Hydraulic Constraints on Transpiration and Stress Tolerance of Cold Desert Shrubs

9319180在木质部导管中空化的物理过程中，木质部压力会导致水分运输中断，不同物种之间的木质部压力可能会有很大差异。这些空化压力为最大抗旱性和水输送能力设定了明确的限制。空化也是由冻融循环引起的，在木质部水中发生冻结和解冻的条件下，空化对水的运输设置了额外的限制。拟议的研究将评估空化和全植物水力传导性在赋予冷漠灌木三齿艾树必要的夏季抗旱性方面所起的作用，同时当春季有水可用时，同时促进最大气孔传导性和木质部流动，但冻融循环很常见。这项工作将扩展目前的工作，以表征水分运输的物理限制的水力参数与胁迫的生理-形态反应之间的整合，包括膨大维持、气孔关闭和叶片脱落。同时，这项研究将补充并可能有助于解释之前的工作，这些工作广泛地描述了这种物种在水分关系、光合作用和生长方面的季节性模式。水力限制水流的遗传分化将在三个生态上不同的亚种Vaseyana、wyomingensis和Tridentata之间进行评估。在三齿艾草中发现的模式将与草本多年生艾草进行比较，以进一步了解与生活史有关的应激反应；这也将提供进化的视角，因为木本艾属可能是从同属草本祖先进化而来的。对不同水分状况下2-3年土壤和植物水分关系、叶面积和物候的实地监测，将结合实验室对冻融循环和水分胁迫的空化反应的确定进行评估，这些空化反应是预测无空化的最大可能流量的基础。温室/实验室实验将允许更准确地确定对土壤和大气干旱的反应，并评估水分胁迫是否在根与叶之间感受到。最终的结果将是更好地了解寒冷沙漠灌木对其独特的季节性气候状况的适应，以及对空化和水力传导性的考虑如何整合到整个植物的应激反应中进行关键评估。*~J PE J！！！F J P J 4 CG时报符号&Amp；宋体TMS RMN“Helv m h S%S%^/Rochelle D Ray Rochelle D Ray

9319180 Sperry Disruption of water transport in the physical process of cavitation in xylem conduits occurs at xylem pressures that can differ widely between species. These cavitation pressures set unambiguous limits to maximum drought tolerance and water transport capacity. Cavitation is also caused by freeze-thaw cycles and sets additional limits to water transport under conditions when freezing and thawing occurs in the xylem water. The proposed research will evaluate the role cavitation and whole -plant hydraulic conductance play in conferring the necessary summer drought tolerance for the cold-desert shrub Artemesia tridentata while at the same time promoting maximum stomatal conductance and xylem flow when water is available in spring but freeze-thaw cycles are common. This work will extend current efforts to characterize the integration between physically limited hydraulic parameters of water transport and physiological-morphological responses to stress including turgor maintenance, stomatal closure, and leaf abscission. At the same time, the research will complement and perhaps help explain previous work which has extensively characterized seasonal patterns in water relations, photosynthesis and growth in this species. Genetic differentiation in hydraulic limitations to water flow will be evaluated among the three ecologically distinct subspecies vaseyana, wyomingensis, and tridentata. The patterns found in A. tridentata will be compared to the herbaceous perennial A. ludoviciana to obtain further insight into stress responses related to life history; this will also provide an evolutionary perspective becaus e woody Artemisia probably evolved from congeneric herbaceous ancestors. Field monitoring of soil and plant water relations, leaf area and phenology for two-three years under differing water regimes will be evaluated in the context of laboratory determinations of the cavitation response to freeze-thaw cycles and water stress that form the basis of predicting maximum possible flows without cavitation. Greenhouse/lab experiments will allow more precise determination of responses to soil and atmospheric drought and evaluate whether water stress is sensed in the root vs. the leaf. The ultimate outcome will be a better understanding of the adaptations of cold-desert shrubs to their unique seasonal climatic regime, and a critical evaluation of how cavitation and hydraulic conductance considerations are integrated into whole plant stress responses. *** ~ J P E J ! ! ! F J P J 4 CG Times Symbol & Arial Tms Rmn " Helv m m m h S % S % ^ / Rochelle D Ray Rochelle D Ray