Effects Of AM Fungi On The Growth And Quality Of Astragalus Membranaceus (Fisch.) Bunge Under Different Nitrogen Levels

Arbuscular mycorrhiza is defined as a mutualistic symbiosis between the majority plants and AM fungi,and it formed dense hyphal nets in rhizosphere soil and cortex cells of roots. The symbiosis can expand absorption range of roots, promote host plant to absorb soil mineral element and water, improve plant stress tolerance, enhance nitrogen fixation of legumes, ameliorate plant quality and reduce amount of fertilizer and pesticide.The nitrogen is very important for growth and development of Astragalus membranaceus, can increase its first flowering node and yield.Astragalus membranaceus is a perennial legume herb,its roots can be used as medicine.And it has the practical efficacy of speeding up metabolism speed and improving immunity.Pot experiments were conducted to study the formation of arbuscular mycorrhiza and the related effects of different AM fungi on growth and quality of Astragalus membranaceus under different nitrogen levels.This paper, through studying changes of various morphological indexes, physiological indexes and medicinal components of Astragalus membranaceus under different nitrogen levels, the results showed that the physiological characteristics and nutritional components of inoculated plants were much better than non-inoculated plants.AM fungi can increase yield and quality of Astragalus membranaceus, meanwhile, reduce nitrogen amount and realize the sustainable utilization of resources and green agriculture. These results provide the theoretical basis and technical support for AM fungi in the application of other medicinal plants.Main research results are as follows:1.The development of arbuscular mycorrhizae from Astragalus membranaceus seedling beginned with spore germination, and arbuscule and vesicles were formed by germ tube elongation, then new spores were formed. In this way, the life history of AM fungi was finished from spore to new spore, it was proved that the process is a typical process of development of arbuscular mycorrhizae.2.After 77 days of Astragalus membranaceus seedling, new bands of POD isozyme were arising when a lot of intracellular vesicles formed, which means AM fungi changed basic nutrient-dependence of host plant from the beginning into the improvement of growth and development when AM fungi coexisted with host plant for some times.3.The results showed that the symbiosis relationship between AM fungi and Astragalus membranaceus formed efficiently. Mycorrhizal infecting rate was promoted after inoculation significantly. Nitrogen amount in soil affected the formation and development of AM symbioses directly. The mycorrhizal infection rate was the best under 50～100 mg N/kg soil. Low or high nitrogen levels could suppress it.4.AM fungi can increase the growth of Astragalus membranaceus. The contents of soluble protein and soluble sugar in the leaves, and the activity of the protective enzymes as well as the content of flavonoid and N and P in the tissue of Astragalus membranaceus is improved by inoculation AM fungi under the suitable nitrogen levels.So it promoted the ability of stress-resistance, anti-aging action, at the same time, improved metabolism level of the mineral element and the medicinal components of host plant. But POD activity and soluble sugar content when the symbiosis between AM fungi and Astragalus membranaceus in short time were opposite to a long time, it may be due to the synergism and antagonism with other components.5.The beneficial effects of AM fungi to growth and the nutritional components of Astragalus membranaceus were more and more obvious with its growth.At the suitable conditions, the growth of Astragalus membranaceus was normal, but the effects of the AM fungi were obvious when Astragalus membranaceus was in stress environment, it can make host plant be normal.The results showed that the effects of the AM fungi were more significantly when the plant was in stress environment.6.There is a best combination relation among AM fungi, amount of nitrogen application and Astragalus membranaceus. Inoculation has most obvious effects on the growth and metabolic activity of Astragalus membranaceus under 50～100 mg N/kg soil.It plays an important role on further using AM fungi to enhance the output and quality of Astragalus membranaceus.