The Experts below are selected from a list of 252 Experts worldwide ranked by ideXlab platform
Akira Kagawa - One of the best experts on this subject based on the ideXlab platform.
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13CO2 Pulse-Labelling of photoassimilates reveals carbon allocation within and between tree rings
Plant cell & environment, 2006Co-Authors: Akira Kagawa, Atsuko Sugimoto, Trofim C. MaximovAbstract:Post-photosynthetic fractionation processes during translocation, storage and remobilization of photoassimilate are closely related to intra-annual δ13C of tree rings, and understanding how these processes affect tree-ring δ13C is therefore indispensable for improving the quality of climate reconstruction. Our first objective was to study the relationship between translocation path and phloem grain. We Pulse-labelled a branch of Larix gmelinii (Rupr.) Rupr. and later analysed the δ13C distribution in the stem. A 13C spiral translocation path closely related to the spiral grain was observed. Our second objective was to study the use of remobilized storage material for earlywood formation in spring, which is a suspected cause of the autocorrelation (correlation of ring parameters to the climate in the previous year) observed in (isotope) dendroclimatology. We Pulse-labelled whole trees to study how spring, summer and autumn photoassimilate is later used for both earlywood and latewood formation. Analysis of intra-annual δ13C of the tree rings formed after the Labelling revealed that earlywood contained photoassimilate from the previous summer and autumn as well as from the current spring. Latewood was mainly composed of photoassimilate from the current year’s summer/autumn, although it also relied on stored material in some cases. These results emphasize the need for separating earlywood and latewood for climate reconstruction work with narrow boreal tree rings.
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temporal photosynthetic carbon isotope signatures revealed in a tree ring through 13co2 Pulse Labelling
Plant Cell and Environment, 2005Co-Authors: Akira Kagawa, Atsuko Sugimoto, Kana Yamashita, Hisashi AbeAbstract:Using a combined method of Pulse-Labelling trees and analysing detailed distribution of 13 C tracer within tree rings, we studied how photo-assimilates incorporated on a given day are then distributed in a tree ring. A branch of a 4-year-old Cryptomeria japonica D.Don tree growing in Tsukuba, Japan was Pulse-labelled with non-radioactive 13 CO 2 on two occasions: 29 May 2001 and 18 September 2001. Two discs were cut from the stem on 4 March 2002, one immediately under and the other 0.5 m below the branch and put through high-resolution δ 13 C analysis. δ 13 C peaks were observed in both the earlywood and latewood of the concerned tree ring, corresponding to each Pulse-Labelling date. The earlywood peaks was broader than the latewood peaks, possibly reflecting seasonal variation of the width of wood developing zone. Half-widths of the peaks were measured and used as indicators for the potential time resolution of tree-ring isotope analysis. The half-widths of the peaks indicated a time resolution no finer than 8.7-28 and 33-42 d in the early and latewood, respectively. Holocellulose extraction yielded only a slight change to the shape of the δ 13 C peaks. 13 C tracer Pulse-labelled in May and September reached tangentially different locations in the lower disc, suggesting a seasonal change in the pathway of carbohydrates. Local consumption of spring assimilates and long-distance downward transport of autumn assimilates were also suggested.
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Temporal photosynthetic carbon isotope signatures revealed in a tree ring through 13CO2 Pulse‐Labelling
Plant Cell and Environment, 2005Co-Authors: Akira Kagawa, Atsuko Sugimoto, Kana Yamashita, Hisashi AbeAbstract:Using a combined method of Pulse-Labelling trees and analysing detailed distribution of 13 C tracer within tree rings, we studied how photo-assimilates incorporated on a given day are then distributed in a tree ring. A branch of a 4-year-old Cryptomeria japonica D.Don tree growing in Tsukuba, Japan was Pulse-labelled with non-radioactive 13 CO 2 on two occasions: 29 May 2001 and 18 September 2001. Two discs were cut from the stem on 4 March 2002, one immediately under and the other 0.5 m below the branch and put through high-resolution δ 13 C analysis. δ 13 C peaks were observed in both the earlywood and latewood of the concerned tree ring, corresponding to each Pulse-Labelling date. The earlywood peaks was broader than the latewood peaks, possibly reflecting seasonal variation of the width of wood developing zone. Half-widths of the peaks were measured and used as indicators for the potential time resolution of tree-ring isotope analysis. The half-widths of the peaks indicated a time resolution no finer than 8.7-28 and 33-42 d in the early and latewood, respectively. Holocellulose extraction yielded only a slight change to the shape of the δ 13 C peaks. 13 C tracer Pulse-labelled in May and September reached tangentially different locations in the lower disc, suggesting a seasonal change in the pathway of carbohydrates. Local consumption of spring assimilates and long-distance downward transport of autumn assimilates were also suggested.
