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  • 1.
    Alewell, C
    et al.
    Institute of Environmental Geosciences, University of Basel, Switzerland.
    Giesler, Reiner
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Klaminder, Jonatan
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Leifeld, J
    Agroscope Reckenholz-Tanikon Research Station ART, Switzerland.
    Rollog, M
    Institute of Environmental Geosciences, University of Basel, Switzerland.
    Stable carbon isotopes as indicators for environmental change inpalsa peats2011In: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189, Vol. 8, p. 1769-1778Article in journal (Refereed)
    Abstract [en]

    Palsa peats are unique northern ecosystems formed under an arctic climate and characterized by a high biodiversity and sensitive ecology. The stability of the palsas are seriously threatened by climate warming which will change the permafrost dynamic and induce a degradation of the mires.

    We used stable carbon isotope depth profiles in two palsa mires of Northern Sweden to track environmental change during the formation of the mires. Soils dominated by aerobic degradation can be expected to have a clear increase of carbon isotopes (δ13C) with depth, due to preferential release of 12C during aerobic mineralization. In soils with suppressed degradation due to anoxic conditions, stable carbon isotope depth profiles are either more or less uniform indicating no or very low degradation or depth profiles turn to lighter values due to an enrichment of recalcitrant organic substances during anaerobic mineralisation which are depleted in 13C.

    The isotope depth profile of the peat in the water saturated depressions (hollows) at the yet undisturbed mire Storflaket indicated very low to no degradation but increased rates of anaerobic degradation at the Stordalen site. The latter might be induced by degradation of the permafrost cores in the uplifted areas (hummocks) and subsequent breaking and submerging of the hummock peat into the hollows due to climate warming. Carbon isotope depth profiles of hummocks indicated a turn from aerobic mineralisation to anaerobic degradation at a peat depth between 4 and 25 cm. The age of these turning points was 14C dated between 150 and 670 yr and could thus not be caused by anthropogenically induced climate change. We found the uplifting of the hummocks due to permafrost heave the most likely explanation for our findings. We thus concluded that differences in carbon isotope profiles of the hollows might point to the disturbance of the mires due to climate warming or due to differences in hydrology. The characteristic profiles of the hummocks are indicators for micro-geomorphic change during permafrost up heaving.

  • 2.
    Alewell, C
    et al.
    Institute of Environmental Geosciences, University of Basel, Switzerland.
    Giesler, Reiner
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Klaminder, Jonatan
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Leifeld, J
    Agroscope Reckenholz-Tänikon Research Station ART, Switzerland.
    Rollog, M
    Institute of Environmental Geosciences, University of Basel, Switzerland.
    Stable carbon isotopes as indicators for micro-geomorphic changes in palsa peats2011In: Biogeoscience Discussions, ISSN 1810-6277, Vol. 8, no 1, p. 527-548Article in journal (Refereed)
    Abstract [en]

    Palsa peats are unique northern ecosystems formed under an arctic climate and characterizedby an unique biodiversity and ecology. The stability of the palsas are seriouslythreatened by climate warming which will change the permafrost dynamic and5 results in degradation of the mires. We used stable carbon isotope depth profiles intwo palsa mires of Northern Sweden to track environmental change during the formationof the mires. Carbon isotope (13C) depth profile of the yet undisturbed mireStorflaket indicated very low to no degradation of the peat in the water saturated depressions(hollows) but increased rates of anaerobic degradation at the Stordalen site.10 The latter might be induced by degradation of the permafrost cores in the uplifted areas(hummocks) and subsequent braking and submerging of the hummock peat intothe hollows due to climate warming. Carbon isotope depth profiles of hummocks indicateda turn from aerobic mineralisation to anaerobic degradation at a peat depthbetween 4 to 25 cm. The age of these turning point was 14C dated between 150 and15 670 years and could thus not be caused by anthropogenically induced climate change.We found the uplifting of the hummocks due to permafrost heave the most likely explanationfor our findings. We thus concluded that differences in carbon isotope profiles ofthe hollows might point to the disturbance of the mires due to climate warming or dueto differences in hydrology. The characteristic profiles of the hummocks are indicators20 for micro-geomorphic change during permafrost up heaving.

  • 3.
    Andersson, Tove
    et al.
    Umeå University, Faculty of Science and Technology, Chemistry.
    Lövgren, Lars
    Umeå University, Faculty of Science and Technology, Chemistry.
    Persson, Per
    Umeå University, Faculty of Science and Technology, Chemistry.
    Giesler, Reiner
    Ecology and Environmental Science.
    Adsorption of Monomethyl Phosphate to the Goethite (-FeOOH)/water Interface2002Conference paper (Other academic)
  • 4.
    Berggren, Martin
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Ström, L
    Laudon, H
    Karlsson, Jan
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Jonsson, Anders
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Giesler, Reiner
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Bergström, Ann-Kristin
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Jansson, Mats
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Lake secondary production fueled by rapid transfer of low molecular weight organic carbon from terrestrial sources to aquatic consumers2010In: Ecology Letters, ISSN 1461-023X, E-ISSN 1461-0248, Vol. 13, no 7, p. 870-880Article in journal (Refereed)
    Abstract [en]

    Ecology Letters (2010) Abstract Carbon of terrestrial origin often makes up a significant share of consumer biomass in unproductive lake ecosystems. However, the mechanisms for terrestrial support of lake secondary production are largely unclear. By using a modelling approach, we show that terrestrial export of dissolved labile low molecular weight carbon (LMWC) compounds supported 80% (34-95%), 54% (19-90%) and 23% (7-45%) of the secondary production by bacteria, protozoa and metazoa, respectively, in a 7-km(2) boreal lake (conservative to liberal estimates in brackets). Bacterial growth on LMWC was of similar magnitude as that of primary production (PP), and grazing on bacteria effectively channelled the LMWC carbon to higher trophic levels. We suggest that rapid turnover of forest LMWC pools enables continuous export of fresh photosynthates and other labile metabolites to aquatic systems, and that substantial transfer of LMWC from terrestrial sources to lake consumers can occur within a few days. Sequestration of LMWC of terrestrial origin, thus, helps explain high shares of terrestrial carbon in lake organisms and implies that lake food webs can be closely dependent on recent terrestrial PP.

  • 5. Björk, R G
    et al.
    Klemendtsson, L
    Molau, Ulf
    Harndorf, J
    Ödman, A
    Giesler, Reiner
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Linkages between N turnover and plant community structure in a tundra landscape2007In: Plant and Soil, Vol. 294, p. 247-261Article in journal (Refereed)
  • 6. Björkvald, L
    et al.
    Giesler, Reiner
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Laudon, Hjalmar
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Humborg, C
    Mörth, C-M
    Landscape variations in stream water SO4 and d34S-SO4 in a boreal stream network2009In: Geochimica et Cosmochimica Acta, ISSN 0016-7037, E-ISSN 1872-9533, Vol. 73, p. 4648-4660Article in journal (Refereed)
    Abstract [en]

    Despite reduced anthropogenic deposition during the last decades, deposition sulphate may still play an important role in the biogeochemical cycles of S and many catchments may act as net sources of S that may remain for several decades. The aim of this study is to elucidate the temporal and spatial dynamics of both SO42− and δ34SSO4 in stream water from catchments with varying percentage of wetland and forest coverage and to determine their relative importance for catchment losses of S. Stream water samples were collected from 15 subcatchments ranging in size from 3 to 6780 ha, in a boreal stream network, northern Sweden. In forested catchments (<2% wetland cover) S–SO42− concentrations in stream water averaged 1.7 mg L−1 whereas in wetland dominated catchments (>30% wetland cover) the concentrations averaged 0.3 mg L−1. A significant negative relationship was observed between S–SO42− and percentage wetland coverage (r2 = 0.77, p < 0.001) and the annual export of stream water SO42− and wetland coverage (r2 = 0.76, p < 0.001). The percentage forest coverage was on the other hand positively related to stream water SO42− concentrations and the annual export of stream water SO42− (r2 = 0.77 and r2 = 0.79, respectively). The annual average δ34SSO4 value in wetland dominated streams was +7.6‰ and in streams of forested catchments +6.7‰. At spring flood the δ34SSO4 values decreased in all streams by 1‰ to 5‰. The δ34SSO4 values in all streams were higher than the δ34SSO4 value of +4.7‰ in precipitation (snow). The export of S ranged from 0.5 kg S ha−1 yr−1 (wetland headwater stream) to 3.8 kg S ha−1 yr−1 (forested headwater stream). With an average S deposition in open field of 1.3 kg S ha−1 yr−1 (2002–2006) the mass balance results in a net export of S from all catchments, except in catchments with >30% wetland. The high temporal and spatial resolution of this study demonstrates that the reducing environments of wetlands play a key role for the biogeochemistry of S in boreal landscapes and are net sinks of S. Forested areas, on the other hand were net sources of S.

