| 1. |
- Björk, Robert G., 1974, et al.
(författare)
-
Climate-related soil changes in tundra ecosystems at Latnjajaure, northern Sweden – an ITEX-IPY project
- 2010
-
Ingår i: International Polar Year Oslo Science Conference.
-
Konferensbidrag (refereegranskat)abstract
- During the 90'ies, the International Tundra Experiment (ITEX) was established as a leading project in arctic and alpine ecology, and has become a model for many later network establishments. The present study capitalizes on the early efforts of ITEX and aims at assessing ecosystem changes in the alpine areas of northern Sweden above timberline, i.e. the tundra, in relation to global change. By using the "old" ITEX plots established during the early years of the program we have measured ecosystem respiration (ER), the Normalized Difference Vegetation Index, and nitrogen (N) mineralization over the growing season. In addition, have soil samples been taken to quantify changes in the carbon (C) and N pool, including 13C and 15N. After 12 to 15 years of open top chamber (OTC) treatment no statistical effect was found on the soil temperature (10 cm soil depth), although the was an overall increase in all OTC by +0.2°C. However, the soil moisture decreased significantly by 3-14%, depending on plant community, in the OTCs compared to ambient conditions. Preliminary, there was a 20-37% non-significant higher mean ER in the OTC compared to the ambient plots over the growing season. Furthermore, the OTC treatment did not affect the growing season mineralization of inorganic N, or total C and N content of the soil. The stable isotope data showed both enrichment and depletion as a consequence of the OTC treatment, but no general pattern was discerned. Thus, this non-significant higher ER is most likely of plant origin than soil, as the plant standing biomass has increased in the OTCs. This study does not support the current consensus that tundra soils will alter their C and N dynamics in response to climate change.
|
|
| 2. |
- Andresen, Louise C., 1974, et al.
(författare)
-
Free amino acids in the rhizosphere
- 2014
-
Ingår i: 19th European Nitrogen Cycle Meeting. September 10-12th 2014, Gent, Belgium.
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)
|
|
| 3. |
|
|
| 4. |
- Björk, Robert G., 1974, et al.
(författare)
-
A Climate Change aspect on root dynamics and nitrogen partitioning in a tundra landscape
- 2005
-
Ingår i: Sediment budgets and rates of sediment transfer across cold environments in Europe. 3rd Workshop of the ESF Network SEDIFLUX, Durham, UK, 15 – 19 December 2005..
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The Arctic Climate Impact Assessment (ACIA) recently reported that Arctic is rapidly changing due to Climate Change. Likewise, the mountains of Europe are going to experience large shifts in plant composition and 41-56% of the alpine species might be on the edge of extinction according to the 1st synthesis of the Global Observation Research Initiative in Alpine Environments (GLORIA). Although the tundra ecosystems are subjected to dramatical changes as a result of Climate Change, there is little knowledge of the effect on root dynamics and its implication on the nitrifying and denitrifying microbial community. Here, we compare nitrification enzyme activity (NEA) and denitrification enzyme activity (DEA) rates along an altitudinal gradient with the effects of climatic warming using Open Top Chambers (OTCs) in consideration with root dynamics and architecture. This study was conducted at Latnjajaure Field Station (LFS) located in the midalpine region in northern Sweden. LFS is the Swedish field site for the International Tundra Experiment (ITEX), established in 1993. This gives an opportunity to investigate long-term effects of climatic warming by OTCs and an altitudinal gradient (1000m to 1365m), both within a very small geographical range. The OTCs used at LFS increases the soil surface temperature by approximately 1.5ºC whereas air temperatures normally falls with 0.6ºC with every hundred meter of increased altitude. To analyse the NEA and DEA we used an anaerobic incubation technique, based on acetylene inhibition technique, resulting in N2O as the only end product, which then were analysed by gas chromatography. Soil cores were additionally sampled in the OTCs to study the effects of climatic warming on the root system. The specific root length, root length density and root biomass were determined for the different root fractions. The results from NEA and DEA contradict each other. The gradient study show decreased NEA and DEA rates with falling altitude, whereas the warming experiment show a slight non significant increase due to the temperature enhancement by OTCs. The preliminary results from the root sampling indicate that there is a plant community specific response in root architecture, which has an output on root biomass and particularly in the fraction of fine roots, although, climatic warming did not have any significant affect on the root biomass. The fact that altitudinal temperature decline did not reduce NEA and DEA rates might in part be explained of the variables measured here, although they are not conclusive.
|
|
| 5. |
- Björk, Robert G., 1974, et al.
