广州地区荷木夜间树干液流补水的影响因子及其对蒸腾的贡献

Water recharge through nighttime stem sap flow of Schima superba in Guangzhou region of Guangdong Province,South China:Affecting factors and contribution to transpiration

明确树木夜间水分补充现象有助于提高总蒸腾量和冠层气孔导度估算的精确度,进一步认识冠层蒸腾与树干液流之间存在的时滞关系.本研究采用热消散探针法测定了广州地区的荷木树干液流密度,同步监测了主要的环境因子,从不同时间尺度分析了树干夜间液流的水分补充现象.结果表明:与白天相比,荷木夜间液流密度较小,旱季变化幅度比湿季大;夜间水分补充的时间段主要在前半夜(18:00—22:00);年内各季节夜间水分补充量之间没有显著差异,与环境因子之间的偏相关关系不显著,但与胸径、树高、冠幅、树干生物量、冠层生物量的回归曲线拟合很好,表明树形特征和生物量能更好地解释夜间补水的变化;各季节夜间水分补充量对总蒸腾量的贡献有显著差异,旱季明显高于湿季.

To understand the nighttime water recharge of tree through its sap flow is beneficial to the precise estimation of total transpiration and canopy stomatal conductance,and to the further understanding of the time lag between canopy transpiration and stem sap flow.By using Granier＇s thermal dissipation probe,this paper measured the stem sap flow of Schima superba,and synchronously measured the main environmental factors including air temperature,relative humidity,photosynthetically active radiation,and soil moisture content,and also analyzed the water recharge through nighttime stem flow of S.superba at daily and seasonal scales.The sap flow density of S.superba was lower at night than at daytime,and the nighttime sap flow density had a larger variation in dry season than in wet season.The water recharge at night generally started from sunset when radiation was approaching zero,and lasted up to midnight（18：00-22：00）.No significant difference was observed in the nighttime water recharge among seasons,and no significant correlations were found between the nighttime water recharge and environmental factors,but the nighttime water recharge was well regressed with the diameter at breast height,tree height,tree canopy size,stem biomass,and canopy biomass,suggesting that tree form features and biomass could better explain the nighttime water recharge.The contribution of nighttime water recharge to the total transpiration varied significantly with seasons,and was obviously higher in dry season than in wet season.