共查询到20条相似文献,搜索用时 31 毫秒
1.
C4 plants are uncommon in cold environments and do not generally occur in the alpine tundra. In the White Mountains of California, however, the C4 grass Muhlenbergia richardsonis is common in the alpine zone at 3,300-3,800 m, with the highest population observed at 3,960 m (13,000 feet) above sea level. This is the highest reported C4 species in North America and is near the world altitude limit for C4 plants (4,000-4,500 m). Above 3,800 m, M. richardsonis is largely restricted to southern slope aspects, with greatest frequency on southeast-facing slopes. In open tundra, M. richardsonis formed prostrate mats with a mean height of 2.5 cm. Neighboring C3 grasses were two to three times taller. Because of its short stature, leaf temperature of M. richardsonis was greatly influenced by the boundary layer of the ground, rising over 20°C above air temperature in full sun and still air and over 10°C above air temperature in full sun and wind velocity of 1-4 m s-1. Thus, although air temperatures did not exceed 15°C, midday leaf temperatures of M. richardsonis were routinely between 25°C and 35°C, a range favorable to C4 photosynthesis. At night, leaf temperature of M. richardsonis was often 5-12°C below air temperature, resulting in regular exposure to subzero temperatures and frosting of the leaves. No visible injury was associated with exposure to freezing night temperatures. The presence of M. richardsonis in the alpine zone demonstrates that C4 plants can tolerate extreme cold during the growing season. The localization to microsites where leaf temperatures can exceed 25°C during the day, however, indicates that even when cold tolerant, C4 plants still require periods of high leaf temperature to remain competitive with C3 species. In this regard, the prostrate growth form of M. richardsonis compensates for the alpine climate by allowing sufficient heating of the leaf canopy during the day. 相似文献
2.
Bacterial biomass and functional diversity in four marine and four freshwater samples, collected from Resolute Bay, Nunavut, Canada, were studied using fluorescent nucleic-acid staining and sole-carbon-source utilization. Viable microbial counts using the LIVE/DEAD BacLight Viability Kit estimated viable marine bacterial numbers from 0.7 to 1.8᎒6 cells/l, which were lower than viable bacterial numbers in freshwater samples (2.1-9.9᎒6 cells/l) (RCBD-ANOVA). Calculations of the Shannon-Wiener diversity index and average well colour development were based on substrate utilization in ECO-Biolog plates incubated at 4°C and 20°C for 38 and 24 days, respectively. The Shannon-Wiener diversity of the marine water samples was significantly greater ( x H'=2.40ǂ.08, P <0.005; RCBD-ANOVA) than that of freshwater samples ( x H'=1.20ǂ.00, P <0.005; RCBD-ANOVA). Differences in microbial diversity between fresh and marine water samples at 4°C ( x 4°C =2.01) and 20°C (x20°C =2.31) were also detected by RCBD-ANOVA analysis. Interactions between water type and incubation temperature were not significant ( F =1.926, F c=5.12). Principal component analysis revealed differences in metabolic substrate utilization patterns and, consequently, the microbial diversity between water types and samples. 相似文献
3.
Underwater light field and phytoplankton absorbance in different surface water masses of the Atlantic sector of the Southern Ocean 总被引:1,自引:0,他引:1
Spectral water transparency and phytoplankton light absorbance were studied in the Atlantic sector of the Southern Ocean during the Southern Ocean JGOFS ANT XIII/2 cruise in early austral summer 1995/1996. The study area comprised three zones, which differed markedly with respect to their hydrographic and planktological characteristics: the Antarctic Polar Frontal Zone with adiatom bloom, the Antarctic Circumpolar Current outside frontal systems with phytoplankton-poor water and a higher flagellate abundance than in the other two areas, and the marginal ice zone with a Phaeocystis bloom. The influence of phytoplankton on spectral water transparency was assessed by two independent procedures: the pigment-specific beam absorption coefficient, aJ*[5], at all stations, as estimated by spectroscopy of in vivo light absorption of plankton on glass fibre filters, and the pigment-specific light attenuation, (kc[5]), as derived by regression analysis of spectral in situ vertical light attenuation coefficients in the sea against concomitant pigment concentrations. Values of aJ*[5] and vertical profiles of light attenuation by phytoplankton exhibited regional differences that corresponded with the three zones from which samples had been collected. These differences can be related to the specific characteristics of the three zones with respect to cell size distribution, pigment composition and biomass. The observed variations in aJ*[5] values should be considered when oceanic primary production is to be estimated by biooptical modelling. 相似文献
4.
