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Carbon Exchange (carbon + exchange)
Selected AbstractsSphagnum under pressure: towards an ecohydrological approach to examining Sphagnum productivityECOHYDROLOGY, Issue 4 2008D. K. Thompson Abstract The genus Sphagnum is the key peat-forming bryophyte in boreal ecosystems. Relying entirely on passive capillary action for water transport, soil moisture is often the limiting factor in Sphagnum production, and hence peat accumulation. While several hydrological models of peat physics and peatland water movement exist, these models do not readily interface with observations and models of peatland carbon accumulation. A conflict of approaches exists, where hydrological studies primarily utilize variables such as hydraulic head, while ecological models of Sphagnum growth adopt the coarse hydrological variables of water table (WT), volumetric water content (VWC) or gravimetric water content (WC). This review examines the potential of soil pressure head as a measurement to link the hydrological and ecological functioning of Sphagnum in peatlands. The non-vascular structure of Sphagnum mosses and the reliance on external capillary transport of water in the mosses make them an ideal candidate for this approach. The main advantage of pressure head is the ability to mechanistically link plot-scale hydrology to cellular-scale water requirements and carbon exchange. Measurement of pressure head may improve photosynthetic process representation in the next generation of peatland models. Copyright © 2008 John Wiley & Sons, Ltd. [source] Plant functional group identity influences short-term peatland ecosystem carbon flux: evidence from a plant removal experimentFUNCTIONAL ECOLOGY, Issue 2 2009Susan E. Ward Summary 1Northern hemisphere peatlands are globally important stores of organic soil carbon. We examined effects of plant functional group identity on short-term carbon (C) flux in an ombrotrophic peatland in northern England, UK, by selectively removing one of each of the three dominant plant functional groups (ericoid dwarf-shrubs, graminoids and bryophytes). Carbon dynamics were quantified by a combination of CO2 flux measurements and 13CO2 stable isotope pulse labelling approaches. 2Significant effects of plant functional group removals on CO2 fluxes and tracer 13C uptake and turnover were detected. Removal of ericoid dwarf-shrubs had the greatest influence on gross CO2 flux, increasing rates of respiration and photosynthesis by > 200% relative to the undisturbed control. After pulse labelling with 13CO2, we found that turnover of recent photosynthate, measured as respired 13CO2, was also greatest in the absence of dwarf-shrubs. 3Analysis of 13C tracer enrichment in leaf tissues from all plant removal treatments showed that the rate of fixation of 13CO2 and turnover of 13C labelled photosynthate in leaf tissue was greatest in graminoids and lowest in bryophytes. Furthermore, graminoid leaf 13C enrichment was greatest when growing in the absence of dwarf-shrubs, suggesting that the presence of dwarf-shrubs reduced the photosynthetic activity of graminoids. 4We conclude that plant functional groups differentially influence the uptake and short-term flux of carbon in peatlands, suggesting that changes in the functional composition of vegetation resulting from global change have the potential to alter short-term patterns of carbon exchange in peatland. [source] Interspecific carbon exchange and cost of interactions between basidiomycete mycelia in soil and woodFUNCTIONAL ECOLOGY, Issue 2 2002J. M. Wells Summary 1.,The outcome of interactions between wood decay basidiomycete fungi is affected by the size of territory held by a mycelium. We investigated the outcomes of interactions between the cord-forming saprotrophs Phanerochaete velutina (DC: Pers.) Parm., Phallus impudicus (L.) Pers. and Hypholoma fasciculare (Huds: Fr) Kumner over 152,155 days, determined as ability to capture or share territory in soil and wood, in terms of decay partitioning and the carbon cost of interactions. 2.,The outcome of interactions in wood alone differed from those in which the fungi competed for an opponents' inoculum in soil microcosms. Competitive ability (the ability to capture or co-occupy an opponent's inoculum) varied according to species and inoculum age. In wood block pairings in the absence of soil there was evidence that P. velutina opportunistically utilized C previously mobilized within an opponent's inoculum. 