Redwood seedling responses to light patterns and intensities
| Authors: | Ronald W. Boldenow, Joe R. McBride |
| Year: | 2017 |
| Type: | General Technical Report |
| Station: | Pacific Southwest Research Station |
| Source: | Gen. Tech. Rep. PSW-GTR-258. Albany, CA: U.S. Department of Agriculture, Forest Service, Pacific Southwest Research Station: 435-446 |
Abstract
Coast redwood (Sequoia sempervirens (D. Don) Endl.) seedlings were grown from seed in controlled environments with 16 hour photoperiods using three light patterns that mimicked full shade (constant light level), intermittent high light such as long duration sun flecks (low light with 15 minutes of intense light every 2 hours), and large openings (4 hours low light, 8 hours high light, 4 hours low light). Each light pattern contained three light intensity levels (33 percent, 66 percent, and 100 percent) with one intensity level in each pattern that provided 5.1 daily light integral (DLI). Among the treatments, the extremes of daily light were 1.6 DLI to 15.5 DLI.
Seedlings increased biomass accumulation with increasing light level with diminishing accumulation at the higher DLIs. The seedlings were most efficient at utilizing light in the full shade and large opening patterns with poor utilization of light in the intermittent sun fleck pattern. Within each pattern, increased light intensity resulted in increased seedling height, stem diameter, branching, branch length, leaf area, specific leaf area, leaf mass, root mass, total mass, root/shoot ratio, stomatal density and needle thickness. In general, maximum net photosynthesis increased with increased light intensity. Quantum efficiency did not vary with intensity within the full shade and large opening patterns. Within the intermittent sun fleck pattern, quantum efficiency was lower in the seedlings grown at the lowest light intensity.
With equal daily light, seedlings in all three patterns had similar branch length, total mass, and leaf mass. However, seedlings in the large opening pattern had greater height and greater stem diameter, but less specific leaf area than the full shade pattern. Seedlings in the intermittent sun fleck pattern had less height, stem diameter, total mass, leaf area, and leaf mass, but greater root/shoot ratios and specific leaf areas than seedlings in the other patterns.
Maximum net photosynthesis was greater in the seedlings grown in the large opening pattern. Quantum efficiency was not affected by light pattern. Photosynthetic light compensation points ranged from 12μEm-2s-1 for seedlings in the low intensity treatment of the shade pattern to 20μEm-2s-1 for seedlings grown at full intensity in the large opening pattern.
Needle morphology varied markedly among light treatments. Needles in the high light treatment of the large opening pattern had a regular pattern of rounded upper epidermal cells and a deeply safranin stained, elongated palisade layer. Needles in the low light treatments of both the full shade and intermittent sun fleck treatments had prismatic shaped cells in the upper epidermis and irregular, lightly safranin stained palisade layers.