List of members August, 1962

We investigated the acclimation of Chondrus crispus to growth at 5°C and 20°C in the laboratory. We were specifically interested in the responses of light-limited photosynthesis to temperature and the effects of short-term thermal changes (of the order of minutes). Thermal acclimation to constant temperatures over 3–4 weeks had significant effects on the light-use characteristics of this species such that in comparison with those grown at 5°C, 20°C-grown plants had higher concentrations of chlorophyll a and total phycobilins, which were associated with larger photosynthetic unit sizes. Plants grown at the higher temperature had greater photosynthetic efficiencies (α) and higher rates of light-limited photosynthesis at a given photon flux density than did plants acclimated to 5°C. Plants acclimated to 20°C were less sensitive to short-term temperature changes than were 5°C-acclimated plants. These results are discussed in terms of (1) the effects of growth temperature on light harvesting and (2) the implications of exposure to constant temperature for short-term thermal responses.     

An analysis of photosynthetic response and adaptation to temperature in higher plants: temperature acclimation in the desert evergreen Nerium oleander L*

Abstract. Factors underlying the process of photosynthetic acclimation to temperature were investigated for the shrub Nerium oleander L. Ramets of a single clone were grown under day/night temperature regimes of 20°C/15°C or 45°C/32°C. Plants grown at the lower temperature regime possessed rates of photosynthesis twice that of the high-temperature grown plants when CO₂ fixation was measured at 20°C. In contrast, the plants grown at the high-temperature regime had twice the rate of CO₂ fixation of the 20°C/l 5°C-grown plants at a measurement temperature of 45° C. It was determined that the ability to acclimate to changes in temperature regime was present in fully mature leaves. A reciprocal transfer of plants between the two growth regimes resulted in the appearance of the CO₂ fixation characteristics appropriate to the new growth temperature after 12–14d. The response of CO₂ fixation to light, temperature, and CO₂ partial pressure and the temperature responses of soluble and membrane-bound photosynthetic enzyme systems were analysed to determine which components might be responsible for the superior photosynthetic performance of the 20°C/I5°C-grown plants at 20°C, and the enhanced high-temperature stability of the 45°C/32°C plants. The measured photosynthetic capacity of the 20°C/15°C plants could not be attributed to gross morphological, stomatal, or other physical changes, or to a general increase in the concentration of components of the photosynthetic process. Only a single enzyme, Fru-P₂ phosphatase, was affected to an extent similar to that of photosynthesis. The enhanced thermal stability of the 45°C/32°C plants may be attributed primarily to an enhanced stability of the chloroplast membrane-bound enzymatic activities and the stability of the photosynthetic carbon metabolism enzymes which require lighl for activation.     

The after-effects of temperature and irradiance during early growth of winter oilseed rape (Brassica napus L. var. oleifera, cv. Górczański) seedlings on the progress of their cold acclimation

Experiments performed under controlled conditions showed that level of PPFD (photosynthetic photon flux density) during early seedlings growth (preceding cold acclimation at +2 °C) was not the key factor for the development of frost resistance. It did not modify the beneficial effects of prehardening (Rapacz 1997, in this issue) at moderately low (+12 °C) day temperature. Now I have shown that the increase of PPFD may replace to some extent prehardening in the development of frost resistance. It was particularly seen in non-prehardened plants, which had been grown under warm-day (+20 °C) conditions. Prehardening performed under controlled conditions, as well as seedlings growth under natural autumn conditions in the field, allowed to maintain a high net-photosynthesis rate at chilling temperatures. A net-photosynthesis rate during cold acclimation at +2 °C corresponded well with higher frost resistance. As a result, seedlings non subjected to prehardening and grown before cold acclimation under low PPFD acclimated better, if the cold treatment was applied only at nights (+20/2 °C day/night). Only under such conditions the photosynthetic rate was sufficiently high to allow plants to reach a higher level of frost resistance. All other plants acclimated better when they were exposed to the hardening temperature continuously during days and nights (+2/2 °C day/night).     

