Effect Of Nitrogen Form On Growth,Physiological And Biochemical Characteristics Of Tobacco Seedlings

Ammonium and nitrate were mainly absorbed by plants. Flue-cured tobacco was nitrate plant. Quality of tobacco leaves supplied by nitrate nitrogen was better than that supplied by ammonium nitrogen, but there was less research about growth response of flue-cured tobacco on different nitrogen form. Plant can absorb directly the organic nitrogen in the soil, especially free state of amino acid nitrogen. However, whether flue-cured tobacco can directly absorb and use amino acid nitrogen, and how amino acid nitrogen effect on growth and physiological were less reported.Two experiments were conducted. Hydroponic experiment was conducted with supplying equal amounts of N in five different ratios of NH₄⁺-N:NO₃^--N（100:0 as 100-0AN, 70:30 as 70-30 AN, 50:50 as 50-50 AN, 30:70 as 30:70AN, 0:100 as 0-100AN）. Sterile-cultured experiment set six treatments with equal amount nitrogen of different nitrogen forms（Z1 NH₄⁺-N:NO₃^--N:Glu-N =100:0:0, Z2 NH₄⁺-N:NO₃^--N:Glu-N =0:100:0, Z3 NH₄⁺-N:NO₃^--N:Glu-N=0:0:100, Z4 NH₄⁺-N:NO₃^--N:Glu-N=50:0:50, Z5 NH₄⁺-N:NO₃^--N: Glu-N=0:50:50、Z6 NH₄⁺-N: NO₃^--N: Glu-N =25:25:50）. In order to ascertain the mechanism of effect of nitrogen form on growth of flue-cured tobacco, the effect of nitrogen form on root growth and development, nitrogen absorption and utilization, photosynthesis, and the emzyme activity of nitrogen assimilation of tobacco seedlings were studied. The main results were indicated as follows:The results of hydroponics experiments indicated that shoot dry weight, total dry weight, root total length, root total surf area and volume, root soluble sugar content, nitrogen content and nitrogen accumulation of stem and leaf and nitrogen distribution ratio of stem and leaf in the treatment of 100-0AN were the lowest; However, root dry weight, root average diameter, root activity and nitrogen content and accumulation of root in the treatment of 0-100 AN were the lowest. Within 20 days after treatment, the root dry weight, nitrogen accumulation of root and plant total dry weight in the treatment of 50-50 AN were the highest. On 25 days after treatment, root and shoot dry weight, root total surf area and volume, root activity, root soluble sugar content, root nitrogen content and accumulation in the treatment of 70-30 AN were the highest; nitrogen content and nitrogen accumulation of leaf in the treatment of 30-70 AN were the highest. Under mixed supply of ammonium and nitrate, plant growth and nitrogen utilization were promoted. Only ammonium or nitrate inhibited growth and nitrogen utilization of tobacco seedlings. The mixture of ammonium and nitrate not only could promote growth and development of tobacco seedlings, but was benifical to nitrogen absorption and uutilization of shoot.The results of hydroponics experiments showed that the net photosynthetic rate（Pn） and glutamine synthetase（GS） activity of tobacco seedlings leaves of 70-30 AN was the highest in the processing cycle; Y（II）, q P and ETR of leaves and GS activity of root of 100-0AN were the highest; the soluble sugar content and sucrose phosphate synthase（SPS） activity of the treatment 100-0AN or 70-30 AN were higher than that of other treatments, and the amylase（AMY） activity of 30-70 AN was significant higher than that of others. Due to different treatment time, there is difference of effect of nitrogen forms on nitrate reductase（NR） activity of leaf and root. Compared with applied single ammonium or nitrate, the mixture of ammonium and nitrate was conductive to enhance net photosynthetic rate of tobacco seedlings. Applied single or a higher proportion of ammonium could increase soluble sugar content and SPS activity of tobacco seedlings leaves, but a higher ratio of nitrate would help improve AMY activity.The results of sterile culture experiments indicated that total root length, total surface area, root total volume and lateral length of treatment Z3 were the highest. Main root length of Z4 was 5.68 times that of Z1, but all leves of lateral root length declined; length of main and a lateral root of Z5 increased by 39.48% and 77.84% respectively compared with that of Z2, and which enhanced lateral root formation and development. The leaf GS activity of treatment Z3 was the highest,but except for Z6, the root GS activity of other treatments had no significant difference. Leaf and root glutamic oxalo acetic transaminase（GOT） activity of Z1 were the highest. Root glutamic pyruvic transaminase（GPT） activity of Z6 were the highest, but leaf GPT activity of Z1 was the highest. Glutamate was beneficial to lateral elongation and formation; the mixture of inoriganic nitrogen and glutamate could mitigate the adverse effects of only ammonium or nitrate on root growth of tobacco seedlings. Glutamate increased leaf GS and GOT activity. The mixture of inorganic nitrogen and glutamate was conductive to enhance root GPT activity, but was detrimental to leaf GPT activity improvement of tobacco seedlings.