Effects Of NaCl Stress On Physiological Characteristics Of Watermelon Seedlings And Alleviation Effects Of Humic Substances

Salt stress is a significant abiotic stress for agricultural production, watermelon(‘the king of the melon')contains rich nutrients, such as glucose, malic acid, fructose, amino acids, lycoypene, vitamin C and so on.The watermelon is widely cultivated in China, and the soil with p H 5-7 is suitalbe for it.Salt stress often affects the production of watermelon. ‘jing xin No.1' and wild watermelon were used as the experimental materials to study the difference of salt tolerance between cultivated and wild watermelon and investigate the effects of humic substances alleviating salt stress. The expected results will provide a physiological theorey basis for watermelon produciton in saline soil. The main results were as follows:1. The experiment was carried out to study the effects of 100 mmol·L-1 Na Cl stress on the change of net photosynthetic rate, plant growth, root activity, proline, MDA content, antioxidant enzymes activities, Na+ and K+ in different watermelon seedlings. The results indicated that salt stress significantly inhibited the growth of ‘Jingxin No.1' and wild watermelon, but wild watermelon was less affected under the same Na Cl concentration and showed stronger salt tolerance,which could be concluded from higher net photosynthetic rate,better growth conditions, proper system of antioxidant enzymes and stronger ability of ion selective absorption in wild watermelon seedlings.2. The effects of different humic substances(HS) concentrationon watermelon tolerance to salt stress was studied through nutrient solution culture. ‘Jingxin No.1' watermelon was used as experimental material, and exogenous HS from 0 to 1.0 g·L-1 was used to treat watermelon plants under 100 mmol ·L-1 Na Cl. The results showed that the application of HS could improve the plant growth conditions, especially 0.3 g·L-1 treatment, in which chlorophyll contents, photosynthesis, Fv/Fm and ?PSII were significantly increased, and the distribution of Na+ and K+ was improved. At the same time, the activities of SOD and CAT were enhanced, and electrolyte leakage percentage and MDA content in Na Cl-treated watermelon plants were significantly decreased by the application of 0.3 g·L-1 HS. As a result, the plant growth was improved.