Significant loss of soil inorganic carbon at the continental scale.

Widespread soil acidification due to atmospheric acid deposition and agricultural fertilization may greatly accelerate soil carbonate dissolution and CO2 release. However, to date, few studies have addressed these processes. Here, we use meta-analysis and nationwide-survey datasets to investigate changes in soil inorganic carbon (SIC) stocks in China. We observe an overall decrease in SIC stocks in topsoil (0-30 cm) (11.33 g C m-2 yr-1) from the 1980s to the 2010s. Total SIC stocks have decreased by ∼8.99 ± 2.24% (1.37 ± 0.37 Pg C). The average SIC losses across China (0.046 Pg C yr-1) and in cropland (0.016 Pg C yr-1) account for ∼17.6%-24.0% of the terrestrial C sink and 57.1% of the soil organic carbon sink in cropland, respectively. Nitrogen deposition and climate change have profound influences on SIC cycling. We estimate that ∼19.12%-19.47% of SIC stocks will be further lost by 2100. The consumption of SIC may offset a large portion of global efforts aimed at ecosystem carbon sequestration, which emphasizes the importance of achieving a better understanding of the indirect coupling mechanisms of nitrogen and carbon cycling and of effective countermeasures to minimize SIC loss.

Soil C:N:P stoichiometry at different altitudes in Mao'er Mountain, Guangxi, China.

We explored vertical distribution of soil organic carbon (C), nitrogen (N) and phosphorus (P) for examining the relationship between soil C:N:P stoichiometry and both altitudes and soil depths in Mao'er Mountain in Guangxi, South China. A total of ten sites from different altitudes were selected and soil genetic horizon samples were collected along soil profiles at each site. Soil organic C, N, P, pH, bulk density and particle size composition were measured. Results showed that soil C, N, C/P ratio and N/P ratio increased with the increases of altitude. Soil P concentrations and C/N ratio increased within low altitudes then decreased or with no obvious changes. Soil C, N, P, C/P and N/P ratios significantly decreased, whereas C/N ratio did not change with the increases of soil depth. Soil C and N highly coupled within horizons (CV of C/N was 4.0%) and soil P had little spatial variability (CV were 31.0% and 22.0% within altitudes and horizons, respectively). The results from redundancy analysis showed that the first two axes explained 74.8% of the variability of C:N:P stoichiometry. Soil pH, bulk density, and altitude had significant effects on C:N:P stoichiometry, whereas clay, silt, and sand had no effect.