Effect of temperature on photosynthesis of Miscanthus clones collected from different elevations

Six to twenty-eight months after transplanting, the net photosynthetic rate (PN) of Miscanthus leaves was measured at leaf temperatures between 18 to 37 °C. PN of clones from high mountain areas was more adaptable to low temperature, while that of clones from low mountain areas was more adaptable to high temperature. The clones from the lowlands were best adapted to both high and low temperatures. These characteristics lasted at least 28 months after transplanting. Thus Miscanthus had differentiated into different ecotypes to adapt to the thermal environments of different elevations. Comparison of the PN values measured in different seasons and durations after transplanting indicated that PN in Miscanthus could acclimate to environments with various temperature ranges resulting from elevation and seasonal changes. This revised version was published online in June 2006 with corrections to the Cover Date.     

Temperature-related differences in mitochondrial function among clones of the cladoceran Daphnia pulex

This study assessed the thermal sensitivity of mitochondrial respiration in the small crustacean Daphnia pulex. More specifically, we wanted to determine if clones that inhabit different latitudes and habitats showed differences in the thermal sensitivity of their mitochondrial function. The experimental design included two clones from temperate environments (Fence from Ontario and Hawrelak from Alberta) and two clones from subarctic environments (A24 from Manitoba and K154 from Quebec). The integrated mitochondrial function was measured with high-resolution respirometry following whole-animal permeabilization. Mitochondrial respiration was performed under six different temperatures (10, 15, 20, 25, 30, and 35 °C) in the clone Hawrelak and at two temperatures (10 and 20 °C) in the three other clones. In the clone Hawrelak, complexes I and II respiration showed higher sensitivity to temperature variation compared to complex IV respiration. Interestingly, the threshold plot showed no excess capacity of complex IV at 20 °C in this clone. The clones showed significant divergence in the ability to oxidize the complex I and complex IV substrates relative to the maximal oxidative phoshorylation capacity of mitochondria. More importantly, some of the clonal divergences were only detected under low assay temperatures, pointing toward the importance of this parameter in comparative studies. Future and more complex studies on clones from wider environmental gradients will help to resolve the link between mitochondrial function and adaptations of organisms to particular conditions, principally temperature.     

能源植物芒草研究进展与综合利用现状

芒草是一类多年生的C4草本植物,因其具有生物量大、纤维素含量高、灰分低、热值高、适应性强、生产成本低等诸多优点被认为是目前最具开发潜力的高产纤维类能源植物之一,因而成为国内外关注和研究的热点。综述了国内外能源芒草的研究进展与综合利用现状,并展望了今后的发展前景。     

Changes in Photosynthesis in Inbred Maize Lines with Different Degrees of Chilling Tolerance Grown at Optimum and Suboptimum Temperatures

The effects of growth temperature on changes in net photosynthetic rate (PN) and the chlorophyll fluorescence induction parameter Fv/Fm were investigated after cold stress in inbred maize lines with different degrees of cold tolerance. There was no significant difference between lines grown at optimum temperatures of 25/23 and 20/18 °C as regards PN and Fv/Fm determined at the growth temperature, but these parameters were lower for plants grown at a suboptimum temperature of 15/13 °C. After cold treatment, the decrease in PN was more pronounced in chilling-sensitive lines. The higher the growth temperature was, the more pronounced decrease occurred in PN and Fv/Fm. Thus at low growth temperature both damaging and adaptive processes occur.     

Hot spots of wheat yield decline with rising temperatures

Many of the irrigated spring wheat regions in the world are also regions with high poverty. The impacts of temperature increase on wheat yield in regions of high poverty are uncertain. A grain yield–temperature response function combined with a quantification of model uncertainty was constructed using a multimodel ensemble from two key irrigated spring wheat areas (India and Sudan) and applied to all irrigated spring wheat regions in the world. Southern Indian and southern Pakistani wheat‐growing regions with large yield reductions from increasing temperatures coincided with high poverty headcounts, indicating these areas as future food security ‘hot spots’. The multimodel simulations produced a linear absolute decline of yields with increasing temperature, with uncertainty varying with reference temperature at a location. As a consequence of the linear absolute yield decline, the relative yield reductions are larger in low‐yielding environments (e.g., high reference temperature areas in southern India, southern Pakistan and all Sudan wheat‐growing regions) and farmers in these regions will be hit hardest by increasing temperatures. However, as absolute yield declines are about the same in low‐ and high‐yielding regions, the contributed deficit to national production caused by increasing temperatures is higher in high‐yielding environments (e.g., northern India) because these environments contribute more to national wheat production. Although Sudan could potentially grow more wheat if irrigation is available, grain yields would be low due to high reference temperatures, with future increases in temperature further limiting production.     

