New progress has been made in the research on the accumulation mechanism of soil organic carbon in agriculture

Carbon and nitrogen inputs strongly affect the formation, turnover and sequestration of soil organic carbon (SOC) in agroecosystems. However, it is unclear how nitrogen fertilization can regulate the contribution of plant-derived carbon and microbial carbon to SOC sequestration under straw returning conditions. In order to fill this gap, based on an 18-year field positioning experiment of straw returning and nitrogen fertilizer application, Professor Tian Xiaohong’s team from the School of Resources and Environment of Northwest A&F University tried to explain the above scientific questions by measuring plant and microbial biomarkers and enzyme activity. Recently, the research results were published in Soil Biology and Biochemistry.

The result is titled “Nitrogen fertilizer builds soil organic carbon under straw return mainly via microbial necromass formation”. (Photo courtesy of the thesis group)

Straw returning and nitrogen application increased soil organic carbon content by 20% and 10%, respectively. Specifically, straw returning increased the proportion of total lignin phenols (mainly vanillin and eugenyl) in SOC by 16%, but reduced the proportion of cinnamon in SOC by 7.5%. This means that some plant residues are selectively retained, while compounds that are less stable than cinnamon are more easily broken down. In addition, the increase of phospholipid fatty acid (PLFA) content and enzyme activity with the return of straw to the field indicated that the decomposition of straw was accelerated. Based on the estimation of amino sugars, straw returning did not change the ratio of microbial residues to SOC. Lignin and amino sugars jointly determined that the contribution of plant-derived carbon and microbial carbon to SOC sequestration remained unchanged under straw returning conditions. Nitrogen application increased the proportion of microbial residues (especially bacterial residues) carbon in soil organic carbon by 6%, thereby reducing the maximum contribution of plant residues to SOC. Therefore, nitrogen application accelerates the use of straw by microorganisms, thereby accelerating the formation of microbial residues. In terms of PLFA composition, Ascomycetes and Basidiomycetes, Actinomycetes, and Gram-negative bacteria are the key contributors to the formation of microbial residues and SOCs. Nitrogen application increased the activity of nitrogen acquisition enzymes and promoted the participation of microbial necrosis blocks in the nutrient cycle, thereby stimulating the growth of plants and microorganisms. Overall, straw returning increased both plant and microbial source carbon, while nitrogen application stimulated microbial biomass and enzyme activity, thereby increasing the ability of straw to be converted into microbial residues. (Source: Yan Tao, China Science News)

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