Microbial community modulation by MgFe-layered double hydroxide and biochar  composite for enhanced crop growth, nitrogen use and reduced metal availability in  paddy soils
Intensive rice cultivation faces the dual challenges of low nitrogen use efficiency and therisk of heavy metal mobilization. In this study, a magnesium-iron layered double hydroxideloaded biochar (Mg/Fe-LDH@BC) composite was synthesized to investigate its efficiency andmechanism in the synergistic regulation of nitrogen and heavy metals in paddy soil. With theaddition of 1% Mg/Fe-LDH@BC, NH4+-N retention increased by 41.7% while NO3--Naccumulation decreased by 9.8%. As a result, nitrogen use efficiency improved and potentialnitrogen losses via denitrification and leaching were reduced. Concurrently, NH3 volatilizationdecreased by 24.2%, and N2O emissions were reduced by over 50%. Also, biosavailability ofmultiple heavy metals including Cu, Zn, Ni, Pb, Cr, and As was suppressed, and promoted riceyield. Furthermore, microbial community analysis revealed that Mg/Fe-LDH@BC optimizedthe rhizosphere microenvironment compared to the control group. It enriched key functionalbacterial communities involved in nitrogen transformation (e.g., Nitrosomonadaceae) andenhanced nitrogen utilization and crop uptake. Sulfur cycle-related bacteria (e.g.,Desulfatitalea) were activated to promote in-situ passivation of heavy metals through sulfideprecipitation during metabolic processes. Moreover, Mg/Fe-LDH@BC strengthened thecomplexity and stability of bacterial co-occurrence networks and improved the resilience andrecovery capacity of the soil ecosystem against external stresses.