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1.
M. P. McGuire 《Coral reefs (Online)》1998,17(4):369-375
Annual and lunar patterns of larval release by the coral Porites astreoides in the Florida Keys were investigated. Corals were collected monthly and maintained in outdoor, flow-through systems to quantify
nightly release of larvae. Planulae were released during a period from 10 days prior to the new moon through 11 days after
the new moon, with a peak in release centered on the new moon. The average duration of larval release by a single colony was
9 nights. Although the correlation was low (r=0.292), there was a positive relationship between colony size and number of larvae released. The majority of larval release
occurred in April and May, although smaller numbers of larvae were observed from June through as late as September. Larval
release appeared to be correlated with the average water temperatures over the 30 days prior to the new moon, peaking when
water temperatures were 24.5–27.5 °C.
Accepted: 3 August 1998 相似文献
2.
We examined monthly changes in polycyclic aromatic hydrocarbons (PAHs) in sediment trap samples collected from the northern
basin of Lake Biwa, Japan, from September 2003 to July 2004 to elucidate the sources of PAHs in the lake. The most abundant
concentrations were those of pyrene and fluoranthene, at μg g−1 levels throughout the sampling period, with a strong positive relationship (r = 0.996, n = 10, P < 0.01). From the monthly changes in each PAH concentration and their ratios, we suspected two different sources: petroleum
sources of lighter PAHs and combustion sources of middle to heavier PAHs. Because pyrene and fluoranthene decreased significantly
with time during the sampling period (P < 0.05) and an abnormally high ratio of phenanthrene to anthracene was reported in September 2003, it appears that petroleum
was accidentally spilled in September 2003. Although perylene was commonly found at μg g−1 levels in the sediment, its concentration was comparable with those of the other PAHs in sediment trap samples. As perylene
showed no significant relationship with other PAHs or other indicator molecules, we suspect that the source of perylene was
different from those of other PAHs, and the perylene was mainly formed from its precursors after deposition. 相似文献
3.
Biomass and metabolism of zooplankton in the Bransfield Strait (Antarctic Peninsula) during austral spring 总被引:1,自引:1,他引:0
Zooplankton biomass (as dry weight), respiration and ammonia excretion were studied in three different size classes (200–500,
500–1000 and >1000 μm) in the Bransfield Strait during December 1991. Average mesozooplankton biomass was 86.45 ± 56.74 mg · dry weight · m−2, which is in the lower range of the values cited in the literature for polar waters. Higher biomass was observed in the Weddell
water. The small size fraction accounted for about 50% of total biomass while the largest one represented 35%. Rather high
metabolic rates were found, irrespective of whether the organisms were incubated in the presence of food. No significant differences
were observed in mass specific respiration and ammonia excretion rates between different temperatures of incubation (0.2–2.3°C)
and between the size classes studied. Because of the very low biomass values observed, the metabolic requirements of mesozooplankton
during December represented a small fraction of the primary production.
Accepted: 5 September 1998 相似文献
4.
Ján Hrvoľ Viera Horecká Jaroslav Škvarenina Katarína Střelcová Jana Škvareninová 《Biologia》2009,64(3):605-609
The paper presents the results of the model computation of actual and potential evapotranspiration as well as evaporation
measurements from the GGI-3000 Pan (evaporimeter) at 3 selected stations of Slovakia for the periods 1971–2000 (2 stations)
and 1986–2000 (1 station). The localities are situated in the most southern parts of Slovakia in 1st Oak stage and on southern slopes of the Carpathian promontories. A model computation of the monthly totals of actual and
potential evapotranspiration was performed by a common solution of energy and water balance equations of the top one-meter
layer of the soil. The model outputs are compared to the measurement data. The dependence of the ratio of actual evapotranspiration/
evaporation measured by the GGI-3000 Pan (E/E
p) on relative evapotranspiration (E/E
o), when E, E
o are calculated, is linear with a high correlation coefficient during the season from April to October. The paper also gives
the comparison results of the mean monthly and annual air temperatures, temperatures of active and saturated surface with
the mean monthly temperature of free water surface in the GGI-3000 Pan at these 3 stations (Bratislava-Koliba, Somotor and
Žihárec). It was found that the mean free water surface temperature for the period from April to October is close to the mean
temperature of saturated surface during that period. The mean temperatures of free water surface in the GGI-3000 Pan from
April to October tend to increase for the period 1971–2000. 相似文献
5.
