Climate change-induced cadmium accumulation in spinach.

Cadmium (Cd) contamination in agricultural soils raises concerns due to its toxicity and mobility in the soil-plant system. A recent soil incubation study found that future climate conditions may further increase Cd mobility in soil [1], but the resulting consequences for its transfer to plants and the human food chain remain unknown.

Here, we investigate the impact of climate change on Cd accumulation by spinach (Spinacia oleracea), chosen as a model plant for leafy crops. Spinach is recognized as a significant source of essential micronutrients yet it also accumulates Cd, even up to toxic levels in edible parts. Four spinach varieties were cultivated in soils with diverse geochemistry and Cd levels under ambient climatic conditions (20°C daytime temperature, ambient atmospheric CO₂ and 50% water holding capacity) and anticipated future climatic conditions (+2.25°C, +290 ppmv CO₂, and 7% less gravimetric water content, [2]).

Three out of four spinach varieties produced significantly higher edible biomass under future climatic conditions than under current conditions. This biomass increase was accompanied by significantly elevated Cd concentrations in the edible parts of all spinach varieties. Transfer factors (soil-to-root and root-to-shoot) indicate that the higher shoot Cd levels were primarily driven by enhanced Cd movement across the soil-root interface, coupled with an increase in the mobile Cd fraction in the soil. Metabolite profiling of the rhizosphere revealed elevated levels of organic acids and metal chelators under future conditions, which mobilized Cd through pH modifications and chelation. Increased plant-derived metabolites, particularly carbon sources, coupled with higher temperatures, promoted microbial growth, as indicated by higher microbial 16S rRNA transcript levels and elevated Krebs cycle metabolites in the soil. This rise in soil microbial metabolism may enhance soil turnover and decomposition, ultimately increasing Cd mobility in soil.

Our findings provide insights into problematic future Cd accumulation in spinach, with potential relevance to other leafy vegetables. This highlights the critical need to address soil contaminants in assessing the impact of climate change on food safety.

[1] Drabesch et al. (2024). Climate-induced microbiome alterations increase cadmium bioavailability in agricultural soils with pH below 7. Communications Earth & Environment.

[2] IPCC (2021). Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report.