Publikasjoner
NIBIOs ansatte publiserer flere hundre vitenskapelige artikler og forskningsrapporter hvert år. Her finner du referanser og lenker til publikasjoner og andre forsknings- og formidlingsaktiviteter. Samlingen oppdateres løpende med både nytt og historisk materiale. For mer informasjon om NIBIOs publikasjoner, besøk NIBIOs bibliotek.
2008
Sammendrag
Det er ikke registrert sammendrag
Sammendrag
Incomplete combustion during vegetation fire can lead to the conversion of plant and soil organic matter (OM) into charcoal. The thermally altered OM is considered to contribute to the stable pool of soil C. Most of the data on thermal alteration of plant material were obtained in the laboratory, whereas fire consequences on ecosystem C storage calls for data collected in natural-fire conditions. The objective of this study was to relate the quality of visually-identified litter charcoal and the temperature recorded during a scrubland prescribed fire. Litter was sampled before and after the fire along a transect in the 30 ha experimental site. Litter-size fractions were analyzed for chemical composition and properties by elementary and isotopic analysis, solid-state 13C nuclear magnetic resonance spectroscopy, differential scanning calorimetry and quantification of oxidation-resistant pyrogenic C. The maximum temperature reached within the litter layer during fire was assessed with thermo-sensitive paints. Our results showed that fire had little effect on bulk litter composition because the fire event induced a large litter fall of both charred and non-charred material, resulting in the impossibility to distinguish new-litter-input and charring processes. As a consequence, the visual identification and separation of burned and unburned material constituted an essential preliminary step for chemical characterization of thermally altered organic matter. Fire temperatures ranged from 370 to 650°C. Charring signifi- cantly increased the litter C concentration by 115 to 142 mg g"1 under the effects of dehydration and aromatization processes occurring above 370°C. A significant correlation appeared between the production of aromatic structures, the decrease of O-alkyl C contribution and the temperature. The relationship between the maximum temperatures reached during the natural fire and the chemical transformation of the litter organic matter appeared highly consistent with previous results obtained under controlled conditions. Heating also led to a significant decrease of the 13C that we interpret as a higher thermal sensitivity of 13C-rich molecules. The elemental composition, NMR and thermal spectra are consistent with the low oxidation-resistant C concentration of this natural charcoal (16±5 % OC), reflecting a low condensation degree compared to graphitic-like model. These findings suggest that leaf-derived charcoal produced during natural vegetation fire may have a lower C storage potential than previously assumed.
Sammendrag
Vegetation fire is the worldwide disturbance that affects the largest area and biggest biomes variety. Fire instantaneously generates large C fluxes to the atmosphere, as gas and soot particles. In the same time, part of ecosystem organic matter (OM) is converted into charred material that may contribute to the stable pool of soil organic carbon (SOC). The net effect of vegetation fire on C sequestration remains uncertain because the two major impacts operate at very different timescales and C budget is highly dependent on ecosystem and fire conditions. The aim of the present research was to assess fire-induced C fluxes to the atmosphere and as new litter and charcoal production during a prescribed fire in a subtropical oak shrub. Pre-fire biomass and post-fire charred and unburned biomass were determined for vegetation leaves and stems, litter and soil in 20 sub-plots installed in a 30-ha area prescribed for fire. Concentrations of C were determined, and fluxes among pools and to the atmosphere were derived from these measurements. In a first assessment, charred OM was visually identified in standing biomass and litter using its black and shiny aspect. In a second step, a strong chemical oxidation with K2Cr2O7/H2SO4 was used to isolate only a highly recalcitrant part of pyrogenic C. After the fire, standing dead biomass was only composed of stems with charred surface. The leaves transferred from vegetation to litter during the fire represented more than a half of post-fire litter. Percentage of initial C pool that was lost to the atmosphere as gas or particles was 55 % from vegetation stems, 80 % from vegetation leaves, and 70 % from litter. Soil C stocks were not significantly modified by fire, in agreement with moderate temperature elevation in the soil proper. Total C release to the atmosphere, including gas and particles, was 2.6 kg C m"2. Visually-identified charcoal represented 5% of remaining stem C (i.e. 60 g C m"2) and 21% of post-fire litter C (i.e. 80 g C m"2). The stem and litter charcoal contained 4±4 % and 16±5 % of highly recalcitrant C, respectively. We assessed that a typical scrubland fire may add between 10 and 140 g C m"2of chemically stable pyrogenic C to the soil. The conversion rate of ecosystem C to chemically stable pyrogenic C would be between 0.2 and 3.4 %.
