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1.
盐碱胁迫下枸杞和柽柳的水力学特性和碳代谢   总被引:3,自引:0,他引:3       下载免费PDF全文
盐碱胁迫是全球范围内重要的非生物胁迫形式之一,但目前对植物水力学特性和碳代谢应对盐碱胁迫响应的研究还不多。本研究以耐盐碱植物枸杞(Lycium chinense Miller)和柽柳(Tamarix chinensis Lour.)为对象,测定不同盐碱程度下两种植物的枝条水势和导水损失率(PLC)、叶片光合作用和气孔导度、不同部位的非结构性碳(NSC)浓度以及植株生长情况。结果显示,重度盐碱胁迫显著降低了两种植物凌晨和正午水势、光合速率和枝条PLC,重度胁迫下柽柳的光合速率、气孔导度和枝条PLC下降程度均大于枸杞,重度盐碱胁迫下枸杞不同部位的NSC浓度均显著降低,但柽柳的地上部分NSC浓度显著增加,根部NSC浓度显著减低。两种植物有不同的应对盐碱胁迫策略,枸杞有较强的气孔调节能力,对水力结构的维持有利,但会限制碳摄取,柽柳气孔调节能力弱,水力结构易受影响,但对碳平衡维持有利。  相似文献   

2.
断根处理对银杏树体水力特征及生长的影响   总被引:1,自引:0,他引:1  
以8年生银杏为试材,采用不同程度的断根处理,测定处理后树体超声(ultrasound acoustic emission,UAE)信号、枝条栓塞程度(percentage loss of hydraulic conductance,PLC)、树干液流通量、气孔导度、蒸腾速率以及叶片水势等生理指标,分析断根对银杏树体水力特征及生长状况的影响.结果表明:断根处理后,在短时间内有大量UAE信号产生,且随断根程度的加重而增大,在6 h出现最大值,随后逐渐降低;枝条的PLC在起初的12 h迅速增加,24 h后增速趋于停滞;银杏树干液流通量、叶片气孔导度、蒸腾速率和水势明显降低,各处理间差异显著.经统计分析,累积UAE(cumulative number of UAE, cUAE)信号量与PLC呈现显著的正相关关系,与液流通量和叶片水势呈负相关关系.次年的单叶面积、新生枝条长度显著下降,下降程度随断根处理的加重而加剧.断根处理在短时间内增加了银杏管胞气穴数量和木质部栓塞的程度,影响到水分输送和叶片蒸腾,最终对叶片和枝条的生长产生负面影响.  相似文献   

3.
施水和钾素添加对元宝枫和女贞木质部栓塞的影响   总被引:1,自引:0,他引:1       下载免费PDF全文
 通过干旱胁迫处理(土壤含水量为田间持水量的30%~40%)和正常水分供给(土壤含水量为田间持水量的70%~80%)两种盆栽控制试验, 研究了耐旱树种元宝枫(Acer truncatum)和中生树种女贞(Ligustrum lucidum)枝条木质部栓塞(以导水率损失百分数(Percentage loss of hydraulic conductivity, PLC)衡量)和水势(Water potential, WP)对钾(K)素添加的响应。结果表明: 两个树种PLC的日变化均呈现先升后降的规律, 而WP呈现相反的变化趋势; 添加K素显著提高了两个树种的PLC, 除了干旱胁迫下的元宝枫, 其他树种和处理的PLC随K素含量的增加而增加; K素显著降低了干旱胁迫下元宝枫和女贞的WP, 但对正常水分供给下两个树种的WP无显著影响; 元宝枫的平均PLC高于女贞, 平均WP低于女贞。以上结果表明, K素可能通过降低枝条的WP, 促进树种木质部栓塞的形成, 达到限制水分进一步丧失的目的。K素在调节气孔运动、渗透作用等方面的作用, 可能是树种木质部栓塞形成的诱因。  相似文献   

