Influence of soil copper and zinc levels on the abundance of methanotrophic, nitrifying, and N₂O-reducing microorganisms in drylands worldwide

Understanding soil microbial populations influencing biogeochemical cycles with potential implications for greenhouse gas (GHG) fluxes emissions is crucial. Methanotrophic, nitrifying and N₂O-reducing microorganisms are major drivers of CH₄ and N₂O fluxes in soils. The metabolism of these organisms relies on enzymes that require as cofactors metal ions scarcely available in the soil, such as copper (Cu) and zinc (Zn). Despite the importance of these ions, how their concentrations relate to the abundance of these microbes at the global scale has not been addressed yet. Here, we used data from a global survey carried out in 47 drylands from 12 countries to evaluate the role of soil Cu and Zn concentrations, and their relationship with aridity, as drivers of the abundance of methanotrophs, archaeal and bacterial nitrifiers, and N₂O reducers. To do so, we performed qPCR analyses of the marker genes pmoA, archaeal and bacterial amoA and nosZI. We did not find an association between the abundance of methanotrophs and Cu or Zn availability. However, our results highlight the importance of Cu influencing the abundance of nitrifying bacteria and N₂O reducers, two main actors involved in the N₂O cycle. Our findings indicate that dryland soils can be prone to reduce the N₂O coming from nitrification to innocuous N₂, but reductions in soil Cu availability (e.g., by increased aridity conditions due to climate change) could shift this trend.