Investigating the Association between Environmental Stresses and Physiological Differentiation in Micranthes petiolaris populations.


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Isabel G Harger
Committee: Alisa Hove, Amy Boyd, Bob Eckstein

Drought escape is a life history strategy wherein traits that promote a faster life cycle (accelerated development, early flowering, low water use efficiency (WUE), small flowers, and fast photosynthetic rates) are evolutionarily advantageous because a species can complete its life cycle before annual seasonal drought occurs. This study is part of a larger project investigating the evolution of drought escape life histories. Micranthes petiolaris is a high elevation perennial species endemic to southern Appalachia. However, a low elevation annual population with different flower morphology was recently discovered in Pickens County, South Carolina. By comparing the photosynthetic rate (A), transpiration rate (E), and instantaneous WUE (WUEi) of these distinct M. petiolaris populations, this study examines the extent to which photosynthetic and water use physiology differ between the populations in an attempt to determine if drought escape is the driving evolutionary force behind these differences. We measured A, E, and leaf temperature of about 100 individuals from each population during the flowering season over two years, and calculated WUEi based on A and E. The photosynthetic rate, transpiration rate, and WUEi all differed significantly between the populations. The mean photosynthetic rate and WUEi were higher for the Pickens County population, while the transpiration rate was lower for the Pickens County population compared to the higher elevation population. Based on this study, the Pickens County population may be escaping drought, but results are inconclusive.