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Plant Biol (Stuttg) 2000; 2(2): 229-242
DOI: 10.1055/s-2000-9163
Original Paper
Georg Thieme Verlag Stuttgart ·New York

Leaf Epidermal Hydathodes and the Ecophysiological Consequences of Foliar Water Uptake in Species of Crassula from the Namib Desert in Southern Africa

C. E. Martin 1,2 , and D. J. von Willert 1
  • 1 Institut für Ökologie der Pflanzen, Westfälische Wilhelms-Universität, Münster, Germany
  • 2 Department of Botany, University of Kansas, Lawrence, Kansas, USA
Further Information

Publication History

July 15, 1999

February 3, 2000

Publication Date:
31 December 2000 (online)

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Abstract:

Epidermal hydathodes were found on leaves of 46 of 48 species of Crassula collected from the Namib Desert in southern Africa. The possibility that these structures might allow the absorption of surface water was investigated in 27 species (including subspecies). The presence of hydathodes on leaf epidermi correlated, in most cases, with increases in leaf thickness and enhanced rates of nocturnal, and sometimes diurnal, CO2 uptake following wetting of the leaves during the night. The precise nature of these responses varied depending on the species. In addition, wetting only the older leaves on the lower portion of the shoot of C. tetragona ssp. acutifolia not only resulted in increased thickness of these leaves, but also effected an increase in leaf thickness and stimulation of CO2 uptake rates in the distal, younger portion of the shoot that was not wetted. Overall, foliar hydathodes were implicated in the absorption of surface water in many species of Crassula such that the ecophysiology of these desert succulents was positively affected. Although rainfall in the Namib Desert is infrequent, surface wetting of the leaves is a more common occurrence as a result of nighttime dew or fog deposition. Presumably, species with hydathodes benefit directly from this source of moisture. These findings have important implications in understanding a relatively unexplored adaptation of some xerophytes to an extremely arid environment.

Abbreviations:

CAM: Crassulacean acid metabolism PPFD: photosynthetic photon flux density vpd: vapor pressure deficit

Key words:

CO2 exchange - Crassula - Crassulacean acid metabolism - dew deposition - hydathodes - leaf thickness - Namib Desert - water movement

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C. E. Martin

Department of Botany University of Kansas

Lawrence

Kansas 66045

USA

Section Editor: H. Lambers

Email: ecophys@falcon.cc.ukans.edu

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