AOBPreview originally published online on March 28, 2003
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Annals of Botany 91: 717-727, 2003
© 2003 Annals of Botany Company
Comparative Ecophysiological Measurements on the Light Responses, Water Relations and Desiccation Tolerance of the Filmy Ferns Hymenophyllum wilsonii Hook. and H. tunbrigense (L.) Smith
1 School of Biological Sciences, University of Exeter, Washington Singer Laboratories, Perry Road, Exeter EX4 4QG, UK
* For correspondence. Fax +44 (0)1392 264668, e-mail M.C.F.Proctor{at}exeter.ac.uk
Received: 20 November 2002; Returned for revision: 15 January 2003; Accepted: 31 January 2003 Published electronically: 28 March 2003
Chlorophyll-fluorescence and infrared gas analyser measurements show saturation of photosynthetic electron flow and CO2 uptake at generally lower irradiances in Hymenophyllum tunbrigense than in H. wilsonii, but with wide variation in both species (63–189 µmol m–2 s–1 PPFD in H. tunbrigense, 129–552 µmol m–2 s–1 PPFD in H. wilsonii), probably related to both site and season. Non-photochemical quenching (at 400 µmol m–2 s–1 PPFD) ranged from 2·1 to 8·1, with no significant difference between the species. Pressure–volume curves from thermocouple-psychrometer measurements give full-turgor osmotic potentials of approx. –1·4 MPa in both species, and indicate low apoplast fractions and high cell-wall elastic moduli. Leaves of H. tunbrigense recovered within 24 h from up to 7 d desiccation at water potentials ranging from –40 MPa (74 % relative humidity, RH) to –220 MPa (20 % RH); after 15 or 30 d, desiccation recovery was slower and less complete, and leaves were severely damaged at the highest and lowest humidities. Hymenophyllum wilsonii recovered well from up to 30 d desiccation at –114 and –220 MPa, but at –40 MPa it showed signs of damage after 15 d, and was severely damaged or killed after 30 d. Results are discussed in relation to the ecological and geographical distributions of the two species, and to the adaptive strategies of filmy ferns in general.
Key words: Chlorophyll fluorescence, desiccation tolerance, filmy ferns, Hymenophyllaceae, Hymenophyllum, light responses, osmotic potential, P–V curves, pressure–volume curves.
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