Combined phosphate-solubilizing bacteria and calcium-magnesium-phosphate fertilizer alleviate Cd toxicity and reduce Cd uptake in wheat: Insights into physiological responses and molecular mechanisms

Cadmium (Cd) in the environment is toxic to plant growth and poses significant risks to human health through the food chain. However, research on the effects and mechanisms of combined application of phosphate-solubilizing bacteria (PSB) and calcium-magnesium-phosphate (CMP) fertilizer in alleviating Cd toxicity and reducing Cd uptake in wheat are lacking. In this study, we investigated the capacity of PSB Burkholderia sp. YM3 to dissolve CMP fertilizer, and evaluated the effects of its combined application with CMP on growth, physiological responses, Cd and phosphorus (P) uptake, and gene expression in wheat seedlings under Cd stress. Our results demonstrated that strain YM3 effectively solubilized CMP fertilizer, thereby releasing soluble calcium, magnesium, and P. Notably, the combined treatment (YM3 +CMP) presented the highest Cd removal efficiency in solution culture, reaching 88.79-90.55 %. This co-application also alleviated Cd-induced toxicity in wheat seedlings, as evidenced by significant reductions in the content of malondialdehyde (MDA:11.16-51.85 %), proline (44.04-49.33 %) and hydrogen peroxide (H₂O₂:44.94-61.93 %), as well as antioxidant enzyme activity. Furthermore, the combined treatment enhanced plant growth, root vigor (77.85-183.14 %), total chlorophyll content (40.79-78.75 %), and total P accumulation (9.23-86.76 %). Critically, YM3 +CMP also significantly reduced Cd uptake in both the aboveground tissues (51.39-54.80 %) and roots (49.73-50.34 %). At the molecular level, YM3 +CMP downregulated the expression of metal transporter genes TaLCT1 and TaNramp5, while upregulating the expression of the zinc transporter gene TaZIP3 and the P transporter genes TaPHT1.2 and TaPHT1.9 under Cd stress (p < 0.05). These results indicate that the combined application of strain YM3 and CMP fertilizer has considerable potential for alleviating Cd-induced toxicity and reducing Cd uptake in wheat seedlings and will contribute to a deeper understanding of the molecular mechanisms underlying the response of wheat to the co-application of PSB and CMP under Cd stress.