Abstract: In order to understand the correlation between physicochemical indexes and microbial communities of pit mud and further to screen out the physicochemical indexes that reflect the quality of pit mud, the microbial community structures in pit muds with different qualities were investigated by high-throughput sequencing, and correlation analysis was carried out between microbial community structure and physicochemical indexes. The results showed that the contents of water, total nitrogen and ammonium nitrogen showed an increasing trend with improved quality of pit mud, and the pH approached 7. Principal component analysis of physicochemical indicators showed that the contents of ammonium nitrogen, total nitrogen, available phosphorus, humic acid, pH and Fe had great influence on pit mud quality. Total nitrogen was positively correlated with Firmicutes, Synergistetes and Actinobacteria, but negatively correlated with Chlorflexi and Proteobacteria. Ammonium nitrogen content was positively correlated with Firmicutes, Synergistetes and Actinobacteria, but negatively correlated with Proteobacteria and Spirochaetes. There was a positive correlation between available phosphorus and Synergistetes or Actinobacteria. Humic acid and Proteobacteria were positively correlated. pH was positively correlated with Firmicutes and Proteobacteria, but negatively correlated Chlorflexi with Spirochaetes. All correlations were statistically significant (P < 0.05 or P＜0.01). Redundancy analysis showed that ammonium nitrogen, total nitrogen, available phosphorus and pH had the greatest influence on microbial communities, followed by water, humic acid, calcium and iron contents. To sum up, total nitrogen, ammonium nitrogen and pH were screened out as quality indicators of pit mud. The better the quality of pit mud, the higher the contents of total nitrogen and ammonium nitrogen and the closer the pH was to 7.

Key words: pit mud, quality, physicochemical, high-throughput sequencing, microbial community, diversity