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  • 1. Björk, Robert G.
    et al.
    Björkman, Mats P.
    Andersson, Mats X.
    Klemedtsson, Leif
    Temporal variation in soil microbial communities in Alpine tundra2008In: Soil Biology and Biochemistry, ISSN 0038-0717, E-ISSN 1879-3428, Vol. 40, no 1, p. 266-268Article in journal (Refereed)
    Abstract [en]

    Temporal variation in soil microbial communities was studied at a mid-alpine environment in Latnjajaure, northern Sweden, using phospholipid fatty acid (PLFA) analysis. The results show two seasonal shifts in microbial composition. The first shift was associated with snowmelt and mainly related to a decrease in fungal PLFAs, accompanied by an increase in branched 17:0 and methylated PLFAs (biomarkers for Gram-positive- and actinobacteria, respectively), resulting in a decrease in the ratio of fungi-to-bacteria. The second shift occurred across the growing season, and was associated with a switch from shorter to longer PLFAs and an increase in 18:1ω7 (biomarker for Gram-negative bacteria). Vegetation, snow cover dynamics, and N turnover seem to be of minor importance to broad-scale microbial community structure in this area.

  • 2. Bokhorst, S.
    et al.
    Bjerke, J. W.
    Melillo, J.
    Callaghan, T. V.
    Phoenix, G. K.
    Impacts of extreme winter warming events on litter decomposition in a sub-Arctic heathland2010In: Soil Biology and Biochemistry, ISSN 0038-0717, E-ISSN 1879-3428, Vol. 42, no 4, p. 611-617Article in journal (Refereed)
    Abstract [en]

    Arctic climate change is expected to lead to a greater frequency of extreme winter warming events. During these events, temperatures rapidly increase to well above 0 °C for a number of days, which can lead to snow melt at the landscape scale, loss of insulating snow cover and warming of soils. However, upon return of cold ambient temperatures, soils can freeze deeper and may experience more freeze–thaw cycles due to the absence of a buffering snow layer. Such loss of snow cover and changes in soil temperatures may be critical for litter decomposition since a stable soil microclimate during winter (facilitated by snow cover) allows activity of soil organisms. Indeed, a substantial part of fresh litter decomposition may occur in winter. However, the impacts of extreme winter warming events on soil processes such as decomposition have never before been investigated. With this study we quantify the impacts of winter warming events on fresh litter decomposition using field simulations and lab studies. Winter warming events were simulated in sub-Arctic heathland using infrared heating lamps and soil warming cables during March (typically the period of maximum snow depth) in three consecutive years of 2007, 2008, and 2009. During the winters of 2008 and 2009, simulations were also run in January (typically a period of shallow snow cover) on separate plots. The lab study included soil cores with and without fresh litter subjected to winter-warming simulations in climate chambers. Litter decomposition of common plant species was unaffected by winter warming events simulated either in the lab (litter of Betula pubescens ssp. czerepanovii), or field (litter of Vaccinium vitis-idaea, and B. pubescens ssp. czerepanovii) with the exception of Vaccinium myrtillus (a common deciduous dwarf shrub) that showed less mass loss in response to winter warming events. Soil CO2 efflux measured in the lab study was (as expected) highly responsive to winter warming events but surprisingly fresh litter decomposition was not. Most fresh litter mass loss in the lab occurred during the first 3–4 weeks (simulating the period after litter fall). In contrast to past understanding, this suggests that winter decomposition of fresh litter is almost non-existent and observations of substantial mass loss across the cold season seen here and in other studies may result from leaching in autumn, prior to the onset of “true” winter. Further, our findings surprisingly suggest that extreme winter warming events do not affect fresh litter decomposition.

  • 3. Haugwitz, Merian Skouw
    et al.
    Michelsen, Anders
    Schmidt, Inger Kappel
    Long-term microbial control of nutrient availability and plant biomass in a subarctic-alpine heath after addition of carbon, fertilizer and fungicide2011In: Soil Biology and Biochemistry, ISSN 0038-0717, E-ISSN 1879-3428, Vol. 43, no 1, p. 179-187Article in journal (Refereed)
    Abstract [en]

