Thermal dependence of clearance and metabolic rates in slow- and fast-growing spats of manila clam Ruditapes philippinarum

Thermal dependence of clearance rate (CR: l h^?1), standard (SMR: J h^?1) and routine metabolic rates (RMR: J h^?1), were analyzed in fast (F)- and slow (S)-growing juveniles of the clam Ruditapes philippinarum. Physiological rates were measured at the maintenance temperature (17 °C), and compared with measurements performed at 10 and 24 °C after 16 h and 14 days to analyze acute and acclimated responses, respectively. Metabolic rates (both RMR and SMR) differed significantly between F and S seeds, irrespective of temperature. Mass-specific CRs were not different for F and S seeds but were significantly higher in F clams for rates standardized according to allometric size-scaling rules. Acute thermal dependency of CR was equal for F and S clams: mean Q ₁₀ were ≈3 and 2 in temperature ranges of 10–17 and 17–24 °C, respectively. CR did not change after 2 weeks of acclimation to temperatures. Acute thermal effects on SMR were similar in both groups (Q ₁₀ ≈ 1 and 1.6 in temperature ranges of 10–17 and 17–24 °C, respectively). Large differences between groups were found in the acute thermal dependence of RMR: Q ₁₀ in F clams (≈1.2 and 1.9 at temperature ranges of 10–17 and 17–24 °C, respectively) were similar to those found for SMR (Q ₁₀ = 1.0 and 1.7). In contrast, RMR of S clams exhibited maximum thermal dependence (Q ₁₀ = 3.1) at 10–17 °C and become depressed at higher temperatures (Q ₁₀ = 0.9 at 17–24 °C). A recovery of RMR in S clams was recorded upon acclimation to 24 °C. Contrasting metabolic patterns between fast and slow growers are interpreted as a consequence of differential thermal sensitivity of the fraction of metabolism associated to food processing and assimilation.     

Thermal acclimation of leaf and root respiration: an investigation comparing inherently fast- and slow-growing plant species

We investigated the extent to which leaf and root respiration (R) differ in their response to short‐ and long‐term changes in temperature in several contrasting plant species (herbs, grasses, shrubs and trees) that differ in inherent relative growth rate (RGR, increase in mass per unit starting mass and time). Two experiments were conducted using hydroponically grown plants. In the long‐term (LT) acclimation experiment, 16 species were grown at constant 18, 23 and 28 °C. In the short‐term (ST) acclimation experiment, 9 of those species were grown at 25/20 °C (day/night) and then shifted to a 15/10 °C for 7 days. Short‐term Q₁₀ values (proportional change in R per 10 °C) and the degree of acclimation to longer‐term changes in temperature were compared. The effect of growth temperature on root and leaf soluble sugar and nitrogen concentrations was examined. Light‐saturated photosynthesis (A_sat) was also measured in the LT acclimation experiment. Our results show that Q₁₀ values and the degree of acclimation are highly variable amongst species and that roots exhibit lower Q₁₀ values than leaves over the 15–25 °C measurement temperature range. Differences in RGR or concentrations of soluble sugars/nitrogen could not account for the inter‐specific differences in the Q₁₀ or degree of acclimation. There were no systematic differences in the ability of roots and leaves to acclimate when plants developed under contrasting temperatures (LT acclimation). However, acclimation was greater in both leaves and roots that developed at the growth temperature (LT acclimation) than in pre‐existing leaves and roots shifted from one temperature to another (ST acclimation). The balance between leaf R and A_sat was maintained in plants grown at different temperatures, regardless of their inherent relative growth rate. We conclude that there is tight coupling between the respiratory acclimation and the temperature under which leaves and roots developed and that acclimation plays an important role in determining the relationship between respiration and photosynthesis.     

