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  • 1.
    Giesler, Reiner
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Esberg, Camilla
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Lagerström, Anna
    Graae, Bente J
    Phosphorus availability and microbial respiration across different tundra vegetation types2012Ingår i: Biogeochemistry, ISSN 0168-2563, E-ISSN 1573-515X, Vol. 108, nr 1-3, s. 429-445Artikel i tidskrift (Refereegranskat)
    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.

  • 2.
    Haei, Mahsa
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Öquist, Mats G.
    Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, 901 83 Umeå, Sweden.
    Ilstedt, Ulrik
    Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, 901 83 Umeå, Sweden.
    Laudon, Hjalmar
    Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, 901 83 Umeå, Sweden.
    The influence of soil frost on the quality of dissolved organic carbon in a boreal forest soil: combining field and laboratory experiments2012Ingår i: Biogeochemistry, ISSN 0168-2563, E-ISSN 1573-515X, Vol. 107, nr 1-3, s. 95-106Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Riparian soils exert a major control on stream water dissolved organic carbon (DOC) in northern latitudes. As the winter climate in northern regions is predicted to be particularly affected by climate change, we tested the sensitivity of DOC formation to winter conditions in riparian soils using an 8 year field-scale soil frost manipulation experiment in northern Sweden. In conjunction with the field experiment, we also carried out a laboratory experiment based on three levels of four winter climatic factors: frost intensity, soil water content, frost duration and frequency of freeze–thaw cycles. We evaluated changes in lability of DOC in soil solution from lysimeter samples taken at different depths (10–80 cm) as well as from DOC extracted from soils in the laboratory, using carbon-specific ultraviolet absorbance at 254 nm (sUVA254). In the field, significantly more labile DOC was observed during the spring and summer from upper horizons of frost-exposed soils, when compared to controls. In addition, the amount of labile DOC was positively correlated with frost duration at a soil depth of 10 cm. In the laboratory, frost intensity was the factor that had the greatest positive influence on DOC lability; it also reduced the C:N ratio which may indicate a microbial origin of the DOC. The laboratory experiment also demonstrated significant interactions between some of the applied climatic factors, such as frost intensity interacting with water content. In combination, field and laboratory experiments demonstrate that winter soil conditions have profound effects on DOC-concentration and quality during subsequent seasons.

  • 3.
    Hansson, Sophia V.
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Kaste, James M.
    College of William & Mary.
    Chen, Keyao
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Bindler, Richard
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Beryllium-7 as a natural tracer for short-term downwash in peat2014Ingår i: Biogeochemistry, ISSN 0168-2563, E-ISSN 1573-515X, Vol. 119, nr 1-3, s. 329-339Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Several factors can affect the integrity of natural archives such as peat records, e.g., decomposition and nutrient cycling, and it has also been hypothesized that some rapid downward transport of atmospherically derived elements may occur. We test this hypothesis by analyzing the short-lived, natural tracer beryllium-7 (tA1/2A = 53.4 days) in five cores from two peatlands. In triplicate hummock cores from a raised bog in southern Sweden, Be-7 could be measured to 20, 18 and 8 cm depth, and in a nutrient-poor mire in northern Sweden to a depth of 16 cm in a Sphagnum lawn core, but only 4 cm in the dominant, more-decomposed fen peat, indicating some spatial variability both within and between sites. Total Be-7 inventories were 320-450 Bq m(-2) in the bog, and 150 Bq m(-2) (lawn) and 240 Bq m(-2) (fen peat) in the mire. 25-79 % of the total inventory of Be-7 was located in the upper 2-cm layer. To further test downwashing, in the laboratory we applied a CuBr-solution to two cores and a Cu-solution to one core taken from the mire Sphagnum lawn, all with low water table conditions. About 50 % of the added Cu and similar to 35 % of the added Br were retained in the surface (2 cm) layer; 1-3 % of the Cu was found at 8-12 cm depth and similar to 1 % of the Br was measured in the lowest level (20-22 cm). Based on our novel approach using Be-7 and experimental work we show that short-term downwashing can occur in peatlands and we suggest the depth of this will depend on the properties of the peat, e.g., bulk density and decomposition, as well as hydrology.