Otolith growth and RNA/DNA ratios of larval stages of Notolepis coatsi, Gobionotothen gibberifrons and Trematomus scotti, three Antarctic fish, were studied during early 1998. RNA/DNA ratios were significantly different between the notothenioids and paralepidids (P<0.01), but similar among notothenioids (P>0.05). The ratios were independent of larval total length and water temperature. Recent otolith growth (based on the last five increments) and biochemical indices correlated slightly, but not significantly. N. coatsi inhabited deeper and colder waters of the Weddell Sea and showed less growth than the other species, which are associated with the Antarctic Peninsula. In all three species, some larvae had very good growth rates though most were rather poor. Recent growth indices might allow the detection and back-dating of growth changes in Antarctic larvae, and provide insight into a crucial yet poorly understood life-phase of these fish. 相似文献
5.
As part of our studies to examine the molecular basis of cold-adaptation, we have determined the kinetic properties, thermal stability and deduced amino acid sequence of the enzyme lactate dehydrogenase (LDH) from an Antarctic zoarcid fish, Lycodichthys dearborni. Unlike Antarctic notothenioid fish which are endemic to the Southern Ocean, zoarcid fish are cosmopolitan and have a substantially longer evolutionary history as a sub-order. The A4-LDH isoform was isolated and purified from the white muscle of L. dearborni. The kinetic parameters KmPYR and kcat were determined at temperatures from 0 to 25°C. KmPYR was substantially higher at low temperatures than those from Antarctic and temperate notothenioid fish, whereas kcat at these temperatures was essentially the same as those of the other fish LDH in this study. The sequence of L. dearborni A4-LDH was determined from cDNA derived from white muscle RNA and found to be similar to, but distinct from, the A4-LDH sequences of Antarctic notothenioid fish. Molecular modelling based on the structure of the A4-LDH from Pagothenia borchgrevinki suggested that three conservative amino acid changes within the core of the protein that are not directly part of the active site but which might nonetheless influence the active site, may be important in cold-adaptation in L. dearborni A4-LDH, and that several other changes on the surface of the protein might also play a role in cold-adaptation. 相似文献
6.
Primary production, light and vertical mixing in Potter Cove, a shallow bay in the maritime Antarctic 总被引:3,自引:1,他引:2
Phytoplankton photosynthesis was measured during spring-summer 1991-1992 in the inner and outer part of the shallow Potter Cove, King George Island. Strong winds characterise this area. Wind-induced turbulent mixing was quantified by means of the root-mean square expected vertical displacement depth of cells in the water column, Zt. The light attenuation coefficient was used as a measure of the influence of the large amount of terrigenous particles usually present in the water column; 1% light penetration ranged between 30 and 9 m, and between 30 and 15 m for the inner and outer cove, respectively. Obvious differences between photosynthetic capacity [P*max; averages 2.6 and 0.6 µg C (µg chlorophyll-a)-1 h-1] and photosynthetic efficiency {!*; 0.073 and 0.0018 µg C (µg chlorophyll-a)-1 h-1 [(µmol m-2 s-1)-1]} values were obtained for both sites during low mixing conditions (Zt from 10 to 20 m), while no differences were found for high mixing situations (Zt>20 m). This suggests different photoacclimation of phytoplankton responses, induced by modifications of the light field, which in turn are controlled by physical forcing. Our results suggest that although in experimental work P*max can be high, wind-induced mixing and low irradiance will prevent profuse phytoplankton development in the area. 相似文献
7.
