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  • 1. Andresen, Louise C.
    et al.
    Jonasson, Sven
    Ström, Lena
    Michelsen, Anders
    Uptake of pulse injected nitrogen by soil microbes and mycorrhizal and non-mycorrhizal plants in a species-diverse subarctic heath ecosystem2008In: Plant and Soil, ISSN 0032-079X, E-ISSN 1573-5036, Vol. 313, no 1, p. 283-295Article in journal (Refereed)
    Abstract [en]

    15N labeled ammonium, glycine or glutamic acid was injected into subarctic heath soil in situ, with the purpose of investigating how the nitrogen added in these pulses was subsequently utilized and cycled in the ecosystem. We analyzed the acquisition of 15N label in mycorrhizal and non-mycorrhizal plants and in soil microorganisms, in order to reveal probable differences in acquisition patterns between the two functional plant types and between plants and soil microorganisms. Three weeks after the label addition, with the 15N-forms added with same amount of nitrogen per square meter, we analyzed the 15N-enrichment in total soil, in soil K2SO4 (0.5 M) extracts and in the microbial biomass after vacuum-incubation of soil in chloroform and subsequent K2SO4 extraction. Furthermore the 15N-enrichment was analyzed in current years leaves of the dominant plant species sampled three, five and 21 days after label addition. The soil microorganisms had very high 15N recovery from all the N sources compared to plants. Microorganisms incorporated most 15N from the glutamic acid source, intermediate amounts of 15N from the glycine source and least 15N from the NH4+ source. In contrast to microorganisms, all ten investigated plant species generally acquired more 15N label from the NH4+ source than from the amino acid sources. Non-mycorrhizal plant species showed higher concentration of 15N label than mycorrhizal plant species 3 days after labeling, while 21 days after labeling their acquisition of 15N label from amino acid injection was lower than, and the acquisition of 15N label from NH4 injection was similar to that of the mycorrhizal species. We conclude that the soil microorganisms were more efficient than plants in acquiring pulses of nutrients which, under natural conditions, occur after e.g. freeze–thaw and dry–rewet events, although of smaller size. It also appears that the mycorrhizal plants in the short term may be less efficient than non-mycorrhizal plants in nitrogen acquisition, but in a longer term show larger nitrogen acquisition than non-mycorrhizal plants. However, the differences in 15N uptake patterns may also be due to differences in leaf longevity and woodiness between plant functional groups.

  • 2. Bjork, Robert G.
    et al.
    Klemedtsson, Leif
    Molau, Ulf
    Harndorf, Jan
    Odman, Anja
    Giesler, Reiner
    Linkages between N turnover and plant community structure in a tundra landscape2007In: Plant and Soil, ISSN 0032-079X, E-ISSN 1573-5036, Vol. 294, no 1-2, p. 247-261Article in journal (Refereed)
    Abstract [en]

    The spatial distribution of organic soil nitrogen (N) in alpine tundra was studied along a natural environmental gradient, covering five plant communities, at the Latnjajaure Field Station, northern Swedish Lapland. The five communities (mesic meadow, meadow snowbed, dry heath, mesic heath, and heath snowbed) are the dominant types in this region and are differentiated by soil pH. Net N mineralization, net ammonification, and net nitrification were measured using 40-day laboratory incubations based on extractable NH4+ and NO3-. Nitrification enzyme activity (NEA), denitrification enzyme activity (DEA), amino acid concentrations, and microbial respiration were measured for soils from each plant community. The results show that net N mineralization rates were more than three times higher in the meadow ecosystems (mesic meadow 0.7 mu g N g(-1) OM day(-1) and meadow snowbed 0.6 mu g N g(-1) OM day(-1)) than the heath ecosystems (dry heath 0.2 mu g N g(-1) OM day(-1), mesic heath 0.1 mu g N g(-1) OM day(-1) and heath snowbed 0.2 mu g N g(-1) OM day(-1)). The net N mineralization rates were negatively correlated to organic soil C/N ratio (r = -0.652, P < 0.001) and positively correlated to soil pH (r = 0.701, P < 0.001). Net nitrification, inorganic N concentrations, and NEA rates also differed between plant communities; the values for the mesic meadow were at least four times higher than the other plant communities, and the snowbeds formed an intermediate group. Moreover, the results show a different pattern of distribution for individual amino acids across the plant communities, with snowbeds tending to have the highest amino acid N concentrations. The differences between plant communities along this natural gradient also illustrate variations between the dominant mycorrhizal associations in facilitating N capture by the characteristic functional groups of plants.

