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1

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Spatial and temporal variability in the responses of Arctic terrestrial ecosystems to environmental change (1999)

Callaghan, Terry V. ; Press, Malcolm C. ; Lee, John A. ; [et al.]

Oxford, UK : Blackwell Publishing Ltd

Polar research 18 (1999), S. 0

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ISSN: 1751-8369

Source: Blackwell Publishing Journal Backfiles 1879-2005

Topics: Geography , Geosciences

Notes: This paper compares the responses of two contrasting Arctic ecosystems to climate change simulations: a polar semi-desert (in Svalbard) and a dwarf shrub heath (at Abisko, northern Sweden). These ecosystems are located close to the northern-and southernmost extremes of the Arctic region, respectively. Inmacts of simulated climatic changes were determined through factorial perturbation experiments, where growing season temperature, nutrient availability and water supply were manipulated. The results are compared with the impact of interannual variation in climate on the growth of a keystone moss species, Hylocomium splendens, from the wider circumpolar area. The perturbation studies revealed that current interannual variability in temperature and the temperate tolerance of many species may exceed predicted changes in mean summer temperature over the next century. Arctic ecosystems differed in their responses to environmental manipulations, with the structure of the dwarf shrub health being affected through shifts in competitive hierarchy, potentially leading to lower biodiversity, and the polar semi-desert being affected through invasion, potentially leading to higher diversity. H. splendens showed negative responses to perturbation at the sub-Arctic site, in contrast to the positive relationship between temperature and growth observed in the natural environment. This apparent discrepancy may result from: (i) artefacts arising from the perturbations, such as lower atmospheric relative humidity; (ii) non-equilibrium responses during the relatively short-term perturbation studies and/or (iii) ecotypic variation in the moss population. Thus, caution should be employed when extrapolating from perturbations studies to both longer time-scales and different ecosystems within the Arctic.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1111/j.1751-8369.1999.tb00293.x

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2

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Effects of ozone depletion and increased ultraviolet-B radiation on northern vegetation (1999)

Björn, Lars Olof ; Callaghan, Terry V. ; Gehrke, Carola ; [et al.]

Oxford, UK : Blackwell Publishing Ltd

Polar research 18 (1999), S. 0

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ISSN: 1751-8369

Source: Blackwell Publishing Journal Backfiles 1879-2005

Topics: Geography , Geosciences

Notes: The stratospheric ozone layer has been depleted at high and mid-latitudes as a consequence of man's pollution of the atmosphere, and this results in increasing ultraviolet-B radiation at ground level. We investigate the effects of further radiation increases on plants and ecosystems by irradiating natural sub-Arctic and Arctic vegetation with artificial UV-B radiation in field experiments extending over several years. Our experimental sites are located at Abisko, in northern Sweden (68°N), and Adventdalen, on the island of Spitsbergen (78°N). Additional UV-B induced interspecific differences in plant response in terms of reduced (or, in one case, increased) growth, changed morphology and changed pigment content. In some cases effects seem to be accumulated from one year to another. Plant litter decomposition is retarded. We are also studying how UV-B enhancement may affect the interaction between species. In some experiments we combine UV-B enhancement with changes in other factors: carbon dioxide concentration, water availability, and temperature. In some cases the effect of radiation enhancement is modified, or even reversed, by such changes. Over a four year period we did not find any significant radiation induced change in species composition, but based on the effects on individual plant species, such changes can be expected to take place over a longer time.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1111/j.1751-8369.1999.tb00311.x

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3

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Effects of enhanced ultraviolet radiation and carbon dioxide concentration on the moss Hylocomium splendens (1996)

SONESSON, MATS ; CALLAGHAN, TERRY V. ; CARLSSON, BENGT Å.

Oxford, UK : Blackwell Publishing Ltd

Global change biology 2 (1996), S. 0

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ISSN: 1365-2486

Source: Blackwell Publishing Journal Backfiles 1879-2005

Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography

Notes: In a laboratory experiment interaction effects of UV-B and CO2 on photosynthesis and growth of the moss Hylocomium splendens were studied. The plants were exposed to two CO2 levels (350 ppm and 600 ppm) and three UV-B levels (no UV-B, ambient UV-B and that corresponding to 20% ozone depletion) for 5 months. The effects were recorded by measuring the photosynthetic response and growth of the plants.There was a statistically significant change in photosynthetic efficiency and maximum photosynthetic rates due to time and to enhanced CO2 concentration, whereas there was no effect due to UV-B. There was a decreased growth due to both UV-B and CO2 and an interaction effect on growth (in length). The UV-B dose corresponding to the ambient level had a larger reducing effect on growth than the highest UV-B dose. This was a counter-intuitive result and the following tentative interpretation was made: differences in the measured UV-A/UV-B/PAR ratios between the treatments could explain the result provided there was a non-linear response to UV over the range of irradiance levels used.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1111/j.1365-2486.1996.tb00050.x

