不同土壤水分条件下中国沙棘雌雄株光合作用、蒸腾作用及水分利用效率特征

采用LI-6400便携式光合系统对野外不同生境(沟底、坡面)和田间不同土壤水分条件下中国沙棘雌雄株的净光合速率和蒸腾速率及水分利用效率特征进行了观测,结果表明,中国沙棘雌雄株在水分条件较好的生境中均表现较强的生活力,净光合速率和蒸腾速率主要受光照强度和大气温度的影响,雄株表现出更高的光合、蒸腾、水分利用效率;在水分条件较差的生境中,雌雄株均通过降低蒸腾和提高水分利用效率来适应逆境,净光合速率和蒸腾速率的影响因子增多,雄株的光合速率大幅度下降,雌株仍保持较高的光合速率,雌株的水分利用效率高于雄株.可见,在反映植物瞬时生理变化的性状方面,雌株对土壤水分减少表现出了更强的适应性,雄株对土壤水分变化表现出了更大的敏感性.     

The sexual dimorphism displayed by the roots of mulberry (Morus alba) saplings depends on the sex of the neighboring plants

桑树幼苗根系表现出的性别二态性取决于相邻植株的性别 雌雄异株植物通常呈现性别二态性,但其雌株和雄株的根系性状和养分吸收如何响应相邻植株 的性别变化尚不清楚。本研究以中国广泛栽培的雌雄异株植物桑树(Morus alba)为试验对象,在水培环境 下,采取雌-雌、雄-雄和雌-雄3种组合种植模式进行试验。植株生长3个月后,分别测定雌雄植株根系的解剖结构、形态、营养浓度和生物量。研究结果表明,在水培环境中,与同性相邻相比,当桑树雄株与异性相邻时,其根系木质部变小,根和径生物量减少,根系中N、P、K浓度增加。相比,当桑树雌株与异性相邻时,其根系木质部变大,细根长度、表面积和体积以及根系δ¹³C和N、P、K浓度增加。雌雄植株根系δ¹³C和N、P、K浓度的变化与根系性状的改变有关。这些结果表明,相邻植株的性别影响了雌雄桑树根系解剖结构和形态。同时,雌雄植株对相邻植株性别改变的响应呈现性别二态性,这种二态性响应影响了雌雄植株水分利用效率和营养吸收。这些发现对于理解森林和自然系统中其它雌雄异株物种的种群动态变化具有重要意义。     

栝楼雌雄植株的光合作用和蒸腾作用特性

对栝楼雌雄植株生长发育关键时期的光合作用和蒸腾作用进行研究.结果表明:在营养生长阶段,栝楼雄株的光合速率、蒸腾速率、气孔导度和水分利用效率均大于雌株;雄株比雌株提前22 d进入生殖生长阶段,当雄株进入生殖生长阶段后,其光合速率、蒸腾速率和气孔导度均大于雌株,但水分利用效率略小于雌株;当雌株进入生殖生长阶段后,其蒸腾速率和气孔导度大于雄株,而光合速率和水分利用效率显著小于雄株.气候因子对栝楼生长发育的影响主要是在营养生长和生殖生长初期,栝楼生长发育后期对气候因子的响应程度减弱.较高的温度和较低的湿度有利干栝楼的生长发育,光照可提高栝楼尤其是雄株的光合速率.进入生殖生长后,雄株的光合速率随光照的增强显著增加,而雌株的光合速率增加不显著;随气温的升高,雄株的蒸腾速率显著提高,雌株的光合速率极显著提高.     

