Cadmium inhibits carbon and nitrogen cycling through soil microbial biomass and reduces soil nitrogen availability

Microbial mediated carbon and nitrogen cycling response to cadmium are often observed in soil; however, a unified framework of this response has not yet been established. By analyzing 1232 observations from 166 publications, we found that cadmium decreased microbial biomass carbon (-16 %) and nitrogen (-21 %), dissolved organic nitrogen (-27 %), nitrification rate (-17 %), microbial respiration rate (-12 %), and β-1,4-glucosidase (-21 %) and urease (-16 %) activities, but increased microbial metabolic quotient (+11 %) and fungal-to-bacterial ratio (+39 %). The cadmium impact was concentration-dependent, becoming more pronounced at higher concentrations. Increasing cadmium concentration reduced soil N mineralization rate and total N content, but increased microbial biomass carbon-to-nitrogen ratio. These results indicate that cadmium reduced carbon and nitrogen assimilation into microbial biomass and limited soil inorganic nitrogen production. Soil bulk density drove soil microbial biomass and nitrogen availability response to cadmium. Lower soil bulk density and higher initial carbon and clay contents and soil pH reduced the negative impact of cadmium on microbial biomass and nitrogen availability, suggesting that anthropogenic activities that enhance soil quality may mitigate the inhibitory effect of cadmium on soil carbon and nitrogen cycling. Our analysis provides critical implications for improving our understanding of the ecological consequences of cadmium on soil carbon and nitrogen cycling.