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4

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Microbial biomass C, N and P in two arctic soils and responses to addition of NPK fertilizer and sugar: implications for plant nutrient uptake (1996)

Jonasson, Sven ; Michelsen, Anders ; Schmidt, Inger K. ; [et al.]

Springer

Oecologia 106 (1996), S. 507-515

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ISSN: 1432-1939

Keywords: Arctic/alpine soils ; Benomyl ; Microbial C, N, P ; Nutrient immobilization ; Plant nutrient uptake

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: Abstract The soil microbial carbon (C), nitrogen (N) and phosphorus (P) pools were quantified in the organic horizon of soils from an arctic/alpine low-altitude heath and a high-altitude fellfield by the fumigation-extraction method before and after factorial addition of sugar, NPK fertilizer and benomyl, a fungicide. In unamended soil, microbial C, N and P made up 3.3–3.6%, 6.1–7.3% and 34.7% of the total soil C, N and P content, respectively. The inorganic extractable N pool was below 0.1% and the inorganic extractable P content slightly less than 1% of the total soil pool sizes. Benomyl addition in spring and summer did not affect microbial C or nutrient content analysed in the autumn. Sugar amendments increased microbial C by 15 and 37% in the two soils, respectively, but did not affect the microbial nutrient content, whereas inorganic N and P either declined significantly or tended to decline. The increased microbial C indicates that the microbial biomass also increased but without a proportional enhancement of N and P uptake. NPK addition did not affect the amount of microbial C but almost doubled the microbial N pool and more than doubled the P pool. A separate study has shown that CO2 evolution increased by more than 50% after sugar amendment and by about 30% after NPK and NK additions to one of the soils. Hence, the microbial biomass did not increase in response to NPK addition, but the microbes immobilized large amounts of the added nutrients and, judging by the increased CO2 evolution, their activity increased. We conclude: (1) that microbial biomass production in these soils is stimulated by labile carbon and that the microbial activity is stimulated by both labile C and by nutrients (N); (2) that the microbial biomass is a strong sink for nutrients and that the microbial community probably can withdraw substantial amounts of nutrients from the inorganic, plant-available pool, at least periodically; (3) that temporary declines in microbial populations are likely to release a flush of inorganic nutrients to the soil, particularly P of which the microbial biomass contained more than one third of the total soil pool; and (4) that the mobilization-immobilization cycles of nutrients coupled to the population dynamics of soil organisms can be a significant regulating factor for the nutrient supply to the primary producers, which are usually strongly nutrient-limited in arctic ecosystems.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00329709

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5

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Inhibition of growth, and effects on nutrient uptake of arctic graminoids by leaf extracts — allelopathy or resource competition between plants and microbes? (1995)

Michelsen, Anders ; Schmidt, Inger K. ; Jonasson, Sven ; [et al.]

Springer

Oecologia 103 (1995), S. 407-418

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ISSN: 1432-1939

Keywords: Allelopathy ; Betula pubescens ssp ; tortuosa ; Cassiope tetragona ; Empetrum hermaphroditum ; Plant-microbe competition

