Addition of activated switchgrass biochar to an aridic subsoil increases microbial nitrogen cycling gene abundances

It has been demonstrated that soil amended with biochar, designed specifically for use as a soil conditioner, results in changes to the microbial populations that reside therein. These changes have been reflected in studies measuring variations in microbial activity, biomass, and community structure. Despite these studies, very few experiments have been performed examining microbial genes involved in nutrient cycling processes. Given the paucity of research in this area, we designed a 6 month study in a Portneuf subsoil treated with three levels (1%, 2%, and 10% w/w ratio) of a biochar pyrolyzed from switchgrass (Panicum virgatum) at 350 °C and steam activated at 800 °C to measure the abundances of five genes involved in N cycling. Gene abundances were measured using qPCR, with relative abundances of these genes calculated based on measurement of the 16S rRNA gene. At the end of the 6 month study, all measured genes showed significantly greater abundances in biochar amended treatments as compared to the control. In soil amended with 10% biochar, genes involved in nitrogen fixation (nifH), and denitrification (nirS), showed significantly increased relative abundances. Lastly, gene abundances and relative abundances correlated with soil characteristics, in particular NO3-N, % N and % C. These results confirm that activated switchgrass-derived biochar, designed for use as a soil conditioner, has an impact on the treated soils microbial communities. We therefore suggest that future use of biochar as a soil management practice should take into account not only changes to the soil's physiochemical properties, but its biological properties as well.

► Portneuf soil was amended with 1%, 2%, or 10% (w/w) activated switchgrass biochar.
► 16S rDNA gene abundances in 10% biochar soil increased 136%, over control soil.
► Gene abundances of nifH, amoA, nirS, and nosZ were also elevated in biochar soils.
► Relative abundance of nifH increased significantly at all biochar amendment rates.
► Relative abundance of nirS increased significantly at 10% biochar application rate.