Effects of temperature and ultraviolet radiation on microbial foodweb structure: potential responses to global change

1. A series of growth experiments were conducted with natural plankton communities from a lake and river in northern Quebec, to evaluate the response of microbial foodweb structure to changes in ambient temperature and solar ultraviolet radiation (UVR). 2. Bioassays were incubated for 6 days at two temperatures (10 and 20 °C) and three near-surface irradiance conditions [photosynthetically active radiation (PAR) + UVA + UVB, PAR + UVA, and PAR only). 3. The concentration of total bacteria showed no net response to temperature, but the percentage of actively respiring bacteria, as measured with the cellular redox probe 5-cyano-2,3-ditolyl tetrazolium chloride (CTC), was up to 57% higher at 20 °C relative to 10 °C. Chlorophyll a concentrations in the < 2 μm size fraction also reacted strongly to temperature, with a net increase of up to 61% over the temperature range of 10–20 °C. 4. The UVR effects were small or undetectable for most of the measured variables; however, the percentage of actively respiring bacteria was significantly inhibited in the presence of UVR at 20 °C, decreasing by 29–48% on day 6 in the lake experiments and by 59% on day 2 in one river experiment. 5. The results show differential sensitivity to temperature among organisms of microbial communities in subarctic freshwaters, and a resilience by the majority of micro-organisms to their present UVR conditions. Microbial foodwebs in northern freshwaters appear to be relatively unresponsive to short-term (days) changes in UVR. However, the observed responses to temperature suggest that climate change could influence community structure, with warmer temperatures favouring picoplanktonic phototrophs and heterotrophs, and a shift in nanoplankton species composition and size structure.     

Seed reserve-dependent growth responses to temperature and water potential in carrot (Daucus carota L.)

Both temperature and soil moisture vary greatly in the surface layers of the soil through which seedlings grow following germination. The work presented studied the impact of these environmental variables on post-germination carrot growth to nominal seedling emergence. The rapid pre-crook downward growth of both the hypocotyl and root was consistent with their requirement for establishment in soil drying from the surface. At all temperatures, both hypocotyl and root growth rates decreased as water stress increased and there was a very distinct temperature optimum that tended to occur at lower temperatures as water stress increased. A model based on the thermodynamics of reversible protein denaturation was adapted to include the effects of water potential in order to describe these growth rate responses. In general, the percentage of seedlings that reached the crook stage (start of upward hypocotyl growth) decreased at the extremes of the temperature range used and was progressively reduced by increasing water stress. A model was developed to describe this response based on the idea that each seedling within a population has lower and upper temperature thresholds and a water potential threshold which define the conditions within which it is able to grow. This threshold modelling approach which applies growth rates within a distribution of temperature and water potential thresholds could be used to simulate seedling growth by dividing time into suitable units.     

大肠杆菌生长温度、膜脂肪酸组成和压力抗性之间的关系

通过对大肠杆菌生长温度、膜脂肪酸组成和压力抗性之间关系研究发现,10℃培养,对数期细胞有最大的压力抗性,随着培养温度的升高直到4 5℃,压力抗性呈下降的趋势;相反,10℃培养,稳定期的细胞对压力最敏感,随着培养温度的升高,压力抗性呈增加趋势,30～37℃时达到最大,之后到4 5℃有下降。对数期和稳定期细胞膜脂中不饱和脂肪酸的组成随温度的上升而下降,这与从全细胞中抽提的磷脂的熔点密切相关。因此,对数期细胞压力抗性随着膜流动性的增大而升高;但稳定期细胞,膜流动性与压力抗性之间不存在简单的对应变化关系     

The Paramecium circadian clock: synchrony of changes in motility, membrane potential, cyclic AMP and cyclic GMP

The behavior of a ciliate protozoan, Paramecium, is known to represent the electrical state of the cell membrane, and regulation of the membrane potential and ciliary motion are known to involve cAMP and cGMP. The present study shows the synchrony of circadian changes in motility, resting membrane potential and cyclic nucleotides in P. multimicronucleatum. Using an automated system for tracking isolated single microorganisms, the isolated Paramecium cells are confirmed to swim fast and straight during the day (and subjective day) and slowly, with frequent turning, at night (and subjective night). The resting membrane potential is more negative during the day than at night. cAMP and cGMP concentrations oscillate in a manner, such that both cAMP and cGMP are higher during the day (or subjective day) than at night (or subjective night). The ratio of cGMP to cAMP during the light and dark cycle (LD) fluctuates, paralleling the fluctuation of the resting membrane potential measured during the LD. These results suggest that the Paramecium will provide an excellent model to explore daily and circadian orchestration of second messengers mediating signals from ambient light/dark cycles and circadian pacemaker to ion channels and cilia, directly involved in daily and circadian cellular outputs of resting membrane potential and motility. Accepted: 23 January 1997     

Relative contributions of leaf area ratio and net assimilation rate to change in growth rate depend on growth temperature: comparative analysis of subantarctic and alpine grasses

