九寨沟针阔混交林的夜间液流及其分配特征研究

利用Granier热扩散探针测定九寨沟针阔混交林3个主要树种2013年的树干液流密度, 分析各树种夜间液流的季节变化特征及夜间茎干补水与夜间蒸腾的分配特征。结果表明, 红桦(Betula albosinensis Burk.)和茶条槭(Acer ginnala Maxim.)的夜间液流占全天液流比例多为0~30%, 油松(Pinus tabulaeformis Carr.)多为0~25%, 但在某些特定条件下, 夜间液流占比会超过40%; 生长季各树种夜间液流占比均呈“U”型变化, 生长季初期和末期较高, 生长季中期较低; 典型晴天内, 各树种夜间液流密度均与饱和水汽压差呈极显著的线性关系(R²>0.95), 表明夜间茎干补水和夜间蒸腾同时发生; 红桦、茶条槭和油松的夜间茎干补水和蒸腾分别占夜间液流活动的80.7%和19.3%, 81.4%和18.6%, 63.9%和 36.1%。

Characteristics of Nighttime Sap Flow and Its Partition in a Mixed Forest in Jiuzhaigou Valley

To investigate the characteristics of nighttime sap flow and its partition into nocturnal water refilling and transpiration, the Granier-type thermal dissipation probes were used to measure sap flux density in 2013 in three main species of a mixed forest in Jiuzhaigou Valley. The results showed that the ratio of nighttime sap flow to daily value mainly ranged from 0 to 30% for Betula albosinensis Burk. and Acer ginnala Maxim., from 0 to 25% for Pinus tabulaeformis Carr., and might excess 40% in some special occasions. It showed a “U-shaped” seasonal variation, with lower ratios in the mid-growing season and higher ratios in the early and late growing season. There was a significant linear relationship between nighttime sap flow and vapor pressure deficit during a clear day, indicating the occurrence of nocturnal transpiration along with refilling. The ratios of nocturnal water refilling and transpiration to the total nighttime sap flow were 80.7% and 19.3%, 81.4% and 18.6%, 63.9% and 36.1%, respectively for the three tree species.