Study On Pb, Cd And Their Compound Pollution On The Physiological, Biochemical Effects And Their Absorption, Accumulation Characteristics Of Tea Plants

Pb and Cd are not only the major heavy metal pollutants in the environment but also the two of the most recognized toxic and harmful environmental elements, they usually concomitantly exist in the nature. When they accumulate to a certain extent in the crops, they will not only seriously affect the growth, yield and quality of the crops, but also can enter the body through the food chain, and cause great harm to the human health. Therefore, this study selected Pb and Cd as the pollutants, the Pb, Cd and their compound pollution on the physiological, biochemical effects and their absorption, accumulation characteristics of tea plants were preliminary studied with indoor solution culture, to provide some theoretical basises and references for revealing the toxicity and patience mechanisms of heavy metals, improving the safety of tea products and the early warning and integrated control of heavy metals. The results show that:1,Pb, Cd and their compound pollution could inhibit the growths of tea plants and make tea plants damaged with different degrees of symptoms. The basic symptoms of tea plants under single Pb treatment and Pb, Cd compound pollution were that the roots blacked gradually, and even decayed, accompanied by white flocculate engendered; the leaves withered with losing water, and yellowed, browned, scorched; the winter buds and the growths of the new shoots were seriously inhibited; and finally, the tea plants dead. But the symptoms of single Cd treatment on tea plants were different, they were that the middle and lower parts of tea plant leaves lightly appeared etiolation and bit shed, the length and weight of the new shoots were was also inhibited, but the growth of the roots were normal, and there were some new roots growing, the total number of buds significantly increased compared with the control. The damages of Pb, Cd compound treatment on the symptoms of tea plants were all much stronger than the single Pb, Cd treatment.2,Pb, Cd and their compound pollution could significantly reduce the photosynthesis of tea plants. With the concentrations of Pb, Cd and their compound treatment increasing, the contents of chlorophyll a, chlorophyll b, total chlorophyll in tea plants and the ratio of a/b all reduced all the time, while the photosynthetic rate (Pn), transpiration rate (Tr), intercellular CO2 concentration (Ci) and stomatal conductance (Gs) also reduced, even the stomatal conductance (Gs) and transpiration rate (Tr) reduced more. The inhibition leveles of Pb, Cd compound treatment on the photosynthesis of tea plants were much stronger than single Pb, Cd treatment.3,The effects of Pb, Cd and their compound pollution on the protective enzymatic activities of tea plants wrer different. With the concentrations of Pb and Pb, Cd compound treatment increasing, the SOD, POD, CAT activities increased at first and then decreased, and the rangeabilities of enzymatic activities under Pb, Cd compound treatment were significantly stronger than single Pb treatment, but the SOD, POD, CAT activities of single Cd treatment increased all the time. In addition, the contents of MDA, proline and the relative conductivity in tea leaves increased obviously with the concentrations of Pb, Cd and their compound treatment increasing, and the increasing number of Pb, Cd compound treatment were more evident, mean that the cell membrane damages of Pb, Cd compound treatment on tea plants were stronger than single Pb, Cd treatment.4,Under Pb, Cd and their compound treatment, the contents of Pb and Cd in different parts of tea plants differently increased with the concentrations of Pb, Cd and their compound treatment increasing. Under single treatment, the mobility of Pb in the tea plants was weak, its accumulation and distribution order in the tea parts was absorbing roots> main roots> main stems> tender stems> mature leaves>new shoots; but the mobility of Cd in the tea plants was much stronger, its accumulation and distribution order in the tea parts was absorbing roots> main roots> tender stems> mature leaves> main stems>new shoots. But under Pb, Cd compound treatment, although the accumulation and distribution order of Pb in the tea parts was still absorbing roots> main roots> main stems> tender stems> mature leaves>new shoots, but overall, the accession of Cd promoted the tea parts to absorb and accumulate Pb, and changed the Pb accumulation capacity of tea plants too; however the accumulation and distribution rule of Cd in the tea parts was changed, it was absorbing roots> main roots> main stems> tender stems> mature leaves>new shoots while lower concentrations, but it was main roots> absorbing roots> main stems> tender stems> mature leaves>new shoots while higher concentrations, the accession of Pb suppressed the absorbing roots, tender stems, mature leaves, new shoots to absorb and accumulate Cd, but promoted the contents of Cd in main roots and main stems, and changed the Cd accumulation capacity of tea plants too.5,Under Pb, Cd and their compound treatment, the catechins components and amino acids components in new shoots changed differently, but the contents of total catechins, caffeine and amino acids decreased obviously with the concentrations of Pb, Cd and their compound treatment increasing, and the decrease extents of Pb, Cd compound treatment were more obviouser, mean that Pb, Cd and their compound treatment could significantly reduce the quality of tea.