Effect Of Nitrogen Forms On Nutrient Absorption And Enzymes Activity Of Wheat Seedlings

Nitrogen plays a very important role for plant growth; ammonium (NH4+-N) and nitrate (NO3--N) are the main forms of nitrogen which the plants can absorb from the soil solution. Root nutrient uptake kinetics is very useful for clarify of absorbing characteristics and screening for favorable absorption genotypes.In this present study, we used wheat seedlings as the material, set three different forms of nitrogen treatment (N03--N treatment alone, NH4+-N treatment alone and mixed nitrogen treatment). In order to determine absorption rate of nitrogen and other mineral elements, and analyze differences in kinetic parameters in different nitrogen forms treatment, and explore the effect of different nitrogen forms on mineral nutrition absorption of wheat, the nutritional depletion techniques and water culture methods were used in this study.The results showed that:mixed nitrogen treatment increased the maximum absorption rate, though the Michaelis constant (Km) and the critical concentration (Cmin) had not significant difference, as compared with the N03--N treatment alone. Mixed nitrogen treatment increased the maximum absorption rate and decreased Cmjn, though the Km had not significant difference, as compared with the NH4+-N treatment alone. The results indicated that mixed nitrogen treatment increased the inherent potential of NH4+ uptake and enhanced the use ability of ammonium ions. The N03--N treatment alone had an inhibit effect on the absorption of the phosphate and sulfate ions. The NH4+-N treatment alone had little effect on the phosphate ions absorption; however, it had a great influence on the sulfate ions uptake. Nitrate ions had a promoting effect on the absorption of K+, Ca2+, Mg2+, Mn2+, Zn2+, Cu2+ and Fe3+ however, ammonium ions had a limited or inhibitory effect on the absorption of K+ Ca2+, Mg2+, Mn2+, Zn+, Cu+and Fe+. In this present study, many quadratic polynomial equations was used to describe the absorption process of nitrogen and other mineral elements in wheat seedlings under different nitrogen forms. These equations, with high goodness of fit, could meet the requirements of analysis of absorption difference from the kinetic parameters obtained from the equations.Nitrate reductase (NR) plays a key role on the assimilation of NO3-. Glutamine synthetase (GS) and glutamate synthase (GOGAT) are crucial and key enzymes for the ammonia assimilation in higher plants. Nitrogen forms and the ratio of ammonium to nitrate have a great impact on metabolic activity of enzymes. In this experiment, wheat was used to study the dynamic activity changes of NR, GS and GOGAT under different nitrogen forms. After 2 days of treatment, NR activity of wheat leaves reached its maximum, and then decreased in the NO3--N treatment alone and the mixed nitrogen treatment, but NR activity in the NO3--N treatment alone was higher than the mixed nitrogen treatment. The NR activity in leaves remained low in NH4+-N treatment alone. The GS activity in leaves of three different nitrogen forms showed a increasing trend during the different nitrogen processing. The GS activity in ammonium treatment was faster than the nitrate treatment; however, in the later period of treatment, the mixed nitrogen treatment was more effective to raising the leaf GS activity than the NH4+-N treatment alone, The GOGAT activity in leaves of three different nitrogen forms also showed a increasing trend during the different nitrogen processing, whereas the NH4+-N nitrogen treatment was more effective to raising the leaf GS activity than the NO3--N treatment alone.Determination of mineral elements received a number of interference factors. Several related ions interference in nitrogen analysis, the reaction time and reaction temperature in the ions determination of ammonium and phosphate, the centrifugation and filtration effect in the determination of SO42- were discussed in this study. In this experiment, the interference effect of SO42-, PO43- and Cl-on the determination of NO3- and NH4+ could be ignored. Temperature range of 25-30℃and 30min of reaction time could meet the requirements of the determination of ammonium ions. Temperature range of 25-30℃and 20-30min of reaction time could also meet the requirements of the determination of phosphate ions. Chromate ions in the suspension of barium chromate prepared by centrifugation were lower significantly than normal standing precipitation. Colorimetric analysis showed no obvious difference between centrifugation and filtration when chromate ions was prepared; however, the centrifugation methods needed less time to prepare the sample solutions, centrifugation operation was also more concise, as compared with filtration methods.