Yansen, Y., Congdon, R.A., and Holtum, J.A.M. (2011) Water supply and photosynthesis in terrestrial, climbing and semi-epiphytic Freycinetia excelsa F. Muell (Pandanaceae). In: Abstract Book of XVIII International Botanical Congress. pp. 526-527. From: IBC2011 XVIII International Botanical Congress, 23-30 July 2011, Melbourne, VIC, Australia.

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Abstract

Freycinetia excelsa is a secondary hemi-epiphytic vine with a three phase life-cycle: terrestrial, terrestrial but climbing a host, and semi-epiphytic. Beginning life as ground-dwelling plant with normal roots, F. excelsa climbs a host and the basal portion of the stem dies back, in most cases remaining connected to the soil via aerial feeder roots. We ask whether water supply and photosynthesis differs between the three morphological forms of F. excelsa.

For all growth forms of F. excelsa, pre-dawn leaf water potentials correlated with volumetric soil moisture, and leaf water potential and CO2 assimilation rates were generally lower in the dry season than in the wet season. Within each season, water potentials of leaves from all growth forms were similar but the patterns of daily CO2 exchange differed, with CO2 uptake by terrestrial plants most affected by dry season conditions. Terrestrial plants exhibited the lowest CO2 exchange in the dry season, but the CO2 exchange rates were similar for the three forms during the wet season.

Stem hydraulic conductivity and xylem anatomy differed between the growth forms. Terrestrial plants, with conventional roots and a main stem, have narrow xylem and lower hydraulic conductivity. In comparison, climbing and semi-epiphytic plants are attached to the soil by narrow aerial roots and hydraulic conductivity of the stem is greater.

Down-regulation of CO2 exchange in the dry season was greatest in the terrestrial plants, but all forms operated at similar pre-dawn water potentials of -1.5 MPa and afternoon water potentials of not less than -2 MPa. The lower hydraulic conductivity of the stems of terrestrial plants may restrict water supply such that down-regulation of CO2 uptake and stomatal opening are necessary to diminish water loss and maintain water potential. Water supplied to climbing and semi-epiphytic plants by aerial roots variously inserted at a number of sites along a stem is evidently sufficient to sustain higher rates of CO2 exchange and water loss.

Item ID:	19956
Item Type:	Conference Item (Poster)
Date Deposited:	11 Mar 2012 23:57
FoR Codes:	06 BIOLOGICAL SCIENCES > 0602 Ecology > 060203 Ecological Physiology @ 50% 06 BIOLOGICAL SCIENCES > 0602 Ecology > 060208 Terrestrial Ecology @ 50%
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