Phosphorus availability to beans via interactions between mycorrhizas and biochar

Background and aims 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. Methods A greenhouse study compared feedstock-derived P with 50 mg P pot −1 of sparingly soluble FePO 4 (Fe-P) or soluble NaH 2 PO 4 (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. Results 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 (>2×) 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. Conclusions 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.