    A long-term field experiment lasting more than a decade was conducted on a subarctic fellfield to investigate effects of changes in nutrient availability on soil microbial C, N and P, soil nutrients, vascular plant biomass and plant-microbial interactions. Additions of NPK fertilizer, labile C (sugar) and fungicide (benomyl) were done in a fully factorial design, replicated in six blocks. The treatments were run for ten years and soil and vegetation samples were collected four years after initiating the experiment, and again after an additional 12 years, to evaluate the long-term effects. Labile C addition resulted in increased microbial biomass and nutrient immobilization after four years, and a long-term decrease in vascular plant biomass, thus suggesting the microorganisms to strongly control soil nutrient availability in periods of high microbial biomass. Fertilization increased the inorganic and total soil nutrient pools of N and P and the fine root biomass, but not the total aboveground vascular plant biomass. The vascular plant biomass increased due to benomyl addition thus indicating the plants to be strongly affected by the microbial community. Overall, the effects of benomyl resulted in more lasting changes in the soil compared to labile C and fertilizer addition. In relation to environmental changes, the indicated strong microbial control of the available nutrients in the fellfield ecosystem might limit ecosystem changes due to increased soil nutrient availability as otherwise expected in arctic soils.

  • 4. Jonasson, S
    et al.
    Castro, J
    Michelsen, A
    Interactions between plants, litter and microbes in cycling of nitrogen and phosphorus in the arctic2006In: Soil Biology and Biochemistry, ISSN 0038-0717, E-ISSN 1879-3428, Vol. 38, no 3, p. 526-532Article in journal (Refereed)
    Abstract [en]

    Estimated nutrient mineralization in northern nutrient-poor ecosystems, measured as differences in soil inorganic nutrients before and after a period of soil incubation in the absence of plants and litter, usually shows a discrepancy of much lower rates than plant nutrient uptake rates. In plots that had been pre-treated by 12 year of warming and fertilizer addition, we incubated soils together with litter and plants added and examined whether the absence of plants and litter in ‘traditional’ incubations could explain the discrepancy. The pre-treatment had no effect on nitrogen (N) mineralization but increased phosphorus (P) mineralization, while litter addition decreased N and increased P mineralization but without any effect on plant and microbial N and P sequestration. Incubations of soils with plants increased N mobilization to the soil inorganic plus plant pools several-fold as compared to the net mineralization in soils without plants. Hence, the presence of plants stimulated mobilization of the growth-limiting N. The growth-sufficient P was not affected by the presence of plants, however. Furthermore, increased plant and microbial N uptake correlated positively, which speaks against competition for plant available N from soil microbes in N-constrained ecosystems, at least during the time-span of 10 weeks the experiment lasted, and instead suggests facilitation. (c) 2005 Elsevier Ltd. All rights reserved.

  • 5. Kokfelt, Ulla
    et al.
    Struyf, Eric
    Randsalu, Linda
    Diatoms in peat – Dominant producers in a changing environment?2009In: Soil Biology and Biochemistry, ISSN 0038-0717, E-ISSN 1879-3428, Vol. 41, no 8, p. 1764-1766Article in journal (Refereed)
    Abstract [en]

    Changes in hydrology and temperature can induce rapid changes in boreal wetland ecosystems. Factors such as hydrosere, permafrost, climate and human interference may disturb the prevailing mire vegetation, whereby a new dominant assemblage can develop. At the transition from one vegetation type to another, the old vegetation may be suppressed, die out or start to decay, and some time may pass until a new mire vegetation is fully established. Here, we demonstrate that diatoms may thrive during such transitions, creating isolated and shallow peat layers with significantly elevated biogenic silica content. Biogenic silica and other nutrients that would otherwise be lost during mineralization in runoff are in this way retained in the ecosystem. Our results imply that silica storage originating from diatoms can be expected to increase in today’s rapidly changing boreal wetlands. The impacts on transport of Si through boreal watersheds are currently unknown.

