晋西黄土区辽东栎和山杨树干液流对环境因子的响应

Whole-tree sap flow of Quercus liaotungensis and Populus davidiana in response to environmental factors in the loess plateau area of western Shanxi Province,northern China

2012年4—10月,应用TDP热扩散探针技术,对生长季晋西黄土区次生林主要组成树种辽东栎和山杨树干液流速率进行测定,结合同步测定的空气相对湿度(RH)、太阳光合有效辐射(PAR)、大气温度(T)和土壤含水量(θ)等环境因子,分析液流速率对环境因子的响应.结果表明:5、6月,影响辽东栎和山杨树干液流速率的主要气象因子是空气饱和水汽压差(VPD)和PAR;7、8月,影响辽东栎和山杨树干液流速率的主要气象因子是VPD和T.除气象因子外,土壤水分条件也是驱动液流变化的重要因素,降雨后θ的增加能够有效影响液流速率,5、6、7、8月,辽东栎降雨后的平均液流速率比降雨前分别增大了28.3%、48.6%、16.9%、11.5%,山杨在6、7、8月降雨后的平均液流速率比降雨前分别增大了0.6%、4.5%、2.3%,辽东栎的增幅明显大于山杨.辽东栎液流速率对降雨后土壤含水量变化更敏感,表现出更高的耗水能力和需水要求,而降雨后山杨的耗水策略仍较保守.液流速率和VPD的关系可以采用指数饱和曲线函数拟合,降雨前后拟合参数的变化说明土壤水分条件的改善能够促进液流速率更快速地到达饱和值.

Sap flow velocity（ SFV） of Quercus liaotungensis and Populus davidiana,which are two main tree species of secondary forests in the Loess Plateau area of western Shanxi Pro-vince,was measured using a thermal dissipation probe during the growing season from April to October 2012.The responses of SFV to vapor pressure deficit（ VPD）,photosynthetically active radiation（ PAR）,air temperature（ T） and soil water content（ θ） were investigated. The results showed that the diurnal changes of SFV of Q. liaotungensis and P. davidiana were mainly influenced by VPD and PAR in May and June,whereas VPD and T were the determining meteorological factors for the diurnal changes of SFV in July and August. Besides the meteorological factors,θ also had an important effect on SFV. The increases in θ during rainfall events resulted in the increases in SFV of both the two tree species. The average SFV of Q. liaotungensis after rainfall events was 28. 3%,48.6%,16.9% and 11.5% higher than that before rainfall events in May,June,July and August,respectively. The average SFV of P. davidiana only increased,respectively,0.6%,4.5% and 2.3% after rainfall events in June,July and August. It showed that Q. liaotungensis had a higher water demand and was more sensitive to soil water condition than P. davidiana,while the latter could mana-ge its water consumption more conservatively after raining. The relationship between SFV and VPD could be approximately expressed using an exponential saturation function. The change of the parameters of the fitted exponential saturation function indicated that the SFV could quickly reach its maximum value as soil moisture increased.