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  • 1.
    Arwidsson, Zandra
    et al.
    Örebro University, School of Science & Technology, Örebro, Sweden; SAKAB AB, Kumla, Sweden.
    Johansson, Emma M.
    Örebro University, School of Science and Technology.
    von Kronhelm, Thomas
    SAKAB AB, Kumla Sweden.
    Allard, Bert
    Örebro University, School of Science and Technology.
    van Hees, Patrick A. W.
    Örebro University, School of Science and Technology. Eurofins Environment Sweden AB, Lidköping, Sweden.
    Remediation of Metal Contaminated Soil by Organic Metabolites from Fungi I—Production of Organic Acids2008In: Water, Air and Soil Pollution, ISSN 0049-6979, E-ISSN 1573-2932, Vol. 205, no 1-4, p. 215-226Article in journal (Refereed)
    Abstract [en]

    Investigations were made on living strains offungi in a bioremediation process of three metal (lead)contaminated soils. Three saprotrophic fungi (Aspergillusniger, Penicillium bilaiae, and a Penicillium sp.) wereexposed to poor and rich nutrient conditions (no carbonavailability or 0.11 M D-glucose, respectively) andmetal stress (25 μM lead or contaminated soils) for5 days. Exudation of low molecular weight organicacids was investigated as a response to the metal andnutrient conditions. Main organic acids identified wereoxalic acid (A. niger) and citric acid (P. bilaiae).Exudation rates of oxalate decreased in response tolead exposure, while exudation rates of citrate were lessaffected. Total production under poor nutrient conditionswas low, except for A. niger, for which nosignificant difference was found between the poor andrich control. Maximum exudation rates were 20 μmoloxalic acid g^−1 biomass h^−1 (A. niger) and 20 μmolcitric acid g^−1 biomass h^−1 (P. bilaiae), in the presenceof the contaminated soil, but only 5 μmol organic acidsg^−1 biomass h^−1, in total, for the Penicillium sp. Therewas a significant mobilization of metals from the soilsin the carbon rich treatments and maximum release ofPb was 12% from the soils after 5 days. This was notsufficient to bring down the remaining concentration tothe target level 300 mg kg^−1 from initial levels of 3,800,1,600, and 370 mg kg^−1in the three soils. Target levelsfor Ni, Zn, and Cu, were 120, 500, and 200 mg kg^−1,respectively, and were prior to the bioremediationalready below these concentrations (except for Cu Soil1). However, maximum release of Ni, Zn, and Cu was28%, 35%, and 90%, respectively. The release of metalswas related to the production of chelating acids, but alsoto the pH-decrease. This illustrates the potential to usefungi exudates in bioremediation of contaminated soil.Nonetheless, the extent of the generation of organicacids is depending on several processes and mechanismsthat need to be further investigated.

  • 2.
    Fransson, Petra M. A.
    et al.
    Department of Forest Mycology and Pathology, Swedish University of Agricultural Sciences, Ulltuna, Sweden.
    Johansson, Emma M.
    Örebro University, School of Science and Technology.
    Elevated CO2 and nitrogen influence exudation of soluble organic compounds by ectomycorrhizal root systems2010In: FEMS Microbiology Ecology, ISSN 0168-6496, E-ISSN 1574-6941, Vol. 71, no 2, p. 186-196Article in journal (Refereed)
    Abstract [en]

    Root and mycelial exudation contributes significantly to soil carbon (C) fluxes, and is likely to be altered by an elevated atmospheric carbon dioxide (CO2) concentration and nitrogen (N) deposition. We quantified soluble, low-molecular-weight (LMW) organic compounds exuded by ectomycorrhizal plants grown under ambient (360 p.p.m.) or elevated (710 p.p.m.) CO2 concentrations and with different N sources. Scots pine seedlings, colonized by one of five different ectomycorrhizal or nonmycorrhizal fungi, received 70 μM N, either as NH4Cl or as alanine, in a liquid growth medium. Exudation of LMW organic acids (LMWOAs), dissolved monosaccharides and total dissolved organic carbon were determined. Both N and CO2 had a significant impact on exudation, especially of LMWOAs. Exudation of LMWOAs was negatively affected by inorganic N and decreased by 30–85% compared with the organic N treatment, irrespective of the CO2 treatment. Elevated CO2 had a clear impact on the production of individual LMWOAs, although with very contrasting effects depending on which N source was supplied.