High thermal acclimation potential of both photosynthesis and respiration in two lowland Plantago species in contrast to an alpine congeneric

Thermal acclimation of photosynthesis and respiration can enable plants to maintain near constant rates of net CO₂ exchange, despite experiencing sustained changes in daily average temperature. In this study, we investigated whether the degree of acclimation of photosynthesis and respiration of mature leaves differs among three congeneric Plantago species from contrasting habitats [two fast‐growing lowland species (Plantago major and P. lanceolata), and one slow‐growing alpine species (P. euryphylla)]. In addition to investigating some mechanisms underpinning variability in photosynthetic acclimation, we also determined whether leaf respiration in the light acclimates to the same extent as leaf respiration in darkness, and whether acclimation reestablishes the balance between leaf respiration and photosynthesis. Three growth temperatures were provided: constant 13, 20, or 27°C. Measurements were made at five temperatures (6–34°C). Little acclimation of photosynthesis and leaf respiration to growth temperature was exhibited by P. euryphylla. Moreover, leaf masses per area (LMA) were similar in 13°C‐grown and 20°C‐grown plants of the alpine species. In contrast, growth at 13°C increased LMA in the two lowland species; this was associated with increased photosynthetic capacity and rates of leaf respiration (both in darkness and in the light). Alleviation of triose phosphate limitation and increased capacity of electron transport capacity relative to carboxylation were also observed. Such changes demonstrate that the lowland species cold‐acclimated. Light reduced the short‐term temperature dependence (i.e. Q₁₀) of leaf respiration in all three species, irrespective of growth temperature. Collectively, our results highlight the tight coupling that exists between thermal acclimation of photosynthetic and leaf respiratory metabolism (both in darkness and in the light) in Plantago. If widespread among contrasting species, such coupling may enable modellers to assume levels of acclimation in one parameter (e.g. leaf respiration) where details are only known for the other (e.g. photosynthesis).     

Adaptation and acclimation of growth and photosynthesis of five Antarctic red algae to low temperatures

Temperature requirements for growth, photosynthesis and dark respiration were determined for five Antarctic red algal species. After acclimation, the stenothermal species Gigartina skottsbergii and Ballia callitricha grew at 0 or up to 5 °C, respectively; the eurythermal species Kallymenia antarctica, Gymnogongrus antarcticus and Phyllophora ahnfeltioides grew up to 10 °C. The temperature optima of photosynthesis were between 10 and 15 °C in the stenothermal species and between 15 and 25 °C in the eurythermal species, irrespective of the growth temperature. This shows that the temperature optima for photosynthesis are located well below the optima from species of other biogeographical regions, even from the Arctic. Respiratory rates rose with increasing temperatures. In contrast to photosynthesis, no temperature optimum was evident between 0 and 25 °C. Partial acclimation of photosynthetic capacity to growth temperature was found in two species. B. callitricha and Gymnogongrus antarcticus acclimate to 0 °C, and 5 and 0 °C, respectively. But acclimation did in no case lead to an overall shift in the temperature optimum of photosynthesis. B. callitricha and Gymnogongrus antarcticus showed acclimation of respiration to 5 °C, and P. ahnfeltioides to 5 and 10 °C, resulting in a temperature independence of respiration when measured at growth temperature. With respect to the acclimation potential of the species, no distinction can be made between the stenothermal versus the eurythermal group. (Net)photosynthetic capacity:respiration (P:R) ratios showed in all species highest values at 0 °C and decreased continuously to values lower than 1.0 at 25 °C. In turn, the low P:R ratios at higher temperatures are assumed to determine the upper temperature growth limit of the studied species. Estimated daily carbon balance reached values between 4.1 and 30.7 mg C g⁻¹ FW day⁻¹ at 0 °C, 16:8 h light/dark cycle, 12–40 μmol m⁻² s⁻¹. Received: 4 November 1999 / Accepted: 7 March 2000     

Thermal Acclimation of Respiration and Photosynthesis in the Marine Macroalga Gracilaria lemaneiformis (Gracilariales,Rhodophyta)

The responses of respiration and photosynthesis to temperature fluctuations in marine macroalgae have the potential to significantly affect coastal carbon fluxes and sequestration. In this study, the marine red macroalga Gracilaria lemaneiformis was cultured at three different temperatures (12, 19, and 26°C) and at high‐ and low‐nitrogen (N) availability, to investigate the acclimation potential of respiration and photosynthesis to temperature change. Measurements of respiratory and photosynthetic rates were made at five temperatures (7°C–33°C). An instantaneous change in temperature resulted in a change in the rates of respiration and photosynthesis, and the temperature sensitivities (i.e., the Q₁₀ value) for both the metabolic processes were lower in 26°C‐grown algae than 12°C‐ or 19°C‐grown algae. Both respiration and photosynthesis acclimated to long‐term changes in temperature, irrespective of the N availability under which the algae were grown; respiration displayed strong acclimation, whereas photosynthesis only exhibited a partial acclimation response to changing growth temperatures. The ratio of respiration to gross photosynthesis was higher in 12°C‐grown algae, but displayed little difference between the algae grown at 19°C and 26°C. We propose that it is unlikely that respiration in G. lemaneiformis would increase significantly with global warming, although photosynthesis would increase at moderately elevated temperatures.     

