Bacterial Community Composition Associated with Pyrogenic Organic Matter Varies with Its Pyrolysis Temperature and Colonization Environment.

Pyrogenic organic carbon (PyOM) is widely distributed in soil ecosystems, and plays an important role in biogeochemical cycling. Many studies have reported changes in soil microbial communities stimulated by PyOM, but very little is known about the microbial communities associated with PyOM particles. Microbes that colonize PyOM can play an important role in PyOM mineralization and crucially affect soil biogeochemical cycling. Here, we generated two manure-based PyOMs with different characteristics (PyOM pyrolysed at a low temperature of 300°C, i.e. PyOM300 and PyOM pyrolysed at a high temperature of 700°C, i.e. PyOM700) and added them to a high carbon (C) (4.15% ) and a low C (0.37%) soil for microbial colonization, and then extracted the PyOMs from soils at the end of the incubation. 16S rRNA gene sequencing showed that Actinobacteria, particularly Actinomycetales, was the dominant taxa in PyOM, regardless of PyOM pyrolysis temperature and soil type. Bacterial communities associated with PyOM particles extracted from high C soils were similar to those in non-PyOM amended soils, indicating soils with sufficient C content resulted in similar bacterial communities. On the other hand, PyOM300 had higher total microbial biomass, and more distinct bacterial communities than PyOM700. More bacterial OTUs preferentially thrived on the low pyrolysis temperature PyOM (PyOM300),while some specific OTUs also thrived on the high pyrolysis temperature PyOM (PyOM700). For instance, Chloroflexi tended to be more prevalent in high pyrolysis temperature PyOM in low C soils. In conclusion, the differences in the colonized bacterial community composition between different PyOMs were strongly influenced by PyOM pyrolysis temperature, i.e. easily mineralizable C (or fused aromatic C) and other properties (e.g. pH, surface area and nutrient content). Our work increases the understanding of the dominant phylogenetic taxa associated with PyOMs, demonstrates mechanisms mediating microbial metabolism and growth in PyOMs, and expands a new research area for pyrogenic organic matter.