Sammendrag
Carbon dioxide and methane -besides water vapor the most powerful greenhouse gases - have been increasing rapidly in recent decades. A huge reservoir of both gases is stored in boreal soils including permafrost, and a major change in the carbon balance of this reservoir might have dramatic impacts on future climate change. So far, Norway has lacked any infrastructure to assess fluxes of both gases from unique boreal ecosystems, e.g., sub-arctic peatlands exposed to oceanic climate. In spring 2008, Bioforsk, SERC and NILU started an initiative to fill this gap by establishing a flux tower station in the Dverberg peatlands on the island of Andøya in Northern Norway. The site is especially suited for such studies, because it extends an existing flux measurement infrastructure in Abisko, N-Sweden and Sodankylä, N-Finland to include an ecosystem with comparatively mild climate, compared to the Alpine Arctic climate of Abisko and the continental- subarctic climate of Sodankylä.
Sammendrag
Recent in situ 13C studies suggest that lignin is not stabilised in soil in its polymerised form. However, the fate of its transformation products remains unknown. The objective of the present research was to provide the first comprehensive picture of the fate of lignin-derived C across its transformations processes: (1) C remaining as undecomposed lignin molecules, (2) C in newly formed humic substances, i.e. no longer identifiable as lignin-polymer C, (3) C in microbial biomass, (4) C mineralised as CO2, and (5) dissolved organic C. To achieve this objective, we designed an incubation experiment with 13C-labelled lignin where both elementary and molecular techniques were applied. Lignin was isolated from 13C labelled maize plants (13C-MMEL) and incubated in an agricultural soil for 44 weeks. Carbon mineralisation and stable isotope composition of the released CO2 were monitored throughout the incubation. Microbial utilisation of 13C-MMEL was measured seven times during the experiment. The turnover rate of the lignin polymer was assessed by 13C analysis of CuO oxidation products of soil lignin molecules. After 44 incubation weeks, 6.0% of initial 13C-MMEL carbon was mineralised, 0.8% was contained in the microbial biomass, and 0.1% was contained in dissolved organic C form. The compound-specific 13C data suggest that the remaining 93% were overwhelmingly in the form of untransformed lignin polymer. However, limited transformation into other humic substances potentially occurred, but could not be quantified because the yield of the CuO oxidation method proved somewhat variable with incubation time. The initial bacterial growth yield efficiency for MMEL was 31% and rapidly decreased to plateau of 8%. A two-pool first-order kinetics model suggested that the vast majority (97%) of MMEL lignin had a turnover time of about 25 years, which is similar to field-estimated turnover times for soil-extractable lignin but much longer than estimated turnover times for fresh plant-residue lignin. We conclude that natural lignin structures isolated from plants are rather unreactive in soil, either due to the lack of easily available organic matter for co-metabolism or due to enhanced adsorption properties. The data also suggest that fairly undecomposed lignin structures are the main reservoir of lignin-derived C in soils.
Forfattere
Haithem Bahri Daniel Rasse Cornelia Rumpel Marie-France Dignac Gerard Bardoux Andre MariottiSammendrag
Recent in situ 13C studies suggest that lignin is not stabilised in soil in its polymerized form. However, the fate of its transformation products remains unknown. The objective of the present research was to provide the first comprehensive picture of the fate of lignin-derived C across its transformations processes: 1) C remaining as undecomposed lignin molecules, 2) C in newly formed humic substances, i.e. no longer identifiable as lignin-polymer C 3) C in microbial biomass, 4) C mineralised as CO2, and 5) dissolved organic C. To achieve this objective, we designed an incubation experiment with 13C-labelled lignin where both elementary and molecular techniques were applied. Lignin was isolated from 13C labelled maize plants (13C-MMEL) and incubated in an agricultural soil for 44 weeks. Carbon mineralisation and stable isotope composition of the released CO2 were monitored throughout the incubation. Microbial utilisation of 13C-MMEL was measured seven times during the experiment. The turnover rate of the lignin polymer was assessed by 13C analysis of CuO oxidation products of soil lignin molecules. After 44 incubation weeks, 6.0% of initial 13C-MMEL carbon was mineralized, 0.8% was contained in the microbial biomass, and 0.1% was contained in dissolved organic C form. The compound-specific 13C data suggest that the remaining 93% were overwhelmingly in the form of untransformed lignin polymer. However, limited transformation into other humic substances potentially occurred, but could not be quantified because the yield of the CuO oxidation method proved somewhat variable with incubation time. The initial bacterial growth yield efficiency for MMEL was 31% and rapidly decreased to plateau of 8%. A two-pool first-order kinetics model suggested that the vast majority (97%) of MMEL lignin had a turnover time of about 25 years, which is similar to field-estimated turnover times for soil-extractable lignin but much longer than estimated turnover times for fresh plant-residue lignin. We conclude that natural lignin structures isolated from plants are rather unreactive in soil, either due to the lack of easily available organic matter for co-metabolism or due to enhanced adsorption properties. The data also suggest that fairly undecomposed lignin structures are the main reservoir of lignin-derived C in soils.