  • 6. Krab, Eveline J.
    et al.
    Berg, Matty P.
    Aerts, Rien
    van Logtestijn, Richard S.P.
    Cornelissen, Johannes H.C.
    Vascular plant litter input in subarctic peat bogs changes Collembola diets and decomposition patterns2013In: Soil Biology and Biochemistry, ISSN 0038-0717, E-ISSN 1879-3428, Vol. 63, p. 106-115Article in journal (Refereed)
    Abstract [en]

    In high-latitude ecosystems climate change induced plant community shifts toward dominance of shrubs and trees will potentially have large consequences for soil carbon dynamics. Changes in the litter layer due to an altered quantity and quality of litter input, or by its indirect effect on the microclimate, might affect the decomposer community. To be able to predict the effects of increased litter input on decomposers and consequently on soil carbon dynamics, we studied the contribution of Collembola to carbon processing in a high-latitude peat bog system. Moreover, we assessed the effects of changing litter inputs on their abundance, diversity and diet choice, using a 13C tracer approach. The δ13C signatures of Collembola in peat moss (Sphagnum fuscum) showed that species differed in their diet. However, when vascular plant litter (Betula pubescens) entered the Sphagnum peat ecosystem, the δ13C signatures of the Collembola, changed and species-specific differences disappeared. There were no significant changes in Collembola species composition and density after Betula litter addition, but all species showed a strong dietary preference for Betula-associated food sources over Sphagnum; 67% of their diet contained carbon originating from Betula litter. Decomposition patterns corresponded to these findings; mass loss (after 406 days of incubation) of Betula increased from 16.1% to 26.2% when decomposing in combination with Sphagnum, and Sphagnum decomposed even slower in combination with Betula litter (from 4.7% to 1.9%). Our results indicate that the change in litter quality rather than its effects on microclimate is the main way in which vascular litter inputs alter the role of Collembola in carbon turnover. Collembola are plastic in their diet choice, which implies that changes in carbon turnover rates in situations where vegetation shifts occur, might well be due to diet shifts of the present decomposer community rather than by changes in species composition.

  • 7. Krab, Eveline J.
    et al.
    Van Schrojenstein Lantman, Irene M.
    Cornelissen, Johannes H.C.
    Berg, Matty P.
    How extreme is an extreme climatic event to a subarctic peatland springtail community?2013In: Soil Biology and Biochemistry, ISSN 0038-0717, E-ISSN 1879-3428, Vol. 59, p. 16-24Article in journal (Refereed)
    Abstract [en]

    Extreme climate events are increasing in frequency and duration and may directly impact belowground foodwebs and the activities of component soil organisms. The soil invertebrate community, which includes keystone decomposers, might respond to these newly induced soil microclimate conditions by shifts in density, species composition, spatial patterning and/or functional traits. To test if and how short-term extreme climatic conditions alter the structure, the vertical stratification and the community weighted trait means of the springtail (Collembola) community in sub-arctic peatbogs, we experimentally subjected Sphagnum peat cores in a field setting to factorial treatments of elevated temperature and episodically increased moisture content. The large precipitation peaks did not affect the springtail community, but an average soil temperature increase of 4 °C halved its density in the shallower peat layers, mainly caused by the reduced dominance of Folsomia quadrioculata. A hypothesized net downward shift of the surface-dwelling springtail community, however, was not observed. We observed species-specific responses to warming but the overall community composition in subsequent organic layers was not significantly altered. Although the effects of an extreme warming event on density, species composition and vertical stratification pattern seemed subtle, functional trait analysis revealed directional community responses, i.e. an overall increase of soil-dwelling species due to warming, even though warming did not alter layer-specific community weighted trait means. We suggest that subtle changes in moisture conditions, due to increased evapotranspiration, have decreased typically surface-dwelling species relative to soil-dwelling species. The extent to which this directional change in the community is maintained after an extreme event, and its costs for the community's resilience to multiple sequential extreme events will consequently determine its longer-term effects on the community and on ecosystem functioning.

  • 8. Ludley, Katherine E.
    et al.
    Robinson, Clare H.
    ‘Decomposer’ Basidiomycota in Arctic and Antarctic ecosystems2008In: Soil Biology and Biochemistry, ISSN 0038-0717, E-ISSN 1879-3428, Vol. 40, no 1, p. 11-29Article in journal (Refereed)
    Abstract [en]

