CONICET | Buscador de Institutos y Recursos Humanos

The capacity of species to persist at low levels of a limiting resource is a key mechanism underpinningcompetitive success. Thus, anthropogenic nutrient deposition may differentially affect certain plant functionalgroups. N-fixing legumes have specialist nutrient-acquisition strategies and are expected to be especiallyvulnerable to increased global nutrient deposition, particularly in regions with nutrient poor soils. The diverselegume family is crucial for nutrient cycling, provisioning of protein-rich crop and pasture production, and as asource of genetic resources for crop and fodder plant breeding. Here, we evaluated the additive and synergisticeffect of nutrient addition on legume cover, richness and biomass in grasslands, worldwide. We measured theresponse of native and non-native N-fixing legumes to 3-6 years of standardized experimental additions of N, P,and K (10:10:10 g m-2 yr-1) plus other nutrients (i.e. Sulphur, Magnesium and trace elements, hereafter K+) in afactorial combination replicated in 45 grasslands spanning 6 continents. Using linear mixed effects models, andthe log-ratio (LR=log (legumeslast/legumesinitial )] as a relative effect, we analysed soil nutrients, local plantcommunity composition, photosynthetically active radiationand climatic conditions, as contingences for thenutrient effects on legumes, globally.Chronic N addition reduced legume cover by 32%, richness by 12% and biomass by 43%, consistently amongnative and non-native legumes. In contrast, P addition significantly increased legume cover (34%), whereaslegumes did not respond to K+. Despite the benefits of P addition, its combination with N resulted in a netreduction of legume cover (22%), indicating that N combined with P resulted in negatively sub-additive cover ofN-fixers. In contrast, non-legume forbs and grasses increased with N addition, concomitant with the reduction inlegume cover. Moreover, N and P addition led to lower PARnon-legume . Finally, N addition promoted greaterlegume decline at sites with lower initial soil N and less legume decline in soils with higher NPratio, highlightingthe detrimental impact of N addition on legumes in N-poor soils. Our global assessment is consistent withbroader conclusions regarding impacts of N and P enrichment on grasslands and highlights the potential scaleof impact of anthropogenic N-fixation on the abundance and diversity of plants with specialized N-acquisitionstrategies as legumes, regardless of the supply of other nutrients.