Photosynthetic capacity and temperature responses of photosynthesis of rubber trees (Hevea brasiliensis Müll. Arg.) acclimate to changes in ambient temperatures

The aim of this study was to assess the temperature response of photosynthesis in rubber trees (Hevea brasiliensis Müll. Arg.) to provide data for process-based growth modeling, and to test whether photosynthetic capacity and temperature response of photosynthesis acclimates to changes in ambient temperature. Net CO₂ assimilation rate (A) was measured in rubber saplings grown in a nursery or in growth chambers at 18 and 28°C. The temperature response of A was measured from 9 to 45°C and the data were fitted to an empirical model. Photosynthetic capacity (maximal carboxylation rate, V _cmax, and maximal light driven electron flux, J _max) of plants acclimated to 18 and 28°C were estimated by fitting a biochemical photosynthesis model to the CO₂ response curves (A–C _i curves) at six temperatures: 15, 22, 28, 32, 36 and 40°C. The optimal temperature for A (T _opt) was much lower in plants grown at 18°C compared to 28°C and nursery. Net CO₂ assimilation rate at optimal temperature (A _opt), V _cmax and J _max at a reference temperature of 25°C (V _cmax25 and J _max25) as well as activation energy of V _cmax and J _max (E _aV and E _aJ) decreased in individuals acclimated to 18°C. The optimal temperature for V _cmax and J _max could not be clearly defined from our response curves, as they always were above 36°C and not far from 40°C. The ratio J _max25/V _cmax25 was larger in plants acclimated to 18°C. Less nitrogen was present and photosynthetic nitrogen use efficiency (V _cmax25/N _a) was smaller in leaves acclimated to 18°C. These results indicate that rubber saplings acclimated their photosynthetic characteristics in response to growth temperature, and that higher temperatures resulted in an enhanced photosynthetic capacity in the leaves, as well as larger activation energy for photosynthesis.     

General introduction to the lists of threatened biotopes,flora and fauna of the trilateral Wadden Sea Area (red data book)

The effect of the acclimation temperature on the temperature tolerance ofPorphyra leucosticta, and on the temperature requirements for growth and survival ofEnteromorpha linza was determined under laboratory conditions. Thalli ofP. leucosticta (blade or Conchocelis phases), acclimated to twenty-five degrees, survived up to 30°C, i.e. 2°C more than those acclimated to 15°C which survived up to 28°C. Lower temperature tolerance of bothPorphyra phases that were acclimated to 15°C was −1°C after an 8-week exposure time at the experimental temperatures. The upper temperature tolerance ofE. linza also increased by 2°C, i.e. from 31 to 33°C, when it was acclimated to 30°C instead of 15°C. The lower temperature tolerance increased from 1 to −1°C, when it was acclimated to 5°C instead of 15°C.E. linza thalli acclimated for 4 weeks to 5 or 10°C reached their maximum growth at 15°C, i.e. at a 5°C lower temperature than those acclimated to 15 or 30°C. These thalli achieved higher growth rates in percent of maximal growth at low temperatures than those acclimated to 15 or 30°C. Thalli acclimated for 1 week to 5°C reached their maximum growth rate at 20°C and achieved growth rates at low temperatures similar to those recorded for thalli acclimated to 15°C. Thalli ofE. linza acclimated for 4 weeks to 5°C lost this acclimation after being post-cultivated for the same period at 15°C. That was not the case with thalli acclimated for 8 weeks to 5°C and post-acclimated for 4 weeks to 15°C. These thalli displayed similar growth patterns at 10–25°C, while a decline of growth rate was observed at 5 or 30°C. The significance of the acclimation potential ofE. linza with regard to its seasonality in the Gulf of Thessaloniki, and its distribution in the N Atlantic, is also discussed.     

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.     

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.     

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.     

Sub-lethal temperature thresholds indicate acclimation and physiological limits in brook trout Salvelinus fontinalis

The upper thermal tolerance of brook trout Salvelinus fontinalis was estimated using critical thermal maxima (CT_max) experiments on fish acclimated to temperatures that span the species' thermal range (5–25°C). The CT_max increased with acclimation temperature but plateaued in fish acclimated to 20, 23 and 25°C. Plasma lactate was highest, and the hepato-somatic index (I_H) was lowest at 23 and 25°C, which suggests additional metabolic costs at those acclimation temperatures. The results suggest that there is a sub-lethal threshold between 20 and 23°C, beyond which the fish experience reduced physiological performance.     