  • 3. Faubert, Patrick
    et al.
    Tiiva, Päivi
    Michelsen, Anders
    Rinnan, Åsmund
    Ro-Poulsen, Helge
    Rinnan, Riikka
    The shift in plant species composition in a subarctic mountain birch forest floor due to climate change would modify the biogenic volatile organic compound emission profile2012In: Plant and Soil, ISSN 0032-079X, E-ISSN 1573-5036, Vol. 352, no 1, p. 199-215Article in journal (Refereed)
    Abstract [en]

    Mountain birch forests dominate in the Subarctic but little is known of their non-methane biogenic volatile organic compound (BVOC) emissions. The dwarf shrubs Empetrum hermaphroditum, Vaccinium myrtillus and Vaccinium uliginosum co-dominate in the forest floors of these forests. The abundance of these three dwarf shrubs relative to each other could be affected by climate warming expected to increase nutrient availability by accelerating litter decomposition and nutrient mineralization. We 1) compared the BVOC emission profiles of vegetation covers dominated by E. hermaphroditum and V. myrtillus plus V. uliginosum in a subarctic mountain birch forest floor, 2) distinguished the BVOCs emitted from plants and soil and 3) measured how the BVOC emissions from the different vegetation covers differed under darkness.

  • 4. Finderup Nielsen, Tora
    et al.
    Ravn, Nynne Rand
    Michelsen, Anders
    Increased CO2 efflux due to long-term experimental summer warming and litter input in subarctic tundra – CO2 fluxes at snowmelt, in growing season, fall and winter2019In: Plant and Soil, ISSN 0032-079X, E-ISSN 1573-5036, Vol. 444, no 1, p. 365-382Article in journal (Refereed)
    Abstract [en]

    Soils of northern latitude tundra ecosystems have accumulated large amounts of carbon that might be released as CO2 when temperature rises and the tree-line moves north. We aim to investigate the potential CO2 flux changes at a subarctic tundra heath under changing climate. We measured daytime ecosystem respiration and photosynthesis at a subarctic heath over a full year under ambient conditions and in factorial long-term (13 years) increased summer temperature and leaf litter addition plots, and in additional short-term (2 years) summer warming plots. Under ambient conditions the ecosystem was a daytime sink of CO2 in the five warmest months, but a net daytime source in the cold season. Thirteen years of summer warming by 1 °C at soil surface increased CO2 emissions, as daytime respiration increased by 37% and photosynthesis by 29% over the year. Short-term warming likewise increased fluxes. Litter addition also increased the emission of CO2 as ecosystem respiration rose by 21% but photosynthesis remained unchanged. Both warming and litter addition significantly enhanced the amount of green biomass. This study suggests that in a changed climate subarctic ecosystems will act as a positive feedback source of atmospheric CO2. It shows the significance of CO2 fluxes outside the growing season and demonstrates a cold-season long- but not short-term legacy effect of increased summer warming on CO2 emission.

