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1.
Taxonomic diversity, physiological tolerance ranges, and nutrient utilization capabilities were determined for bacterial communities in Gulf of Alaska surface waters and sediments. Taxonomic diversity was assessed using Shannon Weaver (H) and equitability (J) indices. Physiological tolerance and nutritional versatility indices were developed to further assess the state of informational heterogeneity within the bacterial communities. The Gulf of Alaska bacterial communities were characteristically diverse; the bacterial populations in these marine ecosystems generally were eurytolerant and nutritionally versatile. The maintenance of a high degree of informational heterogeneity was found to be characteristic of these bacterial communities. It appears to be of adaptive advantage to maintain diverse populations with physiological tolerances whose ranges exceed those experienced within the natural habitat, and for the bacterial communities to possess a high degree of nutritional versatility within these marine ecosystems.  相似文献   

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Natural abundances of nitrogen isotopes, 15N, indicate that, in the same habitat, Alaskan Picea glauca and P. mariana use a different soil nitrogen compartment from the evergreen shrub Vaccinium vitis-idaea or the deciduous grass Calamagrostis canadensis. The very low 15N values (-7.7 ) suggest that (1) Picea mainly uses inorganic nitrogen (probably mainly ammonium) or organic N in fresh litter, (2) Vaccinium (-4.3 ) with its ericoid mycorrhizae uses more stable organic matter, and (3) Calamagrostis (+0.9 ) exploits deeper soil horizons with higher 15N values of soil N. We conclude that species limited by the same nutrient may coexist by drawing on different pools of soil N in a nutrient-deficient environment. The differences among life-forms decrease with increasing N availability. The different levels of 15N are associated with different nitrogen concentrations in leaves, Picea having a lower N concentration (0.62 mmol g–1) than Vaccinium (0.98 mmol g–1) or Calamagrostis (1.33 mmol g–1). An extended vector analysis by Timmer and Armstrong (1987) suggests that N is the most limiting element for Picea in this habitat, causing needle yellowing at N concentrations below 0.5 mmol g–1 or N contents below 2 mmol needle–1. Increasing N supply had an exponential effect on twig and needle growth. Phosphorus, potassium and magnesium are at marginal supply, but no interaction between ammonium supply and needle Mg concentration could be detected. Calcium is in adequate supply on both calcareous and acidic soils. The results are compared with European conditions of excessive N supply from anthropogenic N depositions.Dedicated to Prof. Dr. Drs. h.c. H. Ziegler on the occasion of his 70th birthday  相似文献   

3.
Northern and high‐latitude alpine treelines are generally thought to be limited by available warmth. Most studies of tree‐growth–climate interaction at treeline as well as climate reconstructions using dendrochronology report positive growth response of treeline trees to warmer temperatures. However, population‐wide responses of treeline trees to climate remain largely unexamined. We systematically sampled 1558 white spruce at 13 treeline sites in the Brooks Range and Alaska Range. Our findings of both positive and negative growth responses to climate warming at treeline challenge the widespread assumption that arctic treeline trees grow better with warming climate. High mean temperatures in July decreased the growth of 40% of white spruce at treeline areas in Alaska, whereas warm springs enhance growth of additional 36% of trees and 24% show no significant correlation with climate. Even though these opposing growth responses are present in all sampled sites, their relative proportion varies between sites and there is no overall clear relationship between growth response and landscape position within a site. Growth increases and decreases appear in our sample above specific temperature index values (temperature thresholds), which occurred more frequently in the late 20th century. Contrary to previous findings, temperature explained more variability in radial growth after 1950. Without accounting for these opposite responses and temperature thresholds, climate reconstructions based on ring width will miscalibrate past climate, and biogeochemical and dynamic vegetation models will overestimate carbon uptake and treeline advance under future warming scenarios.  相似文献   

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Emsian (upper Lower Devonian) limestones exposed on Kasaan, Round, and Wadleigh Islands in southeastern Alaska are part of an allochthonous suitc of island are deposits preserved within the accrctionary Alexander Terrane. Ten benthic marine communities, including several new brachiopod associations, are defined on the basis of field data correlated with a cluster analysis. Biologic and sedimentologic evidence is integrated with community group assignments in order to substantiate the paleoecology and evolutionary history of each community. These faunas were adapted to a spectrum of quiet and rough water habitats, including restricted, shallow subtidal areas nearshore, offshore biostromal banks, and open and restricted portions of a lagoon or shelf. Comparisons with coeval assemblages from the Cordillera and elsewhere reveal that these communities are unique to southeastern Alaska. Their origin within an early Paleozoic island are appears to have led to biogeographic isolation from other parts of the Cordillera and the development of a distinct biota at a site offshorc from the ancient continental margin. ▭ Emsian, paleocommunities, community groups, cluster analysis, Alexander Terrane.  相似文献   

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Background: Treeline ecotones represent environmental boundaries that fluctuate in space and time and thus induce changes in plant taxonomic and functional diversity.

