Collaborative Proposal: Mechanisms of Low Temperature Tolerance in Chaparral Shrubs

9507532加利福尼亚南部的Chaparral植被毗邻美国最大的大都市区之一，占据了宝贵的流域土地。灌木林阻止了土壤侵蚀，保持了斜坡的稳定性，为野生动物提供了食物和掩护，并提供了审美和娱乐价值。虽然以前的研究主要集中在灌木林对火和水胁迫的反应上，但越来越多的证据表明，低温耐受性是灌木林分布和丰度的重要因素。基于频率，零度以下的温度事件可能与火灾和干旱一样重要。在冰冻事件发生后，观察到本地植物的生产力下降、伤害和在某些情况下死亡。幼苗可能特别脆弱，因为火灾后植物覆盖面积的减少会使它们在夜间暴露在可能致命的辐射冻结中。本研究将验证以下假设：幼苗比成材更容易受到低温伤害；茎木质部（木材）的冻害栓塞（空气阻塞）可导致茎部死亡；冻害栓塞的数量与木材结构和解冻速度有关。沿海内陆地区最低气温的陡峭梯度和南加州最近被烧毁的地区相结合，提供了一个极好的模型系统。研究结果将对土地使用管理产生影响，例如减轻南加州火灾地区的影响；植树造林项目；并可作为温度敏感树种的气候指标。

9507532 Chaparral vegetation in southern California neighbors one of the largest metropolitan areas in the United States and occupies invaluable watershed land. Chaparral deters soil erosion, maintains slope stability, furnishes browse and cover for wildlife, and provides aesthetic and recreational value. While research has previously focused on the response of chaparral to fire and water stress, there is growing evidence that low temperature tolerance is an important factor underlying chaparral distribution and abundance. Based on frequency, subzero temperature episodes may be as important to chaparral communities as fires and drought. Loss in productivity, injury, and in some cases death of native plants has been observed after freezing events. Seedlings may be particularly vulnerable as the reduction of plant cover after fire can expose them to potentially lethal radiation freezes at night. This research will examine the hypotheqes that seedlings are more vulnerable to low temperature damage than adults, freezing- induced embolism (air blockage) of the stem xylem (wood) can cause shoot death, and the amount of freezing-induced embolism is related to both wood structure and rate of thaw. The combination of a steep gradient in minimum temperatures from the coast inland and recently burned sites in southern California provide an excellent model system. The results will have implications for land use management, such as mitigation of fire-burned areas in southern California; for revegetation projects; and for the use of temperature sensitive species of chaparral as climate indicators.