  • 3.
    Johansson, Emma M.
    Örebro University, School of Science and Technology.
    Impact of root and mycorrhizal exudation on soil carbon fluxes: influence of elevated CO2 and metals2009Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The thesis concerns the behavior of root and ectomycorrhizal (ECM) exudates. In particular, the dynamics of soluble low molecular weight (LMW) organic compounds such as organic acids (LMWOAs), amino acids, monosaccharides, and dissolved organic carbon (DOC) have been studied. Our knowledge of exudation rates for tree roots and especially associated ECM is limited, and also factors influencing exudation rates. Two environmental factors, metal stress and elevated atmospheric CO2 level, have been investigated. Both are of great environmental concern, but function in different ways (detoxification and C allocation) and may be highly important for the C flux caused by root/ECM exudation. The project has been carried out with mycorrhizal and nonmycorrhizal (NM) Scots pine seedlings, or saprotrophic fungi, under both sterile and non-sterile (soil) conditions. Analytical determination of exudates and calculation of exudation rates have been major tools for assessment. Assessing the possibility of using naturally occurring chelating agents (e.g. citrate and oxalate) for bioremediation of metals contaminated soils and development and validation of analytical techniques have been additional foci. The results show that from soil-living fungi and ectomycorrhizal roots exudation rates of especially LMWOAs increase significantly at Cd and Pb stress (1-100 μM), while As (as arsenate) and mixtures of metals with As have little effect. The impact of ECM fungi is large and much higher exudation rates are found when the symbionts are present both for controls and metal treatments compared to NM plants. In soil systems there was a significant mobilization of metals from soils under presence of saprotrophic fungi. Both N as well as elevated CO2 (700 ppm) causes sizable increases in exudation rates, independent of biomass, and is a finding that suggests that the availability of easily degradable carbon in soil raises, which may be highly important for the carbon flux in soil. Mycorrhizal seedlings (10 months old) increased total soil respiration ~50% compared to controls without plants in non-sterile soil systems. Key words: amino acids, 13C, carbon cycle, ectomycorrhiza, elevated CO2, exudation, DOC, LMWOA, metal stress, monosaccharides, oxalate, Pinus sylvestris, saprotrophic fungi, soil respiration

    List of papers
    1. Quantitative analysis of exudates from soil-living basidiomycetes in pure culture as a response to lead, cadmium and arsenic stress
    Open this publication in new window or tab >>Quantitative analysis of exudates from soil-living basidiomycetes in pure culture as a response to lead, cadmium and arsenic stress
    2008 (English)In: Soil Biology and Biochemistry, ISSN 0038-0717, E-ISSN 1879-3428, Vol. 40, no 9, p. 2225-2236Article in journal (Refereed) Published
    Abstract [en]

    Six different ectomycorrhizal fungi (Hebeloma velutipes, Piloderma byssinum, Paxillus involutus, Rhizopogonroseolus, Suillus bovinus and Suillus variegatus) and two saprotrophic fungi (Hypholoma fasciculare andHypholoma capnoides) were exposed to metal stress induced by Pb, Cd and As. After pre-growth ina nutrient solution in Petri dishes, metal exposure was performed either in a nutrient rich solution or ina nutrient poor solution for seven days. The fungi were exposed to two different metal concentrations,low and high (Pb: 10 þ 100 mM; Cd: 1 þ 10 mM; As: 1 þ 10 mM). Exudation of low molecular weightorganic compounds (low molecular weight organic acids (LMWOA), amino acids and dissolved monosaccharides),as well as dissolved organic carbon was quantified as a potential response to the metalstress. The main LMWOA identified was oxalate. Oxalate exudation increased significantly in response toboth low and high Pb and Cd concentrations, as well as low As exposure, relative to nutrient controls.Exposure to As and mixtures of metals (Pb þ Cd, Pb þ As) did not result in any significant increase inoxalate production compared to controls. The presence of a carbon source (glucose) in this study islikely to have been important for exudation of organic compounds. For the nutrient rich (þ1mMglucose) metal treatments exposure to Pb and Cd mainly increased exudation of oxalate and total aminoacids. Production of dissolved monosaccharides, as well as DOC, did not increase significantly in responseto metal exposure, irrespective of nutrient conditions. This may be explained by re-absorption ofthe organic compounds by the mycelium or by the fact that metals had no effect on exudation of thesecompounds.

