Bacterial Community Structure and Biogeochemical Cycling Genes Located within Pyrogenous Organic Matter.

Microbes that colonize pyrogenous organic matter (PyOM) play an important role in PyOM mineralization and crucially affect soil biogeochemical cycling. However, the microbial community structure and functional genes coding for C and N metabolism in the PyOM remain largely unidentified. The PyOMs with aliphatic-dominated structures (produced by pyrolysis at 300 ¢ªC) and aromatic-dominated structures (produced by pyrolysis at 700 ¢ªC) were extracted from a nutrient-sufficient and a nutrient-deficient soil after long-term incubations. The microbial communities within the PyOMs were measured by metagenome sequencing. The bacterial abundance, measured by SEM spectra, CO2 evolution, DOC and DNA concentrations, in PyOM 300 ¢ªC was significantly (p<0.05) larger than that in PyOM 700 ¢ªC, whereas the bacterial diversity, e.g. Chao 1, Shannon and OTU network, showed the opposite trend. The dominant phyla associated with PyOM were the spore-forming Actinobacteria, followed by the Chloroflexi, Alphaproteobacteria and Acidobacteria. The dominant biogeochemical cycling genes were responsible for the conversion of nitrite to ammonia (N transformation) and formate to mercaptoethane sulfonate (Methanogenesis). A significantly higher gene abundance responsible for carbohydrate metabolism occurred in PyOM 300 ¢ªC, compared to PyOM 700 ¢ªC (p < 0.05).This was consistent with the NMR spectra showing that the PyOM 700 ¢ªC was more aromatic than PyOM 300 ¢ªC, inferring that labile C was the principal factor stimulating microbial growth.