A preliminary comparison of the mariculture potential of Porphyra purpurea and Porphyra umbilicalis

Due to their rapid growth and nutrient assimilation,Porphyra spp. are good candidates for bioremediation and polyculture. The production potential of two strains of P. purpurea and P. umbilicalis from north-east USA was evaluated by measuring rates of photosynthesis (as O₂evolution) of material grown at 20 ^°C. Photosynthetic rates of P. umbilicalis were 80%higher than P. purpurea over the temperature range 5–20 ^°C, at both sub-saturating andsaturating irradiances (37 and 289 μmol photonm^-2 s^-1). Porphyra umbilicalis was more efficient at low irradiances (higher α) and had a higher P_max (23.0 vs 15.6 μmolO₂ g^-1 DW min^-1) than P.purpurea, suggesting that P. umbilicalis is a better choice for mass culture, where self-shading maybe severe. This revised version was published online in August 2006 with corrections to the Cover Date.     

Effect of irradiance and temperature on the photosynthesis of a cultivated red alga,Pyropia tenera (= Porphyra tenera), at the southern limit of distribution in Japan

The effect of irradiance and temperature on the photosynthesis of the red alga, Pyropia tenera, was determined for maricultured gametophytes and sporophytes collected from a region that is known as one of the southern limits of its distribution in Japan. Macroscopic gametophytes were examined using both pulse‐amplitude modulated fluorometry and/or dissolved oxygen sensors. A model of the net photosynthesis–irradiance (P‐E) relationship of the gametophytes at 12°C revealed that the net photosynthetic rate quickly increased at irradiances below the estimated saturation irradiance of 46 μmol photons m^?2 s^?1, and the compensation irradiance was 9 μmol photons m^?2 s^?1. Gross photosynthesis and dark respiration for the gametophytes were also determined over a range of temperatures (8–34°C), revealing that the gross photosynthetic rates of 46.3 μmol O₂ mg_chl‐a^?1 min^?1 was highest at 9.3 (95% Bayesian credible interval (BCI): 2.3–14.5)°C, and the dark respiration rate increased at a rate of 0.93 μmol O₂ mg_chl‐a^?1 min^?1°C^?1. The measured dark respiration rates ranged from ?0.06 μmol O₂ mg_chl‐a^?1 min^?1 at 6°C to ?25.2 μmol O₂ mg_chl‐a^?1 min^?1 at 34°C. The highest value of the maximum quantum yield (Fv/Fm) for the gametophytes occurred at 22.4 (BCI: 21.5–23.3) °C and was 0.48 (BCI: 0.475–0.486), although those of the sporophyte occurred at 12.9 (BCI: 7.4–15.1) °C and was 0.52 (BCI: 0.506–0.544). This species may be considered well‐adapted to the current range of seawater temperatures in this region. However, since the gametophytes have such a low temperature requirement, they are most likely close to their tolerable temperatures in the natural environment.     

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.     

EFFECTS OF LIGHT AND TEMPERATURE ON NET PHOTOSYNTHESIS AND DARK RESPIRATION OF GAMETOPHYTES AND EMBRYONIC SPOROPHYTES OF MACROCYSTIS PYRIFERA1

The rates of net photosynthesis as a function of irradiance and temperature were determined for gametophytes and embryonic sporophytes of the kelp, Macrocystis pyrifera (L.) C. Ag. Gametophytes exhibited higher net photosynthetic rates based on oxygen and pH measurements than their derived embryonic sporophytes, but reached light saturation at comparable irradiance levels. The net photosynthesis of gametophytes reached a maximum of 66.4 mg O₂ g dry wt^?1 h^?1 (86.5 mg CO₂ g dry wt^?1 h^?1), a value approximately seven times the rate reported previously for the adult sporophyte blades. Gametophytes were light saturated at 70 μE m^?2 s^?1 and exhibited a significant decline in photosynthetic performance at irradiances 140 μE m^?1 s^?1. Embryonic sporophytes revealed a maximum photosynthetic capacity of 20.6 mg O₂ g dry wt^?1 h^?1 (25.3 mg CO₂ g dry wt^?1 h^?1), a rate about twice that reported for adult sporophyte blades. Embryonic sporophytes also became light saturated at 70 μE m^?2 s^?1, but unlike their parental gametophytes, failed to exhibit lesser photosynthetic rates at the highest irradiance levels studied; light compensation occurred at 2.8 μE m^?2 s^?1. Light-saturated net photosynthetic rates of gametophytes and embryonic sporophytes varied significantly with temperature. Gametophytes exhibited maximal photosynthesis at 15° to 20° C, whereas embryonic sporophytes maintained comparable rates between 10° and 20° C. Both gametophytes and embryonic sporophytes declined in photosynthetic capacity at 30° C. Dark respiration of gametophytes was uniform from 10° to 25° C, but increased six-fold at 30° C; the rates for embryonic sporophytes were comparable over the entire range of temperatures examined. The broader light and temperature tolerances of the embryonic sporophytes suggest that this stage in the life history of M. pyrifera is well suited for the subtidal benthic environment and for the conditions in the upper levels of the water column.     

