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  • 1
    Electronic Resource
    Electronic Resource
    Effects of lifelong [CO2] enrichment on carboxylation and light utilization of Quercus pubescens Willd. examined with gas exchange, biochemistry and optical techniques (2000)
    Oxford, UK : Blackwell Science Ltd
    Plant, cell & environment 23 (2000), S. 0 
    Details
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Lifelong exposure to elevated concentrations of atmospheric CO2 may enhance carbon assimilation of trees with unlimited rooting volume and consequently may reduce requirements for photoprotective pigments. In early summer the effects of elevated [CO2] on carboxylation and light utilization of mature Quercus pubescens trees growing under chronic [CO2] enrichment at two CO2 springs and control sites in Italy were examined. Net photosynthesis was enhanced by 36 to 77%. There was no evidence of photosynthetic downregulation early in the growing season when sink demand presumably was greatest. Specifically, maximum assimilation at saturating [CO2], electron transport capacity, and Rubisco content, activity and carboxylation capacity were not significantly different in trees growing at the CO2 springs and their respective control sites. Foliar biochemical content, leaf reflectance index of chlorophyll pigments (NDVI), and photochemical efficiency of PSII (ΔF/Fm′) also were not significantly affected by [CO2] enrichment except that starch content and ΔF/Fm′ tended to be higher at one spring (42 and 15%, respectively). Contrary to expectation, prolonged elevation of [CO2] did not reduce xanthophyll cycle pigment pools or alter mid-day values of leaf reflectance index of xanthophyll cycle pigments (PRI), despite the enhancement of carbon assimilation. However, both these pigments and PRI were well correlated with electron transport capacity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-3040.2000.00638.x
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  • 2
    Electronic Resource
    Electronic Resource
    Effects of long-term elevated [CO2] from natural CO2 springs on Nardus stricta: photosynthesis, biochemistry, growth and phenology (1998)
    Oxford, UK : Blackwell Publishing Ltd
    Plant, cell & environment 21 (1998), S. 0 
    Details
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Plants of Nardus stricta growing near a cold, naturally emitting CO2 spring in Iceland were used to investigate the long-term (〉 100 years) effects of elevated [CO2] on photosynthesis, biochemistry, growth and phenology in a northern grassland ecosystem. Comparisons were made between plants growing in an atmosphere naturally enriched with CO2 (≈ 790 μmol mol–1) near the CO2 spring and plants of the same species growing in adjacent areas exposed to ambient CO2 concentrations (≈360μmol mol–1). Nardus stricta growing near the spring exhibited earlier senescence and reductions in photosynthetic capacity (≈25%), Rubisco content (≈26%), Rubisco activity (≈40%), Rubisco activation state (≈23%), chlorophyll content (≈33%) and leaf area index (≈22%) compared with plants growing away from the spring. The potential positive effects of elevated [CO2] on grassland ecosystems in Iceland are likely to be reduced by strong down-regulation in the photosynthetic apparatus of the abundant N. stricta species.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-3040.1998.00285.x
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  • 3
    Electronic Resource
    Electronic Resource
    Energy and trace-gas fluxes across a soil pH boundary in the Arctic (1998)
    [s.l.] : Macmillan Magazines Ltd.
