Quantum Yield Of Carbon Fixation Research Articles

The NASA EPIC/DSCOVR Ocean PAR Product

The EPIC/DSCOVR observations of the Earth’s surface lit by the Sun made from the first Lagrange point several times during the day in spectral bands centered on 443, 551, and 680 nm are used to estimate daily mean photosynthetically available radiation (PAR) at the ice-free ocean surface. The PAR algorithm uses a budget approach, in which the solar irradiance reaching the surface is obtained by subtracting from the irradiance arriving at the top of the atmosphere (known), the irradiance reflected to space (estimated from the EPIC Level 1b radiance data), taking account of atmospheric transmission and surface albedo (modeled). Clear and cloudy regions within a pixel do not need to be distinguished, which dismisses the need for often-arbitrary assumptions about cloudiness distribution within a pixel and is therefore adapted to the relatively large EPIC pixels. A daily mean PAR is estimated on the source grid for each EPIC instantaneous daytime observation, assuming no cloudiness changes during the day, and the individual estimates are remapped and weight-averaged using the cosine of the Sun zenith angle. In the computations, wind speed, surface pressure, and water vapor amount are extracted from NCEP Reanalysis 2 data, aerosol optical thickness and Angström coefficient from MERRA-2 data, and ozone amount from EPIC Level 2 data. Areas contaminated by Sun glint are excluded using a threshold on Sun glint reflectance calculated using wind data. Ice masking is based on NSIDC near-real-time ice fraction data. The product is evaluated against in situ measurements at various locations and compared with estimates from sensors in polar and geostationary orbits (MODIS, AHI). Unlike with MODIS, the EPIC PAR product does not exhibit gaps at low and middle latitudes. Accuracy is satisfactory for long-term studies of aquatic photosynthesis, especially given the much larger uncertainties on the fraction of PAR absorbed by live algae and the quantum yield of carbon fixation. The EPIC daily mean PAR product is generated operationally on a Plate Carrée (equal-angle) grid with 18.4 km resolution at the equator and on an 18.4 km equal-area grid, i.e., it is fully compatible with the NASA Greenbelt OBPG ocean-color products. Data are available since the beginning of the DSCOVR mission (i.e., June 2015) from the NASA Langley ASDC website.

Spatial and temporal changes of primary production in a deep peri-alpine lake

ABSTRACTLake productivity is fundamental to biogeochemical budgets as well as estimating ecological state and predicting future development. Combining modelling with Earth Observation data facilitates a new perspective for studying lake primary production. In this study, primary production was modelled in the large Lake Geneva using the MEdium Resolution Imaging Spectrometer (MERIS) image archive for 2002–2012. We used a semi-empirical model that estimates primary production as a function of photosynthetically absorbed radiation and quantum yield of carbon fixation. The necessary input parameters of the model—concentration of chlorophyll a, downwelling irradiance, and the diffuse attenuation coefficient—were obtained from MERIS products. The primary production maps allow us to study decennial temporal (with daily frequency) and spatial changes in this lake that a single sample point cannot provide. Modelled estimates agreed with in situ results (R2 = 0.68) and showed a decreasing trend (∼27%) in production in Lake Geneva for the selected decade. Yet, in situ monitoring measurements missed the general increase of productivity near the incoming Rhône River. We show that the temporal and spatial resolution provided by satellite observations allows estimates of primary production at the basin-scale. The phytoplankton annual primary production was estimated as ∼302 (SD 20) g C m−2 yr−1 for Lake Geneva for 2003 to 2011. This study demonstrates that maps of primary production can be obtained even with reduced resolution (1200 m) MERIS data and relatively simple methods, and thereby calls for deeper integration of remote sensing products into conventional in situ observation approaches.