NEW GENERA OF FRESHWATER CRYPTOMONADS FROM COLORADO

Given their rapid growth and nutrient assimilation rates, Porphyra spp. are good candidates for bioremediation. The production potential of two northeast U.S. Porphyra species currently in culture ( P. purpurea and P. umbilicalis ) was evaluated by measuring rates of photosynthesis (as O₂ evolution) of samples grown at 20° C. Gametophytes of P. umbilicalis photosynthesized at rates that were 80% higher than those of P. purpurea over 5–20° C at both sub-saturating and saturating irradiances (37 and 289 μmol photons m⁻² s⁻¹). Porphyra umbilicalis was both more efficient at low irradiances (higher alpha) and had a higher P_max than did P. purpurea (23.0 vs. 15.6 μmol O₂ g⁻¹ DW min⁻¹), suggesting that P. umbilicalis is a better choice for mass culture where self-shading may be severe. The photosynthesis-irradiance relationship for the Conchocelis stage of P. purpurea was also examined. Tufts of filaments, grown at 10, 15, and 20° C, were assayed at growth temperatures at irradiances ranging from 0–315 μmol photons m⁻² s⁻¹. Tufts were slightly more productive at 15° than at 10° C, but only ca. 4–6% as productive as gametophytes. Maximum rates of net photosynthesis were reduced by 66–74% in tufts grown at 20° C (only about 2% of gametophytes). The Conchocelis stage, however, need not limit mariculture operations; once Conchocelis cultures are established, they can be maintained over the long-term as ready sources of spores for net seeding.     

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.     

Temperature‐dependent phagotrophy and phototrophy in a mixotrophic chrysophyte

The roles of temperature and light on grazing and photosynthesis were examined for Dinobryon sociale, a common freshwater mixotrophic alga. Photosynthetic rate was determined for D. sociale adapted to temperatures of 8, 12, 16, and 20°C under photosynthetically active radiation light irradiances of 25, 66, and 130 μmol photons · m^?2 · s^?1, with concurrent measurement of bacterial ingestion at all temperatures under medium and high light (66 and 130 μmol photons · m^?2 · s^?1). Rates of ingestion and photosynthesis increased with temperature to a maximum at 16°C under the two higher light regimes, and declined at 20°C. Although both light and temperature had a marked effect on photosynthesis, there was no significant difference in bacterivory at medium and high irradiances at any given temperature. At the lowest light condition (25 μmol photons · m^?2 · s^?1), photosynthesis remained low and relatively stable at all temperatures. D. sociale acquired the majority of carbon from photosynthesis, although the low photosynthetic rate without a concurrent decline in feeding rate at 8°C suggested 20%–30% of the carbon budget could be attributed to bacterivory at low temperatures. Grazing experiments in nutrient‐modified media revealed that this mixotroph had increased ingestion rates when either dissolved nitrogen or phosphorus was decreased. This work increases our understanding of environmental effects on mixotrophic nutrition. Although the influence of abiotic factors on phagotrophy and phototrophy in pure heterotrophs and phototrophs has been well studied, much less is known for mixotrophic organisms.     

