Long-term mowing did not alter the impacts of nitrogen deposition on litter quality in a temperate steppe

- N deposition improved litter quality by enhancing N and reducing lignin in litter.
- Annual mowing would not alter the impacts of N deposition on litter quality.
- Changes in plant species composition indirectly alter community litter quality.

Litter quality plays an important role in determining litter decomposition and nutrient cycling in terrestrial ecosystems. We investigated the main and interactive effects of nitrogen (N) addition and mowing on litter quality (%N, lignin, cellulose, and hemicellulose concentrations and lignin:N ratio) of four dominant species in a temperate steppe in northern China. In addition to species-specific impacts, both N addition and mowing can alter community composition by changing relative dominance of individual species, with consequences on litter decomposition. Nitrogen addition significantly increased N concentration of shoot litters at species- and community-level, while mowing did not affect N concentration. Nitrogen addition decreased concentrations of lignin, cellulose, hemicellulose, and lignin:N ratio at both species- and community-level. Mowing decreased lignin and cellulose concentrations, increased hemicellulose concentrations, and did not affect lignin:N ratio at species-level. Mowing decreased cellulose concentrations but did not alter lignin and hemicellulose concentrations, and lignin:N ratio at the community level. Furthermore, mowing did not alter the impacts of N addition on litter quality at both organization levels. Our results suggested that both N addition and mowing can influence litter quality by affecting individual species litter quality and community structure, and thus regulate the processes of litter decomposition and nutrient cycling in grassland ecosystems through a plant-mediated pathway. Importantly, our results showed that the role of annual mowing as a widely-used ecosystem management strategy globally appears to be limited in mediating the impacts of N deposition on plant-mediated nutrient cycling.