Light Saturation Curves Of Photosynthesis Research Articles

Long-term variations in primary production in a eutrophic sub-estuary: Contribution of short-term events

We determined the role of events in generating short-term variability in production, how they contribute to interannual variability, and their relationship to variability in the determinants of production, primarily biomass and photo-physiological parameters. We examined residuals from the seasonal and spatial mean daily rate in a 20-year time series of primary production in a eutrophic sub-estuary of Chesapeake Bay. The seasonal and spatial means of production and residuals were based on natural log-transformed measurements of daily primary production calculated from measurements of light saturation curves of photosynthesis for 20 years at 6 stations on the Rhode River, Maryland (USA). The variance of the residuals was greater than that explained by the seasonal and spatial statistical model, so that the event scale was the largest single source of variance. Residuals were classified as events if they exceeded ±ln(2), signifying a multiplier or divisor of 2 above or below the seasonal-spatial mean. Spatially, events were most frequent at the most upstream station affected by runoff from the local watershed, and temporally most frequent in spring at all stations. Principal component analysis (PCA) of monthly averaged residuals revealed 3 characteristic temporal modes of residual variance, the first of which was associated with variability in spring due to the occurrence of extremely large spring blooms or their complete absence. Interannual variation in annual production was correlated with the strength of expression of these modes. Production events were analyzed in relation to residuals in the determinants of productivity, i.e. phytoplankton chlorophyll biomass, B, the light-saturated photosynthetic maximum normalized to chlorophyll, PmaxB, the diffuse attenuation coefficient for light, and the depth integral of the dimensionless photosynthesis profile. Negatively correlated changes in B and PmaxB were the most common mode of variation among the determinants, and this mode dampened variations in production and were common in fall months. Positively correlated changes in B and PmaxB constituted the second most common mode of variation amongst determinants, and this mode was positively correlated with variations in production and were most common in spring months. The prevalence of the first mode in fall months modulated the impact of major named storms on primary production in this system.

Long-term variations in primary production in a eutrophic sub-estuary. I. Seasonal and spatial patterns

Daily rates of phytoplankton primary production were calculated from measurements of light saturation curves of photosynthesis for 20 yr at 6 stations on the Rhode River, Maryland (USA). Daily production, corrected for the geometry and spectrum of the underwater light field, av- eraged 1319 (range 1.4 to 15 800) mg C m −2 d −1 . Log-transformation of the exact solution for depth- integrated daily production permitted linear analysis of seasonal and spatial patterns in production and the factors that determine it. The seasonal signal was the greatest source of variation, followed by spatial then interannual. The seasonal pattern was driven by coinciding summer maxima in both the chlorophyll a (chl a) biomass, B, and the light saturated photosynthetic rate normalized to chl a, P B max. The spatial pattern was characterized by a region in which production was relatively constant despite declining depth, a station at which production was reduced by truncation of the depth profile of production, and an area where mean production was lowest but variance was highest, due to local flow causing either localized blooms or washout of biomass and high turbidity at the station furthest up the estuary. Analysis of the components contributing to the variance in production indicated that variance in B and P B max added nearly equally to it. Covariance between B and the light attenuation coefficient reduced the variance in production. The analytical approach adopted here allowed these patterns to be discerned against a high degree of overall variability, and should be similarly useful in a wide range of systems.

Biomass, production and horizontal patchiness of sea ice algae in a high-Arctic fjord (Young Sound, NE Greenland)

