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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Claims 11
Claim · model-written summary
Fir had a larger total xanthophyll pool than spruce, though active ratios were similar.
Verbatim
e0“both species showed similar ratios of active to total xanthophylls, fir seedlings had a greater total pool than spruce”
Claim · model-written summary
Fir and spruce had similar active to total xanthophyll ratios.
Verbatim
e0“both species showed similar ratios of active to total xanthophylls”
e1“fir seedlings had a greater total pool than spruce”
Claim · model-written summary
Fir and spruce had similar photochemical and nonphotochemical quenching ratios.
Verbatim
e0“the two species have similar ratios of photochemical (qP) and non-photochemical (qN) quenching of absorbed light energy”
e1“fir seedlings had a greater total pool than spruce”
Claim · model-written summary
High light decreased fir photochemical efficiency less than red spruce.
Verbatim
e0“fir suffers a lower decrease in photochemical efficiency when exposed to the high-light environment than does red spruce”
Claim · model-written summary
Spruce seedlings had greater biomass, height and shoot allocation than fir.
PiceaOrganisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Spruce seedlings exhibited a much greater total biomass, overall height and allocation to shoots compared to roots”
Claim · model-written summary
Spruce had greater photosynthetic rates during both years.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“spruce seedlings exhibited far greater photosynthetic rates during both years”
Claim · model-written summary
Fir allocated more resources to photoprotection and roots.
Verbatim
e0“fir exhibited a more conservative approach allocating more resources to photoprotection and roots”
Claim · model-written summary
Spruce allocated more to growth, biomass and photosynthesis.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Spruce allocated more to growth, biomass, and photosynthesis”
Claim · model-written summary
Spruce had greater foliage and height growth.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“had greater foliage and height growth”
e1“Spruce allocated more to growth, biomass, and photosynthesis”
Claim · model-written summary
The authors expect spruce to compete better after disturbance if moisture is sufficient and partial overstory moderates light.
- Outcome
- competitive edgee0
- Qualifier
- moisture was not limiting and (2) light stress was moderated by a partial overstorye0
Not reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“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”
Claim · model-written summary
The authors infer that balsam fir strategy is superior in high energy settings with correlated light and moisture stress.
- Taxon
- balsam fir
_-_Lark_Harbour%2C_Newfoundland_2019-08-18_(02).jpg?width=60)
Abies balsameae0 - Outcome
- more conservative seedling life-stage strategy of balsam fir would seem to be superiore0
- Qualifier
- light stress and moisture stress are highly correlatede0
Not reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
_-_Lark_Harbour%2C_Newfoundland_2019-08-18_(02).jpg?width=500)
Verbatim
e0“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”