  • 7.
    Esberg, Camilla
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    du Toit, Ben
    Department of Forest and Wood Science, University of Stellenbosch, Private Bag X1, Matieland 7602, South Africa.
    Olsson, Rickard
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Ilstedt, Ulrik
    Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, 901 83 Umeå, Sweden.
    Giesler, Reiner
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Microbial responses to P addition in six South African forest soils2010In: Plant and Soil, ISSN 0032-079X, E-ISSN 1573-5036, Vol. 329, no 1/2, p. 209-225Article in journal (Refereed)
    Abstract [en]

    Forests growing on highly weathered soils are often phosphorus (P) limited and competition between geochemical and biological sinks affects their soil P dynamics. In an attempt to elucidate the factors controlling the relative importance of these two sinks, we investigated the relationship of between soil microbial growth kinetics and soil chemical properties following amendments with C, N and P in six South African forest soils. Microbial growth kinetics were determined from respiration curves derived from measurements of CO2 effluxes from soil samples in laboratory incubations. We found that microbial growth rates after C + N additions were positively related to NaOH-extractable P and decreased with soil depth, whereas the lag time (the time between substrate addition and exponential growth) was negatively related to extractable P. However, the growth rate and lag time were unrelated to the soil’s sorption properties or Al and Fe contents. Our results indicate that at least some of the NaOH-extractable inorganic P may be biologically available within a relatively short time (days to weeks) and might be more labile than previously thought. Our results also show that microbial utilization of C + N only seemed to be constrained by P in the deeper part of the soil profiles.

  • 8.
    Esberg, Camilla
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Lagerström, Anna
    Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, 901 83 Umeå, Sweden.
    Graae, Bente J.
    Department of Biology, NTNU, Høgskoleringen 5, 7491 Trondheim, Norway.
    Giesler, Reiner
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Phosphorus availability and microbial respiration across different tundra vegetation typesManuscript (preprint) (Other academic)
    Abstract [en]

    Phosphorus (P) is an important nutrient in tundra ecosystems that co-limits or in some cases limits primary production. The availability of P is largely driven by soil characteristics, e.g., pH, organic carbon, and abundance of P-sorbing elements such as aluminium (Al) or iron (Fe). We tested how vegetation and soil properties relate to P availability across different tundra vegetation types. The different soil P fractions in the organic top soil were measured and plant foliar nitrogen (N) to P ratio was used as an indicator of plant nutrient status. Microbial and plant bioassays were used to study microbial respiration kinetics and plant biomass response to carbon, N, and P amendments. The distribution of P fractions differed significantly across vegetation types; labile fractions of P were less abundant in meadow sites compared to heath sites. Calcium-phosphates seemed to be an important P-fraction in meadows, but were only found in lower concentrations in the heath. There were only small differences in sorbed P between the vegetation types and this corroborated with the distribution of Al+Fe. Plant N: P ratios and the plant bioassay indicated decreasing P availability from dry heath to mesic heath to mesic meadow. Our results showed that vegetation type was related to soil chemistry and P availability; however, in contrast to other studies, this effect was not related to redistribution of Fe and Al. We conclude that in this tundra ecosystem plants are generally co-limited by N and P, and P availability varies between different vegetation types, which is reflected in both above- and belowground ecosystem processes.

  • 9.
    Esberg, Camilla
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Nilsson, Mats
    Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, 901 83 Umeå, Sweden.
    Giesler, Reiner
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Microbial indices of P availability across a forest productivity gradient in South AfricaManuscript (preprint) (Other (popular science, discussion, etc.))
    Abstract [en]

    Soil microorganisms have the capability to solubilize different fractions of phosphorus (P) and can probably access P fractions unavailable to plants in the short term. However, there are few studies available that attempt to estimate the potentially available microbial P. We compare a wet-chemical extraction procedure for P with a microbial bioassay based on respiration kinetics after amending carbon (C), nitrogen (N), and sub-saturation levels of P in laboratory incubations across a plantation forest productivity gradient in South Africa. We found that the estimated microbial available P was at least 10-fold higher than P fractions conventionally defined as easily plant available based on wet-chemical methods. The microbial P was strongly positively related to sorbed P (i.e. NaOH extractable P) P (r2=0.63, p<0.001) and indicates that this P fraction contributes to the microbial P utilization within a relatively short time frame (<300 hrs) when C and N are not limiting. This was further emphasized by the change in respiration kinetics when the amendment of C and N were combined with phosphate. Addition of phosphate-P increased the growth and maximum respiration (max resp) rates and decreased the amount of time needed to reach max resp in comparison to amendments with only C and N. Our study indicates that sorbed P), a dominant P fraction in highly weathered soils, is most likely accessible to microorganisms.

  • 10. Eshetu, Z
    et al.
    Giesler, R
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Högberg, P
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Historical land use pattern affects the chemistry of forest soils in the Ethiopian highlands2004In: Geoderma, Vol. 118, p. 149-165Article in journal (Refereed)
  • 11.
    Giesler , Reiner
    et al.
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Björkvald , L
    Laudon , Hjalmar
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Mörth , CM
    Spatial and Seasonal Variations in Stream Water delta S-34-Dissolved Organic Matter in Northern Sweden2009In: Environmental Science and Technology, ISSN 0013-936X, E-ISSN 1520-5851, Vol. 43, no 2, p. 447-452Article in journal (Refereed)
    Abstract [en]

    The discharge of terrestrial dissolved organic matter (DOM) by streams is an important cross-system linkage that strongly influences downstream aquatic ecosystems. Isotopic tracers are important tools that can help to unravel the source of DOM from different terrestrial compartments in the landscape. Here we demonstrate the spatial and seasonal variation of delta S-34 of DOM in 70 boreal streams to test if the tracer could provide new insights into the origin of DOM. We found large spatial and seasonal variations in stream water delta S-34-DOM values ranging from -5.2 parts per thousand to + 9.6 parts per thousand with an average of +4.0 +/- 0.6 (N=62; average and 95% confidence interval). Large seasonal variations were found in stream water delta S-34-DOM values: for example, a shift of more than 10 parts per thousand during the spring snowmelt in a wetland-dominated stream. Spatial differences were also observed during the winter base flow with higher delta S-34-DOM values in the fourth-order Krycklan stream at the outlet of the 68 km(2) compared to the small (<1 km(2)) headwater streams. Our data clearly show that the delta S-34-DOM values have the potential to be used as a tracer to identify and generate new insights about terrestrial DOM sources in the boreal landscape.

