Variations of soil viable and necromass carbon affected by biochar incorporation frequencies

Little is known about how biochar incorporation frequency affect soil C sequestration and stabilization, particularly through living microbial carbon (MBC) and dead microbial carbon (amino sugar C, AS-C). Based on a field trial conducted in Northeast China for three years, in which we applied maize straw-derived biochar once (F1) versus annually for three years (F2). Incorporation frequency and growing stages had an interactive effect on MBC, SOC, MBC/SOC, and GluN-C. Both F1 and F2 enhanced MBC, MBC/SOC, AS-C, and AS-C/SOC, and distinct differences were found in MBC and MBC/SOC. Both treatments did not change the distribution of AS fractions, but reduced their ration to SOC. Both F1 and F2 slightly influenced GluN/MurA. F2 greatly promoted the ratio of fungi and bacteria PLFA than F1. Both biochar treatments retained stability of dead microbial biomass residues and microbial community structure. Analysis of PCA showed both biochar treatments had distinctly differences with plots without biochar, and F1 had no significant differences from F2. In some cases, high frequency of biochar incorporation had greater stimulating effect on viable C accumulation, microbial activity, and living microbial community structure.