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 223:15-26 (2001) - doi:10.3354/meps223015 Biomass, production and horizontal patchiness of sea ice algae in a high-Arctic fjord (Young Sound, NE Greenland) Søren Rysgaard1,*, Michael Kühl2, Ronnie Nøhr Glud2, Jens Würgler Hansen1 1Department of Lake and Estuarine Ecology, National Environmental Research Institute, Vejlsøvej 25, 8600 Silkeborg, Denmark 2Marine Biological Laboratory, University of Copenhagen, Strandpromenaden 5, 3000 Helsingør, Denmark *E-mail: sr@dmu.dk ABSTRACT: A study of the variation in sea ice algal distribution and production was performed during June and early July 1999 in Young Sound, northeastern Greenland. Measurements were performed in situ by divers using an underwater pulse-amplitude-modulated (PAM) fluorometer, oxygen microelectrodes and 14C incubations. In early June, Young Sound was covered by ~1.6 m of sea ice and ~30 cm of dry snow, which reflected ~75% of the incident light. These conditions resulted in low irradiance below the sea ice (<2 µmol photons m-2 s-1), low values of chlorophyll a (<1 µg l-1 sea ice) and low primary productivity (<0.05 µgC l-1 h-1) in the bottom ice (0 to 4 cm). The snow cover gradually disappeared during June, resulting in increased light penetration of up to 20 µmol photons m-2 s-1, chl a concentrations of up to 15 µg l-1 (0.6 mgC m-2), and primary production rates of up to 0.2 µgC l-1 h-1 (0.2 mgC m-2 d-1) in the bottom ice. Light saturation curves of photosynthesis were obtained in situ on 3 occasions and showed adaptation of the sea ice algae to low irradiance; Ek values ranged from 12 to 35 µmol photons m-2 s-1. Photosynthesis of sea ice algae resulted in supersaturated oxygen conditions (150 to 200%) at the sea ice-water interface as compared to ambient seawater. In situ investigations of irradiance, algal biomass and photosynthetic activity on different metric scales showed a heterogeneous distribution of sea ice algae. Statistical treatment of the data obtained revealed that algal activity followed the light regime below the sea ice (radii of patches were 50 to 100 m), whereas algal biomass patches were smaller (radii of patches were 5 to 10 m). Sea ice algal production in Young Sound was 2 to 3 mgC m-2 during June and July 1999. Compared to other coastal fast-ice areas this rate is low. We suggest that the low biomass and productivity in Young Sound was caused by a combination of poor light conditions due to snow cover and freshwater drainage from melt ponds and river discharge removing and/or inhibiting the algae at the sea ice-water interface through physical disturbance and exposure to freshwater. The primary production of sea ice algae in Young Sound was <1% of the annual pelagic primary production. KEY WORDS: Sea ice algae · In situ measurements · PAM · Oxygen microprofiles · 14C · P-E curves Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 223. Online publication date: November 28, 2001 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2001 Inter-Research.

Photosynthesis and Transpiration in Damaged and Undamaged Spruce Trees

Abstract The investigations presented here focus on the CO2/H2O gas exchange in damaged and undamaged spruce trees while using open-air measurements as well as measurements under defined conditions in the laboratory. The studies were performed at two different sites in the Hunsrück and the Westerwald mountains. In the laboratory the CO2/H2O gas exchange was measured on detached branches under controlled conditions in the course of two years. CO2 saturation curves were also generated. In addition CO2 compensation points were deter­ mined employing a closed system. In the natural habitat diurnal course measurements of photosynthesis and transpiration as well as light-saturation curves for photosynthesis were performed. In parallel with the photosynthesis and transpiration measurements, measurements of the water potential were taken at both locations. The photosynthetic capacity and transpiration rate show a typical annual course with pronounced maxima in spring and late summer and minima in summer and winter. The needles of the damaged trees exhibit higher transpiration rates and a distinct reduction in photosyn­ thesis than the needles of the undamaged trees during two seasons. The diurnal course measurements of net photosynthesis and transpiration show a maximum in photosynthesis and transpiration in the afternoon in May and September, but a characteristic midday depression in July. Photosynthesis was markedly lower and transpiration higher in the needles of the damaged trees. The damaged trees show a lower increase in the light and CO2 saturation curves and higher CO2 compensation points as compared to the undamaged trees. The water potential reaches much lower values during the course of the day in needles of the dam­ aged trees. The reduction of the photosynthetic rate on one hand and the increase in transpiration on the other hand result in an extreme lowering of the water use efficiency in photosynthesis. The damage to the thylakoid membranes and to the guard cells obviously results in a pro­ found disturbance of the physiological homeostasis of the needles and could thus lead to premature needle loss.

Control of the Photosynthetic Apparatus of Acetabularia mediterranea by Blue Light

During growth, Acetabularia mediterranea requires the action of blue light to maintain high rates of photosynthesis. In the present study, blue light-dependent alterations of the photosynthetic apparatus, which can be detected by analysis of light-saturation curves and by measurements of partial reactions of the photosynthetic electron transport chain, are described. Light-saturation curves of photosynthesis in vivo were measured with a new closed oxygen electrode system after culture of Acetabularia in continuous red or blue light. These curves were compared to those of 2,6-dichlorophenol-indophenol reduction by isolated chloroplast membranes. The analysis lead to the following statements: (a) only one reaction limits electron transport rates in vitro (dichlorophenol-indophenol reduction) at all light intensities irrespective of the light quality during growth, and (b) the limiting step is light driven and located in the reaction center of photosystem II. Presumably, this same reaction determines the flow of electrons under low light intensities in vivo in cells from white, blue, and red light. In addition to photosynthesis, the rates of dark respiration changed due to the action of blue light. Concomitantly, the light compensation point of apparent photosynthesis was shifted during monochromatic irradiations.

Photoecology of the coral Leptoseris fragilis in the Red Sea twilight zone (an experimental study by submersible).

