Granier树干液流测定系统在马占相思的水分利用研究中的应用

Application of Granier＇s Sap Flow System in Water Use of Acacia mangium Forest

摘要:

介绍了Granier热消散探针在树干液流测定中的工作原理,并利用该系统长期监测广东鹤山马占相思林14株样树的液流密度,分析了树木个体内和个体之间液流密度的差异、整树和林段水分利用的量化特征。由于树木边材结构以及周围微环境的差别,树木内和个体间的液流密度差异非常明显,变异系数的平均值分别为15.51%-37.26%、37.46%-50.73%。尽管液流密度的差异较大,但同一株树木不同方位的液流密度之间却呈现明显的线性相关（p＜0.0001）,这是重要的特征值,使得只需测定某一方位的液流密度经尺度外推计算整树和林段蒸腾成为可能。树木液流对环境因子响应的变化规律取决于所参照的时间尺度,日变化主要受光辐射、水汽压差等气候因子的控制,而土壤水份对液流的季节变化影响较大。形态特征明显影响树木的液流,高大树木由于边材较厚、树干粗壮和冠幅较宽而承载较多的辐射能量,因而水分蒸腾较高。对树木液流密度在径向和方位上进行适当的整合,可较准确地计算整树和林段蒸腾。由液流估测的马占相思整树和林段蒸腾的结果显示,该群落的水分利用在时间和空间上均有明显的分化。

Abstract:

In order to characterize the variance in sap flow within and between trees, and to quantify the water use of whole tree and of forest stand, Granier＇s thermal dissipation probes were applied to measure sap flux density （J_s） in 14 sample trees in an Acacia mangium forest in Heshan Station, Guangdong. It showed that the differences of sap flux density recorded on a sunny day in July of 2004 were significant within tree （of different azimuthal sides） with coefficient of variability ranging from 15.51% to 37.26%, and among trees ranging from 37.46% to 50.73%. These variations were mainly attributed to the texture of sapwood and microclimate surrounding the point on trunk where the measurements were conducted. However, the sap flux density on different azimuthal sides showed significant linear correlation （p〈0.0001）, which provided a feature value for scaling up whole-tree transpiration from sap flux density measured on only one azimuthal side. The responses of tree sap flow to environmental factors were different and depended on the time scales. The daily sap flow was mainly controlled by climatic factors such as radiation and vapor pressure deficit, whereas the soil moisture had more influence of seasonal change on the sap flow. The morphological features of tree significantiy affected sap flow. Taller trees with larger sapwood area and canopy size that were load with more radiation demonsrated higher whole-tree transpiration. A proper integration of both azimuthal and radial variations in sap flux density within a tree can be scaled for whole-tree transpiration, which can relatively accurately estimate stand transpiration. The estimation of A. magium forest transpiration from sap flow showed obvious temporal and spatial differentiations of water use within the community.