Carbon and nitrogen dynamics in native Leymus chinensis grasslands along a 1000 km longitudinal transect in northeast China.

The unprecedented variations in global precipitation regime could profoundly impact terrestrial ecosystem structure and function, with consequent feedback to climatic change. However, little is known about complexity in precipitation effects on grassland ecosystem carbon (C) and nitrogen (N) processes at regional scales. We investigated the patterns of shoot and root biomass, litter mass, soil C and N content, microbial community composition and C and N mineralization at 18 sites along a 1000 km precipitation gradient in native Leymus chinensis grasslands of northeastern China. The results show that, with increasing mean annual precipitation (MAP), the biomass of total plant, shoot and litter gradually increased while root biomass remained nearly constant along the gradient. Surprisingly, both soil C and N mineralization rates showed quadratic relationships with MAP, likely due to the relative changes in temperature, soil arbuscular mycorrhizal fungi biomass and N availability. Although soil total C and N content presented sustained increases with water availability, heavy fractions of C and N content reached stable and saturated phases in mesic sites. Overall, ecosystem C and N sequestration enhanced with water availability in terms of C and N storage in shoot, root, litter, and soil along the precipitation gradient. It was concluded from the current study that regional precipitation regime and the indirect effects of precipitation on changes in soil properties and microbial communities would strongly influence on ecosystem C and N dynamics. The temperate grasslands of northeastern China could be utilized as significant ecosystem C and N sinks in the context of mitigating climate change. [ABSTRACT FROM AUTHOR]