    Place, publisher, year, edition, pages
    Amsterdam: Elsevier, 2008
    Keywords
    Amino acids, Ectomycorrhiza, Exudation, Fungi, LMWOA, Metals, Oxalate, Pure culture, Saprotrophic fungi
    National Category
    Natural Sciences
    Research subject
    Environmental Chemistry
    Identifiers
    urn:nbn:se:oru:diva-11838 (URN)10.1016/j.soilbio.2008.04.016 (DOI)
    Available from: 2010-09-14 Created: 2010-09-14 Last updated: 2017-12-12Bibliographically approved
    2. Quantitative analysis of root and ectomycorrhizal exudates as a response to Pb, Cd and As stress
    Open this publication in new window or tab >>Quantitative analysis of root and ectomycorrhizal exudates as a response to Pb, Cd and As stress
    2008 (English)In: Plant and Soil, ISSN 0032-079X, E-ISSN 1573-5036, Vol. 313, no 1-2, p. 39-54Article in journal (Refereed) Published
    Abstract [en]

    We examined exudation of low molecular weight (LMW) organic compounds of ectomycorrhizal (ECM) and non-mycorrhizal (NM) seedlings in relation to metals. Scots pine seedlings, either colonized by one of six different ECM fungi or NM, were grown in Petri dishes containing glass beads and liquid growth medium and exposed to elevated concentrations of Pb, Cd and As. Exudation of LMW organic compounds (LMW organic acids (LMWOAs), amino acids and dissolved monosaccharides) and dissolved organic carbon (DOC) was determined qualitatively and quantitatively and exudation rates were calculated. Metals had a significant impact on exudation, especially of oxalate. For Pb and Cd treatments, exudation of oxalate and total LMWOAs generally increased by 15–45% compared to nutrient controls. Production of amino acids, dissolved monosaccharides and DOC was not significantly stimulated by exposure to metals; however, there were non-significant trends towards increased exudation. Finally, exudation generally increased in the presence of mycorrhizal seedlings compared to NM seedlings. The results suggest that ECM fungi may reduce the toxicity of metals to plants through significant increases in the production of organic chelators. Axenic conditions are required to assess the full potential for production of these molecules but their overall significance in soil ecosystems needs to be determined using additional experiments under more ecologically realistic conditions.

    Place, publisher, year, edition, pages
    Berlin: Springer, 2008
    Keywords
    amino acids, 13C, carbon cycle, ectomycorrhiza, elevated CO2, exudation, DOC, LMWOA, metal stress, monosaccharides, oxalate, Pinus sylvestris, saprotrophic fungi, soil respiration
    National Category
    Natural Sciences Environmental Sciences
    Research subject
    Environmental Chemistry
    Identifiers
    urn:nbn:se:oru:diva-11842 (URN)10.1007/s11104-008-9678-1 (DOI)
    Available from: 2010-09-15 Created: 2010-09-15 Last updated: 2017-12-12Bibliographically approved
    3. Remediation of Metal Contaminated Soil by Organic Metabolites from Fungi I—Production of Organic Acids
    Open this publication in new window or tab >>Remediation of Metal Contaminated Soil by Organic Metabolites from Fungi I—Production of Organic Acids
    Show others...
    2008 (English)In: Water, Air and Soil Pollution, ISSN 0049-6979, E-ISSN 1573-2932, Vol. 205, no 1-4, p. 215-226Article in journal (Refereed) Published
    Abstract [en]

