共查询到20条相似文献,搜索用时 31 毫秒
1.
Odhran S. O'sullivan Mary A. Heskel Peter B. Reich Mark G. Tjoelker Lasantha K. Weerasinghe Aurore Penillard Lingling Zhu John J. G. Egerton Keith J. Bloomfield Danielle Creek Nur H. A. Bahar Kevin L. Griffin Vaughan Hurry Patrick Meir Matthew H. Turnbull Owen K. Atkin 《Global Change Biology》2017,23(1):209-223
High‐temperature tolerance in plants is important in a warming world, with extreme heat waves predicted to increase in frequency and duration, potentially leading to lethal heating of leaves. Global patterns of high‐temperature tolerance are documented in animals, but generally not in plants, limiting our ability to assess risks associated with climate warming. To assess whether there are global patterns in high‐temperature tolerance of leaf metabolism, we quantified Tcrit (high temperature where minimal chlorophyll a fluorescence rises rapidly and thus photosystem II is disrupted) and Tmax (temperature where leaf respiration in darkness is maximal, beyond which respiratory function rapidly declines) in upper canopy leaves of 218 plant species spanning seven biomes. Mean site‐based Tcrit values ranged from 41.5 °C in the Alaskan arctic to 50.8 °C in lowland tropical rainforests of Peruvian Amazon. For Tmax, the equivalent values were 51.0 and 60.6 °C in the Arctic and Amazon, respectively. Tcrit and Tmax followed similar biogeographic patterns, increasing linearly (?8 °C) from polar to equatorial regions. Such increases in high‐temperature tolerance are much less than expected based on the 20 °C span in high‐temperature extremes across the globe. Moreover, with only modest high‐temperature tolerance despite high summer temperature extremes, species in mid‐latitude (~20–50°) regions have the narrowest thermal safety margins in upper canopy leaves; these regions are at the greatest risk of damage due to extreme heat‐wave events, especially under conditions when leaf temperatures are further elevated by a lack of transpirational cooling. Using predicted heat‐wave events for 2050 and accounting for possible thermal acclimation of Tcrit and Tmax, we also found that these safety margins could shrink in a warmer world, as rising temperatures are likely to exceed thermal tolerance limits. Thus, increasing numbers of species in many biomes may be at risk as heat‐wave events become more severe with climate change. 相似文献
2.
Responses of foliar light-saturated net assimilation rate (Amax), capacity for photosynthetic electron transport (Jmax) and mitochondrial respiration rate (Rd) to long-term canopy light and temperature environment were investigated in a temperate deciduous canopy composed of Populus tremula L. in the upper (17–28 m) and of Tilia cordata Mill. in the lower canopy layer (4–17 m). Climatic measurements indicated that seasonal average daily maximum air temperature (Tmax) was 5·5 °C (range 0·7–10·5 °C) higher in the top than in the bottom of the canopy, and strong positive correlations were observed between Tmax and seasonal average integrated quantum flux density (Qint), as well as between seasonal average daily mean temperature and Qint. Because of changes in leaf dry mass and nitrogen per unit area, Amax, Jmax, and Rd scaled positively with Qint in both species at a common leaf temperature (T). According to Jmax versus T response curves and dark chlorophyll fluorescence transients, photosynthetic electron transport was less heat resistant in P. tremula with optimum temperature of Jmax, Topt, of 33·5 ± 0·6 °C than in T. cordata with Topt of 40·7 ± 0·6 °C. This difference was suggested to manifest evolutionary adaptation of photosynthetic electron transport to cooler environments in P. tremula, the range of which extends farther north than that in T. cordata. Possibly because of acclimation to long-term canopy temperature environment, Topt was positively related to Qint in P. tremula, foliage of which was also exposed to higher irradiances and temperatures, but not in T. cordata, in the canopy of which quantum flux densities and temperatures were lower, and gradients in the environmental factors less pronounced. Parallel to changes in Topt, the activation energy for photosynthetic electron transport decreased with increasing Qint in P. tremula, indicating that Jmax of leaves acclimated to colder environment was more responsive to T in lower temperatures than that of high T acclimated leaves. Similar alterations in the activation energy for mitochondrial respiration rate were also observed, indicating that acclimation to temperature of mitochondrial and chloroplastic electron transport proceeds in a co-ordinated manner, and possibly involves long-term changes in membrane fluidity properties. We conclude that, because of correlations between temperature and light, the shapes of Jmax versus T, and Rd versus T response curves vary within tree canopies, and this needs to be taken account in modelling whole canopy photosynthesis. 相似文献
3.
