Effect Of Tea Polyphenols On Mobilization Of Mineral Elements From Acidic Soils

Plant polyphenols are important abundant plants secondary metabolites, and enter into the soil through a variety of pathways including root exudation and leaf litter decomposition, thus affecting chemical recycling of soil elements. China is the homeland of tea, at where the tea industry is developing rapidly, at the same time plentys of Albic Fe-accumuli-Stagnic Anthrosols and Typic Haplic-Perudic Argosols which exist widely in western Sichuan have been used as tea cultivation. Tea polyphenols(TPs) produced only by tea and the highest content of the epigallocatechin gallate (EGCG) in related research was ued as "model" polyphenol. Extraction experiments were performed to estimate the effect of Tea polyphenols on mobilization of mineral elements from acidic soils which are suitable for tea cultivation at different conditions. The obtained data demonstrated that:(1) Results show that the effects of TPs mobilizing soil Si, Al and Fe were higher in Dystric Purpli-Udic Cambosols than in Albic Fe-accumuli-Stagnic Anthrosols and Typic Haplic-Perudic Argosols, the three organic LMWOAs differed in the effect, displaying an order of oxalic acid> citric acid> malic acid, and their effects were more significant than TPs’in the Albic Fe-accumuli-Stagnic Anthrosols and in the Typic Haplic-Perudic Argosols, but not in the Dystric Purpli-Udic Cambosols, where TPs were higher than malic acid in the effect (especially in effect of mobilizing Si, TPs were even higher than all the LMWOAs), which demonstrates that TPs really play an important role in desilicating primitive soil through complexing action and proton effect, and hence predicts that tea cultivation may be conducive to the evolution of the soils into zonal soils; The effects of TPs and LMWOAs were more significant on Al than on that Si and Fe in all the three soils, and moreover, mobilization of Si, Al and Fe occurred simultaneously, which indicates that TPs and LMWOAs may get complexed more efficiently with Al, thus lowering its toxicity, but on the other hand, increasing its mobility and facilitating its entrance into water body and the environment. In terms of effect mobilizing soil base ions, in case of Ca, malic acid was higher than TPs; in the case of Mg and K, LMWOAs were higher than TPs; and in the case of Na, tea extracts ranked first, and were followed by citric acid and then malic acid, and in Albic Fe-accumuli-Stagnic Anthrosols, TPs were higher than LMWOAs. The effects of LMWOAs and TPs mobilizing soil base cations, especially Ca, K and Na, were the highest in Albic Fe-accumuli-Stagnic Anthrosols, and the three base cations though followed an order of Ca> Mg> K in amount mobilized, they were being mobilized simultaneously. So the use of Albic Fe-accumuli-Stagnic Anthrosols for tea cultivation would promote mobilization and migration of Ca, K and Na, which would improve bioavailability of these base cations on the one hand and accelerate soil acidification on the other. It is, therefore, essential to further intensify systematic study of the effects of TPs on mobilization and migration Si, Al and Fe in primitive soils and the effects of conversion of Albic Fe-accumuli-Stagnic Anthrosols into tea gardens on mobilization and migration of base cations in the soil.(2) As the TPs concentration increased, the amount of Si mobilized by tea extracts or catechin from both Albic Fe-accumuli-Stagnic Anthrosols and Typic Haplic-Perudic Argosols increased overall, respectively, while that mobilized by EGCG from both soils decreased after ascent to higher level, and the amounts of Al as well as Fe mobilized by the 3 types of TPs from both soils increased, respectively. Under the same condition of concentration, the amount of Si mobilized from Albic Fe-accumuli-Stagnic Anthrosols was larger than that from Typic Haplic-Perudic Argosols, while the amounts of Al or Fe mobilized by the 3 types of TPs from Typic Haplic-Perudic Argosols were higher than that from Albic Fe-accumuli-Stagnic Anthrosols.(3) As the pH value of EGCG solution increased, the amount of Si mobilized from Albic Fe-accumuli-Stagnic Anthrosols decreased, while that from Typic Haplic-Perudic Argosols increased, and the amount of Al or Fe mobilized from both soils increased, respectively. At the same pH value, the amount of Si mobilized from Albic Fe-accumuli-Stagnic Anthrosols was higher than that from Typic Haplic-Perudic Argosols when pH≤5.5, and that from Typic Haplic-Perudic Argosols in turn was higher than that from Albic Fe-accumuli-Stagnic Anthrosols when pH= 6.5. However, the amount of Al or Fe mobilized from Typic Haplic-Perudic Argosols was always higher than that from Albic Fe-accumuli-Stagnic Anthrosols.(4) The amount of Si, Al, Fe or Mn mobilized by EGCG or citric acid from both Albic Fe-accumuli-Stagnic Anthrosols and Typic Haplic-Perudic Argosols soils increased with increasing temperature overall, which indicated that both EGCG and citric acid can improve the amount of mineral elements mobilized, especially in the season of high temperature. At the same temperature, the comparisons among the amount of mobilized elements showed that EGCG or citric acid mobilized the decreasing amounts of mineral elements in the following order of Al>Si>Fe (Mn), indicating that Al was more easily mobilized than Si, Fe or Mn. The amounts of Fe mobilized by citric acid from 2 soils were larger than that of Mn, similarly, the amount of Fe mobilized by EGCG were also larger than that of Mn from Albic Fe-accumuli-Stagnic Anthrosols, while for Typic Haplic-Perudic Argosols, the opposite phenomenon that EGCG mobilized more Mn than Fe was observed. Meanwhile, with regard to the 2 different soil, the amount of Al, Fe or Mn mobilized by EGCG or citric acid was always higher for Typic Haplic-Perudic Argosols compared to the Albic Fe-accumuli-Stagnic Anthrosols, but the amount of Si mobilized was higher for Albic Fe-accumuli-Stagnic Anthrosols. Moreover, as far as EGCG and citric acid were concerned, citric acid was found to mobilized significantly more Si, Al or Fe than EGCG from 2 soils, suggesting that citric acid had relatively strong ability of mobilizing soil Si, Al and Fe.(5) The amount of mobilized Al, Fe and Mn in 2 soils were both increased with the improvement of shaken times. The process of Al, Fe and Mn mobilizing was divided into fast reactive phase (0-60min), moderate reactive phase (60-240min) and slow reactive phase (4h-24h). Double-constant equation was the optimal model to describe the kinetics of Al, Fe and Mn mobilizing from these 2 soils, and then was elovich equation or parabolic equation, while the relative effect of first-order dynamics equation was not good. Within 24 hours the amount of mobilized in Albic Fe-accumuli-Stagnic Anthrosols was in the order of Al> Fe> Mn, while in Typic Haplic-Perudic Argosols was followed the order of Al> Mn> Fe. The amount of Al, Fe or Mn mobilized and its average rate in Typic Haplic-Perudic Argosols was higher than that of Albic Fe-accumuli-Stagnic Anthrosols.