By isolating soil warming from air and canopy effects under natural extreme heat, they found that sustained soil warming of over 5 °C did not significantly elevate arsenic (As) or most metal (loid) levels in grains. Although porewater As increased seasonally, grain contamination rose only modestly, indicating limited direct food safety risk.
Rice paddies are particularly sensitive to climate change because flooded soils create oxygen-poor conditions that can mobilize redox-sensitive toxic elements such as As and cadmium. Previous warming experiments often combined air and soil heating, making it difficult to determine whether soil temperature alone drives increased metal uptake. Many projections assume that warmer soils stimulate microbial reduction of iron oxides, releasing As into porewater and ultimately into grains. However, plant uptake is regulated not only by soil chemistry but also by root transport, detoxification, and internal sequestration mechanisms. Disentangling soil and air temperature effects has therefore become critical for assessing climate-driven food safety risks.
A study (DOI: 10.48130/ebp-0025-0017) published in Environmental and Biogeochemical Processes on 30 December 2025 by Sha Zhang’s team, Chinese Academy of Sciences, clarifies that soil warming alone does not necessarily increase toxic metal accumulation in rice, refining climate change risk assessments for food safety.
Using a semi-natural mesocosm system established during the extreme heatwave year of 2022, researchers isolated soil warming effects from air and canopy temperatures by creating sun- and shade-facing flooded plots that generated an average soil temperature difference of 5.65 ± 4.84 °C at 5–10 cm depth over a 143-day rice–ratoon season. Three major heatwaves (≥36 °C for at least three consecutive days) were recorded, including 27 days exceeding 40 °C, and both the main and ratoon crops underwent grain filling under these extreme conditions. Porewater from rhizosphere and bulk soils was repeatedly sampled to quantify redox-sensitive and nutrient elements, and grain and vegetative tissues were analyzed to evaluate accumulation and node-to-grain translocation. Despite theoretical expectations that higher temperatures would stimulate microbial Fe reduction and enhance As mobilization, porewater As concentrations in warmed plots did not differ significantly from controls during the main crop and remained relatively low (~6.68 vs. 5.3 μg L⁻¹). Strong linear relationships between porewater Fe and As (R² > 0.65) indicated coupled redox processes, with pronounced increases during the ratoon stage (>450 μg L⁻¹ As), suggesting that prolonged flooding and cumulative heat exposure, rather than transient warming, governed mobilization dynamics. Grain analyses showed that most elements, including As and Cd, were unaffected by soil warming in both seasons (p > 0.5). Seasonal effects were more evident: grain As rose from ~86–100 μg kg⁻¹ in the main crop to ~115–131 μg kg⁻¹ in the ratoon crop, corresponding to higher porewater As, while Cd remained stable due to continuous submergence limiting its mobility. Beneficial elements such as Se and Zn declined in ratoon grains, likely due to restricted node-to-grain translocation. Tissue profiling revealed that grains maintained distinct elemental signatures, reflecting strong physiological regulation, and that ratoon rice exhibited higher translocation rates for several elements, including As.
Overall, the findings show that soil warming alone did not substantially increase grain metal(loid) accumulation, challenging the assumption that hotter soils under climate change will inevitably intensify rice contamination. By isolating soil temperature effects, the study highlights the buffering capacity of flooded paddies and strong plant regulatory control. It underscores the importance of distinguishing soil and air warming pathways and prioritizing water and redox management in climate-adaptive food safety strategies.
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References
DOI
10.48130/ebp-0025-0017
Original Source URL
https://doi.org/10.48130/ebp-0025-0017
Funding Information
This work was supported by the National Key Research and Development Program of China (Grant No. 2023YFC3709100) and the National Science Foundation of China (Grant Nos. 42477116 and 42207013).
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Environmental and Biogeochemical Processes is a multidisciplinary platform for communicating advances in fundamental and applied research on the interactions and processes involving the cycling of elements and compounds between the biological, geological, and chemical components of the environment.