毛白杨茎干不同方位夜间液流变化规律及其主要影响因子

为明确毛白杨(Populus tomentosa)不同方位夜间蒸腾量(Nt)及茎干充水量(Sr)等夜间液流活动的规律, 探究不同方位Nt和Sr的主要影响因子, 该研究使用热扩散的方法监测了宽窄行模式下栽植的毛白杨茎干不同方位夜间液流, 并用图像法区分Nt和Sr。使用自动气象站和机械式张力计监测太阳总辐射(R_s, kW·m^-2)、空气温度(T_a, ℃)、空气相对湿度(RH, %)、风速(v, m·s^-1)、土壤水势(ψ, kPa)等环境因子。通过比较各方位的Nt和Sr等液流活动的大小情况及其与环境因子之间的相关性得到方位间夜间液流的差异性以及各方位夜间液流的主要影响因子。结果显示: 宽行距位于东侧的样树西方位的Nt和Sr均最大, 其中西方位的Sr显著大于其他3个方位; 北方位的Nt显著小于其他3个方位; 其他方位间的Nt和Sr无显著差异; 各方位夜间茎干充水量占夜间液流量的比例(Sr/Q)无显著差异。宽行距位于西侧的样树西方位的Nt和Sr亦均最大, 其中西方位的Sr显著大于东方位和南方位; 南方位的Nt最小, 显著小于西方位和北方位, 其他方位间的Nt和Sr无显著差异; 南方位的Sr/Q显著大于其他3个方位。各方位的Nt和Sr均与水汽压亏缺(VPD)有显著的正相关关系, 部分方位Nt和Sr与T_a和RH有显著相关关系, 没有任何方位Nt和Sr与v和ψ有显著相关关系。Nt和Sr方位间的差异(Nt_CV、Sr_CV)与VPD、T_a、RH、v和ψ均无显著相关关系。此外, Sr受白天的液流活动的影响显著。综上所述, 毛白杨不同方位Nt和Sr等液流活动具有较大的差异, 且西方位是优势方位; VPD是影响各方位Nt和Sr的主要气象因子。

Azimuthal variation in nighttime sap flow and its mainly influence factors of Populus tomentosa

Aims To clarify the azimuthal regularity of nocturnal sap-flow activities of Populus tomentosa, which includes nocturnal transpiration (Nt) and stem water refilling (Sr), and explore the main impact factors of Nt and Sr in different orientations.Methods The thermal dissipation method was used to monitor the nocturnal sap flow of P. tomentosa planted in wide and narrow rows patterns. The image method was used to distinguish Nt and Sr. An automatic weather station measured global solar radiation (R_s, kW·m^-2), air temperature (T_a, ℃), relative humidity (RH, %), wind speed (v, m·s^-1) and other environmental factors. Mechanical tensiometers measured soil water potential (ψ, kPa). The differences of nocturnal sap-flow among orientations and their main impact factors were determined by comparing the magnitudes of Nt and Sr and their correlations with the impact factors.Important findings The results showed that, for trees on the east-wide-row, the west orientation has the largest Nt and Sr. The Sr in the west orientation was significantly larger than that in the other three orientations. In contrast, north oriented Nt was significantly smaller than that in the other three orientations. There was no significant difference in Nt and Sr among other orientations and the proportion of Sr accounted for the nighttime sap flow (Sr/Q) in all orientations. For trees on the west-wide-row, Nt and Sr in the west orientation were also the largest, and the Sr in the west orientation was significantly larger than that in the east and south. The Nt in the south orientation was the smallest and significantly smaller than that in the west and north. There was no significant difference in Nt and Sr among other orientations. The Sr/Q in the south orientation was significantly larger than that in the other three orientations. The Nt and Sr had significantly positive correlations with vapor pressure deficiency (VPD), and Nt and Sr in some orientations had significant correlations with T_a and RH, but Nt and Sr in all orientations had no significant correlation with v and ψ. The variation coefficient of Nt and Sr among the four orientations (Nt_CV and Sr_CV) had no significant correlation with VPD, T_a, RH, v and ψ. In addition, the Sr was significantly affected by the daytime sap flow. In conclusion, there were significant differences in nocturnal sap flow of P. tomentosa such as Nt and Sr, with west being the most dominant. VPD was the mainly meteorological impact factor of Nt and Sr in all orientations at night.