Enhanced release of fluoride from rhizosphere soil of tea plants by organic acids and reduced secretion of organic acids by fluoride supply

Tea plant (Camellia sinensis L.) is a typical fluoride (F)-accumulator species which can grow in the acid soil (pH: 4.0–6.0). Organic acids (OAs) secreted by plant roots can result in soil acidification, soil nutrients release, and subsequent elements' uptake. Rhizosphere soil is the main processes place at the soil–root interface. This study investigated the kinetics of F release from rhizosphere soil of tea plant extracted by malic and citric acids and the effect of F supply on malic and citric acids metabolism. The results showed that both the F release kinetics from rhizosphere in malic and citric acid extractant solutions were well fitted to Elovich equations. F supply induced a decrease in secretion of malic and citric acids and their accumulations in root and leaf. The amount of malic acid release in culture medium was linear with the root malic acid concentration. Both the malate dehydrogenase and citrate synthase activities were decreased under F treatments. This is the first study surveying the F release from rhizosphere of tea plant involved in OAs extractions.