Hydraulic Constraints on Transpiration and Stress Tolerance of Cold Desert Shrubs

9319180 Sperry在木质部导管中空化的物理过程中，水分运输的中断发生在木质部压力下，该木质部压力在物种之间可能差异很大。这些空化压力对最大耐旱性和水运输能力设定了明确的限制。空化也是由冻融循环引起的，并且在木质部水中发生冻融的条件下对水运输设置了额外的限制。拟议的研究将评估空化和全株水力传导率在赋予寒地荒漠灌木Artemesia tridentata必要的夏季耐旱性方面发挥的作用，同时在春季有水但冻融循环常见时促进最大气孔导度和木质部流量。这项工作将扩展目前的努力，以表征物理有限的水力参数之间的整合水运输和生理形态的压力，包括膨压维持，气孔关闭，和叶片脱落的反应。与此同时，这项研究将补充并可能有助于解释以前的工作，这些工作广泛地描述了该物种在水关系，光合作用和生长方面的季节性模式。水流水力限制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A. tridentata将与多年生草本A. ludoviciana获得进一步了解有关的生活史的压力反应，这也将提供一个进化的角度来看，因为木本蒿可能是从同源的草本祖先进化而来。将在实验室确定冻融循环和水胁迫的空化反应的背景下，对不同水制度下土壤和植物水分关系、叶面积和物候的两三年实地监测进行评估，这些空化反应形成了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精确地确定对土壤和大气干旱的反应，并评估根与叶是否感觉到水分胁迫。最终的结果将是更好地了解冷沙漠灌木的适应其独特的季节性气候制度，以及如何空化和水力传导的考虑因素被整合到整个植物的压力反应的关键评价。 *** ~ J P E J ! ! ! F J P J 4 CG Times 符号Arial Tms Rmn“Helv M M M H S % S % ^ / 罗谢尔D雷罗谢尔D雷

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