Growth at Low Temperature Mimics High-Light Acclimation in Chlorella vulgaris

Structural and functional alterations to the photosynthetic apparatus after growth at low temperature (5[deg]C) were investigated in the green alga Chlorella vulgaris Beijer. Cells grown at 5[deg]C had a 2-fold higher ratio of chlorophyll a/b, 5-fold lower chlorophyll content, and an increased xanthophyll content compared to cells grown at 27[deg]C even though growth irradiance was kept constant at 150 [mu]mol m-2 s-1. Concomitant with the increase in the chlorophyll a/b ratio was a lower abundance of light-harvesting polypeptides in 5[deg]C-grown cells as observed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and confirmed by western blotting.The differences in pigment composition were found to be alleviated within 12 h of transferring 5[deg]C-grown cells to 27[deg]C. Furthermore, exposure of 5[deg]C-grown cells to a 30-fold lower growth irradiance (5 [mu]mol m-2 s-1) resulted in pigment content and composition similar to that in cells grown at 27[deg]C and 150 [mu]mol m-2 s-1. Although both cell types exhibited similar measuring-temperature effects on CO2-saturated O2 evolution, 5[deg]C-grown cells exhibited light-saturated rates of O2 evolution that were 2.8-and 3.9-fold higher than 27[deg]C-grown cells measured at 27[deg]C and 5[deg]C, respectively. Steady-state chlorophyll a fluorescence indicated that the yield of photosystem II electron transport of 5[deg]C-grown cells was less temperature sensitive than that of 27[deg]C-grown cells. This appears to be due to an increased capacity to keep the primary, stable quinone electron acceptor of photosystem II (QA) oxidized at low temperature in 5[deg]C- compared with 27[deg]C-grown cells regardless of irradiance. We conclude that Chlorella acclimated to low temperature adjusts its photosynthetic apparatus in response to the excitation pressure on photosystem II and not to the absolute external irradiance. We suggest that the redox state of QA may act as a signal for this photosynthetic acclimation to low temperature in Chlorella.     

Acclimation of chlorophyll biosynthetic reactions to temperature stress in cucumber (Cucumis sativus L.)

The adaptive responses of the greening process of plants to temperature stress were studied in cucumber (Cucumis sativus L. cv. Poinsette) seedlings grown at ambient (25 °C), low (7 °C) and high (42 °C) temperatures. Plastids isolated from these seedlings were incubated at different temperatures and the net syntheses of various tetrapyrroles were monitored. In plastids isolated from control seedlings grown at 25 °C, the optimum temperature for synthesis of Mg-protoporphyrin IX monoester or protochlorophyllide was 35 °C. Temperature maxima for Mg-protoporphyrin IX monoester and protochlorophyllide syntheses were shifted to 30 °C in chill-stressed seedlings. The net synthesis of total tetrapyrroles was severely reduced in heat-stressed seedlings and the optimum temperature for Mg-protoporphyrin IX monoester or protochlorophyllide synthesis shifted slightly towards higher temperatures, i.e. a broader peak was observed. To further study the temperature acclimation of seedlings with respect to the greening process, tetrapyrrole biosynthesis was monitored at 25 °C after pre-heating the plastids (28–70 °C) isolated from control, chill- and heat-stressed seedlings. In comparison to 28 °C-pre-heated plastids the percent inhibition of protochlorophyllide synthesis in 40 °C-pre-heated plastids was higher than for the control (25 °C-grown) in chill-stressed seedlings and lower than for the control in heat-stressed seedlings. Maximum synthesis of total tetrapyrroles and protoporphyrin IX was observed when chloroplasts were heated at 50 °C, which was probably due to heat-induced activation of the enzymes involved in protoporphyrin IX synthesis. Prominent shoulders towards lower or higher temperatures were seen in chill-stressed or heat-stressed seedlings, respectively. The shift in optimum temperature for tetrapyrrole biosynthesis in chill- and heat-stressed seedlings was probably due to acclimation of membranes possibly undergoing desaturation or saturation of membrane lipids. Proteins synthesized in response to temperature-stress may also play an important role in conferring stress-tolerance in plants. Received: 8 October 1998 / Accepted: 19 November 1998     