THE EFFECTS OF TEMPERATURE ON THE PHOTOSYNTHETIC PARAMETERS AND RECOVERY OF TWO TEMPERATE BENTHIC MICROALGAE,AMPHORA CF. COFFEAEFORMIS AND COCCONEIS CF. SUBLITTORALIS (BACILLARIOPHYCEAE)1

Temperature and irradiance are the most important factors affecting marine benthic microalgal photosynthetic rates in temperate intertidal areas. Two temperate benthic diatoms species, Amphora cf. coffeaeformis (C. Agardh) Kütz. and Cocconeis cf. sublittoralis Hendey, were investigated to determine how their photosynthesis responded to temperatures ranging from 5°C to 50°C after short‐term exposure (1 h) to a range of irradiance levels (0, 500, and 1,100 μmol photons · m^?2 · s^?1). Significant differences were observed between the temperature responses of maximum relative electron transport rate (rETRmax), photoacclimation index (E_k), photosynthetic efficiency (α), and effective quantum yield (ΔF/F_m’) in both species. A. coffeaeformis had a greater tolerance to higher temperatures than C. sublittoralis, with nonphotochemical quenching (NPQ) activated at temperatures of 45°C and 50°C. C. sublittoralis, however, demonstrated a more rapid rate of recovery at ambient temperatures. Temperatures between 10°C and 20°C were determined to be optimal for photosynthesis for both species. High temperatures and irradiances caused a greater decrease in ΔF/F_m’ values. These results suggest that the effects of temperature are species specific and that short‐term exposure to adverse temperature slows the recovery process, which subsequently leads to photoinhibition.     

High-temperature inhibition of photosynthesis is greater under sunflecks than uniform irradiance in a tropical rain forest tree seedling

The survival of dipterocarp seedlings in the understorey of south‐east Asian rain forests is limited by their ability to maintain a positive carbon balance. Photosynthesis during sunflecks is an important component of carbon gain. Field measurements demonstrated that Shorea leprosula seedlings in a rain forest understorey received a high proportion of daily photon flux density at temperatures supra‐optimal for photosynthesis (72% at ≥30 °C, 14% at ≥35 °C). To investigate the effect of high temperatures on photosynthesis during sunflecks, gas exchange and chlorophyll fluorescence measurements were made on seedlings grown in controlled environment conditions either, under uniform, saturating irradiance (approximately 539 µmol m^?2 s^?1) or, shade/fleck sequences (approximately 30 µmol m^?2 s^?1/approximately 525 µmol m^?2 s^?1) at two temperatures, 28 or 38 °C. The rate of light‐saturated photosynthesis, under uniform irradiance, was inhibited by 40% at 38 °C compared with 28 °C. However, during the shade/fleck sequence, photosynthesis was inhibited by 59% at 38 °C compared with 28 °C. The greater inhibition of photosynthesis during the shade/fleck sequence, when compared with uniform irradiance, was driven by the lower efficiency of dynamic photosynthesis combined with lower steady‐state rates of photosynthesis. These results suggest that, contrary to current dogma, sunfleck activity may not always result in significant carbon gain. This has important consequences for seedling regeneration processes in tropical forests as well as for leaves in other canopy positions where sunflecks make an important contribution to total photon flux density.     

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.     

Photosynthetic activity of a temperate coral Acropora pruinosa (Scleractinia, Anthozoa) with symbiotic algae in Japan

Physiological properties of the temperate hermatypic coral Acropora pruinosa Brook with symbiotic algae (zooxanthellae) on the southern coast of the Izu Peninsula, Shizuoka Prefecture, central Japan, were compared between summer and winter. Photosynthesis and respiration rates of the coral with symbiotic zooxanthellae were measured in summer and winter under controlled temperatures and irradiances with a differential gasvolumeter (Productmeter). Net photosynthetic rate under all irradiances was higher in winter than in summer at the lower range of temperature (12–20°C), while lower than in summer at the higher range of temperature (20–30°C). The optimum temperature for net photosynthesis was apt to fall with the decrease of irradiance both in summer and winter, whereas it was higher in summer than in winter under each irradiance. At 25/ 50/100 μmol photons nr² s^?1, it was nearly the sea‐water temperature in each season. Dark respiration rate was higher in winter than in summer, especially in the range from 20–30°C. In both seasons the optimum temperature for gross photosynthesis was 28°C under 400 μmol photons nr² s^?1 and lowered with decreasing irradiance up to 22°C under 25 μmol photons nr² s^?1 in summer, while 20°C under the same irradiance in winter. The optimum temperature for production/respiration (P/R) ratio was higher in summer than in winter under each irradiance. Results indicated that metabolism of coral and zooxanthellae is adapted to ambient temperature condition under nearly natural irradiance in each season.     

