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 carbon and nitrogen storage of different land use types in northwestern Shanxi Loess Plateau].

The soil organic carbon (SOC) and total nitrogen (TN) storage under five different land use patterns, i. e. , poplar and Caragana microphylla plantation, C. microphylla artificial shrubland, poplar plantation, bare land and cropland were studied in the hilly [ness Plateau of northwestern Shanxi. The results showed that the contents, densities and storage of SOC and TN varied remarkably under the different land-use patterns. Soil carbon and nitrogen contents and storage in the 0-20 cm soil layer were significantly higher in the 20-40 cm and 40-60 cm soil layers under each of the five land use patterns. In the same soil layer, the contents and densities of SOC and TN under the five land use patterns were in the order of poplar and C. microphylla plantation > C. microphylla artificial shrubland > poplar plantation > bare land > cropland. The SOC storage in the 0-60 cm soil layer was in the order of poplar and C. microphylla plantation (30.09 t x hm(-2)) > C. microphylla artificial shrubland (24.78 t x hm(-2)) > poplar plantation (24.14 t x hm(-2)) > bare land (22.06 t x hm(-2)) > cropland (17.59 t x hm(-2)). Soil TN storage had the same trend as SOC storage, and TN storage in the 0-60 cm soil layer was the highest (4.94 t x hm(-2)) in poplar and Caragana microphylla plantation, followed by C. microphylla artificial shrubland (3.53 t x hm(-2)), poplar plantation (3.51 t x hm(-2)), bare land (3.40 t x hm(-2)), and cropland (2.71 t x hm(-2)). Poplar and C. microphylla plantation and C. microphylla artificial shrubland were the good land use patterns in the process of vegetation construction and ecological restoration in the hilly Loess Plateau of northwestern Shanxi.