Long-term effects of restoration measures on soil C and C: nutrient ratios in a semiarid steppe

Abstract

Quantifying long-term effects of restoration measures on soil carbon (C) and C: nutrient ratios is of great importance for understanding the changes in C cycle of the grassland ecosystem in degradation and restoration, and for managing the grassland for both production and soil C. We investigated soil organic C (SOC) and C: nutrient ratios within the 0–40 cm soil layer in the grasslands restored following the application of different improvement measures, i.e., shallow plowing (SP), harrowing (HA) or natural recovery (NR), and that under sustained animal grazing (GR) in Xilingol steppe (China). The results showed that SOC content and soil C/P decreased, whereas soil C/N increased, significantly with soil depth. Restoration following different measures have all improved SOC contents of grassland ecosystem, and the SOC increasing rate was greatest under NR, and had an order of NR > HA > SP > GR. No significant difference was detected in soil C accumulation rate between shallow plowed (SP: 44.9 g C m−2 yr−1) and harrowed grassland (HA: 60.3 g C m−2 yr−1), and both were significant lower than that in naturally recovered grassland (NR: 123.2 g C m−2 yr−1). Significant linear relationship existed between soil CN and CP. Restored grasslands shared the common slope of soil CN linear regression, which were significantly greater than that of grazing grassland, indicating that ecological restoration changed soil CN coupling relation, and formed a stable soil CN coupling relation. Thus, soil CN stoichiometric relation can be used as an important indicator to diagnose the stages of soil degradation or restoration succession processes of grassland ecosystem.