  • 12.
    Giesler, R
    et al.
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Morth, C
    Mellqvist, E
    Torssander, P
    The humus layer determines SO42 isotope values in the mineral soil2005In: Biogeochemistry, Vol. 74, p. 3-20Article in journal (Refereed)
  • 13.
    Giesler, R
    et al.
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Satoh, F
    Ilstedt, U
    Nordgren, A
    Microbially available phosphorus in boreal forests: Effects of aluminum and iron accumulation in the humus layer2004In: Ecosystems, Vol. 7, p. 208-217Article in journal (Refereed)
  • 14.
    Giesler, Reiner
    et al.
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Andersson, Tove
    Chemistry.
    Lövgren, Lars
    Chemistry.
    Phosphate adsorption in aluminum and iron rich humus soils from forested groundwater discharge areas2000Conference paper (Other academic)
  • 15.
    Giesler, Reiner
    et al.
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Andersson, Tove
    Chemistry.
    Lövgren, Lars
    Chemistry.
    Persson, Per
    Chemistry.
    Phosphate sorption in aluminum- and iron-rich humus soils2005In: Soil Science Society of America Journal, Vol. 69, no 1, p. 77-86Article in journal (Refereed)
    Abstract [en]

    Groundwater discharge areas in boreal forest ecosystems can potentially be areas where Fe and Al accumulate in the forest floor and affect the solubility of P. This study was conducted to determine phosphate sorption properties using humus soils containing high native amounts of Al and Fe. Humus soils were collected from two different forested groundwater discharge areas varying in pH and amount and distribution of At and Fe species. The phosphate sorption capacities were 265 and 216 mmol P kg(-1) dry wt. soil, respectively, for the two humus soils. Pyrophosphate extractable Al and Fe dominated in the first soil, 738 mmol kg(-1) dry wt. The concentration of pyrophosphate extractable Al and Fe in the second soil was 317 mmol kg(-1) dry wt.. whereas citrate-dithionite (CD) extracted 548 mmol Al and Fe kg(-1) dry wt. Using 0.1 mol dm(-3) NaCl as ionic medium gave a higher phosphate sorption compared with deionized water at the midrange additions, but no difference at the highest addition. Phosphate sorption was pH independent when 0.1 mol dm(-3) NaCl was used, whereas deionized water gave a sorption minimum at approximately pH 6. Dissolved organic carbon (DOC) release in solution was positively correlated with phosphate sorption, especially in 0.1 mol dm(-3) NaCl ionic medium. However, dissolved organic P (DOP) was unaffected by the phosphate sorption. Attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) indicated that precipitation of Al and Fe phosphates dominated at higher phosphate additions in the soil with mainly organically bound At and Fe, whereas both surface sorption and precipitation occurs in the soil with a larger amount of CD-extractable Fe.

  • 16.
    Giesler, Reiner
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Esberg, Camilla
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Lagerström, Anna
    Graae, Bente J
    Phosphorus availability and microbial respiration across different tundra vegetation types2012In: Biogeochemistry, ISSN 0168-2563, E-ISSN 1573-515X, Vol. 108, no 1-3, p. 429-445Article in journal (Refereed)
    Abstract [en]

    Phosphorus (P) is an important nutrient in tundra ecosystems that co-limits or in some cases limits primary production. The availability of P is largely driven by soil characteristics, e.g., pH, organic carbon, and abundance of P-sorbing elements such as aluminium (Al) or iron (Fe). We tested how vegetation and soil properties relate to P availability across different tundra vegetation types. The different soil P fractions in the organic horizon were measured and plant foliar nitrogen (N) to P ratio and a plant bioassay was used as indicators of plant nutrient status. Microbial bioassays were used to study microbial respiration kinetics and in response to carbon, N, and P amendments. The distribution of P fractions differed significantly across vegetation types; labile fractions of P were less abundant in meadow sites compared to heath sites. Calcium-phosphates seemed to be an important P-fraction in meadows, but were only found in lower concentrations in the heath. There were only small differences in NaOH–extractable P between the vegetation types and this correlated with the distribution of oxalate-extractable Al. Plant N:P ratios and the plant bioassay indicated decreasing P availability from dry heath to mesic heath to mesic meadow. The microbial bioassay suggests that the heterotrophic microbial community is C-limited with N as a secondary limiting nutrient although there were indications that microbial P availability was lower in the meadow sites. Overall, we suggest that the observed variations in soil P across vegetation types are affecting both plant and microbial function although the differences seem to be relatively small.

  • 17.
    Giesler, Reiner
    et al.
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Högberg, M N
    Strobel, B W
    Richter, A
    Nordgren, A
    Högberg, P
    Production of dissolved organic carbon and low-molecular weight organic acids in soil solution driven by recent tree photosynthate2007In: Biogeochemistry, Vol. 84, p. 1-12Article in journal (Refereed)
  • 18.
    Giesler, Reiner
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Lyon, S. W.
    Morth, C-M
    Karlsson, Jan
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Karlsson, E. M.
    Jantze, E. J.
    Destouni, G.
    Humborg, C.
    Catchment-scale dissolved carbon concentrations and export estimates across six subarctic streams in northern Sweden2014In: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189, Vol. 11, no 2, p. 525-537Article in journal (Refereed)
    Abstract [en]

    Climatic change is currently enhancing permafrost thawing and the flow of water through the landscape in subarctic and arctic catchments, with major consequences for the carbon export to aquatic ecosystems. We studied stream water carbon export in several tundra-dominated catchments in northern Sweden. There were clear seasonal differences in both dissolved organic carbon (DOC) and dissolved inorganic carbon (DIC) concentrations. The highest DOC concentrations occurred during the spring freshet while the highest DIC concentrations were always observed during winter baseflow conditions for the six catchments considered in this study. Long-term trends for the period 1982 to 2010 for one of the streams showed that DIC concentrations has increased by 9% during the 28 yr of measurement while no clear trend was found for DOC. Similar increasing trends were also found for conductivity, Ca and Mg. When trends were discretized into individual months, we found a significant linear increase in DIC concentrations with time for September, November and December. In these subarctic catchments, the annual mass of C exported as DIC was in the same order of magnitude as DOC; the average proportion of DIC to the total dissolved C exported was 61% for the six streams. Furthermore, there was a direct relationship between total runoff and annual dissolved carbon fluxes for these six catchments. These relationships were more prevalent for annual DIC exports than annual DOC exports in this region. Our results also highlight that both DOC and DIC can be important in high-latitude ecosystems. This is particularly relevant in environments where thawing permafrost and changes to subsurface ice due to global warming can influence stream water fluxes of C. The large proportion of stream water DIC flux also has implications on regional C budgets and needs to be considered in order to understand climate-induced feedback mechanisms across the landscape.

  • 19.
    Giesler, Reiner
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Morth, Carl-Magnus
    Karlsson, Jan
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Lundin, Erik J.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Lyon, Steve W.
    Humborg, Christoph
    Spatiotemporal variations of pCO(2) and delta C-13-DIC in subarctic streams in northern Sweden2013In: Global Biogeochemical Cycles, ISSN 0886-6236, E-ISSN 1944-9224, Vol. 27, no 1, p. 176-186Article in journal (Refereed)
    Abstract [en]

    Current predictions of climate-related changes in high-latitude environments suggest major effects on the C export in streams and rivers. To what extent this will also affect the stream water CO2 concentrations is poorly understood. In this study we examined the spatiotemporal variation in partial pressure of CO2 (pCO(2)) and in stable isotopic composition of dissolved inorganic carbon (delta C-13-DIC) in subarctic streams in northern Sweden. The selected watersheds are characterized by large variations in high-latitude boreal forest and tundra and differences in bedrock. We found that all streams generally were supersaturated in pCO(2) with an average concentration of 850 mu atm. The variability in pCO(2) across streams was poorly related to vegetation cover, and carbonaceous bedrock influence was manifested in high DIC concentrations but not reflected in either stream pCO(2) or delta C-13-DIC. Stream water pCO(2) values were highest during winter base flow when we also observed the lowest delta C-13-DIC values, and this pattern is interpreted as a high contribution from CO2 from soil respiration. Summer base flow delta C-13-DIC values probably are more affected by in situ stream processes such as aquatic production/respiration and degassing. A challenge for further studies will be to disentangle the origin of stream water CO2 and quantify their relative importance.

