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  • 1. Berg, B.
    et al.
    Kjonaas, O. J.
    Johansson, M. -B
    Erhagen, Björn
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Åkerblom, S.
    Late stage pine litter decomposition: Relationship to litter N, Mn, and acid unhydrolyzable residue (AUR) concentrations and climatic factors2015Ingår i: Forest Ecology and Management, ISSN 0378-1127, E-ISSN 1872-7042, Vol. 358, s. 41-47Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The aim of this paper is to evaluate relationships between decomposition rates of Scots pine (Pinus sylvestris) and lodgepole pine (Pinus contorta var. contorta) needle litter in the late stage of decomposition (>30% accumulated mass loss), and the progressively changing concentrations of manganese (Mn), nitrogen (N), and acid unhydrolyzable residue (AUR), as well as mean annual temperature (MAT) and mean annual precipitation (MAP). Using available long-term decomposition studies on pine needle litter in a climate gradient in Sweden, we calculated annual mass loss and related to concentrations of Mn, N, and AUR at the start of each one-year period as well as to MAT and MAP. We investigated these relationships for (i) all data on annual mass loss combined and (ii) annual mass loss for five different decomposition categories as defined by accumulated mass loss. We found highly significant, negative, and dominant relationships between annual mass loss and N (R-2 = 0.39) and AUR (R-2 = 0.39), a slight but significant positive relationship to Mn (R-2 = 0.08) and a significant negative relationship to MAT (R-2 = 0.06). The relationships were dynamic, and changed with accumulated mass loss. The rate-dampening effect of N decreased to be a rate-enhancing effect at c. 60-80% accumulated mass loss. A similar trend was found for AUR, becoming rate-enhancing at 70-80% accumulated mass loss. For Scots pine needle litter the effect of MAT on mass loss decreased with increasing accumulated mass loss and changed to a rate-dampening effect at c. 50-70% accumulated mass loss. Mn showed a stimulating effect on mass loss rate in all categories whereas MAP showed no effect in this mainly boreal climatic gradient. The current approach indicates a method for detailed studies of rate-regulating factors for litter decomposition.

  • 2. Berg, Björn
    et al.
    Erhagen, Björn
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Johansson, Maj-Britt
    Nilsson, Mats
    Stendahl, Johan
    Trum, Florence
    Vesterdal, Lars
    Manganese in the litter fall-forest floor continuum of boreal and temperate pine and spruce forest ecosystems: A review2015Ingår i: Forest Ecology and Management, ISSN 0378-1127, E-ISSN 1872-7042, Vol. 358, s. 248-260Artikel, forskningsöversikt (Refereegranskat)
    Abstract [en]

    We have reviewed the literature on the role of manganese (Mn) in the litter fall-to-humus subsystem. Available data gives a focus on North European coniferous forests. Manganese concentrations in pine (Pinus spp.) foliar litter are highly variable both spatially and temporally within the same litter species and for the genus Pinus we found a range from 0.03 to 3.7 mg g(-1). Concentrations were related negatively to site mean annual temperature (MAT) and annual actual evapotranspiration (AET) for pine species litter but not for that of Norway spruce (Picea abies) as a single species. Combined data for several species showed a highly significant relationship to MAT. Manganese peroxidase is an Mn-dependent enzyme, found in white-rot fungi, essential for the degradation of lignin and ligninlike compounds. The decomposition rates of lignified litter tissue (late phase) is positively related to the litter's Mn concentration. Further, the Mn concentration is positively related to the limit value for decomposition - the higher the Mn concentration the smaller the stable litter fraction. Manganese release from decomposing litter appears at least in part to be species related. Thus was release from pine needle litter significantly faster (p < 0.001) than that from the Mn-richer litter of Norway spruce. Over Northern Europe concentrations of total Mn in mor humus as well as extractable Mn in the mineral soil increase with decreasing MAT and over a climatic gradient the Mn concentrations in Norway spruce mor increase more with decreasing MAT than in a gradient with Scots pine. Higher Mn concentrations in humus appear to decrease its stability and result in a higher release of carbon dioxide (CO2) and dissolved organic carbon (DOC). We conclude that this may explain (i) the lower amount of carbon (C) in mor layers under Norway spruce as compared to Scots pine as well as the higher amount of C in mineral soil under spruce. The increase in nitrogen (N) concentration in humus, following N fertilization resulted in a decrease in that of Mn. We have found four cases - empirical - with negative interaction between Mn and N; (i) in pine foliar litter fall concentrations of Mn decrease with site MAT whereas those of N increase, (ii) in decomposing late-stage litter with N retarding and Mn stimulating decomposition, (iii) for the stable phase, limit values are related negatively to N and positively to Mn, and (iv) Mn concentrations in humus decrease with MAT whereas those of N increase. (C) 2015 Elsevier B.V. All rights reserved.

