Biochar Addition Rate Controls GHG Fluxes, Soil Priming, and Microbial Community Composition in Temperate Soils.

Biochar addition to soil may mitigate GHG emissions, sequester recalcitrant C and increase microbial populations all of which benefit agroecosystems. However, after biochar additions net GHG emissions (CO₂, N₂O, and CH₄) have been positive, neutral, or negative depending on the biochar feedstock, pyrolysis temperature, as well as soil type.  We determined the effect of biochar addition rates (0, 1, 5, 10, and 20% by weight) on GHG emissions and microbial community dynamics from four soils varying from a clay to a sand on during a 2 year incubation. To trace CO₂ source, we added C₃ biochar (oak, pyrolyzed at 550°C) to C₄ soils and measured CO₂, N₂O, and CH₄, and total and relative abundance of phospholipid fatty acids (PLFA) and ¹³C signatures in CO₂ and PLFAs.  Biochar addition initially suppressed CO₂, but after 3-4 months, biochar-derived CO₂ was proportional to biochar addition rate. In all soils, N₂O emissions were suppressed, although the reduction to addition rate varied from 20% to 94% depending on soil type. Biochar contribution to total respiration fluxes varied with soil type and the amount of biochar added, suggesting an interaction with microbial activity and the possible need for the microbial community to adapt to the new C source. We will report microbial community structure and abundance as affected by biochar addition rate and soil type, and discuss them in the context of the observed changes in GHG efflux.