CHARACTERIZATION OF PSYCHROPHILIC OSCILLATORIANS (CYANOBACTERIA) FROM ANTARCTIC MELTWATER PONDS

Oscillatorian cyanobacteria dominate benthic microbial mat communities in many polar freshwater ecosystems. Capable of growth at low temperatures, all benthic polar oscillatorians characterized to date are psychrotolerant (growth optima > 15° C) as opposed to psychrophilic (growth optima ≤ 15° C). Here, psychrophilic oscillatorians isolated from meltwater ponds on Antarctica's McMurdo Ice Shelf are described. Growth and photosynthetic rates were investigated at multiple temperatures, and compared with those of a psychrotolerant isolate from the same region. Two isolates showed a growth maximum at 8° C, with rates of 0.12 and 0.08 doublings·d ^{? 1}, respectively. Neither displayed detectable growth at 24° C. The psychrotolerant isolate showed almost imperceptible growth at 4° C and a rate of 0.9 doublings·d ^{? 1} at its optimal temperature of ～23° C. In both photosynthesis versus irradiance and photosynthesis versus temperature experiments, exponentially growing cultures were acclimated for 14 days at 3, 8, 12, 20, and 24° C under saturating light intensity, and [¹⁴C] photoincorporation rates were measured. Psychrophilic isolates acclimated at 8° C showed greatest photosynthetic rates; those acclimated at 3° C were capable of active photosynthesis, but photoincorporation was not detected in cells acclimated at 20 and 24° C, because these isolates were not viable after 14 days at those temperatures. The psychrotolerant isolate, conversely, displayed maximum photosynthetic rates at 24° C, though photoincorporation was actively occurring at 3° C. Within acclimation temperature treatments, short‐term photosynthetic rates increased with increasing incubation temperature for both psychrophilic and psychrotolerant isolates. These results indicate the importance of temperature acclimation before assays when determining optimal physiological temperatures. All isolates displayed photosynthetic saturation at low light levels (<128 μmol·m ^{? 2}·s ^{? 1}) but were not photoinhibited at the highest light treatment (233 μmol·m ^{? 2}·s ^{? 1}). Field studies examining the impact of temperature on photosynthetic responses of intact benthic mats, under natural solar irradiance, showed the mat communities to be actively photosynthesizing from 2 to 20° C, with maximum photoincorporation at 20° C, as well as capable of a rapid response to an increase in temperature. The rarity of psychrophilic cyanobacteria, relative to psychrotolerant strains, may be due to their extremely slow growth rates and inability to take advantage of occasional excursions to higher temperatures. We suggest an evolutionary scenario in which psychrophilic strains, or their most recent common ancestor, lost the ability to grow at higher temperatures while maintaining a broad tolerance for fluctuations in other physical and chemical parameters that define shallow meltwater Antarctic ecosystems.     

Temperature response of photosynthetic light‐ and carbon‐use characteristics in the red seaweed Gracilariopsis lemaneiformis (Gracilariales,Rhodophyta)

The red seaweed Gracilariopsis is an important crop extensively cultivated in China for high‐quality raw agar. In the cultivation site at Nanao Island, Shantou, China, G. lemaneiformis experiences high variability in environmental conditions like seawater temperature. In this study, G. lemaneiformis was cultured at 12, 19, or 26°C for 3 weeks, to examine its photosynthetic acclimation to changing temperature. Growth rates were highest in G. lemaneiformis thalli grown at 19°C, and were reduced with either decreased or increased temperature. The irradiance‐saturated rate of photosynthesis (P_max) decreased with decreasing temperature, but increased significantly with prolonged cultivation at lower temperatures, indicating the potential for photosynthesis acclimation to lower temperature. Moreover, P_max increased with increasing temperature (~30 μmol O₂ · g^?1FW · h^?1 at 12°C to 70 μmol O₂ · g^?1FW · h^?1 at 26°C). The irradiance compensation point for photosynthesis (I_c) decreased significantly with increasing temperature (28 μmol photons · m^?2 · s^?1 at high temperature vs. 38 μmol photons · m^?2 · s^?1 at low temperature). Both the photosynthetic light‐ and carbon‐use efficiencies increased with increasing growth or temperatures (from 12°C to 26°C). The results suggested that the thermal acclimation of photosynthetic performance of G. lemaneiformis would have important ecophysiological implications in sea cultivation for improving photosynthesis at low temperature and maintaining high standing biomass during summer. Ongoing climate change (increasing atmospheric CO₂ and global warming) may enhance biomass production in G. lemaneiformis mariculture through the improved photosynthetic performances in response to increasing temperature.     

