Herbaceous leaf hydraulic trade-offs shape ecosystem function across the Mongolian Plateau

Plant hydraulic traits are fundamental to ecosystem drought responses, yet their integrated roles in mediating community-level functions remain unclear, especially for widespread herbaceous plants in drylands. Through a systematic investigation of herbaceous communities at 306 sites along a precipitation gradient of 152–411 mm across the Mongolian Plateau. We reveal that a community-wide trade-off between plant hydraulic efficiency and safety fundamentally organizes ecosystem function. Increasing aridity drives a strategic shift from efficiency- to safety-oriented traits. This governs a core functional trade-off: hydraulic efficiency enhances aboveground biomass by supporting greater photosynthetic carbon assimilation but reduces water-use efficiency and ecosystem stability, whereas safety traits exhibit the opposite pattern. Our quantified trait-based framework explains substantial variance in biomass (43%), water-use efficiency (40%), and ecosystem stability (60%). These findings establish a predictive mechanism for vegetation dynamics and provide essential insights for resilience-focused ecosystem management.