  • 20. Humborg, Christoph
    et al.
    Mörth, Carl-Magnus
    Sundblom, Marcus
    Borg, Hans
    Blenckner, Thorsten
    Giesler, Reiner
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Ittekot, Venugopalan
    CO2 supersaturation along the aquatic conduit in Swedish watersheds as constrained by terrestrial respiration, aquatic respiration and weathering2010In: Global Change Biology, ISSN 1354-1013, E-ISSN 1365-2486, Vol. 16, no 7, p. 1966-1978Article in journal (Refereed)
    Abstract [en]

    We tested the hypothesis that CO2 supersaturation along the aquatic conduit over Sweden can be explained by processes other than aquatic respiration. A first generalized-additive model (GAM) analysis evaluating the relationships between single water chemistry variables and pCO2 in lakes and streams revealed that water chemistry variables typical for groundwater input, e.g., dissolved silicate (DSi) and Mg2+ had explanatory power similar to total organic carbon (TOC). Further GAM analyses on various lake size classes and stream orders corroborated the slightly higher explanatory power for DSi in lakes and Mg2+ for streams compared with TOC. Both DSi and TOC explained 22–46% of the pCO2 variability in various lake classes (0.01–>100 km2) and Mg2+ and TOC explained 11–41% of the pCO2 variability in the various stream orders. This suggests that aquatic pCO2 has a strong groundwater signature. Terrestrial respiration is a significant source of the observed supersaturation and we may assume that both terrestrial respiration and aquatic respiration contributed equally to pCO2 efflux. pCO2 and TOC concentrations decreased with lake size suggesting that the longer water residence time allow greater equilibration of CO2 with the atmosphere and in-lake mineralization of TOC. For streams, we observed a decreasing trend in pCO2 with stream orders between 3 and 6. We calculated the total CO2 efflux from all Swedish lakes and streams to be 2.58 Tg C yr−1. Our analyses also demonstrated that 0.70 Tg C yr−1 are exported to the ocean by Swedish watersheds as HCO3 and CO32− of which about 0.56 Tg C yr−1 is also a residual from terrestrial respiration and constitute a long-term sink for atmospheric CO2. Taking all dissolved inorganic carbon (DIC) fluxes along the aquatic conduit into account will lower the estimated net ecosystem C exchange (NEE) by 2.02 Tg C yr−1, which corresponds to 10% of the NEE in Sweden.

  • 21.
    Högberg, Mona N.
    et al.
    Department of Forest Ecology, Swedish University of Agricultural Sciences, Umea.
    Myrold, David D.
    Department of Crop and Soil Science, Oregon State University, Corvallis, USA.
    Giesler, Reiner
    Department of Forest Ecology, Swedish University of Agricultural Sciences, Umeå.
    Högberg, Peter
    Department of Forest Ecology, Swedish University of Agricultural Sciences, Umeå.
    Contrasting patterns of soil N-cycling in model ecosystems of Fennoscandian boreal forests2006In: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 147, no 1, p. 96-107Article in journal (Refereed)
    Abstract [en]

    The low plant productivity of boreal forests ingeneral has been attributed to low soil N supply and lowtemperatures. Exceptionally high productivity occurs intoe-slope positions, and has been ascribed to influx of Nfrom surrounding areas and higher rates of soil Nturnover in situ. Despite large apparent natural variationsin forest productivity, rates of gross soil N mineralizationand gross nitrification have never beencompared in Fennoscandian boreal forests of contrastingproductivity. We report contrasting patterns of soilN turnover in three model ecosystems, representing therange in soil C-to-N ratios (19–41) in Fennoscandianboreal forests and differences in forest productivity by afactor close to 3. Gross N mineralization was seventimes higher when soil, microbial, and plant C-to-Nratios were the lowest compared to the highest. Thisprocess, nitrification and potential denitrification correlatedwith inorganic, total and microbial biomass N, butnot microbial C. There was a constant ratio between soiland microbial C-to-N ratio of 3.7±0.2, across wide ratiosof soil C-to-N and fungi-to-bacteria. Soil N-cyclingshould be controlled by the supplies of C and N to themicrobes. In accordance with plant allocation theory, wediscuss the possibility that the high fungal biomass athigh soil C-to-N ratio reflects a particularly high supplyof plant photosynthates, substrates of high-quality C, tomycorrhizal fungi. Methods to study soil N turnoverand N retention should be developed to take into accountthe impact of mycorrhizal fungi on soil N-cycling.

  • 22.
    Johansson, Otilia
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Olofsson, Johan
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Giesler, Reiner
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Palmqvist, Kristin
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Lichen responses to nitrogen and phosphorus additions can be explained by the different symbiont responses2011In: New Phytologist, ISSN 0028-646X, E-ISSN 1469-8137, Vol. 191, no 3, p. 795-805Article in journal (Refereed)
    Abstract [en]

    Responses to simulated nitrogen (N) deposition with or without added phosphorus (P) were investigated for three contrasting lichen species – the N-sensitive Alectoria sarmentosa, the more N-tolerant Platismatia glauca and the N2-fixing Lobaria pulmonaria– in a field experiment.

    To examine whether nutrient limitation differed between the photobiont and the mycobiont within the lichen, the biomass responses of the respective bionts were estimated.

    The lichenized algal cells were generally N-limited, because N-stimulated algal growth in all three species. The mycobiont was P-limited in one species (A. sarmentosa), but the growth response of the mycobionts was complex, as fungal growth is also dependent on a reliable carbon export from the photobiont, which may have been the reason for the decrease of the mycobiont with N addition in P. glauca.

    Our findings showed that P availability was an important factor when studying effects of N deposition, as P supply can both mitigate and intensify the negative effects of N on epiphytic lichens.

  • 23.
    Karlsson, Jan
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Giesler, Reiner
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Global Change and the High-Latitude Environment2008In: EOS: Transactions, ISSN 0096-3941, E-ISSN 2324-9250, Vol. 89, no 10, p. 97-97Article in journal (Other academic)
    Abstract [en]

    High Latitude Terrestrial and Freshwater Ecosystems: Interactions and Response to Environmental Change; Abisko, Sweden, 11–14 September 2007; Terrestrial and aquatic scientists took part in a workshop in Sweden to discuss cross-system linkages that strongly influence the structure and function of terrestrial and aquatic ecosystems, which effects may be altered by future environmental change. Sixty-five researchers, mainly from northern Europe and North America, attended the meeting.

  • 24.
    Karlsson, Jan
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Giesler, Reiner
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Persson, Jenny
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Lundin, Erik
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    High emission of carbon dioxide and methane during ice thaw in high latitude lakes2013In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 40, no 6, p. 1123-1127Article in journal (Refereed)
    Abstract [en]

    The winter period is seldom included in the estimates of aquatic-atmospheric carbon exchange. In this study we quantified the flux of carbon dioxide (CO2) and methane (CH4) over 3 years from 12 small subarctic lakes. The lakes accumulated consistent and high amounts of CO2 and CH4 (56–97% as CO2) over the winter, resulting in a high flux during ice thaw. The CO2 flux during ice thaw increased with increasing mean depth of the lakes, while the CH4 flux was high in lakes surrounded by mires. The ice thaw period was quantitatively important to the annual gas balances of the lakes. For nine of the lakes, 11 to 55% of the annual flux occurred during thaw. For three of the lakes with an apparent net annual CO2 uptake, including the thaw period reversed the balance from sink to source. Our results suggest that the ice thaw period is critically important for the emissions of CO2 and CH4 in small lakes.

