Abstract
The absorption and assimilation patterns of 15NO3− supplied as the Ca2+ and Mg2+ salts to intact ryegrass (Lolium perenne) seedlings were compared. No statistically significant effect of ambient cation on the amounts of 15NO3− absorbed was observed in the initial six hours, but during the subsequent six hours, absorption from Ca(15NO3)2 exceeded that from Mg (15NO3)2.
Lower rates of 15NO3− assimilation were found in roots exposed to Mg(15NO3)2 than in those exposed to Ca(15NO3)2. It was proposed that Mg2+ initiated a restriction in 15NO3− reduction in roots, probably as a consequence of a Mg2+-induced physiological Ca2+ deficiency. Lower 15N translocation rates were also observed from Mg(15NO3)2. These effects of Mg2+ in depressing 15NO3− assimilation and translocation occurred prior to an effect on 15NO3− uptake.
In shoots, larger amounts of reduced 15N products occurred with Ca(15NO3)2 than with Mg(15NO3)2. It was concluded that this was due to enhanced translocation of 15NO3− (and possibly its reduced products) in presence of Ca2+ rather than to specific cation effects on 15NO3− assimilation in the shoots.
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