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1.
Though field data for naturally senesced leaf litter are rare, it is commonly assumed that rising atmospheric CO2 concentrations will reduce leaf litter quality and decomposition rates in terrestrial ecosystems and that this will lead
to decreased rates of nutrient cycling and increased carbon sequestration in native ecosystems. We generally found that the
quality of␣naturally senesced leaf litter (i.e. concentrations of C, N and lignin; C:N, lignin:N) of a variety of native plant
species produced in alpine, temperate and tropical communities maintained at elevated CO2 (600–680 μl l−1) was not significantly different from that produced in similar communities maintained at current ambient CO2 concentrations (340–355 μl l−1). When this litter was allowed to decompose in situ in a humid tropical forest in Panama (Cecropia peltata, Elettaria cardamomum, and Ficus benjamina, 130 days exposure) and in a lowland temperate calcareous grassland in Switzerland (Carex flacca and a graminoid species mixture; 261 days exposure), decomposition rates of litter produced under ambient and elevated CO2 did not differ significantly. The one exception to this pattern occurred in the high alpine sedge, Carex curvula, growing in the Swiss Alps. Decomposition of litter produced in situ under elevated CO2 was significantly slower than that of litter produced under ambient CO2 (14% vs. 21% of the initial litter mass had decomposed over a 61-day exposure period, respectively). Overall, our results
indicate that relatively little or no change in leaf litter quality can be expected in plant communities growing under soil
fertilities common in many native ecosystems as atmospheric CO2 concentrations continue to rise. Even in situations where small reductions in litter quality do occur, these may not necessarily
lead to significantly slower rates of decomposition. Hence in many native species in situ litter decomposition rates, and the time course of decomposition, may remain relatively unaffected by rising CO2.
Received: 12 September 1996 / Accepted: 30 November 1996 相似文献
2.
M. E. Kubiske Kurt S. Pregitzer Carl J. Mikan Donald R. Zak Jennifer L. Maziasz A. Teeri 《Oecologia》1997,110(3):328-336
We tested the hypothesis that elevated CO2 would stimulate proportionally higher photosynthesis in the lower crown of Populus trees due to less N retranslocation, compared to tree crowns in ambient CO2. Such a response could increase belowground C allocation, particularly in trees with an indeterminate growth pattern such
as Populus tremuloides. Rooted cuttings of P. tremuloides were grown in ambient and twice ambient (elevated) CO2 and in low and high soil N availability (89 ± 7 and 333 ± 16 ng N g−1 day−1 net mineralization, respectively) for 95 days using open-top chambers and open-bottom root boxes. Elevated CO2 resulted in significantly higher maximum leaf photosynthesis (A
max) at both soil N levels. A
max was higher at high N than at low N soil in elevated, but not ambient CO2. Photosynthetic N use efficiency was higher at elevated than ambient CO2 in both soil types. Elevated CO2 resulted in proportionally higher whole leaf A in the lower three-quarters to one-half of the crown for both soil types. At elevated CO2 and high N availability, lower crown leaves had significantly lower ratios of carboxylation capacity to electron transport
capacity (V
cmax/J
max) than at ambient CO2 and/or low N availability. From the top to the bottom of the tree crowns, V
cmax/J
max increased in ambient CO2, but it decreased in elevated CO2 indicating a greater relative investment of N into light harvesting for the lower crown. Only the mid-crown leaves at both
N levels exhibited photosynthetic down regulation to elevated CO2. Stem biomass segments (consisting of three nodes and internodes) were compared to the total A
leaf for each segment. This analysis indicated that increased A
leaf at elevated CO2 did not result in a proportional increase in local stem segment mass, suggesting that C allocation to sinks other than the
local stem segment increased disproportionally. Since C allocated to roots in young Populus trees is primarily assimilated by leaves in the lower crown, the results of this study suggest a mechanism by which C allocation
to roots in young trees may increase in elevated CO2.
Received: 12 August 1996 / Accepted: 12 November 1996 相似文献
3.