  • 25.
    Karlsson, Torbjörn
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Persson, Per
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Skyllberg, Ulf
    Mörth, Carl-Magnus
    Giesler, Reiner
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Characterization of Iron(III) in Organic Soils Using Extended X-ray Absorption Fine Structure Spectroscopy2008In: Environmental Science & Technology, Vol. 42, no 15, p. 5449-54Article in journal (Refereed)
    Abstract [en]

    The distribution of different iron (Fe) species in soils, sediments, and surface waters has a large influence on the mobility and availability of Fe, other nutrients, and potentially toxic trace elements. However, the knowledge about the specific forms of Fe that occurs in these systems is limited, especially regarding associations of Fe with natural organic matter (NOM). In this study, extended X-ray absorption fine structure (EXAFS) spectroscopy was used to characterize Fe(III) in organic soils (pH 4.6-6.0) with varying natural Fe content. The EXAFS data were subjected to wavelet transform analysis, to facilitate the identification of the nature of backscattering atoms, and to conventional EXAFS data fitting. The collective results showed the existence of two pools of iron: mononuclear Fe(III)-NOM complexes and precipitated Fe(III) (hydr)oxides. In the soil with lowest pH (4.6) and Fe content mononuclear organic complexes were the completely dominating fraction whereas in soils with higher pH and Fe content increasing amounts of Fe (hydr)oxides were detected. These results are of environmental importance, as the different iron pools most likely have markedly different reactivities.

  • 26.
    Klaminder, J
    et al.
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Yoo, K
    Giesler, R
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Soil carbon accumulation in the dry tundra: Important role played by precipitation2009In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 114, p. G04005-Article in journal (Refereed)
    Abstract [en]

    A positive relationship between the mean annual precipitation (MAP) and soil organic carbon (SOC) is found in most surveys covering the subarctic and boreal region. In this paper we assess mechanisms behind variable SOC pools in dry tundra soils developed along a 50 km long subarctic precipitation (snow) gradient in northern Sweden. Lead 210 is used to infer SOC accumulation rates in the O horizon. Despite an unchanged or even slightly decreasing accumulation rate of SOC in the O horizon (range 0.02–0.06 kg C m−2 yr−1) along with increasing MAP and a relative constant litter input (∼0.04 kg C m−2 yr−1), the SOC pool in the upper 1 m increase significantly with increasing MAP. This trend is mainly due to a progressively buildup of SOC in the mineral soil and argued to be the result of an accelerated vertical translocation of SOC at sites overlain by a thick snowpack. Furthermore, the loss of SOC from the O horizon through wind erosion appears to be more pronounced at snow-poor sites. We estimate that vegetated heath soil may loose >0.02 kg C m−2 yr−1 (∼half of the annual litter fall) due to wind erosion in snow-poor areas. We stress that lateral and vertical translocation processes inherent by precipitation regimes may be of fundamental importance for the long-term SOC accumulation in tundra soil.

  • 27.
    Klaminder, Jonatan
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Giesler, Reiner
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Makoto, Kobayashi
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Physical mixing between humus and mineral matter found in cryoturbated soils increases short-term heterotrophic respiration rates2013In: Soil Biology and Biochemistry, ISSN 0038-0717, E-ISSN 1879-3428, Vol. 57, p. 922-924Article in journal (Refereed)
    Abstract [en]

    Cryoturbation is an important mechanism in the most recent large-scale model describing the build-up of soil organic carbon (SOC) in arctic soils. In this paper, we hypothesize that the physical mixing of humus and mineral soil generated by this process causes previously unconsidered effects on respiration rates. Through laboratory incubations we found that mixing of humus into mineral soil from cryoturbated soils primed heterotrophic respiration rates by about 40%, which was of the same magnitude as the effect generated by a rise in soil temperature from 5 degrees C to 10 degrees C. Our result indicates that cryogenic mixing, if complete, may generate short-term positive effects on heterotrophic respiration rates as long as the mixing does not translocate carbon into much colder soil layers. (C) 2012 Elsevier Ltd. All rights reserved.

  • 28.
    Klaminder, Jonatan
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Yoo, K.
    Rydberg, Johan
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Giesler, Reiner
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    An explorative study of mercury export from a thawing palsa mire2008In: Journal of Geophysical Research, Vol. 113, p. G04034-Article in journal (Refereed)
    Abstract [en]

    Thawing of permafrost and a subsequent accelerated loss of mercury from the soil constitute a possible threat to the quality of high-latitude surface waters. In this paper we estimate the export of mercury generated by a thawing palsa mire in northern Sweden, by assessing net mercury storage changes along thermokarst erosion gradients. Lower mercury inventories in inundated hummocks covered by water (≤3.1 mg Hg m−2) than in noneroding hummocks (between 5.5 and 8 mg Hg m−2) suggests a release of ~40–95% of the mercury pool from hummock peat experiencing subsidence and submerging. The documented expansion of submerged areas between 1970 and 2000 in the studied system indicates that permafrost thawing has initiated a mobilization of 34 to 50 g mercury. We stress the need of further assessing the fate of this mercury because the size of the mobilized mercury pool might be highly significant for subarctic surface waters.

  • 29.
    Lagerström, Anna
    et al.
    Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, 901 83 Umeå, Sweden.
    Esberg, Camilla
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Wardle, David A.
    Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, 901 83 Umeå, Sweden.
    Giesler, Reiner
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Soil phosphorus and microbial response to a long-term wildfire chronosequence in northern Sweden2009In: Biogeochemistry, ISSN 0168-2563, E-ISSN 1573-515X, Vol. 95, no 2/3, p. 199-213Article in journal (Refereed)
    Abstract [en]

    In the prolonged absence of major disturbances, ecosystems may enter a stage of retrogression, which is characterized by decreased ecosystem process rates both above and belowground, and often reduced availability of phosphorus (P). Disturbance through wildfire can increase soil P losses through leaching or erosion, but in the long-term absence of fire, soil P could potentially become increasingly bound in more stable forms that are less available to microbes. We studied forms of P and microbial respiration kinetics in the humus layer of a group of islands that vary considerably in wildfire frequency (40–5,300 years since last fire), and which are known to enter retrogression in the prolonged absence of fire. We found a decrease in labile P with decreasing fire frequency but no change in total P. Soil microorganisms responded more strongly to N than to P addition, and microbial biomass N:P ratios remained unchanged across the gradient. However, the concentration of labile P was the best predictor of microbial respiration responses across the islands, and this provides some evidence that declining access to P could contribute to the decline in soil microbial activity during retrogression. Our results show that even though N is arguably the main limiting nutrient during retrogression in this chronosequence, long term absence of fire also causes a decline in P availability which negatively affects microbial activity. This in turn could potentially impair microbially driven processes such as decomposition and mineralization and further contribute to the reduced availability of soil nutrients during retrogression.

  • 30.
    Lundin, Erik
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Christensen, Torben
    Giesler, Reiner
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Heliasz, Michal
    Klaminder, Jonatan
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Persson, Andreas
    Karlsson, Jan
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    A weak C sink at high latitudes: support from an integrated terrestrial – aquatic C balanceManuscript (preprint) (Other academic)
    Abstract [en]

    High latitude ecosystems have served as net sinks of atmospheric carbon (C) in the Holocene time perspective. However, the ongoing climate warming makes it questionable if high latitude landscapes still function as net C sinks. In this study we used multiyear high resolution C flux data to estimate an integrated terrestrial-aquatic C balance of a sub-arctic catchment. The results indicate large inter annual variability in C fluxes and suggest that the C sink function of this landscape is weak, especially when also accounting for the often neglected C losses from aquatic systems. In fact, our results suggest that it is more likely that the studied catchment serves as a net source of C rather than a net sink. These results highlight the importance of inland waters in the C cycle and that the strength of the C sequestering in the contemporary sub-arctic environment is much weaker than often assumed.

