Microbial colonisation patterns are more affected by plant substrate compositions than termite modulated environments

Background Termites are dominant plant biomass decomposers and important ecosystem engineers that modify soil properties and microbial communities. In fungus-farming termites, mound building contribute to distinctions between three environments: fungal gardens, mound walls, and outside soil away from mounds. Here we determined the properties of these environments for 10 colonies of Macrotermes bellicosus termites and tested their consequences for fungal and bacterial colonisation of two novel substrates presented as compositionally-different types of tea. Lastly, capitalising on the mass loss of tea bags, we evaluated the decomposition rates in these environments across habitats (forest patch, woody savanna, and teak plantation) in central Côte d’Ivoire. Results We confirmed that M. bellicosus termite colonies create distinct local environments that are markedly different in both elemental (e.g., carbon and nitrogen content) and bacterial and fungal community compositions. Fungal colonisation of tea bags in outside soils, and to a lesser extent mound soil, reflected community compositions of soil sources, with dominant colonisers being opportunistic spore-forming saprophytes. Similar communities colonised tea bags within mounds, resulting in poor reflection of the termite gut and fungal comb source communities. Bacterial colonisation was also comparable across environments, but overall poorly reflected source communities, underlining that tea bag properties strongly select for coloniser taxa. Although decomposition rates were more consistent in mound walls and fungal gardens than outside soils, we did not detect significant differences between either of the three environments. Conclusions Our findings point to contrasting tea bag properties strongly selecting for opportunistic colonisers that are not necessarily abundant in source environments and across habitats. This canalisation was most prominent for fungi and likely contributed to the comparable decomposition rates across environments. The omnipresence of fast-colonising fungi to novel substrates in all three environments imply that they remain present and potentially threat termite farms, while termites actively suppress their proliferation within combs. Colonisation here thus best exemplified competitive release owing to reduced suppression of non- Termitomyces fungi. Even so, termite activities markedly shape environmental properties, demonstrating the importance of mound building in generating heterogeneous microbial niches in savannah ecosystems.