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| 2. |
- Christensen, Torben, et al.
(författare)
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Factors controlling large scale variations in methane emissions from wetlands
- 2003
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Ingår i: Geophysical Research Letters. - 0094-8276 .- 1944-8007. ; 30:7
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Tidskriftsartikel (refereegranskat)abstract
- [1] Global wetlands are, at estimate ranging 115-237 Tg CH4/yr, the largest single atmospheric source of the greenhouse gas methane (CH4). We present a dataset on CH4 flux rates totaling 12 measurement years at sites from Greenland, Iceland, Scandinavia and Siberia. We find that temperature and microbial substrate availability (expressed as the organic acid concentration in peat water) combined explain almost 100% of the variations in mean annual CH4 emissions. The temperature sensitivity of the CH4 emissions shown suggests a feedback mechanism on climate change that could validate incorporation in further developments of global circulation models.
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| 3. |
- Ekberg, Anna
(författare)
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Den arktiska tundran värmer
- 2002
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Ingår i: Biologen: medlemsblad för Biologilärarnas förening. - 0345-1127.
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Tidskriftsartikel (populärvet., debatt m.m.)
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| 4. |
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| 5. |
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| 6. |
- Silvola, J, et al.
(författare)
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Effects of elevated CO2 and N deposition on CH4 emissions from European mires
- 2003
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Ingår i: Global Biogeochemical Cycles. - 0886-6236. ; 17:2
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Tidskriftsartikel (refereegranskat)abstract
- [1] Methane fluxes were measured at five sites representing oligotrophic peatlands along a European transect. Five study plots were subjected to elevated CO2 concentration (560 ppm), and five plots to NH4NO3 (3 or 5 g N yr(-1)). The CH4 emissions from the control plots correlated in most cases with the soil temperatures. The depth of the water table, the pH, and the DOC, N and SO4 concentrations were only weakly correlated with the CH4 emissions. The elevated CO2 treatment gave nonsignificantly higher CH4 emissions at three sites and lower at two sites. The N treatment resulted in higher methane emissions at three sites (nonsignificant). At one site, the CH4 fluxes of the N-treatment plots were significantly lower than those of the control plots. These results were not in agreement with our hypotheses, nor with the results obtained in some earlier studies. However, the results are consistent with the results of the vegetation analyses, which showed no significant treatment effects on species relationships or biomass production.
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| 7. |
- Sjödin, Kristina, et al.
(författare)
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Occurrence and correlations of monoterpene hydrocarbon enantiomers in Pinus sylvestris and Picea abies
- 2000
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Ingår i: Journal of Chemical Ecology. - 0098-0331 .- 1573-1561. ; 26:7, s. 1701-1720
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Tidskriftsartikel (refereegranskat)abstract
- The relative amounts and enantiomeric compositions of monoterpene hydrocarbons in branch and trunk xylem, in needles, and in resin from apical buds in 18 Pinus sylvestris trees have been determined and compared with the terpene content in branch xylem and needles of Picea abies. Besides the high amount of (+)-3-carene, an excess of (+)-alpha-pinene has been found in P. sylvestris, whereas in P. abies (-)-alpha-pinene dominates over (+)-alpha-pinene. In P. sylvestris, clear positive correlations were found between (+)-alpha-pinene and (+)-camphene in the four tissues analyzed. Good positive correlations were also observed between (-)-alpha-pinene and (-)-camphene in the two types of xylem, between (+)-alpha-pinene and (+)-beta-pinene in the resin, and between tricyclene and (-)-camphene in resin and needles. In P. abies, positive correlations were found between (+)-alpha-pinene and (+)-camphene in the branch xylem and between tricyclene and (-)-camphene as well as between (-)-alpha-pinene and (-)-camphene in the needles. Complex relationships between (-)-alpha-pinene and (-)-beta-pinene were found both in the P. abies and in the P. sylvestris tissues. The importance of the enantiomeric composition of alpha-pinene for the host selection of Ips typographus, Tomicus piniperda, and Hylobius abietis is discussed.
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| 8. |
- Ström, Lena, et al.
(författare)
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The effect of vascular plants on carbon turnover and methane emissions from a tundra wetland
- 2003
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Ingår i: Global Change Biology. - : Wiley. - 1354-1013. ; 9:8, s. 1185-1192
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Tidskriftsartikel (refereegranskat)abstract
- This paper investigates how vascular plants affect carbon flow and the formation and emission of the greenhouse gas methane (CH4 ) in an arctic wet tundra ecosystem in NE Greenland. We present a field experiment where we studied, in particular, how species-specific root exudation patterns affect the availability of acetate, a hypothesized precursor of CH4 formation. We found significantly higher acetate formation rates in the root vicinity of Eriophorum scheuchzeri compared with another dominating sedge in the wetland, i.e. Dupontia psilosantha . Furthermore a shading treatment, which reduced net photosynthesis, resulted in significantly decreased formation rates of acetate. We also found that the potential CH4 production of the peat profile was highly positively correlated to the concentration of acetate at the respective depths, whereas it was negatively correlated to the concentration of total dissolved organic carbon. This suggests that acetate is a substrate of importance to the methanogens in the studied ecosystem and that acetate concentration in this case can serve as a predictor of substrate quality. To further investigate the importance of acetate as a predecessor to CH4 , we brought an intact peat-plant monolith system collected at the field site in NE Greenland to the laboratory, sealed it hermetically and studied the decomposition of (14) C-labelled acetate injected at the depth of methanogenic activity. After 4 h, (14) CH4 emission from the monolith could be observed. In conclusion, allocation of recently fixed carbon to the roots of certain species of vascular plants affects substrate quality and influence CH4 formation.
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| 9. |
- Vogel, Anna, 1969-
(författare)
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Swedish Dimensional Adjectives
- 2004
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The purpose of this study is to give a thorough and detailed account and analysis of the semantics of twelve Swedish dimensional adjectives: hög ’high/tall’, låg ’low’, bred ’broad/wide’, smal ’narrow’ vid ’broad’, trång ’narrow’, tjock ’thick’, tunn ’thin’, djup ’deep’, grund ’narrow’, lång ’long’ and kort ’short’. Focus has been placed on their spatial, non-metaphorical sense. The study was written within the framework of cognitive linguistics, where lexical definitions may be given in terms of prototypical and peripheral uses. Four sources of data have been considered: a corpus, consisting of contemporary fiction, an elicitation test, designed for the purpose, dictionary articles on the pertinent adjectives, and the author's own linguistic intuition as a native speaker. The methodology has involved categorisation of combinations of adjective and noun, based upon three major themes: orientation, function, and shape. In order to determine prototypical uses, precedence has been given to the outcome of the elicitation test over the corpus search. For both sources, frequency has played an important part. The ranking of senses as stated in the dictionary articles has also been considered.The results indicate that the dimensional adjectives differ quite markedly from each other, as opposed to a structural view where the adjectives traditionally have been regarded as forming a neat patchwork. Adjectives overlap each other for some uses (högt gräs ’high grass’, långt gräs ’long grass’ and even djupt gräs ’deep grass’), while there are also situations in which no dimensional adjective can describe an object. Furthermore, adjectives forming pairs, such as djup – grund ’deep – shallow’, do not exhibit full antonymy, despite the fact that dimensional adjectives are traditionally cited as examples par excellence concerning antonymy.
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