ROOT DEVELOPMENT AND NITROGEN DISTRIBUTION IN MAIZE (ZEA-MAYS L) AS INFLUENCED BY LIGHT AND NITROGEN SUPPLY

Under greenhouse conditions in plant physiological experiments the effect of varied light intensity and the amount of nitrogen on root development and the nitrogen distribution and utilization on maize seedlings (Zea mays L. Cultivar Contessa) was tested. The light intensity was varied by shade. Two energy intensities were chosen with 550-mu-mol +/- 50-mu-mol (complete light exposure) and 180-mu-mol +/- 30-mu-mol (shade). The nitrogen supply in the sand culture experiments represent the supply area of the deficiency of nitrogen (7 ppm N in the soil solution) up to the large oversupply (840 ppm N in the soil solution). The following results were obtained: 1. The root system of completely exposed seedlings is considerably more developed than the root system of the shaded plants. Completely exposed plants react to the increasing supply of nitrogen by a reduction in the root surface. Shaded plants develop their maximum root surface with a medium supply of nitrogen. 2. A large part of the nitrogen supply in the plants comes from the endosperm nitrogen supply in the tested development stage. In both light intensities the seedlings contain a similar high amount of Kjeldahl nitrogen depending on the nitrogen supplied whereby maximum amounts are to be found in the medium nitrogen supply area. With the high nitrogen supply area the Kjeldahl nitrogen amount decreases in the whole plant with both light intensities. On the other hand the total nitrate amount in the plant increases. Depending on the amount of the nitrogen concentration offered and by varying the light intensity, distinct differences in the distribution of the nitrogen fractions between shoot and root can be seen. With completely exposed plants the total nitrate nitrogen amount in the high nitrogen supply area was concentrated mainly in the root. On the other hand shaded plants show a well balanced distribution of the nitrate nitrogen amount between shoot and root in the whole nitrogen supply area. The total nitrate nitrogen amount in the maize seedlings is especially influenced by the amount of the external nitrogen supply, largely independent of the size of the total root surface.