Topsoil moisture fluctuation and its influencing factors under two dominant shrubs in the Gobi Desert

In desert ecosystems, shrubs function as “ecosystem engineers” by redistributing rainfall and shaping topsoil moisture patterns. However, how shrub presence and species identity regulate the spatiotemporal dynamics of topsoil moisture over short and long terms remains a key unanswered question. To address this gap, we investigated two dominant desert shrubs—Reaumuria songarica (R. songarica) and Nitraria sphaerocarpa (N. sphaerocarpa)—during the 2019-2020 growing seasons. By combining daily soil moisture monitoring with periodic gravimetric measurements, we analyzed daily, seasonal, and interannual variations in topsoil moisture dynamics in shrub (R. songarica and N. sphaerocarpa) and bare ground microhabitats to elucidate the effects of rainfall variability and shrub interactions on the spatiotemporal patterns. The results indicated that R. songarica and N. sphaerocarpa microhabitats increased and decreased topsoil moisture, respectively. The magnitude and duration of these effects were regulated by rainfall amount and season, thereby shaping the multiscale dynamic patterns of soil moisture across the three microhabitats. Small rainfall events (R. songarica and bare ground microhabitats. Meanwhile, extreme rainfall events (>25 mm) in autumn markedly increased topsoil moisture across all three microhabitats, with effects lasting up to 32 days. The results revealed scale-dependent patterns in topsoil moisture dynamics. At the daily scale, topsoil moisture under R. songarica and bare ground microhabitats was substantially higher than that under N. sphaerocarpa microhabitats after summer and autumn rainfall events, but not after spring rain events. At the seasonal scale, topsoil moisture under N. sphaerocarpa microhabitats was generally lower than that under the other microhabitats. At the interannual scale, topsoil moisture under N. sphaerocarpa microhabitats was consistently lower than that under R. songarica microhabitats and considerably lower than that under bare ground microhabitats in 2019. Key factor analysis based on RDA indicated that the shrub volume, soil bulk density, and soil hardness collectively explained 31.5% of the variation in postrainfall topsoil moisture across the three microhabitats. In conclusion, the influence of dominant shrubs on topsoil moisture operates across multiple temporal scales, a process governed by the interplay between shrub presence and rainfall variability.