    Investigations were made on living strains offungi in a bioremediation process of three metal (lead)contaminated soils. Three saprotrophic fungi (Aspergillusniger, Penicillium bilaiae, and a Penicillium sp.) wereexposed to poor and rich nutrient conditions (no carbonavailability or 0.11 M D-glucose, respectively) andmetal stress (25 μM lead or contaminated soils) for5 days. Exudation of low molecular weight organicacids was investigated as a response to the metal andnutrient conditions. Main organic acids identified wereoxalic acid (A. niger) and citric acid (P. bilaiae).Exudation rates of oxalate decreased in response tolead exposure, while exudation rates of citrate were lessaffected. Total production under poor nutrient conditionswas low, except for A. niger, for which nosignificant difference was found between the poor andrich control. Maximum exudation rates were 20 μmoloxalic acid g^−1 biomass h^−1 (A. niger) and 20 μmolcitric acid g^−1 biomass h^−1 (P. bilaiae), in the presenceof the contaminated soil, but only 5 μmol organic acidsg^−1 biomass h^−1, in total, for the Penicillium sp. Therewas a significant mobilization of metals from the soilsin the carbon rich treatments and maximum release ofPb was 12% from the soils after 5 days. This was notsufficient to bring down the remaining concentration tothe target level 300 mg kg^−1 from initial levels of 3,800,1,600, and 370 mg kg^−1in the three soils. Target levelsfor Ni, Zn, and Cu, were 120, 500, and 200 mg kg^−1,respectively, and were prior to the bioremediationalready below these concentrations (except for Cu Soil1). However, maximum release of Ni, Zn, and Cu was28%, 35%, and 90%, respectively. The release of metalswas related to the production of chelating acids, but alsoto the pH-decrease. This illustrates the potential to usefungi exudates in bioremediation of contaminated soil.Nonetheless, the extent of the generation of organicacids is depending on several processes and mechanismsthat need to be further investigated.

    Place, publisher, year, edition, pages
    Berlin, Germany: Springer, 2008
    Keywords
    Bioremediation, Citric acid, Fungi, Lead, Organic acids, Oxalic acid
    National Category
    Natural Sciences Environmental Sciences
    Research subject
    Environmental Chemistry
    Identifiers
    urn:nbn:se:oru:diva-11843 (URN)10.1007/s11270-009-0067-z (DOI)000272851000016 ()2-s2.0-75049083063 (Scopus ID)
    Available from: 2010-09-15 Created: 2010-09-15 Last updated: 2017-12-12Bibliographically approved
    4. Quantitative analysis of soluble exudates produced by ectomycorrhizal roots as a response to ambient and elevated CO2
    Open this publication in new window or tab >>Quantitative analysis of soluble exudates produced by ectomycorrhizal roots as a response to ambient and elevated CO2
    2009 (English)In: Soil Biology and Biochemistry, ISSN 0038-0717, E-ISSN 1879-3428, Vol. 41, no 6, p. 1111-1116Article in journal (Refereed) Published
    Abstract [en]

    Despite its potential impact on soil carbon flow, few studies have attempted to quantify the effects of elevated carbon dioxide (CO2) on production of exudates by mycorrhizal plants. In this study we quantified low molecular weight (LMW) organic compounds exuded by non-mycorrhizal (NM) and ectomycorrhizal (ECM) plants in relation to exposure to elevated CO2. Scots pine seedlings, either colonized by one of eight different ECM fungi or non-mycorrhizal (NM), were exposed to either ambient (350 ppm) or elevated (700 ppm) concentrations of CO2. Exudation of LMW organic acids (LMWOAs), amino acids, dissolved monosaccharides and total dissolved organic carbon (DOC) was determined and exudation rates were calculated per g root and fungal dry mass. CO2 had a significant impact on exudation. Under elevated CO2, exudation of total LMWOAs increased by 120–160%, amino acids by 250%, dissolved monosaccharides by 130–270% and DOC by 180–220% compared to ambient CO2 treatment. Net CO2 assimilation rates increased significantly by 41–47% for seedlings exposed to elevated CO2. Exuded C calculated as a percentage of assimilated CO2 increased by 41–88% in the elevated CO2 treatment compared to ambient CO2 treatment.

