Mediterranean grassland soil fungi: Patterns of biodiversity, functional redundancy and soil carbon storage

Soil organic matter is a relevant carbon reservoir and CO2 sink in temperate grassland ecosystems and increased carbon uptake may mitigate climate change. Relatively little is known about the relationship between ecosystem function and soil fungal biodiversity in grasslands. However, this relationship is important because the saprotrophic microorganisms within the decomposer chain may, given their important role in the decomposition processes of litter and dead roots, control soil carbon storage. In this study, we provide the first empirical evidence of natural patterns of soil fungal biodiversity and soil carbon storage in Mediterranean grasslands at different elevations. We observed an asymptotic relationship between morphological and functional trait richness and fungal biodiversity. This relationship is consistent with the redundancy hypothesis of species diversity and ecosystem function. A limited number of fungal species is sufficient to attain morphological and functional variability in the soil fungal assemblages in these grasslands. We found that increasing fungal biodiversity and biochemical specialization were related to higher soil carbon storage (at a higher altitudes and lower slope position), even in fenced-off grasslands. We discuss the main ecological mechanisms controlling soil carbon storage in grasslands within the framework of a conceptual model.