Studies On The Relationship Between Soil Environmental Geochemical Factors And Uptake Of Aluminum From Soil Into Tea Leaves

Tea plant (Camellia sinensis), which is known to be a typical aluminum (Al) accumulator, contains high level of Al in its leaves. A number of reports indicated that some neuropathy such as Alzheimer's disease were related to the content of Al in human's body. Therefore, there will be of theoretical and practical significance to study the relationships between contents of Al in tea leaves and soil enironmental geochemical factors for improving tea garden soil, decreasing contents of Al in tea leaves and further improving human living quality.Generally, the uptake of Al from soil into tea leaves is involved mainly in soil properties as well as forms of Al in soils. In order to investigate distributions of forms of Al in soils (0. 02MCaCl₂ extractable Al extracted with 0. 02M CaCl₂ alone, exchangeable Al, Al complexed by soil organic matter, sorbed inorganic Al, Al oxide dissovled by hydrochloric acid and Al chelated by humic acid extracted with a sequential chemical extractants, i.e. 1M KC1, 0. 1MCuCl₂, 1M NH₄OAc, 1MHC1 and 0. 5M NaOH), the effects of soil properties i.e. contents of clay and organic matter, cation exchange capacity (CEC) and soil pH on the distributions of forms of Al in soils and the uptake of Al by tea leaves and relationships between concentration of Al in tea leaves and amounts of various forms of Al in soils, thirteen tea garden soils and tea leaves (old, mature and young leaf) were collected from the main tea production areas in east China. Meanwhile, blank experiment,rate of recovery for standard materials and duplicated analysis were conducted to ascertain the detection limits, accuracy and precision for all analytical methods. Moreover, a Sampling and Analytical Quality Control Scheme was applied to assess both the analytical and sampling quality using Robust analysis of variance.Results from analysis of soils showed that the distributions of forms of Al in tea garden soils were as follows: Al oxide dissolved by hydrochloric acid and Al-chelated by humic acid, which are much more stable in soil, accounted for the majority in the total extractable Al in soils, from 20 to 60% respectively (the total of the two forms of Al exceeded 70%); Anyone of other forms of Al in soils, which were exchangeable Al, Al complexed by soil organic matter and sorbed inorganic Al, however," generally constituted less than 10%. Al in soils extracted with 0. 02M CaCl2 , which is the most unsteady form of Al in soils, only took up less than 2% in total extractable Al.The relationship between the forms of Al in soil and soil properties showed that: 0. 02M CaCl2 extractable Al always increased with decreasing clay content, CEC and soil pH. Particularly, the negtively correlation of 0. 02M CaCl2 extractable Al with soil pH was the most significant with a sharp increase when the soil pH was lower than approximately 5. 0. This is likely to reflect that the speciation of Al in the soil changes and the species of 0. 02M CaCl2 extractable Al was dominantly the Al3+ion, which is the most stable form of Al in soils at pH value less than 5. 0 according to the thermodynamicequilibrums of Al in soil. Exchangeable Al was positively correlated with CEC, and Al complexed by soil organic matter positively with organic matter content and negtively with soil pH. The effects of contents of clay and organic matter, CEC and soil pH on sorbed inorganic Al, Al oxide dissovled by hydrochloric acid and Al chelated by humic acid were all not significant in this study.Results from determining the contents of Al in tea leaves with different ages showed that the law of distribution of Al in tea leaves was old leaf > mature leaf > > young leaf. The capacity of accumulating Al for tea leaves enhanced obviously with increasing leaf age. The relationship of the concentration of Al in the tea leaves with soil properties showed that the uptake of Al by tea leaves was significantly affected by soil pH , CEC, contents of clay and organic matter, negatively correlated with soil pH, CEC and clay content and positively correlated with organic matter content, while the correlation with soil pH was the most significant. Comparising the relationship between the concentration of Al in mature and young leaves and soil pH and the relationship between the speciation of Al in soil and pH, it suggested that the dominant speices of Al in the soils available for uptake into the tea leaves was the Al3+ ion. Since soil pH was identified as the major factor controlling the uptake of Al from soil into tea leaves, it would seem a reasonable suggestion that decreasing soil acidity and increasing soil pH could be a effective measure to decrease the content of Al in tea leaves.In the comparison the relatonships between theconcentrations of Al in tea leaves and the forms of Al in soils , the uptake of Al by tea leaves was best predicated linearly by the amounts of 0. 02M CaCl2 extractable Al. Consequently, 0. 02M CaCl2 extractable Al could be regarded as the "tea-leaf available" Al. Although the concentrations of Al in the tea leaves also raised a little with increasing exchangeable Al and Al complexed by organic matter, the correlations were not significant at all. This suggested that the availability of the two forms of Al in soil for the uptake of Al from soil into tea leaves were very low. The correlations of the concentrations of Al in tea leaves with sorbed inorganic Al, Al oxide dissolved by hydrochloric acid and Al chelated by humic acid were all not significant, this indicated that the three forms of Al in soil were too stable to be assimilated by tea leaves.Detection limits estimated with reagent blank were diversity for different analytical methods due to the difference in the amount and background of reagent, dilution times and experimental period, even though they were generally much lower than the concentrations of Al in samples. Reagent blank were also used to ascertain the background of the analyte and identify any contamination in the analysis procedure. These results showed that the bias was significantly greater than zero, and hence all determinations had to be corrected by the subtraction of the mean value of the Al contents in the reagent blank. The rate of recovery of standard materials exceeded 85% and the analytical precision were all less than 10%(at 95% confidence limits ). The results from Robust analysis of variance used to separate the analytical variance from the...