The Primary Research About Tolerant To The Screening Of Low Nitrogen Maize Variety And Physiological Mechanism

In the first year of2010,51corn varieties were given low nitrogen stress treatment in the stage of seedling in order to investigate growth and physiological characteristics of corn under this condition. After comprehensive evaluation, typical varieties were selected from the tested materials. Then in the second year of2011, continual comprehensive evaluation and screening were given to the selected materials with some additional varieties. Two years of screening results integrated, symptoms of corn in the seedling stage as reference, typical strong resistance to low nitrogen varieties Aoyu28, Zhenghong311and Chengdan30as well as weak resistance varieties Xianyu508, Sanbei2and Jinyu608were selected as materials to be treated with different levels of low nitrogen stress. Under the condition of low nitrogen stress, growth, photosynthetic fluorescence, nitrogen metabolism, resistance and root physiological characteristics of corns with different performance on resistance to low nitrogen in seedling stage were investigated to reveal the response mechanism to low nitrogen stress. The main conclusions are as follows:1. Under low nitrogen stress condition, in the seedling stage, seedling height, leaf area, content of chlorophyll, nitrogen content and accumulation declined. Although root volume and root-shoot ratio of most varieties increased, eventually the accumulation of dry matter reduced. Different varieties were influenced under low nitrogen stress by different degrees. It showed abilities of resistance to low nitrogen stress were significant different among different varieties.2. Considering coefficient of variation in different varieties, according to order of size of relative value of each index (characters)(value ratio of low nitrogen stress and normal nitrogen treatment),7index which could be used to evaluate and screen resistance ability in the seedling stage as important index were selected from the13index.They were leaf area、plant root volume、plant nitrogen accumulation shoot ratio、shoot dry weight、below ground dry weight、plant dry weight。3. Two comprehensive methods were used to evaluate abilities of resistance to low nitrogen stress in this study. One was comprehensive fuzzy integrated evaluation method (fuzzy membership function method), relative value of each index after normalization process to coefficient of variation among varieties was taken as weight. The other was principal component analysis. By fuzzy membership function method, results of evaluation on the seven selected important index and all13index were consistent, which indicated the front screened index were available. Also, results by fuzzy membership function method and principal component analysis were basic consistent, although certain difference between2years. Results of the two methods in2years integrated, varieties such as Zheng hong311、Ya yu10、Cheng dan30、Lv dan50、Ao yu28showed strong resistance to low nitrogen stress, while varieties such as Xian yu508、Jin yu608、San bei2、Chuan dan428showed weak resistance to low nitrogen stress.4. Generally speaking, under low nitrogen stress condition leaf area、SPAD value、 leaf net photo synthetic rate、transpiration rate, stomatal conductance of corn seedling deceased. Secondly, Fv/Fm、Fv/Fo、Fv’Fm’qP dropped. GS, GOGAT, GOT and GPT and root activity reduced. root active absorption area, Root active absorption area and nitrogen uptake by the accumulation went down. Lastly, content of soluble protein and plant dry weight declined. Reversely, content of MDA, POD activity, content of free praline and soluble sugar increased. The more serious the stress was, the more obvious this effect was. Also, the longer the stress lasted, the more obvious this effect was. But different types and varieties were different. Comparing with varieties of weak resistance to low nitrogen stress, under low nitrogen stress, the index of varieties of strong resistance referred above which declined showed a smaller decline, MDA showed a smaller increase. What is more, activity of POD、content of proline, soluble sugar had a larger increase. As a result, this might be important physiological mechanism to strong resistance to low nitrogen stress.