Degraded vegetation and wind erosion influence soil carbon, nitrogen and phosphorus accumulation in sandy grasslands

A field study was conducted in a semi-arid sand land ecosystem in eastern Inner Mongolia, China, to explore the mechanisms underlying how human-induced environmental degradation in sandy grasslands influences ecosystem plant diversity, productivity, soil erodibility, and soil carbon (C), nitrogen (N) and phosphorus (P) accumulation and storage. We investigated (1) C, N and P accumulation to 20cm soil depth; (2) C, N and P storage in plant litter, above- and below-ground biomass; and (3) the rate of surface wind erosion measured as the amount of aeolian soil accumulating in the traps and C, N and P output from the topsoil removal due to wind erosion during the erosive season in four habitats of differently degraded sandy grasslands. Environmental degradation has resulted in significant and differential reductions in soil C, N and P accumulation within the top 20cm soil layer across habitats. On average, the most severely degraded sandy grassland stored 474%, 198% and 56% less soil C, N and P, while the severely degraded sandy grassland stored 215%, 121% and 27% less soil C, N and P and the moderately degraded sandy grassland stored 111%, 60% and 17% less soil C, N and P than did the lightly degraded sandy grassland. Two key variables associated with reduced soil C, N and P accumulation in sandy grasslands as a result of environmental degradation are reduced plant litter and above- and below-ground biomass production (i.e. less plant C, N and P inputs in the soil) and increased C, N and P output from the removal of nutrient-rich topsoil layers resulted from increased rates of wind erosion. This study suggests a complex mechanism by which environmental degradation influences soil C, N and P accumulation and dynamics via its significant effects on ecosystem plant diversity, productivity and soil erodibility.