R.S The photosynthetic drought physiology of diverse group of southern hemisphere conifer species is correlted with minimum sesonl rinfll. Functionl Ecology 12: Dun, B., Lu, Y., Yin, C., Junttil, O. & Li, C. 25. Physiologicl responses to drought nd shde in two contrsting Pice spert popultions. Physiologi Plntrum 124: Edon, J.S., Petrovic, A.M. & Dwson, T.E Reltionship etween cron isotope discrimintion, wter use efficiency, nd evpo-trnspirtion in Kentucky luegrss. Crop Science 38: Frquhr, G.D., Ehleringer, J.R. & Huick, K.T Cron isotope discrimintion nd photosynthesis. Annul Review of Plnt Physiology nd Plnt Moleculr Biology 4: Fernndez, M., Novillo, C. & Prdos, J.A. 26. Effects of wter nd nutrient vilility in Pinus pinster it. Open pollinted fmilies t n erly ge: growth, gs exchnge nd wter reltions. New Forest 31: Hre, P.D., Cress, W.A. & vn Stden, J Proline synthesis nd degrdtion: model system for elucidting stress-relted signl trnsduction. Journl of Experimentl Botny 5: Htfield, R.D., Grer, J., Rlph, J. & Brei, K Concentrtions in Herceous Plnts: Some Cutionry Notes. Journl of Agriculturl nd Food Chemistry 47:

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