Alterations in internal partitioning of carbon in soybean plants in response to nitrogen stress

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Abstract
Alterations in internal partitioning of carbon were evaluated in plants exposed to limited N supply. Vegetative, nonnodulated soybean plants (G. max (L.) Merrill, ''Ransom'') were grown for 21 days with 1.0 mM NO3- and then exposed to solutions containing 1.0, 0.1, or 0.0 mM NO3- for a 25-day treatment period. In N-limited plants, there were decreases in emergence of new leaves and in the expansion rate and final area at full expansion of individual leaves. As indicated by alterations in accumulation of dry weight, a larger proportion of available C in the plant was partitioned to the roots with decreased availability of N. Partitioning of reduced N to the root also was increased and, in plants devoid of an external N supply, considerable redistribution of reduced N from leaves to the root occurred. The general decrease in growth potential and sink strength for nutrients in leaves of N-limited plants suggested that factors other than simply availability of N likely were involved in the restriction of growth in the leaf canopy and the associated increase in C allocation to the roots.