Seasonal variation in light- and temperature-dependent growth of marine planktonic diatoms in in situ dialysis cultures in the Trondheimsfjord,norway (63°N)

Three species of diatoms, Skeletonema costatum (Grev.) Cleve, Thalassiosira gravida Cleve, and T. pseudonana (Hustedt) Hasle et Heimdal, were grown in in situ dialysis culture in the Trondheimsfjord at depths of 0.5 and 4 m. The rates of growth and the chemical composition of exponentially growing cells were monitored and related to seasonal changes in illumination and temperature. Functions correlating growth rate with temperature were deduced. Growth took place from February to November. During this period temperature ranged from ?1 to 16°C, the average photon flux density (ifI) (per 24 h) from 9 to 570 μE · m^?2 · s^?1 (0.5 m depth), and the length of the days (I > 1 μE · m^?2 · s^?1) from 6 to 24 h. Light-limited growth was evident when the product of the average daily light and the chlorophyll/N ratio was < 10; this occurred mostly in early spring and late autumn. Peak densities (> 800 for the Thalassiosira spp. and > 1300–1400 μE · m^?2 · s^?1 for Skeletonema) seem to inhibit growth. The highest rates recorded were ≈1.6 doubl. · day^?1 (July, 15–16°C).The three species exhibit different ecological behaviour. Skeletonema is eurythermal (Q₁₀ = 1.8), whereas Thalassiosira pseudonana favours high temperatures, and T. gravida temperatures < 10°C. Moreover, Skeletonema has generally less chlorophyll and more phosphorus and ATP (≈ 1.4 ×) than the other two species. In Skeletonema, the ATP level seems related to the light-governed growth rate, and independent of temperature. In Thalassiosira no such correlation was found.     

The effect of light and temperature on the growth and photosynthesis of Gracilariopsis chorda (Gracilariales, Rhodophtya) from geographically separated locations of Japan

The effect of light and temperature on the growth and photosynthesis of the Japanese agarophyte, Gracilariopsis chorda (Gracilariaceae, Rhodophyta), was determined to better understand its physiology so that we could identify candidates for mass cultivation. Above the photosynthetic active radiation of 66 μmol photons m^?2 s^?1, photosynthetic rates saturated for all strains that were collected from six different locations (Hokkaido, Chiba, Tokushima, Saga, Kagoshima, and Okinawa); furthermore, either photosynthesis or growth was observed at all temperature treatments examined in our study (4–32 °C for photosynthesis, 16–32 °C for growth experiments). We identified a temperature range for optimal photosynthesis and growth, which occurred within 20.1–29.1 °C and roughly correlated with the water temperatures of the collection locations and strongly suggests that this species tolerates a wide variety of water temperature. In particular, the Kagoshima strain had the widest range of optimal temperatures (20.8–29.1 °C), whereas the Saga strain had the narrowest range (23.1–27.3 °C). It is important to note that all the optimal temperature ranges overlapped among the strains; therefore, no definitive distinction can be determined. The broad tolerance to temperatures commonly observed from northern to southern Japan suggests that the cultivation of this species should succeed during spring to summer in the majority of the coastal regions in Japan.     

