Deep soil desiccation patterns and ecohydrological feedbacks of vegetation re-establishment in desiccated soils on the Loess Plateau

Abstract

Deep soil water (>200 cm) is a critical water source for sustaining vegetation productivity and long term ecosystem stability in water limited regions. However, under the large scale “Grain for Green” program on the Loess Plateau, deep soil water patterns across different vegetation restoration types remain insufficiently understood. The ecohydrological feedbacks associated with vegetation reestablishment in desiccated soils are also unclear. This study integrated 6,516 observations from 176 sites across the Loess Plateau. We systematically assessed soil water conditions and desiccation characteristics within 0–1000 cm soil profiles under rainfed cropland, natural grassland, artificial grassland, orchards, and ecological forests (including tree and shrub plantations). In addition, a 5-year replanting experiment was conducted on soils with pre-existing deep desiccation (>10 m). The experiment compared the coupled responses of soil water dynamics and plant growth under different vegetation configurations. The results show that deep soil desiccation is widespread during vegetation restoration on the Loess Plateau. Rainfed orchards, ecological forests, and artificial grasslands developed persistent dry layers 3–5 m thick. The most severe desiccation occurred in ecological forests. Following replanting on desiccated soils, deep rooted species (Robinia pseudoacacia L., Caragana korshinskii Kom., and Medicago sativa L.) continuously depleted middle and deep soil water because of their high water consumption. They also preferentially utilized infiltrated rainfall, thereby limiting deep recharge and maintaining or exacerbating soil desiccation. Meanwhile, these species exhibited a rainfall-pulse-driven adaptive growth strategy that supported survival and biomass accumulation. In contrast, shallow rooted vegetation (Poa annua L.) and bare land showed limited utilization of deep soil water. Their low water consumption facilitated downward rainfall infiltration. This promoted the gradual rewetting of desiccated layers from shallow to deeper soil depths, with a maximum recovery depth of 450 cm within five years. Deep rooted vegetation dominated the rainfall responsive water use pattern. In contrast, shallow rooted vegetation or bare land was associated with a water conserving rewetting pattern. The divergence between these patterns reveals a coupled mechanism among soil water storage, rainfall input, and vegetation water use strategies. This finding provides a theoretical basis for vegetation restoration under water limited conditions on the Loess Plateau and in similar dryland regions.