  • 31.
    Lundin, Erik J.
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Giesler, Reiner
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Persson, Andreas
    Thompson, Megan S.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Karlsson, Jan
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Integrating carbon emissions from lakes and streams in a subarctic catchment2013In: Journal of Geophysical Research: Biogeosciences, ISSN 2169-8953, Vol. 118, no 3, p. 1200-1207Article in journal (Refereed)
    Abstract [en]

    Northern inland waters emit CO2 and CH4 to the atmosphere but the importance of these emissions is poorly understood due to a lack of integrated catchment-scale estimates of carbon (C) emissions from lakes and streams. In this study we quantified the annual emission of CO2 and CH4 from 27 lakes and 23 stream segments in a 15km(2) subarctic catchment in northern Sweden. All lakes and streams were net sources of C to the atmosphere on an annual basis. Streams dominated (96%) the aquatic CO2 emission while lakes (61%) dominated the aquatic CH4 emission. Total aquatic C emission from the catchment was estimated to be 9.1gCm(-2)yr(-1) (98% as CO2). Although streams only accounted for 4% of the aquatic area in the catchment, they accounted for 95% of the total emission. The C emissions from lakes and streams were considerably larger than previously reported downstream waterborne export of C from the catchment, indicating that the atmospheric losses of C in the aquatic systems are an important component in the catchment C balance.

  • 32. Lyon, SW
    et al.
    Destouni, G
    Giesler, Reiner
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Humborg, C
    Mörth, CM
    Seibert, J
    Karlsson, Jan
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Troch, PA
    Estimation of permafrost thawing rates in a sub-arctic catchment using recession flow analysis2009In: Hydrology and Earth System Sciences, ISSN 1027-5606, E-ISSN 1607-7938, Vol. 13, no 5, p. 595-604Article in journal (Refereed)
    Abstract [en]

    Permafrost thawing is likely to change the flow pathways taken by water as it moves through arctic and sub-arctic landscapes. The location and distribution of these pathways directly influence the carbon and other biogeochemical cycling in northern latitude catchments. While permafrost thawing due to climate change has been observed in the arctic and sub-arctic, direct observations of permafrost depth are difficult to perform at scales larger than a local scale. Using recession flow analysis, it may be possible to detect and estimate the rate of permafrost thawing based on a long-term streamflow record. We demonstrate the application of this approach to the sub-arctic Abiskojokken catchment in northern Sweden. Based on recession flow analysis, we estimate that permafrost in this catchment may be thawing at an average rate of about 0.9 cm/yr during the past 90 years. This estimated thawing rate is consistent with direct observations of permafrost thawing rates, ranging from 0.7 to 1.3 cm/yr over the past 30 years in the region.

  • 33. Lyon, SW
    et al.
    Mörth, M
    Humborg, R
    Giesler, Reiner
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Destouni, G
    The relationship between subsurface hydrology and dissolved carbon fluxes for a sub-arctic catchment2010In: Hydrology and Earth System Sciences, ISSN 1027-5606, E-ISSN 1607-7938, Vol. 14, no 6, p. 941-950Article in journal (Refereed)
    Abstract [en]

    In recent years, there has been increased interest in carbon cycling in natural systems due to its role in a changing climate. Northern latitude systems are especially important as they may serve as a potentially large source or sink of terrestrial carbon. There are, however, a limited number of investigations reporting on actual flux rates of carbon moving from the subsurface landscape to surface water systems in northern latitudes. In this study, we determined dissolved organic carbon (DOC) and dissolved inorganic carbon (DIC) fluxes from the subsurface landscape for a sub-arctic catchment located in northern Sweden. These are based on observed annual flux-averaged concentrations of DOC and DIC for the 566 km2 Abiskojokken catchment. We demonstrate the importance to correctly represent the spatial distribution of the advective solute travel times along the various flow and transport pathways. The fluxes of DOC and DIC from the subsurface landscape to the surface water system were comparable in magnitude. This balance could shift under future climatic changes that influence the hydrological and biogeochemical system.

  • 34. Mörth, C
    et al.
    Laudon, H
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Mellqvist, E
    Torssander, P
    Giesler, R
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Sources of stream water sulfate during the spring snowmelt in boreal streams: Evidence from δ34S isotope measurements2008In: J. Geophys. Res., Vol. 113, p. G01005-Article in journal (Refereed)
  • 35. Mörth, Carl-Magnus
    et al.
    Torssander, Peter
    Kjønaas, O Janne
    Stuanes, Arne O
    Moldan, Filip
    Giesler, Reiner
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Mineralization of organic sulfur delays recovery from anthropogenic acidification.2005In: Environ Sci Technol, ISSN 0013-936X, Vol. 39, no 14, p. 5234-40Article in journal (Refereed)
  • 36. Nilsson, Lars Ola
    et al.
    Giesler, Reiner
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Bååth, Erland
    Wallander, Håkan
    Growth and biomass of mycorrhizal mycelia in coniferous forests along short natural nutrient gradients.2005In: New Phytol, ISSN 0028-646X, Vol. 165, no 2, p. 613-22Article in journal (Refereed)
  • 37. Olefeldt, David
    et al.
    Roulet, Nigel
    Giesler, Reiner
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Persson, Andreas
    Total waterborne carbon export and DOC composition from ten nested subarctic peatland catchments-importance of peatland cover, groundwater influence, and inter-annual variability of precipitation patterns2013In: Hydrological Processes, ISSN 0885-6087, E-ISSN 1099-1085, Vol. 27, no 16, p. 2280-2294Article in journal (Refereed)
    Abstract [en]

    Waterborne carbon (C) export from terrestrial ecosystems is a potentially important flux for the net catchment C balance and links the biogeochemical C cycling of terrestrial ecosystems to their downstream aquatic ecosystems. We have monitored hydrology and stream chemistry over 3 years in ten nested catchments (0.6–15.1 km2) with variable peatland cover (0%–22%) and groundwater influence in subarctic Sweden. Total waterborne C export, including dissolved and particulate organic carbon (DOC and POC) and dissolved inorganic carbon (DIC), ranged between 2.8 and 7.3 g m–2 year–1, representing ~10%–30% of catchment net ecosystem exchange of CO2. Several characteristics of catchment waterborne C export were affected by interacting effects of peatland cover and groundwater influence, including magnitude and timing, partitioning into DOC, POC, and DIC and chemical composition of the exported DOC. Waterborne C export was greater during the wetter years, equivalent to an average change in export of ~2 g m–2 year–1 per 100 mm of precipitation. Wetter years led to a greater relative increase in DIC export than DOC export due to an inferred relative shift in dominance from shallow organic flow pathways to groundwater sources. Indices of DOC composition (SUVA254 and a250/a365) indicated that DOC aromaticity and average molecular weight increased with catchment peatland cover and decreased with increased groundwater influence. Our results provide examples on how waterborne C export and DOC composition might be affected by climate change.

  • 38. Olsson, P
    et al.
    Linder, S
    Giesler, R
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Högberg, P
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Fertilization of boreal forest reduces both autotrophic and heterotrophic soil respiration2005In: Global Change Biology, Vol. 11, p. 1-9Article in journal (Refereed)
  • 39. Olsson, R
    et al.
    Giesler, Reiner
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Persson, P
    Abiotic hydrolysis of glucose-1-phosphate adsorbed at the water-goethite interface2007In: Geochimica et Cosmochimica Acta, Vol. 71, p. A739-A739 Suppl. SArticle in journal (Refereed)
  • 40.
    Olsson, Rickard
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Giesler, Reiner
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Lindegren, Malin
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Persson, Per
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Abiotic and enzymatic hydrolysis of glucose-6-phosphate on Goethite ParticlesManuscript (preprint) (Other academic)
  • 41.
    Olsson, Rickard
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Giesler, Reiner
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Loring, John
    Pacific Northwest National Laboratory.
    Persson, Per
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Enzymatic hydrolysis of organic phosphates adsorbed on mineral surfaces2012In: Environmental Science and Technology, ISSN 0013-936X, E-ISSN 1520-5851, Vol. 46, p. 285-291Article in journal (Refereed)
    Abstract [en]

