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1.
Altitudinal patterns in host suitability for forest insects 总被引:4,自引:0,他引:4
Conspecific trees growing at high and low-elevations encounter different growing conditions and may vary in their suitability
as hosts for herbivorous insects. Mountain tree populations may be more resistant to herbivory if low temperatures constrain
growth more than they constrain photosynthesis, resulting in increased secondary metabolism (temperature hypothesis). Alternatively,
mountain trees may be fertilized by atmospheric nitrogen deposition and become more palatable to insects (atmospheric deposition
hypothesis). We evaluated these two hypotheses by comparing high- and low-elevation trees with insect bioassays and analyses
of foliar nitrogen and condensed tannin. Contrary to the temperature hypothesis, high-elevation foliage had higher leaf nitrogen
(six of six tree species) and allowed higher growth rates of Lymantria dispar larvae (five of six tree species). The nitrogen deposition hypothesis was broadly supported by measurements from two mountains
showing that high-elevation trees tended to have higher leaf nitrogen, lower leaf tannins, and support higher insect growth
performance than conspecific trees from lower elevations. The deposition hypothesis was further supported by fertilization
studies showing that simulated atmospheric nitrogen deposition changed the foliar chemistry of valley trees to resemble that
of high-elevation trees. Predictions that the altitudinal gradient in foliar chemistry and host suitability should be steepest
on mountains receiving more deposition were largely not supported, but interpretations are complicated by lack of replication
among mountains. In the northeastern United States, increased host suitability of high-elevation trees seems sufficient to
influence the population dynamics and community composition of herbivores. Atmospheric nitrogen deposition offers a promising
hypothesis to explain and predict some important spatial patterns in herbivory.
Received: 21 September 1997 / Accepted: 12 June 1998 相似文献
2.
3.
Invasive capacity of Tamarix ramosissima in a Mojave Desert floodplain: the role of drought 总被引:1,自引:0,他引:1
Tamarix ramosissima (Tamaricaceae) is a woody phreatophyte that has invaded thousands of hectares of floodplain habitat in the southwestern U.S.
In this study, we examined the response of gas exchange and stem sap flow of Tamarix and three co-occurring native phreatophytes (Pluchea sericea (Asteraceae), Prosopis pubescens (Fabaceae) and Salix exigua (Salicaceae)) to drought conditions in an early successional floodplain community in the Mojave Desert of southern Nevada.
In an analysis of a size/age series of each species across the whole floodplain (both mature and successional stands), stem
growth rate was lowest for Tamarix. However, along the same successional chronosequence, Tamarix came to dominate the 50+ year old stands with dense thickets of high stem density. Xylem sap flow, when expressed on a sapwood
area basis, was highest in Tamarix under early drought conditions, but comparable between the four species toward the end of the summer dry season. Multivariate
analysis of the gas exchange data indicated that the four species differentiated based on water use under early drought conditions
and separated based on plant water potential and leaf temperature (indices of drought effects) at the end of the summer dry
season. This analysis suggests that the invasive Tamarix is the most drought tolerant of the four species, whereas Salix transpires the most water per unit leaf surface area and is the least tolerant of seasonal water stress. Therefore, Salix appears to be well adapted to early successional communities. However, as floodplains in this arid region become more desiccated
with age, Tamarix assumes greater dominance due to its superior drought tolerance relative to native phreatophytes and its ability to produce
high density stands and high leaf area.
Received: 8 August 1996 / Accepted: 29 January 1997 相似文献
4.
We examined whether or not sizes of eggs and offspring were related to emergence date or maternal size in a semelparous aquatic
insect (the burrowing mayfly, Hexagenia) in which parental care is lacking and oviposited eggs are passively dispersed. We quantified the size of males and female
imagos over the emergence span at a site on the Detroit River, Canada, and investigated relationships between emergence date
and female size and (1) egg size and (2) size of first-instar nymphs. Although size of female imagos (H. limbata and H. rigida combined) declined significantly (P<0.025) over the emergence season, there was no significant relationship between body length and emergence date for males
of either species. Males were significantly (P<0.001) smaller than females. H. limbata eggs, subsampled from three individuals from each of three size classes of female imagos collected on seven sampling dates,
were measured using video image analysis. Eggs (n=100) oviposited by each of 63 H. limbata imagos were inspected daily for hatching. Newly hatched nymphs were removed, counted and measured. Egg size (P<0.001) and size of first-instar nymphs (P<0.001) varied significantly with emergence date, but not maternal size. The largest eggs and newly hatched nymphs occurred
at peak emergence of adults. The synchronous release of larger (faster-sinking) eggs may result in reduced predation. Plasticity
in egg development time and egg and nymph size may account for the ability of this taxon to recover from episodes of massive
population reduction.
