Rainfall deficit reduces biodiversity and destabilizes a saline-soil plant community

Rainfall deficits are reshaping plant communities worldwide, yet their impacts on salinity-stressed ecosystems remain unclear. In saline systems, rainfall is essential for flushing soil salts and sustaining biodiversity. Here, we tested the hypothesis that rainfall deficit undermines ecosystem stability by eroding biodiversity in these systems. We conducted a 7-year experiment in the Yellow River Delta, simulating summer-autumn rainfall loss under both ambient and elevated winter-spring temperatures. Rainfall loss increased soil salinity (+43.3% under ambient; +25.2% under warming), promoted stress-tolerant species dominance (+36.9%; +8.76%), and reduced species richness (−26.6%; −14.7%). These shifts led to a consistent decline in community stability. Analytical partitioning demonstrated that this destabilization was primarily driven by biodiversity loss rather than by dominance or compensatory effects. Structural equation modeling further confirmed the rainfall-biodiversity-stability pathway. Our findings show that rainfall deficit destabilizes plant communities in saline soils by weakening biodiversity-based buffering, revealing an overlooked vulnerability to intensifying climate extremes.