Date of Award

Spring 2022

Document Type

Thesis Restricted

Degree Name

Master of Science (MS)

Department

Biology

Committee Chairperson

Jessica Schedlbauer, Ph.D.

Committee Member

Jennifer Chandler, Ph.D.

Committee Member

Josh. R. Auld, Ph.D.

Abstract

In Eastern deciduous forests, changes in dominant tree species composition between the canopy and understory suggest the development of novel forests in the near future. Although this pattern is widely documented, there is limited understanding of the physiological performance of emerging understory dominants. This study aims to quantify the understory photosynthetic responses of the natives, Acer rubrum and Fagus grandifolia, and non-native, Acer platinoides. Three individuals per species, each located at three forest understory sites in southeastern Pennsylvania, were selected for study. Photosynthetic induction curves and photosynthetic responses to simulated sunflecks were measured. Specific leaf area and leaf nitrogen per unit area were determined for each leaf. Photosynthetic rates (Anet) did not vary among species at low light, nor during photosynthetic induction at 50, 90, or 100% of full induction. Similar results were observed for stomatal conductance (gs), though at full induction, gs was significantly depressed for A. rubrum (p < 0.05). During sunfleck experiments significantly lower Anet was observed for F. grandifolia (p s in F. grandifolia. Acer platanoides’ photosynthetic performance was indistinguishable from A. rubrum in all three experiments despite significantly lower Narea in the former species (p < 0.05). Variation in the potential for photosynthetic carbon gain exists among these species such that the two Acer species are better adapted to exploit intermittent light availability in the forest understory. Acer platanoides will likely become an increasingly important component of future forests, probably at the expense of native species.

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