Aims: To study changes through time in taxonomic and functional plant diversity patterns along the treeline ecotone.

Methods: In 2002, vegetation was sampled along a gradient from upper montane forest to the treeline–alpine transition in the South Ural Mountains, Russia. In 2014, vegetation was resampled and plant functional traits were collected. We studied spatial and temporal changes in plant species composition, functional composition and functional diversity.

Results: Species composition and diversity changed along the elevational gradient. The functional composition in height, leaf area, specific leaf area and leaf nitrogen content decreased with elevation, whereas functional composition of leaf carbon content increased. We found a temporal shift towards shorter plants with smaller leaves in treeline sites. Functional richness varied in several traits along the elevational gradient, while functional dispersion showed a trend towards increased functional dispersion in height, specific leaf area and leaf nitrogen in the treeline–tundra transition.

Conclusions: Tree encroachment across the treeline ecotone has resulted in a shift in plant species relative abundances and functional diversity, possibly affecting plant community assembly patterns.  相似文献   

8.
The Arctic treeline is advancing in many areas and changes in carbon (C) cycling are anticipated. Differences in CO2 exchange between adjacent forest and tundra are not well known and contrasting conclusions have been drawn about the effects of forest advance on ecosystem C stocks. Measurements of CO2 exchange in tundra and adjacent forest showed the forest was a greater C sink during the growing season in northern Canada. There is, however, reason to expect that forests lose more C than tundra during the wintertime, as forests may accumulate and retain more snow. Deeper snow insulates the soil and warmer soils should lead to greater rates of belowground respiration and CO2 efflux. In this study, I tested the hypotheses that forests maintain a deeper snowpack, have warmer soils and lose more C during winter than adjacent tundra near the Arctic treeline in northwest Alaska. Measurements of snow depth, soil temperature and CO2 efflux were made at five forest and two treeline sites in late winter of three consecutive years. Snow depth and soil temperature were greater in forest than treeline sites, particularly in years with higher snowfall. There was a close exponential correlation between soil temperature and CO2 efflux across sites and years. The temperature-efflux model was driven using hourly soil temperatures from all the sites to provide a first approximation of the difference in winter C loss between treeline and forest sites. Results showed that greater wintertime C loss from forests could offset greater summertime C gain.  相似文献   

9.
The acoustic climate of plant communities   总被引:1,自引:0,他引:1  
Summary During summer season and winter season of 1971 and 1972, the acoustic properties, defined as the acoustic climate, of 8 semi-natural plant communities in the Netherlands were investigated. It appeared that each plant community has its own acoustic climate as a consequence of the specific species composition and the specific acoustic properties of the soil. Seasonal changes influenced the acoustic climate to some extent, since during summer there is a better attenuation of low frequencies and in winter of mid frequencies. Comparing all plant communities the total variation in attenuation differed from 29.6 dB/100 m at 1250 Hz (cps) in winter to 74.6 dB/100 m at 10,000 Hz in summer, as is shown in Table 3. In general best attenuation occurred at low and high frequencies in both seasons, which has to be attributed to soil and foliage characteristics.  相似文献   

10.
17 plant associations belonging to 9 alliances from Spitsbergen are discussed; 7 associations, 2 alliances and 1 order are described as new. The percentage of diploids and polyploids in individual plant communities and their relation to ecology is examined.  相似文献   

11.
Attempts to elucidate the factors controlling the structure of plant communities have relied increasingly on field experiments. This is a powerful approach for testing theoretical predictions that offers important advantages over observational and comparative studies. However, field experiments suffer from intrinsic difficulties as well as more-easily remediable limitations. Recent progress has been made by new approaches including the use of multifactor experiments, and the development and dissemination of better statistical tools.  相似文献   