Size variation in Brachionus plicatilis resting eggs

The effect of temperature and salinity on resting egg size of two Brachionus plicatilis (Rotifers) clones was investigated. Clones were selected according to their different behaviour in laying resting eggs: one clone ejects them, whereas they remain inside the females body in the other clone. The difference in resting eggs size between the two clones is noticeable, although the difference is not as great as that between female body size. An important temperature-salinity interaction on resting egg size has been observed. The general inverse relationship between size and temperature is only true at lower temperatures. At high temperatures size varies around the mean although could be greater than at intermediate temperatures. This is more evident at the intermediate salinity tested which is considered to be the closest to the optimum in our experiments. This pattern of variation suggests that mean size is bigger than expected, in relation to temperature and salinity, when these factors have values close to the extremes of their range, normally found in nature, and to which adaptative mechanisms can evolve. Size is bigger at the salinity — temperature low - low and high - high combinations which are the most commonly found in the temperate environments.     

Are Tropical Highland Frog Calls Cold–adapted? The Case of the Andean Frog Hyla labialis1

Across a wide range of temperatures established in the laboratory, we tape–recorded the advertisement calls of 76 freshly caught Hyla labialis males from three elevationally separated populations in the Eastern Andes of Colombia. Each male was tested once at a single temperature and returned to his capture site after measurement of his snout–vent length. We measured and averaged three characteristics of five to ten successive calls for each individual: number of pulses per call, pulse repetition rate, and call duration. We found that calling activity occurred within temperature ranges that overlapped among frogs from different elevations, but widened and shifted downward with increasing altitude of origin. Males from all sites called at temperatures higher, but not lower, than those naturally occurring during their nightly activity period. No decline in vocal performance was apparent when frogs extended their calling activity into the range of high temperatures selected for basking. Both snout–vent length and temperature affected pulse repetition rate and call duration, while the number of pulses per call was temperature–independent. Compared to the smaller males from lower elevations, the larger, high–mountain males had calls with significandy more pulses, a lower pulse repetition rate, and longer duration. Within each population, rising temperatures caused pulse repetition rate to increase and call duration to decrease significantly, whereas the number of pulses per call remained unchanged. Pulse repetition rate of highland males was the factor least affected by temperature, and it was less sensitive to night temperatures than to day temperatures. This, together with their capacity to call at low temperatures, suggests that highland frog calls are cold adapted.     

Metabolic and physiological responses of Mediterranean high‐mountain and alpine plants to combined abiotic stresses

High‐mountain areas provide excellent opportunities to study the effects of combined abiotic stresses on plant physiology given their variety of steep ecological gradients, low anthropogenic disturbance and remarkable levels of taxonomic diversity. Efficient photoprotective and antioxidant scavenging mechanisms are vital for survival in high‐mountain plants, having its altitudinal and seasonal variations determined by environmental or ontogenetic factors such as the decrease in mean temperatures and water availability. A number of stress indicators have been described in order to rapidly assess plant fitness in high‐mountain environments. For instance, carbon isotope (δ¹³C) and proline content as drought and temperature stress indicators, because of their link to water‐use efficiency and osmotic adjustment; photosynthetic pigments, related to phenology, nutrient status, light and temperature stress; and non‐structural carbohydrate accumulation in response to mild or brief drought conditions. The present review unveils the wide research opportunities available for the study of adaptive responses in high‐mountain plants via stress indicators, and calls attention to the substantial knowledge gap existing between alpine zones and other mountainous regions, such as Mediterranean high‐mountains. The aim is to grant a more holistic understanding of the physiological mechanisms driving plant life in high altitudes and improve the predictions of the effects of changing environments in these species and across ecological scales.     

