EFFECT OF VARIOUS FACTORS ON THE UTILIZATION OF NITROGEN AND IRON BY SPIRODELA POLYRHIZA (L.) SCHLEID.

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Abstract
S. polyrhiza plants were grown in sterile culture solns. under conditions of constant temp. and illumination. The compositions of the solns. were similar except that the source of N was varied. The forms of N studied were guanidine, urea, ammonium, and nitrate. The influence of the concn. of any form of N assimilated by plants is more important than the influence of the pH of the medium, as long as the pH value is moderate (5-8). Nitrate N was more effective over a wider range of concns. than any other form, although ammonium was a better N source at lower concns. Urea was intermediate in its effects. Guanidine appears to be a source of N for plant growth. It is postulated on the basis of the data obtained that iron enters the plant as ferric organic complex ion instead of ferric ion, as hitherto supposed. The molar ratio of organic anion to iron, in addition to its concn., is very important in determining the effectiveness of iron for plant growth.

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