    Nature 394 (1998), S. 469-472 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Studies and models of trace-gas flux in the Arctic consider temperature and moisture to be the dominant controls over land–atmosphere exchange,, with little attention having been paid to the effects of different substrates. Likewise, current Arctic vegetation maps for models of vegetation ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/28839
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  • 4
    Electronic Resource
    Electronic Resource
    Moss functioning in different taiga ecosystems in interior Alaska (1981)
    Springer
    Oecologia 48 (1981), S. 50-59 
    Details
    ISSN: 1432-1939
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Carbon dioxide exchange rates in excised 2-year-old shoot sections of five common moss species were measured by infrared gas analysis in mosses collected from different stands of mature vegetation near Fairbanks, Alaska. The maximum rates of net photosynthesis ranged from 2.65 mg CO2 g-1h-1 in Polytrichum commune Hedw. to 0.25 in Spagnum nemoreum Scop. Intermediate values were found in Sphagnum subsecundum Nees., Hylocomium splendens (Hedw.) B.S.G., and Pleurozium schreberi (Brid.) Mitt. Dark respiration rates at 15°C ranged from 0.24 mg CO2 g-1h-1 in S. subsecundum to 0.57 mg CO2 g-1h-1 in H. splendens. The dark respiration rates were found to increase in periods of growth or restoration of tissue (i.e., after desiccation). There was a strong decrease in the rates of net photosynthesis during the winter and after long periods of desiccation. Due to increasing amounts of young, photosynthetically active tissue there was a gradual increase in the rates of net photosynthesis during the season to maximum values in late August. As an apparent result of constant respiration rates and increasing gross photosynthetic rates, the optimum temperature for photosynthesis at light saturation and field capacity increased during the season in all species except Polytrichum, with a corresponding drop in the compensation light intensities. Sphagnum subsecundum seemed to be the most light-dependent species. Leaf water content was found to be an important limiting factor for photosynthesis in the field. A comparison between sites showed that the maximum rates of net photosynthesis increased with increasing nutrient content in the soil but at the permafrostfree sites photosynthesis was inhibited by frequent moisture stress.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00346987
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  • 5
    Electronic Resource
    Electronic Resource
    Effects of leaf nitrogen availability and leaf position on nitrogen allocation patterns in Vaccinium vitis-idaea and Vaccinium uliginosum (1986)
    Springer
    Oecologia 69 (1986), S. 121-125 
    Details
    ISSN: 1432-1939
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Nitrogen allocation patterns from leaves of Vaccinium vitis-idaea (evergreen) and Vaccinium uliginosum (deciduous) were assessed using a foliar application of 15N labeled ammonium sulfate. These are wild perennial shrubs inhabiting arctic and subarctic regions. More label was transported from labeled leaves of Vaccinium uliginosum then Vaccinium vitis-idaea. In Vaccinium uliginosum, the amount of label transported from the labeled leaf increased as the concentration of nitrogen in the label increased. Current growth in Vaccinium uliginosum was a strong sink for nitrogen because most of the 15N transported from the labeled leaf was contained in this region. In addition, when greater quantities of nitrogen were applied, larger quantities were retained in current growth. Current growth of Vaccinium vitis-idaea, on the other hand, was not as strong a sink because regardless of the nitrogen available thru various label concentrations, the enrichment of current growth was not affected and was not significantly different from older stems or leaves. Yet, in both species, nitrogen was transported freely from leaves of all positions along the stem to all parts of the plant including roots and rhizomes. The position of the leaf along the stem had no effect on the patterns of allocation to other organs.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00399047
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  • 6
    Electronic Resource
    Electronic Resource
    The role of mosses in the phosphorus cycling of an Alaskan black spruce forest (1987)
    Springer
    Oecologia 74 (1987), S. 310-315 
    Details
    ISSN: 1432-1939
    Keywords: Mosses ; Mycorrhizae ; Phosphorus cycling ; Picea mariana