银杏幼苗雌雄株对盐胁迫响应的差别

采用对盆栽银杏(Ginkgo biloba)雌雄幼苗浇灌NaCl(40?mmol L-1)溶液模拟土壤受盐胁迫的方法,研究银杏雌雄幼苗气体交换特征、内在水分利用效率(WUE)、游离脯氨酸含量(Pro)、超氧化物歧化酶(SOD)及过氧化物酶(POD)活性在盐胁迫下的差异.结果表明:(1)盐胁迫后雌株的净光合速率、气孔导度以及蒸腾速率与对照相比分别降低45.87%、25.00%、16.47%,而雄株的气孔导度、胞间CO2浓度和蒸腾速率分别升高了10.00%、8.10%、22.95%;(2)盐胁迫显著降低了银杏幼苗的WUE(P=0.020),与对照下相比,雌、雄WUE分别下降30.47%、46.38%;(3)盐胁迫显著提高了雄株的游离Pro含量,但对雌株影响不显著;(4)盐胁迫使银杏雌、雄幼苗SOD活性分别降低了22.96%、23.18%,但下降幅度均不显著.然而盐胁迫会显著降低雌株的POD活性,但对雄株无显著影响.上述结果同时表明,40?mmol L-1的NaCl溶液不仅会降低银杏雌雄幼苗的光合速率,影响气体交换,还会降低WUE、SOD及POD等酶活性,提高游离Pro含量,但雌株受到的负面效应小于雄株.与雄株相比,雌株在盐胁迫下能通过维持较高的光合速率贮藏能量,较低的蒸腾速率和较高的内在水分利用效率以减少水分散失,以及较高的抗氧化物酶活性来缓解盐胁迫带来的氧化胁迫,使其受到的负面影响减小.     

小五台山青杨雌雄植株树轮生长特性及其对气候变化的响应差异

近年来逆境导致植物雌雄幼苗的生长出现差异被许多控制实验所证实, 而有关气候变化对雌雄异株植物成树生长的潜在影响尚未引起人们广泛的关注。为进一步揭示气候变化对雌雄植株树木径向和密度生长的不同影响, 该文通过树轮生态学的研究方法, 选择小五台山天然青杨(Populus cathayana)种群为研究对象, 对青杨雌雄植株近30年(1982-2011)的树轮生长特性及其与气候的相关性进行了分析。结果显示: 1)在近30年当地气温不断升高的气候条件下, 雌株的年轮最大密度和晚材平均密度均高于雄株(p < 0.05), 但雌雄植株的径向生长无显著差异; 2)雌雄植株年轮最大密度和宽度差值年表的变化趋势具有一致性, 但在年轮最大密度差值年表的变化上雄株波动幅度大于雌株; 3)青杨雌雄植株年轮密度差值年表对温度响应的月份明显不同。雌株年轮最大密度与当年8月的月平均最高气温显著正相关, 而雄株年轮最大密度与当年1月和4月的气温负相关; 4)生长季前的气候变化对青杨雌雄植株的径向生长均有明显的限制作用。此外, 当年6月的高温对于早材生长的限制作用特别明显。上述结果表明, 雌雄异株植物在树木年轮生长方面对全球气候变暖可能具有不同的响应机制, 雌株比雄株更侧重于密度生长。     

Gender-specific characteristics of tree-ring growth and differential responses to climate change in the dioecious tree Populus cathayana in Xiaowutai Mountains,China

近年来逆境导致植物雌雄幼苗的生长出现差异被许多控制实验所证实, 而有关气候变化对雌雄异株植物成树生长的潜在影响尚未引起人们广泛的关注。为进一步揭示气候变化对雌雄植株树木径向和密度生长的不同影响, 该文通过树轮生态学的研究方法, 选择小五台山天然青杨(Populus cathayana)种群为研究对象, 对青杨雌雄植株近30年(1982-2011)的树轮生长特性及其与气候的相关性进行了分析。结果显示: 1)在近30年当地气温不断升高的气候条件下, 雌株的年轮最大密度和晚材平均密度均高于雄株(p < 0.05), 但雌雄植株的径向生长无显著差异; 2)雌雄植株年轮最大密度和宽度差值年表的变化趋势具有一致性, 但在年轮最大密度差值年表的变化上雄株波动幅度大于雌株; 3)青杨雌雄植株年轮密度差值年表对温度响应的月份明显不同。雌株年轮最大密度与当年8月的月平均最高气温显著正相关, 而雄株年轮最大密度与当年1月和4月的气温负相关; 4)生长季前的气候变化对青杨雌雄植株的径向生长均有明显的限制作用。此外, 当年6月的高温对于早材生长的限制作用特别明显。上述结果表明, 雌雄异株植物在树木年轮生长方面对全球气候变暖可能具有不同的响应机制, 雌株比雄株更侧重于密度生长。     