The temperature dimension of the seed germination niche in fen wetlands

The seed germination niche partly determines adaptation, ecological breadth and geographic range in plant species. In temperate wetlands, environmental temperature is the chief regulator of germination timing, but the ecological significance of high and low temperatures during dormancy break and germination is still poorly understood. Our aim was to characterize the temperature dimension of the germination niche in mountain base-rich fens, determining (1) the effect of different temperatures on dormancy break and germination, and (2) whether different germination strategies may be identified at the species level. We conducted laboratory germination experiments with seeds of 15 species from these habitats, collected in 18 fen sites in the Cantabrian Mountains (Spain) for two consecutive years. In all the species, the seeds were totally or conditionally dormant at dispersal and stratification produced a significant increase of germination. In most cases, there was not an obligatory requirement for cold temperatures during dormancy break, since warm stratification promoted germination as well. Although the optimal germination thermoperiod was generally high (30/20 °C), most species could also germinate at lower temperatures after cold-stratification. We also identified a group of species associated to cold-water springs that germinated only at low temperatures. Our results demonstrate that dormancy break in mountain base-rich fens does not obligatorily depend on cold temperatures during overwintering. Furthermore, germination at cool temperatures may be more widespread in wetland habitats than previously thought. The existence of two distinctive germination strategies, ‘warm’ and ‘cool’, can potentially give rise to divergent species responses to climate change.     

Influence of Temperature and Floret Age on Nectar Secretion in Trifolium repens L.

The influence of temperature on nectar secretion in non-pollinatedflorets of Trifolium repens was investigated in growth chambersat 10, 14, 18 and 22°C. The effect of temperature on therate of nectar secretion was significant in all clones. Theoptimum temperature for secretion in three clones varied from10°C for a clone of Icelandic origin, to 18°C in a cloneselected from a Danish variety. Similarly, the average nectaryield varied significantly among clones of different geographicalorigin. One clone secreted two to four times more than othersat 10°C. The optimum day temperature for nectar secretionwas higher when the plants were exposed to low night temperature,presumably a result of decreased night respiration. Nectar accumulatedat the floret base until senescence. Evidence for reabsorptionof nectar was obtained in four clones. Sucrose, fructose andglucose were identified as the major sugars in the nectar. Highnight temperatures led to decreased sucrose percentage in favourof glucose and fructose. The frequency of new florets openingper day was not influenced by temperatures between 10 and 22°Cin one clone, whereas low temperatures significantly decreasedthe number of new florets in another. Few or no modified stomatawere observed in the epidermis of the nectary. The high variationwith respect to nectar secretion at low temperatures, alongwith the high heritability of this quality, suggests that breedingfor high nectar production at low temperature is plausible.The significance of nectar yield in pollination biology is discussed.Copyright1994, 1999 Academic Press Trifolium repens, white clover, nectar, temperature, floret age, flowering, nectary     

TEMPERATURE-DEPENDENT CHANGES IN COLONY SIZE OF THE FRESHWATER PENNATE DIATOM ASTERIONELLA FORMOSA (BACILLARIOPHYCEAE) AND THEIR POSSIBLE ECOLOGICAL IMPLICATIONS1

Changes in colony size (cell number per colony) of Asterionella Formosa Hass. were experimentally evaluated in relation to water temperature using two types of clones having colony sizes of four or eight cells. The clones were isolated from two different temperate freshwater lakes. Both clones showed the same general trend with changing temperature. Most of the colonies were normal in size at low temperatures, but colony size was twice as large at high temperatures. Variable colony sizes were present at low percentages. Colony separation occurred at the oldest connection within the colony after cell division. Culture experiments showed that the rates of specific growth and colony separation were balanced except for a rather short period of time when the temperature was changed. Optical and scanning electron micrography did not show any distinctive morphological structure at the point of connection except for porelli and mucilage pads. Seasonal changes in colony size of A. formosa observed in a freshwater lake are discussed based on these temperature results.     

