Species richness is regulated by shallow soil moisture under variable precipitation

Climate change exacerbates global precipitation imbalances, with potential impacts on plant diversity in desert steppes in diverse terrestrial ecosystems. Compared with meadow and typical steppes, desert steppe could be more sensitive to changing precipitation. However, experimental evidence on how changing precipitation affects plant diversity is still scarce. Compared with meadow and typical steppes, desert steppe could be more sensitive to changing precipitation. However, experimental evidence on how changing precipitation affects plant diversity is still scarce. Based on this, we designed a study to simulate the effects of precipitation on plant diversity in the desert steppe so as to provide theoretical support for the reasonable management, sustainable development and utilization of the desert steppe. We investigated plant diversity and soil moisture content under simulated 2 conditions of extreme precipitation to quantify analyze the effects of precipitation on species richness and soil moisture content in the desert steppe. We established four precipitation treatments in the desert steppe: precipitation reduced by 50% (P1), ambient precipitation (Control, P2), precipitation increased by 50% (P3), and precipitation increased by 100% (P4). We monitored the plant richness, and soil moisture from 2016 to 2018, from May through October. The results showed that: (1) Soil moisture content in the P4 treatment increased by up to 127.8% in 2018 across the 0–40 cm soil profile, while P3 only increased shallow moisture (36.5% at 0–10 cm). (2) Reduced precipitation significantly decreased plant species richness by 59.7% and 42.8% in 2017 and 2018, respectively, while increased precipitation (P3 and P4) did not significantly enhance richness. (3) Species richness showed a significant positive correlation with soil moisture content at 0–10 cm, the relationship between soil moisture content and plant species richness is significantly influenced by precipitation treatment and soil depth. The promoting effect of shallow soil moisture on species richness is more prominent under conditions of increased precipitation. These findings demonstrate that desert steppe biodiversity is highly sensitive to reduced precipitation and shallow soil moisture depletion. Enhancing surface soil moisture retention—through water-conserving vegetation or microtopography management—could be an effective strategy to buffer biodiversity loss under increasing climatic variability.