Ecosystem openness to nitrogen and phosphorus controlled by fertilisation, mowing and plant diversity in a grassland

Abstract Ecosystem openness to nitrogen (N) and phosphorus (P) is determined by the balance of N and P inputs (e.g. fertiliser) and outputs (biomass removal). Plant biodiversity enhances nutrient use efficiency due to species' complementary uptake driven by their variation in roots and growth requirements. It remains unclear how biomass removal (e.g. via mowing) can intensify the effect of N and P input on ecosystem openness, N and P removal and balance, and to what degree these processes are related to plant biodiversity. To assess this, a field experiment was conducted to examine the effects of N fertiliser (0 vs. 4 g N m −2 yr −1 ), P fertiliser (0 vs. 1 g P m −2 yr −1 ) and mowing frequency (3–4 vs. 6–8 mowing events year −1 ) to induce variation in N and P availability as well as plant species diversity. We showed that a greater plant N uptake and N loss were driven by N fertilisation where we observed an increase of δ 15 N (as a measure of openness) of the plant community over time. Phosphorus removal and loss were enhanced by higher mowing frequency with a negative balance when no fertiliser was applied, likely due to mowing‐induced variation in community composition, shortening of the vegetative stage and a greater biomass removal. Furthermore, N fertilisation (without P application) enhanced P removal causing a negative P balance, likely because of N‐induced promotion of vegetative growth and biomass production. Biodiversity enhanced the ability of plant communities in taking up more N and thereby increasing removal with mowing as revealed by greater plant δ 15 N with increased plant diversity, likely due to a greater resource use efficiency. Moreover, the relationship between N and P removal to Shannon–Weiner biodiversity index varied over the year that could be driven by seasonal variation in plant species growth, nutrient demand and availability. Our results provide important information about managing N and P retention and removal through mowing frequency and fertilisation and highlight that these nutrient dynamics are mediated by plant biodiversity. Read the free Plain Language Summary for this article on the Journal blog.