  • 4.
    Isles, Peter D. F.
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap. Rubenstein Ecosystem Science Laboratory, University of Vermont, Burlington, VT, USA; Rubenstein School of Environment and Natural Resources, University of Vermont, Burlington, VT, USA; Vermont EPSCoR, University of Vermont, Burlington, VT, USA.
    Xu, Yaoyang
    Stockwell, Jason D.
    Schroth, Andrew W.
    Climate-driven changes in energy and mass inputs systematically alter nutrient concentration and stoichiometry in deep and shallow regions of Lake Champlain2017Ingår i: Biogeochemistry, ISSN 0168-2563, E-ISSN 1573-515X, Vol. 133, nr 2, s. 201-217Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Concentrations of nitrogen (N) and phosphorus (P) in lakes may be differentially impacted by climate-driven changes in nutrient loading and by direct impacts of temperature and wind speed on internal nutrient cycling. Such changes may result in systematic shifts in lake N:P under future climate warming. We used 21 years of monitoring data to compare long-term and intra-annual trends in total N (TN), total P (TP) and TN:TP at 15 sites in Lake Champlain to concurrent measurements of watershed nutrient inputs and meteorological drivers. TN:TP declined sharply lake-wide, particularly in the past decade, yet the drivers of this trend varied based on site depth. In deep sites, declines were driven by changes in watershed loading of dissolved P and N and (in some cases) by decreases in hypolimnetic dissolved oxygen. In shallow sites, declines in TN:TP were primarily driven by long-term increases in temperature and decreases in wind speed, and exhibited systematic seasonal variability in TN:TP due to the timing of sediment P loading, N removal processes, and external nutrient inputs. We developed a conceptual model to explain the observed trends, and suggest that while climate drivers have affected nutrient dynamics in shallow and deep sites differently, both deep and shallow sites are likely to experience further declines in N:P and increases in cyanobacteria dominance if recent climate trends continue.

  • 5.
    Klaminder, Jonatan
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Bindler, Richard
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Emteryd, Ove
    Appleby, Peter
    Grip, Harald
    Estimating the mean residence time of lead in the organic horizon of boreal forest soils using 210-lead, stable lead and a soil chronosequence2006Ingår i: Biogeochemistry, ISSN 0168-2563, E-ISSN 1573-515X, Vol. 78, nr 1, s. 31-49Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Knowledge about the residence time of lead in the organic horizon (mor layer; O-horizon) overlaying forest mineral soils is important for the prediction of past and future lead levels in the boreal environment. To estimate the mean residence time (MRT) of lead in the mor layer, we use in this study from Northern Sweden three different approaches: (1) lead-210 is applied as a tracer of lead migration; (2) estimations of loss rates of stable lead (concentrations and 206Pb/207Pb ratios) from the mor layer at an undisturbed forest setting, and (3) a study of lead in a soil series with sites of different age (a chronosequence of 20–220 years). In the last two approaches we compared measured inventories in the soil with estimated inventories derived using analyses of lake sediments. The results suggested a MRT of about 250 years in the mor layer in the mature forest and in the older parts of the chronosequence it was at least >170 years. The agreement between the three different approaches gives good credibility to this estimate. It is also supported by a modeling of trends in the 206Pb/207Pb ratio both between single cores and with depth in the mor layer. Our results suggest that it will take centuries for the deeper parts of the mor layer of undisturbed boreal forest soils to fully respond to decreased atmospheric lead pollution. However, data from the chronosequence indicate that the response could be much faster (MRT<50 years) in the mor layer at early stages of forest succession where graminoid and broadleaved litter fall dominates over conifer litter.

  • 6. Kristensen, Jeppe A.
    et al.
    Metcalfe, Daniel B.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap. Department of Physical Geography and Ecosystem Science, Lund University, Lund, Sweden.
    Rousk, Johannes
    The biogeochemical consequences of litter transformation by insect herbivory in the Subarctic: a microcosm simulation experiment2018Ingår i: Biogeochemistry, ISSN 0168-2563, E-ISSN 1573-515X, Vol. 138, nr 3, s. 323-336Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Warming may increase the extent and intensity of insect defoliations within Arctic ecosystems. A thorough understanding of the implications of this for litter decomposition is essential to make predictions of soil-atmosphere carbon (C) feedbacks. Soil nitrogen (N) and C cycles naturally are interlinked, but we lack a detailed understanding of how insect herbivores impact these cycles. In a laboratory microcosm study, we investigated the growth responses of heterotrophic soil fungi and bacteria as well as C and N mineralisation to simulated defoliator outbreaks (frass addition), long-term increased insect herbivory (litter addition at higher background N-level) and non-outbreak conditions (litter addition only) in soils from a Subarctic birch forest. Larger amounts of the added organic matter were mineralised in the outbreak simulations compared to a normal year; yet, the fungal and bacterial growth rates and biomass were not significantly different. In the simulation of long-term increased herbivory, less litter C was respired per unit mineralised N (C:N of mineralisation decreased to 20 +/- 1 from 38 +/- 3 for pure litter), which suggests a directed microbial mining for N-rich substrates. This was accompanied by higher fungal dominance relative to bacteria and lower total microbial biomass. In conclusion, while a higher fraction of foliar C will be respired by insects and microbes during outbreak years, predicted long-term increases in herbivory linked to climate change may facilitate soil C-accumulation, as less foliar C is respired per unit mineralised N. Further work elucidating animal-plant-soil interactions is needed to improve model predictions of C-sink capacity in high latitude forest ecosystems.