Received: 12 March 1996 / Accepted: 24 February 1997 相似文献
5.
The effect of light environment, leaf area, and stored carbohydrates on inflorescence production by a rain forest understory palm 总被引:2,自引:0,他引:2
Saul A. Cunningham 《Oecologia》1997,111(1):36-44
Variation in flowering by long-lived plants may be correlated with current resource availability. If, however, there are
trade-offs between current and future reproduction, or between reproduction and storage or growth, then understanding variation
requires a whole-plant, longer-term perspective. Inflorescence production by Calyptrogyne ghiesbreghtiana Linden ex. H. Wendl., an understory palm, was studied over 3 years. Annual inflorescence production varied greatly and was
correlated with variation in plant size and light environment. There was no trade-off between past inflorescence production
and the frequency of future inflorescence production. On the contrary, individuals that produced more inflorescences than
predicted from their size and light environment tended to continue to do so in subsequent years also. I manipulated the resource
environment of a subset of plants by removal of leaves and/or reproductive spikes. Leaf removal suppressed inflorescence production
for the following 2 years, but spike removal had no effect. One year after leaf removal stored reserves were, on average,
back to pre-treatment levels. There was, however, a negative effect of recent inflorescence production on storage. Plants
with higher levels of storage had higher inflorescence production in the next 75 days. In C. ghiesbreghtiana the resource cost of reproduction is apparent in short-term variation in stored reserves. In contrast, annual inflorescence
production does not follow a trade-off pattern between successive years, but consistently reflects both plant size and the
light environment.
Received: 20 October 1996 / Accepted: 25 January 1997 相似文献
6.
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
7.
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
8.
John L. Maron 《Oecologia》1997,110(2):284-290
Seedlings suffer high mortality in most plant populations, with both competition and herbivory proposed as being important
mechanisms causing seedling death. The relative strength of these factors, however, is often unknown. Here I ask how interspecific
competition for light and insect herbivory jointly affect seedling survival of bush lupine (Lupinus arboreus), a native shrub common to coastal California. Bush lupine seedlings germinate in grasslands during winter, and throughout
spring potentially compete for light with surrounding fast-growing annual grasses. By early summer, after grasses have died,
seedlings can be defoliated by a locally abundant caterpillar, the western tussock moth (Orgyia vetusta). I examined the relative importance of competition and insect herbivory on seedling survival in two separate experiments.
First, I compared seedling mortality in plots either exposed to or protected from tussock moth larvae. Plants were protected
from herbivory by the judicious use of insecticide; control plants were sprayed with water. Tussock moth herbivory resulted
in significantly greater (31%) seedling mortality. To determine the effects of interspecific competition for light on seedling
survival, I manipulated the density of grass surrounding lupine seedlings. I removed all vegetation surrounding some individuals,
and left intact vegetation surrounding others. Reducing competition resulted in a 32% increase in seedling survival from February
to June, as well as changes in seedling growth. To determine whether there are interactive effects of competition and herbivory
on seedling survival, I enclosed tussock moth larvae on half of all surviving seedlings within each of the two prior competition
treatments, comparing growth and survival of defoliated and undefoliated seedlings. Defoliation in June led to an additional
50% mortality for individuals that had grown with competitors through spring, and a 53% additional mortality for seedlings
that grew without competitors through spring. Thus, although competition and herbivory both caused substantial seedling mortality,
there was no statistical interaction between these factors. Competition-free plants were not less vulnerable to herbivory
than plants that previously grew with competitors. Taken together, these experiments indicate that competition and herbivory
are both important sources of mortality for bush lupine seedlings.
Received: 4 April 1996 / Accepted: 5 November 1996 相似文献
9.
