Stable Isotope Probing (SIP)-Enabled Metagenomics of Active Microbial Degraders in Response to Priming Under Biochar Amended Soils.

The use of biochar amendment to soil has the potential to increase soil organic carbon (SOC) and reduce greenhouse gas emissions. Microorganisms can utilize the labile components of fresh plant litter to enhance the degradation of the more recalcitrant soil organic matter fraction. However, changes in the composition and/or function of microbial populations, specifically those involved in the early decomposition of fresh organic matter (FOM), are not well understood. As the limiting steps in organic matter decomposition, microbial community responses can also be linked to changes in C and N related extracellular enzyme activities. In this study we aim to identify the active microbial populations derived from agricultural soil under Napier cultivation that are involved in FOM metabolism and their response to biochar amendment. To accomplish this, ground 13C labeled Napier (Pennisetum purpureum schum) was amended to field soils (oxisols) under two-year field biochar and no biochar treatments and incubated for 14 d. During the experiment, 13CO2 fluxes were monitored to assess respiration of the labeled substrate, bacterial abundance monitored using qPCR of both 12C and 13C labeled DNA and enzyme activities determined through sacrificial replicates. Using these data, three time points were further analyzed using shotgun metagenomics of the SIP-derived DNA heavy and light fractions. This was performed in order to gain insight into changes in microbial functional potentials and composition of the “active” versus “total” microbial community. The combination of SIP with quantitative, metagenomic and enzymatic data offers a unique insight into the microbial ecology of FOM primary degraders that may drive priming effects.