Dynamics of microbial community composition and soil organic carbon mineralization in soil following addition of pyrogenic and fresh organic matter

Pyrogenic organic matter (PyOM) additions to soils can have large impacts on soil organic C (SOC) cycling, both as a direct organic C input, and also through changes in mineralization of existing SOC. The soil microbial community drives SOC fluxes, so understanding how PyOM additions affect soil microbes is essential to understanding how PyOM affects SOC. We studied SOC dynamics and surveyed soil microbial communities after OM additions in a field experiment. We produced and applied either 350oC corn stover PyOM or an equivalent amount of dried corn stover to a Typic Fragiudept soil. Corn stover dramatically increased total and SOC-derived CO2 emissions and caused rapid and persistent changes in bacterial community composition. In contrast, PyOM additions only temporarily increased total soil CO2 fluxes, did not affect SOC-derived CO2 emissions, and bacterial communities responded more slowly. 70% of the OTUs that responded to PyOM additions also increased in response to stover additions. These OTUs likely thrive on easily-metabolizable C that is found both in stover and, to a lesser extent, in PyOM. In contrast, we also identified unique PyOM-responders, which may consume substrates characteristic of PyOM, such as condensed aromatic C ring structures. In particular, members of Gemmatimonadetes tended to increase in relative abundance in response to PyOM but not to fresh organic matter. We demonstrate how PyOM-additions influence the phylogenetic composition of the microbial community in an agricultural soil and identify taxa to target for future investigations of the mechanistic underpinnings of ecological phenomena associated with PyOM additions to soil.