Belowground pathogen transmission: identifying the processes of soilborne fungal pathogens build-up and effects on plant growth
Soil-borne pathogens are drivers of plant community dynamics, enhancing plant diversity and productivity by selectively controlling dominant plant populations. Yet, the mechanisms behind these effects remain poorly understood, particularly regarding how pathogen transmission and host growth responses relate to plant species diversity and composition within communities. We tackled this by planting Leucanthemum vulgare and Arrhenatherum elatius phytometers in experimental plots from a long-term biodiversity experiment, varying in plant species richness and composition. After three months, we used amplicon sequencing to track pathogen accumulation in phytometers' roots and measured its impact on biomass. We correlated these data with plant community richness, phylogenetic distance to phytometers, and shifts in fungal communities in soil and roots. Phylogenetic relatedness between phytometers and neighboring plants heightened the accumulation specific pathogen in L. vulgare roots, primarily transmitted through soil and secondarily via potential root contacts. In contrast, pathogen recruitment in A. elatius was unrelated with the diversity or composition of plant communities. Surprisingly, host-specific pathogen build-up did not affect the growth of either phytometer species. Our findings highlight the complex interplay between plant community properties, host-pathogen interactions, and currently unidentified factors in shaping soil-borne pathogen dynamics and their impacts on overall grassland productivity.