Abiotic environments prevail over plant functional traits in shaping phyllosphere fungal communities of temperate grasslands in China

Phyllosphere fungi play critical roles in plant health and ecosystem functioning. While previous studies have explored the diversity and composition of phyllosphere fungal communities in various ecosystems, they have typically focused on either epiphytic or endophytic fungi at single sites and rarely addressed both groups simultaneously across broad environmental gradients. As a result, the relative importance of abiotic environments, plant traits, and dispersal processes in shaping phyllosphere fungal communities remains unclear, particularly with respect to differences between epiphytic and endophytic fungi. We collected 231 leaf samples from nine sites in temperate grasslands of northern China, and explored the effect of abiotic environments and plant traits on the diversity and structure of phyllosphere fungi at broad spatial scales. Our analysis revealed that aridity, poor soil conditions and leaf pH decreased the relative abundance of endophytic saprophytic fungi, and plants with a "fast-growing" strategy promoted the relative abundance of phyllosphere pathogenic fungi. The positive effects of aridity and poor soils on the richness of endophytic fungi were undermined by soil fungal richness, while the richness and Pielou's evenness of epiphytic fungi was inhibited by the availability of soil resource. Soil organic carbon emerged as a key factor influencing the composition of phyllosphere fungal communities, and dispersal limitation was relatively weak and comparable between endophytic and epiphytic fungi. Our findings provide empirical evidence that abiotic environments prevail over plant traits in structuring phyllosphere fungi at broad spatial scales and reveals assembly patterns that differ from those reported in previous single-site or forest-based studies.