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Abstract
Asimina triloba is replacing shade-tolerant
Acer saccharum as the most abundant seedling in many
Ac. saccharum-dominated forests in the midwestern USA. Selective browsing of
Ac. saccharum by
Odocoileus virginianus and avoidance of
As. triloba contributes to this increased
As. triloba abundance. However, shade tolerance may also be a factor contributing to increasing
As. triloba. We tested our hypothesis that
As. triloba is more shade tolerant than
Ac. saccharum.
Fraxinus quadrangulata is less shade tolerant than
As. triloba and
Ac. saccharum; however, other than
As. triloba, it was the only species that increased stems per hectare in the seedling stratum from 2003 to 2008. We evaluated leaf photosynthetic traits to assess shade tolerance of these three species. Light response curves (LRCs) of
As. triloba,
Ac. saccharum, and
F. quadrangulata saplings were measured under a dense
Ac. saccharum canopy
in situ using a portable infrared gas analyzer and were tested for fit to rectangular hyperbola, nonrectangular hyperbola, and exponential LRC models. Multivariate analysis of covariance, with estimated ambient irradiance and leaf temperature as covariates, tested interspecific differences in gas exchange properties: (R
d [dark respiration], α [LRC initial slope], and A
MAX [maximum photosynthetic rate]). Multivariate contrasts indicated that
F. quadrangulata had significantly higher rates of photosynthesis than the two other species, indicating lesser shade tolerance, whereas
As. triloba had greater initial light response (α values) than
Ac. saccharum, which confers an advantage to
As. triloba under low light conditions. These results implicate greater shade tolerance by
As. triloba as another contributor to its increasing dominance in the understory.
Citation
Slater, Mitchell; Anderson, Roger C.; Juliano, Steven A. 2023. Does the photosynthetic response of
Asimina triloba to low light contribute to its competitive advantage in forest understories compared with
Acer saccharum and F
raxinus quadrangulata?. The Journal of the Torrey Botanical Society. 150(2): 267-281. https://doi.org/10.3159/TORREY-D-22-00003.1.
