Experiments on Photoperiodism, Dormancy, and Leaf Age and Abscission in Sugar Maple

• Published in: Botanical gazette (Chicago, Ill.) Ill.), 1951-01, Vol.112 (4), p.365-393
• Main Author: Olmsted, Charles E.
• Format: Article
• Language: English
• Subjects: Abscission; Age; Cooling; Dormancy; Leaf buds; Leaves; Maple sugar; Photoperiod; Plant growth; Plants
• ISSN: 0006-8071
• DOI: 10.1086/335673

1. A seedling population of sugar maple (Acer saccharum Marsh.), derived from two native seed trees in southeastern Wisconsin, was grown for 7 years (1941-1947) in pots in the University of Chicago greenhouses and gardens. The experimental variables were mainly length of photoperiod and amount of winter chilling, studied particularly in relation to leaf senescence and abscission, onset and completion of bud rest, budbreak, and amount of terminal growth. 2. It was concluded that in this species the loss of green color and leaf abscission under natural conditions are basically conditioned by the naturally decreasing autumnal photoperiod. In the various years and experiments leaves expanding from as early as February to as late as August were mostly abscised in October and November if the plants were maintained on natural photoperiod, either indoors or out. Chronological age of leaves had a limited relation to time of senescence and abscission, youngest leaves persisting a few days longer. Constant photoperiods of 16, 12, and 8 hours, imposed in the greenhouse on first-year seedlings on September 10, resulted in delayed senescence and abscission (up to 5 months for youngest leaves on 16-hour photoperiod) compared with plants outside on natural photoperiod. There was considerable variation in time of these events within any one treatment, but in general the amount of delay was positively related to length of constant photoperiod. A change from 16- to 8-hour photoperiod in December accelerated senescence and abscission as compared with plants remaining on 16-hour photoperiod. In second-year plants leaves of similar chronological age persisted longer when they had expanded and had been maintained inside on 20-hour than on 9-hour light periods; but those on natural photoperiod lost their green color and were abscised in October and November,generally earlier than those on either constant photoperiod.In all experiments loss of green color always preceded abscission. These results all suggest that the natural photoperiodic mechanism leading to senescence and abscission may involve shifting gradients of abscission inhibitors and/or activators conditioned in a complex fashion by changing light-dark ratios in the photoperiodic cycle. Thus, leaves were eventually abscised on any of the photoperiodic treatments employed, but their chronological age had much more influence on the length of their persistence when they were on constant than when on natural photoperiods. Pr