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  • 1
    Electronic Resource
    Electronic Resource
    Effects of lengthened growing season and soil warming on the phenology and physiology of Polygonum bistorta (2000)
    Oxford, UK : Blackwell Science Ltd
    Global change biology 6 (2000), S. 0 
    Details
    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: The phenological and physiological responses of arctic tundra plant species are key to predicting their survival in a warmer climate. One of the consequences of a warmer climate in the Arctic will be a longer growing season. We examined the effects of lengthened growing season and soil warming on the widely distributed forb, Polygonum bistorta L. Three treatments were established near Toolik Lake, Alaska in 1995 and 1996: extended season, extended season with soil warming, and an unmanipulated control. The season was extended by removing the snow load in the spring and keeping the treatments free of snow in the autumn. The spring snow removal extended the snow-free period over that of controls by 8 d in 1995 and 24 d in 1996. As a result, the number of accumulated soil thaw days and consequently the depth of soil thaw increased on the treatment plots. Polygonum bistorta responded to the treatments by becoming active earlier and senescing earlier, resulting in a growth period of similar duration to that of the controls. Leaf size and leaf number were unaffected by the treatments, as were leaf photosynthetic assimilation rates and nutrient concentrations. The results indicate that internal constraints limit the response of this species to lengthened growing season, suggesting that it is a determinant or periodic species. With climate warming, this periodic growth will put P. bistorta at a competitive disadvantage relative to plants that can respond to lengthened growing season.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2486.2000.00316.x
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  • 2
    Electronic Resource
    Electronic Resource
    Ecophysiological analysis of two arctic sedges under reduced root temperatures (2004)
    Oxford, UK; Malden, US : Munksgaard International Publishers
    Physiologia plantarum 120 (2004), S. 0 
    Details
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Shoot physiological activity in arctic vascular plants may be controlled by low soil temperatures. While leaves may be exposed to moderate temperatures during the growing season, root temperatures often remain near freezing. In this study, two tundra sedges, Eriophorum vaginatum and Carex bigellowii, were subjected to reduced soil temperatures, and photosynthetic parameters (light saturated photosynthesis Amax, variable to maximal fluorescence and Fv/Fm stomatal conductance) and abscisic acid concentrations were determined. Stomatal conductance and Amax for both E. vaginatum and C. bigellowii strongly decreased with declining soil temperatures. Decreasing soil temperature, however, impacted Fv/Fm to a much lesser degree. Root and leaf ABA concentrations increased with decreasing root temperature. These observations support the contention that soil temperature is a significant photosynthetic driving factor in arctic sedges exposed to variable root and shoot temperatures. Because these two species comprise approximately 30% of the vascular ground cover of wet tussock tundra, the soil temperature responses of these sedges potentially scale up to significant effects on ecosystem carbon exchange.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.0031-9317.2004.00260.x
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  • 3
    Electronic Resource
    Electronic Resource
    Why leaves are sometimes red (1995)
    [s.l.] : Nature Publishing Group
    Nature 378 (1995), S. 241-242 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] SIR - Anthocyanins are present in leaves of autumn foliage and rapidly developing shoots in tropical trees, but their function has never been satisfactorily explained. In addition, leaf undersurfaces of many tropical rainforest understory herbs are also red because of the presence of antho-cyanins. ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/378241b0
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  • 4
    Electronic Resource
    Electronic Resource
    Effect of CO2-enrichnient on seedling physiology and growth of two tropical tree species (1985)
    Oxford, UK : Blackwell Publishing Ltd
    Physiologia plantarum 65 (1985), S. 0 
    Details
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Seedlings of two tree species from the Atlantic lowlands of Costa Rica, Ochroma la-gopus Swartz, a fast-growing pioneer species, and Pentaclethra macroloba (Willd.) Kuntze, a slower-growing climax species, were grown under enriched atmospheric CO2 in controlled environment chambers. Carbon dioxide concentrations were maintained at 350 and 675 μl 1−1 under photosynthetic photon flux densities of 500 μol m−2 s−1 and temperatures of 26°C day and 20°C night. Total biomass of both species increased significantly in the elevated CO2 treatment; the increase in biomass was greatest for the pioneer species, O. lagopus. Both species had greater leaf areas and specific leaf weights with increased atmospheric CO2. However, the ratio of non-pho-tosynthetic tissue to leaf area also increased in both species leading to decreased leaf area ratios. Plants of both species grown at 675 μl 1−1 CO2 had lower chlorophyll contents and photosynthesis on a leaf area basis than those grown at 350 μl 1−1. Reductions in net photosynthesis occurred despite increased internal CO2 concentrations in the CO2-enriched treatment. Stomatal conductances of both species decreased with CO2-enrichment resulting in significant increases in water use efficiency.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1399-3054.1985.tb08658.x