Effects of light,temperature and salinity on the growth rate of harmful marine diatoms,Chaetoceros convolutus and C. concavicornis that kill netpen salmon

Chaetoceros convolutus and C. concavicornis have been implicated in the death of salmon in netpens in the Pacific Northwest by damaging the salmon's gills. To better understand how environmental factors affect the distribution of these two species, the interacting effects of light, temperature and salinity on growth rate were examined by growing these species under a range of temperatures (4–18 °C), light (10–175 μmol photon m⁻² s⁻¹) and salinities (10–30‰). For C. convolutus, the growth rate showed a hyperbolic relationship with irradiance at 8, 14 and 18 °C and light saturation occurred at 9, 14 and 20 μmol photon m^t s⁻¹ respectively. At 4 °C for C. convolutus and 8 °C for C. concavicornis, cells grew at μ_max, even at the lowest irradiances tested (10 μmol photon m⁻² s⁻¹). For C. convolutus, the amount of light required to saturate growth rate increased with temperature in an approximately linear fashion. The Q₁₀ was 1.88, calculated by averaging over both species. C. concavicornis was the more euryhaline species growing at salinities as low as 17.5‰, while C. convolutus grew only at 25‰ and above.     

Low temperature acclimation of root fatty acid composition, leaf water potential, gas exchange and growth of soybean seedlings

Abstract Root fatty acid composition, photosynthesis, leaf water potentials, stomatal resistances, leaf specific weights, and root: shoot ratios of soybean were measured in two temperature regimes. Groups of soybean plants were grown in controlled chambers of the Duke University Phytotron under two thermoperiods. One group of the plants was grown from seed for 3 weeks in either 29/23°C or 17/11°C thermoperiods, and another group was grown for 2 weeks in 29/23°C and then transferred to the 17/11°C thermoperiod where it remained for 8 days. Broccoli was also grown in either 29/23°C or 17/11°C thermoperiods. Soybean roots contained more unsaturated fatty acids than broccoli roots, although broccoli roots showed a larger increase in unsaturation than soybean roots with decreased temperature. The fatty acid unsaturation in the roots of soybean began to increase rapidly after the temperature regime was changed. The increase was in the new roots produced in the cold regime rather than in the pre-existing roots. The soybean leaf water and osmotic potentials decreased about 0.4 MPa, beginning one day after the transfer from 29/23°C to 17/11°C, but recovered significantly after 8 d. Plants grown at 17/11 °C had lower rates of photosynthesis and adaxial stomatal resistances, but higher root: shoot ratios and specific leaf weights compared to plants grown at 29/23°C. Plants grown and maintained at 29/23°C showed a steady increase in photosynthetic rates over the 8-d experimental period, whether rates were measured in 1 mol m^?3 or 9 mol m^?3 oxygen. Plants transferred to 17/11°C however maintained constant rates of photosynthesis at 1 mol m^?3 O₂, whereas at 9 mol m^?3 rates declined for 2 d then were constant for the remaining 6 d of the experimental period. These results suggest that changes in membrane fatty acid unsaturation is an important aspect of plant acclimation to chilling temperatures in terms of maintaining root permeability and water uptake. However, the degree of unsaturation is not a good indicator of differences in chilling tolerance among species. The apparent acclimation of photorespiration to a constant percentage of photosynthesis suggests a role of photorespiration in the plant.     

Low-temperature photosynthetic performance of a C4 grass and a co-occurring C3 grass native to high latitudes

The photosynthetic performance of C₄ plants is generally inferior to that of C₃ species at low temperatures, but the reasons for this are unclear. The present study investigated the hypothesis that the capacity of Rubisco, which largely reflects Rubisco content, limits C₄ photosynthesis at suboptimal temperatures. Photosynthetic gas exchange, chlorophyll a fluorescence, and the in vitro activity of Rubisco between 5 and 35 °C were measured to examine the nature of the low‐temperature photosynthetic performance of the co‐occurring high latitude grasses, Muhlenbergia glomerata (C₄) and Calamogrostis canadensis (C₃). Plants were grown under cool (14/10 °C) and warm (26/22 °C) temperature regimes to examine whether acclimation to cool temperature alters patterns of photosynthetic limitation. Low‐temperature acclimation reduced photosynthetic rates in both species. The catalytic site concentration of Rubisco was approximately 5.0 and 20 µmol m^?2 in M. glomerata and C. canadensis, respectively, regardless of growth temperature. In both species, in vivo electron transport rates below the thermal optimum exceeded what was necessary to support photosynthesis. In warm‐grown C. canadensis, the photosynthesis rate below 15 °C was unaffected by a 90% reduction in O₂ content, indicating photosynthetic capacity was limited by the capacity of P_i‐regeneration. By contrast, the rate of photosynthesis in C. canadensis plants grown at the cooler temperatures was stimulated 20–30% by O₂ reduction, indicating the P_i‐regeneration limitation was removed during low‐temperature acclimation. In M. glomerata, in vitro Rubisco activity and gross CO₂ assimilation rate were equivalent below 25 °C, indicating that the capacity of the enzyme is a major rate limiting step during C₄ photosynthesis at cool temperatures.     