4.
选用内蒙古科尔沁沙地1年生植物狗尾草(Setaria viridis)和沙米(Agriophyllum squarrosum)为材料,采用盆栽方法研究了它们在不同土壤水分处理下的光合参数和水分利用效率的日变化特征及其与环境因子的相关关系。结果表明,狗尾草和沙米的净光合速率日变化曲线在充分供水条件下均呈单峰型,在轻度干旱胁迫下均呈双峰型,而在重度干旱胁迫下分别呈双峰型和左偏单峰型。狗尾草和沙米的蒸腾速率在不同水分处理下都近似呈双峰型曲线,然而变化程度却不相同。重度干旱胁迫下,狗尾草日平均净光合速率(11.52μmol.m-2.s-1)和蒸腾速率(3.62 mmol.m-2.s-1)分别比相应充分供水处理增加7%和43%,而沙米的日平均净光合速率(7.07μmol.m-2.s-1)和蒸腾速率(5.56 mmol.m-2.s-1)则分别较相应充分供水处理降低13%和36%。重度干旱胁迫下,狗尾草水分利用效率(2.84 mmol.mol-1)比相应充分供水处理降低3.1%,而沙米水分利用效率(1.14mmol.mol-1)则较充分供水处理提高了34%。光合速率下降在充分供水条件下主要是由气孔调节,但在轻度干旱胁迫和重度干旱胁迫处理下非气孔因素调节却起到十分重要的作用。在重度干旱胁迫下,狗尾草仍具有显著高于沙米的的净光合速率和水分利用效率,这可能是其仍然能够在固定沙地分布的原因之一。  相似文献   

5.
短期干旱对水稻叶水势、光合作用及干物质分配的影响   总被引:51,自引:10,他引:41  
采用盆栽水分试验,研究了不同生育期短期干旱处理对水稻叶水势、光合作用和干物质分配的影响.结果表明,干旱胁迫后,水稻叶水势低于对照,午后叶水势回升缓慢。凌晨叶水势随土壤含水量的降低而降低,表现为阈值反应。叶片净光合速率与凌晨叶水势密切相关,低于凌晨叶水势临界值,水稻叶片净光合速率急剧下降在水稻抽穗期和灌浆期叶片净光合速率显著下降的凌晨叶水势临界值为-1.04和-1.13MPa,对应的土壤含水量阈值分别为饱和含水量的61.0%和50.9%,土壤水势分别为-0.133和-0.240MPa干旱胁迫下单叶净光合速率的日变化规律表现为:胁迫较轻时,单叶净光合速率在正午附近出现低谷;胁迫严重时,净光合速率全天低于对照,且不及对照的一半。短期干旱后,水稻叶、根、穗的分配指数均降低,茎鞘的分配指数升高。本研究可为水稻节水灌溉管理和水分限制下水稻的生长模拟提供生理基础和理论依据。  相似文献   

6.
干旱胁迫对夏蜡梅光合特性的影响   总被引:7,自引:0,他引:7  
柯世省 《西北植物学报》2007,27(6):1209-1215
以2年生夏蜡梅(Sinocalycanthus chinensis)苗木为材料,通过盆栽试验,研究土壤干旱胁迫对夏蜡梅叶片光合特性的影响,结果显示:随着干旱胁迫程度的加重,夏蜡梅叶片净光合速率、蒸腾速率、气孔导度显著降低;胞间CO2浓度在轻度和中度胁迫下显著低于对照,但在重度胁迫下显著高于对照;水分利用效率在胁迫下提高,且以中度胁迫为最大.温度升高使叶片净光合速率和水分利用效率降低、蒸腾速率升高,加重了干旱对光合作用的不利影响.对照及轻度和中度干旱胁迫处理的净光合速率、气孔导度和水分利用效率日变化曲线均为双峰型,但重度胁迫下净光合速率和气孔导度日变化转变为峰值很小的单峰型;各处理的蒸腾速率日变化曲线为单峰型并以午间最高.表明夏蜡梅光合作用对干旱胁迫有一定的适应能力,但重度胁迫对其造成严重影响.  相似文献   

7.
夏蜡梅是浙江省特有的濒危单种属物种.本文研究了不同程度土壤水分胁迫和不同温度处理对2年生盆栽夏蜡梅光合作用的影响.结果表明:轻度和中度水分胁迫下夏蜡梅净光合速率分别下降至对照的92.3%和74.3%,净光合速率的降低主要由气孔限制引起;重度水分胁迫下,净光合速率仅为对照的44.4%,主要由非气孔限制引起.夏季夏蜡梅的光合适宜温度范围在20 ℃~28 ℃,39 ℃下其净光合速率、水分利用效率和最大光化学效率显著降低,暗呼吸速率和蒸腾速率显著升高.随着水分胁迫的加重及处理温度的升高,夏蜡梅光补偿点上升,光饱和点、表观量子效率和最大净光合速率下降.重度水分胁迫及高温是制约夏蜡梅生存的重要环境因子.  相似文献   