Thermotolerance of the photosynthetic light reactions in two <Emphasis Type="Italic">Phaseolus</Emphasis> species: a comparative study

The common bean (Phaseolus vulgaris L.) is sensitive to high temperature, while an ecologically contrasting species (Phaseolus acutifolius A. Gray) is cultivated successfully in hot environments. In this study, the two bean species were respectively acclimated to a control temperature of 25 °C and a moderately elevated temperature of 35 °C in order to compare the thermotolerance capabilities of their photosynthetic light reactions. Growth at 35 °C appeared to have no obvious adverse effect on the photosynthetic activities of the two beans, but changed their thermotolerance. After a short period of heat shock (40 °C for up to 4 h), the photosynthetic activities of 25 °C-grown P. vulgaris declined more severely than those of P. acutifolius grown at 25 °C, implying that the basal thermotolerance of P. vulgaris is inferior to that of P. acutifolius. But after acclimating to 35 °C, the thermotolerances of the two species were both greatly enhanced to about the same level, clearly demonstrating the induction of acquired thermotolerance in their chloroplasts, and P. vulgaris could be as good as P. acutifolius. Temperature acclimation also changed plants’ resistance to photoinhibition in a manner similar to those toward heat stress. In addition, acquisition of tolerance to heat and strong irradiance would reduce the dependency of the two beans on xanthophyll pigments to dissipate heat, and also seemed irrelevant to the agents with antioxidant activities such as SOD.     

Temperature requirements ofScytosiphon lomentaria (Scytosiphonales,Phaeophyta) from the Gulf of Thessaloniki,Greece, in relation to geographic distribution

Temperature requirements for growth, reproduction and formation of macrothalli of a day-neutral strain ofScytosiphon lomentaria from the Gulf of Thessaloniki were experimentally determined and correlated with the geographic distribution in the North Atlantic Ocean. The microthallus grew in a wider temperature interval and better at higher temperatures than did the macrothallus. Germlings acclimated to 5 or 15°C grew sufficiently (>20% of maximum rate) and developed into macrothalli at 5–25°C and 5–27°C. Macrothalli acclimated to 10 or 15°C grew sufficiently at 5–20°C. Macrothalli acclimated to 15°C survived at −1°C and reproduced at 5 to 23°C. Regardless of the acclimation temperature, germlings and macrothalli grew optimally (>80% of maximum rate) at 15–25°C and at 10–15°C. The experimental data explain only the southern distribution boundary ofScytosiphon in the North Atlantic. This boundary is composite in nature: on the European coasts it is a growth boundary, whereas on the American coasts it is a lethal one.     

Photosynthesis of temperate Eucalyptus globulus trees outside their native range has limited adjustment to elevated CO2 and climate warming

Eucalyptus species are grown widely outside of their native ranges in plantations on all vegetated continents of the world. We predicted that such a plantation species would show high potential for acclimation of photosynthetic traits across a wide range of growth conditions, including elevated [CO₂] and climate warming. To test this prediction, we planted temperate Eucalyptus globulus Labill. seedlings in climate‐controlled chambers in the field located >700 km closer to the equator than the nearest natural occurrence of this species. Trees were grown in a complete factorial combination of elevated CO₂ concentration (eC; ambient [CO₂] +240 ppm) and air warming treatments (eT; ambient +3 °C) for 15 months until they reached ca. 10 m height. There was little acclimation of photosynthetic capacity to eC and hence the CO₂‐induced photosynthetic enhancement was large (ca. 50%) in this treatment during summer. The warming treatment significantly increased rates of both carboxylation capacity (V_cmax) and electron transport (J_max) (measured at a common temperature of 25 °C) during winter, but decreased them significantly by 20–30% in summer. The photosynthetic CO₂ compensation point in the absence of dark respiration (Γ*) was relatively less sensitive to temperature in this temperate eucalypt species than for warm‐season tobacco. The temperature optima for photosynthesis and J_max significantly changed by about 6 °C between winter and summer, but without further adjustment from early to late summer. These results suggest that there is an upper limit for the photosynthetic capacity of E. globulus ssp. globulus outside its native range to acclimate to growth temperatures above 25 °C. Limitations to temperature acclimation of photosynthesis in summer may be one factor that defines climate zones where E. globulus plantation productivity can be sustained under anticipated global environmental change.     

