The effect of silicon on the kinetics of rice root iron plaque formation

Purpose Aquatic plants, including rice, develop iron (Fe) plaques on their roots due to radial oxygen loss (ROL), and these plaques accumulate both beneficial and toxic elements. Silicon is an important nutrient for rice and both accumulates in Fe plaque and can affect ROL. How these plaques form over time and how Si affects this process remains unclear. Methods Rice was grown in a pot study with 4 levels of added Si. Root Fe plaque formation was monitored weekly using vinyl films placed between the pot and soil. Plants were grown to maturity and then ratooned to also examine the formation of Fe plaque during the ratoon crop. Results Iron plaque formation increased exponentially during the vegetative phase, peaked at the booting phase, then decreased exponentially – a pattern that repeated in the ratoon crop. While the highest Si treatment led to an earlier onset of Fe plaque formation, increasing Si decreased the amount of Fe plaque at harvest, resulting in a minimal net effect. Conclusions The kinetics of Fe plaque formation are dependent on rice growth stage, which may affect whether the Fe plaque is a source or sink of elements such as phosphorous and arsenic.