G. Körtner X. Song F. Geiser 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1998,168(8):631-638
Circadian rhythms have been observed in most mammals, but their importance and function remain controversial with respect
to daily cycles during hibernation. We investigated the timing of arousals from and entries into hibernation for both free-living
and captive mountain pygmy-possums (Burramys parvus). Under both natural and laboratory conditions most arousals and entries were entrained with the light-dark cycle. Entries
occurred mainly during the night and arousals preferably around dusk, which coincides with the onset of the normal activity
phase for the nocturnal pygmy-possums. This entrainment prevailed throughout the hibernation season although only the laboratory
animals were constantly subjected to photoperiodic stimuli, whereas under natural conditions hibernacula are shielded from
photic cues and diurnal temperature fluctuations. Nevertheless, possums left their hibernacula frequently throughout winter
and were occasionally trapped close to the snow surface suggesting that during the periods of post-arousal normothermia they
can be exposed to environmental stimuli. It thus appears that the synchronisation with the photocycle was governed by a temperature-compensated
circadian clock which was reset periodically during short activity periods. For the mountain pygmy-possum, entrainment with
the photocycle probably has two functions:
1. Entrainment ensures that foraging bouts during the hibernation season remain synchronised with the dark phase.
2. Information about the prevailing climatic conditions sampled during short activity periods enables them to time final spring
emergence from hibernation when snow melt begins and ensures that the breeding season can commence as early as possible.
Accepted: 26 August 1998 相似文献
10.
Thomas Waßmer Franziska Wollnik 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1997,167(4):270-279
Body temperature (T
b) of seven European hamsters maintained at constant ambient temperature (T
a = 8 °C) and constant photoperiod (LD 8:16) was recorded throughout the hibernating season using intraperitoneal temperature-sensitive
HF transmitters. The animals spent about 30% of the hibernation season in hypothermia and 70% in inter-bout normothermy. Three
types of hypothermia, namely deep hibernation bouts (DHBs), short hibernation bouts (SHBs), and short and shallow hibernation
bouts (SSHBs), were distinguished by differences in bout duration and minimal body temperature (T
m). A gradual development of SSHBs from the diel minimum of T
b during normothermy could be seen in individual hamsters, suggesting a stepwise decrease of the homeostatic setpoint of T
b regulation during the early hibernation season. Entry into hibernation followed a 24-h rhythm occurring at preferred times
of the day in all three types of hypothermia. DHBs and SHBs were initiated approximately 4 h before SSHBs, indicating a general
difference in the physiological initiation of SSHBs on the one hand and DHBs and SHBs on the other. Arousals from SHBs and
SSHBs also followed a 24-h rhythm, whereas spontaneous arousals from DHBs were widely scattered across day and night. Statistical
analyses of bout length and the interval between arousals revealed evidence for a free-running circadian rhythm underlying
the timing of arousals. The results clearly demonstrate that entries into hypothermia are linked to the light/dark-cycle.
However, the role of the circadian system in the timing of arousals from DHBs remains unclear.
Accepted: 11 December 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.
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
13.
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
14.
研究了西双版纳热带季节雨林6种乔木幼树在林窗中的叶生长与叶虫食动态。6种幼树叶生长主要在雨季(5~10月),在旱季雾凉期(11~2月)叶停止生长。阳性树种旱季干热期(3~4月)开始叶生长,顶极树种至5月雨季初才开始叶生长。表明雾凉期低温抑制两类树种叶生长,干热期水分不足抑制顶极树种叶生长。叶生长同步性(每两个月的叶生长量变异系数C.V.)顺序为:望天树(Shorea chinensis,1.42)>金钩花(Pseuduvaria indochinensis,1.41)>八宝树(Duabanga grandiflora, 1.02)>云南石梓(Gmelina arborea,0.98)>团花树(Anthocephalus chinensis,0.84)和铁刀木(Cassia siamea,0.84)。旱季造成一些种类幼树出现落叶高峰,严重叶虫食也导致云南石梓在7~8月出现落叶高峰。叶虫食主要出现在雨季,团花树和云南石梓在干热期叶生长能减少昆虫取食,但此时铁刀木叶同步生长却不能降低食叶昆虫危害。6种幼树叶生长量年进程与叶虫食量年进程间存在正相关,其中望天树、金钩花、八宝树和团花树分别达到显著(p<0.05)或极显著(p<0.01)水平。望天树和金钩花在雨季初叶同步生长能减轻叶虫食。食叶昆虫偏爱取食幼叶,6种幼树平均幼叶的虫食量占总虫食量的72.9%,幼叶虫食速率平均为成熟叶的4.3倍。 相似文献
15.
