Physiological Characteristics And Influence Factor Of Nitrate-N Use Of Winter Wheat

Nitrate nitrogen is directly used among the important nitrogen forms by higher plants, Marschner thought that importance of nitrate reduce and assimilation for plant growth and development was identical to that of CO2 reduce and assimilation in photosynthesis. Though plant physiologist thought that nitrate-N and ammonium-N had similar value, many research showed nitrate was more important for dryland plant. The key to play the nitrogenous fertilizer role was to enhance its use efficiency. Owing to use of nitrogenous fertilizer on large scale, crop production increased, but brought out many malpractice, which made economic benefit decrease, agricultural cost increase, environment pollute. In order to solve these problems, enhance nitrogen use efficiency, it should be to study physiological and biochemical characteristics and influence factor of nitrate-N use and regulate their process in plant self. So nitrogen could play its role sufficiently and nitrogen use efficiency could be improved.We planted the winter wheat in Hoagland's solution with nitrate N as only N source, to study the effect on nitrate metabolism of winter wheat under different nitrate-N level,and different molybdenum concentration, supply Cl- on shoot and root,and light shading, and CO2 addition. Nitrate-N, ammonium-N ,nitrate reductase activity, total uptake N by plant during cultural period from solution and total N in plants were determined for comprehensive evaluation of the effect. The results as follows:1. Results of effect of different Mo concentration on nitrate metabolism of wheat: Results show that NRA, as regulated by metabolism pool and storage pool, varied continuously during the cultural period. However, at any case, Mo had an obvious effect on it: at the onset of 4 days, the treatment with suitable Mo concentration was the highest in NRA, followed by that treated with high Mo concentration, and that deficient in Mo was the lowest. Thereafter, due to nitrate accumulation in high amount in plants, NRA in the Mo deficient treatment thus became the highest. Nitrate N was negatively correlated with ammonium N, and the sum of nitrate and ammonium concentration was almost stable at any measurement. When nitrate N concentration was higher, ammonium N would become lower, or in visa versa. Such a balance was closely related with Mo supply: at adequate concentration of Mo, the high concentration of ammonium N was opposite to low nitrate N at the onset of 4 days, since then, both concentrations trended to be the same level. The treatment of Mo deficient was similar to the adequate, but nitrate N was no great change and the sum of ammonium and nitrate N concentrations was higher. In contrast, ammonium N concentration in the high Mo treatment was higher than the nitrate concentration throughout the whole period of the culture. Crop uptake nitrogen, which agreed well with nitrate N reduction in the solution, was the highest in the treatment with suitable Mo concentration, followed by that with high Mo treatment while that deficient in Mo was the lowest. Considering the lower total concentration of nitrate and ammonium N in plants and the highest uptake of N by plants, it was clear that adequate Mo supply did not only promote nitrate uptake and transformation into ammonium, but also favored ammonium transformation into organic nitrogen and therefore played an important role in the nitrate N metabolism.2. Results of effect of shading and CO2 addition on nitrate metabolism of wheat: Results shoed that under both natural light and light-shading conditions, addition of CO2 increased nitrate-N uptake and assimilation by plants. However, there were some difference between shots and roots. For shoots, increase of CO2 concentration, nitrate, ammonium and nitrate reductase activity were all decreased; while for the roots, the difference was not so distinct as that in the aboveground part, and the nitrate reductase activity was not decreased, but increased. Since nitrate-N uptake by plants from the solution and the total N in plants were much hig...