Fabrication of Mg/Al-Layered Double Hydroxide–Biochar for Reducing Cadmium and Arsenic Uptake in Soil-Covered Morchella sextelata Cultivation

Cadmium and arsenic accumulation during soil-covered cultivation of Morchella sextelata limits its production in contaminated soils. Two Mg/Al-layered double hydroxide–biochar (LB) composites were prepared using grinding-assisted and coprecipitation procedures and denoted as LB1 and LB2, respectively. The composites were evaluated at 2% (w/w) through a 15 d soil incubation experiment and a staged basket-cultivation experiment with three independent replicates. During incubation, LB2 significantly decreased NH4H2PO4-extractable As and DTPA-extractable Cd by 28.6% and 29.1%, respectively. Sequential extraction showed that LB1 increased the operationally defined residual Cd fraction, whereas LB2 increased the oxidizable Cd fraction and produced the lowest extractable Cd and As concentrations. During cultivation, LB1 reduced total As accumulation in dry fruiting bodies by 53.9%, whereas LB2 reduced Cd accumulation by 40.0%. Amendment-induced changes in soil carbon fractions were associated with Cd and As partitioning and fruiting-body accumulation, although these correlations did not establish causality. The two as-prepared composites therefore produced distinct metal-specific responses under the tested conditions.