(författare)
-
Biocomplexity and biogeochemical cycling in terrestrial ecosystems
- 2008
-
Ingår i: 1st Workshop and planning meeting ‘Winter processes in arctic tundra ecosystems’, Longyearbyen, Svalbard, 9-11 June 2008..
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The activities concerted within Tellus are aiming at adding essential knowledge to the system scale aspects of fluxes and transformation of carbon (C) in the terrestrial domain. The systems studied are the Arctic, the alpine area of the Scandes, and organic soils in southern Sweden (including both forest and agricultural systems). The main research sites are Skogaryd, in the boreal forest, and Latnjajaure Field Station in the western Abisko Mountains. The overall aim with the present work at Skogaryd is to increase our fundamental understanding of process involved in cycling of C and nitrogen (N) in forest ecosystems, and generate high quality data on C/N cycle from drained forested organic soils using micrometeorological methods, laser and automatic chambers techniques. Skogaryd is also included in NitroEurope, an EU project focusing on modelling and up-scaling of greenhouse gas fluxes, and is incorporated in two interdisciplinary research centres at University of Gothenburg, Tellus (http://www.tellus.science.gu.se/english/) and Gothenburg Atmospheric Science Centre (GAC; http://www.chalmers.se/gmv/gac-en/). Furthermore, our research group has been instrumental in the establishment of the International Tundra Experiment (ITEX) network by Professor Ulf Molau who chaired ITEX 1992-1996 and Latnjajaure Field Station have been a master site within the network since 1992. As an outcome, much of the research in Latnjajaure during the 90ies was focused plant responsiveness to global change. However, since 2002 the research has expanded and projects are now running that are dealing with snow-vegetation-soil interactions. Recently, a collaboration with Dr. Elisabeth J. Cooper, of the University Centre in Svalbard (UNIS), and Prof. Bo Elberling, University of Copenhagen, was initiated focusing on winter soil respiration and comparing sub-arctic and high-arctic trace gas fluxes. Currently, we have these projects running in tundra ecosystems: 1.Climate-related changes in tundra ecosystems – An IPY project (PIs Björk and Molau with others). 2.Temporal pattern of CO2, CH4 and N2O fluxes and soil microbial structure in snow-covered ecosystems (PIs Björk, Elberling, Klemedtsson, and Cooper). 3.The responsiveness of tundra ecosystems to warming: linking above- and below-ground components (PI Björk). There is also a project under evaluation by the Swedish Research Council, which are entitled ‘The fate of carbon in high-arctic tundra ecosystems under changing snow cover conditions’. The research questions that we want to address within this winter ecology network are 1) to increase our understand of the C dynamics (thus explicitly linking ecosystem C sequestration pattern and soil microbial dynamics) in tundra ecosystems, and, particularly, (2) to improve the winter resolution of carbon dioxide (and other greenhouse gases) effluxes to the atmosphere. Furthermore, (3) to understand the influence of changing snow cover, both in depth and duration, for the C dynamics in tundra ecosystems.
|
|
| 6. |
- Björk, Robert G., 1974, et al.
(författare)
-
Can present melt-out patterns identify snowbed plant species vulnerable to climate change?
- 2005
-
Ingår i: Second International Conference on Arctic Research Planning – ICARP II, Copenhagen, Denmark, 10 – 12 November 2005..
