Physiological Response Of Alfalfa Under Salt Stress And Salt Resistant Regulation Measures

Alfalfa is mainly planted in salinization area in our country, and salinization of soil is an important factor of low and unstable yield of alfalfa. Therefore, the research on salt tolerance physiological indexes to salt stress and effective regulation measures to resistant salt were important for improving alfalfa yield and providing support and theoretical basis for practice. This research adopted dish of germination, pot planting and field experiments combined method to study salt stress on the whole growth period of salt-tolerant characteristic, photosynthetic characteristics and the influence of the alfalfa yield, as well as different planting patterns, alfalfa varieties, organ material distribution, fresh and dry grass yield regulation. The main results were as follows:1.Among 25 alfalfa varieties, the seed germination rate, relative germination index and relative simple vigor index, proline and superoxide dismutase activity values of Zhong Cao No.3, Alfaking, Xin Mu No.3, Kang Sai were higher, and membrane permeability and malondialdehyde content were low, and they expressed strong salt resistance ability. Zhong Mu No.1, Salt Buster and Warrior presented opposite performances.0.80% Salt concentration could be deem change "inflection point" of each index, and comprehensively analyzed cluster of alfalfa seed germination indexes and physiological characters, the 25 varieties could be divided into three types, the first type included Zhong Cao No.3, Xin Mu No.2, Nordica, Yellow flower alfalfa and kangsai, and they belonged to salt resistance varieties; The second type included Chi Cao No.1, Zhong Mu No.1, Challenger, Salt Buster, Warrior, and they belonged to salt sensitive varieties; The thired type included 2010, and it belonged to the middle type variety.2.The diurnal change of net photosynthetic rate and transpiration rate showed unimodal curve and reached peak at 11:00, and the values were lowest at 17:00; Plasma membrane permeability, malondialdehyde content, superoxide dismutase activity, catalase activity and proline content increased gradually with the increasing of alfalfa growth period, and the other physiological indexes except hydrogen peroxide enzyme activity increased mostly to reduce salt stress with increasing of salt concentration. But 0.20% salt concentration promoted the growth and development of alfalfa, and compared with other treatments increased plant height, net photosynthetic rate, transpiration rate, stomatal conductance of Zhong Cao No.3 and Zhong Mu No.1, and improved superoxide dismutase avtivity, catalase activity and proline content, and reduced the plasma membrane permeability and malondialdehyde content, and increased the yield of the two alfalfa varieties.0.80% salt concentration treatment caused two varieties of alfalfa low yield seriously, and dreased yield by 42.29% and 42.29% respectively. Zhong Cao No.3 showed stronger salt resistance abiluty than Zhong Mu No.1.3.Stem matter accumulated more at the early growth period of alfalfa, and then leaf organ improved more, and then gradually shifted to flower after anthesis.Mixed cropping treatment increased the SPAD value, fresh and dry grass yield, photosynthetic rate, transpiration rate and stomatal conductance of alfalfa. Zhong Cao No.3 and Elymus nutans mixed cropping effect was best, and showed obvious advantages to increase production. At the first cutting in 2014, the fresh grass yield of Zhong Cao.3 among Zhong Cao No.3 and Elymus nutans mixed cropping was higher 9.05% and 2.02% than monoculture Zhong Cao No.3 and Zhong Cao No.3 and Awnless brome mixed cropping respectively, and the dry grass yield was higher 14.99% and 1.99% respectively, and at the second cutting, the fresh grass yield was higher 15.00% and 21.95% respectively, and the dry grass yield was higher 1.99% and 2.09% respectively. Zhong Cao No.3 and Awnless brome mixed cropping treatment obtained high grass yield. Alfalfa and gramineae ranch mixed cropping improved the photosynthetic characteristics and forage yield effectively.4.The suitable mixed cropping and intercropping treatments promoted the accumulation of dry matter, photosynthetic rate, transpiration rate, stomatal conductance, and the grass yield of alfalfa.1:1 intercropping treatment improved the photosynthetic rate, transpiration rate, stomatal conductance and dry grass yield of alfalfa compared with 1:2 and 1:3 intercropping treatments. The photosynthetic rate of alfalfa edge line of the 1:1 intercropping treatment was increased by 25.60%,77.76% and 132.00% compared with 1:2 and 1:3 intercropping treatments respectively, and dry grass yield increased by 28.57%,80.00% and 200.00%, respectively, and transpiration rate and stomatal conductance showed similar trends.5.Correlation analysis of morphologic, photosynthetic physiological indexes, salt-tolerant physiological indexes and fresh grass yield of alfalfa showed that the dry weight of alfalfa, net photosynthetic rate, transpiration rate, intercellular CO2 concentration, superoxide dismutase activity experienced very significantly positive correlation with yield(P<0.01), plasma membrane permeability, proline content and yield showed significantly negative correlation (P<0.01), and all of the indexes had a larger impact on forage yield. The fresh matter and dry matter migtatted to stem and flower organs to promote alfalfa grass yield.