  • 7.
    Lagerström, Anna
    et al.
    Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, 901 83 Umeå, Sweden.
    Esberg, Camilla
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Wardle, David A.
    Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, 901 83 Umeå, Sweden.
    Giesler, Reiner
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Soil phosphorus and microbial response to a long-term wildfire chronosequence in northern Sweden2009Ingår i: Biogeochemistry, ISSN 0168-2563, E-ISSN 1573-515X, Vol. 95, nr 2/3, s. 199-213Artikel i tidskrift (Refereegranskat)
    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.

  • 8. Pokrovsky, Oleg S.
    et al.
    Karlsson, Jan
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Giesler, Reiner
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Freeze-thaw cycles of Arctic thaw ponds remove colloidal metals and generate low-molecular-weight organic matter2018Ingår i: Biogeochemistry, ISSN 0168-2563, E-ISSN 1573-515X, Vol. 137, nr 3, s. 321-336Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    High-latitude boreal and arctic surface/inland waters contain sizeable reservoirs of dissolved organic matter (DOM) and trace elements (TE), which are subject to seasonal freezing. Specifically, shallow ponds and lakes in the permafrost zone often freeze solid, which can lead to transformations in the colloidal and dissolved fractions of DOM and TE. Here, we present results from experimental freeze-thaw cycles using iron (Fe)- and DOM-rich water from thaw ponds situated in Stordalen and Storflaket palsa mires in northern Sweden. After ten cycles of freezing, 85% of Fe and 25% of dissolved organic carbon (DOC) were removed from solution in circumneutral fen water (pH 6.9) but a much smaller removal of Fe and DOC (< 7%) was found in acidic bog water (pH 3.6). This removal pattern was consistent with initial supersaturation of fen water with respect to Fe hydroxide and a lack of supersaturation with any secondary mineral phase in the bog water. There was a nearly two- to threefold increase in the low-molecular-weight (LMW) fraction of organic carbon (OC) and several TEs caused by the repeated freeze-thaw cycles. Future increases in the freeze-thaw frequency of surface waters with climate warming may remove up to 25% of DOC in circumneutral organic-rich waters. Furthermore, an increase of LMW OC may result in enhanced carbon dioxide losses from aquatic ecosystems since this fraction is potentially more susceptible to biodegradation.

  • 9. Puissant, Jérémy
    et al.
    Mills, Robert T. E.
    Robroek, Bjorn J. M.
    Gavazov, Konstantin
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Perrette, Yves
    De Danieli, Sébastien
    Spiegelberger, Thomas
    Buttler, Alexandre
    Brun, Jean-Jacques
    Cécillon, Lauric
    Climate change effects on the stability and chemistry of soil organic carbon pools in a subalpine grassland2017Ingår i: Biogeochemistry, ISSN 0168-2563, E-ISSN 1573-515X, Vol. 132, nr 1-2, s. 123-139Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Mountain soils stock large quantities of carbon as particulate organic matter that may be highly vulnerable to climate change. To explore potential shifts in soil organic matter (SOM) form and stability under climate change (warming and reduced precipitations), we studied the dynamics of SOM pools of a mountain grassland in the Swiss Jura as part of a climate manipulation experiment. The climate manipulation (elevational soil transplantation) was set up in October 2009 and simulated two realistic climate change scenarios. After 4 years of manipulation, we performed SOM physical fractionation to extract SOM fractions corresponding to specific turnover rates, in winter and in summer. Soil organic matter fraction chemistry was studied with ultraviolet, 3D fluorescence, and mid-infrared spectroscopies. The most labile SOM fractions showed high intra-annual dynamics (amounts and chemistry) mediated via the seasonal changes of fresh plant debris inputs and confirming their high contribution to the microbial loop. Our climate change manipulation modified the chemical differences between free and intra-aggregate organic matter, suggesting a modification of soil macro-aggregates dynamics. Interestingly, the 4-year climate manipulation affected directly the SOM dynamics, with a decrease in organic C bulk soil content, resulting from significant C-losses in the mineral-associated SOM fraction (MAOM), the most stable form of SOM. This SOC decrease was associated with a decrease in clay content, above- and belowground plants biomass, soil microbial biomass and activity. The combination of these climate changes effects on the plant–soil system could have led to increase C-losses from the MAOM fraction through clay-SOM washing out and DOC leaching in this subalpine grassland.