The herbivore assemblage, intensity of herbivory and factors determining herbivory levels on the mangrove Kandelia obovata (previously K. candel, Rhizophoraceae) were studied over a 13-month period at two forests with contrasting growing conditions in Hong Kong. Mai
Po was part of an eutrophic embayment in the Pearl River estuary and generally offered more favourable conditions for mangrove
growth, whereas Ting Kok had a rocky substratum and oceanic salinity. Twenty-four insect herbivore species were recorded on
K. obovata, with lepidopteran larvae that consume leaf lamina being the dominant species. While leaf litter production was similar at
the two forests, herbivory level at Mai Po (mean = 3.9% in terms of leaf area loss) was more severe than that at Ting Kok
(mean = 2.3%). Peak herbivory levels were found in summer at both locations (6.5% for Mai Po and 3.8% for Ting Kok). Young
leaves of K. obovata at both locations were generally preferred by the herbivores from the period of late spring to summer. Concentrations of
most feeding deterrents (ash, crude fibre, and total soluble tannins) were significantly higher in both young and mature leaves
at Ting Kok, whereas leaf nutrients (total nitrogen and water) were the same at the two sites. Young leaves at Ting Kok contained
about 30% more tannins than their counterparts at Mai Po. Significant differences in leaf chemistry also existed between young
and mature leaves at either site. The differences were concomitant with the observed patterns of leaf herbivory on K. obovata, and suggest a potential relationship between environmental quality and plant defence against herbivory. 相似文献
16.
Winter production of CO2 and N2O from alpine tundra: environmental controls and relationship to inter-system C and N fluxes 总被引:15,自引:0,他引:15
Fluxes of CO2 and N2O were measured from both natural and experimentally augmented snowpacks during the winters of 1993 and 1994 on Niwot Ridge
in the Colorado Front Range. Consistent snow cover insulated the soil surface from extreme air temperatures and allowed heterotrophic
activity to continue through much of the winter. In contrast, soil remained frozen at sites with inconsistent snow cover and
production did not begin until snowmelt. Fluxes were measured when soil temperatures under the snow ranged from –5°C to 0°C,
but there was no significant relationship between flux for either gas and temperature within this range. While early developing
snowpacks resulted in warmer minimum soil temperatures allowing production to continue for most of the winter, the highest
CO2 fluxes were recorded at sites which experienced a hard freeze before a consistent snowpack developed. Consequently, the seasonal
flux of CO2
–C from snow covered soils was related both to the severity of freeze and the duration of snow cover. Over-winter CO2
–C loss ranged from 0.3 g C m−2 season−1 at sites characterized by inconsistent snow cover to 25.7 g C m−2 season−1 at sites that experienced a hard freeze followed by an extended period of snow cover. In contrast to the pattern observed
with C loss, a hard freeze early in the winter did not result in greater N2O–N loss. Both mean daily N2O fluxes and the total over-winter N2O–N loss were related to the length of time soils were covered by a consistent snowpack. Over-winter N2O–N loss ranged from less 0.23 mg N m−2 from the latest developing, short duration snowpacks to 16.90 mg N m−2 from sites with early snow cover. These data suggest that over-winter heterotrophic activity in snow-covered soil has the
potential to mineralize from less than 1% to greater than 25% of the carbon fixed in ANPP, while over-winter N2O fluxes range from less than half to an order of magnitude higher than growing season fluxes. The variability in these fluxes
suggests that small changes in climate which affect the timing of seasonal snow cover may have a large effect on C and N cycling
in these environments.
Received: 5 April 1996 / Accepted: 25 November 1996 相似文献
17.
Inger Åhman 《Oecologia》1997,111(1):61-68
Many species of dioecious plants show sex-related differences in growth rate and rates of attack by various herbivores and
diseases. The common pattern is for males to grow faster than females and to be less well defended against herbivores. In
willows (Salix spp.), the predominance of female-biased sex ratios has been ascribed in part to differential feeding by herbivores. In this
study of Salix viminalis, seven families grown on agricultural land showed no gender-related variation in shoot biomass or rates of herbivory by insects
(lepidopterans and cecidomyiids). However, Melampsora rust disease was found to be more severe on females than on males when the plants were in a non-reproductive stage. After
flowering and seed-set females tended to be more affected in some families but less affected in others. Although, on average,
there was a female bias in the sex ratio of S. viminalis, sex ratios differed significantly between families. These ratios were not related to any of the recorded biotic agents,
but rather to relationships between families. These results are interpreted in terms of resource allocation between reproduction,
growth and defence, and causes for divergence from the expected patterns are discussed. The results may have implications
for S. viminalis breeding strategies where the aim is to produce biofuel. For instance, these findings suggest that gender can be ignored
when selecting for a high growth rate and resistance to Melampsora and certain insect pests.
Received: 2 November 1996 / Accepted: 8 February 1997 相似文献
18.