A common cylindropuntia in the northwestern Sonoran Desert, Opuntia acanthocarpa, was investigated for the following hypotheses: its lower elevational limit is set by high temperatures, so its seedlings require nurse plants; its upper elevational limit is set by freezing; spine shading is the least at intermediate elevations; and changes in plant size and frequency with elevation reflect net CO2 uptake ability. For four elevations ranging from 230 m to 1,050 m, the mean height of O. acanthocarpa approximately doubled and its frequency increased 14-fold. Nurse plants were associated with only 4% of O. acanthocarpa less than 20 cm tall at the two lower elevations compared with 57% at 1,050 m, where putative freezing damage was especially noticeable, suggesting that nurse plants protect from low temperature damage. Spine shading of the stem doubled from the lowest to the highest elevation. Net CO2 uptake, which followed a Crassulacean acid metabolism pattern, was maximal at day/night air temperatures of 25/15°C and was halved by 4 weeks of drought and by reducing the photosynthetic photon flux from 30 to 12 mol m-2 day-1. The root system of O. acanthocarpa was shallow, with a mean depth of only 9 cm for the largest plants. Root growth was substantial and similar for plants at 25/15°C and 35/25°C, decreasing over 70-fold at 15/5°C and 45/35°C. Based on cellular uptake of the vital stain neutral red, neither roots nor stems tolerated tissue temperatures below -5°C for 1 h while both showed substantial high temperature acclimation, roots tolerating 1 h at 61°C and stems 1 h at 70°C for plants grown at 35/25°C. The increase in height and frequency of O. acanthocarpa with elevation apparently reflected both a greater ability for net CO2 uptake and greater root growth and hence water uptake. This species achieves its greatest ecological success at elevations where it becomes vulnerable to low temperature damage. 相似文献
8.
A full-bridge sensor system for characterising biosuspensions by impedance spectroscopy which avoids cross-sensitivity to temperature is presented. To record a large range of different kinds of cells, frequency is varied between 500 kHz and 50 MHz. The characteristic frequencies of the #-polarisation of animal cells (mouse), yeasts (Saccharomyces cerevisiae) and Escherichia coli bacteria are located in this range. The widespread applicability of this method is demonstrated by measurements on suspensions of different cells and the determination of concentration in a fermentation process. Furthermore, yeast suspensions are characterised at temperatures between T1=24°C and T2=36°C to evaluate the influence of temperature. A reduction of cross-sensitivity of about one order of magnitude compared to a single-sensor results. Changing in the conductivity of the suspension by 26% alters the measured biomass concentration by only 2.8%. 相似文献
9.
A. Mena-Petite A. Robredo S. Alcalde M. Duñabeitia M. González-Moro M. Lacuesta A. Muñoz-Rueda 《Trees - Structure and Function》2003,17(2):133-143
Post-storage gas exchange parameters like CO2 assimilation, stomatal conductance, transpiration, water use efficiency and intercellular CO2 concentrations, together with several chlorophyll a fluorescence parameters: Fo, Fv, Fv/Fm, Fm/Fo and Fv/Fo were examined in radiata pine (Pinus radiata D. Don) seedlings that were stored for 1, 8 or 15 days at 4° or 10°C with or without soil around the roots. Results were analysed in relation to post-storage water potential and electrolyte leakage in order to forecast their vitality (root growth potential) following cold storage, and post-planting survival potential under optimal conditions. During storage at 4° and 10°C, photosynthesis was reduced, being more pronounced in bare-root seedlings than in seedlings with soil around the roots. The depletion of CO2 assimilation seemed not to be solely a stomatal effect as effects on chloroplasts contributed to this photosynthetic inhibition. Thus, the fall in the ratios Fv/Fm, Fv/Fo and Fm/Fo indicated photochemical apparatus damage during storage. Photosynthetic rate was positively correlated with the root growth index and new root length showing that new root growth is dependent primarily on current photosynthesis. Pre-planting exposure of bare-root radiata pine seedlings to temperatures of 10°C for more than 24 h during transportation or storage is not recommended. 相似文献
10.
