Nitrogen‐fixing plants increase soil nitrogen and neighbouring‐plant biomass, but decrease community diversity: A meta‐analysis reveals the mediating role of soil texture

Abstract

Abstract Several recent regional studies have cast doubt on the widespread assumption that nitrogen‐fixing plants (N‐fixers) act as facilitators of neighbouring plant communities. We conducted a meta‐analysis to synthesize the effects of N‐fixers on plant communities and to understand how ecological context moderates these effects. We analysed studies that assessed paired effects of N‐fixers and non‐fixers on soil N, neighbouring‐plant (non‐fixer) biomass and plant community diversity; ecological moderators included climate, soil texture and N‐fixer growth form and invasive status. N‐fixers led to higher soil N and neighbouring‐plant biomass, but lower community diversity compared to non‐fixers. The effect of N‐fixers on neighbouring‐plant biomass was strongly mediated by soil texture; N‐fixer invasive status and growth form were also significant mediators of the facilitative effects of N‐fixers. Synthesis: N‐fixer effects lie on a continuum between facilitation and suppression that is moderated by intrinsic and extrinsic processes, and this analysis provides insight into how these factors moderate the effects of N‐fixers. Overall, N‐fixers facilitate neighbour biomass but suppress diversity, though high variation in these effects can be explained in part by ecological context.