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An in situ study of photosynthetic oxygen exchange and electron transport rate in the marine macroalga Ulva lactuca (Chlorophyta)


Longstaff, BJ and Kildea, T and Runcie, JW and Cheshire, A and Dennison, WC and Hurd, CL and Kana, T and Raven, JA and Larkum, AWD, An in situ study of photosynthetic oxygen exchange and electron transport rate in the marine macroalga Ulva lactuca (Chlorophyta), Photosynthesis Research, 74, (3) pp. 281-293. ISSN 0166-8595 (2002) [Refereed Article]

Copyright Statement

Copyright 2002 Kluwer Academic Publishers

DOI: doi:10.1023/A:1021279627409


Direct comparisons between photosynthetic O2 evolution rate and electron transport rate (ETR) were made in situ over 24 h using the benthic macroalga Ulva lactuca (Chlorophyta), growing and measured at a depth of 1.8 m, where the midday irradiance rose to 400600 μmol photons m−2 s−1. O2 exchange was measured with a 5-chamber data-logging apparatus and ETR with a submersible pulse amplitude modulated (PAM) fluorometer (Diving-PAM). Steady-state quantum yield ((Fm′−Ft)/Fm′) decreased from 0.7 during the morning to 0.45 at midday, followed by some recovery in the late afternoon. At low to medium irradiances (0300 μmol photons m−2 s−1), there was a significant correlation between O2 evolution and ETR, but at higher irradiances, ETR continued to increase steadily, while O2 evolution tended towards an asymptote. However at high irradiance levels (6001200 μmol photons m,sup>−2 s−1) ETR was significantly lowered. Two methods of measuring ETR, based on either diel ambient light levels and fluorescence yields or rapid light curves, gave similar results at low to moderate irradiance levels. Nutrient enrichment (increases in [NO3], [NH4+] and [HPO42-] of 5- to 15-fold over ambient concentrations) resulted in an increase, within hours, in photosynthetic rates measured by both ETR and O2 evolution techniques. At low irradiances, approximately 6.5 to 8.2 electrons passed through PS II during the evolution of one molecule of O2, i.e., up to twice the theoretical minimum number of four. However, in nutrient-enriched treatments this ratio dropped to 5.1. The results indicate that PAM fluorescence can be used as a good indication of the photosynthetic rate only at low to medium irradiances.

Item Details

Item Type:Refereed Article
Keywords:ulva, photosynthesis, chlorophyll fluorescence, method comparison, benthic algae, bioenergetics, electron transport, fluorescence, nutrient uptake, oxygen evolution, PAM, primary production, pulse amplitude modulation
Research Division:Biological Sciences
Research Group:Ecology
Research Field:Ecological physiology
Objective Division:Expanding Knowledge
Objective Group:Expanding knowledge
Objective Field:Expanding knowledge in the biological sciences
UTAS Author:Hurd, CL (Professor Catriona Hurd)
ID Code:93134
Year Published:2002
Web of Science® Times Cited:125
Deposited By:IMAS Research and Education Centre
Deposited On:2014-07-14
Last Modified:2014-08-04

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