8.
避雨环境下苹果幼树水分状态指标对干旱胁迫的响应   总被引:1,自引:1,他引:0  
在避雨环境下进行土壤水势渐进式下降处理,研究了苹果树体水分状态指标对土壤干旱胁迫响应的敏感性,分析了不同水分状态指标与树体水分平衡之间的关系.结果表明: 树干直径日较差(MDS)及中午树干水势(Ψstem)对干旱胁迫最敏感.MDS对参考蒸散(ET0)有明显的响应,且对干旱胁迫比较敏感,与ET0呈显著正相关,相对树干直径日较差(MDSr)与相对土壤水势(Ψr soil)呈显著负相关,树干直径可实现连续性测量及自动化记录.Ψstem对土壤干旱胁迫较敏感,且与ET0呈显著负相关,相对中午树干水势(Ψr stem)与Ψr soil呈显著相关,目前叶水势和树干水势难以实现自动化连续性观测.其他树体水分状态指标,如黎明前叶水势(Ψpd)、树干直径日生长量(DG)和气孔导度(gs)等对中度或重度干旱胁迫也有不同程度的响应,但总体上对土壤水势变化的响应不敏感.  相似文献   

9.
油松幼苗对干旱胁迫的生理生态响应   总被引:8,自引:2,他引:6  
在适宜水分(田间持水量为80%)、轻度干旱(60%)、中度干旱(40%)和重度干旱(20%)4种土壤水分条件下研究了油松的生理生态特征,结果显示; 油松各器官(根、茎、叶)的干物质积累量、干物质积累总量、相对生长率、株高和基径均表现为适宜水分>轻度干旱>中度干旱>重度干旱,而根冠比大小顺序与其相反.气体交换参数(净光合速率、气孔导度、蒸腾速率) 随干旱程度的加剧显著下降,并且净光合速率的下降主要受气孔因素限制.油松的瞬时水分利用效率和长期水分利用效率(稳定碳同位素含量,δ13C)表现适宜水分<轻度干旱<中度干旱<重度干旱,而且中度和重度干旱显著提高油松的水分利用效率.另外,单位干重叶片氮元素含量(N%)随胁迫增加呈下降趋势,而单位干重碳元素含量(C%)却与之相反,从而导致碳氮比随胁迫增加而增加,并且我们的结果显示光合速率与氮含量存在显著正相关. 结果表明,油松可以通过调节自身生长特征、生物量分配模式和叶片营养元素的含量及提高水分利用效率而增强应对干旱胁迫的能力.  相似文献   

10.
为研究土壤含水量对旱季树体水势、树干呼吸和边材非结构性碳水化合物(NSCs)变化特征的影响,设置重度隔水(HD)、轻度隔水(LD)、旱季灌溉(DI)和对照(CK)4个土壤含水量水平,每隔半月监测各参数的动态变化。旱季土壤含水量和枝条水势呈下降趋势,各处理从11月底开始表现出显著差异。各处理树干呼吸与树干温度均具有良好的指数函数关系(R2≥0.65,P0.001),各处理温度敏感系数Q10为DICKLDHD(P0.001)。旱季树干温度和树干呼吸均呈下降趋势,且在1月达到最低。各处理树干温度只在气温较低的冬季达差异显著,树干呼吸总体表现为旱季灌溉增加树干呼吸,而干旱降低树干呼吸。旱季淀粉含量下降,可溶性糖含量上升,非结构性碳水化合物总量总体保持不变。各处理边材淀粉和可溶性糖差异显著,而NSCs总量差异不显著。相比于DI和CK,干旱(LD和HD)加速了旱季边材淀粉分解为可溶性糖的速率。树干呼吸与淀粉、可溶性糖均具有显著回归关系,树干呼吸分别解释了淀粉72%和可溶性49%的旱季变化;枝条水势解释了49%树干呼吸、75%淀粉和85%可溶性糖的旱季变化。土壤含水量很可能通过改变树体组织含水量,进而影响边材NSCs和树干呼吸。这些变量之间紧密的联系可能为干旱可以促进降香黄檀心材形成的猜想提供一定的理论基础。另外,基于树干呼吸与树体水势和NSCs的显著关系,树干呼吸可能也会对树木心材形成有一定指示作用。  相似文献   