3.,In soil systems, short-term (28-day) respiratory losses of preloaded 14C (supplied as glucose) indicated that interaction could have a substantial C cost, depending on the resource quality of the opponents' inocula. Phallus impudicus inocula accumulated 14C from opponents' mycelia during ,deadlock' interactions, although reciprocal interspecific 14C transfer was not observed. 4.,Saprotrophic cord-forming basidiomycetes are considered to be highly conservative of acquired nutrients, representing a significant nutrient reservoir in woodland ecosytems. Here we demonstrate that a potential major pathway for nutrient mineralization by this group is nutrient loss during competitive interactions in soil. [source] Isotopic and petrological evidence of fluid,rock interaction at a Tethyan ocean,continent transition in the Alps: implications for tectonic processes and carbon transfer during early ocean formationGEOFLUIDS (ELECTRONIC), Issue 4 2007A. ENGSTRÖM Abstract We report overprinting stable isotope evidence of fluid,rock interaction below two detachment faults along which mantle rocks were exhumed to the seafloor, between the respective landward and seaward limits of oceanic and continental crust, at a Tethyan ocean,continent transition (OCT). This OCT, which is presently exposed in the Tasna nappe (south-eastern Switzerland) is considered an on-land analogue of the well-studied Iberian OCT. We compare our results with the fault architecture (fault core,damage zone,protolith) described by Caine et al. [Geology (1996) Vol. 24, pp. 1025,1028]. We confirm the existence of a sharp boundary between the fault core and damage zone based on isotopic data, but the boundary between the damage zone and protolith is gradational. We identify evidence for: (1) pervasive isotopic modification to 8.4 ± 0.1, which accompanied or post-dated serpentinization of these mantle rocks at an estimated temperature of 67,109°C, (2) either (i) partial isolation of some highly strained regions [fault core(s) and mylonite] from this pervasive isotopic modification, because of permeability reduction (Caine et al.) or (ii) subsequent isotopic modification caused by structurally channelled flow of warm fluids within these highly strained regions, because of permeability enhancement, and (3) isotopic modification, which is associated with extensive calcification at T = 54,100°C, primarily beneath the younger of the two detachment faults and post-dating initial serpentinization. By comparing the volumetric extent of calcification with an experimentally verified model for calcite precipitation in veins, we conclude that calcification could have occurred in response to seawater infiltration, with a calculated flux rate of 0.1,0.2 m year,1 and a minimum duration of 0.2,4.0 × 104 years. The associated time-averaged uptake flux of carbon during this period was 8,120 mol m,2 year,1. By comparison with the estimated area of exhumed mantle rocks at the Iberian OCT, we calculate a maximum annual uptake flux for carbon of 2,30 Tg year,1. This is an order of magnitude greater than that for carbon exchange at the mid-ocean ridges and 0.1,1.4% of the global oceanic uptake flux for carbon. [source] Impact of past and present land-management on the C-balance of a grassland in the Swiss AlpsGLOBAL CHANGE BIOLOGY, Issue 11 2008NELE ROGIERS Abstract Grasslands cover about 40% of the ice-free global terrestrial surface, but their quantitative importance in global carbon exchange with the atmosphere is still highly uncertain, and thus their potential for carbon sequestration remains speculative. Here, we report on CO2 exchange of an extensively used mountain hay meadow and pasture in the Swiss pre-Alps on high-organic soils (7,45% C by mass) over a 3-year period (18 May 2002,20 September 2005), including the European summer 2003 heat-wave period. During all 3 years, the ecosystem was a net source of CO2 (116,256 g C m,2 yr,1). Harvests and grazing cows (mostly via C export in milk) further increased these C losses, which were estimated at 355 g C m,2 yr,1 during 2003 (95% confidence interval 257,454 g C m,2 yr,1). Although annual carbon losses varied considerably among years, the CO2 budget during summer 2003 was not very different from the other two summers. However, and much more importantly, the winter that followed the warm summer of 2003 observed a significantly higher carbon loss when there was snow (133±6 g C m,2) than under comparable conditions during the other two winters (73±5 and 70±4 g C m,2, respectively). The continued annual C losses can most likely be attributed to the long-term effects of drainage and peat exploitation that