Niche specialization of comammox Nitrospira clade A in terrestrial ecosystems

Comammox Nitrospira are a newly discovered group of nitrifying prokaryotes and might be key contributors to nitrogen cycling in terrestrial ecosystems. Their large-scale distribution patterns and the dominant environmental factors shaping their ecological niches are not yet well documented. Here, we investigated the biogeographic distribution of comammox Nitrospira over 4000 km in eastern Australia and explored the niche specialization of individual comammox Nitrospira phylotypes. Our results revealed that the abundance, richness and community composition of comammox Nitrospira clade A were best predicted by mean annual precipitation (MAP) among all the determined environmental parameters. We identified four phylogenetic clusters of comammox Nitrospira: clade A.1, A.2.1, A.2.2 and A.3. MAP was consistently the strongest factor correlated with the relative abundances of the dominant clades, A.2.1 and A.3. MAP and other variables including soil nitrate, mean annual temperature and total nitrogen showed contrasting effects on the relative abundances of comammox Nitrospira clade A.2.1 and A.3, indicating their potential ecological niche differentiation in the soils. Together, we found a broad distribution of comammox Nitrospira clade A, but not clade B, in various terrestrial ecosystems across eastern Australia, and the abundance and diversity of comammox Nitrospira clade A can be mainly predicted by MAP among all the determined environmental parameters. These findings provide novel evidence for the environmental adaptation and niche specialization of comammox Nitrospira in the terrestrial ecosystems.