Rethinking termite methane emissions: does the mound environment matter?

Termites are important decomposers in tropical ecosystems and emit methane (CH₄) as they digest plant material. Global estimates of termite-derived CH₄ are calculated using termite emission factors (TEF, measured from individuals) and estimated biomass. However, this approach overlooks how the termite mound, via internal and external factors, may influence emissions to the atmosphere. Termite feeding habits, mound methanotrophs and mound structure (internal environment), as well as temperature and season (external environment) can influence net CH₄ emission but remain unparameterized. We investigated how these factors shaped CH₄ emissions from three dominant mound-building termite species (Coptotermes acinaciformis, Nasutitermes magnus, and Amitermes laurensis) in a northern Australian savanna across four seasons. We compared species-level TEFs and emissions at the mound- and landscape-scales to evaluate relative species contributions, both with and without accounting for the internal and external environment. We hypothesized that larger, thinner-walled mounds would emit greater CH₄, and that emissions would be higher at high temperatures and during wet seasons. We expected greater emissions with lower abundances of methanotrophs and pmoA gene copies (involved in CH₄ oxidation) in mound material. Coptotermes acinaciformis individuals had the highest TEFs (1.07 μg CH₄ g⁻¹ termite h⁻¹), N. magnus mounds emitted the most CH₄ (3426 μg CH₄ h⁻¹ m⁻²) and A. laurensis had the highest emissions at the landscape scale (1.04 × 10⁻⁹ Tg CH₄ ha⁻¹ year⁻¹). CH₄ emissions increased with temperature and were highest in the wet-to-dry transition season. Mound structure, bacterial methanotroph communities, and pmoA abundance had no effect on CH₄ emissions. Our results highlight the limitations of relying solely on TEFs to estimate contributions of termites to global CH₄ emissions and emphasize the importance of incorporating external environmental conditions, while further exploring internal mound processes. This information allows more accurate parameterization of termite CH₄ contributions to savanna carbon and global CH₄ budgets.