Effect of pH on growth and Cd accumulation in different rice varieties under hydroponics

Currently, applying lime to cadmium (Cd)-contaminated paddy fields to increase pH and reduce Cd availability is an effective method to control excessive Cd levels in rice grain. However, under hydroponic conditions, the impact of increased pH on Cd accumulation in different rice varieties remains unclear. This study employed three rice varieties (Yuzhenxiang, Shaoxiang 100, Xiangwanxian 12) with different Cd accumulation characteristics under different pH and long-term treatment with 1 μM CdCl₂, to study the effect of pH on growth and Cd accumulation in different rice varieties. The result showed that as pH shifted from 5 to 8, the SPAD values, shoot dry weight, and plant height of the three rice varieties significantly decreased. The main root length, root volume, and root dry weight of Yuzhenxiang, and Shaoxiang100 significantly decreased. Conversely, the root architecture indicators of Xiangwanxian 12 did not change significantly. As for element accumulation, increasing the pH significantly increased the content of Mn in both the shoots and roots of all three varieties. Yuzhenxiang significantly reduced Cd content in both the shoots and roots of rice, while Shaoxiang100 significantly increased Cd content in both parts. Xiangwanxian 12 showed a significant increase in Cd content in the shoots but a decrease in the roots. In terms of subcellular distribution, Yuzhenxiang significantly reduced Cd concentrations in the cell wall and organelles of root cells, resulting in lower Cd concentrations in the root tissue. Conversely, Shaoxiang100 significantly increased Cd concentrations in the cell wall, organelles, and soluble fractions of root cells, leading to higher Cd concentrations in the root tissue. Xiangwanxian 12 also exhibited a decrease in Cd concentrations in the cell wall, organelles, and soluble fraction of root cells, resulting in lower Cd concentrations in the root tissue. Additionally, the expression of the OsNRAMP5 and OsHMA3 gene was significantly increased in Shaoxiang 100, while no significantly change in Yuzhenxiang and Xiangwanxian 12. These results provide important guidance on the impact of pH on Cd accumulation during the vegetative growth stage of different rice varieties.