Effects of herbivore assemblage on the spatial heterogeneity of soil nitrogen in eastern eurasian steppe.
Abstract
The spatial heterogeneity of soil limiting resources is one of the most important factors maintaining biodiversity and ecosystem functions. There is a general concern that herbivore grazing plays a central role in modifying soil resources heterogeneity. However, most studies have examined how large herbivores as a group affect soil heterogeneity. There is limited knowledge about how assemblages of different herbivore species may influence soil heterogeneity, and whether the herbivore assemblage effects might vary with grassland types. Here we conducted a 4-year grazing experiment to examine the effects of different herbivore assemblages (no grazing; cattle grazing; sheep grazing; and mixed grazing of cattle and sheep) on the spatial heterogeneity of soil N availability across three types of grasslands (meadow steppe, typical steppe and desert steppe) in eastern Eurasian steppe. The results showed that all the herbivore grazing increased the heterogeneity of soil N availability in the three grasslands with different precipitation (only cattle grazing and mixed grazing of cattle and sheep in meadow steppe did not reach a statistically significant level). The consistently increased heterogeneity of soil N availability was primarily due to the effect of animal excreta addition, which weakened in drier grasslands, likely because of the slower excreta decomposition. Moreover, sheep excreta contributed more to soil N heterogeneity than that of other herbivore assemblages, and the effect was statistically significant in meadow steppe and typical steppe with relative high precipitation. Synthesis and applications. Our study indicates that sheep could have larger potential to maintain and enhance grassland heterogeneity than cattle especially in grassland ecosystems with high precipitation. We therefore suggest that managing above-ground herbivore species is important for conserving and promoting grassland soil heterogeneity, and that the management should also take into account local environmental conditions such as precipitation.