Dominant species drove the balance between biodiversity and productivity in mown grasslands under nitrogen fertilization

Abstract

Annual mowing, a main management strategy of grasslands, would reduce primary productivity, though might increase plant diversity. Nitrogen (N) fertilization is widely used to raise productivity in global pastures, but always results in biodiversity losses. It is thus a challenge to balance the divergent impacts of mowing and N fertilization on biodiversity and productivity. Here, we examine 9-year responses of aboveground net primary productivity (ANPP) and species richness to mowing across a N addition gradient (0, 2, 5, 10, 20, and 50 g N m⁻² year⁻¹) in a temperate steppe. The negative impacts of mowing on ANPP were exacerbated over time under N fertilization with rates at or lower than 10 g N m⁻² year⁻¹ but were reversed by higher N fertilization rates. Such responses of community-level ANPP were largely driven by the dominant grass, Leymus chinensis (L.c.), instead of species richness. Nitrogen fertilization reversed the negative impacts of mowing on the contribution of L.c. to community-level production over time, with less time being needed for the critical reverse under higher fertilization rates. A “win–win” pattern of biodiversity and production could be reached in the mown grasslands under the N fertilization rate of 5 g N m⁻² year⁻¹, as evidenced by no temporal variation in both production and biodiversity over time in comparison with grasslands under ambient conditions (unmown and non-fertilization). Our results highlight the role of dominant species instead of species diversity in driving the fundamental functioning of mown grasslands and thus facilitate adaptive grassland management.