Diel Patterns of Variable Fluorescence and Carbon Fixation of Picocyanobacteria Prochlorococcus-Dominated Phytoplankton in the South China Sea Basin

The various photosynthetic apparatus and light utilization strategies of phytoplankton are among the critical factors that regulate the distribution of phytoplankton and primary productivity in the ocean. Active chlorophyll fluorescence has been a powerful technique for assessing the nutritional status of phytoplankton by studying the dynamics of photosynthesis. Further studies of the energetic stoichiometry between light absorption and carbon fixation have enhanced understanding of the ways phytoplankton adapt to their niches. To explore the ecophysiology of a Prochlorococcus-dominated phytoplankton assemblage, we conducted studies of the diel patterns of variable fluorescence and carbon fixation by phytoplankton in the oligotrophic South China Sea (SCS) basin in June 2017. We found that phytoplankton photosynthetic performance at stations SEATS and SS1 were characterized by a nocturnal decrease, dawn maximum, and midday decrease of the maximum quantum yield of PSII (/, which has been denoted as both Fv/Fm and /) in the nutrient-depleted surface layer. That these diel patterns of / were similar to those in the tropical Pacific Ocean suggests macro-nutrient and potentially micro-nutrient stress. However, the fact that variations were larger in the central basin than at the basin's edge implied variability in the degree of nutrient limitation in the basin. The estimated molar ratio of gross O2 production to net production of carbon (GOP:NPC) of 4.9:1 was similar to ratios reported across the world's oceans. The narrow range of the GOP:NPC ratios is consistent with the assumption that there is a common strategy for photosynthetic energy allocation by phytoplankton. That photo-inactivated photosystems or nonphotochemical quenching rather than GOP accounted for most of the radiation absorbed by phytoplankton explains why the maximum quantum yield of carbon fixation was rather low in the oligotrophic SCS.

Photophysiological and light absorption properties of phytoplankton communities in the river-dominated margin of the northern Gulf of Mexico.

Spatial and temporal variability in photophysiological properties of phytoplankton were examined in relationship to phytoplankton community composition in the river‐dominated continental margin of the northern Gulf of Mexico (NGOM). Observations made during five research cruises in the NGOM included phytoplankton photosynthetic and optical properties and associated environmental conditions and phytoplankton community structure. Distinct patterns of spatial and temporal variability in photophysiological parameters were found for waters dominated by different phytoplankton groups. Photophysiological properties for locations associated with dominance by a particular group of phytoplankton showed evidence of photoacclimation as reflected by differences in light absorption and pigment characteristics in relationship to different light environments. The maximum rate of photosynthesis normalized to chlorophyll ( PmaxB) was significantly higher for communities dominated (>60% biomass) by cyanobacteria + prochlorophyte (cyano + prochl). The initial slope of the photosynthesis‐irradiance (P‐E) curve normalized to chlorophyll ( αB) was not clearly related to phytoplankton community structure and no significant differences were found in PmaxB and αB between different geographic regions. In contrast, maximum quantum yield of carbon fixation in photosynthesis (Φcmax) differed significantly between regions and was higher for diatom‐dominated communities. Multiple linear regression models, specific for the different phytoplankton communities, using a combination of environmental and bio‐optical proxies as predictor variables showed considerable promise for estimation of the photophysiological parameters on a regional scale. Such an approach may be utilized to develop size class‐specific or phytoplankton group‐specific primary productivity models for the NGOM.

Phytoplankton community composition and photosynthetic physiology in the Australian sector of the Southern Ocean during the austral summer of 2010/2011

