Effects of cultivars, water regimes, and growth stages on cadmium accumulation in rice with different radial oxygen loss

Large areas of paddy fields have been contaminated by cadmium (Cd) in both China and worldwide, resulting in excessive Cd accumulation in rice grains. Here, we investigated the effects of cultivars, water regimes, and growth stages on Cd accumulation in rice with different radial oxygen loss (ROL). Two groups of experiments were conducted: pot trials with soil-added Cd and solution-added agar using 20 rice cultivars and a rhizobag trial with Cd-contaminated soil and pot trial with solution-added agar under flooded and non-flooded water regimes with three growth stages and two cultivars. Different rice cultivars exhibited different porosity, Cd tolerance, and Cd accumulation in grains, which were significantly correlated with ROL. Cd concentration in shoots was significantly lower under the flooded (0.13–1.01, mean 0.56 mg kg−1) than non-flooded regime (0.68–1.39, mean 0.97 mg kg−1). The low Cd-accumulating cultivar showed higher rates of ROL, higher Cd combined with Fe plaque formation, and lower Cd bioavailability in the rhizosphere soil than the high-Cd accumulating cultivar. Rice cultivars grown under flooded regimes effectively reduced Cd accumulation in edible parts, and the later stage was crucial for reducing Cd accumulation. Low Cd-accumulating cultivars generally exhibited a higher ability to reduce Cd bioavailability in the rhizosphere soil.