    Current knowledge concerning ‘decomposer’ Basidiomycota in Arctic and Antarctic ecosystems is based on two sources: (a) collections and surveys of basidiomata, which have resulted in high-quality catalogues of species, although much of the species’ distribution and ecology are tentative and (b) isolations from soils and plant litter which typically result in a “low incidence of basidiomycetes” [Dowding, P., Widden, P., 1974. Some relations between fungi and their environment in tundra regions. In: Holding, A.J., Heal, O.W., MacLean Jr., S.F., Flanagan, P.W. (Eds.), Soil Organisms and Decomposition in Tundra. Tundra Biome Steering Committee, Stockholm, Sweden, pp. 123–150], probably because of selectivity in isolation methods. In the few molecular studies carried out in Arctic and Antarctic soils to date, basidiomycetes, particularly yeasts, have been found. These techniques should give better estimates of the order of magnitude of fungal species richness in Arctic and Antarctic soils, although caution should be used concerning primer choice and amplification conditions. From collections in Arctic regions, species of basidiomycetes appear to be circumpolar in distribution with restricted endemism. Using culture-independent methods, it should be possible to test whether selected Arctic or Antarctic species are truly cosmopolitan, circumpolar, endemic, or are cryptic phylogenetic species. Particularly in Arctic ecosystems, potential ‘decomposer’ fungi in soils and roots may be from phylogenetically diverse taxa, and currently it is unclear whether ‘decomposer’ basidiomycetes are the fungi undertaking the majority of organic matter decomposition in Arctic and Antarctic ecosystems. For example, in some recent studies, wood decomposition in cold Arctic and Antarctic sites appears to proceed via ‘soft rot’ by anamorphic ascomycetes (e.g. Cadophora species), rather than by ‘white rot’ or ‘brown rot’ basidiomycete species. Additionally, it appears basidiomycetes and ascomycetes as ericoid and ectomycorrhizal fungi have the potential to be involved directly in decomposition. Given that profound changes are likely to occur in patterns of vegetation (Arctic and Antarctic) and size of soil carbon (C) pools (particularly in the Arctic) by the end of this century, it is necessary to know more about which species of ‘decomposer’ basidiomycetes are present and to try to define their potentially pivotal roles in ecosystem C (and N) cycling. One solution to characterise further the identity and roles of these fungi in a logical way, is to standardise methods of detection and ‘function’ at networks of sites, including along latitudinal gradients. Results of functional tests should be related to community structure, at least for ‘key’ species.

  • 9. Makarov, M. I.
    et al.
    Malysheva, T. I.
    Cornelissen, J. H. C.
    van Logtestijn, R. S. P.
    Glasser, B.
    Consistent patterns of 15N distribution through soil profiles in diverse alpine and tundra ecosystems2008In: Soil Biology and Biochemistry, ISSN 0038-0717, E-ISSN 1879-3428, Vol. 40, no 5, p. 1082-1089Article in journal (Refereed)
    Abstract [en]

    We studied the vertical patterns of δ15nitrogen in total N and exchangeable NH4+-N through soil profiles in diverse alpine and tundra ecosystems. Soil samples were analyzed from 11 sites located in three mountain areas: NW Caucasus (Russia), the Khibiny Mountains (NW Russia) and Abisko region (N Sweden). Despite differences in the profile patterns of organic matter, nitrogen accumulation and nitrogen availability, we found consistent patterns of 15N distribution through all studied soil profiles. The δ15N values of total N were in general about zero or positive in the surface horizon and increased with soil depth. In contrast with total N, the δ15N values of exchangeable NH4+-N were in general about zero or negative in the surface horizons and decreased with soil depth. NH4+-N was significantly 15N-depleted compared with total N in all mineral horizons, while in the surface organic horizons differences between isotopic composition of total N and NH4+-N were mostly not significant. We do not know the exact mechanism responsible for 15N depletion of NH4+-N with soil depth and further research needs to evaluate the contributions of natural processes (higher nitrification activity and biological immobilization of “lighter” NH4+-N near the soil surface) or artifacts of methodological procedure (contribution of the 15N-enriched microbial N and dissolved organic N near the soil surface). Nevertheless, our finding gives a new possibility to interpret variability in foliar δ15N values of plant species with different rooting depth in alpine and tundra ecosystems, because plants with deeper root systems can probably consume “lighter” rather than “heavier” NH4+-N.

