Photosynthesis and Light in Estuarine Benthic Microalgae

Abstract

The photosynthetic rate of natural populations of benthic microalgae was determined in the laboratory over a r nge of irradiances (75 to 1500 μΕ m~2 s-1 ) and at 15 °C and 20 °C. Values for P B max, 5.3 and 11.7 μg O 2 (μg chl-a)" 1 h -1 and the initial slope of the photosynthesis versus irradiance curve 0.035 and 0.031 μg O 2 (μg chl-fl)-1 h" 1 (μΕ m~2 s" 1 )" 1 at 20 °C and 15°C respectively, feil within the ranges quoted by a number of other workers. However, the overall response of the microalgae to light suggested that they were from a 'sun adapted' algal Community. No photoinhibition was observed, even after 2 hours exposure to the highest irradiance. The low value calculated for Quantum Efficiency (0.025) suggest that these organisms were nutrient limited.

The Photosynthetic Light Dispensation System:application to microphytobenthic primary production measurements

“…In our study, mean maximum photosynthetic rate (02 method, data were converted to carbon by using a factor of 0.32 assuming a PQ of 1.2) was 2.75 * 0.69 mg C mg chl a-' h-' (14C technique: 1.23 * 0.46 mg C mg chl a-' h-'). The photosynthetic rates found by Mills & Wilkinson (1986), which were also obtained with algal suspensions harvested using the lens tissue method, were slightly higher than our data, which had a mean of 3.53 mg C mg chl a-' h-'. These elevated rates could be caused by the higher temperature during their measurements.…”

“…Data analysis was performed immediately afterwards using specifically developed software. Oxygen production was converted to carbon units using a factor of 0.32, assuming a photosynthetic quotient (PQ) of 1.2 (Asmus 1982, Mills & Wilkinson 1986, in order to compare the results to those obtained by the I4C method (see 'Discussion').…”

“…The mean ratio of O2 and 14C was 2.00 + 0.59, excluding the extremely variable high ratios of June 8. The relatively high production rates based on the oxygen method in comparison to the I4C technique could be influenced by using a conversion factor of 0.32 (mg oxygen to mg carbon; Asmus 1982, Mills & Wilkinson 1986 and by the chosen PQ of 1.2.…”

“…However, a lower PQ than 1.8 was chosen by most authors for microphytobenthic primary production, e.g. 1.0 (Hargrave et al 1983, Barranguet et al 1994), 1.2 (Asmus 1982, Mills & Wilkinson 1986, Gatje 1992) and 1.3 (Colijn et al 1983). The nitrogen source is important for the choice of PQ: a higher PQ (1.5 to 1.8) should be taken when nitrate is assimilated and a lower value of approximately 1.25 should be used when a n~n~o n i a is assimilated (Williams et al 1979).…”

Microphytobenthic primary production in the Bodden estuaries, southern Baltic Sea, at two study sites differing in trophic status

“…Pelagic gross photosynthesis was calculated as the sum of respiration and net photosynthesis. Microphytobenthic photosynthetic activity was determined similarly, but also directly by the light/dark shift method, whereby the gross photosynthesis rates for the different sediment layers were related to volume and multiplied by the vertical expansion (z phot ) of the measured profile of photosynthetic activity (Revsbech et al 1981, 1986 Gross primary production rates were expressed as C-equivalents using the conversion factor 1.2 (Mills & Wilkinson 1986) and taking main substrates and products of dioxide fixation into account (Burris 1981, Raine 1983, Sakshaug et al 1997. Gross primary production rates of pelagic and microphytobenthic area were normalised to chlorophyll a concentrations in the water samples and in the flocculent sediment surface layer, respectively, to correct for algal biomass.…”