| Tea is a no alcohol beverage planted mainly in our country. The contents of chemical ingredients and microelements in tea leaves are the material basis and key feature for measurement of tea qualities. Tea tree(Camellia sinensis) is a typical aluminum (Al) accumulator and has high Al content in tea leaves. Some researchers suggested that drinking tea containing high Al frequently may result in Alzheimer’s disease. Thus, the absorption and accumulation of tea plant on Al and the biological effects of A1on tea plant have aroused wide attention by researchers. The bioavailability and biotoxicity of A1to plant is not only dependent on its amounts but also its chemical forms. Acid rain is one of the important environmental problems in our country and even all of the world and it can result in soil acidification. Soil acidification can promote soil Al release and change Al species. Therefore, the increase of acidity of acid rain often accompany with soil soluble Al increase. However, the effects of increase of acidity of acid rain and soluble Al on Al cycling of tea plant, the microelements and chemical ingredients of tea leaves and the coupling relationship between them are not clear. In order to provide information on estimating the combined effects of acid rain and aluminum on aluminum cycling of soil-tea plant system, the growth of tea plant and tea qualities and managing tea garden scientifically. In this study, the aluminum species in tea garden soils of different planting years and distribution pattern of aluminum in tea plant were investigated using position monitor. The effects of simulated acid rain and aluminum addition on the cycling of aluminum from tea garden soils to tea plant, the mineral nutrition, the growth and development and the physiological activities of tea plant and the main chemical qualities of tea leaves were studied in pot experiment and/or hydroculture experiment, and the effects of calcium on the aluminum cycling, mineral nutrition and chemical qualities were preliminary studied. the results were summarized as follows:In order to understand the relationship between the planting years of tea garden farms and soil aluminum species and the distribition of aluminum in the plants, the soil physical and chemical property of tea garden, the distribution of soil aluminum species and the distribution of aluminum in different organs in tea plant and relationship between them were studied with typical tea gardens with different planting years in hilly red soil region. The results showed that total aluminum, extractable aluminum and different aluminum fraction contents in soil increased with the extension of planting years (P<0.05). Exchangeable aluminum, organic aluminum complexes and sorbed inorganic aluminum are lower than hydrous oxide and hydroxide aluminum and humic acid aluminum and the total of the former three account for less than30%of total extractable aluminum, leaf aluminum content also increased with the extension of planting years. The content of aluminum in tea leaves positivejy related the the exchangeable aluminum and organic aluminum complexes, while it has no obvious relation with the content of sorbed inorganic aluminum, hydrous oxide and hydroxide aluminum and humic acid aluminum. Thus, exchangeable aluminum and organic aluminum complexes was the main effective forms for tea plant. The biogeochemical cycles of aluminum in tea garden farm continuously strengthened and accelerated with the extension of plant years.The effects of acid rain and Al addition on Al uptake and accumulation of tea plant, the main chemical quality of tea leaves and the changes of Al forms in red soils were investigated in pot experiments. Al addition increased exchangeable Al, organic Al complexes, sorbed inorganic Al and hydrous oxide and hydroxide Al content in rhizosphere and bulk soils except sorbed inorganic Al in bulk soils. Acid rain increased exchangeable Al and organic Al complexes, decreased sorbed inorganic Al and hydrous oxide and hydroxide Al either in rhizosphere or in bulk soils. However, humic acid Al showed no responses to Al addition and acid rain. Al addition increased Al assimilation and accumulation in tea roots. shoots and leaves. Al assimilation and accumulation were promoted by acid rain at lower Al addition, while inhibited at higher Al addition. The content of tea polyphenol, caffeine, catechin and amino acid increased with the increasing Al addition, while were higher at pH4.5than pH3.0and/or pH6.0acid rain condition within each Al addition. The contents of caffeine, catechin and amino acid in tea leaves were the highest with leaf Al content among7～8mg/g, while the tea polyphenol and flavone generally increased with increasing Al in tea leaves from2to11mg/g. Based on these results, we speculated that moderated acidity of acid rain and suitable Al addition wound be helpful to increase the tea chemical qualities.The main chemical qualities of tea leaves were further studied in solution culture with different pH of acid rain and contents of A1addition. The results showed that the contents of tea polyphenols and caffeine in tea leaves increased firstly and decreased afterwards, and the contents of amino acid, catechin and soluble sugar decreased with increasing acidity, while the flavonoid content showed no difference. With the increasing Al concentrations in solution, the contents of tea polyphenols, caffeine, amino acid, catechin, flavonoid and soluble sugar in tea leaves increased firstly and decreased afterwards. Simulated acid rain and Al addition had significant interactive effects on polyphenols, catechin and flavones, while no interaction on caffeine, soluble sugar and amino acid. The catechin content in tea leaves was inhibited by highest pH and Al concentration in solution. All these results indicated that the moderate acidity and Al content in solution were advantaged to improve tea qualities.The effects of simulated acid rain and aluminum on the growth and development and photosynthesis physiology of tea plants were studied with tea seedlings of variety fudingdabai in a hydroculture experiment. The results showed that suitable aluminum increased the fresh weight, dry weight, shoot length, shoot diameter, root