Temperature-dependent differences in community structure of bacteria involved in degradation of petroleum hydrocarbons under sulfate-reducing conditions

Aim: The aim of this study was to characterize the microbial community involved in anaerobic degradation of petroleum hydrocarbon under low‐ and moderate‐temperature conditions. Methods and Results: Sulfate‐reducing enrichment cultures growing on crude oil and p‐xylene were established at low and moderate temperatures. Bacterial community structures of the cultures were characterized by 16S rRNA gene‐based analysis and organisms responsible for degradation of p‐xylene were investigated by analysis of the bamA gene, involved in anaerobic degradation of aromatic compounds. The PCR‐denaturing gradient gel electrophoresis analysis indicated significant differences in microbial community structures among the cultures, depending on the temperatures of incubation. Difference depending on the temperatures was also observed in the cloning analysis of the bamA gene performed on the p‐xylene‐degrading enrichment cultures. Majority of clones detected in the culture of moderate temperature were related to Desulfosarcina ovata, whereas more diverse bamA gene sequences were obtained from the culture incubated at low temperature. Conclusions: Temperature‐dependent differences in microbial community were demonstrated by the analyses of two genes. It was suggested that sulfate‐reducing bacteria of phylogenetically different groups might be involved in the degradation of petroleum hydrocarbons in different temperature environments. Significance and Impact of the Study: This study is the first report of p‐xylene‐degrading sulfate‐reducing enrichment culture at low temperature. The results of the experiments at low temperature were distinctly different from those reported in previous studies performed at moderate temperatures.     

Seed germination of high mountain Mediterranean species: altitudinal,interpopulation and interannual variability

The germination response of 20 species from high altitude Mediterranean climates, most of them rare endemics, was studied. Our main goal was to model the germination response of a complete set of Iberian high mountain species. The effect of temperature and other parameters, such as spatial and temporal short gradients, on germination were also evaluated. Some seed features (mass and size) were also related to the germination response. Finally, we tested the effect of cold-wet stratification pretreatment when germination was low under natural conditions. Seeds were collected at four locations from 1,900 to 2,400 m a.s.l. in the Sierra de Guadarrama (Spanish Central Range) over two consecutive growing seasons (2001–2002) and submitted to different temperatures and a constant photoperiod of 16 h light/8 h darkness. Most plants readily germinate without treatment, reaching an optimum at relatively high temperatures in contrast to lowland Mediterranean species. Seeds seem to be physiologically prepared for rapid germination even though these plants usually face very intense summer droughts after ripening and dispersal. Germination was also highly variable among altitudes, populations and years, but results were inconsistent among species. Such flexibility could be interpreted as an efficient survival strategy for species growing under unpredictable environments, such as the Mediterranean climate. Finally cold-wet stratification increased germination capacity in five of nine dormant species, as widely reported for many arctic, boreal and alpine species. In conclusion, high mountain Mediterranean species do not differ from alpine species except that a relatively high number of species are ready to germinate without any treatment.     

Hardening and Dehardening of Lolium perenne in Response to Fluctuating Temperatures

Hardening and dehardening responses of two contrasting varietiesof Lolium perenne, measured as LT50 estimates, were followedin fluctuating temperature environments. Unhardened seedlingswere exposed to hardening environments for 7, 14, and 21 d inall combinations of 2, 4, 6, 8 and 10 C with either high dayand low night temperatures or low day and high night temperatures.Seedlings hardened for 28 d at 2 C were exposed to dehardeningenvironments in all combinations of 4, 6, 8, 10, and 12 C withhigh day and low night temperatures. A low day, or night, temperature of 2 C in combination withany other temperature increased hardening compared with theconstant higher temperature. For Premo, a hardy variety, thisincrease was 3 C when night temperature was reduced from 10to 2 C in combination with a day temperature of 10 C. Similarly,a low night temperature reduced the dehardening response ofPremo to higher day temperatures. At 12 C this effect on LT60was greater than 2 C. Much smaller responses to daily periodsof low temperature were found for the less hardy variety, GrasslandsRuanui. During each 24-h period, exposures to 2 C of longer than 4h were required to achieve greater hardening than that achievedin continuous 10 C treatments. Hardiness was not improved furtherby exposures longer than 8 h. Responses to diurnal temperature fluctuations were discussedin relation to possible mechanisms and to changes in hardinessduring the winter under different weather systems. Lolium perenne, cold hardening, cold dehardening, diurnal temperature fluctuations, varieties     