Narrow range of temperature and irradiance supports optimal development of Lessonia corrugata (Ochrophyta) gametophytes: implications for kelp aquaculture and responses to climate change

The kelp Lessonia corrugata (Ochrophyta, Laminariales) is being developed for integrated multi-trophic aquaculture (IMTA) trials in the vicinity of salmon cages in Tasmania, Australia. Gametophytes are vegetally maintained before seeding on hatchery twine; however, the optimal temperature and light conditions for growth and sexual development are unknown. We measured vegetative size of female and male gametophytes and sexual development of females over a range of temperatures and irradiances using a temperature gradient table and neutral density light filters. Over a 4-week experiment, gametophytes were exposed to a combination of thermal (5.7–24.9 °C) and irradiance (10–100 μmol photons m^?2 s^?1) gradients, to assess biological performance. At the temperature extremes (hottest = 24.9 °C, coldest = 5.7 °C), we observed the critical thermal limits for this species and the results reveal a narrow optimal temperature range for growth and sexual development between 15.7 and 17.9 °C, with irradiances between 40 and 100 μmol photons m^?2 s^?1 resulting in fertile female gametophytes. Lessonia corrugata inhabits a small geographic range, found only around Tasmania, south of the Australian mainland, hence oceanic changes such as ongoing increases in sea surface temperatures (SSTs), and altered irradiance regimes may limit recruitment of the early microscopic life stages in the future. Our findings provide optimised culture conditions for aquaculture and information to predict the future geographic range of L. corrugata under ocean global change.

     

Photosynthetic characteristics of charophytes from tropical lotic ecosystems

Responses of photosynthetic rates, determined by oxygen evolution using the light and dark bottles technique, to different temperatures, irradiances, pH, and diurnal rhythm were analyzed under laboratory conditions in four charophyte species (Chara braunii Gmelin, C. guairensis R. Bicudo, Nitella subglomerata A. Braun and Nitella sp.) from lotic habitats in southeastern Brazil. Parameters derived from the photosynthesis versus irradiance curves indicated affinity to low irradiances for all algae tested. Some degree of photoinhibition, [β= ‐(0.30–0.13) mg O2 g^?1 dry weight Ir¹ (μmol photons m^?2 s^?1)^?1], low light compensation points (I_c= 4–20 μmol photons m^?2 s^?1) were found for all species analyzed, as well as low values of light saturation parameter (I_k) and saturation (I_s) 29–130 and 92–169 μmol photons m^?2 s^?1, respectively. Photoacclimation was observed in two populations of N. subglomerata collected from sites with different irradiances, consisting of variations in photosynthetic parameters (higher values of a, and lower of I_k and maximum photosynthetic rate, P_max, in the population under lower irradiance). The highest photosynthetic rates for Chara species were observed at 10–15°C, while for Nitella the highest photosynthetic rate was observed at 20–25°C, despite the lack of significant differences among most levels tested. Rates of dark respiration significantly increase with temperature, with the highest values at 25°C. The results from pH experiments showed highest photosynthetic rates under pH 4.0 for all algae, suggesting higher affinity for inorganic carbon in the form of carbon dioxide, except in one population of N. subglomerata, with similar rates under the three levels, suggesting indistinct use of bicarbonate and carbon dioxide. Diurnal changes in photosynthetic rates revealed a general pattern for most algae tested, which was characterized by two peaks: the first (higher) during the morning (07.00–11.00) and the second (lower) in the afternoon (14.00–17.00). This suggests an endogenous rhythm determining the daily variations in photosynthetic rates.     

Light and temperature effects on photosynthetic activity of E ucheuma denticulatum and K appaphycus alvarezii (brown and green color morphotypes) from Sulawesi Utara,Indonesia