《Ostrich》2013,84(3):221-226
Blue Swallows Hirundo atrocaerulea are Critically Endangered within South Africa. They nest in natural underground holes in mist-belt grasslands. Temperature dataloggers were used to record ground cavity nest (Tn) and ambient temperature (Ta) for one artificial and 11 natural Blue Swallow nests. Mean ground cavity Tn was significantly different to mean Ta. Tn ranged from 17.0 ± 0.1 °C to 28.5 ± 0.3 °C and varied less than Ta (14.0 ± 0.2 to 47.7 ± 0.4 °C). Mean ground cavity Tn averaged 3.3 ± 0.9 °C warmer than mean Ta for 58% of nests, and mean Ta averaged 2.6 ± 0.5 °C warmer than mean ground cavity Tn for 42% of nests. There was no significant difference in mean ground cavity Tn for the aardvark-excavated holes (22.7 ± 1.6 °C) and sinkholes (21.5 ± 1.2 °C). Blue Swallows also nest in man-made holes, potentially a way to increase nesting sites. Mean aardvark-excavated Tn (19.2 ± 0.1 °C) was significantly warmer than mean artificial cavity Tn (18.5 ± 0.2 °C). Further investigation of breeding success of Blue Swallows in relation to Tn, incubation strategies and predation risk needs to be addressed in future studies for a better understanding of their reproductive ecology. 相似文献
4.
The echidna (Tachyglossus aculeatus) maintained a body temperature of 30.7°C ± 1.03 s.d. (N = 23) at ambient temperatures (TA) between 0 and 25°C. It may, however, also become hypothermic at low TA. At TA = 30°C or above the echidna became hyperthermic. The thermoneutral range was about 20–30°C. At low TA the metabolic rate might be increased several fold. The thermal conductance was at a minimum at TA = 20°C, and was not further reduced at lower TA. At higher TA the thermal conductance increased up to five-fold. The evaporation showed little change with increasing TA. At the highest TA we used (33°C) the evaporation on the average accounted for the dissipation of only about one-third of the metabolic heat produced. These findings suggest that the echidna, although it can maintain its body temperature at low ambient temperature, cannot rely upon evaporation as the major avenue for heat loss at high ambient temperature. 相似文献
5.
Abstract The dynamic response of stomata to changes in atmospheric humidity was investigated in Fragaria × ananassa Duch., Picea engelmannii Parry, and Pseudotsuga menziesii (Mirb.) Franco; and the effect of water stress on this response was determined in Pseudotsuga menziesii. The plants were rotated through three regimes of ambient temperature and vapour pressure deficit: 35°C–3. 5kPa, 35°C–0. 5 kPa, and 20°C–1. 5kPa. Branch and leaflet conductance were measured with a steady-state porometer, first at ambient vapour pressure deficit and then at one of four treatment conditions achieved by increasing or decreasing vapour pressure within the porometer cuvette. All three species showed similar stomatal response: enhanced conductance at low vapour pressure deficit and depressed conductance at high vapour pressure deficit. Engelmann spruce was more sensitive than Douglas fir and strawberry. Plant water status significantly altered stomatal response to vapour pressure deficit. The relationship of conductance of xylem water potential was linear under ambient conditions but became curvilinear when conductance was measured above and below ambient vapour pressure deficit. Between ?0. 5 MPa and ?2. 0 MPa xylem water potential, the stomata were sensitive to vapour pressure deficit, but below ? 2. 0 MPa, the sensitivity decreased. 相似文献
6.
