The Analysis For Factors That Affect The Ability Of Growth Promotion Of Alfalfa Rhizobia In Cold And Drought Regions And Screening Of High Efficient Strains

Biological nitrogen fixation is a biochemical process attracting almost the same attention as photosynthesis. With the deepening research of nitrogen fixation bio-organisms, their growth-improving effects have been shown from nitrogen fixation, phosphorus dissolving and growth hormone secret (Hendry G S, 1983).Alfalfa is one of the main cultivated forage legumes in China, the most important way to improve its yield and quality is effective rhizobia inoculation. However, whether alfalfa rhizobia have other biological functions except nitrogen fixation has not been elucidated. So it is vital to find factors affecting noduling and growth-improvement, to screen effective multi-function rhizobia strains for different ecological regions and varieties. In this study, the noduling and its affecting factors in two alfalfa pastures (cv. Algonquin and Longdong) from 5 different eco-regions were analyzed by means of Analytical Hierarchy Process (AHP) in spring, summer and fall.The ability of nitrogen fixation phosphorus dissolving,IAA secret and stress tolerance of selected strains was tested and the main soil physical and chemical factors affecting the above ability were analyzed and discussed by means of multi-regression and path analysis.The results showed that:1) Soil moisture played a vital role on nodule number of alfalfa rhizoia both in long term drought in arid regions and interval drought in irrigation regions. Alfalfa pasture showed nitrogen deficiency under drought stress in drought regions.2) The noduling ability of Algonquin was higher than that of Longdong. This difference could partly attributed to environmental factors and their genetic features. Furthermore, in Gansu province, nodule formation mainly took place in spring, with higher capacity than in summer and autumn. The appropriate temperature for nodule formation could be lower than 15～20℃.3) Taking all the indexes of alfalfa rhizobia into a comprehensive consideration, meanwhile referring to effective nodule rate, the effectiveness of alfalfa rhizobia in different types of soils could be scored as chernozem soil in Qingyang >irrigate soil in Wuwei >podzol soil in Dingxi. Soil from sub-alpine meadow in Gannan had a better effect...