began 119 years ago, with the last significant drainage activities during the Second World War around 1940. The most realistic estimate based on depth profiles of ash content after combustion suggests that there is an 500,910 g C m,2 yr,1 loss associated with the decomposition of organic matter. Our results clearly suggest that putting efforts into preserving still existing carbon stocks may be more successful than attempts to increase sequestration rates in such high-organic mountain grassland soils. [source] Seasonal and annual variation of carbon exchange in an evergreen Mediterranean forest in southern FranceGLOBAL CHANGE BIOLOGY, Issue 4 2008V. ALLARD Abstract We present 9 years of eddy covariance measurements made over an evergreen Mediterranean forest in southern France. The goal of this study was to quantify the different components of the carbon (C) cycle, gross primary production (GPP) and ecosystem respiration (Reco), and to assess the effects of climatic variables on these fluxes and on the net ecosystem exchange of carbon dioxide. The Puéchabon forest acted as a net C sink of ,254 g C m,2 yr,1, with a GPP of 1275 g C m,2 yr,1 and a Reco of 1021 g C m,2 yr,1. On average, 83% of the net annual C sink occurred between March and June. The effects of exceptional events such the insect-induced partial canopy defoliation that occurred in spring 2005, and the spring droughts of 2005 and 2006 are discussed. A high interannual variability of ecosystem C fluxes during summer and autumn was observed but the resulting effect on the annual net C budget was moderate. Increased severity and/or duration of summer drought under climate change do not appear to have the potential to negatively impact the average C budget of this ecosystem. On the contrary, factors affecting ecosystem functioning (drought and/or defoliation) during March,June period may reduce dramatically the annual C balance of evergreen Mediterranean forests. [source] Quantifying carbon sequestration as a result of soil erosion and deposition: retrospective assessment using caesium-137 and carbon inventoriesGLOBAL CHANGE BIOLOGY, Issue 12 2007TIMOTHY ANDREW QUINE Abstract The role of soil erosion in the global carbon cycle remains a contested subject. A new approach to the retrospective derivation of erosion-induced quantitative fluxes of carbon between soil and atmosphere is presented and applied. The approach is based on the premise that soil redistribution perturbs the carbon cycle by driving disequilibrium between soil carbon content and input. This perturbation is examined by establishing the difference between measured carbon inventories and the inventories that would be found if input and content were in dynamic equilibrium. The carbon inventory of a profile in dynamic equilibrium is simulated by allowing lateral and vertical redistribution of carbon but treating all other profile inputs as equal to outputs. Caesium-137 is used to derive rates of vertical and lateral soil redistribution. Both point and field-scale estimates of carbon exchange with the atmosphere are derived using the approach for a field subject to mechanized agricultural in the United Kingdom. Sensitivity analysis is undertaken and demonstrates that the approach is robust. The results indicate that, despite a 15% decline in the carbon content of the cultivation layer of the eroded part of the field, this area has acted as a net sink of 11 ± 2 g C m,2 yr,1 over the last half century and that in the field as a whole, soil redistribution has driven a sink of 7 ± 2 g C m,2 yr,1 (6 ± 2 g C m,2 yr,1 if all eroded carbon transported beyond the field boundary is lost to the atmosphere) over the same period. This is the first empirical evidence for, and quantification of, dynamic replacement of eroded carbon. The relatively modest field-scale net sink is more consistent with the identification of erosion and deposition as a carbon sink than a carbon source. There is a clear need to assemble larger databases with which to evaluate critically the carbon sequestration potential of erosion and deposition in a variety of conditions of agricultural management, climate, relief, and soil type. In any case, this study demonstrated that the operation of erosion and deposition processes within the boundaries of agricultural fields must be understood as a key driver of the net carbon cycle consequences of cultivating land. [source] Importance of changing CO2, temperature, precipitation, and ozone on carbon and water cycles of an upland-oak forest: incorporating experimental results into model