Functional group of grassland plants affects their fungal symbionts more than long-term fertilisation in a field experiment

Abstract

Fertilisation of productive grasslands affects plant communities and the relationship between plants and fungal symbionts. We investigated the effects of manipulated nutrient availability, vegetation composition, and host identity on the communities of symbiotic fungi – arbuscular mycorrhizal fungi (Glomeromycotina, G-AMF) and fine root endophytes (Mucoromycotina, M-FRE). We collected individuals of 16 plant species from the plots of a long-term experiment in a semi-natural grassland with manipulated fertilisation (nitrogen and phosphorus added over 4 years) and vegetation composition (20 years of selective weeding of functional groups). Data from the roots of individual plants were complemented by sampling roots and rhizosphere soil in experimental plots to characterise the effects of fertilisation and plant community on G-AMF at the plant community level.

We found a strong effect of fertilisation on the composition of both fungal groups, but the differences among host species and particularly between their functional groups (forbs and C3 grasses) were much larger. Fertilisation reduced the abundance of both fungal groups in plant roots with a larger decline in G-AMF, and the α-diversity of G-AMF decreased substantially. Our results did not confirm difference of fertilisation effects on fungal symbionts between forb and grass species that was observed in earlier short-term pot experiment. Our results demonstrate the urgent need to perform studies examining the response of symbiotic fungal communities to experimental factors under field conditions, preferably by sampling roots of a wide range of individual plant species.