Phytoplankton population dynamics play an important role in biogeochemical cycles in the Southern Ocean during austral summer. However, the relationship between phytoplankton community composition and primary productivity remains elusive in this region. We investigated the community composition and photosynthetic physiology of surface phytoplankton assemblages in the Australian sector of the Southern Ocean from December 2010 to January 2011. There were significant latitudinal variations in hydrographic and biological parameters along 110°E and 140°E. Surface (5 m) chlorophyll a (chl a) concentrations measured with high-performance liquid chromatography varied between 0.18 and 0.99 mg m−3. The diatom contribution to the surface chl a biomass increased in the south, as estimated with algal chemotaxonomic pigment markers, while the contributions of haptophytes and chlorophytes decreased. In our photosynthesis–irradiance (P–E) curve experiment, the maximum photosynthetic rate normalized to chl a ( $$P_{ \hbox{max} }^{*}$$ ), initial slope (α *), the maximum quantum yield of carbon fixation (Φ c max), and the photoinhibition index (β *) were higher in the region where diatoms contributed >50 % to the chl a biomass. In addition, there were statistically significant correlations between the diatom contribution to the chl a biomass and the P–E parameters. These results suggested that the changes in the phytoplankton community composition, primarily in diatoms, could strongly affect photosynthetic physiology in the Australian sector of the Southern Ocean.

Influence of Amur River discharge on phytoplankton photophysiology in the Sea of Okhotsk during late summer

AbstractWe investigated the photosynthetic parameters of phytoplankton in the Sea of Okhotsk during the late summer of 2006 to characterize their spatiotemporal variability and to test the hypothesis that discharge from the Amur River could influence the algal photophysiology. The highest maximum quantum yield of carbon fixation in photosynthesis (Φcmax; 0.098 mol C mol photons‐1) was found near the Amur River mouth, where nitrate was depleted. However, none of the photosynthetic parameters, including primary productivity (PP) at the surface, were correlated with temperature, daily photosynthetically available radiation (PAR), or ambient nutrient concentrations. Variations in Φcmax depended on the variations in not only the mean chlorophyll a specific absorption coefficient of phytoplankton (ā*ph) but also the slope index of the absorption coefficient of phytoplankton (aph slope), an indicator for the ratio of nonphotosynthetic carotenoids to photosynthetic carotenoids. These results indicated that the phytoplankton assemblages acclimated to the ambient light conditions by regulating their cellular pigments. Additionally, ā*ph and euphotic depth (Zeu) were significantly correlated with salinity, suggesting that photoacclimation of the phytoplankton assemblages observed in this study could be induced by discharge of Amur River. Because spatiotemporal variations in PP were concomitant with Φcmax, ā*ph, and the chlorophyll a concentration, PP models based on inherent optical property (IOP) were suitable for estimating PP in the Sea of Okhotsk. This study is the first to investigate the factors controlling phytoplankton photophysiology in the Sea of Okhotsk, one of the highest primary production areas in the world.

Quantification of a Primary Production Model Using Two Versions of the Spectral Distribution of the Phytoplankton Absorption Coefficient

In a recent publication, we discussed and presented a semi-empirical phytoplankton primary production model. In the present paper, our main purpose is to determine how the algorithms of a primary production model change when different values of specific absorption coefficient by phytoplankton are used in the model. A new version of our earlier model was quantified for this purpose. Differences between the previous and the new models are as follows: (a) the spectra of the specific absorption coefficient of light by phytoplankton differ in the new model from those used in the previous model, and (b) the quantification of the new model brings about a change in the parameters of the algorithm for the quantum yield of carbon fixation. We compared the results of primary production profiles obtained by the new model with those measured in situ and also with the values obtained by the previous model. Due to an adequate choice of quantification parameters, both the old and new models give rather close values of phytoplankton primary production. In the present study, the computational algorithms of both models have been automated. The resulting programs calculate the temporal–spatial variability of phytoplankton primary production, providing hourly values from morning to evening, daily sums, and monthly sums. The input of a table of initial parameters and selected depths produces rapid calculations of the model's results, which are given as vertical profiles of primary production and areal values.

