Variation of soil anaerobic microorganisms connected with anammox processes by 13C-phospholipid fatty acid analysis among long-term fertilization regimes in a crop rotation system

An anaerobic incubation experiment was conducted to evaluate the impacts of different fertilizer treatments on the activity and diversity of anaerobic bacteria combined anammox process. The treatments included no fertilization (CK), inorganic fertilization (IF), pig manure combined with inorganic fertilization (PF), and straw combined inorganic fertilization (SF) during wheat and rice seasons. Various C-13-PLFAs, especially 14:0, 16:1 omega 9c, 16:16 omega 5c, 16:0, 18:1 omega 9c, and 18:0, played significant roles in the anammox reaction and could be biomarkers of anammox. Additionally, fertilizer practices and seasonal changes could significantly affect soil properties, microbial biomass, and bacterial community structure. The abundance of total C-13 and anaerobic microbes was higher in the PF and SF treatments than in the IF and CK treatments in the same season, indicating anaerobic activity and abundance can be enhanced by applying organic-inorganic compound fertilizers. The anammox microbial abundance, marked by the C-13-PLFAs 14:0, 16:1 omega 9c, 16:1 omega 5c, 16:0, 18:1 omega 9c, and 18:0, increased significantly during the crop rotation from the wheat season to the rice season. The proportions of bacteria were higher than those of fungi however the proportions of fungi were much higher than those of actinomycetes in all soils, suggest that fungi also play an important role in metabolizing the C-13-matrix with strong anaerobic activity.