雌雄异株植物山杨的气候响应差异

本文通过建立长白山阔叶红松林内雌雄异株植物山杨树轮宽度序列及标准化年表,分析不同气候条件下的生长差异及其与气候因子的关系,以期揭示性别因素对植株径向生长 气候因子关系的影响.结果表明： 不同气候条件下雌雄植株年径向生长速率存在显著差异,对气候因子的响应也有所不同.1980年以前,山杨雌株年均生长速率显著高于雄株,雌株与生长季末低温、上年生长季末和当年生长季降水量呈显著负相关,山杨雄株则与当年生长季温度呈显著正相关.1980年（含）以后,温度明显上升,尤其是最低温度,植株生长速率出现下降趋势,雌株生长速率显著低于雄株;雌株对低温变化更敏感,与上年生长季末低温呈显著负相关、与春季低温呈显著正相关,雄株与低温的相关关系均未达到显著水平.低温对长白山地区山杨雌株生长具有重要影响,在降水基本保持不变的条件下,低温的上升将明显抑制山杨雌株的生长,而对雄株影响不显著.     

干旱生境中接种丛枝菌根真菌对三叶鬼针草

为阐明丛枝菌根真菌对石灰岩地区适生植物三叶鬼针草(Bidens pilosa L.)光合作用的影响,设置正常浇水(A)、中度干旱胁迫(B)和重度干旱胁迫(C)3个水分处理梯度,比较了不同水分处理条件下接种丛枝菌根真菌Glomus mosseae和未接种三叶鬼针草之间净光合速率、气孔导度、蒸腾速率、胞间CO2浓度、羧化效率、水分利用效率等特征的差异.结果表明,水分胁迫显著降低三叶鬼针草的净光合速率、气孔导度、蒸腾速率和羧化效率.胞间CO2浓度在处理的前期(7d)因干旱胁迫而降低,在后期随土壤含水量的降低而升高;水分利用效率则是中度胁迫的植株、正常浇水处理植株、重度胁迫植株依次降低.在正常浇水条件下接种G. mosseae 对三叶鬼针草光合参数没有产生显著性影响;在中度胁迫条件下,接种植株较未接种植株在水分处理的前28d有更高的净光合速率、气孔导度、蒸腾速率和羧化效率;在重度胁迫条件下,虽然净光合速率、气孔导度、蒸腾速率和羧化效率接种植株高于未接种植株,但是二者并不显著.研究认为,干旱胁迫对三叶鬼针草光合作用的影响在水分处理的前期表现为气孔因素制约,在后期则主要是非气孔因素的影响;在正常浇水条件下接种G. mosseae 对三叶鬼针草的光合作用没有显著性影响,在干旱胁迫条件下,丛枝菌根真菌通过改善三叶鬼针草气孔导度和羧化效率等减弱干旱胁迫对植株的伤害,但是这种保护作用因为土壤水分的严重匮乏以及土壤干旱的时间延长而受到限制.     