  • 10. Makkonen, Marika
    et al.
    Berg, Matty P.
    Hal, Jurgen R. van
    Callaghan, Terry V.
    Press, Malcolm C.
    Aerts, Rien
    Traits explain the responses of a sub-arctic Collembola community to climate manipulation2011In: Soil Biology and Biochemistry, ISSN 0038-0717, E-ISSN 1879-3428, Vol. 43, no 2, p. 377-384Article in journal (Refereed)
    Abstract [en]

    Ecosystems at high northern latitudes are subject to strong climate change. Soil processes, such as carbon and nutrient cycles, which determine the functioning of these ecosystems, are controlled by soil fauna. Thus assessing the responses of soil fauna communities to environmental change will improve the predictability of the climate change impacts on ecosystem functioning. For this purpose, trait assessment is a promising method compared to the traditional taxonomic approach, but it has not been applied earlier. In this study the response of a sub-arctic soil Collembola community to long-term (16 years) climate manipulation by open top chambers was assessed. The drought-susceptible Collembola community responded strongly to the climate manipulation, which substantially reduced soil moisture and slightly increased soil temperature. The total density of Collembola decreased by 51% and the average number of species was reduced from 14 to 12. Although community assessment showed species-specific responses, taxonomically based community indices, species diversity and evenness, were not affected. However, morphological and ecological trait assessments were more sensitive in revealing community responses. Drought-tolerant, larger-sized, epiedaphic species survived better under the climate manipulation than their counterparts, the meso-hydrophilic, smaller-sized and euedaphic species. Moreover it also explained the significant responses shown by four taxa. This study shows that trait analysis can both reveal responses in a soil fauna community to climate change and improve the understanding of the mechanisms behind them.

  • 11. Olsrud, M
    et al.
    Christensen, T R
    Carbon cycling in subarctic tundra; seasonal variation in ecosystem partitioning based on in situ 14C pulse-labelling2004In: Soil Biology and Biochemistry, ISSN 0038-0717, E-ISSN 1879-3428, Vol. 36, no 2, p. 245-253Article in journal (Refereed)
    Abstract [en]

    Carbon assimilation and allocation were studied in a tundra ecosystem in northern Scandinavia. Seasonal variation in the below-ground carbon allocation to dissolved organic carbon (DOC), coarse-, fine-, and hair roots was investigated using in situ C-14 pulse-labelling, adding 2-3 MBq (CO2)-C-14, dm(-2) to the above-ground vegetation. Combining the allocation data with regression models of the seasonal carbon flux made it possible to estimate a temporally explicit ecosystem carbon allocation budget. The ecosystem was a net source of CO2, losing on average 0.97 gC m(-2) d(-1) to the atmosphere, with little variation through the season. There was, however, significant temporal variation in partitioning of recently assimilated carbon. Allocation to below-ground compartments over 32 days following labelling increased from 18% in June to 55% in September. Above-ground allocation showed the opposite trend. Hair roots and DOC were strong sinks in the autumn. Transport of newly assimilated carbon occurred rapidly throughout the season, C-14 appearing in all sampled pools within 4 h of labelling. The seasonal variation in carbon partitioning observed in this study has implications for the residence time of assimilated carbon in the ecosystem. A relatively greater allocation to rapidly decomposing pools, such as hair roots and DOC, would tend to reduce incorporation into woody tissue, increasing the overall rate of carbon cycling and decreasing ecosystem storage. The results of this study will be of value for building and validating mechanistic models of ecosystem carbon flow in tundra and subarctic ecosystems. (C) 2003 Elsevier Ltd. All fights reserved.

  • 12. Olsrud, Maria
    et al.
    Michelsen, Anders
    Wallander, Hakan
    Ergosterol content in ericaceous hair roots correlates with dark septate endophytes but not with ericold mycorrhizal colonization2007In: Soil Biology and Biochemistry, ISSN 0038-0717, E-ISSN 1879-3428, Vol. 39, no 5, p. 1218-1221Article in journal (Refereed)
    Abstract [en]

    The relationship between ergosterol content in ericaceous hair roots and ericoid mycorrhizal (ErM) colonization versus dark septate endophytic (DSE) hyphal colonization was examined in a dwarf shrub-dominated subarctic mire in Northern Sweden. Ergosterol content in hair roots did not correlate with ErM colonization in corresponding root samples. However, a significant positive relationship was found between hair root DSE hyphal colonization and ergosterol content. This is the first study to demonstrate that ergosterol cannot be used as a colonization indicator for ErM in hair roots growing under natural conditions. It also suggests the possibility of using ergosterol as an estimate of DSE hyphal colonization in ericaceous dwarf shrubs. This study has implications for the interpretation of results in field studies where ergosterol was used as a sole proxy for ErM colonization. (c) 2007 Elsevier Ltd. All rights reserved.

