Search

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. [ABSTRACT FROM AUTHOR]

Fungi play an important role in the accumulation and transformation of soil organic matter (SOM) and nutrient cycling. To investigate the relationship between the fungal community and soil organic carbon functional groups under gradient SOM contents in arable mollisols, arable mollisols with 2%-9% SOM content were collected in Northeast China. Solid-state 13 C-NMR technology was used to explore the differences in the functional group structure of SOM, and ITS high-throughput sequencing was used to investigate the fungal community structure. The potential interactions between different taxonomic groups of soil fungal community and their associations with organic carbon molecular structures were compared by constructing molecular ecological networks under low SOM (2%-5%) and high SOM (7%-9%) conditions. The 13 C-NMR results indicated an increase in the relative abundance of Alkyl C (25.8% to 35.9%). The decrease in Alkyl C/O-Alkyl C indicated a smaller degree of decomposition in high SOM soils. Sordariomycetes and Mortierellomycotina dominated the fungal community and their relative abundance increased with the SOM gradient ( P <0.05) from 14.33% to 28.17% and from 7.32% to 23.14%, respectively. The network analysis showed simpler ecological topological properties of the fungal community in low SOM soils, with lower numbers of nodes, edges, and average clustering coefficients than those in high SOM soils. A closer relationship between fungi and organic carbon functional groups, especially LOC, was observed in low SOM soils. The random forest model showed that LOC had the largest amount for fungal interactions in low SOM soils (10%), followed by recalcitrant organic carbon (ROC). In comparison, LOC contributed less to the variations in fungal interactions in high SOM soils (7.4%). With globally increasing soil carbon loss, the limition of the carbon resources, especially the reduction of LOC, may reduce the stability and ecological functions of soil fungal communities.

Climate conditions, soil properties and management practices control soil nitrification process which affects nitrogen cycling and balance in agro-ecosystems. The interaction of temperature, rainfall, soil type and fertilization on the soil nitrification process was studied by a soil transplantation experiment installed in 3 experiment stations of Chinese Ecological Research Network, i.e., Hailun, Fenqiu and Yingtan Agroecological Experiment Station, which represents middle temperature, warm temperature and middle subtropical zone, respectively. Three types of cropland soils were selected, i.e., neutral black soil (Phaeozem), alkaline Chao soil (Cambisol) and acidic red soil (Acrisol). Then one-meter depth soil profiles for each soil were transplanted in 3 stations to build the field experiment. The two-year experimental results (2006-2007) showed soil nitrification intensity (SNI) changed with the temperature and rainfall during the maize tasseling stage. From Hailun to Yingtan, with an increase of monthly average temperature from 22.3 degrees C to 26.8 degrees C and the monthly rainfall from 100.8 mm to 199.6 mm, SNI decreased by 64.2%-67.2% for black soil, 52.1%-52.5% for Chao soil, and 41.7%-75.2% for red soil, respectively. There were significant negative correlations between SNI and temperature and rainfall, with a correlation coefficient of r = -0.354 (p < 0.01) and r = -0.290 (p < 0.01), respectively. The total number of soil nitrobacteria and the intensity of soil nitrification was affected by soil types, which increased in a sequence of Chao soil > black soil > red soil. Among soil properties, pH affected SNI significantly, with a correlation coefficient of r = 0.551 (p < 0.01). In generally, climate condition (temperature and rainfall), soil type and fertilization present an integrated impact on soil nitrification process, and there were significant interactions of climate x soil type, climate x fertilization, soil type x fertilization, and climate x soil type x fertilization.