Abstract
Cadmium (Cd) speciation ratio in arable land determines the Cd exposure risk and Cd uptake in crops. However, the driving mechanisms of Cd speciation change on the vertical scale of paddy fields remain poorly understood. In this study, the effects of plow layer and plow pan on Cd speciation distribution were investigated in a long-term Cd-contaminated rice ecosystem. The Cd accumulative effect within rice grain was enhanced with high levels of activated Cd speciation ratios in soils. Activated Cd speciation ratios were higher in plow layer soils, while stabilized Cd speciation ratios were elevated in plow pan soils. Soil physicochemical properties and soil microbes synergistically affected the Cd speciation changes in different ways between the two soil layers. Soil pH and organic elements in plow layer environment directly hindered the transformation of stabilized Cd speciation, while in plow pan environment, soil pH and organic elements indirectly decreased activated Cd speciation ratios and resulted in the accumulation of stabilized Cd speciation via regulating the predominant bacterial taxa. This study will improve our understanding of how soil environments regulate Cd speciation distributions in rice ecosystems and help to seek effective remediation methods of Cd-contaminated paddy fields to reduce the Cd accumulation in rice.
Highlights
Cadmium (Cd), a highly toxic and carcinogenic heavy metal species, has attracted substantial attention from researchers (Aitio and Tritscher, 2004; Hu et al, 2020)
The aims of this study were to evaluate the responses of Cd speciation distribution to soil properties and soil microbes, and to reveal the transformation mechanisms of Cd speciation regulated by the plow layer and plow pan soil environments
Soil moisture, total K, organic N, and organic H had a significantly positive correlation (p < 0.01) with the F-Red ratio of plow pan soils. These results showed that the differences in soil properties, especially soil pH and organic elements, distinctly impacted the Cd speciation distribution between the plow layer and plow pan soils
Summary
Cadmium (Cd), a highly toxic and carcinogenic heavy metal species, has attracted substantial attention from researchers (Aitio and Tritscher, 2004; Hu et al, 2020). Rice (Oryza sativa L.), as the main food for more than half the global population, readily assimilates Cd via Cadmium Speciation Distribution root uptake (Khan et al, 2017; Shi et al, 2020). Consumption of Cd-contaminated rice enhances the dietary exposure to Cd and threatens human health (Santeramo and Lamonaca, 2021). Cd-contaminated paddy soils are in urgent need of remediation to reduce the Cd bioaccumulation of crops and adverse health effects (Huang et al, 2019). This requires a clear understanding of the biogeochemical behavior of Cd and Cd speciation change controlled by various soil environments (Li et al, 2021)
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