安吉毛竹林水汽通量变化特征及其与环境因子的关系

Water vapor flux variation characteristic and the relationship with its environment factors in phyllostachys edulis forest in Anji

以浙江省安吉县毛竹(Phyllostachys edulis)林生态系统为研究对象,利用涡度相关技术进行观测,获取2011年毛竹林的水汽通量数据,同时结合常规气象观测数据,分析了水汽通量全年变化。结果表明:毛竹林全年水汽通量基本为正值,月尺度上,水汽通量呈单峰型变化趋势,且各月的最大值均在12:00—14:00出现,呈现一定规律性,7月(0.1116 g m-2s-1)最高,12月(0.0209 g m-2s-1)最低;季节尺度上,夏季最高(0.0873 g m-2s-1),呈现典型单峰型变化趋势,春秋季(均为0.0541 g m-2s-1)次之,变化特征与夏季相似,冬季最低(0.0221 g m-2s-1),曲线变化复杂,波动较大。毛竹林全年蒸散量占全年降水量48.26%。2、4、5、11、12月蒸散量略大于降水量,其余月份蒸散量均小于降水量,6月份降水量与蒸散量差别最大。季节尺度上,对毛竹林水汽通量与净辐射进行回归关系分析,夏季最大,R2为0.6111,秋季为0.5295,春季为0.2605,冬季最小0.0455。通过F检验,水汽通量与净辐射有极显著线性关系。在植物生长期,毛竹林水汽通量随饱和水汽压差的增大而增大,植物发育成熟后,当饱和水汽压差增大到一定程度时,其增大反而抑制了水分的蒸散。

Based on the measurements of eddy covariance （EC）, the water vapor flux of Phyllostachys edulis forest ecosystem was analyzed from January to December of 2011 in Anji County, Zhejiang Province of the subtropical China. The annual changes of water vapor flux and its budget, also include the responses to precipitation, net radiation （Rn） and vapor pressure deficit （VPD） were investigated through to combined with conventional meteorological data. The results showed that annual water vapor flux was positive value, which discovered that moso bamboo forest was the source of water vapor, as well as the water vapor flux had distinct diurnal and seasonal variations. On a monthly curve, the diurnal changes of water vapor flux were in a single-peak type, the maximum values were all at 12：00--14：00, showing a regularity pattern, the maximum presented in July （0.1116 g m-2 s-1） ,the minimum （0.0209 g m-2 s-1） in December. On a seasonal scale, the water vapor flux presented a single peak typically in Summer, and the maximum value was 0.0873 g m-2 s-1, the variations of Spring and Autumn were similar to Summer, both of them were 0.0541 g m-2 s-~. However, in Winter it varied much more intricately, fluctuating greatly, which showed that there were some smaller peaks except a high peak. Besides, the annual evapotranspiration of the forest was 744.72 mm, slightly lower than that of other types of woodland Korean Pine forest and Cunninghamia lanceolata forest. The annual evapotranspiration of the moso bamboo forest was about 48.26% of the annual precipitation, which is 1543.10 mm. Except February, April, May, November and December, evapotranspirations of all the other months were less than precipitations. In June, the differences between evapotranspiration and precipitation appeared obviously significant. Rn was the main driving force of evapotranspiration and was a key factor on the energy balance. Through this study of regression relationship between water vapor flux and different net radiation analysis, there were a high correlation between them. And the squares of correlation coefficients （R2） were 0.2605 in Spring, 0.6111 in Summer, 0.5295 in Autumn and 0.0455 in Winter. Therefore, this result showed that there existed significant linear relationship between water vapor flux and net radiation at different temporal scales by F test. In addition, using the data of VPD of the moso bamboo forest from June to September, the height of which was lm from the ground to the canopy, and the result suggested that before moso bamboo vegetation matured, water vapor flux was strongly linearly increased with the increasing of VPD. But the evapotranspiration was depressed after its matured, as the increasing of VPD when it surpassed certain extent. The research suggested that the quadratic equation fitting of correlation coefficient （RE from June to September, 0.4251, 0.2955, 0.3806 and 0.2312） was much higher than the exponential fitting＇s.while the R2 were 0.3708, 0.2021, 0.2666 and 0.2137, and it also displayed that there was significant linear relationship between water vapor flux and VPD by F test during the time series.