Organic matter turnover rates and CO₂ flux from organic matter decomposition of mountain soil profiles in the subtropical area, south China

Two different Ferralsol profiles from the forest and shrub meadow zones in Dinghushan Biosphere Reserve, south China, were sampled at narrow vertical intervals to study soil carbon dynamics in the subtropical area. Soil organic matter (SOM) turnover rates (m) were calculated using numerical models based on SOM Δ¹⁴C. The model results indicate that values of m are high in the upper 10 cm of the profiles and decrease quickly downwards. They suggest that the SOM is composed of compartments with different turnover times. A compartment with rapid turnover rates is predominant in the upper part of the profiles (0-10/12 cm), compartments with slower turnover rates occur in the middle part (10/12-20/70 cm) and only stable compartments occur in the lower part (> 20/70 cm). The CO₂ flux derived from SOM decomposition (CFSD) was calculated from values of m, SOM content, soil bulk density and thickness of various soil layers of the profiles. The results indicate that 98% of the CFSD is from the upper 11 cm of the profiles. The values of m and CFSD for the forest profile are greater than those for the shrub meadow profile. The study suggests that above-ground vegetation is the main factor controlling m and CFSD within the same climate zone, which supports the idea that growth of green crops can intensify the activity of soils as sinks for atmospheric carbon.