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

Abstract

Measurements of rnicrophytobenthos primary production were carried out in the German Wadden Sea in order to test the application of a 'Photosynthetic Light Dispensation System', which was originally developed for photosynthetic research of higher plants. A description of the computercontrolled system, consisting mainly of a subunit providing the irradiance (photosynthetically active radiation, PAR), and a subunit equipped with a Clark-type electrode for measuring oxygen production and respiration processes is given. The system allows rapid and reproducible measurements of photosynthesis-irradiance (P-E) curves at light modes predetermined by the computer and simple, rapid data analysis. Additionally, P-E curves obtained by this system were compared to those received by simultaneously conducted 'T measurements. Primary production measured by the oxygen method was on average 2.00 times higher than the values obtained by the "C method. Production rates varied between 1.7 and 4.1 mg C mg chl a-' h-' with a mean of 2.75 mg C mg chl a-' h-'

Effects of nutrient enrichment and shading on sediment primary production and metabolism in eutrophic estuaries

“…These low light levels would allow little microphytobenthic production even without experimental shading during the summer compared with the experiments in the other seasons (as supported by our measurements). More importantly, and based on photosynthesis-irradiance curves published for other microphytobenthic communities (Hargrave et al 1983, Pinckney & Zingmark 1991, 1993, Blanchard & Montagna 1992, Blanchard & Gall 1994, Wolfstein & Hartig 1998, Dodds et al 1999, Blackford 2002, the additional 50% reduction in light availability imposed by our shading treatment (on average from 86 to 43 µmol photons m -2 s -1 at Magnolia and from 28 to 14 µmol photons m -2 s -1 at Reserve) would only cause a small additional reduction in the rate of absolute microphytobenthic photosynthesis relative to the reduction observed for the experiments in the other seasons. Such a small decrease in absolute microphytobenthic production could have easily remained undetected in our experiment, since it would probably have been overridden by physical and biological differences among the experimental plots such as sediment and organism patchiness, benthic microalgal species composition, detrital input from the adjacent marsh and sediment resuspension.…”

“…Thus, since the shading treatment reduced light availability by 50%, the mean values of light intensity at the sediment surface under the shaded frames should have ranged from approximately 104 to 269 µmol photons m -2 s -1 at Magnolia and from 63 to 295 µmol photons m -2 s -1 at Reserve during the experiments in the fall, winter and spring, which is consistent with the number of direct light measurements we took at the sediment surface under the shaded frames. Published values of the minimum light intensity at which microphytobenthic photosynthesis saturates usually range from 300 to 500 µmol photons m -2 s -1 (Pinckney & Zingmark 1991, 1993, Blanchard & Montana 1992, Blanchard & Gall 1994, Wolfstein & Hartig 1998. This suggests that, during the fall, winter and spring experiments, our shading treatment frequently reduced light availability below saturating levels for microphytobenthic photosynthesis and thus significantly depressed sediment primary production.…”

Light and temperature acclimation of Rhodomonas salina (Cryptophyceae): photosynthetic performance

“…As pointed out by Falkowski et al (1985), small differences in the experimental light field could lead to large differences in the measurements of gross photosynthesis, particularly at subsaturating levels. However, one advantage of the photosynthetic light dispensation system over the microelectrode method is the precise control of environmental conditions such as irradiance and temperature as well as the supply of reproducible and rapid measurements of P-E curves (Wolfstein & Hartig 1998). We therefore believe our results to be accurate, implying that the compensation point for algal photosynthesis (E c ) was at a rela-tively low and more or less constant light level (26 µmol photons m -2 s -1 ± 5.5), but nevertheless above the lowest irradiance examined (10 µmol photons m -2 s -1 ).…”

“…, were measured with a Clarke type oxygen electrode using a computer controlled Light Dispensation System (MK2, ILLUMI-NOVA, described in Wolfstein & Hartig 1998). One measurement of a P-E curve took about 40 min.…”

Estimating areal production of intertidal microphytobenthos based on spatio-temporal community dynamics and laboratory measurements

“…Meanwhile, the classical O 2 methods, such as the oxygen microeclectrodes, even though they allow rapid estimation of temporal distribution patterns with high resolution, remain problematic for spatial resolution by only measuring a tiny point using a microprobe. Estimates of the photosynthetic electron transport rate (ETR) from fluorescence traits have been compared with those of primary production using C 14 radiotracers Wolfstein and Hartig 1998;Barranguet and Kromkamp 2000;Perkins et al 2002), O 2 evolution (Flameling and Kromkamp 1998;Morris and Kromkamp 2003;Serôdio 2003), or both (Hancke et al 2008a). With regard to O 2 production, the relative ETR was confirmed to have a significant correlation with the gross O 2 photosynthetic rate, which was measured nondestructively and simultaneously on the same samples by microelectrodes in situ (Serôdio 2003).…”