Rethinking termite methane emissions: does the mound environment matter?

Abbey R Yatsko, Paul Eggleton, Caleb Jones, Marcos Pérez-Losada, Ignacio Ramos-Tapia, Jeff R Powell , Baptiste Joseph Wijas, Amy E Zanne

Termites are important decomposers in tropical ecosystems, and they emit methane (CH4) from digesting plant matter. Termite contributions to global CH4 emissions are calculated using species-specific termite CH4 emissions from individuals (termite emission factors; TEF) and estimated biomass, which overlooks how the termite mound environment may alter emissions to the atmosphere. Factors such as feeding habits, mound methanotrophs, mound structural traits (size, wall thickness), and environmental conditions (temperature, season) 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 assess species relative contributions with and without accounting for mound environment. We expected larger and thinner-walled mounds would emit greater CH4, while emissions would also be higher at high temperatures and during wet seasons. Finally, we expected greater emissions with a lower abundance of methanotrophs and pmoA (responsible for reducing CH4) gene copies in the mound material. Coptotermes acinaciformis individuals had the highest TEFs (1.07 μg CH4/g termite/h), while N. magnus mounds emitted the most CH4 (3,426 μg CH4/h/m2) and A. laurensis had the highest emissions at the landscape scale (1.04 × 10-9 Tg CH4/ha/yr). CH4 emissions increased with temperature and were highest in the wet-to-dry transition season. Surprisingly, bacterial methanotroph communities and pmoA gene abundance had no direct effect on CH4 emissions. Our results highlight the limitations of using TEFs to estimate the global contributions of termites to atmospheric CH4 emissions and emphasize incorporating the mound environment when calculating net termite CH4 emissions. This information allows more accurate parameterization of termite CH4 contributions to savanna carbon cycling and global CH4 budgets.