北方和温带森林生态系统的蒸腾耗水

Transpiration of Boreal and Temperate Forests

北方和温带森林地处气候变化敏感的中高纬度地区,认识其蒸腾耗水过程的时空动态及其控制因子是评价和预测森林在气候系统中作用的基础.本文综述了北方和温带森林蒸腾耗水的近期研究结果,从叶片、个体和林分3个尺度综合分析了树木蒸腾耗水的变异性及其影响因子,并探讨了其中的尺度转换问题.主要结论如下:尽管相同生活型树木的蒸腾耗水量变异性较大,但针叶树的平均蒸腾耗水量在叶片和个体尺度上显著低于阔叶树,而在林分尺度上针叶林和阔叶林之间差异不显著.3个尺度上的蒸腾作用均受太阳辐射、蒸汽压亏缺、土壤含水量等环境因子的影响,且存在因子间的交互作用,但主导控制因子因时空尺度而异.单株树木蒸腾量与胸径、边材面积和树高均呈显著正相关;林分日蒸腾量最大值与叶面积指数相关显著,而生长季日蒸腾量平均值则与年降水量和年均温呈正相关.这些蒸腾速率与生物环境因子之间的关系模型和不同空间尺度之间的联系是目前森林蒸腾过程尺度转换的基础.本文还讨论了该领域研究中存在的问题和研究热点.

Boreal and temperate forests occur in mid- to high-latitudes where the ongoing climate change is significant. Understanding tempo-spatial dynamics and controlling factors on the transpiration of these forests is fundamental for assessing and predicting the roles of the forests in the climatic system. We reviewed recent studies on the transpiration of boreal and temperate forests to examine the variations in and influencing factors on the transpiration at leaf, individual and stand scales, and to discuss potential issues in spatially scaling of transpiration. There was a great variability in transpiration rates within coniferous and broad-leaved trees, but the mean rate for the former was significantly less than that for the latter at both leaf and individual scales. No significant difference, however, was found at the stand scale. The transpiration was affected by solar radiation, vapor pressure deficit, soil water content, and their interactions, but the controlling factors varied with spatial and temporal scales. The water consumption of individual trees was significantly positively correlated to the diameter at breast height, sapwood area and height. The maximum daily rate of stand transpiration was significantly correlated to the leaf area index. The mean daily rate of stand transpiration in growing seasons was positively related to the mean annual precipitation and temperature. These relationships and linkage of transpiration processes across spatial scales were the current framework of scaling the transpiration process from leaf to stand scales. Potential research issues and priorities in this field were also discussed. Fig 4, Tab 2, Ref86