Phosphorus availability to beans via interactions between mycorrhizas and biochar
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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.
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 (>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.
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.
KeywordsBiochar Iron phosphate Microbial biomass Mycorrhizas Phaseolus vulgaris Phosphorus fixation NLFA Rhizosphere
The authors appreciate financial support from the NSF-Basic Research for Enabling Agricultural Development program (BREAD grant number IOS-0965336), and the Fondation des Fondateurs. Any opinions, findings and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the donors. We thank Daniel Richter for soil, Steve Beebe and CIAT for bean seed, Joseph Morton for AM inoculant and advice on AM in pot experiments, Harry Read for PLFA GC analysis and consultation, and Sara Nason, Kelly Hanley, Akio Enders, and Nick Vail for help in conducting the experiment. Electron microscopy in the online supplement made use of the Cornell Center for Materials Research Shared Facilities which are supported through the NSF MRSEC program (DMR-1120296). We also thank several anonymous referees for their valuable comments.
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