The effect of flutter on the temperature of poplar leaves and its implications for carbon gain 总被引:1,自引:0,他引:1
The leaf temperatures of two poplar species (Populus tremuloides Michx. and P. fremontii Wats.) were characterized by attaching thermocouples to leaves that were either constrained to a fixed position or allowed to flutter naturally. There were no observed temperature differences between fluttering and constrained leaves in the lower canopy, but fluttering leaves at the top of the canopy were as much as 2–4°C cooler than constrained leaves. An increase in heat transfer, a decrease in light interception or both could account for these observed differences in the temperature of fluttering versus constrained leaves. Fluttering can increase the boundary-layer conductance to convective heat exchange by as much as 50 and 20% for laminar and turbulent flow, respectively. The benefit that these leaf temperature differences may provide to the carbon economy of a poplar canopy was dependent on the ambient temperature. Populus fremontii, which is frequently exposed to daytime temperatures exceeding 35°C during summer months in the central valley of California, USA, could show an increase in carbon gain as a result of lower upper canopy leaf temperatures. For aspen, the benefit would be much smaller and often negative because of much lower air temperatures. Lower leaf temperatures may also increase the water use efficiency of poplars. However, the maintenance of lower leaf temperatures may not be the primary adaptive significance of leaf flutter. 相似文献
7.
R. Leuning 《Plant, cell & environment》2002,25(9):1205-1210
The temperature dependence of the photosynthetic parameters Vcmax, the maximum catalytic rate of the enzyme Rubisco, and Jmax, the maximum electron transport rate, were examined using published datasets. An Arrehenius equation, modified to account for decreases in each parameter at high temperatures, satisfactorily described the temperature response for both parameters. There was remarkable conformity in Vcmax and Jmax between all plants at Tleaf < 25 °C, when each parameter was normalized by their respective values at 25 °C (Vcmax0 and Jmax0), but showed a high degree of variability between and within species at Tleaf > 30 °C. For both normalized Vcmax and Jmax, the maximum fractional error introduced by assuming a common temperature response function is < ± 0·1 for most plants and < ± 0·22 for all plants when Tleaf < 25 °C. Fractional errors are typically < ± 0·45 in the temperature range 25–30 °C, but very large errors occur when a common function is used to estimate the photosynthetic parameters at temperatures > 30 °C. The ratio Jmax/Vcmax varies with temperature, but analysis of the ratio at Tleaf = 25 °C using the fitted mean temperature response functions results in Jmax0/Vcmax0 = 2·00 ± 0·60 (SD, n = 43). 相似文献
8.
The thermotropic properties of bovine blood coagulation Factors IX and X, as well as the activation intermediates and products of these proteins, have been investigated by differential scanning microcalorimetry in the presence and absence of Ca2+. Bovine Factor IX displays a single thermal-denaturation transition characterized by a temperature midpoint (TM) of 54.5 ± 0.5 °C and a calorimetric enthalpy (ΔHc) of 105 ± 15 kcal/mol, in the absence of Ca2+. In the presence of Ca2+ concentrations sufficient to saturate its sites on Factor IX, the Tm value is increased to 57.0 ± 0.5 °C and the ΔHc is virtually unchanged. When the activation intermediate, Factor IXα, is similarly analyzed in the absence of Ca2+, a broad, diffuse thermogram was obtained which did not lend itself to calculation of thermodynamic parameters. In the presence of Ca2+, Factor IXα displayed thermograms characterized by a TM of 51.0 ± 0.5 °C and a ΔHc of 109 ± 10 kcal/mol. The activated product, Factor IXaα, in the absence of Ca2+ (the values in the presence of saturating Ca2+ are given in parentheses), undergoes thermal denaturation with a TM of 54.5 ± 0.5 °C (57.0 ± 0.5 °C) and a ΔHc of 158 ±10 kcal/mol (156 ± 10 kcal/mol). Similarly, the terminal-activation product, Factor IXaβ, displays a TM of 51.5 ± 0.5 °C (54.0 ± 0.5 °C) and a ΔHc of 85 ± 5 kcal/mol (126 ± 10 kcal/mol). Bovine blood coagulation Factor X has been analyzed in this same fashion, and shows very similar thermal properties to Factor IX. The thermal denaturation of Factor X is represented by a TM of 54.0 ± 0.5 °C (55.0 ± 0.5 °C) and a ΔHc of 102 ± 10 kcal/mol (118 ± 10 kcal/mol), whereas its activated form, Factor Xaβ, possesses a TM of 55.0 ± 0.5 °C (55.0 ± 0.5 °C) and a ΔHc of 92.0 ± 5 kcal/mol (136 ± 10 kcal/mol). These studies indicate that, for many of these proteins, Ca2+ induces a conformational alteration to a more thermally stable form, which also requires the absorption of greater amounts of heat for thermal denaturation. 相似文献
9.