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Mosses account for 75% of the annual phosphorus accumulation in aboveground parts of an Alaskan black spruce forest, although they comprise only 17% of the phosphorus pool in aboveground vegetation. Sphagnum subsecundum and feathermosses (Hylocomium splendens and Pleurozium schreberi) have a higher capacity to absorb phosphate than do the fine roots of black spruce (Picea mariana) that are situated beneath the moss layer. In three of the four moss species studied, phosphate absorption capacity increases with increasing age of green tissue and decreases with increasing age of brown tissue. In the two feathermosses, which acquire moisture primarily from the air, and in Sphagnum, phosphate absorption is more rapid in green than in brown tissue. In contrast, the endohydric moss Polytrichum commune, which transports water through stem tissue from soil, absorbs phosphate most rapidly from stems in mineral soil. Two treatments designed to reduce activity of mycorrhizae (cutting of roots extending beneath the moss carpet or application to the moss surface of a fungicide that kills mycorrhizal hyphae) tended to increase phosphate retention by mosses and reduce phosphate transfer out of the experimental plots. This suggests that mycorrhizae are an important avenue of phosphorus movement out of the moss carpet and a means by which the black spruce competes with the overlying mosses for nutrients.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00379375
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  • 7
    Electronic Resource
    Electronic Resource
    Factors controlling postfire seedling establishment in southern California chaparral (1992)
    Springer
    Oecologia 90 (1992), S. 50-60 
    Details
    ISSN: 1432-1939
    Keywords: Ceanothus ; Adenostoma ; Chaparral ; Fire ; Seedling establishment
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary This paper discusses the interactions among prefire shrub abundance, soil moisture, and plant and animal species on postfire seedling establishment in mixed chparral in southern California. Postfire germination and survival of seedlings in a stand dominated by a facultative seeder (Adenostoma fasciculatum) and by an obligate seeder (Ceanothus greggii) were monitored for 2 years. Relative to prefire abundance, germination of C. greggii was higher than that of A. fasciculatum. Survival during the first year was also higher in C. greggii than in A. fasciculatum. During the second year, however, mortality of C. greggii was greater than that of A. fasciculatum, mostly due to a psyllid infection. Germination of A. fasciculatum was negatively related to prefire shrub abundance. C. greggii germination was not associated with prefire shrub abundance. Seedling mortality of both species was very strongly related to the depletion of soil moisture the first few months after germination. A. fasciculatum was more sensitive than C. greggii to the drying of the soil, especially in the upper levels. C. greggii seedlings had longer roots, greater root/shoot biomass ratios, higher water potentials, and a later peak in seasonal growth activity compared to A. fasciculatum. Herbs promoted greater survival of A. fasciculatum. Our results indicate that the obligate seeder species, C. greggii, is better adapted to establish seedling in chaparral by producing greater relative germination and greater seedling survival than the facultative seeder species A. fasciculatum. The greater adaptability of C. greggii to the physical environment is counteracted by interspecific interference by plant and animal interactions which tend to favor A. fasciculatum over C. greggii.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00317808
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  • 8
    Electronic Resource
    Electronic Resource
    Response of tussock tundra to elevated carbon dioxide regimes: analysis of ecosystem CO2 flux through nonlinear modeling (1987)
    Springer
    Oecologia 72 (1987), S. 466-472 
    Details
    ISSN: 1432-1939
    Keywords: Elevated CO2 ; Model photosynthesis ; Ecosystem tundra
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The response of tussock tundra to elevated atmospheric concentrations of CO2 was measured at Toolik Lake, Alaska in the summer of 1983. Computer-controlled greenhouses were used to determine diurnal ecosystem flux of CO2 under four treatments: 340 ppm, 510 ppm, and 680 ppm CO2, as well as 680 ppm CO2 with a four degree centrigrade increase in temperature. For the seven days of data analyzed, net daily CO2 flux was significantly different between treatments. Net uptake was positively correlated with CO2 concentration in the chamber and negatively correlated with temperature. A nonlinear model was used to analyze this data set and to determine some of the reasons for different net CO2 flux. This model allowed an estimation of light utilization efficiency, total conductance of CO2, and a comparable measure of total respiration. From this analysis we conclude that nutrient limitations in the arctic decrease the capacity of tundra plants to make use of elevated CO2 concentrations. The plants respond by decreasing conductance in the presence of elevated CO2, which results in approximately equal gross uptake rates for the three CO2 treatments. Apparent changes in system respiration result in higher net uptake under elevated CO2 but this may be due to biases in the data. The treatment with increased temperature exhibited higher conductances and, consequently, higher gross uptake of CO2 than the other treatments. Higher temperatures, however, also increase respiration with the result being lower net uptake than would be expected in the absence of temperature inscreases.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00377581