Community structure and photosynthetic physiology of phytoplankton in the northwest subarctic Pacific during an in situ iron fertilization experiment (SEEDS-II)

Abstract Temporal changes in the abundance, community composition, and photosynthetic physiology of phytoplankton in surface waters were investigated during the second in situ iron (Fe) fertilization experiment in the NW subarctic Pacific (SEEDS-II). Surface chlorophyll a concentration was 0.75 mg m−3 on the day before the first Fe enrichment (i.e. Day 0), increased ca. 3-fold until Day 13 after two Fe additions, and thereafter declined with time. The photochemical quantum efficiency (Fv/Fm) and functional absorption cross-section (σPSII) of photosystem II for total phytoplankton in surface waters increased and decreased inside the Fe-enriched patch through Day 13, respectively. These results indicate that the photosynthetic physiological condition of the phytoplankton improved after the Fe infusions. However, the maximum Fv/Fm value of 0.43 and the maximum quantum yield of carbon fixation (φmax) of 0.041 mol C (mol photon)−1 during the development phase of the bloom were rather low, compared to their theoretical maximum of ca. 0.65 and 0.10 mol C (mol photon)−1, respectively. Diatoms, which were mainly composed of oceanic species, did not bloom, and autotrophic nanoflagellates such as cryptophytes and prasinophytes became predominant in the phytoplankton community inside the Fe-enriched patch. In ferredoxin/flavodoxin assays for micro-sized (20–200 μm in cell length) diatoms, ferredoxin was not detected but flavodoxin expressions consistently occurred with similar levels both inside and outside the Fe-enriched patch, indicating that the large-sized diatoms were stressed by Fe bioavailability inside the Fe-enriched patch even after the Fe enrichments. Our data suggest that the absence of a Fe-induced large-sized diatom bloom could be partly due to their Fe stress throughout SEEDS-II.

Photosynthetic features and primary productivity of phytoplankton in the Oyashio and Kuroshio-Oyashio transition regions of the northwest Pacific

Diel and seasonal changes in the photosynthetic physiology of phytoplankton and primary productivity were investigated during 2005, together with community composition in the Oyashio (OY) and Kuroshio – Oyashio transition (TR) regions of the northwest Pacific. In both regions, diel changes in the maximum photosynthetic rate (P* max) and the light saturation index (Ek) in the photosynthesis – irradiance (P –E) curve were observed, due to diel differences in photo-physiology. In the OY region, the highest values of chlorophyll a concentration, depth-integrated primary production and the maximum quantum yield of carbon fixation in photosynthesis (Fc max) were observed in May when diatom blooms occurred. Furthermore, a higher water-column light utilization efficiency (C) of photosynthesis for phytoplankton was found in the OY region in both May and September. In contrast, in the TR and warm-core ring regions, Fc max was nearly constant, while depth-integrated primary production in May was significantly lower than in the OY region. These results show that the spring phytoplankton assemblages in OY waters had a higher light utilization ability during photosynthesis. Such a high photosynthetic property would contribute to the highest seasonal biological drawdown of surface pCO2 among the world’s oceans (Takahashi, T., Sutherland, S. C., Sweeney, C. et al. (2002) Global sea – air CO2 flux based on climatological surface ocean pCO2, and seasonal biological and temperature effects. Deep-Sea Res. II, 49, 1601– 1622).

Diel variations in the photosynthetic parameters of Prochlorococcus strain PCC 9511: Combined effects of light and cell cycle

We examined the mechanisms related to the diel variations in the parameters of the relationship between the rate of carbon fixation of phytoplankton and irradiance (P vs. E curve). Our goal was to understand what determines the phase of these variations relative to that of the light cycle. We grew the marine prokaryote Prochlorococcus in an axenic cyclostat culture system under a light–dark cycle that mimicked natural conditions at sea surface and followed changes in cell physiology with a 2‐h resolution. Individual cells divide mostly in phase with each other, once a day at the beginning of the dark period. The quantum yields of chlorophyll fluorescence, the maximum quantum yield of carbon fixation (φCmax) and the maximum rate of carbon fixation (PBmax) exhibited diel variations over about factors of 2, 4, and 4, respectively, with maxima at the beginning of the light period. The morning drop in φCmax and the quantum yield of fluorescence, which was accompanied by only a small decrease (<15%) of photochemial efficiency of PSII (Fv/Fm), suggests regulation by light and preceded the drop in PBmax by 4 h. The decrease in PBmax during the day matched a decrease in the transcription level of Rubisco. The quantum yield of fluorescence, φCmax, and PBmax increased again during the dark period, but this recovery was slowed at the time of cell division. Our results suggest that the pattern of diel variations in the photosynthetic parameters is determined both by photoacclimation and the cell‐division cycle.

