Exploration To Mechanisms For NaHSO₃ Improving Yield, Quality Of Spring-Tea And Resistance Of Tea Plant To Low Temperature

Tea, as Chinese traditional industry, is one of the most preponderantly agricultural products in Zhejiang Province. However, the review of the tea production in recent years shows that the low temperature in the early spring has resulted in a large loss of the tea production, especially of the superfine tea production in this area. In this experiment, we used mainly cultivars Ying-shuang, Long-jin 43 and Jiu-ken planted in Hangzhou and treated them with a range of NaHSO₃ concentrations by spraying tea canopy in the early spring during 2004-2006. Growth of bud, contents of tea polyphenols and amino acids of tea, photosynthesis rate (Pn) and chlorophyll florescence, electric conductivity and superoxide dismutase (SOD) activity, and cyclic photophosphorylation of leaf were investigated in order to provide a suitable concentrations and durations for its application, and explore why NaHSO₃ enhances spring-tea growth and resistance of the leaf to low temperature. The results showed the followings:1. When tea plant initiated to sprout in the early spring, the tea canopy was sprayed with 2 mM NaHSO₃. It was found that both length and fresh or dry weight of the tea-young leaf increased and that the tea leaf could be picked 3-4 days earlier than untreated tea plant. NaHSO₃ could increase in contents of tea polyphenols, amino acids and water-extracts of the tea, indicating improvment of tea quality.2. Pn of the over-winter leaf of tea canopy sprayed with 2 mM NaHSO₃ rose about 60% of the control one, which is correspond to neither change in stomatal conductance nor changes in PSII chlorophyll florescence characteristics, electron transport rate, photochemical efficiency and light energy interception. The analysis for the responsive curve of Pn to CO₂ concentrations indicated the significant increase in carboxylation efficiency and RuBP regeneration rate, meaning acceleration of Rubisco activation and ATP formation after NaHSO₃ treatment.3. Low concentration of NaHSO₃ could obviously decrease in the number of frozen buds and leaves of tea plants grown in the field when the plants encountered a heavy sown in the early spring, and it also speeded up the recovery of the bud growth and lowered the electrical conductivity of the leaves after the freezing. Besides it significantly increased photosynthetic rate of tea leaf, NaHSO₃ could enhance light energy transfer from PSII to PSI, speed up cyclic electron flow which often is companied with cyclic photophosphorylation. This is a probable mechanism to improve the resistance of tea plant to freezing injury.