Culture conditions in growth and esterase production by a newly isolated Lactobacillus casei CL96 were investigated using a dextrose-free MRS medium supplemented with different sugars in a 2 l fermentor at different pHs (4.0-9.0) and temperatures (20-50°C). The optimal growth was obtained in basal MRS medium containing 1% (w/v) lactose at pH 7.0 and 30°C. The maximal esterase production was obtained intracellularly during the late logarithmic phase, but during the stationary phase, the esterase activity was released in the culture medium. The enzyme activity was maximal at pH 7.0 and 37°C. Among various substrates (C2-C16) tested, the highest activity was towards C6 and C8. Though the enzyme was produced constitutively, the tributylin induced the enzyme production by 2.5 fold. L. casei CL96 esterase was very active at neutral pH and ambient temperature and might be suitable for biotechnological applications in the dairy industry. 相似文献
11.
In the laboratory rock elephant shrews (Elephantulus myurus; mean body mass 56.6 g) displayed the lowest torpor Tb min yet recorded (ca. 5°C) in a placental daily heterotherm. It was unknown whether these low Tbs were characteristic of daily heterothermy in free-ranging animals. It was also unclear how cost effective these low Tbs were since considerable energy is required to arouse from low Tbs on a daily basis. We continuously measured body temperature once every hour for 85 days in 13 free-ranging E. myurus from May to August 2001 (winter) in Weenen Game Reserve, KwaZulu-Natal, South Africa. We recorded a total of 412 torpor bouts. Free-ranging E. myurus had a high propensity for torpor with females displaying higher torpor frequency than males. The lowest Tb recorded was 7.5°C at Ta=2.7°C and the minimum torpor Tb was strongly correlated with ambient temperature. Torpor arousal was tightly coupled with ambient temperature cycles. Low torpor Tb min at low Tas was therefore cost-effective because the animals offset the high cost of arousal through exogenous passive heating. Laboratory studies under constant ambient temperatures may therefore underestimate the energetic benefits of torpor in free-ranging small mammals that inhabit regions where seasonality is moderate. 相似文献
12.
Most fish species are regularly subjected to periods of starvation during which a reduction of energy turnover might be favourable for the animal. This reduction of energy flux may be achieved by changes in thermal behaviour and/or swimming activity. We investigated such behavioural changes during starvation and subsequent refeeding in roach, Rutilus rutilus, with respect to energetic benefits and growth maximisation. Roach, acclimated to a wide range of temperatures (4, 12, 20, 24, 27 and 30 °C), were fed to excess, subjected to 3 weeks of starvation and subsequently refed in order to determine the temperature dependence of feeding rates, growth rates and conversion efficiency (K1) under control conditions and during compensatory growth. When exposed to a thermal gradient, control animals preferentially selected a temperature of 26.8ǂ.9 °C, which is in the range of the optimal temperatures for feeding, growth and conversion efficiency. Starving fish showed a distinct circadian pattern of the mean selected temperature (MST). They migrated to cooler water in the dark (MSTdark=22.8ǃ.1 °C) but returned to warmer water during daytime. This behaviour may be regarded as a trade-off between the potentially higher food density in warmer water areas and the energetic benefit of selecting cooler water patches. The circadian pattern of MST was gradually abandoned upon refeeding and control values were reached again after 3 weeks. Energetically more effective than behavioural hypothermia was the reduction of swimming activity. During starvation, activity peaks were slightly lower than under control conditions and mean daily activity decreased by about 50%. Swimming velocity, however, was not affected by feeding regime. After a period of starvation fish showed compensatory growth at all temperatures, even below 12 °C, where these animals normally do not grow. This suggests that after a period of starvation the critical temperature for growth shifts to lower values. 相似文献
13.
