Spatial heterogeneity of plant and soil systems at the patch scale in a typical steppe in Inner Mongolia

Spatial heterogeneity in a grassland ecosystem is associated with grassland species diversity and production stability. Understanding the drivers and mechanisms of grassland spatial heterogeneity is essential for the development of best practices in grassland management. To our knowledge, patch-scale spatial heterogeneity of the grassland communities on the steppes on the Mongolian Plateau has not been investigated to date. Here, we investigated the spatial variation of plant communities and soil properties in 216 sites in a rectangular area of 13.5 hm² in a typical steppe dominated by Stipa grandis and Leymus chinensis in Inner Mongolia. Our results showed that plant community patches at these sites could be clustered into four groups, dominated by S. grandis, L. chinensis, Salsola collina, or jointly by S. grandis, L. chinensis, and Cleistogenes squarrosa (mixed patch). The differences in the species compositions among these patches indicated an enhancement of species diversity due to spatial heterogeneity. Soil bulk density, organic carbon (SOC), and nutrients (total nitrogen, TN; total phosphorous, TP) and pH differed among the 4 patch types (P < 0.05), but soil moisture did not (P > 0.05), which suggests that soil nutrients and bulk density are associated with the spatial heterogeneity of plant communities. The differences in soil bulk density and nutrients among these patch types are most likely related to the heterogeneity of grazing impacts at the patch scale. The grassland patches dominated by perennial S. grandis had higher SOC, TN, and TP, and lower soil bulk density than those of patches dominated by annual S. collina. The low nutrient content of the S. collina patches suggests that the growth of dominant species, S. grandis and L. chinensis, was limited on these patches, which provided a favorable condition for the fast growth of annuals such as S. collina using the pulse of water and nutrients following the summer rainfall. Our research provides new insights into the spatial heterogeneity of steppe grasslands, and is helpful for conservation and sustainable management of the steppes.