Variable Light Environments Research Articles

Light limitation of summer primary production in the coastal Gulf of Alaska: physiological and environmental causes

We examined photosynthesis-irradiance (P-E) relationships for coastal Gulf of Alaska phytoplankton communities during summer 2003. Phytoplankton were adapted to high light levels, with elevated light saturation parameters (average Ek 390 µmol photons m -2 s -1 ), low photosynthetic efficiencies (α), and an absence of photoinhibition. Maximum photosynthesis rates (Pmax) ranged from 0.9 to 12.9 µg C µg chl a -1 h -1 and were consistently higher in the nearshore Alaska Coastal Current than elsewhere in the region. Differences between photosynthetic responses of phytoplankton com- munities from near surface versus the subsurface chlorophyll maximum layer were minor. Small phytoplankton ( 20 µm), a difference associated with the higher C:chlorophyll ratios of the small phytoplankton. Acclimation to high light probably arose because of the shallow pycnocline and the highly variable light environment, the latter generated by internal waves and variable cloud cover. Simulations showed that estimated water column productivity, which ranged from 359 to 909 mg C m -2 d -1 , was sensitive to modeled changes in cloud cover and pycnocline depth, through both direct effects on light availability and indirect effects on phytoplankton physiology. Climate change could therefore affect summer primary production rates in the coastal Gulf of Alaska through changes in stratifica- tion, wind mixing energy, and cloud cover. However, summer phytoplankton growth in this region is also limited by nutrient availability and microzooplankton grazing, indicating a potentially complex relationship between phytoplankton production and environmental variability.

Late-successional riparian forest structure results in heterogeneous periphyton distributions in low-order streams

Late-successional riparian forests often regulate autotrophic microhabitats in low-order streams through shading provided by canopies. However, few studies have linked forest structure with periphyton microhabitat in adjoining streams. Our hypotheses were that (1) the heterogeneous horizontal structure in old-growth forests creates more spatially variable below-canopy light environments compared with mature forests and (2) site-specific light availability over streams correlates with spatial distributions of periphyton microhabitat. We surveyed 15 low-order stream reaches in late-successional northern hardwood–hemlock forests in the Adirondack Mountains of New York, USA. We measured forest structure and the below-canopy light environment at all reaches and the periphyton chlorophyll a concentration on artificial substrates in eight reaches. While stand age was not statistically significant, multivariate models of horizontal forest structure (e.g., gap distribution) and topography showed strong relationships (R2 > 0.70) with the below-canopy light environment across all late-successional forests. Furthermore, metrics of below-canopy light availability explained a small but statistically significant proportion of the variation in chlorophyll a concentration. This variation in chlorophyll a indicates that complex late-successional riparian forests, both mature and old-growth, create a mosaic of heterotrophic (shaded) and autotrophic (lighted) microhabitats along low-order streams. These results reveal important and previously unrecognized links between stream habitat heterogeneity and the horizontal heterogeneous late-successional forest structure.

Effects of photoacclimation on the light niche of corals: a process-based approach

The ecology of photosynthetic organisms is influenced by the need to adjust the photosynthetic apparatus to variable light environments (photoacclimation). In this study, we quantified different components of the photoacclimation process for a reef-building coral (Turbinaria mesenterina, Lamarck, 1816): including, variation in absorption cross-section, size of photosynthetic units, turnover time, chlorophyll content, and colony respiration. We used these calibrations to characterize this species’ light niche, and to determine the sensitivity of the niche boundaries to different processes of photoacclimation. Results showed that the breadth of the light niche was most sensitive to the size of the photosynthetic unit, absorption cross-section, and rates of respiration. Habitats with the highest light availability did not lead to maximal energy acquisition. This was because, although corals acclimated to high light have high rates of photosynthesis per unit chlorophyll, their chlorophyll content was strongly reduced. This suggests that potential energetic benefits that could be achieved through increased light harvesting (i.e., increased chlorophyll content) in high-light habitats are outweighed by costs associated with photoprotection. Such costs appear to place an upper bound on the habitat distributions of coral species. Our approach reveals how the photophysiological processes involved in photoacclimation interact to determine the light niche.

