Sheep grazing and local community diversity interact to control litter decomposition of dominant species in grassland ecosystem

- Interactive effects of sheep and plant diversity on litter decomposition were tested.
- Litter decomposition was higher in local species-rich than species-poor communities.
- Sheep grazing accelerated litter decomposition in local species-poor communities.
- Sheep grazing slowed down litter decomposition in local species-rich communities.
- Grazing and diversity exerted negative feedback control over litter decomposition.

Large herbivore grazing, a major land use in grasslands, can constitute a feedback loop with local plant diversity to affect litter decomposition. Here we examined the interactive effects of sheep grazing and local plant community diversity on decomposition of litter of the dominant plant species (Leymus chinensis) in the meadow steppe of China. We found a faster litter decomposition rate in the local species-rich communities compared to the local species-poor communities in the absence of sheep grazing. However, in the presence of sheep grazing, the decomposition rate was significantly reduced in the local species-rich communities while increased in the local species-poor communities. Therefore, sheep grazing and local community diversity constituted a negative feedback loop to modify litter decomposition in this grassland ecosystem. The findings of this study indicate one outcome of herbivore grazing could be to homogenize grassland nutrient cycling in space by balancing litter decomposition rate among local communities, which therefore could increase the homogenization of metacommunity structure. Furthermore, reduced local community diversity may slow ecosystem process rates. Our study indicates that sheep grazing, or equivalent, offsets this negative effect of local plant diversity loss on litter decomposition.