Root Growth in Acer saccharum Marsh. Seedlings: Effects of Light Intensity and Photoperiod on Root Elongation Rates

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Abstract
In a series of controlled environment studies, root elongation rates of 1st yr sugar maple (A. saccharum Marsh.) seedlings appeared to be dependent, at least in part, on current photosynthate production by the shoot. No shoot elongation was observed under short-day (SD) (8 h) or long-day (LD) (16 h) conditions after previous SD exposure. Thus, root growth could be measured without the confounding effects of shoot elongation. Under these conditions, changes in light intensity that altered the photosynthetic production of the shoot system resulted in concomitant changes in root elongation rates. Diurnal rates of root elongation were also followed and, under SD conditions adequate for photosynthesis, night growth exceeded day growth. Reducing light intensities to a level that retarded photosynthesis decreased the differential between night and day growth which was reestablished under high light intensity. Under LD conditions, seedlings not previously exposed to short days expanded their terminal bud and grew normally. Shoot growth took place at the expense of root growth and competition occurred between roots and shoot for growth materials. The present study indicated that factors that affect the photosynthetic production of the shoot system of 1 yr old seedlings markedly affected root elongation rates and may be a factor in the establishment of sugar maple seedlings.