  • 10. Reitzel, Kasper
    et al.
    Ahlgren, Joakim
    DeBrabandere, Heidi
    Waldeback, Monica
    Gogoll, Adolf
    Tranvik, Lars
    Rydin, Emil
    Degradation rates of organic phosphorus in lake sediment2007Ingår i: Biogeochemistry, ISSN 0168-2563, E-ISSN 1573-515X, Vol. 82, nr 1, s. 15-28Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Phosphorus (P) binding groups were identified in phytoplankton, settling particles, and sediment profiles by P-31 NMR spectroscopy from the Swedish mesotrophic Lake Erken. The P-31 NMR analysis revealed that polyphosphates and pyrophosphates were abundant in the water column, but rapidly mineralized in the sediment. Orthophosphate monoesters and teichoic acids degraded more slowly than DNA-P, polyphosphates, and P lipids. Humic acids and organic acids from phytoplankton were precipitated from the NaOH extract by acidification and identified by P-31 NMR spectroscopy. The precipitated P was significantly more recalcitrant than the P compound groups remaining in solution, but does not constitute a major sink of P as it did not reach a stable concentration with depth, which indicates that it may eventually be degraded. Since P also precipitated from phytoplankton, the origin of humic-P can not be related solely to allochthonous P.

  • 11.
    Sponseller, Ryan A.
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Temnerud, Johan
    Bishop, Kevin
    Laudon, Hjalmar
    Patterns and drivers of riverine nitrogen (N) across alpine, subarctic, and boreal Sweden2014Ingår i: Biogeochemistry, ISSN 0168-2563, E-ISSN 1573-515X, Vol. 120, nr 1-3, s. 105-120Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Concentrations of nitrogen (N) in surface waters reflect the export of different organic and inorganic forms from terrestrial environments and the modification of these resources within aquatic habitats. We evaluated the relative influence of terrestrial ecosystem state factors, anthropogenic gradients, and aquatic habitat variables on patterns of N concentration in streams and rivers across Sweden. We analyzed data from 115 national monitoring stations distributed along a 1,300 km latitudinal gradient, draining catchments that differed by more than 10 A degrees C in mean annual temperature (MAT), and more than five orders of magnitude in area. Regional trends in total organic nitrogen (TON) and carbon:nitrogen (C:N) were closely linked to broad-scale gradients in state factors (e.g., MAT), reflecting the importance of long-term ecosystem development on terrestrial organic matter accrual and export. In contrast, trends in nitrate (NO3 (-)), the dominant form of inorganic N, were largely unrelated to state factors, but instead were closely connected to gradients related to anthropogenic inputs (e.g., agricultural cover). Despite large differences in drainage size and cover by lakes and wetlands among sites, these descriptors of the aquatic environment had little influence on spatial patterns of N chemistry. The temporal variability in N concentrations also differed between forms: inorganic N was strongly seasonal, with peaks during dormant periods that underscore biotic control over terrestrial losses of limiting resources. Organic N showed comparatively weaker seasonality, but summertime increases suggest temperature-driven patterns of soil TON production and export-temporal signals which were modified by variables that govern water residence time within catchments. Unique combinations of regional predictors reflect basic differences in the cycling of organic versus inorganic N and highlight variation in the sensitivity of these different N forms to environmental changes that directly alter inputs of resources, or indirectly modify terrestrial ecosystems through shifts in species composition, rates of forest productivity, soil development, and hydrologic routing.

  • 12. Tjerngren, Ida
    et al.
    Karlsson, Torbjörn
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Björn, Erik
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Skyllberg, U
    Potential Hg methylation and MeHg demethylation rates related to the nutrient status of different boreal wetlands2012Ingår i: Biogeochemistry, ISSN 0168-2563, E-ISSN 1573-515X, Vol. 108, nr 1-3, s. 335-350Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Despite methylmercury (MeHg) production in boreal wetlands being a research focus for decades, little is known about factors in control of methylation and demethylation rates and the effect of wetland type. This is the first study reporting potential Hg methylation (k m ) and MeHg demethylation rate constants (k d ) in boreal wetland soils. Seven wetlands situated in northern and southern Sweden were characterized by climatic parameters, nutrient status (e.g. type of vegetation, pH, C/N ratio, specific UV-absorption), iron and sulfur biogeochemistry. Based on nutrient status, the wetlands were divided into three groups; (I) three northern, nutrient poor fens, (II) a nutrient gradient ranging from an ombrotrophic bog to a fen with intermediate nutrient status, and (III) southern, more nutrient rich sites including two mesotrophic wetlands and one alder (Alnus) forest swamp. The k m /k d ratio in general followed %MeHg in soil and both measures were highest at the fen site with intermediate nutrient status. Northern nutrient poor fens and the ombrotrophic bog showed intermediate values of %MeHg and k m /k d . The two mesotrophic wetlands showed the lowest %MeHg and k m /k d , whereas the alder swamp had high k m and k d , resulting in an intermediate k m /k d and %MeHg. Molybdate addition experiments suggest that net MeHg production was mainly caused by the activity of sulfate reducing bacteria. A comparison with other studies, show that k m and %MeHg in boreal freshwater wetlands in general are higher than in other environments. Our results support previous suggestions that the highest MeHg net production in boreal landscapes is to be found in fens with an intermediate nutrient status.

