Forage Quality Improves but Ecosystem Multifunctionality Declines Under Drought and Frequent Cutting in Dry Grassland Mesocosms

Dry grasslands are vast, socioeconomically and ecologically important environments, which are increasingly threatened by multiple stressors. We tested whether plant cover composition could mitigate ecosystem services loss under multiple stressors in dry grassland mesocosms by growing the grass sorghum (Sorghum bicolor) alone (Grass cover) or together with the legume serradella (Ornithopus sativus) (Mixed cover) under frequent cutting and/or increasing water stress. We assessed erosion control, carbon sequestration, forage quantity and quality, and soil fertility, individually and simultaneously (i.e., multifunctionality). Contrary to our hypothesis, the Mixed cover did not improve ecosystem services compared to the Grass cover, except for forage quality, which improved by 30%. In general, the stressors had negative effects: cutting reduced erosion control by 20%, forage quantity by 50%, soil fertility by 40% and multifunctionality by 20%, and severe water stress decreased carbon sequestration by 40%, forage quantity by 30%, soil fertility by 10%, and multifunctionality by 10%. Water stress caused 100% serradella mortality, underscoring this legume&rsquo:s vulnerability to increasing aridity. Combined stressors yielded the lowest service provision. Forage quality was the only service that improved under stress: cutting improved it by 40% and severe water stress by 60%. Our results suggest that while systems combining grasses and legumes may enhance forage quality, grass-dominated systems appear more resilient to multiple stressors in drylands, largely due to their superior efficiency in accessing and conserving limited water and nutrient resources. Given the ongoing trends of aridification and land-use intensification, future research should explore adaptive management strategies that prioritize resource-efficient plant species, foster belowground resource retention, and optimize grazing regimes to sustain resilience and multifunctionality in dry grasslands.