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  • 5
    Electronic Resource
    Electronic Resource
    Drought tolerance and water use by plants along an alpine topographic gradient (1981)
    Springer
    Oecologia 50 (1981), S. 325-331 
    Details
    ISSN: 1432-1939
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary In the alpine zones of western North American mountains, topographic-moisture gradients are the results of winter winds blowing snow from the upper windward slopes and ridgetops into snowdrifts on the lee slopes. Wet meadows at the foot of the lee slope are the result of summer snowmelt. Such gradients are repeated many times in a single mountain range. They are useful units for studies of the effects of drought and water use on patterning of alpine vegetation. The research was done through an entire growing season along a topographic gradient at 3,300 m in the Medicine Bow Mountains, Wyoming. Plant water potentials were measured on 29 species (pre-dawn to sunset) at weekly intervals. Simultaneously, leaf conductances were measured on 16 species of these; the remainder had leaves too small for the porometer. Leaf water potentials were generally lowest on the ridgetop and highest in the wet meadow. Highest mean leaf conductances were in the wet meadow plants; the lowest occurred on plants on the upper windward slope. None of the plants on the ridgetop had leaves large enough for the porometer. Plants of most species at all sites but the wet meadow showed sharply reduced leaf conductance or leaf death at plant water potentials below-1.5 MPa. Deep-rooted species such as Trifolium parryi showed maximal conductance at water potentials as low as-1.7 MPa and little reduction in conductance even at lower water potentials. Plant water potentials and leaf conductances showed close relationships with rooting depth, length of dry periods, and position on the gradient.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00344971
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  • 6
    Electronic Resource
    Electronic Resource
    Effects of irradiance and spectral quality on seedling development of two Southeast Asian Hopea species (1997)
    Springer
    Oecologia 110 (1997), S. 1-9 
    Details
    ISSN: 1432-1939
    Keywords: Key words Tropical rain forest ; Seedling development ; Physiology ; Light climate ; Red:far-red ratio
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract  Seedling developmental responses to understory shade combine the effects of reductions in irradiance and changes in spectral quality. We studied the seedling development of two Southeast Asian dipterocarp trees in response to differences in irradiance (photosynthetic photon flux density, PPFD) and spectral quality (red to far-red ratio, R:FR). The two species, Hopea helferei and H. odorata, are taxonomically closely related but differ in their ecological requirements; H. helferei is more drought-tolerant and typically grows in more open habitats. Seedlings were grown in six different replicated shadehouse treatments varying in percentage of solar PPFD and R:FR. The two species differed in the influence of light variables on most seedling characters, particularly for final height, internode distance, branch/trunk internodes, stem length/mass, leaf area/stem length, petiole length, and growth/mol of photons received. Most of the characters in both taxa were primarily influenced by PPFD, but spectral quality also influenced some characters – more so for H. odorata. The latter species grew more rapidly, particularly in the low PPFD treatments, and its leaves were capable of higher photosynthesis rates. However, growth in H. helferei was not reduced in direct sunlight. The growth of this taxon may be constrained by adaptations, particularly in leaves, for drought tolerance.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004420050126
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  • 7
    Electronic Resource
    Electronic Resource
    Photosynthetic induction responses of two rainforest tree species in relation to light environment (1993)
    Springer
    Oecologia 96 (1993), S. 193-199 
    Details
    ISSN: 1432-1939
    Keywords: Costa Rica ; Hemispherical photography ; Photosynthesis ; Rain forest ; Sunflecks