11.
The volume and complexity of their vascular systems make the dynamics of long-distance water transport in large trees difficult to study. We used heat and deuterated water (D2)) as tracers to characterize whole-tree water transport and storage properties in individual trees belonging to the coniferous species Pseudotsuga menziesii (Mirb.) Franco and Tsuga heterophylla (Raf.) Sarg. The trees used in this study spanned a broad range of height (13.5-58 m) and diameter (0.14-1.43 m). Sap flow was monitored continuously with heat dissipation probes near the base of the trunk prior to, during and following injection of D2O. The transit time for D2O transport from the base of the trunk to the upper crown and the tracer residence time were determined by measuring hydrogen isotope ratios in water extracted from leaves sampled at regular intervals. Transit times for arrival of D2O in the upper crown ranged from 2.5 to 21 d and residence times ranged from 36 to 79 d. Estimates of maximum sap velocity derived from tracer transit times and path length ranged from 2.4 to 5.4 m d(-1). Tracer residence time and half-life increased as tree diameter increased, independent of species. Species-independent scaling of tracer velocity with sapwood-specific conductivity was also observed. When data from this study were combined with similar data from an earlier study of four tropical angiosperm trees, species-independent scaling of tracer velocity and residence time with sapwood hydraulic capacitance was observed. Sapwood capacitance is an intrinsic tissue-level property that appears to govern whole-tree water transport in a similar manner among both tracheid- and vessel-bearing species.  相似文献   

12.
Rates of water uptake by individual trees in a native Australian forest were measured on the Liverpool Plains, New South Wales, Australia, using sapflow sensors. These rates were up-scaled to stand transpiration rate (expressed per unit ground area) using sapwood area as the scalar, and these estimates were compared with modelled stand transpiration. A modified Jarvis-Stewart modelling approach (Jarvis 1976), previously used to calculate canopy conductance, was used to calculate stand transpiration rate. Three environmental variables, namely solar radiation, vapour pressure deficit and soil moisture content, plus leaf area index, were used to calculate stand transpiration, using measured rates of tree water use to parameterise the model. Functional forms for the model were derived by use of a weighted non-linear least squares fitting procedure. The model was able to give comparable estimates of stand transpiration to those derived from a second set of sapflow measurements. It is suggested that short-term, intensive field campaigns where sapflow, weather and soil water content variables are measured could be used to estimate annual patterns of stand transpiration using daily variation in these three environmental variables. Such a methodology will find application in the forestry, mining and water resource management industries where long-term intensive data sets are frequently unavailable.  相似文献   

13.
黄土高原半干旱区侧柏(Platycladus orientalis)树干液流动态   总被引:2,自引:0,他引:2  
应用热扩散式树干茎流计(TDP)于2008年4~10月对黄土高原安塞县侧柏人工林树干液流速率进行了连续测定,并对周围气象、土壤水分等多个环境因子进行了同步测定.结果表明:侧柏在不同月份晴天树干液流速率变化具有明显的昼夜节律性,呈单峰曲线;且各月液流速率日均值受土壤供水水平限制总体上呈下降趋势,即4月份最大,为0.00135 cm · s-1;10月份最小为0.00011cm · s-1;树干液流速率与光合有效辐射、大气温度、水汽压差呈极显著正相关,与相对湿度呈负相关,其相关程度:光合有效辐射>水汽压差>大气温度>相对湿度,并可用线性表达式来估算;侧柏边材面积和地径呈幂指数关系,并以此结合密度估算出样地侧柏人工林的边材面积为4.65m2,最终估算出侧柏人工林生长季总耗水量为1159.6 t · hm-2.  相似文献   