性别和发育阶段对绒毛白蜡光合特征及叶功能性状的影响

雌雄异株植物资源分配模式上往往表现出显著的性别二态性,但在叶片光合及功能性状上是否有差异目前仍未有定论,且与发育阶段的关系尚不明确。阐明上述问题,能够进一步了解雌雄异株植物的生理生态特征,并为理解性别对性二态植物生长发育的影响机制提供理论依据。以雌雄异株绒毛白蜡(Fraxinus velutina Torr.)为研究对象,针对不同发育阶段不同性别植株进行光合特征及叶功能性状测定,采用双因素方差分析了不同发育阶段下雌雄植株光合能力及叶功能性状的性别间差异,采用Pearson检验了雌雄植株各叶功能性状之间的相关性,并采用标准化主轴分析(Standardized major axis regression, SMA)分析不同性别植株净光合速率与叶功能性状的相关性。结果表明性别和发育阶段显著影响植物个体的光合能力和叶功能性状。总体而言,雄树在坐果期和果实成熟期均表现出更强的净光合速率(Pn)、更高的比叶面积(SLA)、叶绿素含量(Chl)和叶氮含量(LNC);而雌树在果实膨大期表现出更强Pn、SLA和Chl。雌雄性别内Pn与SLA、Chl和LNC间均呈显著正相关(P<0.05),雄树的S...     

28种园林植物对大气CO2浓度增加的生理生态反应

通过对28种园林植物在不同CO2浓度水平下的气体交换参数的观测,分析了净光合速率、气孔导度、蒸腾速率和水分利用效率等生理生态指标的变化趋势与规律.结果表明,所测植物净光合速率和水分利用效率随CO2浓度升高而线性增加,但不同植物种类对高CO2浓度的反应存在较大差异.气孔导度和蒸腾速率与CO2浓度呈线性负相关关系.当CO2浓度倍增(350～700 μmol·mol-1)时,28种园林植物净光合速率平均提高31.2%,气孔导度降低16.5%,蒸腾速率下降11.7%,而水分利用效率则提高了49.2%.不同光合途径的植物净光合速率和水分利用效率受CO2浓度增加的影响程度为C3植物较大,C4植物较小, CAM植物介于两者之间.对不同生活型植物而言,影响程度则为草本C3植物较大,乔木C3植物较小,灌木C3植物居于两者之间.     

Sex-specific physiological and growth responses to water stress in <Emphasis Type="Italic">Hippophae rhamnoides</Emphasis> L. populations

Dioecious plant species and those occupying diverse habitats may present special analytical problems to determine effects of environmental stress. Here, sex-specific physiological and growth responses of two contrasting sea buckthorn (Hippophae rhamnoides L.) populations were recorded after exposure to different watering regimes. The populations used were from wet and dry climate regions in China, respectively. In the semi-controlled environmental study, the well-watered and water-deficiency plants which were watered to 100 % and 50 % field capacity were used, respectively. Sexual differences in height growth (HT), dry matter accumulation (DMA), root/shoot ratio (RS), specific leaf area (SLA), net photosynthesis (A), transpiration (E), instantaneous water use efficiency (WUE_i) and carbon isotope composition (δ¹³C) between the male and female individuals were detected under water-deficiency treatment in both populations tested. However, these sexual differences were not detected under well-watered treatment. On the other hand, compared with the wet climate population, the dry climate population showed lower HT, DMA, SLA, A and E, and higher RS under both watering regimes. The dry climate population also showed higher WUE_i and δ¹³C as affected by water deficit than the wet climate population. These morphological and physiological responses to drought showed that the different populations and the different sexual individuals may employ different survival strategies under environmental stress. The male individuals and the dry climate population would have a conservative water-use strategy in response to drought stress.     