    Place, publisher, year, edition, pages
    Amsterdam: Elsevier, 2009
    Keywords
    Ectomycorrhiza, Elevated carbon dioxide, Exudation, Glucosamine, LMWOAs, Pinus sylvestris
    National Category
    Natural Sciences Environmental Sciences
    Research subject
    Environmental Chemistry
    Identifiers
    urn:nbn:se:oru:diva-11845 (URN)10.1016/j.soilbio.2009.02.016 (DOI)000266942900011 ()2-s2.0-67349288511 (Scopus ID)
    Available from: 2010-09-15 Created: 2010-09-15 Last updated: 2017-12-12Bibliographically approved
    5. Elevated CO2 and nitrogen influence exudation of soluble organic compounds by ectomycorrhizal root systems
    Open this publication in new window or tab >>Elevated CO2 and nitrogen influence exudation of soluble organic compounds by ectomycorrhizal root systems
    2010 (English)In: FEMS Microbiology Ecology, ISSN 0168-6496, E-ISSN 1574-6941, Vol. 71, no 2, p. 186-196Article in journal (Refereed) Published
    Abstract [en]

    Root and mycelial exudation contributes significantly to soil carbon (C) fluxes, and is likely to be altered by an elevated atmospheric carbon dioxide (CO2) concentration and nitrogen (N) deposition. We quantified soluble, low-molecular-weight (LMW) organic compounds exuded by ectomycorrhizal plants grown under ambient (360 p.p.m.) or elevated (710 p.p.m.) CO2 concentrations and with different N sources. Scots pine seedlings, colonized by one of five different ectomycorrhizal or nonmycorrhizal fungi, received 70 μM N, either as NH4Cl or as alanine, in a liquid growth medium. Exudation of LMW organic acids (LMWOAs), dissolved monosaccharides and total dissolved organic carbon were determined. Both N and CO2 had a significant impact on exudation, especially of LMWOAs. Exudation of LMWOAs was negatively affected by inorganic N and decreased by 30–85% compared with the organic N treatment, irrespective of the CO2 treatment. Elevated CO2 had a clear impact on the production of individual LMWOAs, although with very contrasting effects depending on which N source was supplied.

    Place, publisher, year, edition, pages
    Hoboken, USA: Wiley-Blackwell, 2010
    Keywords
    Global change, carbon cycling; oxalate, Pinus sylvestris, organic nitrogen, LMWOAs
    National Category
    Natural Sciences Environmental Sciences
    Research subject
    Environmental Chemistry
    Identifiers
    urn:nbn:se:oru:diva-11846 (URN)10.1111/j.1574-6941.2009.00795.x (DOI)000273065000002 ()19889031 (PubMedID)2-s2.0-73049118299 (Scopus ID)
    Available from: 2010-09-15 Created: 2010-09-15 Last updated: 2018-04-19Bibliographically approved
    6. Autotrophic and heterotrophic soil respiration: the effects of non-mycorrhizal and mycorrhizal seedlings under elevated CO2
    Open this publication in new window or tab >>Autotrophic and heterotrophic soil respiration: the effects of non-mycorrhizal and mycorrhizal seedlings under elevated CO2
    (English)Manuscript (preprint) (Other academic)
    National Category
    Natural Sciences Environmental Sciences
    Research subject
    Environmental Chemistry
    Identifiers
    urn:nbn:se:oru:diva-11847 (URN)
    Available from: 2010-09-15 Created: 2010-09-15 Last updated: 2017-10-18Bibliographically approved
  • 4.
    Johansson, Emma M.
    et al.
    Örebro University, School of Science and Technology.
    Fransson, Petra M. A.
    Department of Forest Mycology and Pathology, Swedish University of Agricultural Sciences.
    Ekblad, Alf
    Örebro University, School of Science and Technology.
    van Hees, Patrick A. W.
    Örebro University, School of Science and Technology.
    Autotrophic and heterotrophic soil respiration: the effects of non-mycorrhizal and mycorrhizal seedlings under elevated CO2Manuscript (preprint) (Other academic)
  • 5.
    Johansson, Emma M.
    et al.
    Örebro University, School of Science and Technology.
    Fransson, Petra M. A.
    Department of Forest Mycology and Pathology, Swedish University of Agricultural Sciences.
    Finlay, Roger D.
    Department of Forest Mycology and Pathology, Swedish University of Agricultural Sciences.
    van Hees, Patrick A. W.
    Örebro University, School of Science and Technology.
    Quantitative analysis of exudates from soil-living basidiomycetes in pure culture as a response to lead, cadmium and arsenic stress2008In: Soil Biology and Biochemistry, ISSN 0038-0717, E-ISSN 1879-3428, Vol. 40, no 9, p. 2225-2236Article in journal (Refereed)
    Abstract [en]