Childhood leukemia in Belarus before and after the Chernobyl accident: continued follow-up 总被引:3,自引:0,他引:3
Gapanovich VN Iaroshevich RF Shuvaeva LP Becker SI Nekolla EA Kellerer AM 《Radiation and environmental biophysics》2001,40(4):259-267
Earlier assessments led to the conclusion that due to the added radiation after the Chernobyl accident, childhood leukemia
in Belarus was not recognisably increased in the years 1987–1994 compared to the years 1982–1986, i.e. the period before the
accident. The present paper gives the data of the continued follow-up (1995–1998) which was conducted by the Institute of Haematology and Blood Transfusion, Minsk. In line with the earlier observations no increase has been identified. The incidence rates have been compared to
the data of the newly established Belarussian Childhood Cancer Registry and a tentative explanation is given for apparent differences between the rates from our follow-up and the data reported
earlier by the Belarussian Childhood Cancer Registry.
Received: 20 May 2001 / Accepted: 10 September 2001 相似文献
6.
The dynamics of aseasonal lowland dipterocarp forest in Borneo is influenced by perturbation from droughts. These events might
be increasing in frequency and intensity in the future. This paper describes drought-affected dynamics between 1986 and 2001
in Sabah, Malaysia, and considers how it is possible, reliably and accurately, to measure both coarse- and fine-scale responses
of the forest. Some fundamental concerns about methodology and data analysis emerge. In two plots forming 8 ha, mortality,
recruitment, and stem growth rates of trees ≥10 cm gbh (girth at breast height) were measured in a ‘pre-drought’ period (1986–1996), and in a period (1996–2001) including the 1997–1998
ENSO-drought. For 2.56 ha of subplots, mortality and growth rates of small trees (10–<50 cm gbh) were found also for two sub-periods (1996–1999, 1999–2001). A total of c. 19 K trees were recorded. Mortality rate increased by 25% while both recruitment and relative growth rates increased by
12% for all trees at the coarse scale. For small trees, at the fine scale, mortality increased by 6% and 9% from pre-drought
to drought and on to ‘post-drought’ sub-periods. Relative growth rates correspondingly decreased by 38% and increased by 98%.
Tree size and topography interacted in a complex manner with between-plot differences. The forest appears to have been sustained
by off-setting elevated tree mortality by highly resilient stem growth. This last is seen as the key integrating tree variable
which links the external driver (drought causing water stress) and population dynamics recorded as mortality and recruitment.
Suitably sound measurements of stem girth, leading to valid growth rates, are needed to understand and model tree dynamic
responses to perturbations. The proportion of sound data, however, is in part determined by the drought itself.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
7.
Karibu Fukuzawa Hideaki Shibata Kentaro Takagi Fuyuki Satoh Takayoshi Koike Kaichiro Sasa 《Ecological Research》2007,22(3):485-495
We measured the vertical distribution and seasonal patterns of fine-root production and mortality using minirhizotrons in
a cool–temperate forest in northern Japan mainly dominated by Mongolian oak (Quercus crispula) and covered with a dense understory of dwarf bamboo (Sasa senanensis). We also investigated the vertical distribution of the fine-root biomass using soil coring. We also measured environmental
factors such as air and soil temperature, soil moisture and leaf area indices (LAI) of trees and the understory Sasa canopy for comparison with the fine-root dynamics. Fine-root biomass to a depth of 60 cm in September 2003 totaled 774 g m−2, of which 71% was accounted for by Sasa and 60% was concentrated in the surface soil layer (0–15 cm), indicating that understory Sasa was an important component of the fine-root biomass in this ecosystem. Fine-root production increased in late summer (August)
when soil temperatures were high, suggesting that temperature partially controls the seasonality of fine-root production.
In addition, monthly fine-root production was significantly related to Sasa LAI (P<0.001), suggesting that fine-root production was also affected by the specific phenology of Sasa. Fine-root mortality was relatively constant throughout the year. Fine-root production, mortality, and turnover rates were
highest in the surface soil (0–15 cm) and decreased with increasing soil depth. Turnover rates of production and mortality
in the surface soil were 1.7 year−1 and 1.1 year−1, respectively. 相似文献
8.