Effects of sudden exposure to high light levels on two tree fern species Dicksonia antarctica (Dicksoniaceae) and Cyathea australis (Cyatheaceae) acclimated to different light intensities

We examined the responses of two tree fern species (Dicksonia antarctica and Cyathea australis) growing under shade or variable light (intermittent shade) to sudden exposure to high light levels. Steady-state gas exchange as well as dynamic responses of plants to artificial sunflecks indicated that difference in growth light environment had very little effect on the tree ferns’ capacities to utilise and acclimate to prevailing light conditions. Two weeks of exposure to high light levels (short-term acclimation) led to decreases in all photosynthetic parameters and more negative predawn frond water potentials, mostly irrespective of previous growth light environments. After 3months in high light levels (long-term acclimation), D. antarctica fully recovered, while C. australis previously grown under variable light, recovered only partially, suggesting high light level stress effects under the variable light environments for this species.

Dark Nests and Conspicuousness in Color Patterns of Nestlings of Altricial Birds

Nests of altricial birds exhibit variable spectral properties that may affect the efficacy (conspicuousness) of the colored begging traits that a nestling displays to its parents. Here we explored whether selection for efficient perception has favored the evolution of nestling color designs that maximizes nestling detectability in variable light environments. Visual models were used to estimate how parents perceive the coloration of mouths, flanges, heads, and breasts of nestlings within their nest in 21 species of European birds. We show that the largest chromatic and achromatic contrasts against the nest background appeared for nestling mouths and flanges, respectively. Nestlings of open-nesting species showed a larger general achromatic contrast with the nest than did nestlings of hole-nesting species. However, nestlings of hole nesters showed a more evident achromatic contrast between flanges and other traits than did nestlings of open nesters. In addition, species with larger clutch sizes showed larger general achromatic contrasts with the nest. Gaping traits of open-nesting species contrasting with the nest background were better perceived under rich light regimes than under poor ones. These findings are consistent with a scenario in which selection for nestling detectability in dark environments has favored the evolution of particular achromatic components of gape coloration but also nestling traits that enhance signal efficacy by maximizing color contrasts within a nestling.

Patch structure and ramet demography of the clonal tree, Asimina triloba, under gap and closed-canopy

Clonal understory trees develop into patches of interconnected and genetically identical ramets that have the potential to persist for decades or centuries. These patches develop beneath forest canopies that are structurally heterogeneous in space and time. Canopy heterogeneity, in turn, is responsible for the highly variable understory light environment that is typically associated with deciduous forests. We investigated what aspects of patch structure (density, size structure, and reproductive frequency of ramets) of the clonal understory tree, Asimina triloba, were correlated with forest canopy conditions. Specifically, we compared A. triloba patches located beneath closed canopies and canopy gaps. We also conducted a three-year demographic study of individual ramets within patches distributed across a light gradient. The closed canopy-gap comparison demonstrated that the patches of A. triloba had a higher frequency of large and flowering ramets in gaps compared to closed-canopy stands, but total ramet density was lower in gaps than in closed canopy stands. In the demographic study, individual ramet growth was positively correlated with light availability, although the pattern was not consistent for all years. Neither ramet recruitment nor mortality was correlated with light conditions. Our results indicate that the structure of A. triloba patches was influenced by canopy condition, but does not necessarily depend on the responses of ramets to current light conditions. The lack of differences in ramet recruitment and mortality under varying canopy conditions is likely to be a primary reason for the long-term expansion and persistence of the patches. The primary benefit of a positive growth response to increasing light is the transition of relatively small ramets into flowering ramets within a short period of time.

Effects of Chlorophyllide a Oxygenase Overexpression on Light Acclimation inArabidopsis thaliana

Land plants change the compositions of light-harvesting complexes (LHC) and chlorophyll (Chl) a/b ratios in response to the variable light environments which they encounter. In this study, we attempted to determine the mechanism which regulates Chl a/b ratios and whether the changes in Chl a/b ratios are essential in regulation of LHC accumulation during light acclimation. We hypothesized that changes in the mRNA levels for chlorophyll a oxygenase (CAO) involved in Chl b biosynthesis are an essential part of light response of Chl a/b ratios and LHC accumulation. We also examined the light-intensity dependent response of CAO-overexpression and wild-type Arabidopsis thaliana plants. When wild-type plants were acclimated from low-light (LL) to high-light (HL) conditions, CAO mRNA levels decreased and the Chl a/b ratio increased. In transgenic plants overexpressing CAO, the Chl a/b ratio remained low under HL conditions; thereby suggesting that changes in the CAO mRNA levels are necessary for those in Chl a/b ratios upon light acclimation. Under HL conditions, the accumulation of Lhcb1, Lhcb3 and Lhcb6 was enhanced in plants overexpressing CAO. On the contrary, in a CAO-deficient mutant, chlorina 1-1, theaccumulation of Lhcb1, Lhcb2, Lhcb3, Lhcb6 and Lhca4 was reduced. In comparison to wild-type, beta-carotene levels were reduced in CAO-overexpressing plants, while they were elevated in chlorina 1-1 mutants. These results imply that the transcriptional control of CAO is a part of the regulatory mechanism for the accumulation of a distinct set of LHC proteins upon light acclimation.

