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Effects of Phosphorus Deficiency on Growth and Metabolism of Soybean

1950; University of Chicago Press; Volume: 111; Issue: 4 Linguagem: Inglês

10.1086/335613

1940-1205

S. V. Eaton,

Soil Carbon and Nitrogen Dynamics

1. Sand cultures were used in a study of the effects of phosphorus deficiency on soybean plants. At an early stage of development the main symptom was the deeper green color of the leaves. Later a general chlorosis developed in the interveinal areas of the lower leaves. Finally, the veins became chlorotic, and the leaf soon died. The deficient plants were small, with small leaves and thin, hard stems. The tops were affected more than the roots, so that the top-root ratio of the minus-phosphorus plants was lower than that of plus-phosphorus ones. 2. Phosphorus-deficient stems were low in moisture. The stems of the younger plants were high in total sugars, reducing sugars, and sucrose. These differences in the two sets of stems decreased in the older plants, and at the third harvest all these fractions were in general higher in the complete-nutrient ones. There was much more starch in the minus-phosphorus than in the plus-phosphorus stems at each harvest, and the percentage of starch in the former stems and the differences in the two sets increased with age. Including starch, the phosphorus-starved stems were at each harvest high-carbohydrate ones. The accumulation of carbohydrates in these stems is interpreted as owing to the interference with protein synthesis at the amide rather than at the nitrate-reduction stage as has been found in other plants. Amides accumulated in the minus-phosphorus stems, but nitrates were higher in the plus-phosphorus ones. 3. Total nitrogen, soluble nitrogen, ammonia, and amides were higher in the phosphorus-starved stems; percentages of nitrates were larger in the complete-nutrient ones. The gradients of these fractions were, in general, positive down-ward in the latter stems, but in the former the concentrations were higher at the middle or lower level. More of the total nitrogen was present in the soluble form in the minus-phosphorus than in the plus-phosphorus stems. The accumulation of total soluble nitrogen and amides in the former stems is thought to be caused both by the interruption of protein synthesis at the amide stage and by proteolysis. 4. There were much larger percentages of total phosphorus, soluble phosphorus, and insoluble phosphorus in the complete-nutrient stems than in the phosphorus-deficient ones. The soluble phosphorus of the latter stems made up a larger percentage of the total phosphorus than in the former ones.