Different nitrogen (N) forms affect responses to N form and N supply of rootstocks and grafted grapevines.

Rootstocks play an important role in the cultivation of grapevines. In addition to the uptake and storage of nutrients, rootstocks and their root system affect the growth and metabolite composition of the berries. Nitrogen can be taken up in various forms, such as nitrate, ammonium or amino acids or even small peptides, and is of considerable importance in vigor control and in yield and berry quality. Amino acids in the must adjust fermentation kinetics, constitute a major source for yeast and affect vine metabolism. In the present study, two different experiments were undertaken; nitrate, ammonium, urea, arginine and glutamine at various doses (0; 0.5; 1.0; 3.0 g N/plant) were used to fertilize (i) two hydroponically grown rootstock varieties (Ru140 and SO4) and (ii) grafted grapevines of Vitis vinifera L cv. Regent (rootstock SO4) grown in pots. Accumulation capabilities, generative growth and berry quality were examined. It can be assed that the preferred N form is rootstock-variety-dependent. We demonstrated that grapevines were able to take up nitrogen in the form of amino acids; (arginine to a greater extent than glutamine). Although, growth was reduced, nitrogen content and nitrate reductase activity were comparable for nitrate, ammonium and urea nutrition. In terms of berry quality, only minor differences between the N forms applied were identified. An economic optimum in terms of vine and berry quality was detected. Excessive amounts of nitrogen seemed to lead to the increased growth of green plant tissue. Berry yield increased with increasing nitrogen supply but slightly decreased at the highest dosage, whereas quality parameters such as must pH increased and the total acid concentration was reduced.