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Snowbeds form in topographic depressions which accumulate high amounts of snow during the winter months and the final snowmelt does not occur until late in the growing season. Many species preferentially grow in snowbed habitats and some of these are even limited to habitats in which winter snow accumulates. In connection with the Global Warming forecast, snowbed ecosystems of alpine Europe are regarded as particularly vulnerable in IPCC’s 2001 assessment report. This study is running at Latnjajaure Field Station, in northern Swedish Lapland, where four snowbed plant communi¬ties are studied. The snowbeds are of the “moderate type”, which means that they are melting out before the end of July, and they are situated in both heath and meadow sites. In this study we try to identify vulnerable plant species by the use of snow dynamics and plant community structure. Snowbed plant communi¬ties have high abundances of bryophytes along with high bryophyte diversity, 55 identified bryophytes within the snowbeds. The dominant bryophytes (e.g. Kiaeria stakei, Polytrichastrum sexangulare, Sanionia nivalis, Anthelia juratzkana, Scapania obcordata) are also snowbed specialist. The preliminary results show that earlier melt-out day will increase the vascular plant cover by 0.8 percent per day as well as increase in lichen cover by 0.5 percent per day. Bryophytes will suffer the most by decreasing in abundance by 1.7 percent per day of earlier melt-out day. Although, the response among bryophyte species is not uniform with Kiaeria stakei having the large decrease followed by Anthelia juratzkana, whereas Polytrichastrum sexangulare does not respond at all. There is also interaction among bryophyte species.
|
|
| 7. |
- Björk, Robert G., 1974
(författare)
-
Ectomycorrhizal mycelia production in a forested peatland: effects on greenhouse gas fluxes
- 2012
-
Ingår i: 4th COST meeting ‘Belowground carbon in European forest’, Antalya, Turkey, 28–31 October 2012.
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The role of ectomycorrhizal fungi in key ecosystem processes such as C sequestration and greenhouse gas (GHG) fluxes is surprisingly poorly understood, even though they are undoubtedly of major significance. In this study we have measured the production and isotopic signature of extramatrical mycelium (EMM) of mycorrhizal fungi since 2007 using in-growth mesh bags. We also conducted a trenching experiment, where 50 µm (permit EMM but not roots) or 1 µm (excludes both EMM and roots) mesh was used. Soil respiration was measured using an automatic chamber system, and nitrous oxide (N2O) and methane (CH4) using a closed chamber technique. In general, the EMM production in the peat soil was low compared to other soils, but also varied much between years (from 0.03 to 4.09 g C m-2). The EMM production was also 2 to 6 times higher in the top 10 cm compared to 10-20 cm soil depth depending of year. Over the growing season the EMM production peaked in August, a few weeks before the main sporocarp season. The mycelial delta values also varied with several ‰ within season as well as between years. Interestingly, the δ15N but not the δ13C of the mycelia changed with depth and the differences relative to the SOM were inconsistent. Although the EMM production in the peat soil is low it had a major impact on GHG emissions from the soil. In 2009, the contribution from autotrophic mycelia respiration was 10% of the annual CO2 emissions, while autotrophic root respiration contributed with 23%. This means that 2/3 of the annual CO2 emissions are originated from heterotrophic respiration at this site. For N2O, the exclusion of roots alone did not affect N2O emissions, the simultaneous exclusion of roots and mycorrhizal mycelia doubled N2O emissions, compared to the control plots. The results of the study emphasize the importance of ectomycorrhiza in regulating GHG emissions from forested organic soils.
|
|
| 8. |
- Björk, Robert G., 1974, et al.
(författare)
-
Effect of reduced below-ground C sequestration on greenhouse gas fluxes within dry tundra ecosystems along an altitudinal gradient
- 2008
-
Ingår i: Mountain soils under a changing climate and land-use, Birmensdorf, Switzerland, 6–8 March 2008..