Spatial distribution of leaf water-use efficiency and carbon isotope discrimination within an isolated tree crown 总被引:11,自引:5,他引:6
X. Le Roux T. Bariac H. Sinoquet B. Genty C. Piel A. Mariotti C. Girardin & P. Richard 《Plant, cell & environment》2001,24(10):1021-1032
The spatial variations in the stable carbon isotope composition (δ13C) of air and leaves (total matter and soluble sugars) were quantified within the crown of a well‐watered, 20‐year‐old walnut tree growing in a low‐density orchard. The observed leaf carbon isotope discrimination (Δ) was compared with that computed by a three‐dimensional model simulating the intracanopy distribution of irradiance, transpiration and photosynthesis (previously parameterized and tested for the same tree canopy) coupled to a biophysically based model of carbon isotope discrimination. The importance of discrimination associated with CO2 gradients encountered from the substomatal sites to the carboxylation sites was evaluated. We also assessed by simulation the effect of current irradiance on leaf gas exchange and the effect of long‐term acclimation of photosynthetic capacity and stomatal and internal conductances to light regime on intracanopy gradients in Δ. The main conclusions of this study are: (i) leaf Δ can exhibit important variations (5 and 8‰ in total leaf material and soluble sugars, respectively) along light gradients within the foliage of an isolated tree; (ii) internal conductance must be taken into account to adequately predict leaf Δ, and (iii) the spatial variations in Δ and water‐use efficiency resulted from the short‐term response of leaf gas exchange to variations in local irradiance and, to a much lesser extent, from the long‐term acclimation of leaf characteristics to the local light regime. 相似文献
10.
This study compares the thermal ecology of male bearded dragon lizards (Pogona barbata) from south-east Queensland across two seasons: summer (1994–1995) and autumn (1995). Seasonal patterns of body temperature
(T
b) were explored in terms of changes in the physical properties of the thermal environment and thermoregulatory effort. To
quantify thermoregulatory effort, we compared behavioral and physiological variables recorded for observed lizards with those
estimated for a thermoconforming lizard. The study lizards' field T
bs varied seasonally (summer: grand daily mean (GDM) 34.6 ± 0.6°C, autumn: GDM 27.5 ± 0.3°C) as did maximum and minimum available
operative temperatures (summer: GDM T
max 42.1 ± 1.7°C, T
min 32.2 ± 1.0°C, autumn: GDM T
max 31.7 ± 1.2°C, T
min 26.4 ± 0.5°C). Interestingly, the range of temperatures that lizards selected in a gradient (selected range) did not change
seasonally. However, P. barbata thermoregulated more extensively and more accurately in summer than in autumn; lizards generally displayed behaviors affecting
heat load nonrandomly in summer and randomly in autumn, leading to the GDM of the mean deviations of lizards' field T
bs from their selected ranges being only 2.1 ± 0.5°C in summer, compared to 4.4 ± 0.5°C in autumn. This seasonal difference
was not a consequence of different heat availability in the two seasons, because the seasonally available ranges of operative
temperatures rarely precluded lizards from attaining field T
bs within their selected range, should that have been the goal. Rather, thermal microhabitat distribution and social behavior
appear to have had an important influence on seasonal levels of thermoregulatory effort.
