Fire-mediated disturbances affects microbiome composition and assembly processes in tropical peatlands

Despite being one of the densest terrestrial carbon (C) reserves, tropical peatlands (TP) in Southeast (SE) Asia have been subjected to extensive deforestation, drainage and fire. Specifically, fire can result in dramatic changes to C reserves due to shifts in microbiome composition and assembly, which in turn drive peat decomposition. Moreover, microbial ecology studies have identified processes shaping the microbial assembly such as deterministic, where biotic/abiotic factors determine the relative frequency of species, and stochastic, where random changes in species relative frequencies occur which are independent of changes in environment. However, such processes have not been studied in tropical peatlands in SE Asia, especially in fire degraded areas which were recently discovered as hot spot for CH4 emissions. Therefore, we studied microbiome composition and ecological processes shaping their assembly in intact and burnt TP in Brunei. We found significant differences in microbiome composition between intact and burnt peat, where latter showed higher relative abundance of methane producing archaea (Bathyarchaeia) and lesser relative abundance of methane oxidizing bacteria (Alphaproteobacteria, Gammaproteobacteria) compared to intact peat. These results further support the sustained higher CH4 emissions from fire degraded TP areas. Further, using a null modelling approach we identified different ecological processes shaping microbiome assembly in peat from intact and burnt sites. We found that deterministic processes significantly shaped microbiome assembly in intact peat whereas stochastic processes shaping microbiome assembly in burnt peat. This shows that random changes in microbial relative frequencies in burnt peat is independent of changes in the environment, which suggest that successful restoration of fire degraded TP areas are likely to be difficult using strategies which only manage environmental factors. Deterministic and stochastic processes were significantly associated with pH and dissolved oxygen across both intact and burnt peat. In conclusion, our results provide novel insights into post-fire changes in microbiome composition and assembly processes, which are of critical importance in regulating C dynamics in degraded TP with vast expanse yet to be restored.