Microbial regulation of nitrous oxide emissions from chloropicrin-fumigated soil amended with biochar.

The microbial mechanism underpinning biochar's ability to reduce emissions of the potent greenhouse gas nitrous oxide (NO) is little understood. We combined high-throughput gene sequencing with a dual-label N-O isotope to examine microbial mechanisms operative in biochar made from Crofton Weed (BC1) or pine wood pellets (BC2) and the NO emissions from those biochar materials when present in chloropicrin (CP)-fumigated soil. Both BC1 and BC2 reduced NO total emissions by 62.9-71.9% and 48.8-52.0% in CP-fumigated soil, respectively. During the 7-day fumigation phase, however, both BC1 and BC2 increased NO production by significantly promoting nirKS and norBC gene abundance, which indicated that the NO emission pathway had switched from heterotrophic denitrification to nitrifier denitrification. During the post-fumigation phase, BC1 and BC2 significantly decreased NO production as insufficient nitrogen was available to support rapid population increases of nitrifying or denitrifying bacteria. BC1 and BC2 significantly reduced CP's inhibition of nitrifying archaeal bacteria (AOA, AOB) and the denitrifying bacterial genes (nirS, nirK, nosZ), which promoted those bacterial populations in fumigated soil to similar levels observed in unfumigated soil. Our study provided insight on the impact of biochar and microbes on NO emissions.