Received: 28 April 1997 / Accepted: 29 December 1997 相似文献
11.
We have investigated the effects of temperature on the conductance and voltage-dependent kinetics of cardiac gap junction
channels between pairs of seven-day embryonic chick ventricle myocytes over the range of 14–26°C. Records of junctional conductance
(G
j
) and steady-state unit junctional channel activity were made using the whole-cell double patch-clamp technique while the
bath temperature was steadily changed at a rate of about 4°C/min. The decrease inG
j
upon cooling was biphasic with a distinct break at 21°C. In 12 cell pairs,Q
10 was 2.2 from 26 to 21°C, while between 21 and 14°C it was 6.5. The meanG
j
at 22°C (G
j22
) was 3.0±2.1 nS, ranging in different preparations from 0.24 to 6.4 nS. At room temperature, embryonic cardiac gap junctions
contain channels with conductance states near 240, 200, 160, 120, 80 and 40 pS. In the present study, we demonstrate that
cooling decreases the frequency of channel openings at all conductance levels, and at temperatures below 20°C shifts the prevalence
of openings from higher to lower conductance states: all 240 pS openings disappear below 20°C; 200 pS openings are suppressed
at 17°C; below 16°C 160 and 120 pS events disappear and only 80 and 40 pS states are seen. Temperature also affected the voltage-dependent
kinetics of the channels. Application of a 6 sec, 80 mV voltage step across the junction (V
j80
) caused a biexponential decay in junctional conductance. Decay was faster at lower temperatures, whereas the rate of recovery
ofG
j
after returning toV
j0
was slowed. Cooling reduced the fast decay time constant, increased both recovery time constants, and decreased the magnitude
of GitGj decay, thus leaving a 10–16% larger residual conductance (G
ss/G
init,±80 mVV
j
) at 18 than at 22°C. From these results we propose that embryonic chick cardiac gap junctions contain at least two classes
of channels with different conductances and temperature sensitivities. 相似文献
12.
Responses of canopy duration to temperature changes in four temperate tree species: relative contributions of spring and autumn leaf phenology 总被引:1,自引:0,他引:1
Yann Vitasse Annabel Josée Porté Antoine Kremer Richard Michalet Sylvain Delzon 《Oecologia》2009,161(1):187-198
While changes in spring phenological events due to global warming have been widely documented, changes in autumn phenology,
and therefore in growing season length, are less studied and poorly understood. However, it may be helpful to assess the potential
lengthening of the growing season under climate warming in order to determine its further impact on forest productivity and
C balance. The present study aimed to: (1) characterise the sensitivity of leaf phenological events to temperature, and (2)
quantify the relative contributions of leaf unfolding and senescence to the extension of canopy duration with increasing temperature,
in four deciduous tree species (Acer pseudoplatanus, Fagus sylvatica, Fraxinus excelsior and Quercus petraea). For 3 consecutive years, we monitored the spring and autumn phenology of 41 populations at elevations ranging from 100
to 1,600 m. Overall, we found significant altitudinal trends in leaf phenology and species-specific differences in temperature
sensitivity. With increasing temperature, we recorded an advance in flushing from 1.9 ± 0.3 to 6.6 ± 0.4 days °C−1 (mean ± SD) and a 0 to 5.6 ± 0.6 days °C−1 delay in leaf senescence. Together both changes resulted in a 6.9 ± 1.0 to 13.0 ± 0.7 days °C−1 lengthening of canopy duration depending on species. For three of the four studied species, advances in flushing were the
main factor responsible for lengthening canopy duration with increasing temperature, leading to a potentially larger gain
in solar radiation than delays in leaf senescence. In contrast, for beech, we found a higher sensitivity to temperature in
leaf senescence than in flushing, resulting in an equivalent contribution in solar radiation gain. These results suggest that
climate warming will alter the C uptake period and forest productivity by lengthening canopy duration. Moreover, the between-species
differences in phenological responses to temperature evidenced here could affect biotic interactions under climate warming. 相似文献
13.