The timing of reproduction is one of the most crucial life history traits, with enormous consequences for the fitness of an
individual. We investigated the effects of season and timing of birth on local survival probability in a small mammalian hibernator,
the common dormouse (Muscardinus avellanarius). Local monthly survival probability was lowest in the early active season (May–August, ϕadult = 0.75–0.88, ϕjuvenile = 0.61–0.68), increased during the late active season (August–October), and highest during hibernation (October–May, ϕadult = 0.96–0.98, ϕjuvenile = 0.81–0.94). Consequently, dormice had an extremely high winter survival probability. We observed two peaks in the timing
of reproduction (June and August/September, respectively), with the majority of juveniles born late in the active season.
Although early investment in reproduction seems the better life history tactic [survival probability until onset of reproduction:
ϕborn early = 0.46, 95% confidence interval (CI) 0.28–0.64; ϕborn late = 0.19, 95% CI = 0.09–0.28], only females with a good body condition (significantly higher body mass) invest in reproduction
early in the year. We suggest the high over-winter survival in dormice allows for a unique life history pattern (i.e., combining
slow and fast life history tactics), which leads to a bimodal seasonal birth pattern: (1) give birth as early as possible
to allow even the young to breed before hibernating, and/or (2) give birth as late as possible (leaving just enough time for
these young to fatten) and enter directly into a period associated with the highest survival rates (hibernation) until maturity. 相似文献
9.
It has been suggested, that the inhabitants of northern European regions, who experience little cold-related mortality, protect
themselves outdoors by wearing more clothing, at the same temperature, than people living in southern regions where such mortality
is high. Outdoor clothing data were collected in eight regions from 6583 people divided by sex and age group (50–59 and 65–74
years). Across Europe, the total clothing worn (as assessed by dry thermal insulation and numbers of items or layers) increased
significantly with cold, wind, less physical activity and longer periods outdoors. Men wore 0.14 clo (1 clo=0.115 m2 K W–1) more than women and the older people wore 0.05 clo more than the younger group (both P<0.001). After allowance for these factors, regional differences in insulation and item number were correlated (r=–0.74, P=0.037; r=–0.74, P=0.036 respectively), but not those in clothing layers (r=–0.21; P=0.61), with indices of cold-related mortality. Cold weather most increased the wearing of gloves, scarves and hats. The geographical
variation in the wearing of these three together items more closely matched that in cold-related mortality (r=–0.89, P=0.003). A possible explanation for this may be that they protect the head and hands, where stimulation by cold greatly increases
peripheral vasoconstriction causing a rise in blood pressure that procedure haemoconcentration and raised cardiovascular risk.
Received: 30 September 1999 / Revised: 3 April 2000 / Accepted: 5 June 2000 相似文献
10.
Jan Broucek Peter Kisac Michael Uhrincat 《International journal of biometeorology》2009,53(2):201-208
The objective of this paper was to evaluate the effects of high temperatures on calves. The hypothesis that the red and white
blood cells, health, and performance of calves would be influenced by the temperature period at birth and gender was tested.
Sixty-three Holstein calves were used. They were reared in individual hutches from the second day of life to weaning at the
age of 8 weeks. All calves were allotted to treatment groups according to the temperature period at birth: moderate temperature
period 1 (MT1), high temperature period (HT), moderate temperature period 2 (MT2). The same conditions of nutrition were ensured.
We recorded 62 summer days and 14 tropical days during HT. Sixty-six days with a value above 72.0 of the temperature–humidity
index (THI) and 26 with values greater than 78.0 were found. No significant differences were found in red blood cells with
the exception of hemoglobin between MT1 and MT2 (p = 0.031) during the 8th week. Significant differences were observed among treatment groups in the percentage of eosinophiles
during the 6th week (p = 0.044). The HT calves had the least body weight from the first week to weaning (p = 0.053) and the highest water consumption (p = 0.042). The results emphasize the ability of dairy calves to maintain homeostasis during prolonged periods of heat stress.
The exposure to high temperatures resulted only in a significant decrease of starter concentrate consumption and reduced growth. 相似文献
11.
K. Nonaka Bertrand Desjardins Hubert Charbonneau Jacques Légaré Teiji Miura 《International journal of biometeorology》1998,42(2):89-92
We investigated population-based vital records of the seventeenth and eighteenth century French Canadian population to assess
the effects of marriage season on the outcome of the first births under natural fertility conditions (n=21,698 marriages). Promptness of the first successful conception after marriage differed according to marriage season; the
proportion of marriages with a marriage-first birth interval of 8.0–10.0 months was lowest (34%) for marriages in August–October
(P=0.001). Although the male/female sex ratio of the babies born with an interval of 8.0–10.0 months was generally higher (1.10)
than those with an interval of 10.0–24.0 months (1.05), the marriages in August–October resulted in a significantly reduced
sex ratio (0.96) among only the prompt conceptions (P=0.026). We discuss whether this seasonal reduction of the sex ratio could be partly explained by a clustered pregnancy loss
of male zygotes in early pregnancy.