  • 5. Friggens, Nina L.
    et al.
    Aspray, Thomas J.
    Parker, Thomas C.
    Subke, Jens-Arne
    Wookey, Philip A.
    Spatial patterns in soil organic matter dynamics are shaped by mycorrhizosphere interactions in a treeline forest2019In: Plant and Soil, ISSN 0032-079X, E-ISSN 1573-5036Article in journal (Refereed)
    Abstract [en]

    In the Swedish sub-Arctic, mountain birch (Betula pubescens ssp. czerepanovii) forests mediate rapid soil C cycling relative to adjacent tundra heaths, but little is known about the role of individual trees within forests. Here we investigate the spatial extent over which trees influence soil processes. We measured respiration, soil C stocks, root and mycorrhizal productivity and fungi:bacteria ratios at fine spatial scales along 3 m transects extending radially from mountain birch trees in a sub-Arctic ecotone forest. Root and mycorrhizal productivity was quantified using in-growth techniques and fungi:bacteria ratios were determined by qPCR. Neither respiration, nor root and mycorrhizal production, varied along transects. Fungi:bacteria ratios, soil organic C stocks and standing litter declined with increasing distance from trees. As 3 m is half the average size of forest gaps, these findings suggest that forest soil environments are efficiently explored by roots and associated mycorrhizal networks of B. pubescens. Individual trees exert influence substantially away from their base, creating more uniform distributions of root, mycorrhizal and bacterial activity than expected. However, overall rates of soil C accumulation do vary with distance from trees, with potential implications for spatio-temporal soil organic matter dynamics and net ecosystem C sequestration.

  • 6. Gavazov, Konstantin S.
    et al.
    Soudzilovskaia, Nadejda A.
    van Logtestijn, Richard S. P.
    Braster, Martin
    Cornelissen, Johannes H. C.
    Isotopic analysis of cyanobacterial nitrogen fixation associated with subarctic lichen and bryophyte species2010In: Plant and Soil, ISSN 0032-079X, E-ISSN 1573-5036, Vol. 333, no 1, p. 507-517Article in journal (Refereed)
    Abstract [en]

    Dinitrogen fixation by cyanobacteria is of particular importance for the nutrient economy of cold biomes, constituting the main pathway for new N supplies to tundra ecosystems. It is prevalent in cyanobacterial colonies on bryophytes and in obligate associations within cyanolichens. Recent studies, applying interspecific variation in plant functional traits to upscale species effects on ecosystems, have all but neglected cryptogams and their association with cyanobacteria. Here we looked for species-specific patterns that determine cryptogam-mediated rates of N2 fixation in the Subarctic. We hypothesised a contrast in N2 fixation rates (1) between the structurally and physiologically different lichens and bryophytes, and (2) within bryophytes based on their respective plant functional types. Throughout the survey we supplied 15N-labelled N2 gas to quantify fixation rates for monospecific moss, liverwort and lichen turfs. We sampled fifteen species in a design that captures spatial and temporal variations during the growing season in Abisko region, Sweden. We measured N2 fixation potential of each turf in a common environment and in its field sampling site, in order to embrace both comparativeness and realism. Cyanolichens and bryophytes differed significantly in their cyanobacterial N2 fixation capacity, which was not driven by microhabitat characteristics, but rather by morphology and physiology. Cyanolichens were much more prominent fixers than bryophytes per unit dry weight, but not per unit area due to their low specific thallus weight. Mosses did not exhibit consistent differences in N2 fixation rates across species and functional types. Liverworts did not fix detectable amounts of N2. Despite the very high rates of N2 fixation associated with cyanolichens, large cover of mosses per unit area at the landscape scale compensates for their lower fixation rates, thereby probably making them the primary regional atmospheric nitrogen sink.