Sexually differential tolerance to water deficiency of Salix paraplesia—A female‐biased alpine willow

Salicaceae plants are dioecious woody plants. Previous studies have shown that male individuals are more tolerant to water deficiency than females for male‐biased poplars. However, Salix paraplesia is a female‐biased species in nature. It is still unknown whether female willows are more tolerant to drought stress than males. To better understand the sexually different tolerance to water deficiency in willows, a greenhouse experiment combined with a field investigation was conducted, and physiological traits were tested in male and female S. paraplesia under a drought‐stressed condition (50% of soil water capacity). Our field investigation showed that S. paraplesia was a species with female‐biased sex ratio along altitude gradients (2,400 m, 2,600 m and 2,800 m) in their natural habitats. Our results showed that the height growth, biomass accumulation, total chlorophyll pigment content (TChl), and the net photosynthetic rate were higher in female willows than in males at the low and middle altitudes (2,400 m and 2,600 m) rather than at a high altitude (2,800 m) under well‐watered conditions. Under drought‐stressed conditions, the growth, biomass, and photosynthesis were greatly inhibited in both sexes, while females showed higher biomass and TChl content and suffered less negative effects than did males. Particularly, females that originated from a high altitude showed lower leaf relative electrolyte leakage, malondialdehyde content, and less disorder of chloroplast ultrastructures but a higher peroxidase activity (POD) than that of males. Therefore, S. paraplesia females exhibited a better drought tolerance and self‐protective ability than males from high altitude. There is a reason to speculate that the population structure of S. paraplesia at a high altitude would be likely to further female biases with the increased drought intensity in the alpine regions.     

火炬树雌雄母株克隆生长差异及其光合荧光日变化

火炬树(Rhus typhina Linn.)是兼有雌雄异株和克隆生长特性的外来木本植物。分别探讨火炬树雌雄母株克隆繁殖扩散能力的特点,分析其光合荧光反应的差异。采用CIRAS-2光合仪和FMS-2便携调制式荧光仪,并结合样圆调查法,比较火炬树雌雄母株的克隆分株数量和形态生长指标、光合生理参数的日变化特征,揭示火炬树雌雄异株的资源利用效率和对午间强光缓冲保护能力的雌雄差异。研究结果表明:1)火炬树雄性母株的克隆分株形态生长指标及数量均超过了雌性母株,且雄性母株形成克隆分株的年龄早于雌性母株1a;2)火炬树雄性母株的光能、水分和CO2利用效率和净光合速率均高于雌性母株,此结果为雄性母株克隆生长奠定了较为充足的营养基础;3)在晴天自然光的条件下,火炬树雄性母株未出现光抑制,而雌性母株出现了光抑制现象,非光化学猝灭系数(qN)日变化特征显示雌性母株的热耗散程度较高。因此,火炬树雄性母株的克隆生长力强于雌性母株。     

Sex-specific responses of Populus cathayana to drought and elevated temperatures

Dioecious plant species represent an important component of terrestrial ecosystems. Yet, little is known about sex-specific responses to drought and elevated temperatures. Populus cathayana Rehd, which is a dioecious, deciduous tree species, widely distributed in the northern, central and southwestern regions of China, was employed as a model species in our study. In closed-top chamber experiments, sex-specific morphological, physiological and biochemical responses of P. cathayana to drought and different elevated temperatures were investigated. Compared with the controls, drought significantly decreased the growth and the net photosynthesis rate (A), and increased the intrinsic water use efficiency (WUE(i)), carbon isotope composition (delta13C), and the malondialdehyde (MDA) and abscisic acid (ABA) contents in droughted plants. In contrast, elevated temperatures significantly promoted the growth and the A, but decreased the WUE(i), delta13C, MDA and ABA contents in well-watered individuals. When compared with males, elevated temperatures induced well-watered females to express a greater increase in the height growth (HG), basal diameter (BD), leaf area (LA), total number of leaves (TNL), dry matter accumulation (DMA) and specific leaf area (SLA), and a lower decrease in the A value, transpiration (E), stomatal conductance (g(s)), MDA and ABA contents, while elevated temperatures induced drought-stressed females to exhibit lower values of HG, BD, LA, TNL, DMA, A, E, g(s) and the intercellular CO2 concentration (C(i)), and higher levels of SLA, WUE(i), delta13C, MDA and ABA contents. Our results indicated that the female individuals of P. cathayana are more responsive and suffer from greater negative effects than do males when grown under environments with increased drought stress and elevated temperature.     

