Influence of Photoperiod and Photoperiodic Cycles on the Growth of Coastal Redwood Seedlings

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Abstract
Redwood seedlings were grown under various photoperiods on 24-and 48-hr. cycles to determine the requirements for photoperiod and cycle length in seedling growth. With 1 exception, height growth and dry weight decreased as the total amount of light energy decreased, regardless of the cycle. Continuous light, or no cycle, resulted in maximum dry-weight production but not the tallest trees. Plants under a photoperiod that exceeded the length of the dark period, irrespective of cycle length, showed a positive response to a circadian or hr. cycle compared with a 48-hr. cycle. The plants used light energy for height growth and dry-matter production most efficiently when grown under a 20-hr. photoperiod on a 24-hr. cycle. The distribution of dry matter between tops ?nd roots of the redwood seedlings was only slightly affected by length of photoperiod or length of cycle.

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