Daniel Epron - One of the best experts on this subject based on the ideXlab platform.
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Short-term dynamics and partitioning of newly assimilated carbon in the foliage of adult beech and pine are driven by seasonal variations
2017Co-Authors: Dorine Desalme, Caroline Plain, Masako Dannoura, Pascale Maillard, Dominique Gérant, Pierrick Priault, Daniel EpronAbstract:Carbon (C) allocation is a key process determining C cycling in forest ecosystems. However, the mechanisms underlying the annual patterns of C partitioning in trees, influenced by tree phenology and environmental conditions, are not well identified yet. This study aimed to characterize the short-term dynamics and partitioning of newly assimilated carbon in the foliage of adult European beeches (Fagus sylvatica) and maritime pines (Pinus pinaster) across the seasons. We hypothesized that residence times of recently assimilated C in C compounds should change according to the seasons and that seasonal pattern should differ between deciduous and evergreen tree species, since they have different phenology. 13 CO 2 Pulse-Labelling experiments were performed in situ at different dates corresponding to different phenological stages. In beech leaves and pine needles, C contents, isotopic compositions, and 13 C dynamics parameters were determined in total organic matter (bulk foliage), in polar fraction (PF, including soluble sugars, amino acids, organic acids) and in starch. For both species and at each phenological stage, 13 C amount in bulk foliage decreased following a two-pool exponential model, highlighting the partitioning of newly assimilated C between 'mobile' and 'stable' pools. The relative proportion of the stable pool was maximal in beech leaves in May, when leaves were still growing and could incorporate newly assimilated C in structural C compounds. Young pine needles were still receiving C from previous-year needles in June (two months after budburst) although they are already photosynthesizing, acting as a strong C sink. In summer, short mean residence times of 13 C (MRT) in foliage of both tree species reflected the fast respiration and exportation of recent photosynthates to support the whole tree C demand (e.g., supplying perennial organ growth). At the end of the growing season, pre-senescing beech leaves were supplying 13 C to perennial organs, whereas overwintering pine needles accumulated labelled PF, probably to acclimate to colder winter temperatures. Results of this experiment revealed that the dynamics and the in-leaf partitioning of newly assimilated C varied seasonally according to the phenology of the two species. In the future, coupling 13 C Pulse Labelling with compound-specific isotope analysis will be promising for tracing the allocation of newly assimilated C to various physiological functions such as growth, export, osmoregulation and defence in trees submitted to global changes.
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Allocation of recently assimilated carbon in Beech leaves
2013Co-Authors: Dorine Desalme, Daniel Epron, Pascale Maillard, Dominique Gérant, Pierrick PriaultAbstract:Investigating the short-term dynamics of trees’ carbon allocation is critical for understanding the mechanisms underlying annual patterns of carbon allocation in forest ecosystems, influenced by tree phenology and environmental conditions. Pulse-Labelling with stable carbon isotope (13C) enables to trace the fate of labelled carbon into tree and its release to the atmosphere by respiration. This study aimed at characterizing the short-term allocation pattern of the recently assimilated carbon in beech leaves, from its assimilation to its partitioning among the several carbon-containing metabolic pools, and its evolution across seasons. In situ whole-tree crown 13CO2-Pulse Labelling experiments were performed on 10 adult beeches (20-year-old Fagus sylvatica L.) in a natural regeneration mixed stand located in the state forest of Hesse in Northeastern France. Pulse-Labelling campaigns were conducted four times during the growing season, in May, July, August, and September, in order to cover the different beech growing phases. For each labelled tree, leaf samples were harvested over a 6-day chase period. Purification and quantification of C-containing metabolic pools - including the isolation of soluble carbohydrates (including soluble sugars, amino and organic acids), starch and structural compounds - were performed. Total leaf organic matter (bulk) and metabolic pools δ13C were determined by IRMS. In addition, the isotope composition of leaf CO2 efflux was monitored by incubating leaves and analysing respired CO2 by IRMS. The labelled 13C was rapidly assimilated in leaves of each tree and recovered in starch, soluble carbohydrates, structural compounds, and in leaf CO2 efflux. Variations among the different Labelling periods were observed and the implication of season vs environmental factors will be discussed. Finally, these results will also be used for feeding a leaf-scale compartmental model, which describes the fate of the recently-assimilated carbon among leaf respiration, growth, storage and export, giving the opportunity to isolates kinetics parameters of carbon allocation in leaves.