The partial pressure of CO2 at the sites of carboxylation within chloroplasts depends on the conductance to CO2 diffusion from intercellular airspace to the sites of carboxylation, termed mesophyll conductance (gm). We investigated the temperature response of gm in tobacco (Nicotiana tabacum) by combining gas exchange in high light, ambient CO2 in either 2 or 21% O2 with carbon isotope measurements using tuneable diode laser spectroscopy. The gm increased linearly with temperature in 2 or 21% O2. In 21% O2, isotope discrimination associated with gm decreased from 5.0 ± 0.2 to 1.8 ± 0.2‰ as temperature increased from 15 to 40 °C, but the photorespiratory contribution to the isotopic signal is significant. While the fractionation factor for photorespiration (f = 16.2 ± 0.7‰) was independent of temperature between 20 and 35 °C, discrimination associated with photorespiration increased from 1.1 ± 0.01 to 2.7 ± 0.02‰ from 15 to 40 °C. Other mitochondrial respiration contributed around 0.2 ± 0.03‰. The drawdown in CO2 partial pressure from ambient air to intercellular airspaces was nearly independent of leaf temperature. By contrast, the increase in gm with increasing leaf temperature resulted in the drawdown in CO2 partial pressure between intercellular airspaces and the sites of carboxylation decreasing substantially at high temperature. 相似文献
14.
To study the reliabiliity of formulas for calculating mean skin temperature (T
sk), values were computed by 18 different techniques and were compared with the mean of 10,841 skin temperatures measured by
infrared thermography. One hundred whole-body infrared thermograms were scanned in ten resting males while changing the air
temperature from 40° C to 4° C. Local, regional average and mean skin temperatures were obtained using an image processing
system. The agreement frequency, defined as the percentage of the calculated T
sk values which agreed with the corresponding infrared thermographic T
sk within ±0.2° C, ranged for with the various formulas from 7% to 80%. In many sites, the local skin temperature did not coincide
with the regional average skin temperature. When the local skin temperatures which showed the highest percentage similarity
to the regional average skin temperature within ±0.4° C were applied to the formula, the agreement frequency was markedly
improved for all formulas. However, the agreement frequency was not affected by changing the weighting factors from specific
constants to individually measured values of regional surface area. By applying the physiologically reliable accuracy range
of ±0.2° C in the moderate and ±0.4° C in the cool condition, agreement frequencies of at least 95% were observed in formulas
involving seven or more skin temperature measurement sites, including the hand and foot. We conclude that calculation of a
reliable mean skin temperature must involve more than seven skin temperature measurement sites regardless of ambient temperature.
Optimal sites for skin temperature measurement are proposed for various formulas.
Received: 2 December 1996 / Accepted: 25 June 1997 相似文献
15.
Emma M. Docherty Emanuel Gloor Daniela Sponchiado Martin Gilpin Carlos A. D. Pinto Haroldo M. Junior Ingrid Coughlin Leandro Ferreira João A. S. Junior Antonio C. L. da Costa Patrick Meir David Galbraith 《Plant, cell & environment》2023,46(1):185-198
The continued functioning of tropical forests under climate change depends on their resilience to drought and heat. However, there is little understanding of how tropical forests will respond to combinations of these stresses, and no field studies to date have explicitly evaluated whether sustained drought alters sensitivity to temperature. We measured the temperature response of net photosynthesis, foliar respiration and the maximum quantum efficiency of photosystem II (Fv/Fm) of eight hyper-dominant Amazonian tree species at the world's longest-running tropical forest drought experiment, to investigate the effect of drought on forest thermal sensitivity. Despite a 0.6°C–2°C increase in canopy air temperatures following long-term drought, no change in overall thermal sensitivity of net photosynthesis or respiration was observed. However, photosystem II tolerance to extreme-heat damage (T50) was reduced from 50.0 ± 0.3°C to 48.5 ± 0.3°C under drought. Our results suggest that long-term reductions in precipitation, as projected across much of Amazonia by climate models, are unlikely to greatly alter the response of tropical forests to rising mean temperatures but may increase the risk of leaf thermal damage during heatwaves. 相似文献
16.
