Decomposition characteristics of organic materials and their effects on labile and recalcitrant organic carbon fractions in a semi-arid soil under plastic mulch and drip irrigation

Labile organic carbon （LC） and recalcitrant organic carbon （RC） are two major fractions of soil organic carbon （SOC） and play a critical role in organic carbon turnover and sequestration. The aims of this study were to evaluate the variations of LC and RC in a semi-arid soil （Inner Mongolia, China） under plastic mulch and drip irrigation after the application of organic materials （OMs）, and to explore the effects of OMs from various sources on LC and RC by probing the decomposition characteristics of OMs using in-situ nylon mesh bags burying method. The field experiment included seven treatments, i.e., chicken manure （CM）, sheep manure （SM）, mushroom residue （MR）, maize straw （MS）, fodder grass （FG）, tree leaves （TL） and no OMs as a control （CK）. Soil LC and RC were separated by Huygens D＇s method （particle size-density）, and the average soil mass recovery rate and carbon recovery rate were above 95%, which indicated this method was suitable for carbon pools size analysis. The LC and RC contents significantly （P〈0.01） increased after the application of OMs. Moreover, LC and RC contents were 3.2%-8.6% and 5.0%-9.4% higher in 2016 than in 2015. The applications of CM and SM significantly increased （P〈0,01） LC content and LC/SOC ratio, whereas they were the lowest after the application of TL. However, SOC and RC contents were significantly higher （P〈0.01） after the applications of TL and MS. The correlation analysis indicated the decomposition rate of OMs was positively related with LC content and LC/SOC ratio. In addition, lignin, polyphenol, WOM （total water-soluble organic matter）, WHA （water-soluble humic acid）, HSL （humicdike substance） and HAL （humic acid-like） contents in initial OMs played important roles in SOC and RC. In-situ nylon mesh bags burying experiment indicated the decomposition rates of CM, SM and MS were significantly higher than those of MR, FG, and TL. Furthermore, MS could result in more lignin derivatives, WHA, and HAL polymers in shorter time during the decomposition process. In conclusion, the application of MS in the semi-arid soil under a long-term plastic mulch and drip irrigation condition could not only improve soil fertility, but also enhance soil carbon sequestration.

Carbon sequestration processes and mechanisms in coastal mariculture environments in China

China is the global leader in mariculture production. Increasing sequestered marine carbon(also known as blue carbon) via mariculture activities is a promising approach for mitigating climate change and promoting the development of a low-carbon economy. Mariculture blue carbon is also considered an important component of China's "sea granary". In addition to shellfish and macroalgae yields, which represent carbon removed from mariculture environment, blue carbon also includes other important components, which have been largely neglected in the past, such as the carbon transformed by microbes,dissolved organic carbon(mainly referred to as recalcitrant dissolved organic carbon), and sedimentary particulate carbon. Hence,from different aspects, a comprehensive study on the formation processes and mechanisms of carbon sequestration is of great significance for comprehensively unveiling the carbon sequestration capability in coastal mariculture environment, which will contribute to the sustainable development of the fishery economy and construction of an ecological civilization. Moreover, it may add significant economic benefits to the future carbon-trading market.