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Pulse-Labelling trees to study carbon allocation dynamics: a review of methods, current knowledge and future prospects
Tree physiology, 2012Co-Authors: Daniel Epron, Masako Dannoura, Michael Bahn, Delphine Derrien, Fernando A. Lattanzi, Jukka Pumpanen, Arthur Gessler, Peter Högberg, Pascale Maillard, Dominique GérantAbstract:Pulse-Labelling of trees with stable or radioactive carbon (C) isotopes offers the unique opportunity to trace the fate of labelled CO(2) into the tree and its release to the soil and the atmosphere. Thus, Pulse-Labelling enables the quantification of C partitioning in forests and the assessment of the role of partitioning in tree growth, resource acquisition and C sequestration. However, this is associated with challenges as regards the choice of a tracer, the methods of tracing labelled C in tree and soil compartments and the quantitative analysis of C dynamics. Based on data from 47 studies, the rate of transfer differs between broadleaved and coniferous species and decreases as temperature and soil water content decrease. Labelled C is rapidly transferred belowground-within a few days or less-and this transfer is slowed down by drought. Half-lives of labelled C in phloem sap (transfer pool) and in mature leaves (source organs) are short, while those of sink organs (growing tissues, seasonal storage) are longer. (13)C measurements in respiratory efflux at high temporal resolution provide the best estimate of the mean residence times of C in respiratory substrate pools, and the best basis for compartmental modelling. Seasonal C dynamics and allocation patterns indicate that sink strength variations are important drivers for C fluxes. We propose a conceptual model for temperate and boreal trees, which considers the use of recently assimilated C versus stored C. We recommend best practices for designing and analysing Pulse-Labelling experiments, and identify several topics which we consider of prime importance for future research on C allocation in trees: (i) whole-tree C source-sink relations, (ii) C allocation to secondary metabolism, (iii) responses to environmental change, (iv) effects of seasonality versus phenology in and across biomes, and (v) carbon-nitrogen interactions. Substantial progress is expected from emerging technologies, but the largest challenge remains to carry out in situ whole-tree Labelling experiments on mature trees to improve our understanding of the environmental and physiological controls on C allocation.
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Seasonal variations of belowground carbon transfer assessed by in situ 13CO2 Pulse Labelling of trees
Biogeosciences, 2011Co-Authors: Daniel Epron, Caroline Plain, Masako Dannoura, Jérôme Ngao, Alexandre Bosc, Jean-christophe Lata, Stéphane Bazot, R. Bakker M., Bernd Zeller, P. PriaultAbstract:Soil CO2 efflux is the main source of CO2 from forest ecosystems and it is tightly coupled to the transfer of recent photosynthetic assimilates belowground and their metabolism in roots, mycorrhiza and rhizosphere microorganisms feeding on root-derived exudates. The objective of our study was to assess patterns of belowground carbon allocation among tree species and along seasons. Pure 13CO2 Pulse Labelling of the entire crown of three different tree species (beech, oak and pine) was carried out at distinct phenological stages. Excess 13C in soil CO2 efflux was tracked using tuneable diode laser absorption spectrometry to determine time lags between the start of the Labelling and the appearance of 13C in soil CO2 efflux and the amount of 13C allocated to soil CO2 efflux. Isotope composition (d13C) of CO2 respired by fine roots and soil microbes was measured at several occasions after Labelling, together with d13C of bulk root tissue and microbial carbon. Time lags ranged from 0.5 to 1.3 days in beech and oak and were longer in pine (1.6-2.7 days during the active growing season, more than 4 days during the resting season), and the transfer of C to the microbial biomass was as fast as to the fine roots. The amount of 13C allocated to soil CO2 efflux was estimated from a compartment model. It varied between 1 and 21% of the amount of 13CO2 taken up by the crown, depending on the species and the season. While rainfall exclusion that moderately decreased soil water content did not affect the pattern of carbon allocation to soil CO2 efflux in beech, seasonal patterns of carbon allocation belowground differed markedly between species, with pronounced seasonal variations in pine and beech. In beech, it may reflect competition with the strength of other sinks (aboveground growth in late spring and storage in late summer) that were not observed in oak. We report a fast transfer of recent photosynthates to the mycorhizosphere and we conclude that the patterns of carbon allocation belowground are species specific and change seasonally according to the phenology of the species.
