Document: AND-3-29-17

Douglas fir seedling growth response to different light environments.

SCHAUER, A.J.* ¹, B.J.BOND ¹, S.RADOSEVICH ¹, G.A.RITCHIE ² and D.WOODRUFF ¹

Oregon State University, Corvallis, OR, U.S.A. ¹
George Staebler Forest Resources Research Center, Centralia, WA, U.S.A. ²

Abstract:
We designed an experiment to determine how the growth of Douglas-fir seedlings responds to differences in light quality. Seedlings were subject to side light manipulation or total light manipulation through the use of plastic films that produced a 70% reduction in red light (R), 95% reduction in blue light (B), and 50% reduction in UV radiation (UV). A neutral shade control treatment (N) reduced overall photosynthetically active radiation (PAR), by 40%, approximately the same total PAR reduction as the filters that altered light quality. We also included clear plastic (C) and no plastic (O) control treatments to study the effect of placing the plastic films around the trees. Prior to planting we destructively analyzed 20 seedlings to develop allometric equations that predicted initial mass of roots, stems, and foliage of the experimental trees. In March 1999, seedlings were planted in raised beds and provided with a complete fertilizer. Seedlings, provided with ample water, were allowed to grow for six months before harvesting both roots and shoots. We used a completely randomized experimental design, with 8 trees as replications for each treatment. For all seedlings we determined growth in stem diameter, tree height, and shoot mass in addition to the root mass:shoot mass ratio, leaf mass:stem mass ratio, and specific leaf area. A MANOVA was used to contrast those treatments that reduced PAR with those that did not (R, B, N vs UV, C, O) and indicated a significant overall growth effect (i.e., across all measured response variables) due to PAR (p < 0.0001). A significant overall growth effect due to reduced red light (p < 0.01) was also found when those treatments that reduced red light were contrasted with those treatments that did not (R vs. all others). Overall, we found no significant growth response for the plastic film vs. no enclosure, side light vs. total light, reduced blue light, or reduced UV radiation. These results suggested that alterations in red light can influence some of the growth properties Douglas-fir seedlings exhibit, independently from changes in total PAR, probably due to a phytochrome response to altered red:far-red ratios.

Keywords: light quality; Douglas fir

This abstract is being presented at: 10:30 AM in session:
Poster Session #1: Light Relations.