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Ecophysiological studies on Welwitschia mirabilis in the Namib desert

1983; Elsevier BV; Volume: 2; Issue: 3 Linguagem: Africâner

10.1016/s0022-4618(16)30110-3

1727-9321

B. M. Eller, D. J. von Willert, Enno Brinckmann, R. Baasch,

Ecology and Vegetation Dynamics Studies

To determine which CO2 fixation pathway is used by the gymnosperm Welwitschia mirabilis Hoof. f. an extensive field study on diurnal CO2 gas exchange, 14CO2 incorporation, chemical composition, distribution pattern and variation of organic acids, and transpiration was made in the Welwitschia Flats of the central Namib desert. The CO2 gas exchange of W. mirabilis is that of a C3 plant under arid conditions. No CO2 uptake during the night was detected and the organic acids showed no day-night fluctuations that significantly exceeded the differences observed between the values obtained in a grid sampling over a whole leaf. The daily water loss of W. mirabilis by transpiration is considerable, reaching a peak value of 1,9 mmol m− 2 s− 1 around noon. Problems with respect to water supply to maintain such transpiration rates are discussed. In spite of the evidence for a C3-pathway the δ13C values are in the range of CAM plants. Reasons for such values in W. mirabilis are discussed. Om vas te stel watter CO2-assimileringsroete deur die gimnosperm Welwitschia mirabilis Hook. f. benut word, is ’n uitgebreide veldstudie in die Welwitschia Vlakte van die sentrale Namibwoestyn uitgevoer waartydens ondersoek ingestel is na die etmaalse CO2-gaswisseling, 14CO2-assimilering, chemiese samestelllng, verspreidlngspatroon en konsentrasieveranderings van die organiese sure en die transpirasietempo van die plante. Daar is bevind dat die CO2-gaswisseling van W. mirabilis onder droë toestande ooreenstem met diè van ‘n C3-plant. Geen CO2-opname kon snags waargeneem word nie en die verskil wat tussen die dag-en nagkonsentrasie van die organiese sure verky is, het nie noemenswaardig van die variasie verskil wat gelyktydig tussen verskillende punte op ’n blaar verkry is nie. W. mirabilis plante verloor daagliks, as gevolg van transpirasie. aansienlike hoeveelhede water, ’n Piekwaarde van 1,9 mmol m− 2 s− 1 word teen ongeveer 12h00 bereik. Probleme wat verband hou met watervoorsiening vir so ’n hoë transpirasietempo word bespreek. Nieteenstaande die getuienis dat W. mirabilis ’n C3-roete benut, stem die plant se δ13C-waardes met diè van ’n CSM-plant ooreen. Moontlike redes hiervoor word bespreek.