减雨处理环境下刺槐冠层气孔导度变化特征

Canopy Stomatal Conductance of Robinia pseudoacacia Under Rainfall Exclusion Treatment

[目的]研究冠层气孔导度对蒸腾驱动因子响应的敏感性伴随减雨处理可能发生的变化,以期为揭示树木对气候环境因素的适应策略以及合理制定植被恢复措施提供理论依据。[方法]基于Granier热扩散探针长期监测的刺槐树干液流动态和同步观测的气象数据,比较分析减雨处理和对照环境下冠层气孔导度特征及其对蒸腾驱动因子敏感性的响应。[结果](1)在生长季,刺槐冠层气孔导度日变化与空气水汽压亏缺和太阳辐射保持相同的趋势,但减雨处理样地的冠层气孔导度整体上低于对照样地,同时两样地7月份的冠层气孔导度都明显大于其他月份。(2)刺槐日均冠层气孔导度与日均太阳辐射和空气水汽压亏缺分别符合线性和对数曲线的拟合关系。减雨处理样地冠层气孔导度与各驱动因子的拟合斜率均低于对照样地,由于生长季前期降雨较为充沛且平均土壤含水量高于中后期,各样地在生长季前期的拟合斜率相对较高。(3)冠层气孔导度对空气水汽压亏缺响应的敏感性与参比冠层气孔导度呈线性相关关系,减雨处理样地的敏感性明显较低,同一样地的敏感性也在土壤含水量较高的生长季前期略高。[结论]刺槐冠层气孔导度日变化在不同月份的峰值差异与林分叶面积变化等物候节律或土壤水分等环境因素有关。各样地及不同时期冠层气孔导度对蒸腾驱动因子敏感性具有差异,减雨处理会削弱冠层气孔导度对蒸腾驱动因子的响应敏感性。总体来说,该地区刺槐林分响应空气水汽压亏缺的能力较强,实施减雨处理后调控能力有所下降,但维持在正常水平。

[Objective]The sensitivity of canopy stomatal conductance to transpiration driving factors and the possible changes with rain reduction treatment were studied in order to provide a theoretical basis for revealing the adaptation strategies of trees to climatic and environmental factors and for reasonably formulating vegetation restoration measures.[Methods]Based on the long-term monitoring of trunk sap flow dynamics of Robinia pseudoacacia by Granier's thermal diffusion probe and the synchronously observed meteorological data,the characteristics of canopy stomatal conductance and its sensitivity of response to transpiration drivers under rain reduction treatment and control environment were compared and analyzed.[Results](1)In the growing season,the diurnal variation of canopy stomatal conductance of R.pseudoacacia maintained the same trend as that of air vapor pressure deficit and solar radiation,but the canopy stomatal conductance of the treated sample plot was generally lower than that of the control plot.At the same time,the canopy stomatal conductance of the two sample plots in July was significantly higher than that of other months.(2)The daily average canopy stomatal conductance of R.pseudoacacia conformed to the fitting relationship of linear and logarithmic curves with daily average solar radiation and air vapor pressure deficit,respectively.The fitting slopes of canopy stomatal conductance and driving factors in the rain reduction sample plots were lower than those in the control plots.Due to the abundant rainfall in the early growth season and the higher average soil water content in the middle and late growth season,the fitting slopes of various plots in the early growth season were relatively high.(3)The sensitivity of canopy stomatal conductance in response to air vapor pressure deficit was linearly correlated with the reference canopy stomatal conductance.The sensitivity of rain reduction treatment sample plot was significantly lower,and the sensitivity of the same plot was also slightly higher in the early growth season with high soil water content.[Conclusion]The peak value difference of stomatal conductance of R.pseudoacacia canopy in different months is related to phenological rhythm such as the change of stand leaf area or environmental factors such as soil moisture.The sensitivity of canopy stomatal conductance to transpiration drivers is different in different plots and different periods.Rainfall reduction treatment will weaken the sensitivity of canopy stomatal conductance to transpiration drivers.In general,R.pseudoacacia stands in this area have a strong ability to respond to the air vapor pressure deficit.After the implementation of rain reduction treatment,the regulation ability has decreased,but maintained at a normal level.