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- It has been suggested that global climate change will have a great impact on arctic and alpine areas, affecting the carbon and nitrogen dynamics in these ecosystems. Temperature are widely thought to be the main limiting factors for plants and microorganisms in these tundra ecosystem, and warming the soil in high latitude tundra have been shown to change trace gas (CO2, CH4, and N2O) exchange rates and increase N availability. However, little attention has been paid, to date, to variations in trace gas fluxes with altitude, although it is a key determinant of temperature and should therefore be strongly correlated with these fluxes if temperature is the main variable affecting these processes. The objectives of this study were, therefore, to measure growing season variation in carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) fluxes from heath plant communities along an altitudinal gradient ranging from mid alpine (~950 m a.s.l) to high alpine (~1,365 m a.s.l) zones within an alpine tundra landscape in the subarctic region of Sweden. Furthermore, by reducing the C supply to the root system and mycorrhizal fungi (achieved by clipping the above-ground plant parts) we wanted to decrease the rhizosphere priming effect and thereby change the C sequestration pattern within the ecosystem to be able to separate heterotrophic and root respiration. The study was conducted on the slopes of Mt. Latnjatjårro (1,447 m; 68°21’N, 18°31’E), near Latnjajaure Field Station, 16 km west of Abisko in Northern Sweden. Flux measurements of CO2 were analysed using a portable infra red gas analyser (IRGA) based on the SBA-4 OEM CO2 Analyzer (PP System). Fluxes of CH4 and N2O were sampled using a closed chamber system, where chambers were placed at collars, which were gently pressed into the ground. Air from the chamber was circulated into a headspace bottle and analysed by gas chromatograph. A two-step incubation technique was also used to determine Nitrification Enzyme Activity (NEA) for analysing nitrification in acid soils with low activities, and for Denitrification Enzyme Activity (DEA) an anaerobic incubation technique, based on acetylene inhibition of the N2O-reductase, was used. Preliminary, our results show a decrease in average growing season CO2 efflux with altitude, but not constantly, and although soil temperature in general decreased with altitude there were no perfect fit between soil temperature and average growing season CO2 efflux. Furthermore, the clipping of the above-ground plant parts reduced the CO2 efflux at all altitudes, except at 1,225 m a.s.l., and in August the reduction in CO2 efflux was largest at 950 m a.s.l. (231 mg CO2 m-2 h-1) and decreased with altitude (to 33 mg CO2 m-2 h-1 at 1,365 m a.s.l). However, the proportion of the reduced CO2 efflux, corresponding to root respiration, was relatively constant with altitude (28-43% of total respiration), except at 1,365 m a.s.l where the root respiration only contributed with 12%. The fluxes of CH4 and N2O was very low with poor resolution of the fluxes due to many samples had a flux lower than the limit of detection for the gas chromatograph, thus no particularly pattern was discerned. However, to try to improve the resolution along the altitudinal gradient the NEA and DEA was used and give a potential measure on the nitrification and denitrification rates, which goes back to the actual populations of nitrifiers and denitrifiers in the soil. The results shows that there were a substantial increases with altitude in the activities of nitrifying and denitrifying microbes, this is contrary to expectations and the average growing season CO2 efflux if the decline in mean annual temperature with altitude is the main driver for nitrification and denitrification. Thus, our results are just indicative for the complex interaction that may occur along altitudinal gradients. But, clearly, there is a need for further studies to assess the effects of altitude and temperature on carbon and nitrogen dynamics in high alpine and arctic ecosystems across wide altitudinal ranges.
|
|
| 9. |
- Björk, Robert G., 1974, et al.
(författare)
-
Effect of reduced below-ground C sequestration on greenhouse gas fluxes within dry tundra ecosystems along an altitudinal gradient
- 2008
-
Ingår i: The 15th ITEX workshop, Reykjavik, Iceland, 9–12 October 2008..
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- It has been suggested that global climate change will have a great impact on arctic and alpine areas, affecting the carbon and nitrogen dynamics in these ecosystems. Temperature is widely thought to be the main limiting factor for plants and microorganisms in these tundra ecosystems, and warming the soil in high latitude tundra has been shown to change trace gas (CO2, CH4, and N2O) exchange rates and increase N availability. However, little attention has been paid, to date, to variations in trace gas fluxes with altitude, although altitude is a key determinant of temperature and should therefore be strongly correlated with these fluxes if temperature is a major variable affecting these processes. The objectives of this study were, therefore, to measure growing season variation in carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) fluxes from heath plant communities along an altitudinal gradient ranging from mid alpine (~950 m a.s.l) to high alpine (~1,365 m