Distribution And Diversity Of Complete Ammonia Oxidizers In Paddy Soils In China

Nitrification is an important aspect of the nitrogen biogeochemical cycle and plays an important role in soil ecosystems.Paddy soil is widely distributed in China,accounting for 20% of the country's arable land area,which is an important land resource in China.Recent studies have shown that complete ammonia oxidizers(comammox)can carry out the complete ammonia oxidation process in a single step.However,its relationship with ecological factors in paddy soil is unclear.This study collected 36 paddy soil samples nationwide,was analyzed the relationship between comammox and ecological factors,were clarified the diversity and distribution characteristics of comammox in paddy soils in China,and were established the nucleic acid sequence and protein sequence database of its amo A gene.The main conclusions can be summarized as follow:1.Through agarose gel electrophoresis experiments,it was proved that the comammox clade A and clade B were present in all 36 paddy soil samples.2.We have mined and analyzed the soil sample sequencing and NCBI open source database amo A gene data in this study.We used data editing software such as Bio Edit and MEGA X to compare,delete extra bases and build phylogenetic trees.After revising many trials and errors,the establishment of the comammox amo A gene nucleic acid / protein sequence database was obtained.3.Based on the molecular ecology study of paddy soils in China,the diversity and distribution characteristics of comammox bacteria were systematically analyzed.Linear regression analysis showed that both comammox clade A and clade B had a significantly positive correlation with pH.Spearman correlation analysis showed that the amo A gene abundance of comammox clade A and clade B was positively correlated with pH,soil organic matter(SOM),total carbon(TC),total nitrogen(TN),and microbial biomass nitrogen(MBN),and negatively correlated with mean annual temperature(MAT)and mean annual precipitation(MAP).The principal component analysis showed that pH,TC,MBN,SOM content,TN,latitude,and total sulfur(TS)together explained 91.12% of the variation.Redundant analysis showed that both pH and ammonia explained 81.61% of the variation.pH has the highest interpretation of comammox clade A and clade B.Box plots indicated that the Shannon indexs of comammox clade A were higher than that of clade B for most samples.Phylogenetic analysis showed that amplicon sequence variants(ASVs)were closely related to the three comammox Nitrospira currently purely cultured.The above results indicated that multiple factors jointly drive the distribution of comammox,pH may be the most important influencing factor,and the driving effects of other factors on comammox cannot be ignored.Comammox clade A has richer phylogenetic diversity than clade B.The discovery of comammox has opened a new breakthrough for further revealing the soil nitrogen cycle and its microbiological process.Our research provides basic information for understanding the mechanism of nitrogen cycle in soil.In the future,further research is expected in designing higher specific primers,isolating pure strains of comammox,and exploring the relative contribution of ammonia-oxidizing microorganisms.