Physiological responses of pak choi (Brassica Rapa subsp. Chinensis (L.) Hanelt) to cerium and yttrium in two acidic soils with contrasting textures

Rare earth elements (REEs) are emerging contaminants, but little is known about their soil bioavailability and physiological effects on crops. This study investigated the effects of cerium (Ce) and yttrium (Y) at 0, 25, 50, and 100 mg kg^{- 1} on pak choi (Brassica rapa subsp. chinensis (L.) Hanelt) grown in high clay and low clay soils. Measurements included Ce and Y uptake, biomass, photosynthetic pigments, respiratory activity, and proline concentration. The addition of Ce and Y was associated with elevated Ca, Mg, Fe, and Al in the shoots, supported by the overlapping ion mappings of these elements in the leaves with laser ablation inductively coupled plasma mass spectrometry. The root and shoot biomass of the crop in the high clay soil significantly (p < 0.05) increased from the control to 25 mg Ce kg^{- 1} and 25 mg Y kg^{- 1}, respectively. In both soils, Y was more toxic to photosynthetic pigments than Ce, while respiratory activity was sensitive to both Ce and Y, leading to reduced proline levels. This study demonstrated that the soil bioavailability and physiological responses of the tested crop to Ce and Y were controlled by REEs type and soil texture.