  • 13.
    Vincent, Andrea G
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Schleucher, Jürgen
    Umeå universitet, Medicinska fakulteten, Institutionen för medicinsk kemi och biofysik.
    Gröbner, Gerhard
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Vestergren, Johan
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Persson, Per
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Jansson, Mats
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Giesler, Reiner
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Changes in organic phosphorus composition in boreal forest humus soils: the role of iron and aluminium2012Ingår i: Biogeochemistry, ISSN 0168-2563, E-ISSN 1573-515X, Vol. 108, nr 1-3, s. 485-499Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Organic phosphorus (P) is an important component of boreal forest humus soils, and its concentration has been found to be closely related to the concentration of iron (Fe) and aluminium (Al). We used solution and solid state 31P NMR spectroscopy on humus soils to characterize organic P along two groundwater recharge and discharge gradients in Fennoscandian boreal forest, which are also P sorption gradients due to differences in aluminium (Al) and iron (Fe) concentration in the humus. The composition of organic P changed sharply along the gradients. Phosphate diesters and their degradation products, as well as polyphosphates, were proportionally more abundant in low Al and Fe sites, whereas phosphate monoesters such as myo-, scyllo- and unknown inositol phosphates dominated in high Al and Fe soils. The concentration of inositol phosphates, but not that of diesters, was positively related to Al and Fe concentration in the humus soil. Overall, in high Al and Fe sites the composition of organic P seemed to be closely associated with stabilization processes, whereas in low Al and Fe sites it more closely reflected inputs of organic P, given the dominance of diesters which are generally assumed to constitute the bulk of organic P inputs to the soil. These gradients encompass the broad variation in soil properties detected in the wider Fennoscandian boreal forest landscape, as such our findings provide insight into the factors controlling P biogeochemistry in the region but should be of relevance to boreal forests elsewhere.

  • 14.
    Väisänen, Maria
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap. Arctic Centre, University of Lapland, Rovaniemi, Finland.
    Krab, Eveline J.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Dorrepaal, Ellen
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Carbon dynamics at frost-patterned tundra driven by long-term vegetation change rather than by short-term non-growing season warming2017Ingår i: Biogeochemistry, ISSN 0168-2563, E-ISSN 1573-515X, Vol. 136, nr 1, s. 103-117Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Frost-patterned grounds, such as mostly barren frost boils surrounded by denser vegetation, are typical habitat mosaics in tundra. Plant and microbial processes in these habitats may be susceptible to short-term warming outside the growing season, while the areal cover of barren frost boils has decreased during the past decades due to climate warming-induced shrub expansion. The relative importance of such short-term and long-term climate impacts on carbon (C) dynamics remains unknown. We measured ecosystem CO2 uptake and release (in the field), microbial respiration (in the laboratory), as well as microbial biomass N and soil extractable N in frost boils and the directly adjacent heath in late spring and late summer. These habitats had been experimentally warmed with insulating fleeces from late September until late May for three consecutive years, which allowed us to investigate the direct short-term effects of warming and longer-term, indirect climate effects via vegetation establishment into frost boils. Non-growing season warming increased C uptake at the frost boils in late spring and decreased it in late summer, while the timing and direction of responses was opposite for the heath. Experimental warming had no effects on microbial or ecosystem C release or soil N at either of the habitats. However, C cycling was manifold higher at the heath compared to the frost boils, likely because of a higher SOM stock in the soil. Short-term climate change can thus directly alter ecosystem C uptake at frost-patterned grounds but will most likely not affect microbial C release. We conclude that the C dynamics at frost-patterned grounds under a changing climate depend most strongly on the potential of vegetation to encroach into frost boils in the long-term.

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