| 1. |
- Berg, Björn, et al.
(författare)
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Late stage pine litter decomposition : Relationship to litter N, Mn, and acid unhydrolyzable residue (AUR) concentrations and climatic factors
- 2015
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Ingår i: Forest Ecology and Management. - : Elsevier BV. - 0378-1127 .- 1872-7042. ; 358, s. 41-47
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Tidskriftsartikel (refereegranskat)abstract
- 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 (R2=0.39) and AUR (R2=0.39), a slight but significant positive relationship to Mn (R2=0.08) and a significant negative relationship to MAT (R2=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.
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| 2. |
- Berg, Björn, et al.
(författare)
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Manganese dynamics in decomposing needle and leaf litter : a synthesis
- 2013
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Ingår i: Canadian Journal of Forest Research. - : Canadian Science Publishing. - 0045-5067 .- 1208-6037. ; 43:12, s. 1127-1136
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Tidskriftsartikel (refereegranskat)abstract
- The aim of the present synthesis paper was to determine whether concentration changes and net release of manganese (Mn), as related to accumulated litter mass loss, are related to initial Mn concentration, mean annual temperature (MAT), mean annual precipitation (MAP), and tree genus or species. We also examined whether limit values for decomposition are related to initial litter Mn concentration, MAT, and MAP. We compiled 84 foliar litter decomposition studies, conducted mainly in boreal and temperate forest ecosystems, for which Mn dynamics had been well documented. Manganese concentration and amount were related to accumulated litter mass loss at each sampling time for each single study, as well as for (i) all studies combined (n = 748) and (ii) for species groups viz. Norway spruce (Picea abies (L.) Karst.) (n = 284), pine (Pinus) species (n = 330), and deciduous species (n = 214). The changes in Mn concentration with accumulated mass loss followed quadratic functions showing significantly higher Mn concentrations for Norway spruce vs. Scots pine (Pinus sylvestris L.) (p < 0.0001) and vs. deciduous species (p < 0.01), as well as significantly higher for deciduous species vs. Scots pine (p < 0.0001). Manganese release rates were different among the three species groups (p < 0.001). Still, rates were related to initial Mn concentrations (p < 0.001) for all litter types combined and for the three species groups. Norway spruce released Mn more slowly than pine and deciduous species. Rates were related to climatic factors for litter of Norway spruce and deciduous species. Limit values for all litter and for pine species separately were related to Mn (p < 0.001) and MAT (p < 0.001). For Norway spruce, limit values were related to MAT (p < 0.001) and MAP (p < 0.01). It appears that Norway spruce litter retains Mn more strongly in the litter structure, producing humus richer in Mn than does litter of pine and deciduous species.
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| 3. |
- Berg, Björn, et al.
(författare)
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Manganese in the litter fall-forest floor continuum of boreal and temperate pine and spruce forest ecosystems : a review
- 2015
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Ingår i: Forest Ecology and Management. - : Elsevier BV. - 0378-1127 .- 1872-7042. ; 358, s. 248-260
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Forskningsöversikt (refereegranskat)abstract
- 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 3.7mgg-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.
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| 4. |
- Erhagen, Björn, et al.
(författare)
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Bioavailability of stream dissolved organic carbon (DOC) during spring flood and base flow in high-latitude streams
- 2015
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- An important component of the carbon cycle is the lateral flow of dissolved organic carbon (DOC) from terrestrial ecosystems to streams and rivers. The fate of this carbon depends very much on the bioavailability of DOC (BDOC), which may determine whether DOC is returned to the atmosphere as CO2 or deposited in sediments. This study focuses on the linkages between stream DOC composition, optical characteristics and bioavailability along vegetation gradients in subarctic Sweden. We sampled streams from tundra, birch forest, and boreal forest ecoregions, which encompass large differences in C:N ratios (6.4-30.1) and spectroscopic characteristics, all related to variation in landscape properties. The DOC bioavailability was determined through laboratory bioassays carried out twice during the year (spring-flood and base flow). During spring flood, DOC concentration varied between 0.5 - 6.7 mg L-1 and the BDOC ranged between 3- 24 %, with the highest BDOC from birch forest/tundra and tundra streams. Results suggest that broad-scale transitions in vegetation structure across sub-arctic landscapes have important implications for the quantity and quality of DOC delivered to aquatic ecosystems.
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| 5. |
- Erhagen, Björn, et al.
