Alleviating Effects Of Bacillus Subtilis On The Cucumber Under Salt Stress In Substrate Culture

The cucumber is a major vegetable cultivated in protected condition, having a large cultivated area now. But in protected condition, where the temperature is high, the evaporation capacity of water is large, and rain can not get in, vegetable crops or florist crops are planted continuously, fertilizer is used heavily, which results in high-concentration salt in the soil, puts the crops into salt stress, disturbing its normal physiological metabolism, and finally hinders the healthy, sustainable development of facilities horticulture. It's researched that Bacillus subtilis (B.S) can alleviate the biotic stress and salt stress of plants, and promote its growth. But alleviating effects of B.S on the plant under salt stress wasn't studied deeply in some aspect, such as in the rhizosphere.Effects of Bacillus subtilis on antioxidant system, osmotic substances, rhizosphere enzyme, the shifts of rhizosphere bacterial community and yield, quality in salt-stressed cucumber (cv. Jingyan mini No.2) (Cucumis sativus L.) by substrate culture was studied, discussing the mechanism of B.S alleviating salt stress on cucumber. Main research results were as follows:1. Under lower-concentration salt stress, (i.e. double of nutrient solution level), Bacillus subtilis increased SOD, POD, CAT activities and chlorophyll, carotenoid contents in the leaf, showing that under lower-concentration salt stress, B.S may alleviate the salt stress on cucumber by strengthening the ability of eliminating the reactive oxygen species (ROS) and photosynthesis; Under higher-concentration salt stress, (i.e. four times of nutrient solution level), Bacillus subtilis increased SOD, CAT activities and soluble suger content in the leaf, showing that under higher-concentration salt stress, B.S may alleviate the salt stress on cucumber by strengthening the ability of eliminating the ROS and lowing its osmotic potential.2. Under lower-concentration salt stress, Bacillus subtilis increased dehydrogenase activity, peroxidase activity, and urease activity; significantly increased catalase activity and alkaline phosphatase activity in cucumber rhizosphere; under higher- concentration salt stress, Bacillus subtilis had little influence on rhizosphere enzyme (except peroxidase activity).3. Compared to the untreated control, we can make a conclusion that with B.S, there is a significant shift on the community of the rhizosphere bacterial, which can help the host to adjust to the environment quickly.4. Under lower-concentration salt stress, Bacillus subtilis significantly increased the yield, water content, titratable acid content of cucumber fruits, and significantly decreased contents of Vc, crude protein and soluble solid in cucumber fruit; under higher-concentration salt stress, Bacillus subtilis significantly increased the yield, Vc, sugar-acid ratio, crude protein content of cucumber fruit, and decreased soluble solid content.