马占相思整树蒸腾的日变化和季节变化特征

Diurnal and seasonal changes in whole-tree transpiration of Acacia mangium.

为深刻揭示华南丘陵退化荒坡植被恢复树种的水分利用特征,运用Granier热消散式探针法对马占相思的树干液流进行了连续测定,并同步测定样树周围环境因子如光合有效辐射、总辐射、空气温度、空气湿度、土壤湿度等.结果表明,马占相思树干东、南、西、北各方位测得的液流密度存在显著差异,并显著相关;以北方位液流密度为自变量,其他各方位液流密度作为因变量进行回归分析,发现回归系数随时间和个体的变化而变化.对9月和2月的液流和光合有效辐射及水蒸气压亏缺的日变化作了对比,发现存在较大差异,分析认为是由于环境因子如温度低、雨雾多及落叶较多造成的.相关分析得出各样树间整树液流季节变化格型一致.分析了液流与环境因子的相关关系后发现树干液流与光合有效辐射、总辐射、温度、水蒸气压亏缺在不同时间尺度上(日内、日间、年内)均具有显著相关关系;与土壤湿度则在任何时间尺度(日内、日间、年内)不存在相关关系.此外,精确计算得出马占相思整树全年的平均蒸腾量为9 380.9 kg,最大整树蒸腾量为14 076.6 kg,最小整树蒸腾量为6 229.8 kg,个体间差异较大.

In order to explore the water use characteristics of re-vegetation tree species in degraded hilly lands in south China, sap flow of Acacia mangium was measured continuously using Granier＇ s thermal dissipation probe method. Simultaneously, environmental factors such as photosynthetically active radiation （PAR）, global radiation, air temperature, air relative humidity, and soil relative humidity were also monitored. Sap flux density at four orientations （east, south, west and north） on the trunk was significantly different, and the sap flux density at different orientations was highly pair-wise correlated ; but the regression coefficients were different among individual trees and varied seasonally. The seasonal patterns of sap flow of the trees were all similar. The correlations between sap flow, PAR, global radiation, air temperature and VPD were significant at any time scales（hourly, daily and monthly）. However, there was no significant correlation between sap flow and relative soil water content at above time scales. The mean annual sap flow per tree was 9 380.9 kg, while individual tree sap flow ranged from 6 229.8 to 14 076.6 kg according to individual tree＇s social status and canopy size.