Niche differentiation of comammox Nitrospira and canonical nitrifiers in riparian wetland ecosystems around Taihu Lake

Purpose Complete ammonia oxidation (comammox) overturned the traditional two-step nitrification theory. Newly discovered comammox Nitrospira and canonical nitrifiers (ammonia-oxidizing archaea and ammonia-oxidizing bacteria) collaboratively perform the oxidation of ammonia in ecosystems. However, the niche distribution of three ammonia oxidizers is controversial. In this study, we explored the distribution and diversity of comammox Nitrospira in riparian wetland ecosystems around Taihu Lake. Materials and methods Soil samples were collected from five habitats: wheat field, vegetable field, peach orchard, tea orchard, and small camphor forest. The abundances and diversity of comammox Nitrospira amo A gene were measured. Results and discussion The amo A gene abundance of comammox Nitrospira varied greatly, ranging from 1.83 × 10 5 to 8.35 × 10 7 copies/g. Temperature, total nitrogen, total carbon, and pH showed significant correlations with the amo A gene abundance of three ammonia oxidizers. High-throughput sequencing suggested that the community structure of comammox Nitrospira showed both spatial and temporal heterogeneity. Total carbon and pH could be the prime environmental factors causing the niche differentiation between comammox Nitrospira and canonical nitrifiers. Moisture content and NH 4 + affected the community structure of comammox Nitrospira . Conclusions Three ammonia oxidizers distributed widely in riparian wetland ecosystems around Taihu Lake. Canonical nitrifiers were more competitive than comammox Nitrospira in most soil samples. Meanwhile, comammox Nitrospira seemed to prefer inhabiting oligotrophic conditions. Collectively, our study expands the general insights into the niche distribution of comammox Nitrospira and the driving environmental factors in riparian wetland ecosystems around Taihu Lake.