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Photosynthetic induction of in situ saplings of two Costa Rican rainforest tree species wre compared in relation to their light environment, using infrared gas analysis and hemispherical photography. The species studied were Dipteryx panamensis, a climax species found in bright microsites, and Cecropia obtusifolia, a pioneer species. In the morning, when leaves were most responsive, induction time necessary to reach 90% of the lightsaturated rate of photosynthesis was on average 16 min for Dipteryx and 10 min for Cecropia. However, induction times for both species increased in the afternoon resulting in shorter daily average induction times for Dipteryx than for Cecropia. Dipteryx also maintained higher levels of induction for a longer period under low light conditions than did Cecropia. The two species differed in the way they adjusted to light availability. Dipteryx saplings growing in shady sites had faster rates of induction than saplings growing in bright sites, with no difference in light-saturated photosynthetic rate. In contrast, Cecropia saplings growing in bright sites had higher light-saturated photosynthetic rates than saplings growing in shady sites, with no difference in rates of induction. Dipteryx appears to exploit temporal variation in light availability by refining the quickness of the induction response to the light environment, while Cecropia adjusts its scale of exploitation by realizing a higher lightsaturated photosynthetic rate in sites of higher light.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00317732
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  • 8
    Electronic Resource
    Electronic Resource
    Effects of light regime on the growth, leaf morphology, and water relations of seedlings of two species of tropical trees (1983)
    Springer
    Oecologia 58 (1983), S. 314-319 
    Details
    ISSN: 1432-1939
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract An experiment was conducted with Heliocarpus appendiculatus, a pioneer or large gap species of tropical moist forest in Costa Rica, and Dipteryx panamensis, a small gap species. Seedlings were grown in full sun, partial (80%) shade, and full (98%) shade. After one month of growth they were switched between environments and grown for two more months. Growth in height of Heliocarpus was greatly affected by irradiance, being increased in response to full shade and decreased in full sun. Height of Dipteryx was unaffected by irradiance level. Survival of Heliocarpus seedlings was only 49% in full shade, whereas Dipteryx had 100% survival. Biomass of Heliocarpus was not significantly greater in full sun than in partial shade whereas it was for Dipteryx. The response of root: shoot ratio was similar for both species. They were lowest in full shade and highest in full sun. Heliocarpus exhibited greater changes in leaf thickness, specific leaf weight, and stomatal density than did Dipteryx. Stomatal conductance of both species was lower in full shade and full sun than in partial shade. The results of the experiment indicate that growth of Heliocarpus is more plastic than that of Dipteryx in response to changes in irradiance. Previous environment did not affect the response to the present environment in either species. Both species responded positively to increases in irradiance.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00385229
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  • 9
    Electronic Resource
    Electronic Resource
    Soil respiration of Alaskan tundra at elevated atmospheric carbon dioxide concentrations (1986)
    Springer
    Plant and soil 96 (1986), S. 145-148 
    Details
    ISSN: 1573-5036
    Keywords: Alaskan tundra ; CO2 enrichment ; Soil respiration
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary CO2 efflux from tussock tundra in Alaska that had been exposed to elevated CO2 for 2.5 growing seasons was measured to assess the effect of long- and short-term CO2 enrichment on soil respiration. Long-term treatments were: 348, 514, and 683 μll−1 CO2 and 680 μll−1 CO2+4°C above ambient. Measurements were made at 5 CO2 concentrations between 87 and 680 μll−1 CO2. Neither long- or short-term CO2 enrichment significantly affected soil CO2 efflux. Tundra developed at elevated temperature and 680 μll−1 CO2 had slightly higher, but not statistically different, mean respiration rates compared to untreated tundra and to tundra under CO2 control alone.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02375005
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  • 10
    Electronic Resource
    Electronic Resource
    Photosynthesis and successional status of Costa Rican rain forest trees (1984)
    Springer
    Photosynthesis research 5 (1984), S. 227-232 
    Details
    ISSN: 1573-5079
    Keywords: Light saturation ; stomatal conductance ; tropical trees
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Seven tree species from three different light environments in the wet lowland forests of Costa Rica were grown under controlled environment conditions to assess light related photosynthetic potentials. Light saturated photosynthesis rates were clearly related to light levels of the field environments. Mean saturated, net photosynthetic rates ranged from 6.8 to 11.3 to 27.7 μmol m−2 sec−1 for plants from heavy shade, canopy light gaps and man-made clearings respectively. Light saturation of plants from clearings occurred at photosynthetic photon flux densities greater than 1000 μmol m−2 sec−1 whereas plants from heavy shade environments became light saturated near 500 μmol m−2 sec−1. Plants that normally occur in intermediate light environments were intermediate in light saturation levels. Mean maximum stomatal conductances ranged from 1.0 to 7.3 mm sec−1 and followed a pattern similar to photosynthetic rates.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00030022
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