Effects of foliar and soil application of sodium silicate on arsenic toxicity and accumulation in rice (Oryza sativa L.) seedlings grown in As-contaminated paddy soils

Abstract

ABSTRACTSilicon (Si) and arsenite (iAsIII) share the same pathway of uptake and translocation in rice (Oryza sativa L.), and it has been reported that Si can decrease arsenic (As) uptake by rice in hydroponic culture. Due to the competitive sorption between Si and As for the soil minerals, different extents of effects on As toxicity and uptake by rice as influenced by soil Si application were found. In order to avoid the competitive sorption between Si and As for the soil minerals, foliar applications of Si might be a more efficient alternative to reduce As uptake by rice. Therefore, the aim of this study was to investigate the effects of Si foliar and soil applications on the growth and As accumulation in rice seedlings. In this study, three application rates of Si (as sodium silicate) were applied to (1) the foliage and (2) the soil, of rice grown in two soils with different Si retention capacities and As contents. The results showed that there were no significant differences in Si concentrations in shoots among different Si foliar applications, and it had no significant effect on the growth and As accumulation in rice seedlings. In contrast, soil applications of Si caused a decrease in As accumulation in shoots grown in the tested soils, resulting from a high Si/As ratio in the soil pore water allowing enough Si to out-compete the As for uptake by roots. These results were further supported by the significant negative correlation found between Si and As in the shoots. However, a growth inhibition of rice plants was also observed due to As toxicity from the addition of excessive treatments of Si into As-contaminated soils. Therefore, the results of this study suggest that foliar applications of Si are not able to decrease As accumulation in rice seedlings, but that the application of moderate amounts of Si into As-contaminated soils could effectively reduce As uptake by rice seedlings.