Dynamics of nirK type denitrifying bacterial community in static aerobic high temperature composting

Abstract:

[Background] In the process of composting, different denitrification microorganisms interact with each other to produce a large amount of gaseous nitrogen, which not only leads to nitrogen loss, but also reduces the compost efficiency. However, the current knowledge about the changes in the structure of denitrifying bacterial community, especially the correlation between the community structure and physicochemical factors is still lacking. [Objective] We studied the denitrifying bacteria in compost to reveal the dynamic changes of denitrifying bacterial communities and to provide scientific data of the mechanism of compost nitrogen cycle. [Methods] We designed a static aerobic high-temperature composting process to treat dairy manure and rice stalk. High throughput sequencing technique was used to unravel the dynamic changes of nirK type denitrifying bacteria community. Spearman was used to analyze the correlation between the dominant denitrifying bacteria and physicochemical indexes. [Results] The compost was matured as shown by physicochemical and biological indexes. The community structure of nirK type denitrifying bacteria was significantly different. The analysis of phylum classification level showed that the main denitrifying bacteria were Proteobacteria and unclassified denitrifying bacteria. The order classification level shows that the dominant genera mainly belong to Rhizobiales, Rhodobacterales and Burkholderiales. Among them, Rhizobiales species were the most, but the relative abundance of Burkholderiales was the highest. Spearman correlation analysis shows that Unclassified_k_norank_d_Bacteria and Unclassified_o_Rhizobiales were significantly negatively correlated with the pH, TOC (total organic carbon), C/N, water content (P<0.05). There was significantly positive correlation with TKN (total kjeldahl nitrogen) and NO3?-N (P<0.05), the other dominant genera were significantly positively correlated with the pH, TOC, C/N and water content (P<0.05), and significantly negatively correlated with the TKN and NO3?-N (P<0.05). It was found that only the Unclassified_o_Burkholderiales, Unclassified_p_Proteobacteria, Pusillimonas and Paracoccus were significantly related to NH4+-N (P<0.05). [Conclusion] The static aerobic high-temperature composting technology used in this paper can shorten the composting cycle. At different stages of composting, the community structure of nirK type denitrifying bacteria was significantly different, and the change of the community structure was significantly affected by the physicochemical indexes. This study will be useful to reveal the nitrogen conversion law in compost and provide a theoretical basis for improving the composting process.