| Soil salinization is one of the world rising environmental problems. Generally, saline-alkali soil is also followed by low content of phosphorus (P), plants which live in it are suffered with lack of phosphorus, as well as salt-alkaline stress.By mixing NaCl, Na2SO4 Na2CO3 and NaHCO3 in various proportions,20 kinds of salt-alkali conditions with different salinities and pH were established. Seedings of Medicago sativa Zhongmu No.1 and M.sativa Longdong were stressed under these salt-alkali conditions. Growing and physiological indices, photosynthetic characteristics, as well as the content and uptake of P were determined to reveal the resistance mechanisms in M.sativa under salt-alkaline stresses. The results showed that,1 After 7 days of various stresses, M.sativa Zhongmu No.1 seedings in the control group and the groups of pHa and pHb increased their solution pH with increasing salinity and alkalinity, meanwhile the group of pHc and pHd reduced their solution pH. Under the same treatment condtions, seedings of M.sativa Longdong reduced the solution pH in all groups. Under 150 mM salinity and 10.59 pH value, more than 1/3 seedings of M.sativa Zhongmu No.1 can survive. Although most M.sativa Longdong seedings were survival, they were not as good as M.sativa Zhongmu No.1 seedings. M.sativa Zhongmu No.1 seedings had better salinity tolerance.2 Shoot height and root length of the two alfalfas were significantly decreased under pHc and pHd condition with increasing salinity. Compared to the control, the dry weight of M.sativa Zhongmu No.1 seedings increased under stresses, and the rate of increase declined in the high salt-alkaline stress. The dry weight of M.sativa Longdong seedings was lower than control in heavy salt-alkaline stress condition. With the increasing salinity, shoot dry weight of M.sativa Zhongmu No.1 seedings were reduced,which was fewer decreased than that of root weight, as a result shoot ratios was decreased. The changes of root weight of M.sativa Longdong seedings were small under 150mM salinity of pHc and pHd conditions, while its shoot dry weight were significantly decreased, which made shoot ratios increase.3 With increasing salinity and alkalinity, M.sativa Zhongmu No.1 seedings significantly increased Pn, and sharply decreased Tr by adjusting the open or close of stomatal, therefore it improved the water use efficiency effectively. Conditions of 75mM salinity or more, WUE of M.sativa Zhongmu No.1 seedings were 2.7-4.3 times higher than that of the control group. Compared with control, Pn in the group of pHa, pHb, pHc, pHd under 100 mM salinity increased by 129.7%,151.5%,100.0%,125.6%; Tr respectively decreased by 26.2%,22.0%,20.7%, 46.8%, and then WUE were 3.2 times,3.4 times,2.7 times and 4.3 times higher. Tr of M.sativa Longdong seedings were higher than the control, as a result it had poor efficiency of water use and loss of water quickly.Water potential of M.sativa Longdong seedings were 1.4-16.4 times lower than that of M.sativa Zhongmu No.1, which maybe benefit to the absorption of water.4 The P content of M.sativa Zhongmu No.1 seedings were higher than M.sativa Longdong seedings, the P content of whole plant were decreased with the increase of salt concentrations in two alfalfas. In M.sativa Zhongmu No.1 seedings, under pHa and pHb conditions, its relative amounts of P uptake in roots were about 100% to 126.7% compared with control. But P content were lower than control in the same conditions, which the relative amounts were about only 90%. At the same time, the dry weight of roots increased, therefore it could be explained as dilution effect. P uptake abilitise of M.sativa Longdong roots decreased under stress condition. The distribution of P content in M.sativa Zhongmu No.1 seedings was root> leaf> stem, that of M.sativa Longdong seedings was root> stem> leaf. Metabolic efficiency of P in M.sativa Zhongmu No.1 seedings was better than M.sativa Longdong seedings.5 Combined actions of salt stress and alkaline stress had a synergistic effect.
|
PDF Full Text Request