Buoyancy was measured for 258 specimens representing 13 species of adult and sub-adult nototheniids, bathydraconids, and channichthyids from the South Shetland Islands. Measurements were expressed as percentage buoyancy (%B)=Wwater/Wair᎒2. There were no neutrally buoyant species and mean values for %B were 3.07-6.11%, with channichthyids at the low end and benthic nototheniids and bathydraconids at the high end. All species showed an ontogenetic decrease in %B with increasing body weight. With the exception of Champsocephalus gunnari, there was no sexual dimorphism in %B within this sample. With some exceptions, values for %B were consistent with life-history information. Sub-adult Dissostichus mawsoni were not neutrally buoyant, as are large adults. Notothenia rossii had a significantly lower %B than closely related N. coriiceps. Benthic Gobionotothen gibberifrons had a lower %B than semipelagic Lepidonotothen larseni. Although they exhibit some diversification in life history, the four channichthyids in the sample were similar in %B. Neutral buoyancy is rare in notothenioids and may be confined to a single nototheniid clade. 相似文献
14.
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 (Pmax), irradiance at maximal photosynthesis (Imax), and compensation irradiance (Ic) varied with salinity, temperature, and species. The Pmax 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 (Imax) 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 Pmax values but higher Imax values than those of P. abbottiae. The Pmax 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 Pmax 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 (Ic) 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. 相似文献
15.
Temperature response of parameters of a biochemically based model of photosynthesis. II. A review of experimental data 总被引:24,自引:5,他引:19
B. E. Medlyn E. Dreyer D. Ellsworth M. Forstreuter P. C. Harley M. U. F. Kirschbaum X. Le Roux P. Montpied J. Strassemeyer A. Walcroft K. Wang & D. Loustau 《Plant, cell & environment》2002,25(9):1167-1179
The temperature dependence of C3 photosynthesis is known to vary with growth environment and with species. In an attempt to quantify this variability, a commonly used biochemically based photosynthesis model was parameterized from 19 gas exchange studies on tree and crop species. The parameter values obtained described the shape and amplitude of the temperature responses of the maximum rate of Rubisco activity (Vcmax) and the potential rate of electron transport (Jmax). Original data sets were used for this review, as it is shown that derived values of Vcmax and its temperature response depend strongly on assumptions made in derivation. Values of Jmax and Vcmax at 25 °C varied considerably among species but were strongly correlated, with an average Jmax : Vcmax ratio of 1·67. Two species grown in cold climates, however, had lower ratios. In all studies, the Jmax : Vcmax ratio declined strongly with measurement temperature. The relative temperature responses of Jmax and Vcmax were relatively constant among tree species. Activation energies averaged 50 kJ mol?1 for Jmax and 65 kJ mol?1 for Vcmax, and for most species temperature optima averaged 33 °C for Jmax and 40 °C for Vcmax. However, the cold climate tree species had low temperature optima for both Jmax(19 °C) and Vcmax (29 °C), suggesting acclimation of both processes to growth temperature. Crop species had somewhat different temperature responses, with higher activation energies for both Jmax and Vcmax, implying narrower peaks in the temperature response for these species. The results thus suggest that both growth environment and plant type can influence the photosynthetic response to temperature. Based on these results, several suggestions are made to improve modelling of temperature responses. 相似文献
16.