Knowledge concerning the effects of several abiotic factors on the physiology of carrageenophytes is essential both in ecological and economic standpoints, to ensure their sufficient supply for the sustainability of seaweed‐based industries. This paper presents the photosynthetic characteristics of farmed carrageenophytes, E ucheuma denticulatum and K appaphycus alvarezii [brown (BRN) and green (GRN) color morphotypes] from Sulawesi Utara (Sulawesi Island), Indonesia, as determined by examining their photosynthetic response across different temperatures and irradiances using dissolved oxygen measurements and pulse‐amplitude modulated fluorometer. Net photosynthesis–irradiance ( P – E ) curves at 26°C revealed that net photosynthetic rates of the three seaweeds gradually increased until the estimated saturation irradiances ( E _k ) of 58 μmol photons m^{? 2} s^?1 (49–68 μmol photons m^{? 2} s^?1, 95% Bayesian prediction intervals; BPI) for E . denticulatum, and 158 and 143 μmol photons m^{? 2} s^?1 (134–185 and 99–203 μmol photons m^{? 2} s^?1, 95% BPI) for BRN and GRN K . alvarezii, respectively; and that no photoinhibition was observed at the highest irradiance of 1000 μmol photons m^{? 2} s^?1. All seaweed samples exhibited photosynthetic tolerance to high PAR as shown by their recovery in maximum quantum yields (F_v / F_m ) following chronic exposures; as well as tolerance over a broad range of temperature, which is from 19 to 33°C for E . denticulatum, 20–29°C for BRN K . alvarezii, and 17–32°C for GRN K . alvarezii. Temperature responses of these carrageenophytes indicated that they were well‐adapted to the annual seawater temperatures in the cultivation site; however, they are also likely close to threshold levels for thermal inhibition, given the decline in F_v / F_m above 30°C.     

SHORT‐TERM EFFECT OF TEMPERATURE ON THE PHOTOKINETICS OF MICROALGAE FROM THE SURFACE LAYERS OF ANTARCTIC PACK ICE1

Microalgae growing within brine channels (85 psu salinity) of the surface ice layers of Antarctic pack ice showed considerable photosynthetic tolerance to the extreme environmental condition. Brine microalgae exposed to temperatures above ?5°C and at irradiances up to 350 μmol photons·m^?2·s^?1 showed no photosynthetic damage or limitations. Photosynthesis was limited (but not photoinhibited) when brine microalgae were exposed to ?10°C, provided the irradiance remained under 50 μmol photons·m^?2·s^?1. The highest level of photosynthetic activity (maximum relative electron transport rate [rETR_max]) in brine microalgae growing within the surface layer of sea ice was at approximately 18 μmol electrons·m^?2·s^?1, which occurred at ?1.8°C. Effective quantum yield of PSII and rETR_max of the halotolerant brine microalgae exhibited a temperature‐dependent pattern, where both parameters were higher at ?1.8°C and lower at ?10°C. Relative ETR_max at temperatures above ?5°C were stable across a wide range of irradiance.     

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.     

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.     

Photosynthetic performance at low temperature of Bouteloua gracilis Lag., a high-altitude C4 grass from the Rocky Mountains, USA

The mechanisms controlling the photosynthetic performance of C₄ plants at low temperature were investigated using ecotypes of Bouteloua gracilis Lag. from high (3000 m) and low (1500 m) elevation sites in the Rocky Mountains of Colorado. Plants were grown in controlled‐environment cabinets at a photon flux density of 700 μ mol m^?2 s^?1 and day/night temperatures of 26/16 °C or 14/7 °C. The thermal response of the net CO₂ assimilation rate (A) was evaluated using leaf gas‐exchange analysis and activity assays of ribulose‐1,5‐bisphosphate carboxylase/oxygenase (Rubisco), phosphoenolpyruvate carboxylase (PEPCase) and pyruvate,orthophosphate dikinase (PPDK). In both ecotypes, a reduction in measurement temperature caused the CO₂‐saturated rate of photosynthesis to decline to a greater degree than the initial slope of A versus the intercellular CO₂ response, thereby reducing the photosynthetic CO₂ saturation point. As a consequence, A in normal air was CO₂‐saturated at sub‐optimal temperatures. Ecotypic variation was low when grown at 26/16 °C, with the major difference between the ecotypes being that the low‐elevation plants had higher A; however, the ecotypes responded differently when grown at cool temperature. At temperatures below the thermal optimum, A in high‐elevation plants grown at 14/7 °C was enhanced relative to plants grown at 26/16 °C, while A in low‐elevation plants grown at 14/7 °C was reduced compared to 26/16 °C‐grown plants. Photoinhibition at low growth temperature was minor in both ecotypes as indicated by small reductions in dark‐adapted F_v/F_m. In both ecotypes, the activity of Rubisco was equivalent to A below 17 °C but well in excess of A above 25 °C. Activities of PEPCase and PPDK responded to temperature in a similar proportion relative to Rubisco, and showed no evidence for dissociation that would cause them to become principal limitations at low temperature. Because of the similar temperature response of Rubisco and A, we propose that Rubisco is a major limitation on C₄ photosynthesis in B. gracilis below 17 °C. Based on these results and for theoretical reasons associated with how C₄ plants use Rubisco, we further suggest that Rubisco capacity may be a widespread limitation upon C₄ photosynthesis at low temperature.     

