Station Biologique, CNRS and Université Paris VI, 29680 Roscoff, France.
INORGANIC CARBON LIMITATION OF PHOTOSYNTHESIS IN ULVA ROTUNDATA (CHLOROPHYTA)1
Version of Record online: 27 OCT 2004
Journal of Phycology
Volume 27, Issue 6, pages 667–672, December 1991
How to Cite
Levavassur, G., Edwards, G. E., Osmond, C. B. and Ramus, J. (1991), INORGANIC CARBON LIMITATION OF PHOTOSYNTHESIS IN ULVA ROTUNDATA (CHLOROPHYTA). Journal of Phycology, 27: 667–672. doi: 10.1111/j.0022-3646.1991.00667.x
Received 15 March 1991. Accepted 22 July 1991.
We acknowledge support from NSF grant OCE-8812157 to C.B.O. and J.R., a CNRS/NSF exchange fellowship to G.L., and a Kramer Fellowship from Duke University to G.E.E. We are grateful lo colleagues at Duke University Marine Laboratory for their hospitality and support. Larry Giles helped with measurements of δ13C values, and John Raven made helpful comments on their interpretation.
- Issue online: 27 OCT 2004
- Version of Record online: 27 OCT 2004
- δ13 C values;
- O2 electrode;
- quantum yield;
- Ulva rotundata
A computerized oxygen electrode Astern was used to make rapid and accurate measurements of photosynthetic light and dissolved inorganic carbon (DIC) response cures with a macroalga. Ulva rotundata Blid. was grown in an outdoor, continuous flow system in seawater under sunlight or 9% of sunlight at Beaufort, North Carolina. The light compensation points in the shade- and sun-grown plants, measured in seawater, were at photon flux densities (PFDs) of 16 and 27 μmol. Photons·m−2·s−1, respectively but the quantum yield of O2 evolution was not significantly different. Rates of photosynthesis in seawater per unit area of thallus under saturating light and rates of dark respiration were about 1.5-fold higher in sun- than in shade-grown plants. The concentration of DIC in seawater (approximately 2 mM) limited photosynthesis at absorbed PFDs above 60–70 μmol photons·m−2·s−1 Addition of 20 mM inorganic carbon had no effect on quantum yield but caused about a 1.5-fold increase in the light-saturated photosynthetic rate in both shade- and sun-grown Ulva. The effect of DIC supplementation was greatest in plants grown in October and least in plants grown in June. The light- and DIC-saturated rate of photosynthesis in seawater was similar to the maximum rate obtained by exposing Ulva to 10% CO2, in the gas phase. The carbon isotope values (δ13C, reflecting the 13C/12C ratio compared to a standard) of Ulva grown in the same seawater supply were dependent on light and agitation. Samples from Beaufort Inlet were more negative (δ13C value, −20.03‰) than those grown in bright light with agitation (δ13C value, −17.78‰ outdoors; −17.23‰ indoors), which may indicate DIC supply limited carbon uptake in seawater.