Received: 5 January 1998 / Accepted: 9 September 1998 相似文献
12.
We have examined the relationship between phenological data and concurrent large-scale meterological data. As phenological
data we have chosen the beginning of the flowering of Galanthus nivalis L. (flowering date) in Northern Germany, and as large-scale meteorological data we use monthly mean near-surface air temperatures
for January, February and March. By means of canonical correlation analysis (CCA), a strong linear correlation between both
sets of variables is identified. Twenty years of observed data are used to build the statistical model. To validate the derived
relationship, the flowering date is downscaled from air temperature observations of an independent period. The statistical
model is found to reproduce the observed flowering dates well, both in terms of variability as well as amplitude. Air temperature
data from a general circulation model of climate change are used to estimate the flowering date in the case of increasing
atmospheric carbon dioxide concentration. We found that at a time of doubled CO2 concentration (expected by about 2035) G. nivalis L. in Northern Germany will flower ∼2 weeks and at the time of tripled CO2 concentration (expected by about 2085) ∼4 weeks earlier than presently.
Received: 7 August 1996 / Accepted: 27 November 1996 相似文献
13.
V. Kaden E. Lange A. Hänel A. Hlinak L. Mewes G. Hergarten B. Irsch J. Dedek W. Bruer 《European Journal of Wildlife Research》2009,55(2):153-159
The objective of this study was to retrospectively evaluate the occurrence of porcine parvovirus (PPV), Aujeszky’s disease
virus (ADV), transmissible gastroenteritis virus (TGEV), porcine respiratory coronavirus (PRCV), porcine reproductive and
respiratory syndrome virus (PRRSV) and swine influenza virus (SIV) in selected wild boar populations in Germany (n
= 1,221). Commercial enzyme linked immunosorbent assay and hemagglutination inhibition tests were used for serological monitoring.
The serosurvey revealed seroprevalence rates of 64.28%, 11.26%, 7.87%, 7.84%, 3.82% and 1.59% for PPV, ADV, PRCV, SIV, PRRSV
and TGEV, respectively. The seroprevalence rates differed between populations and age classes with the highest number of antibody-positive
wild boars in older animals (>1 year old). No antibodies to TGEV were found in Baden–Wuerttemberg and in Mecklenburg–Western
Pomerania (investigation period 1997/1998). In addition, sera collected in Mecklenburg–Western Pomerania in 1997/1998 were
negative for SIV. Even though the seroprevalence rates established for these viruses, except for PPV, were relatively low,
wild boars may act as a reservoir for pathogens and a source of infection for domestic pigs and humans. Based on the epidemiological
situation, no risk of a spread of these viruses should emanate from wild boars, neither for wildlife nor for livestock. However,
effective and science-based disease monitoring programmes should continuously be carried out in wild boar populations. 相似文献
14.
Judit Kocsis Balázs Madaras Éva Katalin Tóth George Füst Zoltán Prohászka 《Cell stress & chaperones》2010,15(2):143-151
Many findings indicate that measuring the serum concentration of soluble 70-kD heat shock protein (soluble HSP70) may provide
important information in cardiovascular, inflammatory, and pregnancy-related diseases; however, only scarce data are available
in cancer. Therefore, using a commercial ELISA kit, we measured soluble HSP70 concentration in the sera of 179 patients with
colorectal cancer. We investigated the relationship between soluble HSP70 concentration and mortality, during 33.0 (24.4–44.0) months
long follow-up. High (>1.65 pg/ml, median concentration) soluble HSP70 level was a significant (hazard ratio: 1.88 (1.20–2.96,
p = 0.005) predictor of mortality during the follow-up period. When we compared the soluble HSP70 levels in patients with non-resected
primary tumors as compared to those who were recruited into the study 4–6 weeks after the tumor resection they were found
to be significantly (p = 0.020) higher in the former group. Since the patients with non-resected primary tumors had also distant metastasis and
died early, we limited the further analysis to 142 patients with no distant metastasis at the beginning of the follow-up.
