Plant phylogeny, traits and fungal community composition as drivers of plant–soil feedbacks

Abstract Plant–soil feedbacks (PSFs) are key drivers of plant community dynamics. However, our understanding of the factors moderating PSFs remains limited. We examined how plant phylogenetic relatedness and functional traits determine PSFs via their influence on rhizosphere fungal communities, especially arbuscular mycorrhizal fungi (AMF) and fungal pathotrophs. We conducted a glasshouse PSF experiment using 21 temperate grassland plant species, where each focal species was exposed to soils conditioned by heterospecific plants of increasing phylogenetic dissimilarity. We tested whether phylogenetic distance between plant species, functional traits or the degree to which species associate with AMF or fungal pathotrophs, explained the magnitude and direction of PSF responses. None of the measured plant traits explained PSFs, although the relative abundance of AMF was weakly and positively related to PSFs. Across all plant species, phylogenetic relatedness did not explain PSFs. However, species‐specific effects of phylogenetic relatedness on the outcome of PSFs were detected. In particular, significant relationships with phylogenetic relatedness were observed only for species characterised by the highest rhizosphere relative abundance of AMF or fungal pathotrophs. For Centaurea nigra and Vicia cracca (both high AMF abundance) and Anthoxanthum odoratum (high pathotroph abundance), we found that PSF became more positive with increased phylogenetic distance between focal and conditioning species, showing a shift towards increased performance in conspecific than heterospecific soils. Meanwhile, as phylogenetic dissimilarity between Poa trivialis (high pathotroph abundance) and the soil conditioning species increased, more negative PSFs were observed, indicating improved performance in soils conditioned by increasingly distant heterospecific species. Synthesis . Our results suggest that plant traits and phylogenetic relatedness are poor predictors of plant–soil feedbacks (PSFs) among temperate grassland plant species. Hence, despite known effects of these factors in shaping rhizosphere microbial communities, the way plant species respond to these microbial communities is not related to the same characteristics. The occurrence of significant relationships between phylogenetic distance and PSFs in species with high relative abundances of mycorrhizal or pathogenic fungi suggests that the tendency to accumulate fungal mutualists or pathotrophs may be an important moderator of the relationship between plant phylogenetic relatedness and the magnitude and direction of PSFs.