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Termite mounds mitigate half of termite methane emissions.

ABSTRACT: Termites are responsible for ∼1 to 3% of global methane (CH4) emissions. However, estimates of global termite CH4 emissions span two orders of magnitude, suggesting that fundamental knowledge of CH4 turnover processes in termite colonies is missing. In particular, there is little reliable information on the extent and location of microbial CH4 oxidation in termite mounds. Here, we use a one-box model to unify three independent field methods-a gas-tracer test, an inhibitor approach, and a stable-isotope technique-and quantify CH4 production, oxidation, and transport in three North Australian termite species with different feeding habits and mound architectures. We present systematic in situ evidence of widespread CH4 oxidation in termite mounds, with 20 to 80% of termite-produced CH4 being mitigated before emission to the atmosphere. Furthermore, closing the CH4 mass balance in mounds allows us to estimate in situ termite biomass from CH4 turnover, with mean biomass ranging between 22 and 86 g of termites per kilogram of mound for the three species. Field tests with excavated mounds show that the predominant location of CH4 oxidation is either in the mound material or the soil beneath and is related to species-specific mound porosities. Regardless of termite species, however, our data and model suggest that the fraction of oxidized CH4 (f ox) remains well buffered due to links among consumption, oxidation, and transport processes via mound CH4 concentration. The mean f ox of 0.50 ± 0.11 (95% CI) from in situ measurements therefore presents a valid oxidation factor for future global estimates of termite CH4 emissions.

SUBMITTER: Nauer PA

PROVIDER: S-EPMC6310829 | biostudies-other | 2018 Dec

REPOSITORIES: biostudies-other

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Termite mounds mitigate half of termite methane emissions.

Nauer Philipp A PA Hutley Lindsay B LB Arndt Stefan K SK

Proceedings of the National Academy of Sciences of the United States of America 20181126 52

Termites are responsible for ∼1 to 3% of global methane (CH4) emissions. However, estimates of global termite CH4 emissions span two orders of magnitude, suggesting that fundamental knowledge of CH4 turnover processes in termite colonies is missing. In particular, there is little reliable information on the extent and location of microbial CH4 oxidation in termite mounds. Here, we use a one-box model to unify three independent field methods-a gas-trace ...[more]

PMID: 30478040

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Project description:BackgroundThe major greenhouse gas from ruminants is enteric methane (CH4) which in 2010, was estimated at 2.1 Gt of CO2 equivalent, accounting for 4.3% of global anthropogenic greenhouse gas emissions. There are extensive efforts being made around the world to develop CH4 mitigating inhibitors that specifically target rumen methanogens with the ultimate goal of reducing the environmental footprint of ruminant livestock production. This study examined the individual and combined effects of supplementing a high-forage diet (90% barley silage) fed to beef cattle with the investigational CH4 inhibitor 3-nitrooxypropanol (3-NOP) and canola oil (OIL) on the rumen microbial community in relation to enteric CH4 emissions and ruminal fermentation.Results3-NOP and OIL individually reduced enteric CH4 yield (g/kg dry matter intake) by 28.2% and 24.0%, respectively, and the effects were additive when used in combination (51.3% reduction). 3-NOP increased H2 emissions 37-fold, while co-administering 3-NOP and OIL increased H2 in the rumen 20-fold relative to the control diet. The inclusion of 3-NOP or OIL significantly reduced the diversity of the rumen microbiome. 3-NOP resulted in targeted changes in the microbiome decreasing the relative abundance of Methanobrevibacter and increasing the relative abundance of Bacteroidetes. The inclusion of OIL resulted in substantial changes to the microbial community that were associated with changes in ruminal volatile fatty acid concentration and gas production. OIL significantly reduced the abundance of protozoa and fiber-degrading microbes in the rumen but it did not selectively alter the abundance of rumen methanogens.ConclusionsOur data provide a mechanistic understanding of CH4 inhibition by 3-NOP and OIL when offered alone and in combination to cattle fed a high forage diet. 3-NOP specifically targeted rumen methanogens and partly inhibited the hydrogenotrophic methanogenesis pathway, which increased H2 emissions and propionate molar proportion in rumen fluid. In contrast, OIL caused substantial changes in the rumen microbial community by indiscriminately altering the abundance of a range of rumen microbes, reducing the abundance of fibrolytic bacteria and protozoa, resulting in altered rumen fermentation. Importantly, our data suggest that co-administering CH4 inhibitors with distinct mechanisms of action can both enhance CH4 inhibition and provide alternative sinks to prevent excessive accumulation of ruminal H2.

Dataset Information

Termite mounds mitigate half of termite methane emissions.

Publications

Termite mounds mitigate half of termite methane emissions.

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