  • 7.
    George, T. S.
    et al.
    James Hutton Inst, Dundee DD2 5DA, Scotland.
    Giles, C. D.
    James Hutton Inst, Dundee DD2 5DA, Scotland.
    Menezes-Blackburn, D.
    Univ Lancaster, Lancaster Environm Ctr, Lancaster LA1 4YQ, England.
    Condron, L. M.
    Lincoln Univ, Christchurch 7647, New Zealand.
    Gama-Rodrigues, A. C.
    Univ Estadual Norte Flumninense Darcy Ribeiro, UENF, Lab Solos, Av Alberto Lamego 2000, Campos Dos Goytacazes, RJ, Brazil.
    Jaisi, D.
    Univ Delaware, Plant & Soil Sci, 160 Townsend Hall, Newark, DE 19716 USA.
    Lang, F.
    Univ Freiburg, Chair Soil Ecol, Fac Environm & Nat Resources, Bertoldstr 17, D-79098 Freiburg, Germany.
    Neal, A. L.
    Rothamsted Res, Harpenden AL5 2JQ, Herts, England.
    Stutter, M. , I
    Almeida, D. S.
    Sao Paulo State Univ, UNESP, Dept Crop Sci, Coll Agr Sci, 1780 Jose Barbosa de Barros St, Botucatu, SP, Brazil.
    Bol, R.
    Forschungszentrum Julich, Inst Bio & Geosci IBG Agrosphere 3, D-52425 Julich, Germany.
    Cabugao, K. G.
    Oak Ridge Natl Lab, POB 2008, Oak Ridge, TN 37831 USA.
    Celi, L.
    Univ Turin, Soil Biogeochem, DISAFA, Largo Braccini 2, I-10095 Turin, Italy.
    Cotner, J. B.
    Univ Minnesota, 1479 Gortner Ave St Paul, Twin, MN 55108 USA.
    Feng, G.
    China Agr Univ, Beijing, Peoples R China.
    Goll, D. S.
    IPSL LSCE CEA CNRS UVSQ Saclay, Lab Sci Climat & Environm, Gif Sur Yvette, France.
    Hallama, M.
    Univ Hohenheim, Inst Soil Sci, Emil Wolff Str 27, D-70599 Stuttgart, Germany.
    Krueger, J.
    Univ Freiburg, Chair Soil Ecol, Fac Environm & Nat Resources, Bertoldstr 17, D-79098 Freiburg, Germany.
    Plassard, C.
    INRA, UMR ECO & SOLS, Montpellier, France.
    Rosling, Anna
    Uppsala universitet, Evolutionsbiologi.
    Darch, T.
    Rothamsted Res, Okehampton EX20 2SB, Devon, England.
    Fraser, T.
    Univ Reading, Sch Agr Policy & Dev, Ctr Agrienvironm Res, POB 237, Reading RG6 6AR, Berks, England.
    Giesler, R.
    Umea Univ, Dept Ecol & Environm Sci, Climate Impacts Res Ctr, S-98107 Abisko, Sweden.
    Richardson, A. E.
    CSIRO Agr & Food, Canberra, ACT, Australia.
    Tamburini, F.
    ETH, D USYS, Tannenstr 1, CH-8092 Zurich, Switzerland.
    Shand, C. A.
    James Hutton Inst, Aberdeen AB15 8QH, Scotland.
    Lumsdon, D. G.
    James Hutton Inst, Aberdeen AB15 8QH, Scotland.
    Zhang, H.
    Univ Lancaster, Lancaster Environm Ctr, Lancaster LA1 4YQ, England.
    Blackwell, M. S. A.
    Rothamsted Res, Okehampton EX20 2SB, Devon, England.
    Wearing, C.
    Univ Lancaster, Lancaster Environm Ctr, Lancaster LA1 4YQ, England.
    Mezeli, M. M.
    James Hutton Inst, Dundee DD2 5DA, Scotland.
    Almas, A. R.
    Norwegian Univ Life Sci, Dept Environm Sci, Post Box 5003, N-1432 As, Norway.
    Audette, Y.
    Univ Guelph, 50 Stone Rd East, Guelph, ON N1G 2W1, Canada.
    Bertrand, I
    INRA, UMR ECO & SOLS, Montpellier, France.
    Beyhaut, E.
    Natl Inst Agr Res Uruguay, Montevideo, Uruguay.
    Boitt, G.
    Lincoln Univ, Christchurch 7647, New Zealand.
    Bradshaw, N.
    Univ Sheffield, Dept Chem & Biol Engn, Mappin St, Sheffield S1 3JD, S Yorkshire, England.
    Brearley, C. A.
    Univ East Anglia, Sch Biol Sci, Norwich Res Pk, Norwich NR4 7TJ, Norfolk, England.
    Bruulsema, T. W.
    Int Plant Nutr Inst, 18 Maplewood Dr, Guelph, ON N1G 1L8, Canada.
    Ciais, P.
    IPSL LSCE CEA CNRS UVSQ Saclay, Lab Sci Climat & Environm, Gif Sur Yvette, France.
    Cozzolino, V
    Univ Napoli Federico II, Ctr Interdipartimentale Ric Risonanza Magnet Nucl, Via Univ 100, I-80055 Portici, Italy.
    Duran, P. C.
    Univ La Frontera, Temuco, Chile.
    Mora, M. L.
    Univ Napoli Federico II, Ctr Interdipartimentale Ric Risonanza Magnet Nucl, Via Univ 100, I-80055 Portici, Italy.
    de Menezes, A. B.
    Univ Salford, Sch Environm & Life Sci, Manchester M5 4WT, The Crescent, England.
    Dodd, R. J.
    Bangor Univ, Sch Environm Nat Resources & Geog, Bangor LL57 2UW, Gwynedd, Wales.
    Dunfield, K.
    Univ Guelph, 50 Stone Rd East, Guelph, ON N1G 2W1, Canada.
    Engl, C.
    Queens Univ Belfast, Med Biol Ctr, Sch Biol Sci, 97 Lisburn Rd, Belfast BT9 7BL, Antrim, North Ireland;Queens Univ Belfast, Med Biol Ctr, Inst Global Food Secur, 97 Lisburn Rd, Belfast BT9 7BL, Antrim, North Ireland.
