Divergent nutrient strategies mediate plant diversity responses to key functional group loss in desert steppes

Background Key plant functional groups (PFGs) are crucial for maintaining desert steppe stability. Their loss may trigger ecosystem degradation by disrupting plant–soil nutrient cycling and altering plant diversity. Methods A three-year field removal experiment was conducted in a desert steppe to investigate the effects of selectively removing key plant functional groups—graminoids, legumes, and their combination—on plant diversity, plant–soil nutrient strategies, and underlying mechanisms. Results Results showed temporal shifts in the Shannon and dominance indices following an inverted “V” pattern, while β-diversity heterogeneity increased spatially. Graminoid removal reduced species turnover but increased nestedness, alleviating plant carbon limitation by enhancing nitrogen and phosphorus accumulation. Legume removal intensified carbon limitation despite increasing soil nitrogen. Plant diversity was significantly correlated with plant–soil total carbon and soil moisture. Nutrient strategies were the strongest predictors of α- and β-diversity, with aboveground biomass, C/N ratios, bulk density, and soil moisture also key. Structural equation modeling indicated graminoid removal indirectly reduced α-diversity via decreased biomass and plant carbon, while legume removal directly increased β-diversity. Conclusion The loss of either PFG drives deterministic ecological processes through nutrient pathways, whereas combined loss directly reduces diversity. Protecting key PFGs—especially graminoids—and understanding their role in nutrient cycles are essential for desert steppe conservation.