Soil moisture shapes the responses of Quercus wutaishansea forest stand transpiration to potential evapotranspiration in the Liupan Mountains, Northwest China

With climate change, accelerated increases in potential evapotranspiration (PET) and decreases in relative extractable water (REW) are increasingly affecting stand transpiration (T). However, the responses of T to PET under limited REW are still unclear, especially in forests of dryland region. In the present study, we partitioned the effects of 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 dryland regions should be paid more attention in forest management and vegetation restoration in future.