Spatial distribution characteristics of throughfall in <i>Artemisia ordosica</i> shrublands and its impact on shallow soil moisture in desert steppe.

We investigated the spatial distribution of throughfall in <i>Artemisia ordosica</i>, a typical sand-binding shrub species commonly planted in desert steppe. Based on field observations during the growing seasons of 2021 and 2022, we examined throughfall, vegetation characteristics, meteorological variables, and shallow soil moisture (0-60 cm soil layer) within and outside the shrub canopy, aiming to elucidate the spatial heterogeneity of throughfall in shrublands and assess its influence on soil moisture replenishment. We further quantified the relative contributions of key biotic and abiotic factors influencing throughfall by using boosted regression tree (BRT) model. The results showed that 31 effective rainfall events occurred over the study period, with a cumulative precipitation of 333.15 mm. The mean throughfall amount per event was 8.03 mm, corresponding to an average throughfall rate of 69.9%. The minimum rainfall threshold required to generate measurable throughfall was 0.69 mm. Spatially, throughfall exhibited a heterogeneous pattern characterized by a "rain peak" at the shrub periphery and a "drought center" near the shrub core. The BRT analysis revealed that abiotic factors played a dominant role in regulating throughfall, with rainfall amount contributing the most (89.8%), followed by relative humidity and wind speed. In contrast, the contribution of biotic factors was minor (<3%). The average shallow soil moisture recharge under the shrub canopy (2.88 mm, with a recharge rate of 3.6%·h^-1) was slightly higher than that in the area outside the canopy (2.69 mm and 3.3%·h^-1), with respective increases of 6.6% and 9.1%. However, these differences were not statistically significant. The findings suggested that rainfall under the canopy of <i>A. ordosica</i> provided relatively more effective moisture replenishment to shallow soil layers. Rainfall amount and throughfall amount were the two most critical factors influencing shallow soil moisture recharge.