Drought intensity shifts the roles of dominant species traits and species diversity on productivity resistance in arid grasslands

The intensification of drought under climate change impairs the productivity and stability of grassland ecosystems. Yet, how the mechanisms regulating aboveground net primary productivity (ANPP) resistance of arid grasslands across drought gradients remain poorly understood. Here, we quantified the effects of drought intensity on ANPP resistance using a five-year precipitation gradient (ambient, -20%, -40%, -60%) in the desert steppe of Inner Mongolian. We found that drought treatments of -20%, -40% and -60% reduced annual average ANPP by 40.2%, 55.0% and 55.1%, respectively. Multi-year cumulative drought at -40% and -60% significantly reduced both ANPP and its resistance. Although the magnitude of decline was similar across intensities, the underlying drivers diverged. Under moderate drought (-20%), resistance was primarily driven by the functional traits of dominant species, whereas under severe drought (-40% and -60%), the effect of dominant species weakened and species richness became the main driver. Our findings demonstrate that increasing drought intensity weakens the role of dominant species while enhancing the contribution of species diversity in sustaining ecosystem resistance. This study highlights the necessity of conserving both dominant species and species diversity to maintain the functionality and stability of arid grassland ecosystems under future climate drying.