Soil Moisture Shapes the Responses of Quercus Wutaishansea Forest Stand Transpiration to Potential Evapotranspiration in the Liupan Mountains, Northwest China

Abstract

Stand transpiration (T) is an important biophysical indicator of the forest hydrological cycle and ecosystem energy partitioning and can be used to determine the effects of drought on forest ecosystems. Therefore, clarifying how changes in soil moisture affect the mechanism of transpiration response to potential evapotranspiration (PET) is crucial for developing forest management strategies based on soil moisture conditions, especially in natural forests in drought-prone semi-arid regions. In the present study, we partitioned the effects of relative extractable soil water (REW) and PET on T in oak (Quercus wutaishansea) forest stands in the Liupan Mountains, northwest China. The results showed that the reduction in REW due to drought resulted in a significant decrease in T. When REW was higher, i.e., above 0.5, there was a linear relationship of T with PET but an exponential relationship when REW was lower than 0.5. Moreover, REW in the soil layer of 20-60 cm rather than that in the soil layer of 0-20 cm plays a decisive role in T during drought. More REW, such that at the mid- and downslope sites, would be helpful to mitigate the decline in T under drought to some extent compared with less REW that at the upslope sites. These remind us that the soil moisture in semi-arid regions should be paid more attention in forest management and vegetation restoration in future.

Keywords: transpiration, potential evapotranspiration, drought, relative extractable water, dryland region