    Six different ectomycorrhizal fungi (Hebeloma velutipes, Piloderma byssinum, Paxillus involutus, Rhizopogonroseolus, Suillus bovinus and Suillus variegatus) and two saprotrophic fungi (Hypholoma fasciculare andHypholoma capnoides) were exposed to metal stress induced by Pb, Cd and As. After pre-growth ina nutrient solution in Petri dishes, metal exposure was performed either in a nutrient rich solution or ina nutrient poor solution for seven days. The fungi were exposed to two different metal concentrations,low and high (Pb: 10 þ 100 mM; Cd: 1 þ 10 mM; As: 1 þ 10 mM). Exudation of low molecular weightorganic compounds (low molecular weight organic acids (LMWOA), amino acids and dissolved monosaccharides),as well as dissolved organic carbon was quantified as a potential response to the metalstress. The main LMWOA identified was oxalate. Oxalate exudation increased significantly in response toboth low and high Pb and Cd concentrations, as well as low As exposure, relative to nutrient controls.Exposure to As and mixtures of metals (Pb þ Cd, Pb þ As) did not result in any significant increase inoxalate production compared to controls. The presence of a carbon source (glucose) in this study islikely to have been important for exudation of organic compounds. For the nutrient rich (þ1mMglucose) metal treatments exposure to Pb and Cd mainly increased exudation of oxalate and total aminoacids. Production of dissolved monosaccharides, as well as DOC, did not increase significantly in responseto metal exposure, irrespective of nutrient conditions. This may be explained by re-absorption ofthe organic compounds by the mycelium or by the fact that metals had no effect on exudation of thesecompounds.

  • 6.
    Johansson, Emma M.
    et al.
    Örebro University, School of Science and Technology.
    Fransson, Petra M. A.
    Department of Forest Mycology and Pathology, Swedish University of Agricultural Sciences.
    Finlay, Roger D.
    Department of Forest Mycology and Pathology, Swedish University of Agricultural Sciences.
    van Hees, Patrick A. W.
    Örebro University, School of Science and Technology.
    Quantitative analysis of root and ectomycorrhizal exudates as a response to Pb, Cd and As stress2008In: Plant and Soil, ISSN 0032-079X, E-ISSN 1573-5036, Vol. 313, no 1-2, p. 39-54Article in journal (Refereed)
    Abstract [en]

    We examined exudation of low molecular weight (LMW) organic compounds of ectomycorrhizal (ECM) and non-mycorrhizal (NM) seedlings in relation to metals. Scots pine seedlings, either colonized by one of six different ECM fungi or NM, were grown in Petri dishes containing glass beads and liquid growth medium and exposed to elevated concentrations of Pb, Cd and As. Exudation of LMW organic compounds (LMW organic acids (LMWOAs), amino acids and dissolved monosaccharides) and dissolved organic carbon (DOC) was determined qualitatively and quantitatively and exudation rates were calculated. Metals had a significant impact on exudation, especially of oxalate. For Pb and Cd treatments, exudation of oxalate and total LMWOAs generally increased by 15–45% compared to nutrient controls. Production of amino acids, dissolved monosaccharides and DOC was not significantly stimulated by exposure to metals; however, there were non-significant trends towards increased exudation. Finally, exudation generally increased in the presence of mycorrhizal seedlings compared to NM seedlings. The results suggest that ECM fungi may reduce the toxicity of metals to plants through significant increases in the production of organic chelators. Axenic conditions are required to assess the full potential for production of these molecules but their overall significance in soil ecosystems needs to be determined using additional experiments under more ecologically realistic conditions.

