Impacts of naturally-occurring soil fungi on seeds of meadow plants

Although soil fungi may represent an ecologically important cause of mortality of buried seeds, few studies have provided direct evidence of the pathogenicity of fungi colonizing seeds in natural habitats. In response, we conducted a series of experiments to investigate the impacts of soil fungi from a range of habitats on seeds of meadow plants. We compared the survival of seeds of four grasses in five habitats, and isolated fungi from these seeds. We then tested the pathogenicity of selected isolates against two standard sets of plant species: the original four grasses and a broad range of old field species. We found that the soil community contained a large variety of seed-colonizing fungi. Some, but not all, examples of these fungi caused seed mortality; others may be harmless commensals. Some of these isolates negatively affected a broad range of plant species, but others had a more restricted host range; as a result, pathogenicity varied depending upon the particular plant-fungus combination. Few between-habitat differences in seed survival were detected. Our results demonstrate that fungal seed pathogens are common, ubiquitous, and potentially lethal, but that their effects depend on the particular combination of fungus and plant species considered.