不同地理种源长白落叶松生理生态特性的研究

在人工气候室中测定了１０个种源长白落叶松二年生硬枝扦插苗的光合、水分生理生态参数。结果表明,不同种源的长白落叶松生理生态参数变异较大,但有一定规律可循。各种源的总光合速率＞最大净光合速率＞净光合速率＞半饱和光强时的净光合速率＞光呼吸速率＞呼吸速率,只偶有例外。各参数中呼吸速率在各种源间变异最小,光呼吸速率变异较大,总光合速率变异最大。各参数在种源间的变化趋势均与净光合速率一致,即净光合速率大的种源其它参数也大,净光合速率小的种源其它参数也小。相对光呼吸在各种源间变异较大,其释放的ＣＯ２相当于光合固定ＣＯ２的总量的１／３。光补偿点、饱和点和半饱和点在各种源间的变异较大。水分利用率在各种源间的较大变异主要是由净光合速率引起,与蒸腾速率关系不大。净光合速率占总光合速率的百分比、呼吸功效、ＣＯ２补偿点、蒸腾速率和水势在各种源间变异不大     

铝胁迫对青杨雌雄幼苗生理生态特征的影响

以青杨雌雄幼苗为对象,研究铝胁迫(Al³⁺浓度为216 mg·kg^-1)下其生理生态特征及光合作用的差异.结果表明：铝胁迫下,青杨幼苗的丙二醛和可溶性蛋白含量显著增加(P<0.001),且雄株的丙二醛显著低于雌株,而可溶性蛋白显著高于雌株;雄株过氧化物酶活性显著增加、超氧化物歧化酶活性显著降低,而雌株无显著变化;雌雄幼苗的光合速率显著降低(P=0.001),雌株的蒸腾速率显著下降(P=0.007)、瞬时水分利用效率显著增加,而雄株均无显著变化;雌株幼苗的叶绿素a含量、总叶绿素含量和叶绿素a/b值显著降低,而雄株的叶绿素a/b值显著高于雌株;雌株的比叶面积显著降低、雄株的比叶面积显著增加,而叶和茎的干物质量无显著变化.与雌株相比,青杨雄株的可溶性蛋白含量、抗氧化酶活性、叶绿素含量和光合速率较高,其抗逆性更强.     

Reciprocal grafting separates the roles of the root and shoot in sex‐related drought responses in Populus cathayana males and females

Drought stress responses and sensitivity of dioecious plants, such as Populus cathayana Rehd., are determined by different mechanisms in each sex. In general, males tend to be more resistant while females are more sensitive. Here, we used reciprocal grafting between males and females to determine the relative importance of roots and shoots when plants are exposed to drought stress. Total dry matter accumulation (DMA), photosynthetic capacity, long‐term water‐use efficiency (Δ), water potential and ultrastructure of mesophyll cells were evaluated to determine the different roles of root and shoot in sex‐related drought responses. Plants with male roots were found to be more resistant and less sensitive to water stress than those with female roots under drought conditions. On the contrary, plants with female shoots grew better than those with male shoots under well‐watered conditions. These results indicated that the sensitivity of males and females to water stress is primarily influenced by root processes, while under well‐watered conditions sexual differences in growth are primarily driven by shoot processes. Furthermore, grafting female shoot scion onto male rootstock was proved to be an effective mean to improve resistance to water stress in P. cathayana females.     