Photosynthetic temperature response of the Antarctic vascular plants Colobanthus quitensis and Deschampsia antarctica 总被引:1,自引:0,他引:1
The photosynthetic temperature response of the Antarctic vascular plants Colobanthus quitensis and Deschampsia antarctica was examined by measuring whole-canopy CO2 gas exchange and chlorophyll (Chl) a fluorescence of plants growing near Palmer Station along the Antarctic Peninsula. Both species had negligible midday net photosynthetic rates (Pn) on warm, usually sunny, days (canopy air temperature [Tc]> 20°C), but had relatively high Pn on cool days (Tc<10°C). Laboratory measurements of light and temperature responses of Pn showed that high temperature, not visible irradiance, was responsible for depressions in Pn on warm sunny days. The optimal leaf temperatures (Tl) for Pn in C. quitensis and D. antarctica were 14 and 10°C, respectively. Both species had substantial positive Pn at 0°C Tl, which were 28 (C. quitensis) and 32% (D. antarctica) of their maximal Pn, and we estimate that their low-temperature compensation points occurred at ?2°C Tl (C. quitensis) and ?3°C (D. antarctica). Because of the strong warming trend along the peninsula over recent decades and predictions that this will continue, we were particularly interested in the mechanisms responsible for their negligible rates of Pn on warm days and their unusually low high-temperature compensation points (i.e., 26°C in C. quitensis and 22°C in D. antarctica). Low Pn at supraoptimal temperature (25°C) appeared to be largely due to high rates of temperature-enhanced respiration. However, there was also evidence for direct impairment of the photosynthetic apparatus at supraoptimal temperature, based on Chl fluorescence and Pn/intercellular CO2 concentration (ci) response curve analyses. The breakpoint or critical temperature (Tcr) of minimal fluorescence (Fo) was ≈42°C in both species, which was well above the temperatures where reductions in Pn were evident, indicating that thylakoid membranes were structurally intact at supraoptimal temperatures for Pn. The optimal Tl for photochemical quenching (qp) and the quantum yield of photosystem II (PSII) electron transfer (φPSII) were 9 and 7°C in C. quitensis and D. antarctica, respectively. Supraoptimal temperatures resulted in lower qp and greater non-photochemical quenching (qNP), but had little effect on Fo, maximal fluorescence (Fm) or the ratio of variable to maximal fluorescence (Fv/Fm) in both species. In addition, carboxylation efficiencies or initial slopes of their Pn/ci response were lower at supraoptimal temperatures, suggesting reduced activity of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco). Although continued warming along the peninsula will increase the frequency of supraoptimal temperatures, Tc at our field site averaged 4.3°C and was below the temperature optima for Pn in these species for the majority of diurnal periods (86%) during the growing season, suggesting that continued warming will usually improve their rates of Pn. 相似文献
17.
A model for growth and overflow metabolism of Saccharomyces cerevisiae was applied to simulate continuous cultivations in a pH-auxostat. The concentrations of glucose, biomass and ethanol are controlled by the flow ratio r between fresh medium and titrant solution, both of which are pH-regulated. A critical value of r could be derived, below which the culture becomes substrate depleted, resulting in a stop-flow condition with retained biomass but without growth. At r-values slightly above the critical value the pH-auxostat is substrate limited and unstable. Further increase of the r value results in a stable continuous culture growing at wmax. Thus, the pH-auxostat complements the chemostat in the growth range at or close to wmax. Even at wmax conditions, the ethanol concentration can be controlled at a low level. 相似文献
18.
