Dynamic photosynthesis of species from cool-temperate rainforests

Closed forests are spatially variable and the light environment can also be spatially and temporally variable. The understorey of some evergreen closed forests is amongst the darkest environments habitable by higher plants (Allen & Pearcy, 2000a). In this layer, the light environment is characterized by diffuse irradiance of low intensity interrupted by intense sunflecks that might last from a second or less to fifteen minutes or more. For leaves acclimated to shade, the photosynthetic response to a sudden increase in irradiance (via sunflecks) is not instantaneous owing to biochemical and stomatal limitations. We are examining the response of gas exchange to simulated sunflecks in a range of species from cool-temperate rainforests dominated by Nothofagus cunninghamii.

Sunflecks are also potentially harmful to plants because of the time-lag (as described above) between the beginning of a sunfleck and the realization of maximum rates of photosynthesis. This time-lag leads to the quantum of absorbed irradiance being, at least temporarily, in excess of what is used in photochemistry (Logan et al., 1997; Watling et al., 1997; Thiele et al., 1998) and can cause ‘photoinhibition’ (defined as a persistent decrease in quantum use efficiency). Only a handful of studies have examined photoinhibition in relation to sunflecks. We are using a combination of gas exchange, chlorophyll fluorescence and analyses of xanthophyll pigments to quantify photoinhibition.

Funding: Partial support from an ARC Discovery grant.

Partner investigators: M. Tausz (Karl-Franzens Universität Graz, & University of Melbourne).

Location: Cool-temperate rainforest at Mt Donna Buang, Victoria (SE Australia).

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