Bedrock lithology dictates plant water-use niches in Karst ecosystems

Conventional models of plant-water relations prioritize climatic and edaphic factors, largely overlooking the foundational role of bedrock. In water-limited karst ecosystems, where soil is thin and hydrology is fracture-controlled, the lithological template may critically govern vegetation function. This study tests the hypothesis that bedrock composition—specifically, the contrast between dolomite and limestone—creates distinct hydrological niches that filter for divergent plant functional strategies, thereby determining ecosystem vulnerability. We conducted a monthly trait-based analysis of 13 dominant woody species across paired dolomite and limestone terrains in Southwest China. We integrated measurements of water-source use (xylem δD and δ¹⁸O) with key leaf economic traits (water content, area, specific area, chlorophyll). We found that dolomite-supported plants exhibit a consistent water-conservative syndrome: significantly lower leaf water content, smaller leaf area, lower specific leaf area, and reduced chlorophyll (P < 0.01). Isotopic data revealed that dolomite plants underwent pronounced seasonal shifts in water acquisition, indicative of reliance on fleeting, shallow moisture pockets. In stark contrast, limestone-supported plants maintained more stable trait values and exploited a more reliable water source, likely from deeper, rock-hosted reservoirs. This fundamental divergence demonstrates that bedrock lithology is a primary selective force, engineering plant hydraulic strategies at the community level. Consequently, dolomite landscapes foster inherently less resilient communities more vulnerable to climatic extremes, while limestone systems support greater hydrological buffering capacity. Our findings establish a bedrock-centric framework for plant hydrology, with urgent implications for predicting climate change impacts and guiding conservation in karst regions and other bedrock-dominated ecosystems worldwide.