simulationsGLOBAL CHANGE BIOLOGY, Issue 9 2005Paul J. Hanson Abstract Observed responses of upland-oak vegetation of the eastern deciduous hardwood forest to changing CO2, temperature, precipitation and tropospheric ozone (O3) were derived from field studies and interpreted with a stand-level model for an 11-year range of environmental variation upon which scenarios of future environmental change were imposed. Scenarios for the year 2100 included elevated [CO2] and [O3] (+385 ppm and +20 ppb, respectively), warming (+4°C), and increased winter precipitation (+20% November,March). Simulations were run with and without adjustments for experimentally observed physiological and biomass adjustments. Initial simplistic model runs for single-factor changes in CO2 and temperature predicted substantial increases (+191% or 508 g C m,2 yr,1) or decreases (,206% or ,549 g C m,2 yr,1), respectively, in mean annual net ecosystem carbon exchange (NEEa,266±23 g C m,2 yr,1 from 1993 to 2003). Conversely, single-factor changes in precipitation or O3 had comparatively small effects on NEEa (0% and ,35%, respectively). The combined influence of all four environmental changes yielded a 29% reduction in mean annual NEEa. These results suggested that future CO2 -induced enhancements of gross photosynthesis would be largely offset by temperature-induced increases in respiration, exacerbation of water deficits, and O3 -induced reductions in photosynthesis. However, when experimentally observed physiological adjustments were included in the simulations (e.g. acclimation of leaf respiration to warming), the combined influence of the year 2100 scenario resulted in a 20% increase in NEEa not a decrease. Consistent with the annual model's predictions, simulations with a forest succession model run for gradually changing conditions from 2000 to 2100 indicated an 11% increase in stand wood biomass in the future compared with current conditions. These model-based analyses identify critical areas of uncertainty for multivariate predictions of future ecosystem response, and underscore the importance of long term field experiments for the evaluation of acclimation and growth under complex environmental scenarios. [source] Long-term carbon exchange in a sparse, seasonally dry tussock grasslandGLOBAL CHANGE BIOLOGY, Issue 10 2004John E. Hunt Abstract Rainfall and its seasonal distribution can alter carbon dioxide (CO2) exchange and the sustainability of grassland ecosystems. Using eddy covariance, CO2 exchange between the atmosphere and a sparse grassland was measured for 2 years at Twizel, New Zealand. The years had contrasting distributions of rain and falls (446 mm followed by 933 mm; long-term mean=646 mm). The vegetation was sparse with total above-ground biomass of only 1410 g m,2. During the dry year, leaf area index peaked in spring (November) at 0.7, but it was <0.2 by early summer. The maximum daily net CO2 uptake rate was only 1.5 g C m,2 day,1, and it occurred before mid-summer in both years. On an annual basis, for the dry year, 9 g C m,2 was lost to the atmosphere. During the wet year, 41 g C m,2 was sequestered from the atmosphere. The net exchange rates were determined mostly by the timing and intensity of spring rainfall. The components of ecosystem respiration were measured using chambers. Combining scaled-up measurements with the eddy CO2 effluxes, it was estimated that 85% of ecosystem respiration emanated from the soil surface. Under well-watered conditions, 26% of the soil surface CO2 efflux came from soil microbial activity. Rates of soil microbial CO2 production and net mineral-N production were low and indicative of substrate limitation. Soil respiration declined by a factor of four as the soil water content declined from field capacity (0.21 m3 m,3) to the driest value obtained (0.04 m3 m,3). Rainfall after periods of drought resulted in large, but short-lived, respiration pulses that were curvilinearly related to the increase in root-zone water content. Coupled with the low leaf area and high root : shoot ratio, this sparse grassland had a limited capacity to sequester and store carbon. Assuming a proportionality between carbon gain and rainfall during the summer, rainfall distribution statistics suggest that the ecosystem is sustainable in the long term. [source] The growth respiration component in eddy CO2 flux from a Quercus ilex mediterranean forestGLOBAL CHANGE BIOLOGY, Issue 9 2004S. Rambal Abstract Ecosystem respiration, arising from soil decomposition as well as from plant maintenance and growth, has been shown to be