Inoculation with phosphate-solubilizing bacteria reduce the transport of cadmium in Brassica napus L. by reshaping phosphate-solubilizing microbes in rhizosphere

Phosphorus-solubilizing bacteria (PSB) are widely recognized for their potential to alleviate cadmium (Cd) stress in plants, particularly in acidic soils with low phosphorus (P) availability. However, how exogenous PSB interact with indigenous P-cycling microbial communities and regulate soil enzyme-mediated processes involved in Cd accumulation remains poorly understood. Here, we investigated the effects of inoculation with a PSB strain, Providencia rettgeri ( P . rettgeri ), on soil physicochemical properties, phosphatase activities, and phoC - and phoD -harboring bacterial communities in the rhizosphere of Brassica napus grown in Cd-contaminated acidic soil. The results showed that bacteria inoculation under Cd stress increased soil organic matter and decreased available phosphorus content and phosphatase activities. Although inoculation increased Cd retention in rhizosphere soil, it significantly reduced Cd translocation and bioconcentration factor in plant tissues. The phoC -harboring bacterial community exhibited lower sensitivity to Cd stress and bacterial inoculation than the phoD -harboring community and formed a more densely connected network structure. PhoC -harboring bacteria Stenotrophomonas and phoD- harboring bacteria Bradyrhizobium were the keystone species in phoC - and phoD- harboring bacterial network, respectively. Structural equation modeling further revealed that bacterial inoculation indirectly reduced plant Cd accumulation primarily through modifying soil chemical properties and enzyme activities, rather than through direct effects of phoC - or phoD -harboring bacterial attributes. These findings highlight the distinct ecological roles of phoC - and phoD -harboring bacterial communities in regulating phosphorus cycling and Cd bioavailability, providing mechanistic insights into how PSB inoculation modulates plant Cd accumulation in acidic soils.