Effect of Zoige alpine wetland degradation on the density and fractions of soil organic carbon

Abstract

Following the degradation succession from swamp to swampy meadow to meadow in Zoige, a swamp, swampy meadow, and meadow, which were all adjacent, were chosen as research plots. The soil organic carbon (SOC) content of 0cm to 50cm soil layers decreased with degradation. However, the SOC contents all decreased with soil depth before and after the degradation, degradation led to larger soil bulk density. Thus, the SOC density at 0cm to 50cm were 36.95% and 51.94% lower in the swamp and meadow, respectively, than that in swampy meadow. The carbon–nitrogen (C:N) ratios in the three plots were not significantly different. However, the extent of C:N ratio was more extensive in the meadow than in the swamp and swampy meadow. Dissolved organic carbon (DOC) changed in the same trend as SOC with degradation and soil depth. At 0cm to 50cm soil depth, the ratio of DOC to SOC was lower in the swampy meadow than in the swamp. In addition, the soil hydrological condition in the meadow was not beneficial for DOC moving down. Thus, in 0cm to 20cm soil layers, the ratio of DOC to SOC was higher in the meadow than in the swamp and swampy meadow. This finding was contrary to that in 20–50cm soil layers. With the wetland degradation content of light fraction (LF) organic carbon (LFOC) decreased. The swampy meadow had the highest HOFC content, followed by the swamp, and then the meadow. The meadow had the highest C:N ratios in LF and HF in 0cm to 50cm soil layers, followed by swamp and then swampy meadow. The C:N ratio in LF was higher than in HF. The ratio of LFOC and HFOC to SOC in the swampy meadow was not significantly different from that of the swamp. The LFOC-to-SOC ratios of the swampy meadow and swamp were significantly higher than that of the meadow. This result is contrary to that of HFOC. With degradation, more residues of animal and plants decomposed more thoroughly. At 0cm to 50cm soil layers, SOC content decreased, SOC density first increased then decreased, and most SOC was stored in a more complex and stable form. After degradation, the long-term positive feedback of SOC under warming climate maybe even stronger than that before degradation, and that may promote climate change more. Then, the ecological environment in Zoige, located in high latitude and cold area which is sensitive to climate change, may be influenced more severely.