THE ACCLIMATED RESPONSE OF GROWTH,PHOTOSYNTHESIS, COMPOSITION,AND CARBON BALANCE TO TEMPERATURE IN THE PSYCHROPHILIC ICE DIATOM NITZSCHIA SERIATA1

Nitzschia seriata Cleve, a common member of marine bottom ice communities in the Arctic, was grown in unialgal batch cultures to test for compensatory mechanisms for the low temperatures (?1.8° C) typical of its natural habitat. The upper lethal limit for growth was between 12° and 15°C, and the optimum was between 6° and 12° C. The Arrhenius function adequately (R²= 73%) fitted the relationship between growth rate and temperature from – 1.6° up to 10° C, with an average Q₁₀ of 1.9 over the entire range. Light-saturated and light-limited rates of photosynthesis (normalized to chlorophyll a or cell carbon) showed complete compensation from 12° to 4° C. Photosynthetic rates, especially at light saturation, declined rapidly at temperatures below 4° C. Susceptibility to photoinhibition was greatest at the lowest growth temperatures. Cellular composition (chlorophyll a, protein, polysaccharide, and lipid contents) was not systematically related to temperature in any simple way, although cell size (carbon per cell) was maximal at the lowest growth temperature. Dark respiration was unmeasurably low (<0.015 day^?1) at all growth temperatures. The strategy of adaptation in N. seriata may be characterized as optimizing efficiency and compensation, rather than maximization, of growth rate.     

Respiration of the growing shoots of Scots pine

The respiratory CO₂ exchange and the growth of the annual shoots were followed in Scots pine (Pinus sylvestris L.) trees growing under extreme continental forest-steppe conditions near the lake Baikal. The temperature coefficient of dark respiration (Q₁₀) in growing shoots dropped down from 3.2–4.0 (in the temperature range of 10–20°C) to 1.5–2.0 (in the temperature range of 20–30°C). The changes in averaged daily respiration rates correlated with the changes in shoot growth increments and temperature (with the multiple determination coefficient of 0.94). Growth respiration of the axial shoots during the phenophase reached 80% of the total respiration costs, with the coefficients of growth respiration and maintenance respiration 0.32 and 0.021. In young crown shoots, the average value of CO₂ evolution in the light combined for the whole observation period (years 1976–2004) was about 1 kg/dm², that is 9% of CO₂ evolution from the trunk surface.     

Thermal acclimation and photoacclimation of photosynthesis in the brown alga Laminaria saccharina

Thermal acclimation and photoacclimation of photosynthesis were compared in Laminaria saccharina sporophytes grown at temperatures of 5 and 17 °C and irradiances of 15 and 150μmol photons m^?2 s^?1. When measured at a standard temperature (17°C), rates of light-saturated photosynthesis (P_max) were higher in 5 °C-grown algae (c. 3.0 μmol O₂ m^?2 s^?1) than in 17 °C-grown algae (c. 0.9 μmol O₂ m_-2 s_-1). Concentrations of Rubisco were also 3-fold higher (per unit protein) in 5 °C-grown algae than in algae grown at 17 °C. Light-limited photosynthesis responded similarly to high temperature and low light Photon yields (α) were higher in algae grown at high temperature (regardless of light), and at 5 °C in low light, than in algae grown at 5 °C in high light Differences in a were correlated with light absorption; both groups of 17 °C algae and 5 °C low-light algae absorbed c. 75% of incident light, whereas 5 °C high-light algae absorbed c. 55%. Increased absorption was correlated with increases in pigment content PSII reaction centre densities and the fucoxanthin-Chl ale protein complex (FCP). Changes in a were also attributed, in part, to changes in the maximum photon yield of photosynthesis (0_max). PSI reaction centre densities were unaffected by growth temperature, but the areal concentration of PSI in low-light-grown algae was twice that of high-light-grown algae (c. 160.0 versus 80.0 nmol m^?2). We suggest that complex metabolic regulation allows L, saccharina to optimize photosynthesis over the wide range of temperatures and light levels encountered in nature.     