  • 3.
    Erhagen, Björn
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap. Swedish Univ Agr Sci SLU, Dept Forest Ecol & Management, S-90183 Umeå, Sweden.
    Ilstedt, Ulrik
    Nilsson, Mats B.
    Temperature sensitivity of heterotrophic soil CO2 production increases with increasing carbon substrate uptake rate2015Ingår i: Soil Biology and Biochemistry, ISSN 0038-0717, E-ISSN 1879-3428, Vol. 80, s. 45-52Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Temperature profoundly affects saprotrophic respiration rates, and carbon quality theory predicts that the rates' temperature Sensitivity should increase as the quality of the carbon source declines. However, reported relationships between saprotrophic respiration responses to temperature and carbon quality vary widely. Some of this variability may arise from confounding effects related to both substrate quality and substrate availability. The importance of these variables, as well as substrate diffusion and uptake rates, for the temperature sensitivity of saprotrophic respiration has been validated theoretically, but not empirically demonstrated. Thus, we tested effects of varying substrate uptake rates on the temperature sensitivity of organic carbon degradation. For this purpose we created a model system using the organic layer (O-horizon), of a boreal forest soil, specifically to test effects of varying monomer uptake and release rates. The addition of both monomers and polymers generally increased the temperature sensitivity of saprotrophic respiration. In response to added monomers, there was a linear increase in the temperature sensitivity of both substrate-induced respiration and the specific growth rate with increasing rate of substrate uptake as indicated by the CO2 production at 14 degrees C. Both of these responses diverge from those predicted by the carbon quality theory, but they provide the first empirical evidence consistent with model predictions demonstrating increased temperature sensitivity with increased uptake rate of carbon monomers over the cell membrane. These results may explain why organic material of higher carbon quality induces higher temperature responses than lower carbon quality compounds, without contradicting carbon quality theory. 

  • 4. Öquist, Mats G.
    et al.
    Erhagen, Björn
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap. Department of Forest Ecology & Management, Swedish University of Agricultural Sciences (SLU), Umeå, Sweden.
    Haei, Mahsa
    Sparrman, Tobias
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Ilstedt, Ulrik
    Schleucher, Jürgen
    Umeå universitet, Medicinska fakulteten, Institutionen för medicinsk kemi och biofysik.
    Nilsson, Mats B.
    The effect of temperature and substrate quality on the carbon use efficiency of saprotrophic decomposition2017Ingår i: Plant and Soil, ISSN 0032-079X, E-ISSN 1573-5036, Vol. 414, nr 1, s. 113-125Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Background and aims: Mineralization of soil organic matter (SOM) constitutes a major carbon flux to the atmosphere. The carbon use efficiency (CUE) of the saprotrophic microorganisms mineralizing SOM is integral for soil carbon dynamics. Here we investigate how the CUE is affected by temperature, metabolic conditions, and the molecular complexity of the substrate.

    Methods: We incubated O-horizon soil samples (with either 13C–glucose or 13C–cellulose) from a boreal coniferous forest at 4, 9, 14, and 19 °C, and calculated CUEs based on the amount of 13C–CO2and 13C–labelled microbial biomass produced. The effects of substrate, temperature, and metabolic conditions (representing unlimited substrate supply and substrate limitation) on CUE were evaluated.

    Results: CUE from metabolizing glucose was higher as compared to cellulose. A slight decrease in CUE with increasing temperature was observed in glucose amended samples (but only in the range 9–19 °C), but not in cellulose amended samples. CUE differed significantly with metabolic conditions, i.e. CUE was higher during unlimited growth conditions as compared to conditions with substrate limitation.

    Conclusions: We conclude that it is integral to account for both differences in CUE during different metabolic phases, as well as complexity of substrate, when interpreting temperature dependence on CUE in incubation studies.

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