Mechanistic understanding of the biochar-induced inhibition of growth and soil phosphorus solubilization by Bacillus megaterium

Abstract

Due to the complex composition of biochar and the potential interactions between the components that jointly make up biochar, previous studies have always shown controversial results regarding impacts of biochar on soil phosphorus (P) solubilization. Using a nested experimental design, this study investigated the effects of different components of biochar, i.e. whole biochar (BC), dissolved biochar (DBC) and washed biochar (WBC) on the microbial-mediated P solubilizing process. The growth of Bacillus megaterium, acid/alkaline phosphatase activity, differential metabolites of bacteria and metabolic pathways were measured in treatments with biochar pyrolyzed at 200, 300, 400, 500 and 600 °C. Results showed that BC, DBC and WBC all negatively affected the growth and alkaline phosphatase activity of B. megaterium, and BC500/WBC500 and BC400/WBC400 had the greatest impacts. The negative effects of high-temperature biochar on cell proliferation were caused by persistent free radicals and included down-regulation of histidine metabolism by BC400 and interference in nucleotide metabolism by BC600. The impacts of low-temperature biochar on cell proliferation and alkaline phosphatase activity were highly related to the metal content. Using the independent action model, antagonistic effects were found between DBC and WBC on inhibiting B. megaterium growth, while these biochars had synergistic effects on inhibition of alkaline phosphatase activity. Overall, this study provides insights on how biochar adversely modulates microbial-mediated P solubilization.