The heat increment of feeding in house wren chicks: magnitude, duration, and substitution for thermostatic costs 总被引:3,自引:3,他引:0
Mark. A. Chappell Gwendolyn C. Bachman Kimberly A. Hammond 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1997,167(4):313-318
The heat increment of feeding (HIF), a transient postprandial increase in metabolic rate, is the energy cost of processing
a meal. We measured HIF in house wren chicks (Troglodytes aedon) ranging in mass from 1.6 to 10.3 g. This mass range (age 2–10 days) spanned a transition from blind, naked, ectothermic
chicks through alert, endothermic birds with nearly complete feathering. We fed chicks crickets (2.7–10% of chick body mass)
and determined HIF from continuous measurements of oxygen consumption rate (O2) before and after meals. At warm ambient temperatures (T
a) of 33–36 °C, the magnitude of HIF (in ml O2 or joules) was linearly related to meal mass and was not affected by chick mass. HIF accounted for 6.3% of ingested energy,
which is within the range of results for other carnivorous vertebrates. The duration of HIF was inversely related to chick
mass; 10-g chicks processed a standard meal approximately twice as fast as 2-g chicks. HIF duration increased with increasing
meal mass. The peak O2 during HIF, expressed as the factorial increase above resting metabolism, was independent of body mass and meal mass. In
large, endothermic chicks ( > 8 g), HIF substituted for thermoregulatory heat production at low T
a.
Accepted: 11 December 1996 相似文献
4.
P. Meier J. Zettel 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1997,167(4):297-304
In the Swiss Prealps Entomobrya nivalis hibernates in an inactive state, hidden under bark flakes on spruce. For freeze avoidance it relies on thermal hysteresis
proteins (THPs) and polyols (mainly ribitol, with small amounts arabitol and threitol). Polyols are present only during the
inactive state, THPs additionally protect during the transition phase in spring and autumn, when animals are still active
but frosts may occur. Peak values were recorded in February/March for THPs (3.5 °C hysteresis between melting and freezing
point) and for polyols (26 μg mg−1 FW; hemolymph osmolality 680 mosmol l−1). E. nivalis is able to control its hemolymph osmolality independently of body water content. Mean osmolality in summer was 350– 440 mosmol l−1, in winter it was elevated to 650 mosmol l−1, due to a synthesis mainly of ribitol. Body water content varied between 1.8 and 3.3 mg H2O mg−1 DW, depending on humidity conditions. Experiments on triggering of antifreeze synthesis showed the action of temperature
and photoperiod as cues, but there was also evidence for an endogenous rhythm. No clear correlation between antifreeze concentration
and supercooling ability could be established, suggesting that gut content or other parameters also play an inportant role.
Accepted: 18 November 1995 相似文献
5.
Influence of stand structure on carbon-13 of vegetation, soils, and canopy air within deciduous and evergreen forests in Utah, United States 总被引:15,自引:0,他引:15
Carbon isotope ratios (δ13C) were studied in evergreen and deciduous forest ecosystems in semi-arid Utah (Pinus contorta, Populus tremuloides, Acer negundo and Acer grandidentatum). Measurements were taken in four to five stands of each forest ecosystem differing in overstory leaf area index (LAI) during
two consecutive growing seasons. The δ13Cleaf (and carbon isotope discrimination) of understory vegetation in the evergreen stands (LAI 1.5–2.2) did not differ among canopies
with increasing LAI, whereas understory in the deciduous stands (LAI 1.5–4.5) exhibited strongly decreasing δ13Cleaf values (increasing carbon isotope discrimination) with increasing LAI. The δ13C values of needles and leaves at the top of the canopy were relatively constant over the entire LAI range, indicating no
change in intrinsic water-use efficiency with overstory LAI. In all canopies, δ13Cleaf decreased with decreasing height above the forest floor, primarily due to physiological changes affecting c
i/c
