The Accumulation And Distribution Characteristics Of Cr³⁺ And Cd²⁺ In Tea Plants Cultured In Hydroponics And The Way Of Controlling

The tea quality security is the current hot spot topic of current tea industrial development and tea study research in our country, the content over standards and harmfulness of toxic heavy metals are its key problems. And, Chromium ion and cadmium ion pollutions are the material effect factors of pollutes the tea quality and safety. They can be absorbed by the two ways of roots and leaves of tea plants from the environment such as Soil and Atmospheric, and be accumulated in the tea plant organs, finally remained in the tea products, then damage tea quality and safety. Tea plant express a strong tolerance ability and Resistibility of Cr and Cd. Research on the accumulation character and control means of Cr3⁺ and Cd²⁺ in tea plant by the hydroponics system, has the important theoretical and practical significance of the prevention and control of the source of chromium and cadmium pollution in tea.The theory and methods of Cultivation of tea plant, tea physiology, plant physiology and plant nutrition was used in this paper, to investigate the Cr and Cd accumulation characters and tolerance characteristics in tea plant. Meanwhile, explore control measures of tea plant absorbing Cr3⁺ and Cd²⁺. The main results are as follows.（1） The systematic study was conducted on Cr3⁺ tolerance ability、accumulation and distribution of tea plant. The results show that, The roots of tea plant can absorb a large number of chromium ion as 498.65-2478.77 mg/kg, and accumulated in roots、stems and leaves, respectively by, the roots 2478.77 mg/kg, bottom stem 604.63 mg/kg, middle stem 379.81 mg/kg, top stem 24.12 mg/kg, and leaves 31.79 mg/kg; Tea plant shows strong ability of chromium ion tolerance and accumulation. Cultured in 50 mg/L Cr solution for 1-45d, some symptom （such as roots turn brown and black, leaves yellowing and turn brown spots.） were suffering in tea plant gradually. Cultured 45 d in 10-90 mg/L Cr solution and cultured in stilled water with Cr solution of the same concentration foliar on the leaves, the fraction where is polluted accumulate the most, The most Cr3⁺ content in leaves and roots are:cultured in Cr solution, leaves 57.23 mg/kg and roots 2897.97 mg/kg, Which the distribution rate of roots are 70.11%; cultured in stilled water with Cr solution foliar on the leaves, leaves 2461.86 mg/kg and roots 95.85 mg/kg, Which the distribution rate of leaves are 85.35%. Cultured in 80-90 mg/L Cr solution, some symptom （such as roots turn brown and black, until necrosis, leaves yellowing and turn brown spots to the whole leaf withered, until fall off.） were suffering in tea plant gradually. Cultured in stilled water with 80-90 mg/L Cr solution foliar on the leaves, some symptom （such as roots turn dark brown, leaves yellowing and turn brown spots to the whole leaf withered） were suffering in tea plant gradually.（2） Solution containing NH⁴⁺、-PO4^2-、K⁺、Ca²⁺ and Al3⁺ ions significantly impact on the tea plant uptake and accumulate of chromium ion. Separately, low concentration of N solution by Cultured in NH⁴⁺ and Cr solution or cultured in Cr solution with N solution foliar on the leaves, without reducing effect on accumulation of Cr3⁺, but the high concentration of N （≥ 60 mg/L） solution decreased the Cr3⁺ concentration, the inhibition rates of the accumulation of Cr3⁺ in tea plant are as high as:foliar N on the leaves 35.19%, added N to the roots 54.73%. P had no decrease the accumulation of Cr3⁺ in tea leaves, but it can significantly decrease the accumulation of Cr3⁺ in tea stems and roots. K can significantly decrease the accumulation of Cr3⁺ in tea plant organs, the largest decreasing rate of Cr3⁺accumulation in tea leaves is 35.78%. Certain concentration of Ca²⁺ and Al3⁺ can decrease the Cr3⁺ accumulation in tea leaves and stems, the largest decreasing rates of Cr3⁺ accumulation in tea leaves are Ca²⁺ 26.28% and Al3⁺ 51.92%.（3） The systematic study was conducted on Cd²⁺ tolerance ability、accumulation and distribution of tea plant. The results show that, The roots of tea plant can absorb a large number of Cadmium ion as 889.31-1699.63 mg/kg, and accumulated in roots、stems and leaves, respectively by, the roots 1669.42 mg/kg, bottom stem 207.55 mg/kg, middle stem 42.38 mg/kg, top stem 1.45 mg/kg, and leaves 2.84 mg/kg; Tea plant shows strong ability of Cadmium ion tolerance and accumulation. Cultured in 5 mg/L Cd solution for 1-45 d, some symptom （such as roots turn brown and black, then die, leaves turn brown spots, Marginal scorch, the lower part of leaves fall off.） were suffering in tea plant gradually. Cultured 45d in 1-9 mg/L Cd solution and cultured in stilled water with Cd solution of the same concentration foliar on the leaves, the fraction accumulate the most at leaves and roots, and the most Cd²⁺ concentration are:cultured in Cd solution, leaves 1.42 mg/kg and roots 1606.41 mg/kg, Which the distribution rate of roots are 88.96%; cultured in stilled water with Cd solution foliar on the leaves, leaves 57.18 mg/kg and roots 34.89 mg/kg, Which the distribution rate of leaves are 45.16%. Cultured in 8-9 mg/L Cd solution, some symptom （such as roots turn dark black, Partial necrosis, leaves marginal withered to the whole leaf scorch, about 50% About 50% plants’ leaves whole fell off.） were suffering in tea plant gradually. Cultured in stilled water with 8-9 mg/L Cd solution foliar on the leaves, some symptom （such as roots turn dark brown, Leaf lesion expand to tip withered, about 60% leaves dry,20% leaves fell of） were suffering in tea plant gradually.（4） Solution containing NH⁴⁺、-PO42、K⁺、Ca²⁺ and Al3⁺ ions significantly impact on the tea plant uptake and accumulate of Cadmium ion. Separately, cultured in Cd solution with N solution foliar on the leaves, can significantly decrease the accumulation of Cd²⁺ in tea plant organs, the largest decreasing rate of Cd²⁺ accumulation in tea leaves is 29.11%. Cultured in NH⁴⁺ and Cd solution, can promote Cd²⁺ of roots translocation and distribution. P and K can significantly decrease the accumulation of Cd²⁺ in tea plant organs, the largest decreasing rate of Cd²⁺ accumulation in tea leaves are P 51.32% and K 31.47%. Certain concentration of Ca²⁺ and Al3⁺ can decrease the Cd²⁺ accumulation in tea leaves and stems, the largest decreasing rates of Cd²⁺ accumulation in tea leaves are Ca²⁺ 44.21% and Al3⁺ 63.64%.All the results are aimed at enrich the related content of physiology of tea plant, and build a theory to control the accumulation of Cr3⁺ and Cd²⁺ in the plants from the material part on, and to ensure the quality and safety of tea.