The role of heartwood water storage for sem-arid trees under drought

Abstract

Stem water storage is an important water pool in forests. However, we know little about the heartwood water use processes and the water use strategies of trees in semi-arid temperate forests. We investigated Simon poplar (Populus simonii), a heartwood water storage tree species. A combination of methods (sap flow, the dendrometer and the soil–plant–atmosphere canopy model were used to trace the water use dynamics of Simon poplar trees. The aim was to understand how this heartwood water storage tree species survives under drought stress.Our field data showed that P. simonii had significantly higher heartwood water content (60%) than other tree species (30%) in the same region. The enhanced tree water deficit (TWD) and continuous stem shrinkage showed that the heartwood water supply was able to maintain sap flow (1.5–4.6 mm/d) during early growing season droughts. The strong water absorption ability of the roots resulted in the quick recovery of TWD, which caused the rain water could hardly reach 50 cm depth in the soil. The weakened link between transpiration and root water assimilation of heartwood water storage trees meant that sap flow was more sensitive to drivers such as air temperature (R = −0.71, p < 0.01) and vapor pressure deficit (R = 0.69, p < 0.01).These results suggest that heartwood water storage may buffer drought events during the growing season and reduce the wide fluctuation in interannual precipitation. Therefore, heartwood water storage needs to be taken into account when calculating the soil–plant–atmosphere continuum and creating tree survival models.