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

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.