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Atmospheric phenanthrene pollution modulates carbon allocation in red clover (Trifolium pratense L.)
Environmental Pollution, 2011Co-Authors: Dorine Desalme, Caroline Plain, Daniel Epron, Philippe Binet, Nadine Bernard, Daniel Gilbert, Marie-laure Toussaint, Genevieve ChiapusioAbstract:The influence of atmospheric phenanthrene (PHE) exposure (160 mgm 3) during one month on carbon allocation in clover was investigated by integrative (plant growth analysis) and instantaneous 13CO2 Pulse-Labelling approaches. PHE exposure diminished plant growth parameters (relative growth rate and net assimilation rate) and disturbed photosynthesis (carbon assimilation rate and chlorophyll content), leading to a 25% decrease in clover biomass. The root-shoot ratio was significantly enhanced (from 0.32 to 0.44). Photosynthates were identically allocated to leaves while less allocated to stems and roots. PHE exposure had a significant overall effect on the 13C partitioning among clover organs as more carbon was retained in leaves at the expense of roots and stems. The findings indicate that PHE decreases root exudation or transfer to symbionts and in leaves, retains carbon in a non-structural form diverting photosynthates away from growth and respiration (emergence of an additional C loss process).
Hisashi Abe - One of the best experts on this subject based on the ideXlab platform.
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temporal photosynthetic carbon isotope signatures revealed in a tree ring through 13co2 Pulse Labelling
Plant Cell and Environment, 2005Co-Authors: Akira Kagawa, Atsuko Sugimoto, Kana Yamashita, Hisashi AbeAbstract:Using a combined method of Pulse-Labelling trees and analysing detailed distribution of 13 C tracer within tree rings, we studied how photo-assimilates incorporated on a given day are then distributed in a tree ring. A branch of a 4-year-old Cryptomeria japonica D.Don tree growing in Tsukuba, Japan was Pulse-labelled with non-radioactive 13 CO 2 on two occasions: 29 May 2001 and 18 September 2001. Two discs were cut from the stem on 4 March 2002, one immediately under and the other 0.5 m below the branch and put through high-resolution δ 13 C analysis. δ 13 C peaks were observed in both the earlywood and latewood of the concerned tree ring, corresponding to each Pulse-Labelling date. The earlywood peaks was broader than the latewood peaks, possibly reflecting seasonal variation of the width of wood developing zone. Half-widths of the peaks were measured and used as indicators for the potential time resolution of tree-ring isotope analysis. The half-widths of the peaks indicated a time resolution no finer than 8.7-28 and 33-42 d in the early and latewood, respectively. Holocellulose extraction yielded only a slight change to the shape of the δ 13 C peaks. 13 C tracer Pulse-labelled in May and September reached tangentially different locations in the lower disc, suggesting a seasonal change in the pathway of carbohydrates. Local consumption of spring assimilates and long-distance downward transport of autumn assimilates were also suggested.
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Temporal photosynthetic carbon isotope signatures revealed in a tree ring through 13CO2 Pulse‐Labelling
Plant Cell and Environment, 2005Co-Authors: Akira Kagawa, Atsuko Sugimoto, Kana Yamashita, Hisashi AbeAbstract:Using a combined method of Pulse-Labelling trees and analysing detailed distribution of 13 C tracer within tree rings, we studied how photo-assimilates incorporated on a given day are then distributed in a tree ring. A branch of a 4-year-old Cryptomeria japonica D.Don tree growing in Tsukuba, Japan was Pulse-labelled with non-radioactive 13 CO 2 on two occasions: 29 May 2001 and 18 September 2001. Two discs were cut from the stem on 4 March 2002, one immediately under and the other 0.5 m below the branch and put through high-resolution δ 13 C analysis. δ 13 C peaks were observed in both the earlywood and latewood of the concerned tree ring, corresponding to each Pulse-Labelling date. The earlywood peaks was broader than the latewood peaks, possibly reflecting seasonal variation of the width of wood developing zone. Half-widths of the peaks were measured and used as indicators for the potential time resolution of tree-ring isotope analysis. The half-widths of the peaks indicated a time resolution no finer than 8.7-28 and 33-42 d in the early and latewood, respectively. Holocellulose extraction yielded only a slight change to the shape of the δ 13 C peaks. 13 C tracer Pulse-labelled in May and September reached tangentially different locations in the lower disc, suggesting a seasonal change in the pathway of carbohydrates. Local consumption of spring assimilates and long-distance downward transport of autumn assimilates were also suggested.
