New Advances in Fern Ecology
Kirkpatrick, Ruth .
Desiccation-tolerance in American cheilanthoid ferns.
VEGETATIVE desiccation-tolerance is the ability of green plant tissues to recover from the almost complete loss of protoplasmic water and is thought to have been a prerequisite for early land plants. The ability of photosynthetic tissues to recover from an almost completely desiccated state has been repeatedly lost and sometimes regained during the evolutionary history of land plants. This pattern suggests that desiccation-tolerance is metabolically expensive and that selection has often favored other strategies to cope with lack of water availability, such as drought-tolerance and desiccation-resistance. The gain or re-evolution of vegetative desiccation-tolerance is hypothesized to occur when plants are under strong selective pressures associated with extremely xeric conditions. Cheilanthoid ferns of southwestern United States and Mexico have evolved chemical and structural adaptations that enable them to thrive in exposed rocky habitats where they experience extended dry periods each year. I quantified desiccation-tolerance among a sample of greenhouse-cultivated cheilanthoids and assessed this feature from phylogenetic and biogeographic perspectives. Forty-five greenhouse-cultivated and fully hydrated plants representing 21 species were allowed to dry to ambient conditions. Measurements of photosynthesis, transpiration, and chlorophyll fluorescence during dehydration and rehydration revealed levels of metabolic activity and water-use-efficiency, and also provided assessments of photosystem IIís ability to photosynthesize. Different species were found to be desiccation-tolerant (D-T), moderately D-T, or poorly D-T. The history of these physiological responses was evaluated by mapping them onto a molecular-based cheilanthoid phylogeny and assessing any correlations with environmental variables. Preliminary results suggest that desiccation-tolerance is pleisiomorphic in cheilanthoid ferns and has decreased in lineages with species whose habitats are wetter, cooler, and/or subject to shorter periods of drought.
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1 - University of California, Berkeley, Department of Integrative Biology, University and Jepson Herbaria, 1001 Valley Life Sciences Bldg. #2465, Berkeley, California, 94720, USA
Presentation Type: Symposium or Colloquium Presentation
Date: Monday, July 31st, 2006
Time: 8:45 AM