Document: DAV-3-30-30

Light and temperature effects on the photosynthetic characteristics of boreal C4 and C3 grasses.

KUBIEN, D.S.* and R.F.SAGE

University of Toronto, Toronto, ON, Canada 1

Abstract:
The limits on the success of C4 plants in boreal climates were investigated using the grass species Muhlenbergia glomerata (C4) and Calamogrostis canadensis (C3). The hypothesis that C4 plants are more susceptible to photoinhibition at low temperature than their C3 competitors was tested by assessing the effects of light and temperature on the photosynthetic characteristics of these species using gas-exchange and fluorescence techniques. Plants were grown in controlled-environment chambers at 14/10oC or 26/22oC. Dark-adapted Fv/Fm values were higher in the C3 species from either growth regime, with the difference being greater in the cool-grown treatment. At a leaf temperature of 10oC, the light-saturated net CO2 assimilation rate of the cool-grown C3 species was nearly twice that of the cool-grown C4 plants, and light saturation occurred at a higher quantum flux. When plants were grown at 26/22oC, the C3 species still showed higher CO2 assimilation rates at 10oC, but the difference was reduced. Muhlenbergia from either growth regime showed higher assimilation than Calamogrostis when measured at 25oC. The quantum yield of PSII (MISSING CHARACTER ENTITY: phisPSII) was considerably lower when measured at 10oC than at 25oC in both species. At 10oC, MISSING CHARACTER ENTITY: phisPSII reached a minimum value at a lower irradiance in the cool-grown C4 species than the C3. In contrast to earlier reports, MISSING CHARACTER ENTITY: phisPSII/MISSING CHARACTER ENTITY: phisCO2 was found to vary with temperature in the C4 species, particularly at higher irradiance. Our results indicate that photoinhibition occurs at a lower quantum flux in the C4 species at 10oC, and thus a greater incidence of photodamage, or a greater cost of photoprotection, will be present in M. glomerata in field situations.

Keywords: light and temperature response, C4, C3, gas exchange,fluorescence,

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This abstract is being presented at: 1:00 PM in session:
Oral Session #10: Light Relations in Plants.