  • 7.
    Johansson, Emma M.
    et al.
    Örebro University, School of Science and Technology.
    Fransson, Petra M. A.
    Department of Forest Mycology and Pathology, Swedish University of Agricultural Sciences.
    Finlay, Roger D.
    van Hees, Patrick A. W.
    Örebro University, School of Science and Technology.
    Quantitative analysis of soluble exudates produced by ectomycorrhizal roots as a response to ambient and elevated CO22009In: Soil Biology and Biochemistry, ISSN 0038-0717, E-ISSN 1879-3428, Vol. 41, no 6, p. 1111-1116Article in journal (Refereed)
    Abstract [en]

    Despite its potential impact on soil carbon flow, few studies have attempted to quantify the effects of elevated carbon dioxide (CO2) on production of exudates by mycorrhizal plants. In this study we quantified low molecular weight (LMW) organic compounds exuded by non-mycorrhizal (NM) and ectomycorrhizal (ECM) plants in relation to exposure to elevated CO2. Scots pine seedlings, either colonized by one of eight different ECM fungi or non-mycorrhizal (NM), were exposed to either ambient (350 ppm) or elevated (700 ppm) concentrations of CO2. Exudation of LMW organic acids (LMWOAs), amino acids, dissolved monosaccharides and total dissolved organic carbon (DOC) was determined and exudation rates were calculated per g root and fungal dry mass. CO2 had a significant impact on exudation. Under elevated CO2, exudation of total LMWOAs increased by 120–160%, amino acids by 250%, dissolved monosaccharides by 130–270% and DOC by 180–220% compared to ambient CO2 treatment. Net CO2 assimilation rates increased significantly by 41–47% for seedlings exposed to elevated CO2. Exuded C calculated as a percentage of assimilated CO2 increased by 41–88% in the elevated CO2 treatment compared to ambient CO2 treatment.

  • 8.
    van Hees, Patrick A. W.
    et al.
    Örebro University, Department of Natural Sciences.
    Johansson, Emma M.
    Örebro University, Department of Natural Sciences.
    Jones, D. L.
    Dynamics of simple carbon compounds in two forest soils as revealed by soil solution concentrations and biodegradation kinetics2008In: Plant and Soil, ISSN 0032-079X, E-ISSN 1573-5036, Vol. 310, no 1-2, p. 11-23Article in journal (Refereed)
    Abstract [en]

    Simple compounds in soil such as organic acids, amino acids and monosaccharides are believed to be important in regulating many aspects of terrestrial ecosystem functioning (e.g. C cycling, nutrient acquisition). Understanding the fate and dynamics of these low molecular weight (MW) compounds is therefore essential for predicting ecosystem responses to disturbance. Our aim was to quantify the amounts of these compounds in two podzolic forest soil profiles (O, E, Bs and C horizons) and to quantify their contribution to total soil respiration. The total concentration of organic acids, amino acids and monosaccharides in soil solution comprised on average 15 +/- 10% of the total dissolved organic C (DOC), with declining concentrations in the deeper soil layers. Dissolved organic N (DON) was the dominant form of N in soil solution and free amino acids contributed to 34% of this pool. The mineralization behaviour of glucose and galactose was described by parabolic (Michaelis-Menten) type kinetics with V-max and K (M) values in the range of < 1-250 mu mol kg(-1) h(-1) and 15-1,100 mu M, respectively. Assuming that (1) microbially mediated substrate turnover follows Michaelis-Menten kinetics, and (2) steady state soil solution concentrations, we calculated the rate of CO2 efflux attributable to the mineralisation of the three classes of low MW compounds. Our results indicated that in the O horizon, the turnover of these substrates could comprise similar to 100% of the basal, heterotrophic, soil respiration. In contrast, in the deeper mineral soil < 20% of total soil respiration could be attributable to the mineralization of these compounds. Our compound-specific approach has identified the main substrates contributing to soil respiration in forest topsoils. However, our results also suggest that soil respiration in subsoils may be attributable to compounds other than organic acids, amino acids and monosaccharides.

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