Document: ROB-3-29-26

Effects of light and nitrogen availability on the growth, photosynthetic performance and resource use of regenerating tree species in New England forest ecosystems.

HARRINGTON, R.A.* and J.H.FOWNES

University of Massachusetts, Amherst, MA 01003 USA ¹

Abstract:
We examined how light and nitrogen (N) affected growth and resource-use efficiency in seedlings of six northern hardwoods forest tree species. Betula papyrifera, Betula lenta, Pinus strobus, Acer rubrum, Quercus rubra, and Tsuga canadensis seedlings were collected from the field and grown for five months in a greenhouse under two light levels (full sun and 15% incident) and two levels of N availability (Control and N enrichment equivalent to 150 kg/ha) in a split plot design. Relative growth rate and light-saturated photosynthesis (area-basis) increased with increasing N availability but did not differ significantly with light treatment. Leaf area ratio increased and leaf mass per area decreased in shade, but were unaffected by N availability. Above-:below-ground biomass ratio increased under low light or high N availability. A surprising result was that Betula papyrifera, usually considered shade-intolerant, responded strongly to N but not light, suggesting that its strategy is actually opportunist for high N in gaps. In conclusion, N availability affected photosynthetic plasticity and growth while light affected morphological plasticity.

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