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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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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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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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In situ mineralization of nitorgen and phosphorus of arctic soils after perturbations simulating climate change (1993)

Jonasson, Sven ; Havström, Mats ; Jensen, Michael ; [et al.]

Springer

Oecologia 95 (1993), S. 179-186

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ISSN: 1432-1939

Keywords: Arctic-Alpine ; Climate change ; N and P mineralization ; Nutrient immobilization ; Soils

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: Abstract Seasonal net nitrogen (N) and phosphorus (P) mineralization was investigated at Abisko, Swedish Lapland in soils of a subarctic heath and in soils of a colder (by about 4° C), high altitude fellfield by (a) using in situ soil incubation in soils which had been shaded or subjected to two levels of increased temperature, combined with (b) reciprocal transplantation of soils between the two sites. Proportionally large and significant net seasonal mineralization of N, in contrast to non-significant P mineralization, was found in untransplanted and transplanted fellfield soil. In contrast, P was mineralized in proportionally large amounts, in contrast to low N mineralization, in the transplanted and untransplanted heath soil. The differences indicate that P was strongly immobilized in relation to N at the fellfield and that N was more strongly immobilized than P in the heath soil. The immobilization in both soils remained high even after a temperature change of 4–5° C experienced by transplanted soils. Air temperature increases of up to 4–5° C in greenhouses resulted in a soil temperature increase of 1–2° C and did not cause any extra increase of net N and P mineralization. The results suggest that soil temperature increases of up to 2° C, which are likely to occur by the end of the next century as an effect of a predicted 4–5° C rise in air temperature, have only small effects on net mineralization in at least two characteristic tundra soils. These effects are probably smaller than the natural fluctuation of plant available nutrients from site to site, even within the same plant community. A further soil temperature increase of up to 4–5° C may enhance decomposition and gross mineralization, but the rate of net mineralization, and hence the change of nutrient availability to the plants, depends on the extent of microbial immobilization of the extra nutrients released.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00323488

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Small-scale vegetation pattern related to the growth of Lycopodium annotinum and variations in its micro-environment (1988)

Svensson, Brita M. ; Callaghan, Terry V.

Springer

Plant ecology 76 (1988), S. 167-177

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ISSN: 1573-5052

Keywords: Cluster analysis ; Micro-topography ; Modular growth ; Patch ; Sub-arctic ; TWINSPAN

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: Abstract Small-scale variations in topography, soil depth and species occurrence were studied in a sub-arctic/sub-alpine brich forest in Swedish Lapland in order to evaluate the effects of various micro-habitats on the growth and distribution of Lycopodium annotinum. Micro-topographical variation in the study plot (280 by 420 cm) reached 100 cm, while soil depth varied from 0 to more than 50 cm over small distances of 10's of centimetres. Nineteen species were recorded in the plot and dwarf shrubs and L. annotinum were the most frequent. A micro-scale vegetation pattern was detected by a polythetic agglomerative cluster analysis and also by the divisive TWINSPAN analysis. The distribution patterns of the species appeared to be associated with variation in moisture regimes, which in turn were associated with variations in micro-topography. Lycopodium annotinum performed best when growing on the sides of valleys with deciduous dwarf shrubs and Deschampsia flexuosa, and when evergreen dwarf shrubs were absent.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00045477

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