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- Cornelissen, C, et al.
(författare)
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Global change and arctic ecosystems : is lichen decline a function of increases in vascular plant biomass?
- 2001
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Ingår i: Journal of Ecology. - : Wiley. - 0022-0477 .- 1365-2745. ; 89:6, s. 984-994
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Tidskriftsartikel (refereegranskat)abstract
- 1 Macrolichens are important for the functioning and biodiversity of cold northern ecosystems and their reindeer-based cultures and economics. 2 We hypothesized that, in climatically milder parts of the Arctic, where ecosystems have relatively dense plant canopies, climate warming and/or increased nutrient availability leads to decline in macrolichen abundance as a function of increased abundance of vascular plants. In more open high-arctic or arctic-alpine plant communities such a relationship should be absent. To test this, we synthesized cross-continental arctic vegetation data from ecosystem manipulation experiments simulating mostly warming and increased nutrient availability, and compared these with similar data from natural environmental gradients. 3 Regressions between abundance or biomass of macrolichens and vascular plants were consistently negative across the subarctic and mid-arctic experimental studies. Such a pattern did not emerge in the coldest high-arctic or arctic-alpine sites. The slopes of the negative regressions increased across 10 sites as the climate became milder (as indicated by a simple climatic index) or the vegetation denser (greater site above-ground biomass). 4 Seven natural vegetation gradients in the lower-altitude sub- and mid-arctic zone confirmed the patterns seen in the experimental studies, showing consistent negative relationships between abundance of macrolichens and vascular plants. 5 We conclude that the data supported the hypothesis. Macrolichens in climatically milder arctic ecosystems may decline if and where global changes cause vascular plants to increase in abundance. 6 However, a refining of our findings is needed, for instance by integrating other abiotic and biotic effects such as reindeer grazing feedback on the balance between vascular plants and lichens.
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- Fogel, W.A., et al.
(författare)
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Neuronal storage of histamine in the brain and tele-methylimidazoleacetic acid excretion in portocaval shunted rats
- 2002
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Ingår i: Journal of Neurochemistry. - : Wiley. - 0022-3042 .- 1471-4159. ; 80:3, s. 375-382
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Tidskriftsartikel (refereegranskat)abstract
- Rats with portocaval anastomosis (PCA), an animal model of hepatic encephalopathy (HE), have very high brain histamine concentrations. Our previous studies based on a biochemical approach indicated histamine accumulation in the neuronal compartment. In this study, immunohistochemical evidence is presented which further supports the amine localization in histaminergic neurons. These neurons become pathological in appearance with cisternae frequently seen along histaminergic fibres in many brain areas, including the hypothalamus, amygdala, substantia nigra and cerebral cortex. Such formations were not observed in sham-operated animals. The neuronal deposition is predominant, and unique for histamine. It serves as a mechanism to counterbalance excessive brain neurotransmitter formation evoked by PCA. However, there are other mechanisms. The data provided here show that there is also a significant increase in histamine catabolism in the shunted rats, as reflected by both the higher brain N-telemethylhistamine (t-MeHA) concentration and urinary excretion of N-tele-methylimidazoleacetic acid (t-MelmAA), a major brain histamine end product. The stomach, in addition to the brain, is a site of enhanced histamine synthesis in portocavally shunted subjects. After gastrectomy or food deprivation to eliminate the contribution of the stomach, shunted rats excrete significantly more t-MelmAA, implying the role of the CNS. This last finding suggests that under strictly defined conditions, namely in parenterally fed HE patients with abnormal plasma L-histidine, the measurement of urinary t-MelmAA might provide valuable information concerning putative brain histaminergic activity.
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- Thunes, KH, et al.
(författare)
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The arthropod community of Scots pine (Pinus sylvestris L.) canopies in Norway
- 2004
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Ingår i: Entomologica Fennica. - 0785-8760. ; 15:2, s. 65-90
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Forskningsöversikt (refereegranskat)abstract
- We summarise the findings of arthropods collected by fogging the canopy of 24 pine trees in two sites in Eastern and Western Norway. From the samples, taken in 1998 and in 1999, almost 30,000 specimens were determined to 512 species, with Diptera being most species rich (210 species), followed by Coleoptera (76 species) and Araneae (49 species). Of the 96 new species records, nine were new to science (5 Diptera and 4 Oribatida), two were new to the European, three to the Scandinavian and 82 to the Norwegian faunas. The paper demonstrates the need for detailed faunistical inventories of European forests.
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- Falkengren-Grerup, Ursula, et al.