The present study shows that the relative contributions of leaf area ratio (LAR) and net assimilation rate (NAR) to variation among species in relative growth rate (RGR) depend on growth temperature. We grew three subantarctic and three alpine Poa species at daytime temperatures of 7, 12 and 17 degrees C, and analysed interspecific and temperature-related variation in RGRs by growth analysis. Variation in NAR accounted for most of the interspecific differences in RGR at low growth temperature, whereas variation in both NAR and LAR contributed strongly to interspecific differences in RGR at high growth temperature. For most species, the increase in RGR from 7 to 12 degrees C was attributable to an increase in LAR, whereas the increase in RGR from 12 to 17 degrees C was attributable to an increase in NAR. There were no differences between native subantarctic and alpine species in the plasticity of growth responses to temperature. However, Poa annua, a species introduced to the subantarctic, showed much greater growth plasticity than other species. There was little difference among species in tolerance of high-temperature extremes.     

Physiological responses of Opuntia ficus-indica to growth temperature

The influences of various day/night air temperatures on net CO₂ uptake and nocturnal acid accumulation were determined for Opuntia ficus-indica, complementing previous studies on the water relations and responses to photosynthetically active radiation (PAR) for this widely cultivated cactus. As for other Crassulacean acid metabolism (CAM) plants, net nocturnal CO₂ uptake had a relatively low optimal temperature, ranging from 11°C for plants grown at day/night air temperatures of 10°C/0°C to 23°C at 45°C/35°C. Stomatal opening, which occurred essentially only at night and was measured by changes in water vapor conductance, progressively decreased as the measurement temperature was raised. The CO₂ residual conductance, which describes chlorenchyma properties, had a temperature optimum a few degrees higher than the optimum for net CO₂ uptake at all growth temperatures. Nocturnal CO₂ uptake and acid accumulation summed over the whole night were maximal for growth temperatures near 25°C/15°C, CO₂ uptake decreasing more rapidly than acid accumulation as the growth temperature was raised. At day/night air temperatures that led to substantial nocturnal acid accumulation (25°C/15°C.). 90% saturation of acid accumulation required a higher total daily PAR than at non-optimal growth temperatures (10°C/0°C and 35°C/25°C). Also, the optimal temperature of net CO₂ uptake shifted downward when the plants were under drought conditions at all three growth temperatures tested, possibly reflecting an increased fractional importance of respiration at the higher temperatures during drought. Thus, water status, ambient PAR, and growth temperatures must all be considered when predicting the temperature response of gas exchange for O. ficus-indica and presumably for other CAM plants.     

Influence of the growth rate calculation on the relationship between growth rate and temperature

Three calculations of the growth rate (e.g. slope of a plot of the log10 of cfu ml-1 vs time, mum of the Gompertz equation and the reciprocal of time to obtain 108 cfu ml-1) were compared for Escherichia coli TG1 growing in tryptone soy broth medium at temperatures ranging from 14 to 39 degrees C. Up to now, the influence of using such different definitions on the relationship between microbial growth rate and temperature has never been investigated. In order to compare these calculation procedures, a dimensionless analysis based on the following normalized variables, mudim = mu/muopt and Tdim = [T-Tmin]/[Topt-Tmin], was used (Dantigny 1998). The influence of suboptimal temperatures on the growth rate was represented by means of a Belehràdek-type model based on a power function law: [mudim] = [Tdim]alpha. The influence of the different growth rate calculations on the model constants was assessed. Despite the great dependence of the raw growth rate values on the calculation procedure, the dimensionless analysis demonstrated that the alpha-value is independent of the growth rate definition. This result suggests that any definition for the growth rate can be utilized in studies aimed at determining the influence of temperature on microbial growth and highlights the interest of using dimensionless variables to overcome differences in the order of magnitude of the growth rate data and to avoid confusion between definitions.     

Life history responses of the cabbage beetle Colaphellus bowringi to temperature change

Temperature is considered one of the most important mediators of phenotypic plasticity in ectotherms. Here, we investigated life history traits of the cabbage beetle, Colaphellus bowringi Baly (Coleoptera: Chrysomelidae), at a wide range of temperatures (16, 19, 22, 24, 26 and 28°C). The larval and pupal times were significantly decreased with increasing rearing temperature and growth rate was positively correlated with temperature. However, the relationship between body size and rearing temperature in C. bowringi did not follow the temperature–size rule; both males and females reached the highest body weight at 19°C. Females were significantly larger than males at all temperatures. Male pupae lost significantly more weight at metamorphosis compared to females. However, diapausing males gained significantly higher weight after feeding compared to diapausing females at higher temperatures of 22, 24, 26 and 28°C. Body weight tended to decrease with increasing rearing temperature, whereas sexual size dimorphism (SSD) tended to increase with increasing rearing temperature; thus, Rensch's rule is upheld. The degree to which SSD changed with temperature varied with different development stages. SSD was lowest in pupae, highest in newly emerged adults and intermediate in diapausing adults.