Thermal adaptation of Tetrahymena membranes with special reference to mitochondria II. Preferential interaction of cardiolipin with specific molecular species of phospholipid

A specific effect of cardiolipin on fluidity of mitochondrial membranes was demonstrated in Tetrahymena cells acclimated to a lower temperature in the previous report (Yamauchi, T., Ohki, K., Maruyama, H. and Nozawa, Y. (1981) Biochim. Biophys. Acta 649, 385–392). This study was further confirmed by the experiment using fluorescence polarization of 1,6-diphenyl-1,3,5-hexatriene (DPH). Anisotropy of DPH for microsomal and pellicular total lipids from Tetrahymena cells showed that membrane fluidity of these lipids increased gradually as the cells were incubated at 15°C after the shift down of growth temperature from 39°C. However, membrane fluidity of mitochondrial total lipids was kept constant up to 10 h. This finding is compatible with the result obtained using spin probe in the previous report. Additionally, the break-point temperature of DPH anisotropy was not changed in mitochondrial lipids whereas those temperatures in pellicular and microsomal lipids lowered during the incubation at 15°C. Interaction between cardiolipins and various phospholipids, which were isolated from Tetrahymena cells grown at 39°C or 15°C and synthesized chemically, was investigated extensively using a spin labeling technique. The addition of cardiolipins from Tetrahymena cells grown at either 39°C or 15°C did not change the membrane fluidity (measured at 15°C) of phosphatidylcholine from whole cells grown at 39°C. On the other hand, both cardiolipins of 39°C-grown and 15°C-grown cells decreased the membrane fluidity of phosphatidylcholine from Tetrahymena cells grown at 15°C. The same results were obtained for phosphatidylcholines of mitochondria and microsomes. Membrane fluidity of phosphatidylethanolamine, isolated from cells grown at 15°C, was reduced to a small extent by Tetrahymena cardiolipin whereas that of 39°C-grown cells was not changed. Representative molecular species of phosphatidylcholines of cells grown at 39°C and 15°C were synthesized chemically; 1-palmitoyl-2-oleoylphosphatidylcholine for 39°C-grown cells and dipalmitoleoylphosphatidylcholine for 15°C-grown ones. By the addition of Tetrahymena cardiolipin, the membrane fluidity of 1-palmitoyl-2-oleoylphosphatidylcholine was not changed but that of dipalmitoleoylphosphatidylcholine was decreased markedly. These phenomena were caused by Tetrahymena cardiolipin. However, bovine heart cardiolipin, which has a different composition of fatty acyl chains from the Tetrahymena one, exerted only a small effect.     

Increased acute thermal tolerance and little change to hematology following acclimation to warm water in juvenile Striped Bass,Morone saxatilis

Striped Bass naturally inhabit a wide range of temperatures, yet little is known about the processes that control their acute and chronic temperature limits. The objective of this study was to determine the effect of temperature acclimation on acute thermal maxima and physiology of juvenile Striped Bass. Juvenile fish were acclimated to 15, 25 or 30 °C for 4 weeks, then split into two sampling groups: post-acclimation and post-critical thermal maximum trials. We found that fish survived in all acclimation temperatures with little change to underlying hematology, and that critical thermal maximum (CT_max) increased with increasing acclimation temperature. At CT_max, fish acclimated to 30 °C had elevated plasma cortisol, lactate and potassium levels. These results suggest that, while 30 °C is likely to be outside their thermal optima, Striped Bass can survive at high temperatures. This ability to cope with warm temperatures may provide an advantage with increasing global temperatures.

