Effect of tea plantation age on the distribution of fluoride and its fractions within soil aggregates in the hilly region of Western Sichuan, China

Long-term tea plantation (Camellia sinensis L.) could markedly change the pools of total fluoride (T-F) in soil extractable fractions. However, the effects of different chronosequence phases on the changes of fluoride fractions in these plantations are poorly understood. In this study, we have investigated the distribution of extractable fluoride fractions in four differently aged tea plantations (16, 23, 31, and 53 years old, respectively), in Zhongfeng Township of Ming-shan County, Sichuan, Southwest China. This study aimed to determine the effects of the age of various tea plantations with respect the contents of T-F, also considering the water-soluble fluoride (Ws-F), the exchangeable fluoride (Ex-F), the Fe/Mn oxide-bound fluoride (Fe/Mn-F), the organic matter-bound fluoride (Or-F), and the residual fluoride (Res-F) within soil aggregates. The T-F, Ws-F, Ex-F, and Res-F contents increased with the decreasing of particle size except for Fe/Mn-F and Or-F. Along with the increase of tea plant life, the contents of Ws-F and Ex-F within soil aggregates gradually increased. In addition, the trends of extractable Fe/Mn-F and Or-F were opposite to that of highly available fluoride after 23 years. The results of this study show that fluoride is easily transformed into highly available phases in long-term tea plantations, improving the absorption of fluoride for tea plants.