Action spectrum and maximum quantum yield of carbon fixation in natural phytoplankton populations: implications for primary production estimates in the ocean

Spectral and non-spectral measurements of the maximum quantum yield of carbon fixation for natural phytoplankton assemblages were compared in order to evaluate their effect on bio-optical models of primary production. Field samples were collected from two different coastal regions of NW Spain in spring, summer and autumn and in a polar environment (Gerlache Strait, Antarctica) during the austral summer. Concurrent determinations were made of spectral phytoplankton absorption coefficient [ a ph( λ)], white-light-limited slope of the photosynthesis–irradiance relationships ( α B), carbon uptake action spectra [ α B( λ)], broad-band maximum quantum yields ( φ m), and spectral maximum quantum yields [ φ m( λ)]. Carbon uptake action spectra roughly followed the shape of the corresponding phytoplankton absorption spectra but with a slight displacement in the blue–green region that could be attributed to imbalance between the two photosystems PS I and PS II. Results also confirmed previous observations of wavelength dependency of maximum quantum yield. The broad-band maximum quantum yield ( φ m) calculated considering the measured spectral phytoplankton absorption coefficient and the spectrum of the light source of the incubators was not significantly different form the averaged spectral maximum quantum yield [ φ max (λ) ] ( t-test for paired samples, P=0.34). These results suggest that maximum quantum yield can be estimated with enough accuracy from white-light P– E curves and measured phytoplankton absorption spectra. Primary production at light limiting regimes was compared using four different models with a varying degree of spectral complexity. No significant differences ( t-test for paired samples, P=0.91) were found between a spectral model based on the carbon uptake action spectra [ α B( λ) — model a] and a model which uses the broad-band φ m and measured a ph( λ) (model b). In addition, primary production derived from constructed action spectra [ a c B( λ) from a ph( λ) and α B (model c) was also not significantly different from that derived from total spectral model a ( t-test for paired samples, P=0.60). It was found, however, that primary production at low light regimes can be strongly overestimated (44%) when a ph( λ) is derived from chlorophyll concentrations. A white-light model based on broad-band α B (model d), which does not consider phytoplankton light absorption, yields values 17% lower than those of model a. It is concluded that primary production at light-limited conditions can be computed accurately from broad-band maximum quantum yield estimates or from constructed action spectra provided that a ph( λ) is measured. However, given that phytoplankton absorption coefficients are necessary for both approaches and as computations based on φ m showed less variability, we suggest that the maximum quantum yield proxy should be used.

Implications of bio‐optical modeling of phytoplankton photosynthesis in Antarctic waters: Further evidence of no light limitation in the Bransfield Strait

During the cruise ECOANTAR 94 photosynthesis versus irradiance relationships, phytoplankton spectral absorption, quantum yield of carbon fixation, and water column light regime were determined in the eastern Bransfield Strait and surrounding areas of the Weddell Sea and Weddell‐Scotia Confluence, to determine if photosynthesis is light limited in these areas. There were no significant differences in the light‐saturated chlorophyll‐specific rate of photosynthesis (P Bm), light‐limited slope (±B), light saturation parameter (EkPAR), and the maximum quantum yield (Φm) between surface and subsurface water for several water masses in the area, which indicates that the photosynthetic response in the upper mixed layer was uniform. There were also no significant differences between the spectral light saturation parameter (EkPUR) and the mean absorbed irradiance by phytoplankton in the upper mixed layer (EumlPUR). These similarities suggest that phytoplankton photosynthesis was not light limited in this Antarctic region during the cruise period. This was also affirmed by the fact that the average operational quantum yield of the water column (0.03 mol C [mol photons]−1) was half of the mean maximum quantum yield (0.06 mol C [mol photons]−1). Primary production is underestimated by 24% when broadband models are compared with spectral ones. These results have important implications for the modeling of carbon flows in the Southern Ocean.

