Phosphorus availability to beans via interactions between mycorrhizas and biochar

We sought to understand biochar's role in promoting plant phosphorus (P) access via arbuscular mycorrhizas (AM), focusing on whether P solubility and biochar-P proximity altered AM enhancement of P uptake in a mycorrhizal crop legume. A greenhouse study compared feedstock-derived P with 50 mg P pot(-1) of sparingly soluble FePO4 (Fe-P) or soluble NaH2PO4 (Na-P) at different proximities to biochar (co-pyrolyzed, mixed with biochar, mixed with soil) on Phaseolus vulgaris P uptake, specific root length (SRL), AM colonization, AM neutral lipids, and microbial biomass-P. Biochar increased AM colonization by 6 % (p < 0.01) and increased Fe-P uptake from 3.1 to 3.8 mg plant(-1), with AM-related Fe-P uptake increased by 12 % (p < 0.05). Regardless of proximity, biochar applied with Fe-P was enriched (> 2x) with AM hyphae. Biochar-P proximity did not alter P uptake, but shifted uptake towards AM for Fe-P and roots for Na-P. Soluble P located on biochar increased total plant + microbial P (p < 0.05). Biochar reversed (p < 0.05) reductions in SRL induced by AM. Biochar enhanced AM's access to sparingly soluble P, and root/microbial access to soluble P. Biochar augments sparingly soluble P uptake at scales larger than biochar particles, perhaps by reducing P sorption or facilitating root/hyphal exploration.