LOW THERMAL LIMIT OF GROWTH RATE OF SYMBIODINIUM CALIFORNIUM (DINOPHYTA) IN CULTURE MAY RESTRICT THE SYMBIONT TO SOUTHERN POPULATIONS OF ITS HOST ANEMONES (ANTHOPLEURA SPP.; ANTHOZOA,CNIDARIA)1

Symbiodinium californium (#383, Banaszak et al. 1993 ) is one of two known dinoflagellate symbionts of the intertidal sea anemones Anthopleura elegantissima, A. xanthogrammica, and A. sola and occurs only in hosts at southern latitudes of the North Pacific. To investigate if temperature restricts the latitudinal distribution of S. californium, growth and photosynthesis at a range of temperatures (5°C–30°C) were determined for cultured symbionts. Mean specific growth rates were the highest between 15°C and 28°C (μ 0.21–0.26 · d^?1) and extremely low at 5, 10, and 30°C (0.02–0.03 · d^?1). Average doubling times ranged from 2.7 d (20°C) to 33 d (5, 10, and 30°C). Cells cultured at 10°C had the greatest cell volume (821 μm³) and the highest percentage of motile cells (64.5%). Growth and photosynthesis were uncoupled; light‐saturated maximum photosynthesis (P_max) increased from 2.9 pg C · cell^?1 · h^?1 at 20°C to 13.2 pg C · cell^?1 · h^?1 at 30°C, a 4.5‐fold increase. Less than 11% of daily photosynthetically fixed carbon was utilized for growth at 5, 10, and 30°C, indicating the potential for high carbon translocation at these temperatures. Low temperature effects on growth rate, and not on photosynthesis and cell morphology, may restrict the distribution of S. californium to southern populations of its host anemones.     

Evidence of temperature‐independent metabolic rates in diurnal Namib Desert tenebrionid beetles

To investigate whether the sensitivity to environmental temperature varies between nocturnal and diurnal species of tenebrionid beetle, the metabolic rates of three diurnal species (Onymacris plana Peringuey, Onymacris rugatipennis Haag and Physadesmia globosa Haag) and three nocturnal species (Epiphysa arenicola Penrith, Gonopus sp. and Stips sp.) of beetles from the Namib Desert are measured over a range of temperatures (15–40 °C) that are experienced by these beetles in their natural habitat. The diurnal species O. plana, O. rugatipennis and P. globosa exhibit temperature‐independent metabolic rates (mean Q₁₀ = 1.2) within temperature ranges that are ecologically relevant for diurnal desert beetles (30–40 °C). Onymacris plana, in particular, has a 20–40 °C rate–temperature slope (0.007 log₁₀ mL O₂ h^?1 g^?1 °C^?1; Q₁₀ = 1.1) that is less than half that of the other five beetle species (0.022–0.063 log₁₀ mL O₂ h^?1 g^?1 °C^?1; Q₁₀ ranges from 1.3–1.9), suggesting that O. plana is more metabolically independent of temperature than the other nocturnal and diurnal tenebrionids being investigated. Animals with metabolic rates that are decoupled from body temperature (or ambient temperature) may have an ecological advantage that allows them to exploit thermal and spatial niches during extreme temperature conditions.     

PHOTOSYNTHESIS AND RESPIRATION OF THE CONCHOCELIS STAGE OF ALASKAN PORPHYRA (BANGIALES,RHODOPHYTA) SPECIES IN RESPONSE TO ENVIRONMENTAL VARIABLES1