A. Sommer B. Klein H. O. Pörtner 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1997,167(1):25-35
Temperature dependent changes in the mode of energy metabolism and in acid-base status were studied in the range from −1.7
to 26 °C in two populations of Arenicola marina collected in summer as well as in winter from intertidal flats of the North Sea (boreal) and the White Sea (subpolar). Extreme
temperatures led to an accumulation of anaerobic end products, indicating the existence of both a low and a high critical
temperature, beyond which anaerobic metabolism becomes involved in energy production. In summer animals from the North Sea
the high critical temperature was found at temperatures above 20 °C, and the low critical temperature below 5 °C. Latitudinal
or seasonal cold adaptation lead to a more or less parallel shift of both high and low critical temperature values to lower
values. Between critical temperatures intracellular pH declined with rising temperature. Slopes varied between −0.012 and
−0.022 pH- units/°C. In summer animals from the North Sea, the slope was slightly less than in White Sea animals, but differences
appeared independent of the season. However, slopes were no longer linear beyond critical temperatures. A drop in intracellular
pH at low temperatures coincided with the accumulation of volatile fatty acids in the body wall tissue of North Sea animals.
A failure of active pHi adjustment is held responsible for the reduced ΔpHi/ΔT at temperatures above the high critical temperature. Extracellular pH was kept constant over the whole temperature range
investigated. The ability of North Sea animals to adapt to temperatures beyond the critical temperature is poor compared to
White Sea specimens. The larger range of temperature fluctuations at the White Sea is seen as a reason for the higher adaptational
capacity of the subpolar animals. A hypothesis is proposed that among other mechanisms critical temperature values are set
by an adjustment of mitochondrial density and thus, aerobic capacity.
Accepted: 20 August 1996 相似文献
19.
Kathleen Donohue 《Oecologia》1997,110(4):520-527
A factorial design of three densities of siblings at three local distances from seed parents was employed to distinguish
effects of density from effects of dispersal distance on lifespan and fruit production of Cakile edentula var. lacustris, a plant with heteromorphic seeds. The segmented fruits produce two seed types: proximal and distal, with distal seeds having
greater mass and greater dispersibility. Effects of longer distances (0.5 km and 30 km) on lifespan and fruit production were
investigated using plants at low density. The prediction was tested that the greater seed mass of distal seeds increases fitness
when seeds are dispersed into sites of unknown quality away from the home site or when seeds are dispersed to low density.
High density caused earlier mortality and lower probability of reproduction. Distance from the maternal plant did not influence
lifespan or reproduction at distances of 15 m or less, but lifespan was longer 0.5 km from the home site. No interaction was
detected between the effects of density and distance on either lifespan or total fitness. Environmental conditions that influence
fitness did not vary as a function of dispersal distance in this system, and favorable conditions at the home site did not
persist between generations. Therefore, selection on dispersion patterns in natural conditions is likely to be through effects
of density rather than dispersal distance. Proximal seeds had greater reproduction than distal seeds at the home site, and
distal seeds had greater reproduction at the more distant sites (but not the most distant site), as expected, but these performance
differences could not be attributed to differences in mass between the two seed types. Reduced seed mass was favored at the
most distant site, but larger seed mass was favored most strongly at low density. Seeds that are dispersed to low density
are larger, suggesting that although kin selection may limit the effectiveness of individual selection to increase seed mass
under conditions of sibling competition, density-dependent individual selection on seed mass, rather than distant-dependent
selection, also contributes to the observed associations among seed type, seed mass and dispersal ability.
Received: 21 October 1996 / Accepted: 4 December 1996 相似文献
20.
J. T. Kemp M. K. Balasubramanian K. L. Gould 《Molecular & general genetics : MGG》1997,254(2):127-138
The organization of the actin cytoskeleton plays an integral role in cell morphogenesis of all eukaryotes. We have isolated
a temperature-sensitive mutant in Schizosaccharomyces pombe, wat1-1, in which acting patches are delocalized, resulting in an elliptically shaped cell phenotype. Molecular cloning and DNA sequencing
of wat1
+ showed that the gene encodes a 314 residue protein containing WD-40 repeats. Cells lacking wat1
+ are slow growing but viable at 25° C and temperature-sensitive for growth above 33° C. At restrictive temperature, wat1-d strains are phenotypically indistinguishable from wat1-1. When combined with a deletion for the wat1
+ gene, cdc mutants failed to elongate at restrictive temperature and exhibited alterations in actin patch localization. This
analysis suggests that wat1
+ is required directly or indirectly for polarized cell growth in S. pombe. Wat1p and a functional, epitope-tagged, version of Wat1p can be overproduced without inducing alterations in cell morphology.
Received: 18 September 1996 / Accepted: 22 October 1996 相似文献