14.
Páramos are high elevation tropical ecosystems in northern Andes, with large water yield and water regulation. One of the main and representative species growing in these páramos is the genus Espeletia, known as frailejones. There is a lack of knowledge of Espeletia ecophysiology, maybe due to its unusual anatomical modifications and the specific climatic conditions of these ecosystems. Therefore, it is important to determine the relationships between the anatomical modifications of Espeletia, its physiological functioning, and its contribution to the ecohydrologic functioning of páramos. Consequently, we studied the physiology of frailejones in two Colombian páramos, focused on the identification of conductive tissues inside the stems, calculated the age, and measured sapflow, using the heat ratio method. Results show that Espeletia spp. have a central pith that increases with height, as the size of secondary xylem decreases. Frailejones respond quickly to the changing conditions of weather factors controlling transpiration such as solar radiation, temperature, and fog presence. However, although environmental factors favor transpiration, the sapflow tends to decrease—a particular behavior of the Espeletia transpiration processes—since this occurs chaotically over time, including sapflow at night. The transformation of sapflow velocity to depth of water in a basin shows that the water lost through their transpiration is very low, which contributes to the high runoff ratio of páramo ecosystems. For the first time, we determine by radiocarbon the real ages of three E. hartwegiana, and their mean growth rates to range between 3.8 and 6.9 cm year?1.  相似文献   

15.
Heat-pulse techniques are routinely used to estimate transpiration from canopies of woody plants typically without any local calibration, mainly because of the difficulty of doing so in the field and, frequently, lack of detailed weather data. This is despite concerns that the techniques may produce erroneous values under certain conditions, such as when evaporative demand is high. In this study, we used a micrometeorological approach to validate transpiration from irrigated olives deduced from heat-pulse technique by ascertaining precise values for the parameters that are critical for converting heat-pulse velocity to sapflow. The micrometeorological approach involved limited data on stomatal conductance (gs), obtained hourly with a porometer on four contrasting days, and was used to calibrate a simple model for predicting conductance. Predicted stomatal conductance (gsm) agreed well with that measured, and when both were used to calculate hourly transpiration, they produced values that were within 10% of each other. This was despite brief underestimations of transpiration based on gsm (Tm) in the early hours of the day that arose from poor determination of incident radiation at this time. We then used Tm to iteratively set the values for the various parameters, including the time-out value that accounts for zero-flow conditions, needed to convert heat-pulse velocity to sapflow, for the four days. The best fit between Tm and transpiration from sapflow (Ts) was obtained with time-out value set to 120 s. All heat-pulse velocity data were therefore analysed with this time-out value to obtain sapflow and, hence, transpiration (Ts). Comparison of Tm and Ts for the whole season showed that the former tended to produce higher values on certain days when vapour pressure deficit (D) was high in summer (December–February). While Ts occasionally produced larger values than Tm under the mild conditions of autumn (March–April). Totals of the daily transpiration during the 190-day period were within 10% of each other. Responsible Editor: Yan Li  相似文献   

16.
The study was conducted in order to determine whether water stress affects the accumulation of dry matter in tomato fruits similarly to salinity, and whether the increase in fruit dry matter content is solely a result of the decrease in water content. Although the rate of water transport to tomato fruits decreased throughout the entire season in saline water irrigated plants, accumulation rates of dry matter increased significantly. Phloem water transport contributed 80–85% of the total water transport in the control and water-stressed plants, and over 90% under salinity. The concentration of organic compounds in the phloem sap was increased by 40% by salinity. The rate of ions transported via the xylem was also significantly increased by salinity, but their contribution to fruit osmotic adjustment was less. The rate of fruit transpiration was also markedly reduced by salinity. Water stress also decreased the rate of water transport to the tomato fruit and increased the rate of dry matter accumulation, but much less than salinity. The similar changes, 10–15%, indicate that the rise in dry matter accumulation was a result of the decrease in water transport. Other parameters such as fruit transpiration rates, phloem and xylem sap concentration, relative transport via phloem and xylem, solutes contributing to osmotic adjustment of fruits and leaves, were only slightly affected by water stress. The smaller response of these parameters to water stress as compared to salinity could not be attributed to milder stress intensity, as leaf water potential was found to be more negative. Measuring fruit growth of girdled trusses, in which phloem flow was inactive, and comparing it with ungirdled trusses validated the mechanistic model. The relative transport of girdled as compared to ungirdled fruits resembled the calculated values of xylem transport.  相似文献   