  • 13. Ravn, Nynne R.
    et al.
    Ambus, Per
    Michelsen, Anders
    Impact of decade-long warming, nutrient addition and shading on emission and carbon isotopic composition of CO2 from two subarctic dwarf shrub heaths2017In: Soil Biology and Biochemistry, ISSN 0038-0717, E-ISSN 1879-3428, Vol. 111, no Supplement C, p. 15-24Article in journal (Refereed)
    Abstract [en]

    Abstract This study investigated ecosystem respiration, soil respiration and carbon isotopic composition in CO2 emitted from two subarctic shrub heaths with contrasting moisture regimes. The reported measurements were conducted 22 years (mesic heath) and 12 years (wet heath) upon initiation of in situ climate change related manipulations of temperature, nutrient availability and light. The aim was to quantify expected climatic change effects on soil and ecosystem respiration, and to investigate whether the emitted CO2 originates from old carbon stores in the soil or from newly fixed carbon. Ecosystem and soil respiration was measured using closed chambers and CO2 in the soil profile was sampled with gas probes installed at different depths. At the mesic heath ecosystem respiration was increased 46% by warming while soil respiration increased 133% by nutrient addition. At the wet heath, warming increased ecosystem respiration by 99% and soil respiration by 58%. Litter addition, short time warming and shading generally did not change ecosystem- and soil respiration. The carbon isotope compositions of the sources to CO2 were not significantly altered by any of the treatments at the two heaths across the growing season. However, there was a tendency across growing season towards an increased ÎŽ13C source value after 22 years of warming in the mesic shrub heath, and the effect was statistically significant in June, indicating increased decomposition of 13C enriched material. Hence, although more of the old carbon stock in the soil was possibly mineralized under warmed conditions, indicating a risk of long lasting positive feedback on climate warming, the effect was only periodically strong enough to gain statistical significance, despite strong warming-induced effect on ecosystem respiration, and may be counteracted by increased C gain by higher primary production.

  • 14. Rinnan, Riikka
    et al.
    Michelsen, Anders
    Baath, Erland
    Jonasson, Sven
    Mineralization and carbon turnover in subarctic heath soil as affected by warming and additional litter2007In: Soil Biology and Biochemistry, ISSN 0038-0717, E-ISSN 1879-3428, Vol. 39, no 12, p. 3014-3023Article in journal (Refereed)
    Abstract [en]

    Arctic soil carbon (C) stocks are threatened by the rapidly advancing global warming. In addition to temperature, increasing amounts of leaf litter fall following from the expansion of deciduous shrubs and trees in northern ecosystems may alter biogeochemical cycling of C and nutrients. Our aim was to assess how factorial warming and litter addition in a long-term field experiment on a subarctic heath affect resource limitation of soil microbial communities (measured by thymidine and leucine incorporation techniques), net growing-season mineralization of nitrogen (N) and phosphorus (P), and carbon turnover (measured as changes in the pools during a growing-season-long field incubation of soil cores in situ). The mainly N limited bacterial communities had shifted slightly towards limitation by C and P in response to seven growing seasons of warming. This and the significantly increased bacterial growth rate under warming may partly explain the observed higher C loss from the warmed soil. This is furthermore consistent with the less dramatic increase in the contents of dissolved organic carbon (DOC) and dissolved organic N (DON) in the warmed soil than in the soil from ambient temperature during the field incubation. The added litter did not affect the carbon content, but it was a source of nutrients to the soil, and it also tended to increase bacterial growth rate and net mineralization of P. The inorganic N pool decreased during the field incubation of soil cores, especially in the separate warming and litter addition treatments, while gross mineralized N was immobilized in the biomass of microbes and plants transplanted into the incubates soil cores, but without any significant effect of the treatments. The effects of warming plus litter addition on bacterial growth rates and of warming on C and N transformations during field incubation suggest that microbial activity is an important control on the carbon balance of arctic soils under climate change. (c) 2007 Elsevier Ltd. All rights reserved.