This association remained significant even after multiple Cox-regression analysis had been performed to adjust the data for
age and sex (p = 0.028); age, sex, and TNM-T stage (p = 0.041); age, sex, and TNM-N stage (p = 0.021); age, sex, and histological grade (p = 0.023); or age, sex, and tumor localization (p = 0.029). Further analysis showed that the significant association between high HSP70 levels and poor survival is in the
strongest in the group of <70-year-old female patients (HR: 5.52 (2.02-15.15), p = 0.001), as well as in those who were in a less advanced stage of the disease at baseline. These novel findings indicate
that the serum level of soluble HSP70 might prove a useful, stage-independent prognostic marker in colorectal cancer without
distant metastasis. 相似文献
15.
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
16.
Planulation by Favia fragum at the high-latitude reef of Bermuda was examined during July and August of 2004–2007. In 2004 and 2005, observations were
extended to June and September; however, planulation only occurred in July and August, when temperatures were increasing toward
and during the annual high. Planulation peaked 6–12 days after the new moon, corresponding to the pattern found for F. fragum in the Caribbean. Mean monthly fecundity was also similar to that found in the Caribbean; however, annual and monthly fecundity
were variable, being lowest in July 2005, which coincided with lowest mean SST. These results indicate that although fecundity
and lunar timing of planulation by F. fragum are not affected by latitude, reproductive seasonality may be shorter at high-latitude reefs. Understanding reproductive
events at latitudinal extremes gives insight to environmental controls on coral reproduction, which will aid in future management
and restoration efforts. 相似文献
17.
Ibarrola I Larretxea X Navarro E Iglesias JI Urrutia MB 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》2008,178(4):501-514
Seasonal variation in size-dependence of seawater clearance rate, absorption efficiency, oxygen consumption, gill area, length
of the crystalline style and dry weight of digestive gland was analyzed in cockles Cerastoderma edule from the Mundaka Estuary, Spain. Experimental determinations were performed monthly (from July 1998 to November 1999) in
cockles being fed with Tetraselmis suecica (organic content: 87.84 ± 1.95%) at a concentration of 3 mm3/l for 3 days. Analysis of covariance reveals no seasonal differences in both size-dependence of seawater clearance rate and
oxygen consumption, which were found to scale to dry body weight with mass-exponents of 0.56 and 0.62, respectively. No significant
correlation was found between absorption efficiency and body weight. Mass-exponents for gill area, dry weight of the digestive
gland and length of the crystalline style remained constant among seasons showing values of 0.62, 0.34 and 0.82, respectively.
Seasonal trends for every physiological determination were calculated for a standard size (200 mg) cockle: standardized clearance
rates and oxygen consumptions followed a similar trend with minimum values in winter (≈0.5 l/h and ≈100 μl O2/h, respectively) and maximum values during spring–summer (≈1.7 l/h and ≈250 μl O2/h, respectively), whereas absorption efficiency and food throughput time showed both the opposite pattern with highest values
corresponding to winter months (≈50–60% and ≈5–6 h, respectively), and lowest (≈30% and ≈3–4 h, respectively) to summer–autumn.
Scope for growth exhibited minimum values in winter followed by a rapid increase along the winter–spring transition, maximum
values being attained in spring (May) and summer (July). Exponential decline of seasonal values of absorption efficiency associated
to rising ingestion rates of organic matter presented an asymptotic minimum at 0.35. Absorption efficiency was positively
related to food throughput time, whereas the latter fell to a minimum of 3.548 h with increasing food intake. So, maintenance
of throughput time—and consequently absorption efficiency—along with enhanced filtering activity provided cockles with higher
absorption rates improving scopes for growth registers during spring and summer. These dynamics might be explained as the
consequence of the seasonal digestive adjustments in cockles, which, in fact, were found to increase the size of the digestive
organs during that period. 相似文献
18.
The majority of lignin-degrading basidiomycetes are able to depolymerize humic acids. In this presentation the relationship
and possible similarities between enzymes involved in lignin degradation and humic acid depolymerization were examined on
the genetic level. We have cloned fragments of the gene encoding the extracellular ligninolytic enzyme laccase from Clitocybula dusenii, Nematoloma frowardii and a fungal strain designated i63-2, and compared the three sequences with those of several other published laccase genes.
The sequenced fragments displayed a high homology both on the DNA (97%–77%) and amino acid (100%–85%) level. Furthermore,
the expression of this gene in the above-mentioned fungi was demonstrated by a nested polymerase chain reaction with cDNA
as template.
