Phyllosphere pathogen diversity and leaf functional traits covary at a local scale in subtropical forests

The plant pathogenic fungi diversity colonizing plant leaves has been largely understudied, creating a knowledge gap in understanding relationships between plant-pathogen and plant growth trade-offs. Here, we investigated the diversity of phyllosphere pathogenic fungi across 84 individuals from 12 dominant species in a subtropical forest and tested how leaf functional traits and plant ecological strategies (CSR theory) influence pathogen communities. High-throughput sequencing and FUNGuild classification were used to quantify pathogenic fungal diversity, while key traits were used a compute CSR strategy scores. We found that host species, rather than habitat, exerted a stronger influence on phyllosphere pathogenic fungi diversity. Leaf functional traits, including pH, C:N, and dry weight, were shown to affect phyllosphere pathogen diversity. However, stochastic processes primarily drove the spatial variation in phyllosphere pathogenic community assembly. Regression analyses revealed a significant negative association between the relative proportion of Ruderal strategies and pathogen diversity. In other words, as the proportion of traits associated with fast growth and high reproductive potential (i.e., ruderal strategies) increased, pathogen richness and diversity significantly decreased. This counterintuitive finding suggests that, despite expectations of lower defense investments, fast-growing ruderal species may experience reduced pathogen colonization—possibly due to rapid leaf turnover or other mechanisms that limit pathogen establishment. Finally, Variance partitioning further indicated that variation in pathogen diversity was more strongly structured by plant species identity than by spatial or taxonomic scales. Family and intraspecific level explained the highest degree of variation. Our findings provide new insights into how host traits mediate plant–pathogen interactions, with implications for forest management and the conservation of plant diversity in subtropical forests.