The composition and spectral properties of three different forms of light-harvesting complex II

Different aggregates of LHC II play a very important role in regulating the light absorption and excitation energy transfer of plant. Trimeric LHC II was purified from spinach thylakoid membrane. In order to obtain the dimeric and monomeric LHC II, the trimer was treated with the mixture of 2% OGP and 10 microg/mL PLA(2), then loaded onto the sucrose density gradient in the presence of 0.06% triton X-100. The LHC II trimer, dimer and monomer isolated by sucrose density gradient all contained three polypeptides with molecular weight of 29, 28 and 26 kd respectively. The pigment composition showed much difference in the content of Chl b and xanthophyll among three forms of LHC II. To study the light capture and excitation energy transfer in different forms of LHC II, the absorption and fluorescence spectra were analyzed. The results clearly showed that the efficiency of energy absorption and transfer was different in the three kinds of LHC II, the highest for trimeric LHC II, intermediate for dimeric LHC II, and the lowest for monomeric LHC II. It was suggested that there might be a physiological homeostasis of different aggregates of LHC II in plants, which is significant for the plant self-regulating upon exposure to variable light environment.

Spectral sensitivity of larval and juvenile coral reef fishes: implications for feeding in a variable light environment

The spectral sensitivity of larval and juvenile stages of 3 species of coral reef fishes, Apogon compressus (Apogonidae), Pomacentrus amboinensis (Pomacentridae) and Premnas biaculeatus (Pomacentridae) has been investigated using feeding behaviour. Ontogenetic and taxonomic differences in spectral sensitivity were determined by establishing the minimum light intensity at which larvae and juveniles could strike prey at 12 restricted wavelength bands between 355 and 650 nm. Following construction of chromatic action spectra, the wavelength of maximum sensitivity (λmax) and the median wavelength (λP50) of the 3 species were found to be located close to 500 nm. All 3 species increased in sensitivity during growth, with A. compressus becoming the most sensitive prior to settlement. Ontogenetic shifts in spectral sensitivity towards longer wavelengths occurred in P. amboinensis and P. biaculeatus, but not in A. compressus. Spectral efficiency (wavelength-dependent efficiency of photon capture) was modelled for eutrophic and oligotrophic coral reef waters (Jerlov types Oceanic IA, Oceanic III and Coastal 1) at 2 different optical depths. Spectral efficiency was highest in the intermediate coral reef water type (JOIII) in all 3 larval fish taxa throughout early ontogeny, regardless of water depth. The results imply that the larvae would be able to feed across a broad spectrum of coral reef water types and depths.

In situ field measurements of photosynthetic rates of tropical tree species: a test of the functional group hypothesis

We examined photosynthetic characteristics of 21 tree species from a Panamanian forest differing in successional status. We hypothesized that functional guilds of species, grouped by successional status, would differ in photosynthetic performance and that pioneers would be more sensitive to seasonality and more variable in response to light than intermediate or shade tolerants. Steady-state leaf-level photosynthesis (A) was measured in situ on eight trees per species. Light response curves were generated by fitting a hyperbolic model to these data. Average light saturated photosynthetic rates (Amax) were then calculated for each species. Variability of light, photosynthesis, and leaf characteristics were quantified using coefficients of variation (CV). Significant differences were detected among species and functional groups for A, Amax, and leaf N concentration. Functional group explained 46% of the observed variation in A. Pioneers exhibited higher light-saturated photosynthetic rates than intermediates; both were higher than shade tolerants. Intermediates were the most seasonally plastic group and had the highest leaf N concentration. Shade tolerants were found in lower, more variable light environments than pioneers. A strong positive correlation between diameter growth rate and photosynthetic rate (r2= 0.55, p = 0.004) was observed across species. Our results tend to confirm the hypothesis that physiological traits can be used to differentiate among functional groups of plants. However, no evidence was found for higher plasticity of pioneer compared with shade-tolerant species.Key words: tropical trees, physiological plasticity, photosynthesis, nitrogen, growth, tropical succession.

