Interactions of silicon and arbuscular mycorrhizal fungi on phosphorus uptake during rice vegetative growth

• Co-application of Si and AMF on P uptake in rice was regulated by soil P levels; • Si played dual roles in regulating AMF functioning based on P availability; • Si reduced AMF colonization rate under low P, diminishing AMF functioning; • Si enhanced AMF-PSB cooperation under high P, strengthening P uptake; • Soil P status is important when using Si and AMF for P optimization in agroecosystems. Silicon (Si) and arbuscular mycorrhizal fungi (AMF) improve phosphorus (P) nutrition in crops, but the mechanisms underlying their interactive effects on P uptake by roots remain elusive. This study investigated the impact of Si and AMF ( Rhizophagus irregularis DAOM) on P uptake at rice ( Oryza sativa L.) late jointing stage grown in soils with low and high P availability (18.2 vs 62.1 mg P kg −1 ) under greenhouse conditions. Under low P availability, AMF increased P content in rice leaves and stems by 16.1 % and 11.8 %, respectively. However, simultaneous Si application with AMF inoculation counteracted this positive effect, reducing the P content in leaves and stems by 15.9 % and 8.28 %, respectively, compared to AMF alone, due to a 20.8 % decrease in AMF colonization rate. This reduction may be associated with Si deposition on root cell walls and increased competition between AMF and P-solubilizing bacteria (PSB). In contrast, under high P availability, the combination of Si and AMF increased stem P content by 8.42 % compared to AMF alone, linked to Si-induced raise in PSB abundance. This could strengthen cooperation between AMF and PSB, as AMF mycelial secretions provide easily available carbon sources for PSB, and PSB dissolved insoluble P forms for AMF uptake. These findings highlight the crucial role of soil P availability in modulating the efficacy of Si and AMF co-application to increase P uptake during rice vegetative growth. Under low P availability, Si reduces AMF functioning by decreasing colonization rates, while under high P availability, Si reinforces the P-promoting effects of AMF by stimulating PSB abundance. This study emphasizes the importance of considering soil P status when developing strategies that employ Si and AMF to optimize P utilization in agroecosystems.