the most important component of carbon exchange in most terrestrial ecosystems. The goal of this study was to estimate the growth component of whole-ecosystem respiration in a Mediterranean evergreen oak (Quercus ilex) forest over the course of 3 years. Ecosystem respiration (Reco) was determined from night-time carbon dioxide flux (Fc) using eddy correlation when friction velocity (u*) was greater than 0.35 m s,1 We postulated that growth respiration could be evaluated as a residual after removing modeled base Reco from whole-ecosystem Reco during periods when growth was most likely occurring. We observed that the model deviated from the night-time Fc -based Reco during the period from early February to early July with the largest discrepancies occurring at the end of May, coinciding with budburst when active aboveground growth and radial growth increment are greatest. The highest growth respiration rates were observed in 2001 with daily fluxes reaching up to 4 g C m,2. The cumulative growth respiration for the entire growth period gave total carbon losses of 170, 208, and 142 g C m,2 for 1999, 2001, and 2002, respectively. Biochemical analysis of soluble carbohydrates, starch, cellulose, hemicellulose, proteins, lignin, and lipids for leaves and stems allowed calculation of the total construction costs of the different growth components, which yielded values of 154, 200, and 150 g C for 3 years, respectively, corresponding well to estimated growth respiration. Estimates of both leaf and stem growth showed very large interannual variation, although average growth respiration coefficients and average yield of growth processes were fairly constant over the 3 years and close to literature values. The time course of the growth respiration may be explained by the growth pattern of leaves and stems and by cambial activity. This approach has potential applications for interpreting the effects of climate variation, disturbances, and management practices on growth and ecosystem respiration. [source] Simulating vegetation processes along the Kalahari transectGLOBAL CHANGE BIOLOGY, Issue 3 2004F. I. Woodward Abstract The Sheffield Dynamic Global Vegetation Model has simulated the structure and net carbon exchange of vegetation at five sites along the Kalahari transect where there is a strong gradient in precipitation from 299 to 918 mm yr,1. There has been a decline in precipitation of 8 mm yr,1 along the whole of the transect since about 1970. Simulations of vegetation dynamics and structure indicate that this decline has exerted a notable effect on the vegetation, with reductions in woody plant cover at the dry end of the transect and reductions in tree density at the wetter end. These changes were driven primarily by reductions in the net primary production and increased rates of mortality, with rather small impacts of fire. [source] The contribution of bryophytes to the carbon exchange for a temperate rainforestGLOBAL CHANGE BIOLOGY, Issue 8 2003Evan H. DeLucia Abstract Bryophytes blanket the floor of temperate rainforests in New Zealand and may influence a number of important ecosystem processes, including carbon cycling. Their contribution to forest floor carbon exchange was determined in a mature, undisturbed podocarp-broadleaved forest in New Zealand, dominated by 100,400-year-old rimu (Dacrydium cupressimum) trees. Eight species of mosses and 13 species of liverworts contributed to the 62% cover of the diverse forest floor community. The bryophyte community developed a relatively thin (depth <30 mm), but dense, canopy that experienced elevated CO2 partial pressures (median 46.6 Pa immediately below the bryophyte canopy) relative to the surrounding air (median 37.6 Pa at 100 mm above the canopy). Light-saturated rates of net CO2 exchange from 14 microcosms collected from the forest floor were highly variable; the maximum rate of net uptake (bryophyte photosynthesis , whole-plant respiration) per unit ground area at saturating irradiance was 1.9 ,mol m,2 s,1 and in one microcosm, the net rate of CO2 exchange was negative (respiration). CO2 exchange for all microcosms was strongly dependent on water content. The average water content in the microcosms ranged from 1375% when fully saturated to 250% when air-dried. Reduction in water content across this range resulted in an average decrease of 85% in net CO2 uptake per unit ground area. The results from the microcosms were used in a model to estimate annual carbon exchange for the forest floor. This model incorporated hourly variability in average irradiance reaching the