干旱（致死）过程中兴安落叶松水力特征动态变化

Severe droughts have been associated with regional-scale forests mortality worldwide. Determing the physiological mechanisms of drought-induced tree mortality is therefore one of a key research priority for forestry scientists for future investigations. The objective of this project is to reveal the temporal dynamics of hydraulics underlying drought mortality based on general hydraulic framework, directly relevant to hydraulic failure in situ. We established two different levels of rainfall manipulation experiments (control, 50% rain exclusion, and 100% rain exclusion) in three plots replicated three times in Dahurian larch plantations during the growing seasons to monitor the real hydraulic behaviour of trees in a natural environment at Maoershan Forest Research Station, Northeast Forestry University. We will utilize existing equipment and instrumentation to implement the treatments, monitor environmental conditions and make ecophysiological and growth measurements. We will explore the problem from a whole-plant perspective by investigating hydraulic traits directly and in situ including the changes of xylem cavitation and embolism, vulnerability to xylem embolism, stem sapflow, water potential, and stomatal conductance during chronic and acute water stress, and root, leaf and xylem anatomical characteristics to try to identify the physiological mechanisms contributing to the tree drought mortality.

干旱导致树木死亡的生理机制因缺乏野外实例而成为世界林业科技研究热点之一。本项目以气候变化敏感区- - 高纬度北方森林优势种- - 兴安落叶松为研究对象，通过基本保持树木自然生长环境的野外原地定位控雨实验，基于观测生态学，采用水力胁迫指标与水分通量指标相结合，就地连续系统地监测不同干旱强度兴安落叶松木质部空穴化栓塞、水分运输速率及针叶气孔导度动态变化过程，揭示不同干旱强度兴安落叶松在土壤-针叶之间木质部水力联系的全景动态变化过程及其定量化关系。研究结果为树木因干旱死亡提供实例，并为未来可能的干旱化趋势下兴安落叶松的进一步发展提供一定的理论依据，并具有重要的科学意义。

项目以气候变化敏感区的高纬度北方森林优势种，具有重要的木材生产与生态功能的兴安落叶松为研究对象，通过基本保持树木自然生长环境的野外原地定位控雨实验，基于观测生态学，采用水力胁迫指标与水分通量指标相结合，就地连续系统地监测不同干旱强度兴安落叶松水势、水分参数、水分运输速率及针叶气孔导度动态变化过程。结果表明兴安落叶松枝条中午水势由低到高依次为减雨100%、减雨50%、对照。减雨100%、减雨50%和对照兴安落叶松枝条中午水势季节变幅依次为0.81，0.68和0.54MPa，前两者与对照样木中午水势之差最高值分别为0.49和0.37MPa。3个处理样木枝条清晨与中午水势之差保持基本稳定，均约为0.71MPa。减雨100%和减雨50%样木针叶气孔导度较对照下降84%和79%，水分利用效率较对照升高140%和58%。减雨100%和减雨50%样木枝条相对含水量相似，平均较对照低7%。不同处理样木压力－容积曲线主要水分参数保持相对稳定。以上结果表明干旱处理后，兴安落叶松能够通过降低气孔开度，提高水分利用效率，自身进行一定程度的渗透调节，保持相对稳定的清晨中午水势梯度和相对含水量。在等水/非等水行为连续体中，兴安落叶松具有近等水特性。该结论对于未来可能的干旱化趋势下兴安落叶松的进一步发展提供了重要的理论依据。