Stomatal behaviour in a beech canopy: an analysis of Bowen ratio measurements compared with porometer data 总被引:3,自引:0,他引:3
M. HERBST 《Plant, cell & environment》1995,18(9):1010-1018
On the basis of measurements or stand transpiration and microclimate, the bulk stomatal or bulk leaf conductance (gL) of a beech forest in northern Germany was calculated for periods in which leaves were fully expanded and the canopy was dry. This conductance depends strongly on light and humidity conditions above the forest. During periods with photosynthetic photon flux densities Q > 1200 μmol m?2s?1, gL was reduced from 1500mmol m?2s?1 at a vapour pressure deficit D= 0.5kPa to 500 mmol m?2s?1 at D= 2kPa. Light saturation of gL was not reached until Q= 1200 μmol m?2s?1 at low D, or until even higher Q at higher D. The dependence of gL, on Q and D was described mathematically by a non-linear equation that requires two empirical parameters. Values for gL as simulated by this equation provided a satisfactory agreement with independent porometer data collected on single leaves and scaled up to the canopy. A comparison of stomatal and aerodynamic conductances showed a strong coupling between the forest canopy and the atmosphere, indicating that transpiration of the beech forest is controlled mainly by the stomata. 相似文献
17.
The application of 136 atm of helium pressure to an aqueous dispersion of dipalmitoylphosphatidylcholine increased the temperature of the primary phase transition at 40.4 ± 0.2 °C by 3.0 °C. The lower temperature pretransition at 30.5 ± 0.5 °C, thought to be due to phosphate headgroup reorganization, was increased by 1.7 °C. Addition of 4% dipalmitoylphosphatidic acid to the dipalmitoylphosphatidylcholine affected the phase transition in the head group region more than in the hydrocarbon chain region. The pressure and temperature data obtained, taken together with the literature value for the bilayer volume expansion during solid-fluid phase transition, and inserted into the Clausius-Clapeyron equation yield a ΔH value of 8.8 kcal/mole for this phase transition. This value is within experimental error of the ΔH value obtained from differential scanning calorimetry and serves to support the validity of the data and the experimental technique. Phase transition was observed by electron spin resonance measurement of the exclusion of the small spin label Tempo (2,2,6,6-tetramethylpiperidine-N-oxyl) from the solid domains of the bilayer. This result offers a possible explanation for the direct antagonism by high pressure of the effects of the inhalation anesthetics. 相似文献
18.
Willis CK Turbill C Geiser F 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》2005,175(7):479-486
Data on thermal energetics for vespertilionid bats are under-represented in the literature relative to their abundance, as
are data for bats of very small body mass. Therefore, we studied torpor use and thermal energetics in one of the smallest
(4 g) Australian vespertilionids, Vespadelus vulturnus. We used open-flow respirometry to quantify temporal patterns of torpor use, upper and lower critical temperatures (T
uc and T
lc) of the thermoneutral zone (TNZ), basal metabolic rate (BMR), resting metabolic rate (RMR), torpid metabolic rate (TMR),
and wet thermal conductance (C
wet) over a range of ambient temperatures (T
a). We also measured body temperature (T
b) during torpor and normothermia. Bats showed a high proclivity for torpor and typically aroused only for brief periods. The
TNZ ranged from 27.6°C to 33.3°C. Within the TNZ T
b was 33.3±0.4°C and BMR was 1.02±0.29 mlO2 g−1 h−1 (5.60±1.65 mW g−1) at a mean body mass of 4.0±0.69 g, which is 55 % of that predicted for a 4 g bat. Minimum TMR of torpid bats was 0.014±0.006 mlO2 g−1 h−1 (0.079±0.032 mW g−1) at T
a=4.6±0.4°C and T
b=7.5±1.9. T
lc and C
wet of normothermic bats were both lower than that predicted for a 4 g bat, which indicates that V. vulturnus is adapted to minimising heat loss at low T
a. Our findings support the hypothesis that vespertilionid bats have evolved energy-conserving physiological traits, such as
low BMR and proclivity for torpor. 相似文献
19.
