Westfälische Wilhelms-Universität
Münster
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Institut für Ökologie der Pflanzen Hindenburgplatz 55 48143 Münster Geschäftsführender Direktor: Prof. Dr. D.J. von Willert |
Tel. (0251) 83-23831
Fax: (0251) 83-21705 e-mail: pfloek@uni-muenster.de www: uni-muenster.de/Biologie/pflanzenoekologie |
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Forschungsschwerpunkte 2001 - 2002 Fachbereich 13 - Biologie
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Variability of CAM in leaf-deciduous succulents
Seasonal or
drought-induced deciduousness is a common adaptational strategy in aboveground persitent succulent species
native to the Succulent Karoo (South Africa). This feature may appear together with crassulacean acid
metabolism (CAM) in stems and/or leaves. Due to differences in morphology or life cycle, different species
may exhibit different degrees of flexibility in the expression of CAM. The potential for CAM plasticity has not
been investigated in leaf-deciduous succulents of the Succulent Karoo. Diurnal gas exchange and nocturnal
organic acid accumulation were measured to investigate whether the expression of CAM may vary in
Tylecodon paniculatus (L.F.) Toelken (Crassulaceae), Monilaria moniliformis
(Mesembryanthemaceae) and Ceraria fruticulosa H. Pearson & Stephens (Portulacaceae), a selection of
leaf-deciduous succulents. These species differ both in leaf and stem morphology. In the seasonal deciduous
Tylecodon paniculatus only obligate CAM was found, regardless of the plant water status. When
droughted Monilaria moniliformis switches directly from CAM-cycling (C3-like diurnal
gas exchange patterns combined with nocturnal acid accumulation) to CAM-idling (gas exchange completely
ceased while acid accumulation still continued). This seasonal deciduous species has also both succulent
leaves and stem. A highly flexible CAM expression (CAM-cycling, full-CAM and CAM-idling) was observed
in the drought deciduous Ceraria fruticulosa (non-succulent stem showing no CAM) in response to
changes in water availability. The ecological significance of the observed diversity in the flexibility of CAM
expression was discussed in terms of morphological traits, and the relative ecological significance of both
metabolic adaptation and leaf-deciduousness.
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