a (> 60%) and to a minor extent due to δ13C of canopy air (< 40%). This intra-canopy depletion of δ13Cleaf was lowest in the open stand (1‰) and greatest in the denser stands (4.5‰). Although overstory δ13Cleaf did not change with canopy LAI, δ13C of soil organic carbon increased with increasing LAI in Pinus contorta and Populus tremuloides ecosystems. In addition, δ13C of decomposing organic carbon became increasingly enriched over time (by 1.7–2.9‰) for all deciduous and evergreen dry temperate
forests. The δ13Ccanopy of CO2 in canopy air varied temporally and spatially in all forest stands. Vertical canopy gradients of δ13Ccanopy, and [CO2]canopy were larger in the deciduous Populus tremuloides than in the evergreen Pinu contorta stands of similar LAI. In a very wet and cool year, ecosystem discrimination (Δe) was similar for both deciduous Populus tremulodies (18.0 ± 0.7‰) and evergreen Pinus contorta (18.3 ± 0.9‰) stands. Gradients of δ13Ccanopy and [CO2]canopy were larger in denser Acer spp. stands than those in the open stand. However, 13C enrichment above and photosynthetic draw-down of [CO2]canopy below tropospheric baseline values were larger in the open than in the dense stands, due to the presence of a vigorous understory
vegetation. Seasonal patterns of the relationship δ13Ccanopy versus 1/[CO2]canopy were strongly influenced by precipitation and air temperature during the growing season. Estimates of Δe for Acer spp. did not show a significant effect of stand structure, and averaged 16.8 ± 0.5‰ in 1933 and 17.4 ± 0.7‰ in 1994. However,
Δe varied seasonally with small fluctuations for the open stand (2‰), but more pronounced changes for the dense stand (5‰).
Received: 15 April 1996 / Accepted: 19 October 1996 相似文献
6.
This study investigated the effects on running economy (RE) of ingesting either no fluid or an electrolyte solution with
or without 6% carbohydrate (counterbalanced design) during 60-min running bouts at 80% maximal oxygen consumption (V˙O2max). Tests were undertaken in either a thermoneutral (22–23°C; 56–62% relative humidity, RH) or a hot and humid natural environment
(Singapore: 25–35°C; 66–77% RH). The subjects were 15 young adult male Singaporeans [V˙O2max = 55.5 (4.4 SD) ml kg−1 min−1]. The RE was measured at 3 m s−1 [65 (6)% V˙O2max] before (RE1) and after each prolonged run (RE2). Fluids were administered every 2 min, at an individual rate determined
from prior tests, to maintain body mass (group mean = 17.4 ml min−1). The V˙O2 during RE2 was higher (P < 0.05) than that during the RE1 test for all treatments, with no differences between treatments (ANOVA). The mean increase
in V˙O2 from RE1 to RE2 ranged from 3.4 to 4.7 ml kg−1 min−1 across treatments. In conclusion, the deterioration in RE at 3 m s−1 (65% V˙O2max) after 60 min of running at 80% V˙O2max appears to occur independently of whether fluid is ingested and regardless of whether the fluid contains carbohydrates or
electrolytes, in both a thermoneutral and in a hot, humid environment.
Accepted: 30 October 1997 相似文献
7.
C. Traeholt 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1997,167(3):177-184
Five water monitor lizards, Varanus salvator salvator, and four clouded monitor lizards, Varanus bengalensis nebulosus, were caught on Tioman island in Malaysia. A radio-thermistor transmitter was implanted into the buccal cavity of each animal,
and they were released into an enclosure measuring 5.5 × 6.5 metres. The lizards were observed for 9 and 8 days, respectively,
before and after the parietal eye was covered with aluminium foil. With uncovered parietal eye, both species showed a clear
diurnal rhythm, being active only during day time. After covering the parietal eye, the mean locomotor activity of five V. s. salvator decreased from 791 to 107 min · day–1 but remained unchanged around 850 min · day–1 for V. b. nebulosus. The mean duration of locomotor activity decreased in V. s. salvator and V. b. nebulosus after the parietal eye was covered, but V. b. nebulosus maintained its locomotor activity by increasing the number of locomotor bouts. The water monitor spent very little time on
thermoregulation. Its body temperature ranged between 26.3 and 28.4 °C, which decreased after the parietal eye was covered.
