Sap flow of black locust in response to environmental factors in two soils developed from different parent materials in the lithoid mountainous area of North China

Whole-plant water use is affected by meteorological factors, soil water availability, and soil texture. Although water use by plants growing in lithoid mountainous areas with thin soil layers has been studied, the effect of soil parent material on whole-plant water use remained unclear. In the present study, we used thermal dissipation probe sensors to examine the effects of soil water availability and various meteorological factors on black locust sap flow in cinnamon and brown soils, originating from different parent materials. The results showed that vapour pressure deficit (VPD) and reference evapotranspiration rate (ET0) were more closely correlated with sap flow than solar radiation (Rs) and relative humidity (RH), but that Rs and ET0 explained more of the variation in sap flow than did the other two factors. Decreasing ET0 and VPD was produced a more sensitive sap flow response in trees that were growing in the cinnamon soil than in those growing in the brown soil, whereas the sap flow response to relative extractable water (REW) was less sensitive in the cinnamon soil than in the brown soil. REW and ET0 were the main environmental factors affecting sap flow. Furthermore, soil water content in cinnamon soil was not the only water source available to trees, as the exponential curve explained only 56% of the relationship between sap flow and REW. This finding indicated that soil parent material may have an important influence on plant water utilization. Future studies of plant water use should devote more attention to soil parent materials.