Study On Water-Comsumption Characteristic And Drought-Resistance Mechanism Of Three Leguminous Pasture In Loess Plateau

Laboratory physiological experiments and outdoor pot-culture experiments of three leguminous pasture in Loess Plateau(Astragalus adsurgens,Melilotus albus,Lespedeza hedysaroides)were studied. As to outdoor pot-culture experiments, every experimental material had three water treatments: appropriate water treatment,moderate stress,severe stress, of which soil water content were 75%,55% and 40% of the max field moisture capacity, respectively. In outdoor pot-culture experiments, the works included determining physiological drought-resistance indexes during seed imbibition period and seedlings. The ability of drought-resistant of three leguminous pasture were comprehensively evaluated by combining two different periods to study the differences of the water-consumption characteristic and drought-resistance of three leguminous pasture, the result provided theoretical basis of making artificial grassland, restoring ecology and introducing superior pasture. The main results are as follows:1. The water consumption of the three Leguminous pastures showed Astragalus adsurgens>Lespedeza hedysaroide>Melilotus albus, under three different soil water contents, that showed CK>MD>SD. Water consumption characteristics of the three leguminous pasture under different soil water content was basically similar, and the distribution proportion of total water consumption in every ten or thirty days was also similar. During the water-stress time, the water consumption trend of month was single-peak curve, the highest water consumption of three Leguminous pastures concentrated on June,July and Agust, and the highest value of water consumption was in July; The water consumption trend of ten days was multi-peak waving curve, which concentrated on the last ten days in June to the last ten days in July.2. It was studied by biological characteristic and germination characteristic in water stress of three Leguminous pastures seed. The main results are as follows:Three species were different in biological characteristic of seed, seed water content and seed imbibition rate of Astragalus adsurgens was higher than others, seed vitality of Lespedeza hedysaroides was higher others;As the drought became intensified .the total seed germination rate, seedling fresh weights, drought resistance index, growth of radicel and plumule of three species tended to decline and those of Melilotus albus presented the largest decrement;The low consistence PEG-6000 could improve the seed germinations of Lespedeza juncea , the seedlings growth of Astragalus adsurgens and those of drought resistance index;The comprehensive evaluation of three species by membership function method indicated that the drought resistances of three species decreases in the order of Lespedeza hedysaroides ,Astragalus adsurgens,Melilotus albus.3. It was studied by physiological and biological drought resistance indexes under water stress in three Leguminous pastures seedlings. The main results are as follows: the ability of drought-resistance was different between seed imbibition period and seedlings. By studying water physiological indexes, Astragalus adsurgens had higher RWC, the more stable change, lower degree of WSD, and better water preserving capacity to suit drought condition by preventing water loss; By studying osmotic substances accumulating, it showed the content of Pro,soluble sugar,Ca2+and K+ of Leguminous pastures had increased as soil water content decreased, but the quantity of osmotic substances of Astragalus adsurgens and Melilotus albus was more than Lespedeza hedysaroides; In the water-stress condition, the degree of damage of Lespedeza hedysaroides leaf was less than others, and it had higher antioxidant enzyme activities of SOD,APX, higher Car content to enhance the ability of drought-resistance by clearing away ROS, at the same time, Astragalus adsurgens and Melilotus albus also had higher protective enzyme activity of SOD,POD and APX in order to lessen the damage by drought. It showed different species had different drought-resistance mechanisms to accommodate and fight with the drought condition. The last, The comprehensive evaluation of three species seedlings by membership function method indicated that the drought resistances of three species decreases in the order of Astragalus adsurgens,Melilotus albus, Lespedeza hedysaroides.4. Different soil water content had effected on the growth of seedlings,biological mass and WUE. The main results are as follows: with soil water content decreasing, the speed of growth and length of roots and stem of three Leguminous pastures had showed decreasing trend; meanwhile, the total biological mass also declined, but the root/shoot rate were different in three species according with the variation degrees of the pastures dry weight decline, the root/shoot rate of Astragalus adsurgens decreased as soil water content had increased, the rate of Melilotus albus showed opposite change, as to Lespedeza hedysaroides , the differences of the root/shoot rate among three pasturs were not significant; according to WUE, it showed the WUE of three Leguminous pastures with water stress treatment were higher than control group, and three species decreased in the order of Astragalus adsurgens, Lespedeza hedysaroides ,Melilotus albus.