© 1997 Heron Publishing—Victoria, Canada
Acclimation of shade-developed leaves on saplings exposed to late-season canopy gaps
Shawna L. Naidu and Evan H. DeLucia
Department of Plant Biology, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA / Received July 29, 1996
Summary
We hypothesized that photoinhibition of shade-developed leaves of deciduous hardwood saplings would limit their ability to
acclimate photosynthetically to increased irradiance, and we predicted that shade-tolerant sugar maple (Acer saccharum Marsh.) would be more susceptible to photoinhibition than intermediately shade-tolerant red oak (Quercus rubra L.). After four weeks in a canopy gap, photosynthetic rates of shade-developed leaves of both species had increased in response
to the increase in irradiance, although final acclimation was more complete in red oak. However, photoinhibition occurred
in both species, as indicated by short-term reductions in maximum rates of net photosynthesis and the quantum yield of oxygen
evolution, and longer-term reductions in the efficiency of excitation energy capture by open photosystem II (PSII) reaction
centers (dark-adapted Fv/Fm) and the quantum yield of PSII in the light (φPSII). The magnitude and duration of this decrease were greater in sugar maple than in red oak, suggesting greater susceptibility
to photoinhibition in sugar maple. Photoinhibition may have resulted from photodamage, but it may also have involved sustained
rates of photoprotective energy dissipation (especially in red oak). Photosynthetic acclimation also appeared to be linked
to an ability to increase leaf nitrogen content. Limited photosynthetic acclimation in shade-developed sugar maple leaves
may reflect a trade-off between shade-tolerance and rapid acclimation to a canopy gap.
Keywords:
Acer saccharum, carbon gain, chlorophyll fluorescence, gap, irradiance, leaf absorptance, leaf nitrogen content, photoinhibition, Quercus rubra, red oak, sugar maple.