Sammendrag
Carbon from complex and structural plant molecules has long been considered more efficiently retained in soils than that of soluble molecules. This dominant paradigm is now being challenged by data emerging from recent isotopic-labeling and compoundspecific isotopic studies. We recently demonstrated that large proportions of plantresidue lignin decompose within a year of incorporation to soils, and that soilextracted lignin has a turnover time of about 20 years (Rasse et al, 2006). In contrast, turnover time of soil-extracted polysaccharides can reach 40 years (Gleixner et al., 2002). Long-term incubation studies have shown that C from labeled glucose is better conserved in certain soil types than C from more complex molecules such as cellulose (e.g. Vinten et al, 2002). These studies suggest that the initial decomposability of plant molecules has limited impact on the long-term fate of their constitutive C in soils. Here we will present a new model where soluble molecules have a competitive advantage over structural molecules for the long-term preservation of their constitutive C in soils. Implementation of compound-specific data in quantitative soil models will also be discussed.
Forfattere
Marie-France Dignac C Rumpel Daniel Rasse M Mendez-Millan H Bahri S Derenne G Bardoux A MariottiSammendrag
How the chemical composition of plant biomolecules controls their dynamics in soils at the long-term scale remains largely unknown. Stabilisation mechanisms in soils might depend upon the chemical nature of organic matter. These mechanisms either involve soil mineral constituents or are related to chemical recalcitrance of specific molecules such as lignins. Physical and physico-chemical protection mechanisms may act differently on above- and belowground tissues of plants, leading to contrasting contributions of these tissues to soil organic matter (SOM). Cutins and suberins are specific for above and the belowground tissues of higher plants, respectively. Their molecular constituents can be used as biomarkers of the inputs of these plant tissues to soils. In this study, the molecular turnover of specifically plant-derived constituents in soils were estimated using compound specific isotopic tracer techniques applied to agricultural lands converted from C3 plant to C4 plant cropping. We assessed the specific residence times of lignins, cutins and suberins in soils, in order to compare the contributions of above- and belowground tissues to SOM. Lignin turnover in soil was faster than that of total organic carbon. Contrasting dynamics in soils were observed among lignin monomers as well as among cutin/suberin markers, which might be related to their chemical nature, their position into the polymeric structure and/or to the plant tissue in which they are present. This study, combining compound specific isotope measurements with a long term field trial helped understanding soil carbon turnover on a molecular level.
Forfattere
Knut G Berdal Thomas Bøhn Jihong Liu Clarke Merethe Aasmo Finne Askild Lorentz Holck Helge Klungland Casper Linnestad Richard Meadow Arne Mikalsen Anne Ingeborg Myhr Audun Helge Nerland Ingolf Nes Kaare Magne Nielsen Hilde-Gunn Opsahl Sorteberg Odd Egil Stabbetorp Vibeke Thrane Rose VikseSammendrag
Det er ikke registrert sammendrag
Forfattere
Knut G Berdal Jihong Liu Clarke Merethe Aasmo Finne Helge Klungland Casper Linnestad Arne Mikalsen Anne Ingeborg Myhr Audun Helge Nerland Ingolf Nes Kaare Magne Nielsen Hilde-Gunn Opsahl Sorteberg Odd Egil Stabbetorp Vibeke ThraneSammendrag
Det er ikke registrert sammendrag