(författare)
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Temperature response of litter and soil organic matter decomposition is determined by chemical composition of organic material
- 2013
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Ingår i: Global Change Biology. - : Wiley-Blackwell. - 1354-1013 .- 1365-2486. ; 19:12, s. 3858-3871
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Tidskriftsartikel (refereegranskat)abstract
- The global soil carbon pool is approximately three times larger than the contemporary atmospheric pool, therefore even minor changes to its integrity may have major implications for atmospheric CO2 concentrations. While theory predicts that the chemical composition of organic matter should constitute a master control on the temperature response of its decomposition, this relationship has not yet been fully demonstrated. We used laboratory incubations of forest soil organic matter (SOM) and fresh litter material together with NMR spectroscopy to make this connection between organic chemical composition and temperature sensitivity of decomposition. Temperature response of decomposition in both fresh litter and SOM was directly related to the chemical composition of the constituent organic matter, explaining 90% and 70% of the variance in Q10 in litter and SOM respectively. The Q10 of litter decreased with increasing proportions of aromatic and O-aromatic compounds, and increased with increased contents of alkyl- and O-alkyl carbons. In contrast, in SOM, decomposition was affected only by carbonyl compounds. To reveal why a certain group of organic chemical compounds affected the temperature sensitivity of organic matter decomposition in litter and SOM, a more detailed characterisation of the (13) C aromatic region using Heteronuclear Single Quantum Coherence (HSQC) was conducted. The results revealed considerable differences in the aromatic region between litter and SOM. This suggests that the correlation between chemical composition of organic matter and the temperature response of decomposition differed between litter and SOM. The temperature response of soil decomposition processes can thus be described by the chemical composition of its constituent organic matter, this paves the way for improved ecosystem modelling of biosphere feedbacks under a changing climate.
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| 6. |
- Erhagen, Björn, et al.
(författare)
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Temperature sensitivity of heterotrophic soil CO2 production increases with increasing carbon substrate uptake rate
- 2015
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Ingår i: Soil Biology and Biochemistry. - : Elsevier BV. - 0038-0717 .- 1879-3428. ; 80, s. 45-52
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 7. |
- Erhagen, Björn
(författare)
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Temperature sensitivity of soil carbon decomposition : molecular controls and environmental feedbacks
- 2013
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The world's soils contain three times as much carbon as the atmosphere. Thus, any changes in this carbon pool may affect atmospheric CO₂ levels with implications for climate change. Anthropogenic contributions to global carbon and nitrogen cycles have increased in the last century. Both temperature and nitrogen influence decomposition processes and are therefore critical in determining CO₂ return to the atmosphere. Kinetic theory predicts that the chemical composition of soil organic matter represents a dominant influence on the temperature response of decomposition. However, empirical observations and modeling indicate that this relationship is constrained by other factors. We address a number of research questions related to these factors, which are central to a thorough understanding of temperature sensitivity in decomposition. Specifically it offers one of the first empirical observations consistent with modeling in demonstrating increased temperature sensitivity for the uptake of carbon monomers over microbial cell membranes. Using NMR spectroscopy we were able to demonstrate how temperature response is directly related to the chemical composition of the organic material present. The thesis shows how increased soil nitrogen reduces temperature response. The key mechanism behind this observation, we suggest, is the influence of nitrogen on the chemical composition of organic matter, mediating a direct effect on temperature response. Given that nitrogen availability in terrestrial ecosystems has doubled relative to preindustrial levels, this observation may be vital in understanding the net effect of temperature increase on CO₂ return to the atmosphere. The proportion of carbon in plant litter transformed by microorganisms into biomass (carbon use efficiency; CUE) is a central factor determining global land-atmosphere CO₂ exchange. CUE was highly sensitive to whether carbon monomers or polymers were degraded; yet temperature had no clear effect on CUE. The majority of soil organic matter is comprised of polymers, highlighting the importance of using these as model substrates in studies of CUE. This thesis represents a major contribution to our understanding of the intrinsic and external controls acting on temperature sensitivity of decomposition, and thus to regulation of CO₂ return to the atmosphere under a changing climate.
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| 8. |
- Feng, Wenting, et al.
(författare)
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Millennia-old organic carbon in a boreal paleosol : chemical properties and their link to mineralizable carbon fraction
- 2016
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Ingår i: Journal of Soils and Sediments. - : Springer Science and Business Media LLC. - 1439-0108 .- 1614-7480. ; 16:1, s. 85-94
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Tidskriftsartikel (refereegranskat)abstract
- Little is known about the biogeochemical properties of millennia-old soil organic matter (SOM) in boreal forest paleosols and whether these properties contribute to the persistence of several millennia-old SOM. In this study, we assessed the physicochemical properties of a well-drained paleosol and looked for links between these properties and the mineralizable carbon (C) fraction. We studied a well-drained paleosol located under a typical forest podzol in Northern Sweden, in which up to 7-kyr-old SOM was preserved according to C-14 dating. We assessed the elemental compositions of the outermost 2-mu m and 10-nm soil particle surfaces by using energy-dispersive X-ray scanning electron microscopy and X-ray photoelectron spectroscopy, respectively. We also conducted a 5-week laboratory incubation of samples from both the paleosol and the podzol to quantify their mineralizable C fractions and analyzed the thermal stability of soil samples before and after incubation by using temperature-programmed desorption coupled with mass spectrometry techniques. Proxies for weathering (i.e., total mineral surface area and Al/Si and Fe/Si ratios of particle surfaces) suggested that the paleosol was at the same weathering stage as the contemporary forming podzol. Mineral soil particle surfaces of both the paleosol and podzol were dominated by aliphatic and ether/alcohol C functional groups. The incubation and thermal analysis showed that the mineralizable C fraction of the paleosol was smaller than that of the podzol, and losses of thermally labile SOM due to microbial degradation during the incubations were only detected in the mineral free O horizon of the podzol. Moreover, the mineralizable C fraction of the sampled podzol-paleosol sequence was correlated to the proportion of ether/alcohol C functional groups at the outermost 10-nm soil particle surfaces. Based on the links between microbial decomposition and the chemistry of soil particle surfaces and the thermal stability difference between organic and mineral soils induced by microbial decomposition, we conclude that the intrinsic chemical properties of SOM and its chemical surroundings is important for SOM preservation over a millennia timescale in the studied soil.