The clouded monitor thermoregulated around 28.8–36.0 °C, which remained unchanged after the parietal eye was covered. In both
species, there was a strong correlation between body temperature and ambient temperature. Behavioural abnormalities were recorded
among V. s. salvator with covered parietal eye. They were often observed to be active by night and often slept outside a burrow. The circadian
rhythm of V. b. nebulosus appeared unaffected by shielding of its parietal eye. Captivity combined with shielded parietal eye induced agonistic behaviour
in both species.
Accepted: 11 September 1996 相似文献
8.
S. J. Brown R. B. Child S. H. Day A. E. Donnelly 《European journal of applied physiology and occupational physiology》1997,75(4):369-374
Indirect indices of exercise-induced human skeletal muscle damage and connective tissue breakdown were studied following
a single bout of voluntary eccentric muscle contractions. Subjects (six female, two male), mean (SD) age 22 (2) years performed
a bout of 50 maximum voluntary eccentric contractions of the knee extensors of a single leg. The eccentric exercise protocol
induced muscle soreness (P < 0.05 Wilcoxon test), chronic force loss, and a decline in the 20:100 Hz percutaneous electrical myostimulation force ratio
[P < 0.01, repeated measures analysis of variance (ANOVA)]. Serum creatine kinase (CK) and lactate dehydrogenase (LDH) activities
were elevated (P < 0.01, repeated measures ANOVA) following the bout. The mean (SD) CK and LDH levels recorded 3 days post-exercise were 2815
(4144) IU · l–1 and 375 (198) IU · l–1, respectively. Serum alkaline phosphatase activity showed no changes throughout the study, and a non-significant increase
(P = 0.058, repeated measures ANOVA) in pyridinoline was recorded following the bout. Urinary hydroxyproline (HP) and hydroxylysine
(HL) excretion, expressed in terms of creatinine (Cr) concentration, increased after exercise (P < 0.05 and P < 0.01, respectively, repeated measures ANOVA). An increased HP:Cr was recorded 2 days post-exercise and HL:Cr was increased
above baseline on days 2, 5, and 9 post-exercise. This indirect evidence of exercise-induced muscle damage suggests that myofibre
disruption was caused by the eccentric muscle contractions. Elevated urine concentrations of indirect indices of collagen
breakdown following eccentric muscle contractions suggests an increased breakdown of connective tissue, possibly due to a
localised inflammatory response.
Accepted: 9 October 1996 相似文献
9.
A.-W. Pan J. He Y. Kinouchi Hisao Yamaguchi Hiroshi Miyamoto 《European journal of applied physiology and occupational physiology》1997,75(5):388-395
The present study investigated the mechanism of diving bradycardia. A group of 14 healthy untrained male subjects were examined
during breath-holding either out of the water (30–33°C), in head-out immersion, or in whole-body submersion (27–29°C) in a
diving pool. Blood velocity, blood volume flow in the carotid artery, diastolic blood pressure and electrocardiogram were
measured and recorded during the experiments. The peak blood velocity increased by 13.6% (P < 0.01) and R-wave amplitude increased by 57.1% (P < 0.005) when the subjects entered water from air. End-diastolic blood velocity in the carotid artery increased significantly during breath-holding, e.g. increased from 0.20 (SD 0.02) m · s−1 at rest to 0.33 (SD 0.04) m · s−1 (P < 0.001) at 50.0 s in breath-hold submersion to a 2.0-m depth. Blood volume flow in the carotid artery increased by 26.6%
(P < 0.05) at 30 s and 36.6% (P < 0.001) at 40 s in breath-hold submersion to a 2.0-m depth. Diastolic blood pressure increased by 15.4% (P < 0.01) at 60 s during breath-holding in head-out immersion. Blood volume flow, and diastolic blood pressure increased significantly more and faster during breath-holding in submersion than out of the
water. There was a good negative correlation with the heart rate: the root mean square correlation coefficient r was 0.73 (P < 0.001). It was concluded that an increased accumulation of blood in the aorta and arteries at end-diastole and decreased
venous return, caused by an increase in systemic peripheral resistance during breath-holding, underlies diving bradycardia.
