Soil incubation study on the coupled effect of climate change and soil cadmium

Healthy soils with taxonomically and functionally diverse microbiomes are crucial for ensuring food security, ecosystem functioning, and climate feedbacks. Climate change and heavy metals inde-pendently stress soil microbiomes. Their coupled impacts, however, have yet to be resolved. Here we show that future climatic conditions non-linearly affect soil cadmium, altering the soil mi-crobiome and accompanying nutrient cycles, with soil pH being the dependent factor. For soils with a pH<7, and especially during summer temperatures, future climatic conditions increased the frac-tion of porewater cadmium and led to an increasingly divergent taxonomic and functional microbi-ome structure. As a metabolic example, microbial ammonium oxidation released protons which liberated cadmium through cation exchange from mineral surfaces. When porewater cadmium reached concentrations at which toxicity to non-cadmium-tolerant bacteria was exerted, microbial activity and subsequent nutrient cycling decreased, limiting carbon and nitrogen emissions. In con-trast, soil pH>7 limited future climate impacts on cadmium mobilization, but they were nonetheless imprinted on microbiome structure. Subsequent nutrient cycling increased under future climatic conditions, stimulating soil respiration and nitrous oxide release. Our findings illustrate the coupling of climate change with soil contaminant availability in modifying the soil microbiome and conse-quential impacts on microbial activity and, thus, crop production and climate feedback.