Effects of Aged Biochar on Remediation of Cd-Contaminated Soil and Greenhouse Gas Emission in Chinese Cabbage (Brassica chinensis L.) Growth

Biochar has demonstrated effectiveness in environmental remediation. However, the physicochemical properties of biochar change with natural aging, which potentially impacts its efficacy. This study was designed to evaluate the effects of aged biochar (at 1% and 5% rates) on the growth of Chinese cabbage, greenhouse gas emission, and Cd remediation in soils. Canada goldenrod (Solidago canadensis L.) feedstock biochar was subjected to three artificial aging processes (freeze–thaw cycle, dry–wet cycle, and hydrogen peroxide oxidation) to prepare aged biochar. Results showed that aging significantly altered properties and structure of biochar. Biochar addition had no effect on CH4 emissions, but it decreased cumulative N2O emission (all treatments) and increased cumulative CO2 emission (only the pristine biochar at 5% application rate). Aged biochar showed no effect on microbial life strategy and Shannon index. However, PB-5% application shifted the life history strategies of A-strategists (resource acquisition microbe) towards Y-strategists (high-yield microbe) such as Proteobacteria, Gemmatimonadota, Bacteroidota, Firmicutes and Actinobacteriota, which partially attributed to the enhanced soil CO2 emission. Aged biochar reduced plant uptake Cd and soil available Cd concentrations by up to 36.6% and 34.0%, respectively, ascribing to improved soil physicochemical properties and functional bacterial abundance.