Nitrogen retention driven by cooperative succession of bacterial communities through promoting nitrogen fixation and inhibiting denitrification during straw composting with amino acids addition

Composting is a biological aerobic fermentation process that decomposes organic solid waste and converts it into humus. However, in the process of mineralization or humification of organic matter, a large amount of nitrogen will be lost. Therefore, it is very essential to find strategies to increase nitrogen retention during composting. This study elucidated the biological mechanism underlying the promotion of nitrogen retention during straw composting through the addition of leucine (TL) and phenylalanine (TP). The results indicated that the total nitrogen (TN) content of TL and TP composting final products were 92.97% and 103.90% higher than that of the initial composting, respectively, and 92.68% and 92.58% higher than CK (no amino acids addition) control group. This was due to the succession of bacterial community structure, from a low-modularity relationship with a small amount of high aggregation to a large number of high modular cooperation. This evolution of bacterial community complexity and stability played an important role in nitrogen transformation. The increase of keystones in TL and TP regulated the change of bacterial community function. The change of this interaction made the nitrogen-fixing gene (nifH) abundance and nitrogen-fixing effect significantly improve and inhibits denitrification in high temperature. The negative growth of nitrogen loss rate also confirmed the key role of nitrogen-fixing bacteria. Therefore, amino acids addition played a positive role in improving the nitrogen retention of straw composting.