P. Eliáš 《Biologia Plantarum》1979,21(4):266-274
The variation in stomatal activity within the crowns ofAcer campestre, Carpinus betulus andQuercus cerris was measured by vapour exchange porometer on several summer days in an oak-hornbeam forest, in SW Slovakia, Czechoslovakia.
Variation resulted from crown position in the forest stand and from leaf position within the canopy. The highest stomatal
conductance was in sunlit sun leaves in the upper part of the canopy. Stomatal conductance decreased with increasing depth
in the canopy. The steepest decrease was in the upper canopy, in the intermediate zone between fully sunlit and fully shaded
leaves, and was caused by the decline in leaf irradiance and in stomatal density. In codominant trees, the conductance in
shade leaves at the base of the crown was significantly lower than in the sun leaves at the top of the crown. In a dominant
tree,Q. cerris, the differences in stomatal conductance were small and most frequently insignificant. Variation in incident light also determined
the diurnal variation of stomatal conductance with respect to crown aspect. Differences between sun leaves on the east and
west facing aspects of the overstory crown ofQ. cerris were demonstrated for several days. 相似文献
20.
Liang Fang Pierre Martre Kaining Jin Xinmiao Du Peter E. L. van der Putten Xinyou Yin Paul C. Struik 《Global Change Biology》2023,29(2):505-521
Extreme climatic events, such as heat waves, cold snaps and drought spells, related to global climate change, have become more frequent and intense in recent years. Acclimation of plant physiological processes to changes in environmental conditions is a key component of plant adaptation to climate change. We assessed the temperature response of leaf photosynthetic parameters in wheat grown under contrasting water regimes and growth temperatures (Tgrowth). Two independent experiments were conducted under controlled conditions. In Experiment 1, two wheat genotypes were subjected to well-watered or drought-stressed treatments; in Experiment 2, the two water regimes combined with high, medium and low Tgrowth were imposed on one genotype. Parameters of a biochemical C3-photosynthesis model were estimated at six leaf temperatures for each factor combination. Photosynthesis acclimated more to drought than to Tgrowth. Drought affected photosynthesis by lowering its optimum temperature (Topt) and the values at Topt of light-saturated net photosynthesis, stomatal conductance, mesophyll conductance, the maximum rate of electron transport (Jmax) and the maximum rate of carboxylation by Rubisco (Vcmax). Topt for Vcmax was up to 40°C under well-watered conditions but 24–34°C under drought. The decrease in photosynthesis under drought varied among Tgrowth but was similar between genotypes. The temperature response of photosynthetic quantum yield under drought was partly attributed to photorespiration but more to alternative electron transport. All these changes in biochemical parameters could not be fully explained by the changed leaf nitrogen content. Further model analysis showed that both diffusional and biochemical parameters of photosynthesis and their thermal sensitivity acclimate little to Tgrowth, but acclimate considerably to drought and the combination of drought and Tgrowth. The commonly used modelling approaches, which typically consider the response of diffusional parameters, but ignore acclimation responses of biochemical parameters to drought and Tgrowth, strongly overestimate leaf photosynthesis under variable temperature and drought. 相似文献