Accepted: 22 November 1996 相似文献
10.
Water relations dynamics during simulated sunflecks at high (36°C) and medium (27°C) temperatures and high and low vapour
pressure deficits beween leaf and air (VPD) were studied on shade-grown Piper auritum H.B. & K. plants, a pioneer tree, common in gaps and clearings of tropical rain forests. The leaves of P. auritum wilt rapidly when exposed to high light. Exposure to high VPD and high light caused substantial and rapid dehydration of
leaves. Dehydration could be prevented under high humidity irrespective of temperature. Water stored in leaf cells served
as initial source for transpiration upon high light exposure. This effect increased with increasing VPD and temperature. The
pronounced decrease in leaf water content over time in high light caused a rapid decrease in leaf water potential (Ψl) and a concomitant increase in water potential gradient (ΔΨ/Δx) between trunk and leaf, yet the high leaf elasticity (small bulk elastic modulus, ε) allowed turgor maintenance under most
conditions. Under high VPD and high temperature, stomata remained open and ΔΨ/Δx frequently exceeded 0.95 MPa · m−1, the cavitation-inducing threshold (ΔΨ/Δx
cav) causing high rates of acoustic emissions from stems and leaf petioles and leading to concomitant losses in hydraulic conductance
per leaf area (k
l). At medium temperature (high VPD), stomatal closure contained xylem embolism by keeping ΔΨ/Δx at or below this threshold. We argue that wilting substantially contributes to creating a sufficient driving force for water
uptake from the soil, and reducing the VPD (through a decrease in radiation load and thus leaf temperature) to avoid excessive
dehydration.
Received: 3 March 1996 / Accepted: 10 November 1996 相似文献
11.
Stem respiration of ponderosa pines grown in contrasting climates: implications for global climate change 总被引:7,自引:0,他引:7
We examined the effects of climate and allocation patterns on stem respiration in ponderosa pine (Pinus ponderosa) growing on identical substrate in the cool, moist Sierra Nevada mountains and the warm, dry, Great Basin Desert. These environments
are representative of current climatic conditions and those predicted to accompany a doubling of atmospheric CO2, respectively, throughout the range of many western north American conifers. A previous study found that trees growing in
the desert allocate proportionally more biomass to sapwood and less to leaf area than montane trees. We tested the hypothesis
that respiration rates of sapwood are lower in desert trees than in montane trees due to reduced stem maintenance respiration
(physiological acclimation) or reduced construction cost of stem tissue (structural acclimation). Maintenance respiration
per unit sapwood volume at 15°C did not differ between populations (desert: 6.39 ± 1.14 SE μmol m−3 s−1, montane: 6.54 ± 1.13 SE μmol m−3 s−1, P = 0.71) and declined with increasing stem diameter (P = 0.001). The temperature coefficient of respiration (Q
10) varied seasonally within both environments (P = 0.05). Construction cost of stem sapwood was the same in both environments (desert: 1.46 ± 0.009 SE g glucose g−1 sapwood, montane: 1.48 ± 0.009 SE glucose g−1 sapwood, P = 0.14). Annual construction respiration calculated from construction cost, percent carbon and relative growth rate was greater
in montane populations due to higher growth rates. These data provide no evidence of respiratory acclimation by desert trees.
Estimated yearly stem maintenance respiration was greater in large desert trees than in large montane trees because of higher
temperatures in the desert and because of increased allocation of biomass to sapwood. By analogy, these data suggest that
under predicted increases in temperature and aridity, potential increases in aboveground carbon gain due to enhanced photosynthetic
rates may be partially offset by increases in maintenance respiration in large trees growing in CO2-enriched atmospheres.
