Plant pathogenic fungi decrease in soil inhabited by seed-dispersing ants

摘要

One benefit of animal-mediated seed dispersal is that dispersers may deposit the seeds in protected or enriched microhabitats favorable for seedling survival. Ants are a common seed disperser, and seeds deposited in soils occupied by ant colonies have higher germination and survival rates, benefits attributed to enriched soil conditions and protection from seed predators and fire. Fungal pathogens also devastate young plants, and fungal protection may be an additional benefit of ant-mediated seed dispersal. Ants secrete anti-microbial compounds that appear to suppress the spread of fungal and bacterial diseases in ant colonies, and they confer fungal pathogen protection to the seeds they handle. If fungal protection is a potential benefit of ant-mediated dispersal, we expected that ant-occupied soil (soils inhabited by ants for colony nesting) would contain fewer phytopathogenic fungi than proximate soils without ant nests. We tested this hypothesis with ant soils from the Aphaenogaster rudis complex; the dominant seed-dispersing ants in eastern deciduous forests. We investigated published Aphaenogaster soil fungi data and conducted our own metataxonomic analysis of ant-occupied and unoccupied soils to identify phytopathogenic fungi and investigate whether ant colony presence corresponds with reduced plant fungal pathogens in the soil. We found reduced phytopathogenic fungi presence and richness in soils containing ant colonies as compared to nearby control soils indicating that the presence of ant colonies was concomitant with a reduction in plant pathogens. Ant chemical secretions protect colonies from microbial pathogens in the crowded, moist nest conditions. Plant seeds also thrive in these locations and environments, where they are subject to phytopathogenic fungi. Multiple hypotheses explain the benefits ant-mediated seed dispersal provides plants, but heretofore, fungal protection has been suggested, but not tested. Soil occupation by ants corresponds to phytopathogenic fungi declines, which have the potential to benefit plants.