(författare)
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Plant nitrate use in deciduous woodland: the relationship between leaf N, N-15 natural abundance of forbs and soil N mineralisation
- 2004
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Ingår i: Soil Biology & Biochemistry. - : Elsevier BV. - 0038-0717. ; 36:11, s. 1885-1891
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Tidskriftsartikel (refereegranskat)abstract
- Our aim was to study whether the in situ natural abundance N-15 (delta(15)N)-values and N concentration of understory plants were correlated with the form and amount of mineral N available in the soil. Also to determine whether such differences were related to earlier demonstrations of differences in biomass increase in the same species exposed to nutrient solutions with both NO3- and NH4+ or to NH4+ alone. Several studies show that the delta(15)N of NO3- in soil solution generally is isotopically lighter than the delta(15)N of NH4+ due to fractionation during nitrification. Hence, it is reasonable to assume that plant species benefiting from NO3- in ecosystems without significant NO3- leaching or denitrification have lower delta(15)N-values in their tissues than species growing equally well, or better, on NH4+. We studied the delta(15)N of six 4 understory species in oak woodlands in southern Sweden at 12 sites which varied fivefold in potential net N mineralisation rate (minNH(4)(+) + NO3-). The species decreased in benefit from NO3- in the following order: Geum urbanum, Aegopodium podagraria, Milium effusum, Convallaria majalis, Deschampsia flexuosa and Poa nemoralis. Four or five species demonstrated a negative correlation between minNO(3)(-) and leaf delta(15)N and a positive correlation between minNO(3)(-) and leaf N concentration. In wide contrast, only D. flexuosa, which grows on soils with little nitrification, showed a positive correlation between minNH(4)(+) and the leaf N concentration and delta(15)N-value. Furthermore, delta(15)N of plants from the field and previously obtained indices of hydroponic growth on NH4+ relative to NH4+ + NO3- were closely correlated at the species level. We conclude that delta(15)N may serve as a comparative index of uptake of NO3- among understory species, preferably in combination with other indices of N availability. The use of 5 15 N needs careful consideration of known restrictions of method, soils and plants.
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- Olsrud, Maria, et al.
(författare)
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Response of ericoid mycorrhizal colonization and functioning to global change factors
- 2004
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Ingår i: New Phytologist. - : Wiley. - 1469-8137 .- 0028-646X. ; 162:2, s. 459-469
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Tidskriftsartikel (refereegranskat)abstract
- Here, we investigated effects of increased atmospheric CO2 concentration, increased temperatures, and both factors in combination on ericoid mycorrhizal colonization, mycorrhizal functioning and below-ground carbon allocation in a subarctic forest understorey, to evaluate the hypothesis that photosynthesis is a primary driver for mycorrhizal colonization. Treatment effects on ecosystem processes were investigated using C-14-pulse labelling and photosynthesis measurements in combination with analysis of ergosterol content in roots. The effects on delta(15)N in leaves were also studied. Ergosterol content in hair roots was positively correlated with ecosystem photosynthesis and was higher in heat- and CO2-treated plots. Leaves from CO2 Plots tended to be more depleted in N-15 compared with controls both for Vaccinium myrtillus and V. vitis-idaea. Our results suggest that changes in ecosystem photosynthesis, plant carbon (C) Allocation may give rise to changing mycorrhizal colonization under elevated CO2 and temperature. The role of mycorrhizas in ecosystem N-cycling may change on a long-term basis as inorganic N availability declines with increasing levels of atmospheric CO2.
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- Schmidt, I K, et al.
(författare)
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Long-term manipulation of the microbes and microfauna of two subarctic heaths by addition of fungicide, bactericide, carbon and fertilizer
- 2000
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Ingår i: Soil Biology & Biochemistry. - 0038-0717. ; 32:5, s. 707-720
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Tidskriftsartikel (refereegranskat)abstract
- Nutrient availability is a major constraint to plant production and carbon storage in arctic ecosystems, but there are few studies coupling processes in the decomposer and microbial food web and the implications these processes have on the control of nutrient mineralization. We studied the relationship between microbial biomass and the abundance of microbivore and the role of grazing on nutrient turnover after annual addition of carbon (sucrose), fertilizer (NPK), fungicide (benomyl) and bactericides (streptomycin and penicillin) to two dwarf shrub communities, a low and a high altitude heath. After four years of repeated additions, we measured microbial biomass by fumigation-extraction and phospholipid fatty acid (PLFA) analysis, the fungal to bacterial biomass ratio by PLFA analysis and estimated the numbers of protozoa and nematodes, assigned into feeding groups. The fungal to bacterial ratio of nematode feeding groups was around 0.2, indicating a bacterial-based food web in both communities. The size of the microbial biomass did not change after the additions, except when the amount of available carbon was increased (low altitude heath) or when addition of carbon was combined with fertilizer (high altitude heath). In contrast, fertilizer but not carbon increased the number of microbivores. This suggests that the amount of available carbon and not grazing pressure controls the size of the microbial biomass, Furthermore, it suggests that the food quality, e.g. nutrient content of the micro-organisms, had a larger effect on the microbivore than the size of the microbial biomass. The addition of bactericides and fungicide did not significantly change the fungal to bacterial biomass ratio of the micro-organisms. We could not detect any effects of the bactericides. In contrast, the fungicide strongly decreased nematode density, least in the fungal feeders, probably due to increased abundance of the insensitive Aphelenchoides ssp. (C) 2000 Elsevier Science Ltd. All rights reserved.
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