Radial oxygen loss of Typha latifolia outperforms microbial effects in heavy metal(loid) stabilization.

Wetland plants play a critical role in the remediation of tailings pond wetlands. Their unique radial oxygen loss (ROL) and rhizosphere microbial communities can modify soil properties (e.g., Eh, C, N), collectively stabilizing heavy metal(loid)s. However, the relative importance of these two pathways remains unclear. To address this, we conducted a stratified rhizosphere (divided into layers a-c) microcosm experiment comprising four treatments: unplanted tailings (MB) were compared with Typha latifolia-planted tailings (MT) to isolate the effects of ROL, and Typha latifolia-planted moderately polluted soil (PS) was compared with unpolluted soil (US) to evaluate ROL under different contamination levels and soil properties. Results indicated that available Pb, Zn, and Cd in layers a-c decreased by 78.4%, 86.7%, and 24.6% in MT compared to MB. Structural equation modeling revealed that ROL had the highest path coefficient (0.98) for heavy metal(loid) concentrations in MT. Furthermore, increased carbon and nitrogen contents enhanced ROL-driven stabilization of heavy metal(loid)s. Variance partitioning analysis showed microbial communities explained 1.9% of variance in MB, MT, and PS, but 81.8% in US. These results indicate that ROL is more crucial than microbial communities in heavy metal(loid) stabilization. Management strategies that increase carbon and nitrogen availability are expected to enhance ROL, thereby facilitating the remediation of heavy metal(loid)s.