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Use of Carbohydrate and Nitrogen Root Reserves in the Regrowth of Alfalfa from Greenhouse Experiments under Light and Dark Conditions¹

Alfalfa (Medicago sativa L.) plants were allowed to regrow 42 days in the dark and light with and without (roots only) intact crowns. A significant amount of new roots was produced only on actively photosynthesizing plants. No major change in fresh weight-unit volume of the original roots was noted, except for an increase during the period of 21 to 42 days with plants grown undisturbed in the light which then were actively reaccumulating root reserves.

A small proportion of the root nonstructural carbohydrates, but none of the total nitrogen, was used in root respiration. Most of the nonstructural carbohydrates were translocated from the roots and used for the production of new tops and roots, and root carbohydrates were used in far greater amounts than root nitrogen. Even so, photosynthate from new leaves was an important factor in recovery growth. Current hotosynthetic energy contributed 0, 52, 70, 83, 89, and 93% of the increase in total plant weight of plants grown undisturbed in the light at 7, 14, 21, 28, 35, and 42 days, respectively.

Key Words: Root Growth • Root Volumes • Top Growth • Root Nonstrutural Carbohydrates • Root Nitrogen • Respiratory Losses

² Professor of Agronomy and Rockefeller Graduate Fellow (now Forage Research Specialist, Instituto de Investigaciones Agropecurias, Casilla 5427, Santiago, Chile), University of Wisconsin, Madison, Wisconsin, 53706. The financial assistance of the Rockefeller Foundation during the period of graduate study of the junior author at the University of Wisconsin is gratefully acknowledged. We also acknowledge the advice provided by Dr. J. A. Eastin.

Received for publication December 12, 1968.