Submitted to: Applied Soil Ecology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 1/12/2013
Publication Date: 3/20/2013
Citation: Ducey, T.F., Ippolito, J.A., Cantrell, K.B., Novak, J.M., Lentz, R.D. 2013. Addition of activated switchgrass biochar to an aridic subsoil increases microbial nitrogen cycling gene abundances. Applied Soil Ecology. 65:65-72. Interpretive Summary: Biochars success as a soil conditioner can also lead to changes in the soils microbial population. What is unknown is whether these changes are beneficial or harmful. To study these changes and determine their effects, we measured the abundances of several genes involved in nitrogen cycling. In this study we used a biochar made from pyrolyzed switchgrass that was steam activated. This biochar was added to a Portneuf soil collected from the B horizon to simulate a soil that had undergone severe erosion. In soils amended with biochar, the abundances of these genes all increased. The overall abundance of bacteria in the soils also increased with biochar addition. Relative abundances of these genes, representing the percentage of the total microbial population that carried a specific gene, remained consistent with slight increases in two of the genes studied. This indicates that while the overall cycling of nitrogen may increase in soils amended with biochar, the individual steps in the pathway should occur in similar percentages.
Technical Abstract: 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 six-month study in a Portneuf soil (coarse-silty, mixed, superactive, mesic Durinodic Xeric Haplocalcid) 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 four genes involved in nitrogen (N) cycling. Gene abundances were measured using qPCR, with relative abundances of these genes calculated based on measurement of the 16S rDNA gene. At the end of the six-month study, all measured genes showed significantly greater abundances in biochar amended treatments as compared to the control, potentially increasing the amount of N cycled in soils receiving such treatments. 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 nitrate nitrogen, % N and % carbon. In toto, 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.