length and root volume, promoted root activities and chlorophyll a, a/b and the total of chlorophyll content and increased photosynthesis (Pn), transpiration (Tr), stomatal conductance (Gs) and intercellular CO2concentration of tea leaves. Suitable acidity of acid rain increased fresh weight, dry weight, shoot length, shoot diameter and root volume, promoted root activities, chlorophyll a, b and total of chlorophyll and Pn, Tr, Gs and Ci. Suitable aluminum and moderate acidity of acid rain were benefical to the increase of each index measured, promoted root activities, chlorophyll a, b, a/b and the total of chlorophyll, Pn, Tr, Gs and Ci, while higher aluminum and acidity of acid rain were harm to the increase of each index measured, inhibited root activities, and decreased chlorophyll a. b, a/b and the total of chlorophyll. Suitable aluminum and moderate acidity of acid rain increased chloroplast volume, quantity of thylakoid and its lamellar, while higher aluminum and acidity of acid rain destroyed the structure of chloroplast with thylakoid vacuolized and membrane completely broken. The results suggested that suitable aluminum and moderate acidity of acid rain were beneficial to the growth of tea plant, the activity of tea roots, the photosynthesis of tea leaves and the chloroplasts structure and chlorophyll. The effects of aluminum and acid rain on the growth of tea plant were related with activities of tea roots and photosynthesis. The photosynthesis of tea plant may be affected by the overall effects of stamotal conductance, chlorophyll content and chloroplast structure.The aluminum and some nutrition elements in tea plant were measured in pot experiment with different pH of acid rain and contents of exogenous Al treatment. The results showed that the content of aluminum in roots, shoots and leaves of tea plant increased with increasing aluminum treatment. Acid rain increased aluminum accumulation in roots, shoots and leaves of tea plant under suitable aluminum treatment, while the simulated acid rain at high acidity and the aluminum at high concentration inhibited aluminum accumulation in tea plant. Exogenous aluminum promoted P and Cu accumulation in roots, shoots and leaves of tea plant and K accumulation in shoots and leaves, while had no obvious effects on K in roots of tea plant. Exogenous aluminum inhibited Ca, Mg, Zn accumulation in roots of tea plant, and had no obvious effect on their translocation in tea plant, thus these element increased in the shoots and leaves of tea plant. Simulated acid rain had no apparent effects on P in roots and shoots, while simulated acid rain at pH4.5increased P accumulation in tea leaves. Simulated acid rain had no apparent effects on Cu, K, Ca, Mg and Zn content in tea plant. Exogenous aluminum promoted Fe accumulation in roots, shoots and leaves. Under exogenous aluminum treatment, simulated acid rain obviously decreased Fe content in roots, shoots and leaves.The physiological characteristics effects of simulated acid rain and aluminum on tea plants were studied in a hydroponic experiment with three pH levels of3.0,4.0and5.0and four aluminum degree of0,10,20and30mg/L. The results showed that superoxide dismutase (SOD), peroxidase (POD), catalase (CAT) and ascorbate peroxidase (APX) in tea leaves increased firstly and decreased later with increasing Al concentration and increased with increasing acidity of acid rain. At higher Al concentration, the decrease of SOD, POD, CAT and APX caused by Al were intensified by acid rain. The superoxide anion radical (O2-) generation rate and malonaldehyde (MDA) content in tea leaves treated with10mg/L A1showed no difference compared with that without Al treatment, and than increased with increasing Al concentration. O2-generation rate and MDA content in tea leaves was not affected by acid rain. The increases of them caused by Al were intensified by acid rain at high Al concentration. Proline content in tea leaves increased with increasing A1concentration and was not affected by acid rain. The accumulation of proline in tea leaves caused by A1was intensified by acid rain. The soluble sugar in tea leaves increased firstly and decreased later with increasing A1concentration. Acid rain at pH3.0significantly increased soluble sugar content in tea leaves. These results suggested that Tea plant can adapt to acid rain and lower Al contentration by strengthening antioxidase activities and increasing osmoregulation substance. However, higher A1concentration are harmful to growth of tea plant and the harm of tea plant caused by Al are aggravated by acid rain.In order to provide information on improving the qualities and security of tea leaves, the effects of Ca addition on uptake and accumulation of Ca, Al and other mineral nutrition of tea plants and main chemical qualities of tea leaves were studied with one-year cutting seedlings of varity fudingdabai. The results showed that Ca addition increased tea polyphenol, caffeine, catechin, flavone, total sugar and amino acid contents of tea leaves under the treatment without Al or with different levels of Al addition. Ca addition decreased Al uptake and accumulation of tea plant, but increased Ca uptake and accumulation. Ca addition increased uptake and accumulation of P and K and had no effects on Fe uptake and accumulation of tea plant. Ca decreased uptake and accumulation of Cu when Al concentration were lower than20mg/L, while had no effects on that when Al concentration were30mg/L. Ca decreased the uptake and accumulation of Mg and Zn of tea plant. While Cu, Mg and Zn content of tea plant treated with Ca are not less than that of control (no aluminum and normal calcium). These results suggested that Ca addition had no evident effects on the use of these elements for tea plant under Al stress. Taken together, suitable Ca can increased these chemical qualities of tea leaves determined in this paper, decreased Al content and increased Ca content of tea leaves, and had no effects on other mineral nutrition for use of tea plants. Thus, application of Ca in tea garden can increase qualities of tea leaves, increase Ca and decrease Al content of tea leaves, and increase security of tea. |
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