    Frazao, J. J.
    Univ Sao Paulo, CENA, Ave Centenario 303, BR-13416000 Piracicaba, SP, Brazil.
    Garland, G.
    ETH, D USYS, Tannenstr 1, CH-8092 Zurich, Switzerland.
    Jimenez, J. L. Gonzalez
    Johnstown Castle Co, TEAGASC, Environm Res Ctr, Wexford, Ireland.
    Graca, J.
    Johnstown Castle Co, TEAGASC, Environm Res Ctr, Wexford, Ireland.
    Granger, S. J.
    Rothamsted Res, Okehampton EX20 2SB, Devon, England.
    Harrison, A. F.
    Ctr Ecol & Hydrol, Lib Ave, Lancaster LA1 4AP, England.
    Heuck, C.
    Univ Bayreuth, Bayreuth Ctr Ecol & Environm Res BayCEER, Dept Soil Biogeochem, Dr Hans Frisch Str 1-3, D-95448 Bayreuth, Germany.
    Hou, E. Q.
    Chinese Acad Sci, South China Bot Garden, Guangdong Prov Key Lab Appl Bot, 723 Xingke Rd, Guangzhou 510650, Guangdong, Peoples R China.
    Johnes, P. J.
    Univ Bristol, Sch Geog Sci, Univ Rd, Bristol BS8 1SS, Avon, England;Univ Bristol, Sch Chem, Univ Rd, Bristol BS8 1SS, Avon, England.
    Kaiser, K.
    Martin Luther Univ Halle Wittenberg, Soil Sci & Soil Protect, von Seckendorff Pl 3, D-06120 Halle, Saale, Germany.
    Kjaer, H. A.
    Univ Copenhagen, Ctr Ice & Climate, Niels Bohr Inst, Copenhagen, Denmark.
    Klumpp, E.
    Uppsala universitet, Evolutionsbiologi.
    Lamb, A. L.
    British Geol Survey, NERC Isotope Geosci Facil, Nottingham NG12 5GG, England.
    Macintosh, K. A.
    Queens Univ Belfast, Med Biol Ctr, Sch Biol Sci, 97 Lisburn Rd, Belfast BT9 7BL, Antrim, North Ireland;Queens Univ Belfast, Med Biol Ctr, Inst Global Food Secur, 97 Lisburn Rd, Belfast BT9 7BL, Antrim, North Ireland.
    Mackay, E. B.
    Ctr Ecol & Hydrol, Lib Ave, Lancaster LA1 4AP, England.
    McGrath, J.
    Queens Univ Belfast, Med Biol Ctr, Sch Biol Sci, 97 Lisburn Rd, Belfast BT9 7BL, Antrim, North Ireland;Queens Univ Belfast, Med Biol Ctr, Inst Global Food Secur, 97 Lisburn Rd, Belfast BT9 7BL, Antrim, North Ireland.
    McIntyre, C.
    Univ Bristol, Sch Geog Sci, Univ Rd, Bristol BS8 1SS, Avon, England;Univ Bristol, Sch Chem, Univ Rd, Bristol BS8 1SS, Avon, England.
    McLaren, T.
    ETH, D USYS, Tannenstr 1, CH-8092 Zurich, Switzerland.
    Meszaros, E.
    ETH, D USYS, Tannenstr 1, CH-8092 Zurich, Switzerland.
    Missong, A.
    Forschungszentrum Julich, Inst Bio & Geosci IBG Agrosphere 3, D-52425 Julich, Germany.
    Mooshammer, M.
    Univ Vienna, Dept Microbiol & Ecosyst Sci, Althanstr 14, A-1090 Vienna, Austria.
    Negron, C. P.
    Univ La Frontera, Temuco, Chile.
    Nelson, L. A.
    Univ Northern British Columbia, 3333 Univ Way, Prince George, BC V2N 4Z9, Canada.
    Pfahler, V
    Rothamsted Res, Okehampton EX20 2SB, Devon, England.
    Poblete-Grant, P.
    Univ La Frontera, Temuco, Chile.
    Randall, M.
    Brigham Young Univ, Provo, UT 84602 USA.
    Seguel, A.
    Univ La Frontera, Temuco, Chile.
    Seth, K.
    Lincoln Univ, Christchurch 7647, New Zealand.
    Smith, A. C.
    British Geol Survey, NERC Isotope Geosci Facil, Nottingham NG12 5GG, England.
    Smits, M. M.
    Hasselt Univ, Ctr Environm Sci, Bldg D,Agoralaan, B-3590 Diepenbeek, Belgium.
    Sobarzo, J. A.
    Univ La Frontera, Temuco, Chile.
    Spohn, M.
    Univ Bayreuth, Bayreuth Ctr Ecol & Environm Res BayCEER, Dept Soil Biogeochem, Dr Hans Frisch Str 1-3, D-95448 Bayreuth, Germany.
    Tawaraya, K.
    Yamagata Univ, Tsuruoka, Yamagata 9978555, Japan.
    Tibbett, M.
    Univ Reading, Sch Agr Policy & Dev, Ctr Agrienvironm Res, POB 237, Reading RG6 6AR, Berks, England.
    Voroney, P.
    Univ Guelph, 50 Stone Rd East, Guelph, ON N1G 2W1, Canada.
    Wallander, H.
    Lund Univ, Dept Biol, Biol Bldg Solvegatan 35, S-22362 Lund, Sweden.
    Wang, L.
    Forschungszentrum Julich, Inst Bio & Geosci IBG Agrosphere 3, D-52425 Julich, Germany.
    Wasaki, J.
    Hiroshima Univ, Grad Sch Biosphere Sci, Assessment Microbial Environm, Hiroshima, Japan.
    Haygarth, P. M.
    Univ Lancaster, Lancaster Environm Ctr, Lancaster LA1 4YQ, England.
    Organic phosphorus in the terrestrial environment: a perspective on the state of the art and future priorities2018In: Plant and Soil, ISSN 0032-079X, E-ISSN 1573-5036, Vol. 427, no 1-2, p. 191-208Article in journal (Refereed)
    Abstract [en]