Phil Ineson - One of the best experts on this subject based on the ideXlab platform.
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fast assimilate turnover revealed by in situ 13co2 Pulse Labelling in subarctic tundra
Polar Biology, 2012Co-Authors: Jens-arne Subke, Harry W. Vallack, Andreas Heinemeyer, Vincenzo Leronni, Robert Baxter, Phil InesonAbstract:Climatic changes in Arctic regions are likely to have significant impacts on vegetation composition and physiological responses of different plant types, with implications for the regional carbon (C) cycle. Here, we explore differences in allocation and turnover of assimilated C in two Subarctic tundra communities. We used an in situ 13C Pulse at mid-summer in Swedish Lapland to investigate C allocation and turnover in four contrasting tundra plant communities. We found a high rate of turnover of assimilated C in leaf tissues of Betula nana and graminoid vegetation at the height of the growing season, with a mean residence time of Pulse-derived 13C of 1.1 and 0.7 days, respectively. One week after the Pulse, c. 20 and 15%, respectively, of assimilated label-C remained in leaf biomass, representing most likely allocation to structural biomass. For the perennial leaf tissue of the graminoid communities, a remainder of approximately 5% of the Pulse-derived C was still traceable after 1 year, whereas none was detectable in Betula foliage. The results indicate a relatively fast C turnover and small belowground allocation during the active growing season of recent assimilates in graminoid communities, with comparatively slower turnover and greater investment in belowground allocation by B. nana vegetation.
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short term dynamics of abiotic and biotic soil 13co2 effluxes after in situ 13co2 Pulse Labelling of a boreal pine forest
New Phytologist, 2009Co-Authors: Jens-arne Subke, Peter Högberg, Harry W. Vallack, Tord Magnusson, Sonja G. Keel, Daniel B. Metcalfe, Phil InesonAbstract:Physical diffusion of isotopic tracers into and out of soil pores causes considerable uncertainty for the timing and magnitude of plant belowground allocation in Pulse-Labelling experiments. Here, we partitioned soil CO(2) isotopic fluxes into abiotic tracer flux (physical return), heterotrophic flux, and autotrophic flux contributions following (13)CO(2) Labelling of a Swedish Pinus sylvestris forest. Soil CO(2) efflux and its isotopic composition from a combination of deep and surface soil collars was monitored using a field-deployed mass spectrometer. Additionally, (13)CO(2) within the soil profile was monitored. Physical (abiotic) efflux of (13)CO(2) from soil pore spaces was found to be significant for up to 48 h after Pulse Labelling, and equalled the amount of biotic label flux over 6 d. Measured and modelled changes in (13)CO(2) concentration throughout the soil profile corroborated these results. Tracer return via soil CO(2) efflux correlated significantly with the proximity of collars to trees, while daily amplitudes of total flux (including heterotrophic and autotrophic sources) showed surprising time shifts compared with heterotrophic fluxes. The results show for the first time the significance of the confounding influence of physical isotopic CO(2)-tracer return from the soil matrix, calling for the inclusion of meaningful control treatments in future Pulse-chase experiments.
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Short‐term dynamics of abiotic and biotic soil 13CO2 effluxes after in situ 13CO2 Pulse Labelling of a boreal pine forest
The New phytologist, 2009Co-Authors: Jens-arne Subke, Peter Högberg, Harry W. Vallack, Tord Magnusson, Sonja G. Keel, Daniel B. Metcalfe, Phil InesonAbstract:Physical diffusion of isotopic tracers into and out of soil pores causes considerable uncertainty for the timing and magnitude of plant belowground allocation in Pulse-Labelling experiments. Here, we partitioned soil CO(2) isotopic fluxes into abiotic tracer flux (physical return), heterotrophic flux, and autotrophic flux contributions following (13)CO(2) Labelling of a Swedish Pinus sylvestris forest. Soil CO(2) efflux and its isotopic composition from a combination of deep and surface soil collars was monitored using a field-deployed mass spectrometer. Additionally, (13)CO(2) within the soil profile was monitored. Physical (abiotic) efflux of (13)CO(2) from soil pore spaces was found to be significant for up to 48 h after Pulse Labelling, and equalled the amount of biotic label flux over 6 d. Measured and modelled changes in (13)CO(2) concentration throughout the soil profile corroborated these results. Tracer return via soil CO(2) efflux correlated significantly with the proximity of collars to trees, while daily amplitudes of total flux (including heterotrophic and autotrophic sources) showed surprising time shifts compared with heterotrophic fluxes. The results show for the first time the significance of the confounding influence of physical isotopic CO(2)-tracer return from the soil matrix, calling for the inclusion of meaningful control treatments in future Pulse-chase experiments.