Physiological response to complex environments in annual Polygonum species of contrasting ecological breadth.

Individual physiological response to complex environments is a major factor in the ecological breadth of species. This study compared individual patterns of both long-term and short-term response to controlled, multifactorial environments in four annual Polygonum species that differ in field distribution (P. cespitosum, P. hydropiper, P. lapathifolium, and P. persicaria). To test long-term response, instantaneous net photosynthetic rate and stomatal conductance were measured in situ on one full-sib replicate from five inbred lineages from each of five field populations per species, raised in all possible combinations of low or high light; dry, moist, or flooded soil; and poor or rich nutrient status. Short-term plastic adjustment to changes in light level was examined by switching individual plants of the four species from one of six multifactorial growth environments to the contrasting light environment, and measuring assimilation rates 1 h after transfer. The Polygonum species differed significantly in their patterns of long-term photosynthetic response to particular resources and resource combinations. The species known to have relatively broad ecological distributions (P. persicaria and P. lapathifolium) maintained high photosynthetic performance in a variety of moisture and nutrient environments when grown in high light, while the more narrowly distributed P. hydropiper maintained such functional levels only if given both high light and ample macronutrients. P. cespitosum, a species limited to shaded habitats, maintained low photosynthetic rates across the environmental range. Complex differences among the species in instantaneous water use efficiency (WUE) reflected their highly specific and to some extent independent patterns of photosynthetic and stomatal response to the multifactorial environments. The species also differed significantly in short-term physiological adjustment to changes in light level. Plants of P. persicaria and P. cespitosum reached 78% and 98%, respectively, of their maximum photosynthetic rates 1 h after transfer from low to high light, but P. hydropiper and P. lapathifolium plants reached only c. 60% of their maximum rates. When switched from high to low light, P. persicaria and P. cespitosum plants maintained 64-76% of their maximum rates, while P. hydropiper and P. lapathifolium plants decreased photosynthetic rates sharply to less than 50% of their maximum rates. These results indicate that the latter two species will be less able to maintain effective functional levels in variable light environments, a result consistent with their distributions in the field.

Light adaptation in the cyanobacterium Synechococcus sp. PCC 7942 measured by the dual-modulation fluorometer

In photosynthetic organisms, the fluorescence emission competes for excitation energy with photochemistry. An increase in the fluorescence yield reflects limitation of photochemistry and vice versa. This relationship is widely used in photosynthesis research to monitor photosynthetic activity of plants by noninvasive fluorescence measurements. Plants respond to the changes in irradiance by photosynthetic adaptation processes that allow concerted operation of the two photosystems in a variable light environment. Here, we demonstrate the power of the dual-modulation fluorometry using an example of the light adaptation in the cyanobacterium Synechococcus sp. PCC 7942. It is shown that upon an exposure to a strong white light, the photosynthetic apparatus undergoes a sequence of adaptation processes including photoinhibition and reduction of the Photosystem II effective absorption cross-section (antenna size) that modify the fluorescence yield. The adaptation also includes exchange of two forms of the Photosystem II reaction center protein D1 differing in their primary structure.

Blue and red light reversibly control psbA expression in the cyanobacterium Synechococcus sp. strain PCC 7942.

The three psbA genes encoding the photosystem II D1 protein in Synechococcus sp. strain PCC 7942 respond differentially to an increase in intensity of white light through transcriptional induction of psbAII and psbAIII and accelerated degradation of psbAI and psbAIII messages. We report that the genes exhibit a novel photoreversible response involving blue and red light that is almost indistinguishable from the high-white light response. Transfer of cells from white to low-fluence blue light caused a decrease in the level of the psbAI message and increased levels of psbAII and psbAIII messages, whereas transfer to red or far-red light had little effect. Five min of blue light was sufficient to trigger psbAII and psbAIII induction; five min of subsequent red irradiation attenuated this response, whereas subsequent green or far-red light (or darkness) had no effect. Response to both high and blue light was insensitive to inhibitors of photosynthetic electron transport. We propose that Synechococcus modulates photosystem II biosynthesis in a variable light environment through a photoreception signal pathway, which is independent of photosystem II activity and which is distinct from red/green-reversible control of chromatically adapting cyanobacteria and the red/far-red-reversible phytochrome of plants.