17.
The sudden changes in the rates of transpiration and water uptake which occurred when the osmotic potential of the nutrient solution surrounding the roots of young wheat plants was rapidly changed were studied. The transpiration was measured by the aid of the microwave hygrometer and the water uptake by a recording poto-meter specially built for this investigation. When the osmotic potential of the nutrient solution was rapidly increased by adding mannitol, there was a temporary transpiration increase. The maximum increase was greater but the total time of the temporary increase shorter when a higher mannitol concentration was used. The quantity of water transpired by the shoots due to the temporary transpiration increase seemed to be fairly constant irrespectively of the mannitol concentration. The water transport to the shoots was immediately reduced when the osmotic potential was rapidly increased. The immediate reduction was greater when a higher mannitol concentration was used. After the immediate reduction the rate of water transport increased without delay. When the osmotic potential of the nutrient solution was rapidly decreased by withdrawing mannitol there was a temporary transpiration decrease, and the water transport to the shoots was immediately increased. After this increase the rate of water transport started to decrease at once. When, however, the mannitol concentration had been 0.30 M or higher, the transpiration rate increased progressively, and the change of the rate of water transport was small. The results indicate that the primary effect of the rapidly changed osmotic potential is localized to the root surface. The rapidly reduced water transport to the shoots after adding mannitol brings about the temporary transpiration increase. The course of events after withdrawing mannitol is just the reverse to that when adding mannitol.  相似文献   

18.
 The use of stem sap flow data to estimate diurnal whole-tree transpiration and canopy stomatal conductance depends critically upon knowledge of the time lag between transpiration and water flux through the stem. In this study, the time constant for water movement in stems of 12-year-old Pinus taeda L. individuals was estimated from analysis of time series data of stem water flux and canopy transpiration computed from mean daytime canopy conductance, and diurnal vapor pressure deficit and solar radiation measurements. Water uptake through stems was measured using a constant-heat sapflow probe. Canopy transpiration was correlated to stem uptake using a resistance-capacitance equation that incorporates a time constant parameter. A least-squares auto-regression determined the parameters of the resistance-capacitance equation. The time constants for ten loblolly pine trees averaged 48.0 (SE = 2.0) min and the time lag for the diurnal frequency averaged 47.0 (SE = 2.0) min. A direct-cross correlation analysis between canopy transpiration and sap flow time series showed maximum correlation at an approximately 30 min lag. Residuals (model-predicted minus actual stem flow data) increased with increasing soil moisture depletion. While the time constants did not vary significantly within the range of tree sizes studied, hydraulic resistance and capacitance terms were individually dependent on stem cross-sectional area: capacitance increased and resistance decreased with stem volume. This result may indicate an inverse adjustment of resistance and capacitance to maintain a similar time constant over the range of tree sizes studied.  相似文献   

19.
We show that sapflow is a useful tool for studies of water fluxes in forest ecosystems, because (i) it gives access to the spatial variability within a forest stand, (ii) it can be used even on steep slopes, and (iii) when combined with eddy correlation measurements over forests, it allows separation of individual tree transpiration from the total water loss of the stand. Moreover, sapflow techniques are quite easy to implement. Four sapflow techniques currently coexist, all based on heat diffusion in the xylem. We found a good agreement between three of these techniques. Most results presented here were obtained using the radial flow meter (Granier 1985). Tree sapflow is computed as sap flux density times sapwood area. To scale up from trees to a stand, measurements have to be made on a representative sample of trees. Thus, a number of trees in each circumference class is selected according to the fraction of sapwood they represent in the total sapwood area of the stand. The variability of sap flux density among trees is usually low (CV. 10–15%) in close stands of temperate coniferous or deciduous forests, but is much higher (35–50%) in a tropical rain forest. It also increases after thinning or during a dry spell. A set of 5–10 sapflow sensors usually provides an accurate estimate of stand transpiration. Transpiration measured on two dense spruce stands in the Vosges mountains (France) and one Scot's pine plantation in the Rhine valley (Germany) showed that maximum rate was related to stand LAI and to local climate. Preliminary results comparing the sapflow of a stand of Pinus banksiana to the transpiration of large branches, as part of the BOREAS programme in Saskachewan, Canada showed a similar trend. For modelling purposes, tree canopy conductance (gc) was calculated from Penman-Monteith equation. In most experiments, calculated canopy conductance was dependent on global radiation (positive effect) and on vapour pressure deficit (negative effect) in the absence of other limiting factors. A comparison of the vapour pressure deficit response curves of gc for several tree species and sites showed only small differences among spruce, oak and pine forests when including understorey. Tropical rainforests exhibited a similar behaviour.  相似文献   

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