     

ADAPTATION OF PHOTOSYNTHESIS IN LAMINARIA SACCHARINA (PHAEOPHYTA) TO CHANGES IN GROWTH TEMPERATURE1

The effect of growth temperature on photosynthetic metabolism was studied in the kelp Laminaria saccharina (L.) Lamour. Photosynthesis was subject to phenotypic adaptation, with almost constant photosynthetic rates being achieved at growth temperatures between 0 and 20° C. This response involved: (1) an inverse relationship between growth temperature and photosynthetic capacity, (2) a reduction in the Q₁₀ value for photosynthesis of L. saccharina grown at 0 and 5° C compared with 10, 15 and 20° C grown sporophytes, and (3) an acquired tolerance of photosynthesis to temperatures between 15–25° C (which inhibited photosynthesis in 0 and 5° C grown L. saccharina) in sporophytes grown at 10, 15 and 20° C. The physiological basis of these adaptations is discussed in terms of observed changes in activities and kinetics of the Calvin cycle enzyme ribulose-1, 5-bisphosphate carboxylase (oxygenase) and efficiency of light harvesting-electron transport systems.     

Thermal acclimation of locomotor performance in tadpoles of the frog Limnodynastes peronii

Previous analyses of thermal acclimation of locomotor performance in amphibians have only examined the adult life history stage and indicate that the locomotor system is unable to undergo acclimatory changes to temperature. In this study, we examined the ability of tadpoles of the striped marsh frog (Limnodynastes peronii) to acclimate their locomotor system by exposing them to either 10 °C or 24 °C for 6 weeks and testing their burst swimming performance at 10, 24, and 34 °C. At the test temperature of 10 °C, maximum velocity (U_max) of the 10 °C-acclimated tadpoles was 47% greater and maximum acceleration (A_max) 53% greater than the 24 °C-acclimated animals. At 24 °C, U_max was 16% greater in the 10 °C-acclimation group, while there was no significant difference in A_max or the time taken to reach U_max (T-U_max). At 34 °C, there was no difference between the acclimation groups in either U_max or A_max, however T-U_max was 36% faster in the 24 °C-acclimation group. This is the first study to report an amphibian (larva or adult) possessing the capacity to compensate for cool temperatures by thermal acclimation of locomotor performance. To determine whether acclimation period affected the magnitude of the acclimatory response, we also acclimated tadpoles of L. peronii to 10 °C for 8 months and compared their swimming performance with tadpoles acclimated to 10 °C for 6 weeks. At the test temperatures of 24 °C and 34 °C, U_max and A_max were significantly slower in the tadpoles acclimated to 10 °C for 8 months. At 10 °C, T-U_max was 40% faster in the 8-month group, while there were no differences in either U_max or A_max. Although locomotor performance was enhanced at 10 °C by a longer acclimation period, this was at the expense of performance at higher temperatures. Accepted: 25 June 1999     

Cold acclimation in warmer extended autumns impairs freezing tolerance of perennial ryegrass (Lolium perenne) and timothy (Phleum pratense)

The effect of variable autumn temperatures in combination with decreasing irradiance and daylength on photosynthesis, growth cessation and freezing tolerance was investigated in northern‐ and southern‐adapted populations of perennial ryegrass (Lolium perenne) and timothy (Phleum pratense) intended for use in regions at northern high latitudes. Plants were subjected to three different acclimation temperatures; 12, 6 and 9/3°C (day/night) for 4 weeks, followed by 1 week of cold acclimation at 2°C under natural light conditions. This experimental setup was repeated at three different periods during autumn with decreasing sums of irradiance and daylengths. Photoacclimation, leaf elongation and freezing tolerance were studied. The results showed that plants cold acclimated during the period with lowest irradiance and shortest day had lowest freezing tolerance, lowest photosynthetic activity, longest leaves and least biomass production. Higher acclimation temperature (12°C) resulted in lower freezing tolerance, lower photosynthetic activity, faster leaf elongation rate and higher biomass compared with the other temperatures. Photochemical mechanisms were predominant in photoacclimation. The northern‐adapted populations had a better freezing tolerance than the southern‐adapted except when grown during the late autumn period and at the highest temperature; then there were no differences between the populations. Our results indicate that the projected climate change in the north may reduce freezing tolerance in grasses as acclimation will take place at higher temperatures and shorter daylengths with lower irradiance.     

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.