Matthew H. Turnbull David Whitehead David T. Tissue William S. Schuster Kim J. Brown Victor C. Engel Kevin L. Griffin 《Oecologia》2002,130(4):515-524
Photosynthesis and related leaf characteristics were measured in canopies of co-occurring Quercus rubra L. (red oak), Quercus prinus L. (chestnut oak) and Acer rubrum L. (red maple) trees. Mature (20+ m tall) trees were investigated at sites of differing soil water availability within a catchment (a drier upper site and a wetter lower site). Leaf photosynthetic characteristics differed significantly between species and in response to site and position in the canopy. Photosynthetic capacity (Amax) was significantly greater at the wetter site in all canopy strata in A. rubrum but not in Q. rubra or Q. prinus. Our findings for A. rubrum are generally consistent with those predicting that species with higher specific leaf area (SLA) will have higher Amax per unit leaf nitrogen (N) and that species with leaves with lower SLA (e.g. Q. rubra and Q. prinus) will have shallower slopes of the Amax-N relationship. Importantly, the relationships between Amax and Narea (and by implication photosynthetic nitrogen-use efficiency, PNUE) differed in A. rubrum between the sites, with PNUE significantly lower at the drier site. The lower photosynthetic capacity and PNUE must substantially reduce carbon acquisition capacity in A. rubrum under these field conditions. Maximum stomatal conductance (gsmax) differed significantly between species, with gsmax greatest in Q. rubra and Q. prinus. In Q. rubra and Q. prinus, gsmax was significantly lower at the upper site than the lower site. There was no significant response of gsmax to site in A. rubrum. These stomatal responses were consistent with the Ci/Ca ratio, which was significantly lower in leaves of Q. rubra and Q. prinus at the upper site, but did not differ between sites in A. rubrum. Leaf '13C was significantly lower in A. rubrum than in either Q. rubra or Q. prinus at both sites. These findings indicate differences in stomatal behaviour in A. rubrum which are likely to contribute to lower water use efficiency at both sites. Our results support the hypothesis that the two Quercus species, in contrast to A. rubrum, maintain photosynthetic capacity at the drier site whilst minimising transpirational water loss. They also suggest, based primarily on physiological evidence, that the ability of A. rubrum to compete with other species of these deciduous forests may be limited, particularly in sites of low moisture availability and during low rainfall years. 相似文献
19.
Hawes TC Marshall CJ Wharton DA 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》2011,181(6):713-719
Antarctic springtails are exemplars of extreme low temperature adaptation in terrestrial arthropods. This paper represents
the first examination of such adaptation in the springtail, Gressittacantha terranova. Acclimatization state was measured in field-fresh samples over a 22-day period at the beginning of the austral summer. No
evidence of temperature tracking was observed. Mean temperature of crystallization (T
c) for all samples was −20.67 ± 0.32°C and the lowest T
c recorded was −32.62°C. Ice affinity purification was used to collect antifreeze proteins (AFPs) from springtail homogenate.
The purified ice fraction demonstrated both thermal hysteresis activity and recrystallisation inhibition. Growth-melt observations
revealed that ice crystals grow normal to the c-axis (basal plane). Reverse-phased HPLC produce one clearly resolved peak (P1) and one compound peak (P2). Mass spectrometry
identified the molecular mass of P1 as 8,599 Da. The P1 protein was also the most prominent in P2, although additional peptides
of 6–7 KDa were also prominent. The main AFP of the Antarctic springtail, G. terranova has been isolated, although like other AFP-expressing arthropods, it shows evidence of expressing a family of AFPs. 相似文献
20.
Maturation to adulthood and successful reproduction in the Antarctic fairy shrimp, Branchinecta
gaini, must be completed within a physiologically challenging temporal window of ca. 2.5 months in the southern Antarctic Peninsula.
Although adults show considerable metabolic opportunism at positive temperatures, little is known of their tolerance of two
physiological insults potentially typical to pool life in the maritime Antarctic: sub-zero temperatures and salinity. B. gaini are freeze-avoiding crustaceans with temperatures of crystallisation (T
cs) of −5°C. No antifreeze proteins were detected in the haemolymph. Adults osmoregulate in relation to temperature, but rapid
mortality in saline solutions of even low concentration, indicate they cannot osmoregulate in relation to salinity. Survival
of ice encasement at temperatures above their T
c was found to be pressure but not time dependent: at severe inoculative ice pressures, there was little immediate survival
and none survived after 48 h below −2°C; at mild inoculative ice pressures, immediate survival was ca. 100% at −3°C, but <20%
after 48 h. There was no significant difference in survival after 1 and 6 h encasement at −3°C. Observations of ventilation
suggest that it is not low temperature per se, but ice that represents the primary cryo-stress, with ventilatory appendages
physically handcuffed below the freezing point of pool water. Both sub-zero temperatures and salinity represent real physiological
constraints on adult fairy shrimp. 相似文献