Plasticity of growth rate and metabolism in Daphnia magna populations from different thermal habitats

The aim of this study was to evaluate the effect of temperature on growth and aerobic metabolism in clones of Daphnia magna from different thermal regimes. Growth rate (increment in size), somatic juvenile growth rate (increment in mass), and oxygen consumption were measured at 15 and 25 degrees C in 21 clones from one northern and two southern sites. There were no significant differences in body size and growth rate (increase in length) at both 15 and 25 degrees C among the three sites. Clones from southern site 2 had a higher mass increment than clones from the other two sites at both temperatures. Clone had a significant effect on growth (body length) and body size at both temperatures. As expected, age at maturity was lower at 25 degrees C (4.5 days) than at 15 degrees C, (11.6 days) and body sizes, after the release of the third clutch, were larger at 15 degrees C than at 25 degrees C. Northern clones had higher oxygen consumption rates and specific dynamic action (SDA) than southern clones at 15 degrees C. By contrast, southern clones from site 1 had a higher oxygen consumption and SDA than subarctic clones at 25 degrees C. Clones from southern site 2 had high oxygen consumption rates at both temperatures. Our results reveal important differences in metabolic rates among Daphnia from different thermal regimes, which were not always reflected in growth rate differences.     

Thermal constraints on embryonic development as a proximate cause for elevational range limits in two Mediterranean lacertid lizards

Local adaptation and range restrictions in alpine environments are central topics in biogeographic research with important implications for predicting impacts of global climate change on organisms. Temperature is strongly coupled to elevation and greatly affects life history traits of oviparous reptiles in mountain environments. Thus, species may encounter barriers for expanding their ranges if they are unable to adapt to the changing thermal conditions encountered along elevational gradients. We sought to determine whether thermal requirements for embryonic development provide a plausible explanation for elevational range limits of two species of lacertid lizards that have complementary elevational ranges in a Mediterranean mountain range (Psammodromus algirus is found at elevations below 1600 m and Iberolacerta cyreni is found at elevations above 1600 m). We combined experimental incubation of eggs in the laboratory with modelled estimates of nest temperature in the field. In both species, increasing temperature accelerated development and produced earlier hatching dates. The species associated with warmer environments (P. algirus) experienced an excessive hatching delay under the lowest incubation temperature. Moreover, newborns from eggs incubated at low temperatures showed poor body condition and very slow rates of postnatal growth. In contrast, eggs of the strictly alpine species I. cyreni exhibited shorter incubation periods than P. algirus that allowed hatching before the end of the active season even under low incubation temperatures. This was countered by lower reproductive success at higher temperatures, due to lower hatching rates and higher incidence of abnormal phenotypes. Elevational range limits of both species coincided well with threshold temperatures for deleterious effects on embryonic development. We suggest that incubation temperature is a major ecophysiological factor determining the elevational range limits of these oviparous lizards with predictable consequences for mountain distributions under future warmer climates.     

Aphid clonal resistance to a parasitoid fails under heat stress

Parasitoid virulence and host resistance are complex interactions depending on metabolic rate and cellular activity, which in aphids additionally implicate heritable secondary symbionts among the Enterobacteriaceae. As performance of the parasitoid, the aphid host and its symbionts may differentially respond to temperature, the success or failure of aphid parasitism is difficult to predict when temperature varies. We tested the hypothesis that resistance of the pea aphid Acyrthosiphon pisum to the parasitoid Aphidius ervi, which is linked to aphid secondary symbionts, may depend on temperature in several resistant and non-resistant aphid clonal lineages of different geographic origin and of known bacterial symbiosis, using experiments in controlled environments. Complete immunity to A. ervi at 20 degrees C in three different aphid clones whose symbiosis is characterized by the possession of Hamiltonella defensa reversed to high susceptibility at 25 degrees C and especially 30 degrees C, suggesting that the aphid's immune responses to the establishment and early development of the parasitoid is strongly reduced at moderately high temperatures. There was no evidence that a pea aphid control genotype that was susceptible to A. ervi at 20 degrees C could become more resistant as temperature increases, as has been suggested for insect fungal pathogens. By contrast, our results suggest that aphid clonal resistance to A. ervi and related parasitoids is characteristic of cool temperature conditions, similar to various other fitness attributes of aphids. Based on evidence that H. defensa symbionts characterized all three A. ervi resistant pea aphid clones studied, but was absent in control aphids that remained susceptible at all temperatures, we suggest that secondary symbiosis plays a key role in the heat sensitivity of aphid clonal resistance. Our study may also indicate that aphid natural control of variably susceptible host populations by aphid parasitoids is more likely at moderate to high temperatures.     

