Biochar application influences microbial assemblage complexity and composition due to soil and bioenergy crop type interactions

Abstract

Enhancement of soil fertility and mitigation of atmospheric greenhouse gases are potential benefits of biochar amendments with proximate links to microbiological processes, yet the impact of biochar on the soil microbial community is poorly resolved. Here, we assessed changes in bacterial community composition and microbial assemblage patterns with biochar amendment in two soils with contrasting fertility under two cropping systems; perennial grass and annual sweet corn rotation at two time periods. Overall, soil type exerted the greatest effect on the soil microbial community, followed by sampling time and cropping system which exerted a greater effect on the microbial community than biochar treatment. The influence of biochar on community composition was most pronounced in the highly weathered, low fertility Oxisol, than the high fertility Mollisol. We further investigated microbial assemblage architecture using random-matrix theory based molecular ecological network analyses. Microbial assemblage complexity increased with biochar amendment, with the largest impact associated with the Oxisol, accompanied by more negative OTU co-variations, indicating enhanced competition and/or niche partitioning in concert with an increase in the number of putative “keystone species”. Network analysis suggests that biochar addition, especially in the highly weathered, low fertility Oxisol, confers higher-level organization, competition, and complexity to the soil microbiome that may result in higher resistance to change due to environmental perturbation and thereby increase system sustainability.