    The dynamics of phosphorus (P) in the environment is important for regulating nutrient cycles in natural and managed ecosystems and an integral part in assessing biological resilience against environmental change. Organic P (P-o) compounds play key roles in biological and ecosystems function in the terrestrial environment being critical to cell function, growth and reproduction. We asked a group of experts to consider the global issues associated with P-o in the terrestrial environment, methodological strengths and weaknesses, benefits to be gained from understanding the P-o cycle, and to set priorities for P-o research. We identified seven key opportunities for P-o research including: the need for integrated, quality controlled and functionally based methodologies; assessment of stoichiometry with other elements in organic matter; understanding the dynamics of P-o in natural and managed systems; the role of microorganisms in controlling P-o cycles; the implications of nanoparticles in the environment and the need for better modelling and communication of the research. Each priority is discussed and a statement of intent for the P-o research community is made that highlights there are key contributions to be made toward understanding biogeochemical cycles, dynamics and function of natural ecosystems and the management of agricultural systems.

  • 8. Krab, Eveline J.
    et al.
    Cornelissen, Johannes H. C.
    Lang, Simone I.
    van Logtestijn, Richard S. P.
    Amino acid uptake among wide-ranging moss species may contribute to their strong position in higher-latitude ecosystems2008In: Plant and Soil, ISSN 0032-079X, E-ISSN 1573-5036, Vol. 304, no 1, p. 199-208Article in journal (Refereed)
    Abstract [en]