Photosynthetic and Stomatal Responses of Avena sativa (Poaceae) to a Variable Light Environment

The net photosynthetic (A), stomatal conductance to water vapor (g), water use efficiency (WUE = A/transpiration), and leaf water potential (ψ) responses of cultivated oats (A vena saliva) were determined under an experimental regime of alternating full sun (photosynthetic photon flux density, PPFD > 1,700 μmol · m-2-sec-1) and shade (300-400 μmol · m-2 · sec-1 PPFD). Less extensive measurements were made on winter wheat (Triticum aestivum) to test the generality of crop species' responses. The rates of stomatal opening/closing after changes in PPFD in A vena and Triticum were compared with previously determined rates for native grasses and forbs to assess how domestication might have altered stomatal dynamics. Characteristics of Avena under alternating sun and shade were 1) rapid fluctuations in A between full sun (~27 μmol · m-2 · sec-1) and shade rates (~12 -13 μmol · m 2sec 1); 2) slower changes in g, causing progressive stomatal closure during the measurement sequence and possible stomatal limitation of A; 3) no change in leaf ψ; and 4) a net reduction in WUE. Triticum had similar sun/shade A, g, and WUE dynamics, except that Triticum stomata returned to full-sun g between shade periods. The rates of change of g in Avena and Triticum were lower than for some desert and subalpine native species, but were similar to rates for species in adjoining native habitat. The basic stomatal dynamics of Avena and Triticum may typify many cultivated C, species, and these data indicate that crop stomatal behavior has not diverged significantly from that of native species.

The Role of Ribulose-1,5-Bisphosphate Regeneration in the Induction Requirement of Photosynthetic CO2 Exchange under Transient Light Conditions

The temporally variable light environment of natural plant canopies presents distinct limitations to carbon assimilation, partially as a result of the photosynthetic induction requirement that develops when leaves are shaded. This study was undertaken with soybean (Glycine max L.) leaves to further identify factors contributing to the activation state of the fast component of induction during low photosynthetic photon flux density (PPFD) periods. Determination of pool sizes of carbon reduction cycle intermediates at low light and upon return to saturating light indicated that different limitations to photosynthetic activity arise over the time course of a 10-minute low PPFD period. Photosynthetic activity upon reillumination was limited by the regeneration of ribulose 1,5-P(2). There was an increase in the levels of fructose 1,6-P(2), sedoheptulose 1,7-P(2), triose-P, ribose 5-P, and ribulose 5-P pools, indicating inactivation of stromal enzymes, most notably fructose 1,6-bisphosphatase, sedoheptulose 1,7-bisphosphatase, and ribulose 5-P kinase. The fast-induction component was the most important factor limiting assimilation during rapid, brief light transients, during which the decay of the slow component was minimal. This may be particularly significant for upper leaves in soybean canopies that generally experience very rapid light transients.

Assessment of environmental suitability for growth of Zostera marina L. (eelgrass) in San Francisco Bay

The relationship between turbidity and light availability, and its subsequent effect on the depth distribution of Zostera marina L. (eelgrass) in San Francisco Bay was explored. The average daily period of irradiance-saturated photosynthesis ( H sat) required for the maintenance of whole plant carbon balance and growth, based on measured rates of photosynthesis and respiration as well as data available in the literature, were estimated to be between 3 and 5 h. Estimates of average H sat availability in the field were determined from laboratory measurements of the phytosynthesis vs. irradiance ( P vs. I) response and from field observations of light attenuation measured at five sites in San Francisco Bay. Although plants were found to be low-light adapted with regard to their P vs. I response, they were limited to depths shallower than −2 m mean lower low water (MLLW) at all sites. The −2 m depth limit corresponded fairly well to predicted H sat requirements at two sites where turbidity was relatively low and constant, but depth limits of eelgrass were less than 1.5 m at three sites subjected to extremely turbid and variable light environments, much shallower than predicted from calculations of mean daily carbon requirements and H sat availability. Thus, in addition to the mean light environment, periods of extreme light attenuation that last from days to weeks may be important in controlling eelgrass growth and productivity in highly turbid and dynamic estuaries such as San Francisco Bay.

