Aspects of assimilation and accumulation of nitrate in some cultivated plants
1975
Darwinkel, A.
In a study on the accumulation of nitrate nitrogen in plants, turnip, rape, oats, Italian ryegrass, Westerwolths ryegrass, carrot and spinach were used. During growth the production and distribution of dry matter and the contents of total N and NO 3 -N were measured. NO 3 accumulation occurs when the N uptake exceeds assimilation. The uptake was largely dependent on N supply and plant species, whereas the conversion was closely associated with production and distribution of dry matter. Leaf blades contain high organic N and low NO 3 concentrations. The activity of the nitrate reductase was mainly located in leaf blades. This activity was highest in a young immature leaf and was lower the older the leaf. Production of leaves affected the NO 3 conversion considerably. During the growth period a gradual decrease of the conversion took place per unit dry matter produced, because of a smaller demand for proteins. The total N content in the dry matter, above which NO 3 accumulation takes place, was high in a young plant, but decreased during growth, whereas an increasing part of the extra NO 3 absorbed accumulated simultaneously. Turnips accumulated most NO 3 , because of their high N uptake. Other plant species could also reach NO 3 levels that are toxic for cattle. In rape and Italian ryegrass this is caused by a high N uptake, in oats and carrot by a poor conversion.
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