    Esters of phosphoric acid constitute a sizable fraction of the total phosphorus supply in the environment and thus play an important role in the global phosphorus cycle. Enzymatic hydrolysis of these esters to produce orthophosphate is often a required reaction preceding phosphorus uptake by plants and microorganisms. Generally, adsorption to environmental particles is assumed to limit this process. Here we show, however, that the rate of enzymatic hydrolysis of glucose-1-phosphate (G1P) adsorbed on goethite by acid phosphatase (AcPase) can be of the same order of magnitude as in aqueous solution. The surface process releases carbon to the solution whereas orthophosphate remains adsorbed on goethite. This hydrolysis reaction is strictly an interfacial process governed by the properties of the interface. A high surface concentration of substrate mediates the formation of a catalytically active layer of AcPase, and although adsorption likely reduces the catalytic efficiency of the enzyme, this reduction is almost balanced by the fact that enzyme and substrate are concentrated at the mineral surfaces. Our results suggest that mineral surfaces with appropriate surface properties can be very effective in concentrating substrates and enzymes thereby creating microchemical environments of high enzymatic activity. Hence, also strongly adsorbed molecules in soils and aquatic environments may be subjected to biodegradation by extracellular enzymes.

  • 42.
    Olsson, Rickard
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Giesler, Reiner
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Loring, John S
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Persson, Per
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Adsorption, desorption, and surface-promoted hydrolysis of Glucose-1-phosphate in Aqueous Goethite (α-FeOOH) Suspensions2010In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 26, no 24, p. 18760-18770Article in journal (Refereed)
    Abstract [en]

    Adsorption, desorption, and precipitation reactions at environmental interfaces govern the fate of phosphorus in terrestrial and aquatic environments. Typically, a substantial part of the total pool of phosphorus consists of organophosphate, and in this study we have focused on the interactions between glucose-1-phosphate (G1P) and goethite (α-FeOOH) particles. The adsorption and surface-promoted hydrolysis reactions have been studied at room temperature as a function of pH, time, and total concentration of G1P by means of quantitative batch experiments in combination with infrared spectroscopy. A novel simultaneous infrared and potentiometric titration (SIPT) technique has also been used to study the rates and mechanisms of desorption of the surface complexes. The results have shown that G1P adsorption occurs over a wide pH interval and at pH values above the isoelectric point of goethite (IEP(goethite) = 9.4), indicating a comparatively strong interaction with the particle surfaces. As evidenced by IR spectroscopy, G1P formed pH-dependent surface complexes on goethite, and investigations of both adsorption and desorption processes were consistent with a model including three types of surface complexes. These complexes interact monodentately with surface Fe but differ in hydrogen bonding interactions via the auxiliary oxygens of the phosphate group. The apparent desorption rates were shown to be influenced by reaction pathways that include interconversion of surface species, which highlights the difficulty in determining the intrinsic desorption rates of individual surface complexes. Desorption results have also indicated that the molecular structures of surface complexes and the surface charge are two important determinants of G1P desorption rates. Finally, this study has shown that surface-promoted hydrolysis of G1P by goethite is base-catalyzed but that the extent of hydrolysis was small.

  • 43.
    Olsson, Rickard
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Giesler, Reiner
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Persson, Per
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Adsorption mechanisms of glucose in aqueous goethite suspensions2011In: Journal of Colloid and Interface Science, ISSN 0021-9797, E-ISSN 1095-7103, Vol. 353, no 1, p. 263-268Article in journal (Refereed)
    Abstract [en]

    The adsorption of glucose and polysaccharides onto solid surfaces is important in several areas of science and engineering including soil chemistry and mineral processing. In this work we have studied the adsorption of D-glucose at the water-goethite (α-FeOOH) interface as a function of pH using batch adsorption measurements and a simultaneous infrared and potentiometric technique. Molecular orbital calculations were also performed in order to support interpretations of the infrared spectroscopic data. Infrared spectroscopy has shown that glucose adsorbs at the water-goethite interface with an intact ring structure and that the β-form is favored relative to the α isomer. The collective spectroscopic and macroscopic results were fully consistent with an adsorption mechanism where glucose interacts with goethite surface sites via hydrogen bonding interactions. Specific infrared peak shifts indicated that glucose primarily acts as a hydrogen bond donor and that it interacts with acceptor sites that become increasingly more prevalent as the surface is deprotonated. These results are in general agreement with the acid/base model for mono- and polysaccharide interactions at metal oxide surfaces, but contradict the inner sphere hypothesis that was proposed based on ex situ spectroscopic measurements.

  • 44.
    Persson, Per
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Andersson, Tove
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Nelson, Hanna
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Sjöberg, Staffan
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Giesler, Reiner
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Lövgren, Lars
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Surface complexes of Monomethyl Phosphate stabilized by Hydrogen Bonding on Goethite (α-FeOOH) NanoparticlesManuscript (preprint) (Other academic)
  • 45.
    Persson, Per
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Andersson, Tove
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Nelson, Hanna
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Sjöberg, Staffan
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Giesler, Reiner
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Lövgren, Lars
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Surface complexes of monomethyl phosphate stabilized by hydrogen bonding on goethite (α-FeOOH) nanoparticles2012In: Journal of Colloid and Interface Science, ISSN 0021-9797, E-ISSN 1095-7103, Vol. 386, no 1, p. 350-358Article in journal (Refereed)
    Abstract [en]

    Typically, a significant fraction of phosphorus in soils is composed of organic phosphates, and this fraction thus plays an important role in the global phosphorus cycle. Here we have studied adsorption of monomethyl phosphate (MMP) to goethite (α-FeOOH) as a model system in order to better understand the mechanisms behind adsorption of organic phosphates to soil minerals, and how adsorption affects the stability of these molecules. The adsorption reactions and stability of MMP on goethite were studied at room temperature as a function of pH, time and total concentration of MMP by means of quantitative batch experiments, potentiometry and infrared spectroscopy. MMP was found to be stable at the water-goethite interface within the pH region 3-9 and over extended periods of time, as well as in solution. The infrared spectra indicated that MMP formed three predominating pH-dependent surface complexes on goethite, and that these interacted monodentately with surface Fe. The complexes differed in hydrogen bonding interactions via the auxiliary oxygens of the phosphate group. The presented surface complexation model was based on the collective spectroscopic and macroscopic results, using the Basic Stern approach to describe the interfacial region. The model consisted of three monodentate inner sphere surface complexes where the MMP complexes were stabilized by hydrogen bonding to a neighboring surface site. The three complexes, which had equal proton content and thus could be defined as surface isomers, were distinguished by the distribution of charge over the 0-plane and β-plane. In the high pH-range, MMP acted as a hydrogen bond acceptor whereas it was a hydrogen bond donor at low pH.

  • 46.
    Roehm, Charlotte L
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Giesler, Reiner
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Karlsson, Jan
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Bioavailability of terrestrial organic carbon to lake bacteria: the case of a degrading subarctic permafrost mire complex2009In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 114, p. G03006-Article in journal (Refereed)
    Abstract [en]

    Permafrost degradation can result in the loss of significant amounts of carbon, through release to the atmosphere in the form of carbon dioxide and/or methane and through export downstream to lakes and rivers. The fate of this carbon in lake ecosystems is poorly understood. We investigated the capacity of lake bacteria to utilize carbon from different soils from an adjacent mire. Dark bioassays were undertaken to measure the dynamics of the bioavailability and chemical character of dissolved organic carbon (DOC). The soils ranged from already degraded minerotrophic fens to ombrotrophic active layer and soils from the permafrost layer. Our study shows that soil DOC was rapidly consumed by bacteria collected from lake water, particularly within the first 48 h (about 85% of the total consumed DOC). The mean DOC consumption by lake bacteria was 0.087 mg L−1 d−1 when supplied with lake water DOC and varied between 0.382 mg L−1 d−1 (permafrost soil) and 0.491 mg L−1 d−1 (degraded fen soil) when supplied with terrestrial DOC. Thus, the data suggest that export of DOC from degrading permafrost mires at any stage of degradation can potentially increase rates of respiration by fourfold to sevenfold and can have pronounced effects both on receiving lake ecosystems and on the land-atmosphere carbon balance. In this study we also propose simple predictive models, incorporating weight-averaged molecular weight and specific UV absorption in combination with other simple qualitative parameters for the estimation of potential bioavailability of soil DOC in aquatic ecosystems.