Depth-dependent photoadaptational responses of the Red Sea zooxanthellate coral (Leptoseris fragilis) were studied down to 160 m from the research submersible GEO. Light saturation curves for photosynthesis revealed, with I C=1-2, I K=10.9 and I sat=20 μE·cm-2·sec-1, the lowest values of photokinetic parameters ever reported for a symbiotic coral. In summer, positive net production occurs only around noon at approx. 100m depth. Biomass parameters of corals at 100-135 m are negatively correlated with depth in algal cell density, protein, chlorophyll and carotenoid but not in pigment ratios or cell based pigment content. Coral size decreased with depth. Corals transplanted from 110-120 m original depth to 40, 70, 90 and 160 m showed high survival after one year. O2-production and dark O2-uptake increased with decreasing transplantation depth. After one year, transplants at 70 and 90 m but not at 40 m had higher algae density and pigment concentrations. The host light-harvesting systems described by Schlichter, Fricke and Weber (1986) are partially destroyed in 40 m but not in 70 and 90 m transplants. Different light exposures alter P-I-responses (P max, I C, I K, I sat) but not biomass parameters, indicating molecular or biochemical adaptation. The coraal's optimal light fields lie between 70 to 90 m. Its exceptional bathymetric distribution is linked with the newly discovered host light-harvesting systems which probably enhance photosynthetic performance in a dim environment.

Bathymetric adaptations of reef-building corals at davies reef, great barrier reef, Australia. II. Light saturation curves for photosynthesis and respiration

Light saturation ( P- I) curves for oxygen production and consumption were constructed in the laboratory for corals collected from depths of 1 to 45 m on the southeastern (seaward) side of Davies Reef, Great Barrier Reef, Australia. This depth range represents a gradient of from 82.6 to 2.9% of surface light, which was measured as photosynthetic photon flux density (PPFD) between 400 and 700 nm. Adaptative changes in photokinetic parameters were observed over the entire range of light intensities. The compensation intensity ( I c ), I k , the intensity at which photosynthesis was 95% light saturated ( I 0.95), and the respiration rate (− R), all decreased with decreasing light intensity. The maximal rate of photosynthesis when normalized on the basis of coral chlorophyll- a content ( P ma g ) tended to decrease with decreasing irradiance but the change was not statistically significant. The P R ratio ( P m g −R ), the initial slope of a light saturation curve (α), and the maximum rate of photosynthesis when normalized by coral protein content ( P mp g ), all increased with decreasing light intensity. The logarithms of the values for each variable parameter were proportional to the logarithms of the fraction of the surface PPFD ( T) transmitted to the depth at which the corals grew. This enabled changes in these parameters to be accurately estimated for corals growing at any depth on the reef. Comparison of experimental data with published values for “saturating” irradiance and P ma g , suggests that the endosymbiotic algae within reef-building corals are photosynthetically intermediate between classical “sun” and “shade” plants.

Modeling light saturation curves for photosynthesis: An exponential function

A model for light saturation curves of photosynthesis is presented. This model describes the relationship between the rate of gross photosynthesis and irradiance. Experimental data suggest that in many cases this model can be simplified to the hyperbolic tangent function.

Control of the Light Saturation Point for Photosynthesis in Tomato

AbstractThe light saturation curves for photosynthesis in Lycopersicon esculentum have been studied for a yellow‐green mutation and for hormone treated plants. Comparisons have been made between saturation point and the size of the photosynthetic unit in these plants. These data suggest a function in the regulation of photosynthetic rates.

Weitere Untersuchungen zur Variabilit�t der photosynthetischen Einheit

The light saturation curves of photosynthesis of a yellow Chlorella mutant and the normal green strain have been investigated with monochromatic light at 15 different wavelengths in the range from 400 to 700 nm.

Monochromatic Light Saturation Curves for Photosynthesis in Chlorella

We used a small oxygen electrode and a grating monochromator of 10 mmu half-band width to determine light-saturation curves of photosynthesis for films of Chlorella pyrenoidosa no more than 1 cell thick. All curves were referenced to the lightsaturated rate observed in 5 mw/cm(2) of 680 mmu. To a close approximation (+/- 2%) the light-saturated rate was independent of wavelength over the region in which light intensity was sufficient to make the test (450-705 mmu). At wavelengths of high absorption we obtained intensities sufficient to cause photoinhibition. As a measure of photoinhibition we used the breakpoint, the lowest intensity at which rate of photosynthesis decreased with time. In general, the saturated rate was slightly lower and the estimated breakpoint was considerably lower at wavelengths of high absorption. Maximum rate of absorption of quanta at the breakpoint was highest in the far-red (>/= 700 mmu), lower and relatively constant in the near-red (630-680 mmu), and lowest in the blue. At 435 and 450 mmu the breakpoint occurred below saturation. We attribute small deviations in maximum rate of photosynthesis to effects of photoinhibition. Independence of wavelength observed for the light-saturated rate is consistent with models of photosynthesis in which maximum rate is limited by the same dark reaction at all wavelengths.