Received: 4 November 1996 / Accepted: 23 January 1997 相似文献
12.
Shizuo Suzuki 《Oecologia》1998,117(1-2):169-176
Leaf demography, seasonal changes in leaf quality and leaf-beetle herbivory of a herbaceous perennial plant, Sanguisorba tenuifolia, were compared between low- and high-elevation sites. Leaf nitrogen concentration was higher and leaf mass per area (LMA)
was lower at the higher site than at the lower one. At the lower site, with a long growth period, plants produced many leaf
cohorts and leaves emerged throughout the growing season. At the higher site, with a short growth period, however, leaf emergence
was concentrated early in the growing season. The improvement of leaf quality and acceleration of leaf emergence at higher
altitude are seen as adaptations to a short growing season. Results of a feeding trial suggested that leaf quality for the
leaf-beetle Galerucella grisescens was higher at the higher site, but plants at the higher site showed less damage. Oviposition of G. grisescens was seasonal and unimodal at both altitudes, but the period of oviposition was shorter and its density lower at the higher
site. The low temperature and short growth period at the higher site appear to reduce the activity of the leaf-beetles, resulting
in a decrease in damage by herbivory, despite better leaf quality.
Received: 11 December 1997 / Accepted: 24 July 1998 相似文献
13.
V. M. King B. K. Follett 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1997,180(5):541-551
c-fos induction was investigated as a potential component in the avian photic entrainment pathway and as a possible means of locating
the central pacemaker in birds. In both quail (Coturnix coturnix japonica) and starlings (Sturnus vulgaris) exposure to 1 h of light induced Fos-lir in the visual suprachiasmatic nucleus but not in the medial suprachiasmatic nucleus. However, the degree of c-fos induction in the visual suprachiasmatic nucleus was similar at different circadian times despite the fact that the light
pulses caused differential phase shifts in the locomotor rhythm. For golden hamsters the same experiment resulted in significantly
different levels of Fos-lir in the suprachiasmatic nucleus, as well as different phase shifts. Starlings and hamsters were also entrained to T-cycles that caused a large daily phase shift (T = 21.5 h in starlings, T = 22.67 hours in hamsters), or no daily phase shift (T = free running period). No difference in the induced levels of Fos-lir in the visual suprachiasmatic nucleus region was observed between the two groups of starlings, but in hamsters there were
significantly different levels of Fos-lir in the suprachiasmatic nucleus between the two groups.
Accepted: 15 November 1996 相似文献
14.
Photoperiodic time measurement regulating larval diapause in the pitcher-plant mosquito, Wyeomyia smithii, varies in a close relationship with latitude. The critical photoperiod mediating the maintenance and termination of diapause
is positively correlated with latitude (r
2 = 0.977) among six populations from southern (30–31° N), intermediate (40° N), and northern (46–49° N) latitudes in North
America. The developmental response to unnaturally short and to unnaturally long photoperiods declines with increasing latitude,
so that longer critical photoperiods are associated with a downward rather than a lateral shift in the photoperiodic response
curve. Exotic light and dark cycles of varying period (T) with a short (10 h) photophase and a scotophase ranging from 14
(T = 24) to 62 (T = 72) h, reveal two geographic patterns: a decline in perturbability of the photoperiodic clock with increasing
latitude, and no change with latitude in the 21-h period of rising and falling development with increasing T. These results
show (1) that there is a rhythmic component to photoperiodic time measurement in W. smithii, (2) that the period of this rhythm is about 21 h in all populations, and (3) that more northern populations show decreasing
responsiveness to photoperiod and increasing stability against perturbation by exotic period lengths (T > 24). Previous studies
on W.␣smithii indicate that this single temperate species of a tropical and subtropical genus has evolved from south to north. We therefore
conclude that the evolution of increasing critical photoperiod in W. smithii during its adaptive radiation into North America has more likely involved the amplitude and not the period of the underlying
circadian pacemaker.
Received: 22 July 1996 / Accepted: 30 September 1996 相似文献
15.
