Pyrogenic organic matter effects on soil bacterial community composition

Pyrogenic organic matter (PyOM) is produced by the incomplete combustion of organic matter, and can represent a large portion of total soil organic carbon in both fire-affected systems and managed systems where PyOM is added intentionally as a soil amendment. The effects of PyOM on the structure of soil microbial communities remain a topic of fundamental interest, and a number of studies have begun to identify and characterize the PyOM-associated microbial community. However, it is unclear to what extent the effects of PyOM on soil bacteria are consistent. Our goals were to synthesize current related studies to (1) determine if there is a detectable and consistent “charosphere” community that characterizes PyOM-amended soils, (2) distinguish consistent responders at the phylum level to PyOM amendments, and (3) identify individual PyOM-responsive taxa that increase in relative abundance consistently across different soil types. We re-analyzed publicly available raw 16S Illumina sequencing data from studies that investigated the bacterial communities of PyOM-amended soils. We determined that soil source is more important than PyOM for shaping the trajectory of the community composition. Although we were able to identify a few genera that respond positively and somewhat consistently to PyOM amendments, including Nocardioides, Micromonospora, Ramlibacter, Noviherbaspirillum, and Mesorhizobium, in general, neither phylum-level nor genus-level responses to PyOM were consistent across soils and PyOM types. We offer suggestions for our future efforts to synthesize the effects PyOM may have on soil microbial communities in an array of different systems. Due to the dual challenges of high functional diversity at fine taxonomic scales in bacteria, and diverse ranges of soil and PyOM properties, researchers conducting future studies should be wary of reaching a premature consensus on PyOM effects on soil bacterial community composition. In addition, we emphasize the importance of focusing on effect sizes, their real-world meanings, and on cross-study effect consistency, as well as making data publicly available to enable syntheses such as this one.