Distinguishing Carbon and Nitrogen Storage in Plant and Soil of Grassland Under Different Climates in the Loess Plateau, China

Grassland covers approximately one-third of the area of the Loess Plateau and plays an important role in the carbon (C) and nitrogen (N) cycles. This study was conducted to estimate the C and N storage of grassland ecosystems under different climates (semi-humid, semi-arid and arid). Results indicated that about 90% of the ecosystem C and N were stored in the soil. Soil organic carbon (SOC) density of grasslands in different climatic zones decreased in the order, semi-humid (53.34 Mg C ha−1) > semi-arid (50.22 Mg C ha−1) > arid (19.13 Mg C ha−1) climatic zone. Also, grassland in the semi-humid climatic zone had the highest belowground biomass C (1.01 Mg C ha−1) and N (0.25 Mg N ha−1) density; whereas grassland in the semi-arid climatic zone had the highest aboveground biomass C (1.06 Mg C ha−1) and N (0.26 Mg N ha−1) density. C and N storage of grassland ecosystem in the arid climatic zone was significantly lower than that in the other two climatic zones (p < 0.05). The vegetation community density, cover, and richness, above- and belowground biomass, and climatic factors significantly influenced the C and N distribution in this region (p < 0.05). The mean annual precipitation emerged as the most important variable for C and N accumulation. Grassland with mean annual precipitation of 350–630 mm might have high C and N sequestration potential. Results of this study provide reliable reference information for predicting C and N dynamics in similar agroecological systems.