In this study, sun leaf carbon isotope composition (δ13C) of two co-occurring woody Mediterranean species (Quercus pubescens Willd., a deciduous oak, and Q. ilex L., an evergreen one) was investigated on four sites with different water availability. The total range of δ13C values was 4.4 and 3.1‰ for Q. pubescens and Q. ilex respectively. The intra-site variability was about 3‰. Total mean per species was equal. There were significant differences
among sites, but at each site means of δ13C were not significantly different between species. A simple physiological model predicts no difference in intrinsic water-use
efficiency (WUEi) between evergreen and deciduous oaks. The relationship between site means of δ13C and water parameters suggests that there is a leaf functional adjustment with respect to available water resource. No correlation
was found between δ13C and the contents of any mass-based biochemical constituent. Nevertheless there was a significant correlation between δ13C and leaf mass per area of Q. ilex. For both species, there is also a positive correlation between leaf δ13C and individual crown area, i.e. a structural characteristic at tree level. Causal relations between δ13C and plant-environment interactions are discussed.
Received: 25 October 1996 / Accepted: 19 January 1997 相似文献
16.
In order to test whether an increased export of carbohydrates by leaves and starch mobilization are critical for floral transition
in Arabidopsis thaliana, the Columbia ecotype as well as its starchless mutant pgm and starch-in-excess mutant sex1 were investigated. Induction of flowering was achieved by exposure of plants to either one long day (LD) or one displaced
short day (DSD). The following conclusions were drawn: (i) Both the pgm and sex1 mutants have a late-flowering phenotype in days shorter than 16 h. (ii) When inductive treatments cause a large percentage
of induced plants, there is always a large, early and transient increase in carbohydrate export from leaves. By contrast,
when an inductive treatment results in only a low percentage of induced plants (pgm plants exposed to one DSD), the export of carbohydrates from leaves is not increased, supporting the idea that phloem carbohydrates
have a critical function in floral transition. (iii) Starch mobilization is not required to obtain an increased carbohydrate
export when induction is by one LD (extended period of photosynthesis), but is absolutely essential when induction is by one
DSD (period of photosynthesis unaffected). (iv) Floral induction apparently increases the capability of the leaf phloem-loading
system.
Received: 27 August 1997 / Accepted: 6 March 1998 相似文献
17.
T. Ruf A. I. Korytko A. Stieglitz K. R. Lavenburg J. L. Blank 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1997,167(3):185-192
We investigated pineal function as well as reproductive and energetic characteristics in male deer mice (Peromyscus maniculatus) that differentially respond to short photoperiod with full, partial or no gonadal regression. In mice at both high (23 °C)
and low temperature (1 °C), these phenotypic differences in reproductive responses to short days were not reflected by differences
in urinary excretion of 6-sulphatoxy-melatonin, the main metabolite of pineal melatonin. Neither duration nor amplitude or
phase-angle of nocturnal peaks in 6-sulphatoxymelatonin significantly differed between reproductive phenotypes at either temperature.
Differences in testis size were, however, associated with different energy requirements. In gonadally regressed males only,
food intake and body weight were significantly (P < 0.01) reduced by up to 29% and 13% respectively. Chronic cold exposure (5 °C) had no effect on the proportion of males
undergoing testicular regression under short days, but caused a general elevation in body weights among all mice (P < 0.05). Phenotypic differences in body weight and food intake were maintained in the cold. Together, these results suggest
that within-population variation of reproductive responses in male deer mice is based on post-pineal differences in the regulation of gonadal function, and that phenotypic characteristics in reproductive and energetic
responses to short days are largely unaffected by ambient temperature.
Accepted: 2 October 1995 相似文献
18.