  • 15. Rinnan, Riikka
    et al.
    Rinnan, Åsmund
    Application of near infrared reflectance (NIR) and fluorescence spectroscopy to analysis of microbiological and chemical properties of arctic soil2007In: Soil Biology and Biochemistry, ISSN 0038-0717, E-ISSN 1879-3428, Vol. 39, no 7, p. 1664-1673Article in journal (Refereed)
    Abstract [en]

    Abstract Applicability of near infrared reflectance (NIR) and fluorescence spectroscopic techniques was tested on highly organic arctic soil. Soil samples were obtained at a long-term climate change manipulation experiment at a subarctic fell heath in Abisko, northern Sweden. The ecosystem had been exposed to treatments simulating increasing temperature (open-top greenhouses), higher nutrient availability (NPK fertilization) and increasing cloudiness (shading cloths) for 15 years prior to the sampling. For each of the 72 samples from the 0 to 5cm soil depth and 36 samples from the 5 to 10cm depth, the wavelength range of 400–2500nm (visible and near infrared spectrum) was scanned with a NIR spectrophotometer and fluorescence excitation-emission matrices (EEMs) were recorded with a spectrofluorometer. Principal component analyses of the visible, NIR and fluorescence spectra clearly separated the treatments, which indicates that the chemical composition of the soil and its spectral properties had changed during the climate change simulation. Similarly to the results from the conventional analyses of soil chemical and microbiological properties, fertilization treatment posed strongest effects on the spectra. Partial least-squares (PLS) regression methods with cross-validation were used to analyse relationships between the spectroscopic data and the chemical and microbiological data derived from the conventional analyses. The fluorescence EEMs of the dried solid soil samples were moderately related to soil ergosterol content (correlation coefficient r=0.84), bacterial activity analysed by leucine incorporation technique (r=0.78) and total phospholipid fatty acid (PLFA) content (r=0.74), but in general fluorescence provided inferior predictions of the chemical and microbiological variables to NIR. NIR was highly related to soil organic matter content (r>0.9) and showed promising predictions of soil ergosterol content (r>0.9), microbial biomass C, microbial biomass P, and total PLFA contents (r=0.78–0.79). These results suggest that especially NIR could be used to predict soil organic matter and fungal biomass. Since it is rapid and inexpensive, and requires little sample mass, it could be used as a ‘quick and dirty’ technique to estimate progression of the treatment responses in long-term ecosystem experiments, where extensive soil sampling is to be avoided.

  • 16. Romero-Olivares, A. L.
    et al.
    Allison, S. D.
    Treseder, K. K.
    Soil microbes and their response to experimental warming over time: A meta-analysis of field studies2017In: Soil Biology and Biochemistry, ISSN 0038-0717, E-ISSN 1879-3428, Vol. 107, no Supplement C, p. 32-40Article in journal (Refereed)
    Abstract [en]

    Abstract Numerous field studies have found changes in soil respiration and microbial abundance under experimental warming. Yet, it is uncertain whether the magnitude of these responses remains consistent over the long-term. We performed a meta-analysis on 25 field experiments to examine how warming effects on soil respiration, microbial biomass, and soil microbial C respond to the duration of warming. For each parameter, we hypothesized that effect sizes of warming would diminish as the duration of warming increased. In support of our hypothesis, warming initially increased soil respiration, but the magnitude of this effect declined significantly as warming progressed as evidenced by the two longest studies in our meta-analysis. In fact, after 10 years of warming, soil respiration in warmed treatments was similar to controls. In contrast, warming effect sizes for fungal biomass, bacterial biomass, and soil microbial C did not respond significantly to the duration of warming. Microbial acclimation, community shifts, adaptation, or reductions in labile C may have ameliorated warming effects on soil respiration in the long-term. Accordingly, long-term soil C losses might be smaller than those suggested by short-term warming studies.

  • 17. Sorensen, Pernille Lärkedal
    et al.
    Michelsen, Anders
    Jonasson, Sven
    Ecosystem partitioning of 15N-glycine after long-term climate and nutrient manipulations, plant clipping and addition of labile carbon in a subarctic heath tundra2008In: Soil Biology and Biochemistry, ISSN 0038-0717, E-ISSN 1879-3428, Vol. 40, no 9, p. 2344-2350Article in journal (Refereed)
    Abstract [en]

