Soil biota, carbon cycling and crop plant biomass responses to biochar in a temperate mesocosm experiment

Background and aims: Biochar addition to soil is a carbon capture and storage option with potential to mitigate rising atmospheric CO2 concentrations, yet the consequences for soil organisms and linked ecosystem processes are inconsistent or unknown. We tested biochar impact on soil biodiversity, ecosystem functions, and their interactions, in temperate agricultural soils. Methods: We performed a 27-month factorial experiment to determine effects of biochar, soil texture, and crop species treatments on microbial biomass (PFLA), soil invertebrate density, crop biomass and ecosystem CO2 flux in plant-soil mesocosms. Results: Overall soil microbial biomass, microarthropod abundance and crop biomass were unaffected by biochar, although there was an increase in fungal-bacterial ratio and a positive relationship between the 16:1ω5 fatty acid marker of AMF mass and collembolan density in the biochar-treated mesocosms. Ecosystem CO2 fluxes were unaffected by biochar, but soil carbon content of biochar-treated mesocosms was significantly lower, signifying a possible movement/loss of biochar or priming effect. Conclusions: Compared to soil texture and crop type, biochar had minimal impact on soil biota, crop production and carbon cycling. Future research should examine subtler effects of biochar on biotic regulation of ecosystem production and if the apparent robustness to biochar weakens over greater time spans or in combination with other ecological perturbations.