Multi-temporal variations in evapotranspiration partitioning and its controlling factors of a xerophytic shrub ecosystem

Partitioning evapotranspiration (ET) into its components of canopy interception (Ic), transpiration (T) and soil evaporation (E) enhances understanding of hydrological cycle and plant water use strategy in drylands. However, variations in all three ET components and their fractions across multi -temporal scales (daily, monthly, annual), and their controlling factors remain poorly understood for shrub ecosystems. In this study, we aimed to address these issues by measuring daily rainfall partitioning, sap flow, soil evaporation and soil moisture in a xerophytic shrub (Salix psammophila) ecosystem in northern China during 2019-2021. We found T dominated ET with a mean ratio of T to ET ranging 61.7 %-71.1 %, which was consistently higher than the mean ratio of Ic and E to ET ranging 12.1 %-41.5 % and 24.5 %-32.2 %, respectively, from daily to annual scales (p < 0.05). There was no significant difference in mean ratio of T to ET among different temporal scales (p > 0.05), while mean ratios of Ic and E to ET were significantly higher at daily scale than those at monthly and annual scales (p < 0.05). Compared with monthly and annual scales, ET components and their ratios at daily scale were more responsive to bio-/abiotic factors. ET components were more susceptible to be affected by the influencing factors when compared to their ratios, regardless of the temporal scales. Specifically, daily ET components and their ratios were mainly controlled by precipitation and solar radiation. In addition, soil moisture also explained 10.2 % and 10.9 % of the variations of daily T and ET, respectively. At monthly scale, however, variations in T and ET were mainly controlled by LAI with explained variance of 26.6 % and 32.4 %, respectively. Our results highlighted the significant differences in ET partitioning and their different responses to bio- and abiotic factors at various temporal scales of the shrub ecosystems in drylands.