Received: 3 February 1998 / Received revision: 31 August 1998 / Accepted: 3 September 1998 相似文献
19.
D. O Otieno C. Kurz-Besson J. Liu M. W. T. Schmidt R. Vale-Lobo do T. S. David R. Siegwolf J. S. Pereira J. D. Tenhunen 《Plant and Soil》2006,283(1-2):119-135
Studies were conducted to examine changes in soil (Ψs) and plant water status during summer in a 16-year old Quercus suber plantation in southern Portugal. Continuous measurements were conducted between May 2003 and August 2004, while discontinuous
measurements were conducted on a monthly basis between May and September 2003 and repeated between March and September 2004.
Intensive measurements were conducted on five trees with mean height and DBH of 5.3 m and 11.6 cm, respectively, growing at
close proximity to each other. Weather conditions and soil water potential (Ψs) at the rhizosphere of each of the trees measured
at 0.3 and 1 m soil depth were continuously monitored. Predawn (Ψpd) and midday (Ψmd) leaf water potentials were determined
every month. Soil and plant samples were also collected in June and September from different locations within the study site
for δ18O isotope composition analysis. Pressure–volume (p–v) curves were constructed from plant shoots at different times during the vegetative period to determine osmotic potential
at full saturation (Π100), water potential at turgor loss point (Ψtlp), relative water content at turgor loss point (R*tlp) and bulk modulus of elasticity (ε). Significant P < 0.05 decline in Ψs occurred between May and September, the lowest value recorded being –2.0 MPa. Decline in soil moisture
affected tree water status, but decline in leaf water potential varied significantly (P < 0.05) among the trees. At the end of summer drought, lowest Ψpd measured was –1.7 MPa while the highest measured during
this time was –0.8 MPa. Differences among trees were attributed to differences in rooting depth, as shown by regression analysis
of 18O isotopes. Radial stem growth ceased when Ψs within the upper 0.3 m depth approached –1.5 MPa. The upper soil layers contributed
approximately 33% of the total tree water requirement, between spring and mid summer when drought was experienced by trees.
Deep soil layers however, supplied most of the water required during drought and no growth was recorded during this time.
Stressed trees increased solute concentration of their tissues by a Magnitude of 0.7 MPa while bulk tissue elastic modulus
increased by about 17 MPa. The study emphasizes the significance of roots as determinants of tree productivity and survival
in the Mediterranean ecosystems. 相似文献
20.
Water loss through inflorescences may place extreme demands on plant water status in arid environments. Here we examine how
corolla size, a trait known to influence pollination success, affects the water cost of flowering in the alpine skypilot, Polemonium viscosum. In a potometry experiment, water uptake rates of inflorescences were monitored during bud expansion and anthesis. Corolla
volume of fully expanded flowers predicted water uptake during bud expansion (R
2=0.61, P=0.0375) and corolla surface area predicted water uptake during anthesis (R
2=0.59, P=0.044). To probe mechanisms underlying the relationship between corolla size and water uptake, cell dimensions and densities
were measured in several regions of fully expanded corollas. Corolla length was positively correlated with cell length in
the middle of the corolla tube and cell diameter in the corolla lobe (Pearson's r from 0.26–0.33, n=86, P ≤ 0.05). Cell density was negatively correlated with cell dimensions in the upper corolla tube and lobe (Pearson's r from –0.39 to –0.42, P ≤ 0.0015). These findings suggest that more water may be required to maintain turgor in large corollas in part because their
tissues have lower cell wall densities. The carbon cost of water use by flowers was assessed in krummholz and tundra habitats
for P. viscosum flowering, respectively, during dry and wet portions of the growing season. For plants in full flower, average leaf water
potentials were significantly more negative (P=0.0079) at mid-day in the krummholz (June) than in the tundra (July), but were similar before dawn (P=0.631). Photosynthetic rate at the time of flowering declined significantly with increasing corolla size in the krummholz
(P=0.0376), but was unrelated to corolla size on the tundra (P>0.72). Plants losing water through large corollas may close leaf stomata to maintain turgor. If photosynthesis limits growth
in this perennial species, then the water cost of producing large flowers should exacerbate the cost of reproduction under
dry conditions. Such factors could select for flowers with smaller corollas in the krummholz, countering pollinator-mediated
selection and helping maintain genetic variation in corolla size components of P. viscosum.
Received: 5 May 1998 / Accepted: 2 October 1998 相似文献