In the context of global climate change, precipitation variability poses profound challenges to plant communities in arid and semi-arid ecosystems, where water availability is the primary limiting factor for plant growth and coexistence. To explore the diversity of functional traits and water adaptation strategies of coexisting plants in response to precipitation changes, this study focused on the desert steppe of Ningxia, China. A field experiment was conducted using rainout shelters to simulate five precipitation treatments: 50% reduction (P_-50%), 30% reduction (P_-30%), ambient precipitation (P_CK), 30% increase (P_+30%), and 50% increase (P_+50%). During the early, middle, and late growing seasons, we measured a comprehensive set of functional traits for five coexisting plant species, including leaf traits, root traits, and biomass allocation traits. The results revealed two key findings:(1) The synergistic evolution among functional traits of different species formed differentiated drought-resistant strategies. Stipa breviflora gradually shifted to a more conservative water use pattern through the synergistic adjustment of root-shoot ratio and leaf morphology. Lespedeza potaninii relied on deep root expansion to enhance deep water acquisition. Convolvulus ammannii adopted a drought-tolerant strategy, optimizing root and leaf structures to maintain water balance. Polygala tenuifolia was sensitive to changes in water conditions, quickly adapting to drought through the trade-off between root investment and water storage; Leymus secalinus relied on shallow water absorption and grew rapidly, with both preferring an "resource-acquisitive" strategy. Except for Convolvulus ammannii, Stipa breviflora, Lespedeza potaninii, Leymus secalinus, and Polygala tenuifolia all adopted the drought-resistant strategy of reducing above-ground growth and increasing underground growth. (2) Extreme precipitation treatments (P_+50% and P_-50%) significantly increased the level of functional diversity in the desert steppe plant community. Compared with the P_CK treatment, under P_+50% and P_-50% treatments, the community's functional richness index (FRic) increased by 839% and 350% respectively; the functional evenness index (FEve) increased by 462% and 487% respectively; the functional divergence index (FDiv) increased by 756% and 456% respectively; and Rao's quadratic entropy index (QE) increased by 458% and 379% respectively. This indicates that under extreme water conditions, community functions tend to diversify, niche differentiation is enhanced, and the functional differences and synergistic effects among species are improved. This study provides a new perspective for understanding the adaptation mechanisms and stability maintenance of plant communities in arid ecosystems.This study provides novel insights into how plant communities in arid ecosystems adapt to precipitation variability through trait differentiation and trade-offs, highlighting the critical role of functional trait diversity in maintaining community stability under changing climates. These findings contribute to a deeper understanding of adaptation mechanisms in water-limited ecosystems and offer theoretical support for predicting and managing the responses of desert steppe communities to future climate change.