Hydraulic Constraints on Transpiration and Stress Tolerance of Cold Desert Shrubs

9319180 Sperry木质部导管空化物理过程中水运输的中断发生在木质部压力下，不同物种之间的木质部压力差异很大。这些空化压力对最大耐旱性和水运能力设定了明确的限制。冻融循环也会引起空化，并且在木质部水发生冻结和融化的条件下，空化对水的输送设置了额外的限制。本研究将评估空化和全株水力导度在寒漠灌木蒿（artemisia tridentata）夏季耐旱性中所起的作用，同时在春季水分充足但经常出现冻融循环的情况下，促进气孔导度和木质部流动最大化。这项工作将扩展目前的工作，以表征水运输的物理限制的水力参数和对压力的生理形态反应之间的整合，包括膨胀维持、气孔关闭和叶片脱落。同时，该研究将补充并可能有助于解释先前的工作，这些工作广泛地描述了该物种的水关系，光合作用和生长的季节模式。在三个生态上不同的亚种vaseyana， wyomingensis和tridentata之间，将评估水力限制水流的遗传分化。本研究将三叉草与多年生草本陆氏草进行比较，以进一步了解与生活史有关的应激反应；这也将提供一个进化的视角，因为木本蒿可能是从同源的草本祖先进化而来的。将在实验室确定冻融循环和水压力对空化反应的背景下，对土壤和植物水分关系、叶面积和物候进行2 - 3年的实地监测，这些空化反应是预测无空化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，并评估根系和叶片是否感知到水分胁迫。最终的结果将是更好地了解冷沙漠灌木对其独特的季节性气候制度的适应性，并对如何将空化和水力传导因素整合到整个植物的应激反应中进行关键评估。*** ~ jpE J!!!fjpj4 CG时代符号& & Arial Tms Rmn " Helv m m m 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