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Rice and rice-based foodstuffs are important pathways for inorganic As dietary intake. This work shows a detailed picture of As content and speciation in Italian rice, which contributes to more than one-half of the European production, and addresses the role of soil chemistry and agronomic management on As concentration in rice grain, in view of ameliorative strategies. The mean total As content in Italian white rice was 155 ± 65 μg kg with significant differences among producing areas, while the mean inorganic As was 102 ± 26 μg kg, largely below the E.U. limit of 200 μg kg for white rice, although part of the production would not be suitable for baby food production, which requires less than 100 μg kg of inorganic As. The differences in As content and speciation in rice among the studied areas resulted from the complex interactions of soil, plant, and anthropic factors. Among others, Si nutrition seemed to play a key role in regulating As transfer from soil to plant.

Phosphorus (P) cycling in paddy soil is closely related to iron (Fe) redox wheel; its availability to rice has thus generally been ascribed to Fe minerals reductive dissolution. However, the literature aimed to identify the best method for predicting rice available P does not uniformly point to Fe reductants. Rice plants can indeed solubilize and absorb P through many strategies as a function of P supply, modifying the chemical environment. Therefore, this study aims to estimate P availability in paddy soils coupling the redox mechanisms driving P cycling with concurrent plant responses. Soil available P was estimated in three groups of paddy soils with low, medium, or high P content assessing easily desorbable pools (0.01 M calcium chloride, Olsen, Mehlich-III, anion exchanging resins) and Fe-bound P pools (EDTA, citrate-ascorbate, and oxalate). Rice P uptake and responses to P availability were assessed by a mesocosm cultivation trial. Although P released in porewater positively correlated with dissolved Fe(II), it did not with plant P uptake, and readily desorbable P pools were better availability predictors than Fe-bound pools, mainly because of the asynchrony observed between Fe reduction and plant P demand. Moreover, in low P soils, plants showed higher Fe(II) oxidation, enhanced root growth, and up-regulation of P root transporter encoding genes, plant responses being related with changes in P pools. These results indicate the generally assumed direct link between Fe reduction and rice P nutrition in paddy soils as an oversimplification, with rice P nutrition appearing as the result of a complex trade-off between soil redox dynamics, P content, and plant responses.