forest floor, water content of the bryophyte layer, and air and soil temperature. The annual net carbon uptake by forest floor bryophytes was 103 g m,2, compared to annual carbon efflux from the forest floor (bryophyte and soil respiration) of ,1010 g m,2. To put this in perspective of the magnitude of the components of CO2 exchange for the forest floor, the bryophyte layer reclaimed an amount of CO2 equivalent to only about 10% of forest floor respiration (bryophyte plus soil) or ,11% of soil respiration. The contribution of forest floor bryophytes to productivity in this temperate rainforest was much smaller than in boreal forests, possibly because of differences in species composition and environmental limitations to photosynthesis. Because of their close dependence on water table depth, the contribution of the bryophyte community to ecosystem CO2 exchange may be highly responsive to rapid changes in climate. [source] The evolution of, and revolution in, land surface schemes designed for climate modelsINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 5 2003A. J. Pitman Abstract The land surface is a key component of climate models. It controls the partitioning of available energy at the surface between sensible and latent heat, and it controls the partitioning of available water between evaporation and runoff. The land surface is also the location of the terrestrial carbon sink. Evidence is increasing that the influence of the land surface is significant on climate and that changes in the land surface can influence regional- to global-scale climate on time scales from days to millennia. Further, there is now a suggestion that the terrestrial carbon sink may decrease as global temperatures increase as a consequence of rising CO2 levels. This paper provides the theoretical background that explains why the land surface should play a central role in climate. It also provides evidence, sourced from climate model experiments, that the land surface is of central importance. This paper then reviews the development of land surface models designed for climate models from the early, very simple models through to recent efforts, which include a coupling of biophysical processes to represent carbon exchange. It is pointed out that significant problems remain to be addressed, including the difficulties in parameterizing hydrological processes, root processes, sub-grid-scale heterogeneity and biogeochemical cycles. It is argued that continued development of land surface models requires more multidisciplinary efforts by scientists with a wide range of skills. However, it is also argued that the framework is now in place within the international community to build and maintain the latest generation of land surface models. Further, there should be considerable optimism that consolidating the recent rapid advances in land surface modelling will enhance our capability to simulate the impacts of land-cover change and the impacts of increasing CO2 on the global and regional environment. Copyright © 2003 Royal Meteorological Society [source] Insights into the processing of carbon in the South Florida Cypress Wetlands: a whole-ecosystem approach using network analysisJOURNAL OF BIOGEOGRAPHY, Issue 3 2000Cristina Bondavalli Abstract Aim The aim of this research was to investigate the potential of the South Florida Cypress Wetlands as a carbon-accumulating system. Location This ecosystem is part of the Big Cypress Natural Preserve, located in the south-west part of Florida (USA) between the Mangrove Swamps that border the Gulf of Mexico and the Everglades. Methods This investigation was carried out by constructing networks of carbon exchange between the living and nonliving components that comprise this ecosystem. By means of these networks potential for carbon accumulation has been assessed by identifying and quantifying pathways for the transfer of carbon, assessing the efficiency between trophic levels, and evaluating the importance of material cycling. These analyses are commonly referred to as network analysis. Results Results obtained show that dependency on detritus by higher trophic levels is rather low and so is the trophic efficiency. Yet, less than 10% of the carbon that flows through the system is recycled and the magnitude of internal ascendency reaches only 40% of the total system ascendency. Main,conclusions All these results support the hypothesis that the South Florida Cypress Wetlands are predominately flow-through in nature and that carbon accumulation in this environment is noticeable. [source] | |||||||||||||