Heat tolerance,temperature acclimation,acute oxidative damage and canalization of haemoglobin expression in <Emphasis Type="Italic">Daphnia</Emphasis>

Daphnia is a widespread freshwater zooplankton species, which is both a classic and emerging new model for research in ecological physiology, ecotoxicology and evolutionary biology of adaptation to novel environments. Heat tolerance in Daphnia is known to depend both upon evolutionary history of a genotype and on individuals’ acclimation to elevated temperature and to correlate with the level of haemoglobin expression. We demonstrate the existence of north–south gradient of heat tolerance in North American D. pulex, which is not associated with any parallel changes in haemoglobin expression. Geographically distinct clones differ in the way their haemoglobin expression changes due to acclimation to a sub-stressful (28°C) temperature, but these changes are not correlated with the latitude of clones’ origin. Likewise, the effect of acclimation to sub-stressful temperature is independent from, and cannot be fully explained by, haemoglobin expression changes during acclimation. The degree of oxidative damage to haemoglobin, measured as the ratio of absorbance at 540:576 nm at the acclimation temperature, is a strong predictor of 28°C-acclimated Daphnia survival during an acute heat exposure. The comparison of haemoglobin expression in resistant and tolerant clones acclimated to different temperatures indicates that tolerant clones exhibit canalization of haemoglobin expression, possessing a high level of haemoglobin even at non-stressful temperatures. We discuss the evolutionary biology of adaptation and acclimation to elevated temperatures in an ecologically important component of freshwater ecosystems in the context of global climate change.     

Photosynthetic 14CO2 fixation products in altitudinal ecotypes of Trifolium repens L. with different temperature requirements

Summary Two Trifolium repens clones from natural meadows at 600 m and 2030 m above sea level, and with differing dependence on temperature of their rate of apparent photosynthesis, were grown under controlled environments. Radioactive products in detached leaves were examined after 20 and 40 s periods of steady state photosynthesis in ¹⁴CO₂ at 3° C and 24° C. Glycine and serine were hardly labeled at 3° C. At 24° C, the leaves of the alpine clone showed significantly, (P<0.025) more activity in these amino acids than those from the low altitude clone. It is suggested that the alpine clone has a higher photorespiration. This is supported by the labeling pattern of glucose, fructose, sucrose, and glucose-6-phosphate.The high altitude clone requires lower temperatures for photosynthesis than the low altitude clone. It is suggested, that this is caused by its higher photorespiration, which reduces net photosynthesis at high temperatures. The lower photorespiration activity of the low altitude clone can be interpreted as an adaptation to its warmer habitat.     

Variability of the clonal structure of Yersinia pseudotuberculosis population under different conditions

In a series of experiments the dynamics of the clonal structure of Y. pseudotuberculosis population was evaluated by cytopathogenicity in soil extract, as well as in associations with blue-green algae (cyanobacteria) and infusoria, under different temperature conditions. In all variants of experiments made at low environmental temperature (10 degrees C) a considerable part of Y. pseudotuberculosis clones (25-40%) was found to be cytopathogenic, while at 22 degrees C such clones were absent or had low cytopathogenicity. At the same time experiments made under the same temperature conditions (10 degrees C) showed the variability of the clonal structure of the bacterial population in different associations and sterile soil extract, as well as at different periods of the experiments. At low temperatures Y. pseudotuberculosis virulent (cytopathogenic) clones, in contrast to avirulent ones, were characterized by the presence of virulence plasmid p45, as well as high urease and catalase activity. The results of the experiments are discussed from the viewpoint of the clonal concept of bacterial populations and their pathogenicity.