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  • 9
    Electronic Resource
    Electronic Resource
    Fire intensity and herbivory effects on postfire resprouting of Adenostoma fasciculatum in southern California chaparral (1991)
    Springer
    Oecologia 85 (1991), S. 429-433 
    Details
    ISSN: 1432-1939
    Keywords: Adenostoma fasciculatum ; California chaparral ; Fire intensity ; Herbivory
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Resprouting is the main regeneration mechanism after fire in Mediterranean-type ecosystems. Herbivores play an important role in controlling postfire seedling establishment, but their influence on regeneration by resprouting is less well known. To study the effects of fire intensity on resprouting of Adenostoma fasciculatum in southern California chaparral, and its interaction with herbivory, we conducted an experimental burn at three levels of fire intensity. We found that increasing fire intensity increased plant mortality, reduced the number of resprouts per plant, and delayed the time of resprouting. Herbivory increased with fire intensity, and was related to the time of resprouting. Plants resprouting later in the season and out of synchrony with the main flush were attacked more readily by herbivores. Post-resprouting mortality also increased with fire intensity and was significantly associated with herbivory in the higher fire intensity plots. Fire intensity effects on chaparral regeneration by resprouting may be farreaching through effects on the population structure, resprout production, and growth of Adenostoma fasciculatum.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00320621
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  • 10
    Electronic Resource
    Electronic Resource
    Carbon balance in tussock tundra under ambient and elevated atmospheric CO2 (1990)
    Springer
    Oecologia 83 (1990), S. 485-494 
    Details
    ISSN: 1432-1939
    Keywords: Ecosystem carbon balance ; Elevated CO2 ; Tussock tundra ; Global change ; Greenhouse effect
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Whole ecosystem CO2 flux under ambient (340 μl/l) and elevated (680 μl/l) CO2 was measured in situ in Eriophorum tussock tundra on the North Slope of Alaska. Elevated CO2 resulted in greater carbon acquisition than control treatments and there was a net loss of CO2 under ambient conditions at this upland tundra site. These measurements indicate a current loss of carbon from upland tundra, possibly the result of recent climatic changes. Elevated CO2 for the duration of one growing season appeared to delay the onset of dormancy and resulted in approximately 10 additional days of positive ecosystem flux. Homeostatic adjustment of ecosystem CO2 flux (sum of species' response) was apparent by the third week of exposure to elevated CO2. Ecosystem dark respiration rates were not significantly higher at elevated CO2 levels. Rapid homeostatic adjustment to elevated CO2 may limit carbon uptake in upland tundra. Abiotic factors were evaluated as predictors of ecosystem CO2 flux. For chambers exposed to ambient and elevated CO2 levels for the duration of the growing season, seasonality (Julian day) was the best predictor of ecosystem CO2 flux at both ambient and elevated CO2 levels. Light (PAR), soil temperature, and air temperature were also predictive of seasonal ecosystem flux, but only at elevated CO2 levels. At any combination of physical conditions, flux of the elevated CO2 treatment was greater than that at ambient. In short-term manipulations of CO2, tundra exposed to elevated CO2 had threefold greater carbon gain, and had one half the ecosystem level, light compensation point when compared to ambient CO2 treatments. Elevated CO2-acclimated tundra had twofold greater carbon gain compared to ambient treatments, but there was no difference in ecosystem level, light compensation point between elevated and ambient CO2 treatments. The predicted future increases in cloudiness could substantially decrease the effect of elevated atmospheric CO2 on net ecosystem carbon budget. These analyses suggest little if any long-term stimulation of ecosystem carbon acquisition by increases in atmospheric CO2.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00317199
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