Responses to drought stress among sex morphs of Oxyria sinensis (Polygonaceae), a subdioecious perennial herb native to the East Himalayas

It is generally accepted that dioecious plants occur more frequently in dry and nutrient‐poor habitats, suggesting that abiotic stress factors could contribute to evolution of dioecy from hermaphrodite. Therefore, experimental investigations on the responses of subdioecious species, a special sexual system comprising male, female, and hermaphrodite plants, to abiotic stress factors could quantify the contribution of selective pressure on the evolution of dioecy. In this study, we evaluated the physiological responses of different sex morphs of Oxyria sinensis Hemsley, a perennial herb native to the East Himalayas, to drought stress. Male, female, and hermaphrodite plants of O. sinensis were subjected to low, moderate, and high drought stress conditions in a glasshouse. Generally, with increasing water stress, the values of most measured variables slightly decreased, whereas water‐use efficiency slightly increased. Furthermore, there were no significant differences in most of the measured parameters among the sex morphs under each drought stress treatment, indicating that O. sinensis might be well‐adapted to drought stress conditions as its typical habitat is the dry and hot habitats of xerothermic river valleys. However, nitrogen‐use efficiency was significantly higher in male and female plants than in hermaphrodite plants under high drought stress conditions, suggesting that that nitrogen‐use efficiency under conditions of drought stress might have contributed to the evolution of dioecy from the hermaphrodite to some degree.     

Interspecific Transition Among Caragana microphylla,C. davazamcii and C. korshinskii Along Geographic Gradient. Ⅱ. Characteristics of Photosynthesis and Water Metabolism

The characteristics of photosynthesis and water metabolism of Caragana microphylla Lam., C. davazamcii Sancz. and C. korshinskii Kom. populations in different sites (117.6o-105.7o E, 44.6o-38.8o N) were studied. (1) From the east to the west, the responses of the three species to photosynthetically available radiation (PAR) in net photosynthesis rate increased, the relative humidity of the air which corresponded to the occurrence of maximum photosynthesis rate decreased, and the corresponding air temperature increased. Along the same gradient, the before-noon superiority of the photosynthesis became evident, and the photosynthesis rate and the light use efficiency (LUE ) increased, while the transpiration rate decreased, thus the water use efficiency (WUE ) increased notably, and the leaf water content decreased gradually. From the east to the west, the plants took a water-saving strategy step by step with higher photosynthesis rate and lower transpiration rate. These physiological changes in the plants were adaptable to the conditions of light, temperature and humidity in the habitat of the plants, and might be the biological foundation for the geographical transition among C. microphylla , C. davazamcii and C. korshinskii. (2) The adaptation of photosynthetic system of C. microphylla , C. davazamcii and C. korshinskii to PAR, air humidity and temperature exhibited the interspecific continuity, which was consistent with the environmental gradient. In different species and different sites, the diurnal changes of net photosynthesis rate, the daily cumulative value of net photosynthesis, the diurnal changes of transpiration rate, the daily cumulative value of transpiration, the water use efficiency and the diurnal changes of leaf water content varied with longitudinal descent (from the east to the west). The characteristics of photosynthesis and water metabolism indicated that the geographical transition among C. microphylla , C. davazamcii and C. korshinskii was in gradual change, and these three species formed a geographical cline.     

Adaptive responses of Populus kangdingensis to drought stress

We measured dry matter accumulation and allocation, photosynthesis, lipid peroxidation, osmotic adjustment, antioxidative defences and ABA content of Populus kangdingensis C. Wang et Tung under three different watering regimes (100%, 50% and 25% of the field capacity) to characterize the morphological, physiological and biochemical basis of drought resistance in woody plants. The results showed that drought stress caused pronounced inhibition of the growth and photosynthesis rate, and that the stomatal limitation to photosynthesis was dominant. The decrease in stomatal conductance effectively controlled water loss and increased water use efficiency. Drought also affected many physiological and biochemical processes, including increases in free proline, malondialdehyde and ABA content, and superoxide dismutase activity. On the other hand, the ABA content of leaves was significantly higher than that of stem and roots under all watering regimes; the high level of ABA in the leaf may result from the large import of ABA to leaves from other organs. These results demonstrate that there are a large set of parallel changes in the morphological, physiological and biochemical responses when plants are exposed to drought stress; these changes may enhance the capability of plants to survive and grow during drought periods.