Mechanisms of N-doped microporous biochar decreased Cd transition in rhizosphere soils and its impact on soil bacterial community composition

Soil cadmium (Cd) contamination has garnered considerable attention. This study employed batch sorption experiments and rhizobox experiments to examine the impact of nitrogen-doped microporous biochar (NBB) on the temporal and spatial distribution of Cd in the rhizosphere of rice plants, with the aim of elucidating the underlying mechanisms. The results indicated that the adsorption of Cd(II) onto NBB was predominantly governed by chemical reactions. When applied to soil, the NBB significantly hindered the migration of Cd from the bulk soil to the rhizosphere. Additionally, the application of NBB decreased the redox potential (Eh) in the rhizosphere soil and increased the relative abundance of Anaeromyxobacteraceae, Geobacteraceae, Desulfurisporaceae, and Syntrophomonadaceae, which could facilitate the reduction of soil Cd availability. Furthermore, the NBB2 treatment encouraged the formation of iron plaque on the root surface, thereby limiting the uptake of Cd from the soil into the root system. Moreover, the N-doped microporous biochar treatment resulted in lower Cd levels in the stele of root, an effect that was associated with increased sulfur (S) content in the stele and epidermis, suggesting a potential role for S in Cd sequestration. Ultimately, the application of N-doped microporous biochar resulted in diminished Cd accumulation in the rice tissues.