Reinhardt, Keith , Smith, William K. .
The effects of clouds and diffuse light on leaf-level photosynthetic gas exchange in two conifer tree species and two broadleaved shrubs.
Recent studies have shown that photosynthesis may increase under diffuse light regimes (e.g. cloud-generated) compared to direct (collimated) irradiance at the canopy and ecosystem levels, but there have been few studies investigating leaf-level photosynthesis in diffuse light environments. In this study we investigated leaf-level photosynthesis and chlorophyll fluorescence under diffuse light versus collimated light in both natural (field) and experimentally-generated (greenhouse) conditions for two conifer tree species (Abies fraseri (Pursh) Poir. and Picea pungens Englem.) and two broadleaved shrubs (Rhododendron catawbiense Michx. and R. ponticum L.). For the broadleaved Rhododendron species, there were no differences in maximum photosynthesis (<15% difference) due to diffuse vs. direct irradiance in field or greenhouse conditions. However, leaf conductance and transpiration at saturating light levels (gsat and Esat, respectively) were up to 40% greater and 20% less, respectively, in diffuse light conditions. For needle-leaved conifer shoots, maximum shoot-level photosynthesis in diffuse light was 20-50% greater than in direct light for fir and spruce in field and greenhouse conditions, respectively. Fir gsat increased by 60% in diffuse light in the field, while Esat was about 20% less under diffuse light conditions in the field compared to sunny conditions. Greenhouse differences in gsat and Esat for spruce under diffuse lighting were similar in direction but not in magnitude (~50% of differences in the field). Differences in leaf chlorophyll fluorescence in both the field and the greenhouse were minimal. Maximum quantum yield of PSII (Fv/Fm) was between 0.76-0.84 for all species, with no significant differences in non-photochemical quenching (NPQ). Therefore, the increase in shoot-level photosynthesis in spruce in diffuse light was attributed to differences in shoot versus broadleaf architecture, and not photosynthetic biochemistry, suggesting that gains in canopy-level photosynthesis in diffuse light are most likely an emergent property.
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1 - Wake Forest University, Biology, Winston-Salem, NC, 27106, USA
2 - Wake Forest University, Department of Biology, Winston-Salem, NC, 27106, USA
Presentation Type: Oral Paper:Papers for Topics
Location: Cottonwood A/Snowbird Center
Date: Monday, July 27th, 2009
Time: 8:00 AM