12.
Competition and allelopathy in aquatic plant communities   总被引:2,自引:0,他引:2  
The paper reviews the published literature on the studies of competition and allelopathy in aquatic plant communities. Taking a broader view of the community, the studies on interactions between macrophytes and microphytes, macrophytes and macro-invertebrates and microbial communities are also reviewed. The role of these interactions in the structure and dynamics of aquatic communities has been discussed in light of the current hypotheses concerning competition in terrestrial communities. The available information suggests that the aquatic plants of various growth forms differ greatly among themselves in their responses and adaptations to competition and allelopathy. The possible application of these interactions in biological control of plant pests and in agriculture is also summarized. We conclude that the observed differences in these interactions between the terrestrial and aquatic environment are due to the effects of water as a non-resource variable as well as due to special adaptive characteristics of aquatic plants. Further we hypothesize that the aquatic plants adopt both competitive and allelopathic strategies under different conditions and in interactions with different plants. The review highlights that our knowledge of both competition and allelopathy among aquatic plant communities is inadequate and fragmentary, and therefore, both extensive and intensive studies are required.  相似文献   

13.
The vegetation of the mountains of the Fynbos Biome is classified and described, mostly on the basis of vegetation structure and higher taxa. Various gradients can be recognized. A gradient in soil conditions runs from coarse textured, nutrient-poor soils in non-grassy fynbos (Mountain Fynbos) through grassy fynbos and grassy non-fynbos (Eastern Fynbos and Grasslands & Grassy Shrubland) to finer textured and less nutrient-poor soils in the non-fynbos Karroid & Renoster Shrubland. Another gradient of significance can be likened to the tropical gradient running from the dry conditions of hot semi-deserts to savannas or grasslands to woodlands. At the dry extreme an open shrubland occurs (Karroid & Renoster Shrubland, Asteraceous Fynbos), at intermediate positions a herbland occurs (Restioid Fynbos) and at the wet extreme another type of shrubland occurs (Ericaceous Fynbos). This kind of moisture gradient occurs on individual mountains with the xeric end being at the base of the north slopes, and the mesic end being on the upper south aspects. Soil characteristics are closely linked to this gradient; the better developed soils being found on the south aspects. Another moisture gradient is apparent in the vegetation. This gradient runs from the mesic southern coastal mountains to the north west where summer droughts are extremely severe although total rainfall may be similar.Nomenclature follows that used in the Government Herbarium, Stellenbosch.I thank William Bond, Richard Cowling, John Rushworth, Eddy van der Maarel and Marinus Werger for critical comments and discussion.  相似文献   

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Guo  Qinfeng 《Plant Ecology》1998,139(1):71-80
The effects of microhabitat differentiation on small-scale plant community structure in the Chiuhuahuan Desert were studied using multivariate analysis. The results showed that microhabitats (i.e., kangaroo rat mounds, ant mounds, shrubs, half-shrubs, and open areas) played a critical role in structuring small-scale plant community structure and maintaining species diversity. Annual plants were much more sensitvive to the presence of differentiated microhabitats than perennials and winter annuals exhibited stronger microhabitat perferences than summer annuals. Species diversity was highest on ant mounds while open areas supported the lowest diversity during both winter and summer. Biomass was highest in the shrub habitats followed by kangaroo rat mounds, ant mounds, half-shrubs, and open areas. Much of the diversity of these plants could be explained by the individualistic responses of species to the biotic effect of other plants or to disturbance by animals, or individualistic responses of species to differences in microenvironments.  相似文献   

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Banzan Kumazawa reported some 300 years ago in Japan that rain or dew which washes the leaves of red pine (Pinus densiflora) is harmful to crops growing under the pine. De Candolle suggested also in 1832 that certain weeds secrete toxins which inhibit growth of crop plants. Despite these suggestions, it is only in the past 70 years that appreciable research has been done in the field of allelopathy and only in the past 15 years that much research has been directed toward elucidating some of the many roles of allelopathy in ecological processes. Some of the more notable ecological phenomena and processes in which allelopathy has been implicated are: succession, patterning of vegetation, prevention of seed decay prior to germination, inhibition of nitrification by climax ecosystems, dormancy of seeds, promotion of infection by pathogens, and resistance to infection.  相似文献   

20.
Although microbes associated with shallow-water corals have been reported, deepwater coral microbes are poorly characterized. A cultivation-independent analysis of Alaskan seamount octocoral microflora showed that Proteobacteria (classes Alphaproteobacteria and Gammaproteobacteria), Firmicutes, Bacteroidetes, and Acidobacteria dominate and vary in abundance. More sampling is needed to understand the basis and significance of this variation.  相似文献   

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