Photosynthetic performance and resistance to photoinhibition of Zea mays L. leaves grown at sub-optimal temperature

The performance of the photosynthetic apparatus was examined in the third leaves of Zea mays L. seedlings grown at near-optimal (25 °C) or at suboptimal (15 °C) temperature by measuring chlorophyll (ChI) a fluorescence parameters and oxygen evolution in different temperature and light conditions. In leaf tissue grown at 25 and 15 °C, the quantum yield of PSII electron transport (ψ_PSII) and the rate of O₂ evolution decreased with decreasing temperature (from 25 to 4 °C) at a photon flux density of 125 μmol m^?2 s^?1. In leaves grown at 25 °C, the decrease of ψ_PSII correlated with a decrease of photochemical ChI fluorescence quenching (q_p), whereas in leaves crown at 15 °C q_p was largely insensitive to the temperature decrease. Compared with leaves grown at 25 °C, leaves grown at 15 °C were also able to maintain a higher fraction of oxidized to reduced Q_A (greater q_p) at high photon flux densities (up to 2000 μmol m^?2 s^?1), particularly when the measurements were performed at high temperature (25 °C). With decreasing temperature and/or increasing light intensity, leaves grown at 15 °C exhibited a substantial quenching of the dark level of fluorescence F₀ (q₀) whereas this type of quenching was virtually absent in leaves grown at 25 °C. Furthermore, leaves grown at 15 °C were able to recover faster from photo inhibition of photosynthesis after a photoinhibitory treatment (1200 μmol m^?2 s^?1 at 25, 15 or 6 °C for 8 h) than leaves grown at 25 °C. The results suggest that, in spite of having a low photosynthetic capacity, Z. mays leaves grown at sub optimal temperature possess efficient mechanisms of energy dissipation which enable them to cope better with photoinhibition than leaves grown at near-optimal temperature. It is suggested that the resistance of Z. mays leaves grown at 15 °C to photoinhibition is related to the higher content of carotenoids of the xanthophyll cycle (violaxanthin + antheraxanthin + zeaxanthin) measured in these leaves than in leaves grown at 25 °C.     

PRODUCTIVITY OF THE FILAMENTOUS ALGA PITHOPHORA OEDOGONIA (CHLOROPHYTA) IN SURREY LAKE,INDIANA1

Biomass, akinete numbers, net photosynthesis, and respiration of Pithophora oedogonia were monitored over two growing seasons in shallow Surrey Lake, Indiana. Low rates of photosynthesis occurred from late fall to early spring and increased to maximum levels in late spring to summer (29–39 mgO₂·g^?1 dry wt·h^?1). Areal biomass increased following the rise in photosynthesis and peaked in autumn (163–206g dry wt·m^?2). Photosynthetic rates were directly correlated with temperature, nitrogen, and phosphorus over the entire annual cycle and during the growing season. Differences in photosynthetic activity and biomass between the two growing seasons (1980 and 1981) were apparently related to higher, early spring temperatures and higher levels of NO₃-N and PO₄-P in 1981. Laboratory investigations of temperature and light effects on Pithophora photosynthesis and respiration indicated that these processes were severely inhibited below 15°C. The highest P_max value occurred at 35°C (0.602 μmol O₂·mg^?1 chl a·min^?1). Rates of dark respiration did not increase above 25°C thus contributing to a favorable balance of photosynthetic production to respiratory utilization at high temperatures. Light was most efficiently utilized at 15°C as indicated by minimum values of I_k(47 μE·m^?2·s^?1) and I_c (6 μE·m^?2·s^?1). Comparison of P. oedogonia and Cladophora glomerata indicated that the former was more tolerant of temperatures above 30°C. Pithophora's tolerance of high temperature and efficient use of low light intensity appear to be adaptive to conditions found within the dense, floating algal mats and the shallow littoral areas inhabited by this filamentous alga.