PARENT SESSION
Contributed Oral Session 123: Photosynthesis and Water Relations: Leaf Architecture
Thursday, August 11, 8:00 AM - 11:30 AM, Meeting Room 522 A, Level 5, Palais des congrès de Montréal
Decreased photosynthetic capacity is adaptive in response to drought: Evidence from natural selection on leaf physiology in contrasting wet and dry environments.
Sherrard, Mark*,1, Maherali, Hafiz1, 1 University of Guelph, Guelph, Ontario, Canada
ABSTRACT- Physiological variation is often assumed to be adaptive based on broad correlations with environmental resource gradients. However, these adaptive assumptions are rarely tested by examining whether there is a direct impact of physiological variation on fitness in a natural population. Using phenotypic selection analyses, we tested whether gas exchange, CO2-saturated photosynthesis (Amax) and water-use efficiency (WUE) followed adaptive expectations in response to wet and dry environments in greenhouse populations of Avena barbata. There was univariate and multivariate selection for increased photosynthetic rate, Amax and WUE in the wet environment. In contrast, there was no selection on photosynthetic rate, stomatal conductance or WUE in the dry environment. In addition there was selection for decreased Amax in the dry environment. Photosynthetic rate and Amax may be favoured in the wet environment because they increase net carbon gain for reproductive investment. Our results also suggest that increased WUE was selected for in the wet environment because of strong positive selection on photosynthetic rate. Selection for reduced Amax in the dry environment suggests that down regulation of photosynthesis when stomata limit CO2 diffusion into the leaf is adaptive. Contrary to previous hypotheses, there was no evidence that high WUE, high photosynthetic rate and low stomatal conductance are adaptive in a dry environment.
Key words: photosynthesis, water-use efficiency, natural selection, drought stress