Fruit colour responses of ‘Granny Smith’ apple to variable light environments

Abstract Fifteen sequences of sunlight exposure and exclusion were imposed on fruit of ‘Granny Smith’ apple (Malus domestica Borkh.) by covering individual fruit with opaque paper bags. Fruit were harvested at commercial maturity and fruit background colour, blush, soluble solids concentration, flesh firmness, and starch pattern index were measured. The following year, seven of the same sequences were repeated and fruit colour was measured at 10-day intervals beginning from fruit drop until commercial harvest. A strong linear relationship between fruit colour lightness and hue (visually perceived colour) was evident in both years. Fruit became lighter as greenness decreased while an increasing yellowness only slightly increased lightness. Longer durations of light exclusion resulted in lighter coloured fruit, but for a given duration of shading, fruit exposed 1 month before harvest were lighter than fruit which remained shaded until harvest. All fruit became lighter in colour with time, although the rate ...

Optimal leaf photosynthetic capacity in terms of utilizing a natural light environment

The optimal photosynthetic capacity of a leaf maximizing long-term net carbon gain under a variable light environment was investigated using a simple mathematical model. Two assumptions were made: (1) light response of gross photosynthesis of a leaf is the Blackman rate-limiting type, light-saturated photosynthetic rate ( P max ) being defined as the photosynthetic capacity, and (2) (cost for construction and maintenance of a leaf): P max ratio is constant irrespective of P max . The relative frequency distribution of photon irradiance rather than its average critically affects the predicted optimal P max . Photosynthesis of a leaf with the optimal P max is light-saturated during the proportion of time equal to the cost: P max ratio. A model modified to incorporate a transitional region between the light-limited and -saturated regions of light response showed essentially the same result. In addition, the optimal P max was predicted to be low with the increasing width of the transitional region. The present model predicts the advantage of low photosynthetic capacity under light-limited conditions as well as in habitats where the leaf cost is high, which agrees with empirical observations.

Light-Harvesting Function in the Diatom Phaeodactylum tricornutum

The distribution of excitation energy between photosystems I and II (PSI and PSII) was investigated in the marine diatom Phaeodactylum tricornutum (Bohlin) using light-induced changes in fluorescence yield and rate of modulated O(2) evolution. The intensity dependence of the fast fluorescence rise in dark adapted cells (+/-DCMU) suggests that light absorbed by the major antenna complex was not delivered preferentially to PSII but is more equally distributed between the photosystems. Reversible, slow fluorescence yield changes measured in the absence of DCMU were correlated with decreased initial fluorescence and rate constants for PSII photochemistry, increased variable fluorescence, alteration of the fluorescence excitation and emission spectra, and could be effected by either 510 nm (PSII) or 704 nm (PSI) light. Slow, reversible fluorescence yield changes were also observed in the presence of DCMU, but were characterized by a loss of both initial and variable fluorescence and could not be induced by PSI light. The absence of slow changes in the yield of fluorescence and rate of modulated O(2) evolution, following addition or removal of PSI background light to modulated PSII excitation, does not support regulation of excitation energy density in PSI at the expense of PSII. The results suggest that adjustments are made at the level of excitation energy transfer to the PSII reaction center which prevent prolonged loss of photosynthetic capacity. Energy distribution is regulated by ionic distributions independently of the plastoquinone pool redox state. These differences in light-harvesting function are probably a response to the aquatic light field and may account for the success of diatoms in low and variable light environments.

LIGHT DEPENDENCE OF GROWTH AND PHOTOSYNTHESIS IN PHAEODACTYLUM TRICORNUTUM (BACILLARIOPHYCEAE)1

ABSTRACT Phaeodactylum tricornutum Bohlin was maintained in exponential growth over a range of photon flux densities (PFD) from 7 to 230 μmol·m−2s−1. The chlorophyll a‐specific light absorption coefficient, maximum quantum yield of photosynthesis, and C:N atom ratio were all independent of the PFD to which cells were acclimated. Carbon‐ and cell‐specific, light‐satuated, gross photosynthesis rates and dark respiration rates were largely independent of acclimation PFD. Decreases in the chlorophyll a‐specific, gross photosynthesis rate and the carbon: chlorophyll ratio and increases of cell‐ or carbon‐specific absorption coefficients were associated with an increase in cell chlorophyll a in cultures acclimated to low PFDs. The compensation PFD for growth was calculated to be 0.5 μmol·m−2s−1. The maintenance metabolic rate (2 × 10−7s−1), calculated on the basis of the compensation PFD, is an order of magnitude lower than the measured dark respiration rate(2.7 × 10−6mol O2·mol C−1s−1). Maintenance of high carbon‐specific, light‐saturated photosynthesis rates in cells acclimated to low PFDs may allow effective use of short exposures to high PFDs in a temporally variable light environment.