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: Abstract Previous research has shown that plant extracts, e.g. from boreal dwarf shrubs and trees, can cause reduced growth of neighbouring plants: an effect known as allelopathy. To examine whether arctic and subarctic plants could also be affected by leaching of phytochemicals, we added extracts from the commonly occurring arctic dwarf shrubs Cassiope tetragona and Empetrum hermaphroditum, and from mountain birch, Betula pubescens ssp. tortuosa to three graminoid species, Carex bigelowii, Festuca vivipara and Luzula arcuata, grown in previously sterilized or non-sterilized arctic soils. The graminoids in non-sterilized soil grew more slowly than those in sterilized soil. Excised roots of the plants in non-sterilized soil had higher uptake rate of labelled P than those in sterilized soil, demonstrating larger nutrient deficiency. The difference in growth rate was probably caused by higher nutrient availability for plants in soils in which the microbial biomass was killed after soil sterilization. The dwarf shrub extracts contained low amounts of inorganic N and P and medium high amounts of carbohydrates. Betula extracts contained somewhat higher levels of N and much higher levels of P and carbohydrates. Addition of leaf extracts to the strongly nutrient limited graminoids in non-sterilized soil tended to reduce growth, whereas in the less nutrient limited sterilized soil it caused strong growth decline. Furthermore, the N and P uptake by excised roots of plants grown in both types of soil was high if extracts from the dwarf shrubs (with low P and N concentrations) had been added, whereas the P uptake declined but the N uptake increased after addition of the P-rich Betula extract. In contrast to the adverse extract effects on plants, soil microbial respiration and soil fungal biomass (ergosterol) was generally stimulated, most strongly after addition of the Betula extract. Although we cannot exclude the possibility that the reduced plant growth and the concomitant stimulation of microbial activity were caused by phytochemicals, we believe that this was more likely due to labile carbon in the extracts which stimulated microbial biomass and activity. As a result microbial uptake increased, thereby depleting the plant available pool of N and P, or, for the P-rich Betula extract, depleting soil inorganic N alone, to the extent of reducing plant growth. This chain of events is supported by the negative correlation between plant growth and sugar content in the three added extracts, and the positive correlation between microbial activity, fungal biomass production and sugar content, and are known reactions when labile carbon is added to nutrient deficient soils.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00328678

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6

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Shoot biomass, δ13C, nitrogen and chlorophyll responses of two arctic dwarf shrubs to in situ shading, nutrient application and warming simulating climatic change (1996)

Michelsen, Anders ; Jonasson, Sven ; Sleep, Darren ; [et al.]

Springer

Oecologia 105 (1996), S. 1-12

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ISSN: 1432-1939

Keywords: Altitude ; Carbon isotopes ; Cassiope tetragona ; Empetrum hermaphroditum ; Global change

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: Abstract As climatic change might induce ecophysiological changes in plants which affect their long-term performance, we investigated responses in above-ground biomass, δ13C, nitrogen and chlorophyll of two evergreen arctic dwarf shrubs, Cassiope tetragona and Empetrum hermaphroditum, to 5 (biomass, N) or 6 years of shading, nutrient application and air/soil warming at a dwarf shrub dominated tree-line heath (450 m a.s.l) and a high altitude fellfield (1100 m a.s.l.) in Swedish Lapland. Warming enhanced the green biomass (equivalent to the last 3–4 years of leaf production) and the ratio of green to brown biomass of C. tetragona at the fellfield, and diluted the shoot N concentration. Fertilizer application led to higher shoot N concentration and larger green-to-brown biomass ratio at both sites, and fertilizer application and warming generally had an additive effect on the green biomass. We conclude that both warming and increased soil nutrient availability stimulated the growth of C. tetragona at the fellfield whereas at the heath there was a clear increase in production only if enhanced temperature was combined with nutrient application. Across treatments C. tetragona at the fellfield had 0.6‰ higher δ13C and 1.4 mg g-1 more leaf N, and the soil organic matter δ13C was 1.0‰ higher at the fellfield than at the heath. However, an increase in shoot N concentration with altitude does not necessarily lead to higher δ13C as no differences in δ13C were observed when leaf N of the two dwarf shrubs was increased by fertilizer application c. tetragona in non-warmed plots had higher δ13C values than those from warmed plots at the same altitude, which provides the first in situ experimental validation of the theory that temperature partly is responsible for altitudinal trends in plant carbon isotope discrimination. Increased biomass and chlorophyll concentration of C. tetragona in warmed plots points to increased assimilation, at least at the fellfield. As the δ13C-based and, therefore, time-integrated estimate of the ratio of CO2 concentration in the leaf intercellular spaces to that in the atmosphere (C i/C a) also increased, warming probably enhanced the stomatal conductance relatively more than the C assimilation, which may be harmful if climatic change leads to reduced soil moisture content and increased plant competition for water. At both sites C. tetragona and E. hermaphroditum responded to shade by increasing the concentration of shoot N and photosynthetic pigments whereas biomass production (and therefore also net photosynthesis) did not decline. Shade was accompanied by a 0.6–1.3‰ (E. hermaphroditum) or 1.2–2.2‰ (C. tetragona) decrease in δ13C. This could be due to enhanced stomatal conductance with shading, and perhaps to shade reducing the ericoid mycorrhizal uptake of soil organic C, a factor which has been overlooked as an influence on plant δ13C.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00328785

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