    Plants that can take up amino acids directly from the soil solution may have a competitive advantage in ecosystems where inorganic nitrogen sources are scarce. We hypothesized that diverse mosses in cold, N-stressed ecosystems share this ability. We experimentally tested 11 sub-arctic Swedish moss species of wide-ranging taxa and growth form for their ability to take up double labelled (15N and 13C) glycine and aspartic acid in a laboratory setup as well as in a realistic field setting. All species were able to take up amino acids injected into the soil solution to some extent, although field uptake was marginal to absent for the endohydric Polytrichum commune. The 11 moss species on average took up 36 ± 5% of the injected glycine and 18 ± 2% of the aspartic acid in the lab experiment. Field uptake of both glycine (24 ± 5%) and aspartic acid (10 ± 2%) was lower than in the lab. Overall differences in uptake amongst species appeared to be positively associated with habitat wetness and/or turf density among different Sphagnum species and among non-Sphagnum species, respectively. Species from habitats of lower inorganic N availability, as indicated tentatively by lower tissue N concentrations, showed relatively strong amino acid uptake, but this was only significant for the field uptake among non-Sphagnum mosses. Further experiments are needed to test for consistent differences in amino acid uptake capacity among species and functional groups as determined by their functional traits, and to test how the affinity of cold-biome mosses for amino acids compares to that for ammonium or nitrate. Still, our results support the view that widespread moss species in cold, N-stressed ecosystems may derive a significant proportion of their nitrogen demand from free amino acids. This might give them a competitive advantage over plants that depend strongly on inorganic N sources.

  • 9.
    Lett, Signe
    et al.
    Umeå universitet, Institutionen för ekologi, miljö och geovetenskap.
    Michelsen, Anders
    Department of Biology, Terrestrial Ecology Section, University of Copenhagen, Øster Farimagsgade 2D, Copenhagen, DK-1353 K, Denmark.
    Seasonal variation in nitrogen fixation and effects of climate change in a subarctic heath2014In: Plant and Soil, ISSN 0032-079X, E-ISSN 1573-5036, Vol. 379, no 1-2, p. 193-204Article in journal (Refereed)
    Abstract [en]

