Abstract
Aims Cover crops enhance agroecosystem multifunctionality by modulating biodiversity, yet knowledge of their functional diversity remains limited. This study aimed to systematically evaluate the effects of cover crop species richness (SR) and functional group richness (FGR) on ecosystem multifunctionality (EMF) in citrus orchards. Methods This study assessed 33 cover crop planting schemes in citrus orchards in Southwest China, using six species arranged in gradients of SR (1, 2, 3, 4, 6) and FGR (1, 2, 3). Seasonal variations in soil properties, cover crop yield, and weed biomass were measured. Individual ecosystem functions and EMF across SR and FGR gradients were evaluated. The Random Forest Model and Structural Equation Modeling identified key drivers and mechanisms of EMF. Results (1) Cover crop polycultures suppressed weeds, increasing seasonal cover crop yield by 10–30% compared to single-species cover crops. They reduced soil temperature in spring, summer, and autumn while increasing it in winter. (2) SR and FGR exhibited quadratic correlations with EMF. FGR had a stronger influence, maximizing EMF (Mmde = 13.66) at a lower threshold (Tmde = 77%), compared to SR (Mmde = 12.86, Tmde = 84%). (3) Key EMF predictors included cover crop yield, soil alkali-hydrolyzable nitrogen, weed biomass ( p < 0.01), and soil organic matter, temperature, urease activity (0.01 < p < 0.05). SR and FGR directly enhanced EMF via cover crop yield (0.51) and indirectly via reduced weeds biomass (-0.33). Yield and weed biomass further acted through soil properties (temperature: 0.06, organic matter: 0.09, alkali-hydrolyzable nitrogen: 0.26). Conclusions FGR manipulation outperforms SR for enhancing EMF, offering a sustainable citrus orchard management strategy.