2020 ESA Annual Meeting (August 3 - 6)

COS 218 Abstract - Methanogen activity and community structure in methane consuming tropical forest soils

Hannah Shulman, Microbiology & Plant Pathology, University of California, Riverside, Riverside, CA, Emma L. Aronson, University of California Riverside and Michael F. Allen, Plant Pathology and Microbiology, University of California Riverside, Riverside, CA
Background/Question/Methods:

Tropical rainforests play an important role in the global methane cycle. Our ongoing research activities at La Selva Biological Station in Costa Rica have shown that these soils are a methane sink, and that methane consumption increases as the soil moisture drops during the dry season or acute climatic events. In this study, we analyze the composition and activity of methane producing (methanogenic) and methane consuming (methanotrophic) soil microorganisms in order to determine the impact of soil microbial communities on ecosystem function across time and soil habitat.

Leaf cutter ants are ecosystem engineers in these soils; transporting labile carbon to lower horizons, depleting the litter layer, and altering the movement of water and air through the soil matrix. This study therefore also analyzes how ant-driven changes in carbon input influences methanogenesis.

In order to quantify methanogenic activity, transcription of the methyl coenzyme M reductase A (mcrA) gene was quantified by reverse-transcriptase quantitative PCR (RT-qPCR) analysis of RNA and DNA extracted from soils. The mcrA gene was also sequenced using PacBio long read sequencing technology to determine the community composition of methanogenic archaea. To analyze methanotrophic activity, the particulate methane monooxygenase (pmoA) gene was analyzed with qPCR. Additionally, overall microbial abundance and transcriptional activity was estimated with 16S RT-qPCR analysis.

Results/Conclusions:

Our results reveal that in methane consuming soils, expression of mcrA is positively correlated with methane consumption, which was contrary to our hypothesis. However, mcrA expression and the abundance of methanotrophs are negatively correlated. While mcrA expression was variable, abundance of methanogen bodies was similar across all treatments. In soils of leaf cutter ant nests, total microbial abundance, activity, and mcrA expression is lower, which may be driven by lower soil moisture. Our results also describe the balance between different methanogenic clades and the relationship between methanogenic activity and community structure, determined by phylogenetic analysis of the mcrA gene.

Overall, these results indicate that in tropical rainforest soils, the same environmental conditions promoting the activity of methanogenic archaea may also induce the consumption of methane or prevent methane from escaping the soil. Methanogenic archaea are active in tropical rainforest soils and widespread across different soil types, but further research is needed for a process-based understanding of their role in organic matter mineralization and methane flux.