El-Nino Southern Oscillation (ENSO)-induced drying of the tropics increases methane (CH4) consumption by forest soils and reduces regional atmospheric CH4. This research utilizes a soil ecosystem observatory (SEO) to determine the role of methane-cycling soil microorganisms in this seasonal shift of tropical CH4 consumption. As CH4 in tropical soils is strictly consumed by methanotrophic bacteria, the objective of this research was to compare the abundance of soil microbes in response to ENSO-induced drying across soil profiles. Additionally, the effect of leaf-cutter ants on both methane-cycling microbes and CH4 consumption was examined in soils sampled from nests. To determine methanotroph abundance, real-time qPCR was used to quantify pmoA, the gene encoding the first enzymatic step of CH4 oxidation, methane monooxygenase. Additionally, We analyzed patterns of diversity in the broader microbial community with metagenomic sequencing of 16S ribosomal DNA.
Results/Conclusions
Phylogenies constructed from 16S sequences revealed .02-.04% abundance of Verrucomicrobial methanotrophs as well as anaerobic and aerobic ammonia oxidizing bacteria (AOB) ranging from .05-1.0%. Microbial species richness was increased by ENSO-induced drying in leaf-cutter ant nest compared to non-nest controls. Abundance of the methane-consuming gene pmoA was higher in all alluvial soils and significantly lower in residual ant nests than residual non-nest controls, but was not affected by ENSO. Gene copy number of pmoA was inversely correlated with soil and nest patterns of CH4 consumption. Our results show that methanotroph communities are influenced by historical traits of soils as well as the contemporary influence of leaf-cutter ants. The relationship between methanotrophs and methane consumption in soils evades simplicity. This work contributes to a growing ecosystem-level framework aimed at understanding the environmental pressures governing the structure and function of soil microbial communities.