Nitrous Oxide (N2O) Emissions by Termites: Does the Feeding Guild Matter?

In the tropics, termites are major players in the mineralization of organic matter leading to the production of greenhouse gases including nitrous oxide (N2O). Termites have a wide trophic diversity and their N-metabolism depends on the feeding guild. This study assessed the extent to which N2O emission levels were determined by termite feeding guild and tested the hypothesis that termite species feeding on a diet rich in N emit higher levels of N2O than those feeding on a diet low in N. An in-vitro incubation approach was used to determine the levels of N2O production in 14 termite species belonging to different feeding guilds, collected from a wide range of biomes. Fungus-growing and soil-feeding termites emit N2O. The N2O production levels varied considerably, ranging from 13.14 to 117.62 ng N2O-N d(-1) (g dry wt.)(-1) for soil-feeding species, with Cubitermes spp. having the highest production levels, and from 39.61 to 65.61 ng N2O-N d(-1) (g dry wt.)(-1) for fungus-growing species. Wood-feeding termites were net N2O consumers rather than N2O producers with a consumption ranging from 16.09 to 45.22 ng N2O-N d(-1) (g dry wt.)(-1). Incubating live termites together with their mound increased the levels of N2O production by between 6 and 13 fold for soil-feeders, with the highest increase in Capritermes capricornis, and between 14 and 34 fold for fungus-growers, with the highest increase in Macrotermes muelleri. Ammonia-oxidizing (amoA-AOB and amoA-AOA) and denitrifying (nirK, nirS, nosZ) gene markers were detected in the guts of all termite species studied. No correlation was found between the abundance of these marker genes and the levels of N2O production from different feeding guilds. Overall, these results support the hypothesis that N2O production rates were higher in termites feeding on substrates with higher N content, such as soil and fungi, compared to those feeding on N-poor wood.