Carbon flux and soil organic carbon content and density of different community types in a typical steppe ecoregion of Xilin Gol in inner Mongolia, China

Carbon fluxes and contents are integral components of the global carbon cycle. The photosynthetic and respiratory rates were measured at the levels of leaves and canopies for different community types in a typical steppe ecoregion in Xilin Gol, Inner Mongolia, Northern China. Soil Organic Carbon (SOC) content and density and above-biomass were surveyed in each community type. The results show: 1) thicketized Caragana microphylla and Achnatherum splendens communities exhibit higher above-ground biomass, Maximum Net Photosynthesis Rate (Pnmax), Gross Ecosystem Productivity (GEP), Net Ecosystem Exchange (NEE), and Ecosystem Respiration (ER) (p < 0.05) than other communities; 2) degraded Artemisia frigida community contained significantly lower biomass, Pnmax, and NEE (p < 0.05), but significantly higher ER (p < 0.05) than the native Leymus chinensis community, 3) degraded Allium polyrhizum community exhibited the lowest levels of all measured indices (p < 0.05); 4) thicketized and degraded communities exhibited significantly lower SOC content and densities than the L. chinensis community (p < 0.05). The research suggests that the typical steppe communities undergoing shrub encroachment or degradation may ultimately lead to decreases in SOC content and densities by as much as 15–30% and weakened carbon sink functioning of typical steppe ecosystems.