    Low temperatures and high soil moisture restrict cycling of organic matter in arctic soils, but also substrate quality, i.e. labile carbon (C) availability, exerts control on microbial activity. Plant exudation of labile C may facilitate microbial growth and enhance microbial immobilization of nitrogen (N). Here, we studied 15N label incorporation into microbes, plants and soil N pools after both long-term (12 years) climate manipulation and nutrient addition, plant clipping and a pulse-addition of labile C to the soil, in order to gain information on interactions among soil N and C pools, microorganisms and plants. There were few effects of long-term warming and fertilization on soil and plant pools. However, fertilization increased soil and plant N pools and increased pool dilution of the added 15N label. In all treatments, microbes immobilized a major part of the added 15N shortly after label addition. However, plants exerted control on the soil inorganic N concentrations and recovery of total dissolved 15N (TD15N), and likewise the microbes reduced these soil pools, but only when fed with labile C. Soil microbes in clipped plots were primarily C limited, and the findings of reduced N availability, both in the presence of plants and with the combined treatment of plant clipping and addition of sugar, suggest that the plant control of soil N pools was not solely due to plant uptake of soil N, but also partially caused by plants feeding labile C to the soil microbes, which enhanced their immobilization power. Hence, the cycling of N in subarctic heath tundra is strongly influenced by alternating release and immobilization by microorganisms, which on the other hand seems to be less affected by long-term warming than by addition or removal of sources of labile C.

  • 18. Strom, Lena
    et al.
    Christensen, Torben R.
    Below ground carbon turnover and greenhouse gas exchanges in a sub-arctic wetland2007In: Soil Biology and Biochemistry, ISSN 0038-0717, E-ISSN 1879-3428, Vol. 39, no 7, p. 1689-1698Article in journal (Refereed)
    Abstract [en]

    Here we present results from a field experiment in a sub-arctic wetland near Abisko, northern Sweden, where the permafrost is currently disintegrating with significant vegetation changes as a result. During one growing season we investigated the fluxes of CO(2) and CH(4) and how they were affected by ecosystem properties, i.e., composition of species that are currently expanding in the area (Carex rotundata, Eriophorum vaginatum and Eriophorum angustifolium), dissolved CH(4) in the pore water, substrate availability for methane producing bacteria, water table depth, active layer, temperature, etc. We found that the measured gas fluxes over the season ranged between: CH(4) 0.2 and 36.1 mg CH(4) m(-2) h(-1), Net Ecosystem Exchange (NEE) -1000 and 1250 mg CO(2) m(-2) h(-1) (negative values meaning a sink of atmospheric CO(2)) and dark respiration 110 and 1700 mg CO(2) m(-2) h(-1). We found that NEE, photosynthetic rate and CH(4) emission were affected by the species composition. Multiple stepwise regressions indicated that the primary explanatory variables for NEE was photosynthetic rate and for respiration and photosynthesis biomass of green leaves. The primary explanatory variables for CH(4) emissions were depth of the water table, concentration of organic acid carbon and biomass of green leaves. The negative correlations between pore water concentration and emission of CH(4) and the concentrations of organic acid, amino acid and carbohydrate carbon indicated that these compounds or their fermentation by-products were substrates for CH(4) formation. Furthermore, calculation of the radiative forcing of the species expanding in the area as a direct result of permafrost degradation and a change in hydrology indicate that the studied mire may act as an increasing source of radiative forcing in future. (c) 2007 Elsevier Ltd. All rights reserved.

  • 19. Ushio, Masayuki
    et al.
    Makoto, Kobayashi
    Klaminder, Jonatan
    Takasu, Hiroyuki
    Nakano, Shin-ichi
    High-throughput sequencing shows inconsistent results with a microscope-based analysis of the soil prokaryotic community2014In: Soil Biology and Biochemistry, ISSN 0038-0717, E-ISSN 1879-3428, Vol. 76, no Supplement C, p. 53-56Article in journal (Refereed)
    Abstract [en]

    In the present study, we perform the first direct analysis on how the composition of the prokaryotic soil community differs depending on whether high-throughput sequencing or fluorescent in situ hybridization (FISH) coupled with catalyzed reporter deposition (CARD) is used. Soil samples were collected along short (<3 m) tundra vegetation gradients from Northern Sweden. Relative abundances of Acidobacteria and Bacteroidetes estimated by the high-throughput sequencing were higher than those estimated by CARD–FISH, while relative abundances of Archaea and α-Proteobacteria estimated by high-throughput sequencing were lower than those estimated by CARD-FISH. The results indicated that the high-throughput sequencing overestimates/underestimates the relative abundance of some microbial taxa if we assume that CARD-FISH can provide potentially more quantitative data. Great caution should be taken when interpreting data generated by molecular technologies (both of high-throughput sequencing and CARD-FISH), and supports by multiple approaches are necessary to make a robust conclusion.

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