a.s.l) zones within an alpine tundra landscape in the subarctic region of Sweden. Furthermore, by reducing the C supply to the root system and mycorrhizal fungi (achieved by clipping the above-ground plant parts) we wanted to decrease the rhizosphere priming effect and thereby change the C sequestration pattern within the ecosystem to be able to separate heterotrophic and autotrophic respiration. The study was conducted on the slopes of Mt. Latnjatjårro (1,447 m a.s.l.; 68°21’N, 18°31’E), near Latnjajaure Field Station, 16 km west of Abisko in Northern Sweden. Flux measurements of CO2 were analysed using a portable infra red gas analyser (IRGA) based on the SBA-4 OEM CO2 Analyzer (PP System). Fluxes of CH4 and N2O were sampled using a closed chamber system, where chambers were placed on collars, which were gently pressed into the ground. Air from the chamber was circulated into a headspace bottle and analysed by gas chromatograph. A two-step incubation technique was also used to determine Nitrification Enzyme Activity (NEA) for analysing nitrification in acid soils with low activities, and for Denitrification Enzyme Activity (DEA) an anaerobic incubation technique, based on acetylene inhibition of the N2O-reductase, was used. Our results show a decrease in average growing season CO2 efflux with altitude, but not consistently, and although soil temperature in general decreased with altitude there was only a loose association between soil temperature and average growing season CO2 efflux. Furthermore, the clipping of the above-ground plant parts reduced the CO2 efflux at all altitudes, except at 1,225 m a.s.l., and in August the reduction in CO2 efflux was largest at 950 m a.s.l. (231 mg CO2 m-2 h-1) and decreased with altitude (to 33 mg CO2 m-2 h-1 at 1,365 m a.s.l.). However, the proportion of the reduced CO2 efflux, corresponding to autotrophic respiration, was relatively constant with altitude (28-43% of total respiration), except at 1,365 m a.s.l. where the autotrophic respiration only contributed 12%. The fluxes of CH4 and N2O were very low, and resolution was constrained by the large number of samples with apparent fluxes below the limit of detection for the gas chromatograph, thus no particular pattern could be identified. However, to try to improve the resolution along the altitudinal gradient, the NEA and DEA were used, and give a potential measure of the nitrification and denitrification rates, which goes back to the actual populations of nitrifiers and denitrifiers in the soil. The results show that there were a substantial increases with altitude in the activities of nitrifying and denitrifying microbes; this is contrary to expectations and the average growing season CO2 efflux if the decline in mean annual temperature with altitude is the main driver for nitrification and denitrification. Thus, our results are indicative of the complex interaction that may occur along altitudinal gradients. But, clearly, there is a need for further studies to assess the effects of altitude and temperature on carbon and nitrogen dynamics in high alpine and arctic ecosystems across wide altitudinal ranges.
|
|
| 10. |
- Björk, Robert G., 1974, et al.
(författare)
-
Extramatrical mycelia production and turnover in two drained Norway spruce forests
- 2010
-
Ingår i: 1st COST meeting ‘Belowground carbon in Europeanforest’, Birmensdorf, Switzerland, 26–28 January 2010..
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Root systems form important associations with fungi, so called mycorrhiza, which in spruce forests are dominated by ectomycorrhiza. Ectomycorrhizal fungi is functionally important in water and nutrient capture, and therefore probably have major influence on the overall ecosystem functioning. In addition to transferring water and nutrient to its host plant the fungus receive photosynthetic C. The extramatrical mycelium (EMM) is thereby an important sink for carbon in boreal forests, but estimation of the actual EMM production is rare. The objective was to quantify the annual and seasonal production and turnover of EMM in two drained coniferous soils. The study was conducted in two Norway spruce stands at Skogaryd Research Forest, southwest Sweden. One of the sites was a mineral soil (“the mineral site”), with high organic content, and affor-ested in 1962. The other site was a peat soil of minerotrophic origin (“the peat site”), drained in the 1870s and afforested in 1951. In-growth tubes (10-20 cm long) were used to estimate EMM production and turnover through sequential harvesting during 2007-2009. Preliminary results show a higher EMM production at the mineral site than at the peat site. At the peat site the annual EMM production varied largely between years, 0.1-10.1 gdw m-2 (no annual data are currently available for the mineral site). Interestingly, a significant EMM production from December to 15th of June at the mineral site was found, most likely occurring during late May-early June. How-ever, the major EMM production (21-53 mg m-2 d-1) occurred mid-August to mid-September at both sites. It was not possible to calculate an EMM turnover the first two years due to the large spatial vari-ability. Our study suggests that high EMM production coincides with fine root production, and can equal one-fourth of belowground production. However, the large spatial variability in EMM production accentuates the need to increase within sub-site replication.
|
|