  • 47. Schnurer, Ylva
    et al.
    Persson, Per
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Nilsson, Mats
    Nordgren, Anders
    Giesler, Reiner
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Effects of surface sorption on microbial degradation of glyphosate2006In: Environ Sci Technol, ISSN 0013-936X, Vol. 40, no 13, p. 4145-50Article in journal (Refereed)
    Abstract [en]

    Over the past 100 years Drosophila has been developed into an outstanding model system for the study of evolutionary processes. A fascinating aspect of evolution is the differentiation of sex chromosomes. Organisms with highly differentiated sex chromosomes, such as the mammalian X and Y, must compensate for the imbalance in gene dosage that this creates. The need to adjust the expression of sex-linked genes is a potent force driving the rise of regulatory mechanisms that act on an entire chromosome. This review will contrast the process of dosage compensation in Drosophila with the divergent strategies adopted by other model organisms. While the machinery of sex chromosome compensation is different in each instance, all share the ability to direct chromatin modifications to an entire chromosome. This review will also explore the idea that chromosome-targeting systems are sometimes adapted for other purposes. This appears the likely source of a chromosome-wide targeting system displayed by the Drosophila fourth chromosome

  • 48. Sundqvist, Maja K.
    et al.
    Giesler, Reiner
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Graae, Bente J.
    Wallander, Håkan
    Fogelberg, Elisabeth
    Wardle, David A.
    Interactive effects of vegetation type and elevation on aboveground and belowground properties in a subarctic tundra2011In: Oikos, ISSN 0030-1299, E-ISSN 1600-0706, Vol. 120, no 1, p. 128-142Article in journal (Refereed)
    Abstract [en]

    An improved knowledge of how contrasting types of plant communities and their associated soil biota differ in their responses to climatic variables is important for better understanding the future impacts of climate change on terrestrial ecosystems. Elevational gradients serve as powerful study systems for answering questions on how ecological processes can be affected by changes in temperature and associated climatic variables. In this study, we evaluated how plant and soil microbial communities, and abiotic soil properties, change with increasing elevation in subarctic tundra in northern Sweden, for each of two dominant but highly contrasting vegetation types, namely heath (dominated by woody dwarf shrubs) and meadow (dominated by herbaceous species). To achieve this, we measured plant community characteristics, microbial community properties and several soil abiotic properties for both vegetation types across an elevation gradient of 500 to 1000 m. We found that the two vegetation types differed not only in several above- and belowground properties, but also in how these properties responded to elevation, pointing to important interactive effects between vegetation type and elevation. Specifically, for the heath, available soil nitrogen and phosphorus decreased with elevation whereas fungal dominance increased, while for the meadow, idiosyncratic responses to elevation for these variables were found. These differences in belowground responses to elevation among vegetation types were linked to shifts in the species and functional group composition of the vegetation. Our results highlight that these two dominant vegetation types in subarctic tundra differ greatly not only in fundamental aboveground and belowground properties, but also in how these properties respond to elevation and are therefore likely to be influenced by temperature. As such they highlight that vegetation type, and the soil abiotic properties that determine this, may serve as powerful determinants of how both aboveground and belowground properties respond to strong environmental gradients.

  • 49.
    Sundqvist, Maja K.
    et al.
    Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, Umeå, Sweden.
    Giesler, Reiner
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Wardle, David A
    Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, Umeå, Sweden.
    Within- and across-species responses of plant traits and litter decomposition to elevation across contrasting vegetation types in subarctic tundra2011In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 6, no 10, p. e27056-Article in journal (Refereed)
    Abstract [en]

    Elevational gradients are increasingly recognized as a valuable tool for understanding how community and ecosystem properties respond to climatic factors, but little is known about how plant traits and their effects on ecosystem processes respond to elevation. We studied the response of plant leaf and litter traits, and litter decomposability across a gradient of elevation, and thus temperature, in subarctic tundra in northern Sweden for each of two contrasting vegetation types, heath and meadow, dominated by dwarf shrubs and herbaceous plants respectively. This was done at each of three levels; across species, within individual species, and the plant community using a community weighted average approach. Several leaf and litter traits shifted with increasing elevation in a manner consistent with greater conservation of nutrients at all three levels, and the most consistent response was an increase in tissue N to P ratio. However, litter decomposition was less directly responsive to elevation because the leaf and litter traits which were most responsive to elevation were not necessarily those responsible for driving decomposition. At the community level, the response to elevation of foliar and litter traits, and decomposability, varied greatly among the two vegetation types, highlighting the importance of vegetation type in determining ecological responses to climatic factors such as temperature. Finally our results highlight how understanding the responses of leaf and litter characteristics of functionally distinct vegetation types, and the processes that they drive, to temperature helps provide insights about how future climate change could affect tundra ecosystems.

  • 50.
    Sundqvist, Maja K.
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. Swedish Univ Agr Sci, Dept Forest Ecol & Management, SE-90183 Umea, Sweden.
    Liu, Zhanfeng
    Chinese Acad Sci, South China Bot Garden, Key Lab Vegetat Restorat & Management Degraded Ec, Guangzhou 510650, Guangdong, Peoples R China.
    Giesler, Reiner
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Wardle, David A.
    Swedish Univ Agr Sci, Dept Forest Ecol & Management, SE-90183 Umea, Sweden.
    Plant and microbial responses to nitrogen and phosphorus addition across an elevational gradient in subarctic tundra2014In: Ecology, ISSN 0012-9658, E-ISSN 1939-9170, Vol. 95, no 7, p. 1819-1835Article in journal (Refereed)
    Abstract [en]

    Temperature and nutrients are major limiting factors in subarctic tundra. Experimental manipulation of nutrient availability along elevational gradients (and thus temperature) can improve our understanding of ecological responses to climate change. However, no study to date has explored impacts of nutrient addition along a tundra elevational gradient, or across contrasting vegetation types along any elevational gradient. We set up a full factorial nitrogen (N) and phosphorus (P) fertilization experiment in each of two vegetation types (heath and meadow) at 500 m, 800 m, and 1000 m elevation in northern Swedish tundra. We predicted that plant and microbial communities in heath or at lower elevations would be more responsive to N addition while communities in meadow or at higher elevations would be more responsive to P addition, and that fertilizer effects would vary more with elevation for the heath than for the meadow. Although our results provided little support for these predictions, the relationship between nutrient limitation and elevation differed between vegetation types. Most plant and microbial properties were responsive to N and/or P fertilization, but responses often varied with elevation and/or vegetation type. For instance, vegetation density significantly increased with N + P fertilization relative to the other fertilizer treatments, and this increase was greatest at the lowest elevation for the heath but at the highest elevation for the meadow. Arbuscular mycorrhizae decreased with P fertilization at 500 m for the meadow, but with all fertilizer treatments in both vegetation types at 800 m. Fungal to bacterial ratios were enhanced by N + P fertilization for the two highest elevations in the meadow only. Additionally, microbial responses to fertilization were primarily direct rather than indirect via plant responses, pointing to a decoupled response of plant and microbial communities to nutrient addition and elevation. Because our study shows how two community types differ in their responses to fertilization and elevation, and because the temperature range across this gradient is similar to 3 degrees C, our study is informative about how nutrient limitation in tundra may be influenced by temperature shifts that are comparable to those expected under climate change during this century.

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