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| 9. |
- Soucemarianadin, Laure N., et al.
(författare)
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Two dimensional NMR spectroscopy for molecular characterization of soil organic matter : Application to boreal soils and litter
- 2017
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Ingår i: Organic Geochemistry. - : Elsevier BV. - 0146-6380 .- 1873-5290. ; 113, s. 184-195
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Tidskriftsartikel (refereegranskat)abstract
- Organic soils in boreal ecosystems and peatlands represent a huge global carbon pool and their composition strongly affects soil properties. Nevertheless, the characterization of soil organic matter (SOM) molecular composition, which is essential for elucidating soil carbon processes and turnover, is not easily achieved, and further advances in the area are greatly needed. Two dimensional (2D) liquid state H-1-C-13 nuclear magnetic resonance (NMR) spectroscopy has been used on dimethyl sulfoxide (DMSO) extracts of SOM to achieve molecular level characterization, with signals from many identifiable molecular groups observable. Here we show that a simple and fast sample preparation allows acquisition of 2D H-1-C-13 NMR spectra from extracts of plant litter and organic layers in boreal ecosystems, with fast data acquisition. Our 2D NMR spectra revealed several differences in the DMSO extracts of different tree litter samples, O-horizons of forest soil, peat-forming moss (Sphagnum) and peat. The results mirror established differences between OM in soils and litter of different forest ecosystems (e.g. between deciduous and coniferous litter) but also provide indications for research to untangle previously conflicting results (e.g. cutin degradation in soil or carbohydrate degradation in peat). Thus, combination of 2D NMR methods can greatly improve analysis of litter composition and SOM composition, thereby facilitating the elucidation of their roles in biogeochemical and ecological processes that are critical for foreseeing feedback mechanisms for SOM turnover as a result of global environmental change.
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| 10. |
- Zeh, Lilli, et al.
(författare)
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Plant functional types and temperature control carbon input via roots in peatland soils
- 2019
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Ingår i: Plant and Soil. - : Springer. - 0032-079X .- 1573-5036. ; 438:1-2, s. 19-38
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Tidskriftsartikel (refereegranskat)abstract
- Aims: Northern peatlands store large amounts of soil organic carbon (C) that can be very sensitive to ongoing global warming. Recently it has been shown that temperature-enhanced growth of vascular plants in these typically moss-dominated ecosystems may promote microbial peat decomposition by increased C input via root exudates. To what extent different plant functional types (PFT) and soil temperature interact in controlling root C input is still unclear. In this study we explored how root C input is related to the presence of ericoid shrubs (shrubs) and graminoid sedges (sedges) by means of a factorial plant clipping experiment (= PFT effect) in two peatlands located at different altitude (= temperature effect).Methods: By selective clipping of shrub and sedge shoots in mixed vegetation at two Alpine peatland sites we interrupted the above- to belowground translocation of C, thus temporarily inhibiting root C release. Subsequent measurements of soil respiration, dissolved organic carbon (DOC) concentration and stable isotope composition (13C) of DOC in pore water were used as proxies to estimate the above- to belowground transfer of C by different PFT.Results: We found that soil respiration rates and DOC concentrations temporarily decreased within 24 h after clipping, with the decrease in soil respiration being most pronounced at the 1.4 °C warmer peatland after clipping shrubs. The transient drop in DOC concentration coincided with a shift towards a heavier C isotope signature, indicating that the decrease was associated with inhibition of a light C source that we attribute to root exudates. Together these results imply that shrubs translocated more C into the peat than sedges, particularly at higher temperature.Conclusions: We showed that plant functional type and temperature interact in controlling root C input under field conditions in peatlands. Our results provide a mechanistic evidence that shrubs may potentially promote the release of stored soil C through root-derived C input.
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