Elevation trend in bacterial functional gene diversity decouples from taxonomic diversity

Abstract

Elevational patterns in taxonomic diversity have been widely studied, but there has been little attention given to patterns in functional gene diversity. We used a metagenomic approach - along with amplicon data - to study trends in functional gene diversity in bacteria along a 2,300 m elevational gradient on Mt. Norikura, Japan. We hypothesized that in accordance with a global scale study by Bahram et al. (2018), functional gene diversity would show a mid-elevation minimum, due to a pH minimum pH and MAP maximum in the mid-elevations. Instead, we observed a mid-elevation maximum in functional gene diversity, and a decrease with increasing pH values from acidic to near neutral. We also found a weak negative relationship between OTU diversity and functional diversity. There appear to be no obvious ecological mechanisms to explain why the observed midelevation peak in functional diversity occurs. The trends observed here demonstrate that it is also necessary to consider more complex localised trends that would largely remain hidden from broad global studies. The fact that functional gene diversity in bacteria is decoupled from taxonomic diversity emphasizes that each should be treated as separate dimensions of diversity.