Effect of Nickel Application on Growth and Nitrogen Metabolism in Rapeseed Supplied with Different Sources of Nitrogen

Very little information is available about the effect of Ni nutrition on nitrogen metabolism in plants in the presence and absence of urea and various amino acids. Consumption of high amounts of urea in rapeseed fields shows the necessity of study the effect of nickel on improving the efficiency of nitrogen metabolism in this condition.The purpose of this nutrient solution culture expriment study was to investigate the effect of nickel in the presence and absence of urea and three types of amino acids including histidine (His), arginine (Arg), and tryptophan (Tri) on growth and metabolism of nitrogen in rapeseed.

This greenhouse experiment was conducted in a completely randomized design in factorial arrangement of split plots and three replications in solution culture on rapeseed (Hyola-401 variety). The main plots of the experiment consisted of nutrient solution with urea and urea-free nutrient solution, and subplots consisting of nickel at three levels of zero, 5 and 10 micromoles of nickel sulfate and amino acid at four levels including non-use of amino acid and the use of tryptophan, arginine and histidine amino acids At a concentration of 100 μM. At the end of the experiment, dry weight of the shoots and roots, the concentration and uptake of nickel and some nitrogen compounds such as nitrogen, nitrate, ammonium, urea and amino acids of the shoots and roots as well as the activity of the urease enzyme in these two parts, was measured.

Regardless of Ni concentration and amino acid treatment, shoot dry weight of plants in the urea-based nutrition solution was significantly lower than those in the urea-free nutrient solution. In the urea-based nutrient solution, application of 5 µM Ni in combination with histidine significantly increased the shoot dry weight. Similar results were observed in the urea-free nutrient solution. In the urea-based nutrient solution, the positive effect of Ni on the shoot growth of the plant increased in the presence of amino acids. The presence of Ni in combination with amino acids increased the leaf activity of urease; although the urease activity in the plants grown in the urea-based nutrint solution was far higher than those grown in the non-urea solution.

The effect of Ni application on nitroent metabolism and plant growth was dependent on the applied level of Ni and the presence or absence of urea and amino acids. Nickel at the 5 µM level positively affected nitrogen metabolism and growth of plants supplied with urea while it had no effect on the plants unsupplied with urea. In the urea-based nutrint solution, the presence of amino acids particularly, His had stimulative effect on the plant root grwoth. Regardless of urea treatment, Ni at the 10 µM Ni level was toxic for rapeseed; although the presence of amino acids led to significant decrease of Ni toxicity effect.