干旱区植物群落土壤水盐及根系生物量的空间分布格局

Spatial distributions of soil water,salts and roots in an arid arbor-herb community

为研究干旱区群落根系生物量的空间分布格局及其与土壤中水分、盐分的关系,以宁夏沙湖地区的沙枣-芨芨草群落为研究对象,以立木冠幅的20%为带宽,由立木向空旷地依次划分8个冠幅梯度带(Z1-Z8),采用分层挖掘法对群落中植物根系生物量密度、土壤含水率、土壤溶液电导率的垂直与水平分布特征进行了研究。结果表明:随着离沙枣立木距离的增加,群落中植物根系生物量密度逐渐减小,总根系生物量密度较高层次的埋深渐次增加,各层次土壤含水率及不同土壤层次间土壤含水率的差异性依次变大,表浅层土壤溶液电导率趋势性上升,但在较深层次,位于立木冠层垂直投影区边缘的Z3带的电导率最低,向沙枣立木方向、空旷地方向两侧递增;同时发现,群落中两种主要物种间根系生物量密度较高的土壤层次总体上相互分离,离立木较近各带出现下层土壤含水率低于上层的逆含水率梯度层。总体上,群落中地下生物量、土壤水分、土壤溶液电导率的垂直与水平分布特征揭示,植物根系吸水与土壤水分蒸发是影响土壤剖面中盐分、水分分布与运动的两个主导因子。

To understand the spatial distributions of root systems and their potential controlling factors such as soil water content （SWC） and salinity in the arid regions of China, we conducted a field study in an Elacagnus angustifolia- Achnatherum splendens community developed on saline-alkali soils in Sand Lake, Ningxia Autonomous Region of the Northwest China. Specifically, eight locations from the base of E. angustifolia individuals to the adjacent open area were placed in a 50 m × 50 m plot. The width of the gradient was set to be 20% of the crown diameter. We excavated five soil pits along the transect to measure root biomass, SWC and salinity at 5 vertical depths. We found the changes of the following variables as one moves away from the plant base： decreased mean root biomass density （RMD） in each soil layer, lowered SWC in each layer, and elevated variation among the layers and the electric conductivity （EC） increases in top layers. However, the EC in deep soil layers showed a concavity pattern with a minimal value at the edge of crowns. Interestingly, we also found that the soil layers with the highest RMD of the two dominant species tended to be vertically separated; and there existed a vertically-reversed change of SWC near the plant base. Our field data on the horizontal and vertical distributions of belowground biomass, SWC and EC supported us with a preliminary conclusion that plant absorption and evaporation are the two primary drivers affecting the distribution and movements of salts and water in the soil.