Hilde Spielvogel Armando Rodriguez Brigitte Sempore Esperanza Caceres J.-M. Cottet-Emard Laurent Guillon R. Favier 《European journal of applied physiology and occupational physiology》1997,75(5):400-406
The present study was undertaken to determine the haematological and cardiovascular status, at rest and during prolonged
(1 h) submaximal exercise (approximately 70% of peak oxygen uptake) in a group (n = 12) of chronic coca users after chewing approximately 50 g of coca leaves. The results were compared to those obtained
in a group (n = 12) of nonchewers. At rest, coca chewing was accompanied by a significant increase in heart rate [from 60 (SEM 4) TO 76 (SEM 3)
beats · min−1], in haematocrit [from 53.2 (SEM 1.2) to 55.6 (SEM 1.1)%] in haemoglobin concentration, and plasma noradrenaline concentration
[from 2.8 (SEM 0.4) to 5.0 (SEM 0.5) μmol · l−1]. It was calculated that coca chewing for 1 h resulted in a significant decrease in blood [−4.3 (SEM 2.2)%] and plasma [−8.7 (SEM 1.2)%]
volume. During submaximal exercise, coca chewers displayed a significantly higher heart rate and mean arterial blood pressure.
The exercise-induced haemoconcentration was blunted in coca chewers compared to nonchewers. It was concluded that the coca-induced
fluid shift observed at rest in these coca chewers was not cumulative with that of exercise, and that the hypovolaemia induced
by coca chewing at rest compromised circulatory adjustments during exercise.
Accepted: 29 October 1996 相似文献
19.
S. R. Soffe 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1997,180(6):711-715
Young Xenopus tadpoles were used to test whether the pattern of discharge in specific sensory neurons can determine the motor response
of a whole animal. Young Xenopus tadpoles show two main rhythmic behaviours: swimming and struggling. Touch-sensitive skin sensory neurons in the spinal cord
of immobilised tadpoles were penetrated singly or in pairs using microelectrodes to allow precise control of their firing
patterns. A single impulse in one Rohon-Beard neuron (= light touch) could sometimes trigger “fictive” swimming. Two to six
impulses at 30–50 Hz (= a light stroke) reliably triggered fictive swimming. Neither stimulus evoked fictive struggling. Twenty-five
or more impulses at 30–50 Hz (= pressure) could evoke a pattern of rhythmic bursts, distinct from swimming and suitable to
drive slower, stronger movements. This pattern showed some or all the characteristics of “fictive” struggling. These results
demonstrate clearly that sensory neurons can determine the pattern of motor output simply by their pattern of discharge. This
provides a simple form of behavioural selection according to stimulus.
Accepted: 28 November 1996 相似文献
20.
Sherri M. Jones Timothy A. Jones Roshni Shukla 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1997,180(6):631-638
Short-latency vestibular-evoked potentials to pulsed linear acceleration were characterized in the quail. Responses occurred
within 8 ms following the onset of stimuli and were composed of a series of positive and negative peaks. The latencies and
amplitudes of the first four peaks were quantitatively characterized. Mean latencies at 1.0 g ms−1 ranged from 1265 ± 208 μs (P1, N = 18) to 4802 ± 441 μs (N4, N = 13). Amplitudes ranged from 3.72 ± 1.51 μV (P1/N1, N = 18) to 1.49 ± 0.77 μV (P3/N3, N = 16). Latency-intensity (LI) slopes ranged from −38.7 ± 7.3 μs dB−1 (P1, N = 18) to −71.6 ± 21.9 μs dB−1 (N3, N = 15) and amplitude-intensity (AI) slopes ranged from 0.20 ± 0.08 μV dB−1 (P1/N1, N = 18) to 0.07 ± 0.04 μV dB−1 (P3/N3, N = 11). The mean response threshold across all animals was −21.83 ± 3.34 dB re: 1.0 g ms−1 (N = 18). Responses remained after cochlear extirpation showing that they could not depend critically on cochlear activity.
Responses were eliminated by destruction of the vestibular end organs, thus showing that responses depended critically and
specifically on the vestibular system. The results demonstrate that the responses are vestibular and the findings provide
a scientific basis for using vestibular responses to evaluate vestibular function through ontogeny and senescence in the quail.
Accepted: 18 January 1997 相似文献