Acclimation to Drought and Cold Stress in Holly (Ilex): Evergreen Tolerance and Deciduous Escape
Bryn Mawr College. Department of Biology
Place of Publication
Table of Contents
Exploration of the differences between physiological adjustment in evergreen and deciduous trees can help us gain a better understanding of how temperate ecosystems will fare under anthropogenic climate change. I compared foliar osmotic adjustment and stomatal conductance of a deciduous and an evergreen species of Ilex over the growing and dormant season in order to explore differential adjustment strategies with respect to leaf habit. I found that the hollies showed distinct drought tolerance across the year and utilized different methods of managing winter water stress consistent with their respective leaf habits. Evergreen I. opaca demonstrated osmotic adjustment throughout the growing season and into the dormant season while maintaining stable rates of gas exchange. In contrast, deciduous I. verticillata showed osmotic adjustment only during the growing season, then ceased adjustment once the dormant season arrived. Instead, I. verticillata protects itself from cold, dry winter conditions through down-regulation of gas exchange in conjunction with leaf color change and senescence. These results confirm our hypotheses that evergreen and deciduous species regulate themselves differently, and highlight the differences in the impacts that climate change will have on temperate trees based on their leaf habit.