    Nitrogen fixation associated with cryptogams is potentially very important in arctic and subarctic terrestrial ecosystems, as it is a source of new nitrogen (N) into these highly N limited systems. Moss-, lichen- and legume-associated N-2 fixation was studied with high frequency (every second week) during spring, summer, autumn and early winter to uncover the seasonal variation in input of atmospheric N-2 to a subarctic heath with an altered climate. We estimated N-2 fixation from ethylene production by acetylene reduction assay in situ in a field experiment with the treatments: long- vs. short-term summer warming using plastic tents and litter addition (simulating expansion of the birch forest). N-2 fixation activity was measured from late April to mid November and 33 % of all N-2 was fixed outside the vascular plant growing season (Jun-Aug). This substantial amount underlines the importance of N-2 fixation in the cold period. Warming increased N-2 fixation two- to fivefold during late spring. However, long-term summer warming tended to decrease N-2 fixation outside the treatment (tents present) period. Litter alone did not alter N-2 fixation but in combination with warming N-2 fixation increased, probably because N-2 fixation became phosphorus limited under higher temperatures, which was alleviated by the P supply from the litter. In subarctic heath, the current N-2 fixation period extends far beyond the vascular plant growing season. Climate warming and indirect effects such as vegetation changes affect the process of N-2 fixation in different directions and thereby complicate predictions of future N cycling.

  • 10. Ravn, Nynne Marie Rand
    et al.
    Elberling, Bo
    Michelsen, Anders
    The fate of 13C15N labelled glycine in permafrost and surface soil at simulated thaw in mesocosms from high arctic and subarctic ecosystems2017In: Plant and Soil, ISSN 0032-079X, E-ISSN 1573-5036, Vol. 419, no 1, p. 201-218Article in journal (Refereed)
    Abstract [en]

    Nutrient distribution and carbon fluxes upon spring thaw are compared in mesocosms from high arctic and subarctic ecosystems dominated by Cassiope tetragona or Salix hastata/Salix arctica, in order to evaluate the possibility of plant and microbial utilization of an organic compound in thawing permafrost and surface soil.

  • 11. Schwieger, Sarah
    et al.
    Kreyling, Jürgen
    Milbau, Ann
    Blume-Werry, Gesche
    Autumnal warming does not change root phenology in two contrasting vegetation types of subarctic tundra2017In: Plant and Soil, ISSN 0032-079X, E-ISSN 1573-5036Article in journal (Refereed)
    Abstract [en]

    Root phenology is important in controlling carbon and nutrient fluxes in terrestrial ecosystems, yet, remains largely unexplored, especially in the Arctic. We compared below- and aboveground phenology and ending of the growing season in two contrasting vegetation types of subarctic tundra: heath and meadow, and their response to experimental warming in autumn.

  • 12.
    Sundqvist, Maja K.
    et al.
    Umeå universitet, Institutionen för ekologi, miljö och geovetenskap.
    Wardle, David A.
    Department of Forest Ecology and Management, SLU, Umeå, Sweden.
    Vincent, Andrea
    Umeå universitet, Institutionen för ekologi, miljö och geovetenskap.
    Giesler, Reiner
    Umeå universitet, Institutionen för ekologi, miljö och geovetenskap.
    Contrasting nitrogen and phosphorus dynamics across an elevational gradient for subarctic tundra heath and meadow vegetation2014In: Plant and Soil, ISSN 0032-079X, E-ISSN 1573-5036, Vol. 383, no 1-2, p. 387-399Article in journal (Refereed)
    Abstract [en]

    This study explores soil nutrient cycling processes and microbial properties for two contrasting vegetation types along an elevational gradient in subarctic tundra to improve our understanding of how temperature influences nutrient availability in an ecosystem predicted to be sensitive to global warming. We measured total amino acid (Amino-N), mineral nitrogen (N) and phosphorus (P) concentrations, in situ net N and P mineralization, net Amino-N consumption, and microbial biomass C, N and P in both heath and meadow soils across an elevational gradient near Abisko, Sweden. For the meadow, NH4 (+) concentrations and net N mineralization were highest at high elevations and microbial properties showed variable responses; these variables were largely unresponsive to elevation for the heath. Amino-N concentrations sometimes showed a tendency to increase with elevation and net Amino-N consumption was often unresponsive to elevation. Overall, PO4-P concentrations decreased with elevation and net P immobilization mostly occurred at lower elevations; these effects were strongest for the heath. Our results reveal that elevation-associated changes in temperature can have contrasting effects on the cycling of N and P in subarctic soils, and that the strength and direction of these effects depend strongly on dominant vegetation type.

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