Spatial dynamics of phosphorus mobilization by mycorrhiza

Abstract

Symbiosis with arbuscular mycorrhizal fungi (AMF) is a crucial strategy for plants to overcome phosphorus (P) deficiency, which is common in soils worldwide. This study explored the role of AMF in P mobilization using a maize-AMF symbiosis model under two levels of P availability in soil: 5.9 mg P kg⁻¹ and 19 mg P kg⁻¹. A newly developed three-compartment rhizobox was used to combine soil zymography with high-resolution diffusive gradients in thin-films (DGT) imaging, revealing P mobilization within the mycorrhizosphere through intensive soil-hyphae-root interactions. The AMF inoculation increased maize growth at both P levels, and was more pronounced at 19 mg P kg⁻¹, including a 10 % increase in plant biomass and a 24 % increase in P content. AMF hyphae penetrated a nylon mesh barrier, facilitating P uptake from a compartment inaccessible to roots, thereby underscoring the critical role of AMF in raising plant P acquisition, particularly under P limitation. Soil zymography revealed increased acid phosphatase activity in the AMF-inoculated mycorrhizosphere compared to non-inoculated soil, coinciding with P-depletion microzones around the roots (as shown by DGT imaging). AMF inoculation expanded the hotspot area of acid phosphatase activity by 77 % compared to the control soil without AMF. This enzymatic boost of P mobilization and expansion in root system architecture increased root P uptake, alleviating plant P deficiency. In conclusion, the raise of the soil volume for P mobilization through AMF-plant symbiosis present potential strategy to increase P use efficiency in agricultural systems.