Torben R Christensen - One of the best experts on this subject based on the ideXlab platform.
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carbon partitioning in a wet and a semiwet subarctic mire ecosystem based on in situ 14c Pulse Labelling
Soil Biology & Biochemistry, 2011Co-Authors: Maria Olsrud, Torben R ChristensenAbstract:In this study we quantify the partitioning of recent assimilates to above- and below-ground carbon (C) pools in two subarctic mire ecosystems - wet minerotrophic and semiwet ombrotrophic mire - using in situ C-14 Pulse-Labelling. Ecosystem C partitioning to rhizomes, coarse roots, fine roots, dissolved organic carbon (DOC) and microbes were quantified twice during the growing season at three different soil depths. Finally the C-14-partitioning data from this and a previous study were combined to estimate the overall C partitioning of the three main vegetation types of a Scandinavian subarctic mire in early and late summer. The semiwet ombrotrophic ecosystem hosted a much larger root biomass on an area basis compared to the wet minerotrophic ecosystem which might be due to differences in the soil nutrient level. Microbial C was found to be the largest C-pool in both ecosystems. Ecosystem C-14 partitioning was poorly related to plant biomass for the semiwet and the wet ecosystem. Overall a higher partitioning of recent assimilates to below-ground compartments was apparent in August-September compared to June-July, while the opposite was found for the above-ground C-pools. In the semiwet ecosystem twice as much C-14 was found in DOC compared to the wet ecosystem, where root density, litter and above-ground biomass were important controls of the C-14-recovery in DOC. Plant-derived DOC was estimated to be 15.4 versus 12.9 mg C m(-2) d(-1) in the semiwet and wet ecosystem, respectively. Graminoid dominated and dwarf shrub dominated vegetation types of the subarctic mire Stordalen differ with respect to the relative amount of recently assimilated C partitioned to C-pools with "slow" versus "fast" decomposition rate. The capacity for sequestration of recently fixed C within "slow" C-pools might affect the ecosystem C balance (NEE) and C-storage. The potential for vegetation changes might therefore be an important factor to consider in studies of response of ecosystem C-dynamics to global change factors in subarctic mires. (C) 2010 Elsevier Ltd. All rights reserved. (Less)
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carbon cycling in subarctic tundra seasonal variation in ecosystem partitioning based on in situ 14c Pulse Labelling
Soil Biology & Biochemistry, 2004Co-Authors: Maria Olsrud, Torben R ChristensenAbstract:Carbon assimilation and allocation were studied in a tundra ecosystem in northern Scandinavia. Seasonal variation in the below-ground carbon allocation to dissolved organic carbon (DOC), coarse-, fine-, and hair roots was investigated using in situ C-14 Pulse-Labelling, adding 2-3 MBq (CO2)-C-14, dm(-2) to the above-ground vegetation. Combining the allocation data with regression models of the seasonal carbon flux made it possible to estimate a temporally explicit ecosystem carbon allocation budget. The ecosystem was a net source of CO2, losing on average 0.97 gC m(-2) d(-1) to the atmosphere, with little variation through the season. There was, however, significant temporal variation in partitioning of recently assimilated carbon. Allocation to below-ground compartments over 32 days following Labelling increased from 18% in June to 55% in September. Above-ground allocation showed the opposite trend. Hair roots and DOC were strong sinks in the autumn. Transport of newly assimilated carbon occurred rapidly throughout the season, C-14 appearing in all sampled pools within 4 h of Labelling. The seasonal variation in carbon partitioning observed in this study has implications for the residence time of assimilated carbon in the ecosystem. A relatively greater allocation to rapidly decomposing pools, such as hair roots and DOC, would tend to reduce incorporation into woody tissue, increasing the overall rate of carbon cycling and decreasing ecosystem storage. The results of this study will be of value for building and validating mechanistic models of ecosystem carbon flow in tundra and subarctic ecosystems. (C) 2003 Elsevier Ltd. All fights reserved. (Less)
