Nitrate modifies urea root uptake and assimilation in wheat seedlings

BACKGROUND: Some authors suggest that nitrate improves the effects of ammonium and urea nutrition on plant growth via an increase in both the root uptake of ammonium and urea, and the further activation of its assimilation. In order to verify these hypotheses, wheat (Triticum aestivum L.) seedlings were grown with various nitrogen supplies containing the main nitrogen forms (ammonium, nitrate and urea). Root nitrogen uptake and the concentration of each of the nitrogen forms in roots and shoots were studied. RESULTS: Results indicated that nitrate increases root uptake of ammonium and urea, with this effect being highly significant when the three nitrogen forms are supplied simultaneously. Nitrate significantly increased both urea and ammonium assimilation in the shoot of plants fed urea‐and‐nitrate. However, nitrate did not significantly affect ammonium assimilation in either shoots or roots in plants fed ammonium‐and‐nitrate. CONCLUSION: The beneficial effect of nitrate seems to be related to an enhancement of root uptake of ammonium and urea, although their assimilation was significantly increased in urea‐fed plants, but not in ammonium‐fed plants.