Photosynthesis and respiration of three Alaskan Porphyra species, P. abbottiae V. Krishnam., P. pseudolinearis Ueda species complex (identified as P. “pseudolinearis” below), and P. torta V. Krishnam., were investigated under a range of environmental parameters. Photosynthesis versus irradiance (P–I) curves revealed that maximal photosynthesis (P_max), irradiance at maximal photosynthesis (I_max), and compensation irradiance (I_c) varied with salinity, temperature, and species. The P_max of Porphyra abbottiae conchocelis varied between 83 and 240 μmol O₂ · g dwt^?1 · h^?1 (where dwt indicates dry weight) at 30–140 μmol photons · m^?2 · s^?1 (I_max) depending on temperature. Higher irradiances resulted in photoinhibition. Maximal photosynthesis of the conchocelis of P. abbottiae occurred at 11°C, 60 μmol photons · m^?2·s^?1, and 30 psu (practical salinity units). The conchocelis of P. “pseudolinearis” and P. torta had similar P_max values but higher I_max values than those of P. abbottiae. The P_max of P. “pseudolinearis” conchocelis was 200–240 μmol O₂ · g dwt^?1 · h^?1 and for P. torta was 90–240 μmol O₂ · g dwt^?1 · h^?1. Maximal photosynthesis for P. “pseudolinearis” occurred at 7°C and 250 μmol photons · m^?2 · s^?1 at 30 psu, but P_max did not change much with temperature. Maximal photosynthesis for P. torta occurred at 15°C, 200 μmol photons · m^?2 · s^?1, and 30 psu. Photosynthesis rates for all species declined at salinities <25 or >35 psu. Estimated compensation irradiances (I_c) were relatively low (3–5 μmol · photons · m^?2 · s^?1) for intertidal macrophytes. Porphyra conchocelis had lower respiration rates at 7°C than at 11°C or 15°C. All three species exhibited minimal respiration rates at salinities between 25 and 35 psu.     

Temperature modification of respiratory metabolism and caloric intake of Pandalus borealis (Krøyer) first zoeae

Oxygen consumption rates (Q_O2) of laboratory reared stage one zoeae of Pandalus borealis (Krøyer) at 1.5, 3, 4.5, 6, and 9°C were 1.5, 2.2, 2.6, 3.6 and 4.1μ O₂ · mg^?1 · h^?1, respectively. These values of Q_O2 correspond to 0.26, 0.38, 0.44, 0.60, and 0.70 μl O₂ · individual^?1 · h^?1. At 10.5 °C oxygen consumption rates decreased suggesting thermally induced respiratory stress.The equation log₁₀Q_O2 = 0.55 log₁₀T°C + 0.086 describes the relationship between Q_O2 (μl O₂ · mg^?1 · h^?1) and sea-water temperature between 1.5 and 9°C. Corresponding values of Q_O2 for an individual (μl O₂ · h^?1) exhibited the relationship log₁₀Q_O2 = 0.55 log₁₀T°C ?0.686.The minimum daily metabolic caloric requirements for an individual zoea ranged from 0.04 at 3 °C to 0.07 calories per day at 8 °C. The number of calories ingested daily ranged from 0.4 to 0.5 at 3 to 8 °C.     

Photosynthesis of Marine Macroalgae from Antarctica: Light and Temperature Requirements

The photosynthetic performance of macroalgae isolated in Antarctica was studied in the laboratory. Species investigated were the brown algae Himantothallus grandifolius, Desmarestia anceps, Ascoseira mirabilis, the red algae Palmaria decipiens, Iridaea cordata, Gigartina skottsbergii, and the green algae Enteromorpha bulbosa, Acrosiphonia arcta, Ulothrix subflaccida and U. implexa. Unialgal cultures of the brown and red algae were maintained at 0°C, the green algae were cultivated at 10°C. I_K values were between 18 and 53 μmol m^?2 s^?1 characteristic or low light adapted algae. Only the two Ulothrix species showed higher I_K values between 70 and 74 μmol m^?2 s^?1. Photosynthesis compensated dark respiration at very low photon fluence rates between 1.6 and 10.6 μmol m^?2 s^?1. Values of α were high: between 0.4 and 1.1 μmol O₂ g^?1 FW h^?1 (μmol m^?2 s^?1)^?1 in the brown and red algae and between 2.1 and 4.9 μmol O₂ g^?1 FW h^?1 (μmol m^?2 s^?1)^?1 in the green algal species. At 0°C P_max values of the brown and red algae ranged from 6.8 to 19.1 μmol O₂ g^?1 FW h^?1 and were similarly high or higher than those of comparable Arctic-cold temperate species. Optimum temperatures for photosynthesis were 5 to 10°C in A. mirabilis, 10°C in H. grandifolius, 15°C in G. skottsbergii and 20°C or higher in D. anceps and I. cordata. P: R ratios strongly decreased in most brown and red algae with increasing temperatures due to different Q₁₀ values for photosynthesis (1.4 to 2.5) and dark respiration (2.5 to 4.1). These features indicate considerable physiological adaptation to the prevailing low light conditions and temperatures of Antarctic waters. In this respect the lower depth distribution limits and the northern distribution boundaries of these species partly depend on the physiological properties described here.