Wood biochar impacts soil phosphorus dynamics and microbial communities in organically-managed croplands

Biochar (a carbon-rich product from pyrolysis of organic materials) addition to agricultural soils has been proposed as a novel technology for enhancing soil C storage and fertility; however, few studies have evaluated the effects of biochar on nutrients from an integrated perspective. Previous studies have demonstrated that biochar has the potential to improve bioavailable phosphorus (P) of sandy soils in organic farming systems; yet the underlying mechanisms remain poorly understood. We hypothesized that the unique characteristics of wood biochar could induce changes in soil microbial communities, which would subsequently drive biotic controls on soil P availability through microbial solubilization and/or mineralization and that this would be reflected in microbial P gene expression. To test this hypothesis, we determined the abundance and diversity of bacterial and fungal communities as related to microbial communities in sandy soils of organically-managed farmlands amended with locally produced wood biochar. A series of soil biochemical properties and genes encoding synthesis of phosphatase and those encoding the production of small molecular weight organic acids (involved in metal chelation and P solubilization) were directly quantified to help understand soil P mobilization following biochar addition. Three months after the application of wood biochar, the bioavailability of soil P was found to be elevated and a shift towards a bacterial dominated community was observed. Contrary to our hypothesis; however, the abundance of genes dictating soil phosphatase synthesis or organic acids production remained unaltered following biochar amendment. We suggest that the shift in P bioavailability could be controlled by abiotic mechanisms such as biochar-induced surface organic matter stabilization or adsorption/desorption of P associated with organo-mineral complexes. Although there was no specific molecular evidence of soil microorganism-mediated P mobilization, locally produced wood biochar had a positive effect on surface soil P bioavailability which could benefit agricultural soil health and ecosystem service delivery in organic farming systems.