The nitrogen‐fixing potential of plant communities depends on climate and land management

Abstract

Aim The occurrence, relative richness and abundance of N‐fixing plants are the main features of the N‐fixing potential of vascular plant communities. We aimed to unveil how climate, biome type and land management regime affect the N‐fixing potential of vegetation. Since the world is witnessing an invincible transition of all those environmental factors during the last century, we examined the global growth trends of N‐fixers throughout recent history. Location Global. Taxon Vascular plant species. Materials and Methods We conducted a meta‐analysis of publicly available vegetation data from 290 communities. Combined with the species' N‐fixation capability, we examined the occurrence, abundance and richness of N‐fixing vascular species across varying climate conditions, land use regimes and potential habitat types. Results There are relatively more N‐fixing vascular plants in warmer and drier climatic conditions. Management of communities by cutting woody plants, grazing and mowing hay increases the number and abundance of N‐fixing species. The effect of management is pronounced in wet conditions, where a dense canopy would otherwise emerge. As a result, semi‐natural grasslands exhibit higher N‐fixer occurrence than natural grasslands and non‐tropical forests, cessation of management results in a temporary increase in the abundance of N‐fixers. Repeated observations of sites indicated that the global occurrence of N‐fixers increased slightly in managed communities from 1906 to 2018, but there were no other temporal trends. Main conclusions The overall number of N‐fixers in plant communities is low. The occurrence, relative richness and abundance of N‐fixing species are higher in sparse vegetation in dry climates and in extensive management where biomass is removed from communities. A probable explanation is the high light availability in dry vegetation and due to biomass removal, which provides a competitive advantage to light‐demanding N‐fixers. A lack of consistent temporal trends suggests that global change is not yet an active driver of N‐fixing potential in plant communities.