Nitrogen- and irradiance-dependent variations of the maximum quantum yield of carbon fixation in eutrophic, mesotrophic and oligotrophic marine systems

Natural variability of the maximum quantum yield of carbon fixation ( φ C max), as determined from the initial slope of the photosynthesis-irradiance curve and from light absorption measurements, was studied at three sites in the northeast tropical Atlantic representing typical eutrophic, mesotrophic and oligotrophic regimes. At the eutrophic and mesotrophic sites, where the mixed layer extended deeper than the euphotic layer, all photosynthetic parameters were nearly constant with depth, and φ C max averaged between 0.05 and 0.03 molC (mol quanta absorbed) −1, respectively. At the oligotrophic site, a deep chlorophyll maximum (DCM) existed and φ C max varied from ca 0.005 in the upper nutrient-depleted mixed layer to 0.063 below the DCM in stratified waters. firstly, φ C max was found roughly to covary with nitrate concentration between sites and with depth at the oligotrophic site, and secondly, it was found to decrease with increasing relative concentrations of non-photosynthetic pigments. The extent of φ C max variations directly related to nitrate concentration was inferred from variations in the fraction of functional PS2 reaction centers ( f), measured using fast repetition rate fluorometry. Covariations between f and nitrate concentration indicate that the latter factor may be responsible for a 2-fold variation in φ C max. Moreover, partitioning light absorption between photosynthetic and non-photosynthetic pigments suggests that the variable contribution of the non-photosynthetic absorption may explain a 3-fold variation in φ C max, as indicated by variations in the effective absorption cross-section of photosystem 2 ( σ PS2). Results confirm the role of nitrate in φ C max variation, and emphasize those of light and vertical mixing.

Relationship between the maximum quantum yield of carbon fixation and the minimum quantum yield of chlorophyll a in vivo fluorescence in the Gulf of St. Lawrence

Intensive monitoring of the maximum quantum yield of carbon fixation (&,,,) and of the minimum quantum yield of chlorophyll a in vivo fluorescence ($& was followed along the path of drifting buoys in the estuary and the Gulf of St. Lawrence, Canada. Samples were collected every third hour during two 24-h periods. Over the 170 measurements, &,,X varied by a factor of 20 [from 0.004 to 0.08 mol C (mol quanta))‘]. As predicted by a model of primary processes in photosystem 2, a significant and positive linear relationship was observed between $,,, and q5I;,. In the estuary, the covariability of &,,,, and $t;, seems to be driven by light, because it was observed only during daytime and was characterized by a parallel increase of &,,, and $r;, with depth. Examination of the spectral values of $FO suggests a contribution of photoprotectant carotenoids. In the gulf, because a parallel, although weaker, increase of &,, and rbr;, with depth also persisted during nighttime, nutrient deficiency is probably an additional cause of covariation between (6,,, and cbr;,. In both regions, an overall diel cycle was observed for $,,X with a maximum at around noon; $I;, did not show a clear diel periodicity. Despite the vertical covariability of &,,X and 4F0, the diel cycle of &,,X was uncoupled to $FO and thus to photosystem 2 activity. These results suggest a significant diel variation in the photosynthetic quotient of natural phytoplankton.

Variability in spectral and nonspectral measurements of photosynthetic light utilization efficiencies

Variability in spectral and nonspectral measurements of photosynthetic light utilization efficiencies