Author

Sarah Zazzaro

Date of Award

5-2009

Level of Access

Campus-Only Thesis

Degree Name

Master of Science (MS)

Department

Ecology and Environmental Sciences

Advisor

Michael E. Day

Second Committee Member

Michael S. Greenwood

Third Committee Member

Ruth Hutchins

Abstract

Red spruce is a major component of the Acadian forest and an important timber resource. Unfortunately, populations are decreasing, with red spruce often replaced by balsam fir. As the 'gate-keeper' for the success of tree species is usually the more vulnerable seedling life-stage, we have focused our attention on differences between seedlings and how they respond to silvicultural practices. Previous studies suggest balsam fir is a competitive stress on red spruce during early development, and understory light conditions may favor regeneration of one species over the other. In this study we evaluated how seedlings of the two species performed after a simulated overstory removal, with light environments rapidly changing from relatively closed canopy to open sky. We grew first-year and two-year-old seedlings in an understory light environment (10% sunlight), and in mid growing season relocated half of the seedlings to full sunlight. To seedlings sunlight can be both a resource and a stress which can be quantified by growth, resource allocation, photosynthetic parameters, and photoprotective mechanisms. Xanthophyll pigments dissipate excess energy absorbed from sunlight and in turn help protect the plant from photoinhibition. Therefore, total zanthophyll concentration along with the ratio of active forms (zeaxanthin and antheraxanthin) to total zanthophylls are indicative of ability to withstand high-light stress. In addition, chlorophyll fluorescence was used to quantify stress on photosystem II resulting from the experimental treatments, as well as the relative amounts of intercepted sunlight dissipated through photochemical and non-photochemical pathways. While both species showed similar ratios of active to total xanthophylls, fir seedlings had a greater total pool than spruce. Fluorescence data indicated that the two species have similar ratios of photochemical (qP) and non-photochemical (qN) quenching of absorbed light energy. However, the fluorescence parameter Fv/Fm, used to assess damage to photosystem II, suggests that fir suffers a lower decrease in photochemical efficiency when exposed to the high-light environment than does red spruce. Spruce seedlings exhibited a much greater total biomass, overall height and allocation to shoots compared to roots. In addition, spruce seedlings exhibited far greater photosynthetic rates during both years. Overall, fir exhibited a more conservative approach allocating more resources to photoprotection and roots relative to foliar biomass and photosynthetic systems. Spruce allocated more to growth, biomass, and photosynthesis and had greater foliage and height growth. Therefore, we expect that spruce seedlings would have a competitive edge due to its greater photosynthetic rates and leaf area in post-harvest or post-disturbance environments when (1) moisture was not limiting and (2) light stress was moderated by a partial overstory. In higher energy environments, where light stress and moisture stress are highly correlated, the more conservative seedling life-stage strategy of balsam fir would seem to be superior.

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