bluuebunny/crossref_metadata_2025 huggingface dataset:
Seasonal variation of gross nitrification rates at three differently treated long-term fertilisations sites
Authors: Stange C. F. , Neue H.-U.
Published: April 2010

Abstract. The formation of nitrate (nitrification) in soils is an important process that influences the form of N available for plant uptake and the potential off-site N losses. Gross nitrification is one of the main sources of nitrous oxide (N2O) and nitric oxide (NO) from soils. A field experiment was designed to verify the idea that gross nitrification rates in soils can be readily predicted by a model approach where seasonal variability is described only by soil moisture and soil temperature and the magnitude of gross nitrification is controlled by the soil organic matter (SOM). Gross nitrification rates were measured by a Barometric Process Separation (BaPS), first described by Ingwersen et al. (1999). The BaPS measurements were validated with the commonly used 15N pool dilution technique measurements at six times. In general, the rates determined from both measurement approaches were in the same order of magnitude and showed a good correlation. The effects of three different fertilisations (mineral fertiliser, manure and the control) over more than 100 years on gross nitrification rates were investigated. During 2004 soil probes from the long-term "static fertilisation experiment" at Bad Lauchstädt were sampled weekly and were measured in the laboratory under field conditions and subsequently under standardised conditions (16°C soil temperature and −30 kPa matrix potential) with the Barometric Process Separation system (BaPS). Gross nitrification rates determined by the BaPS-method under field conditions showed a high temporal variability and ranged from 5 to 77 μg N h−1 kg−1 dry mass, 2 to 74 μg N h−1 kg−1 dry mass and 0 to 49 μg N h−1 kg−1 dry mass with respect to manure, mineral fertiliser and control. The annual average was 0.32, 0.26 and 0.18 g N a−1 kg−1 dry mass for the manure site, mineral fertiliser site and control site, respectively. On all sites gross nitrification revealed a strong seasonal dynamic. Three different methods (a temperature and soil moisture dependency model from Recous et al., 1998, a multiple linear regression and the method proposed in this paper) were applied for reproducing the measured results. On the manure site 78% to 80%, on the mineral fertiliser site 66% to 72% and on the control site 39% to 56% of the observed variations could be explained by the tested models. Gross nitrification rates determined under standardised conditions did not show any seasonal trends but did also however reveal high temporal variability.
Ammonia sources and sinks in an intensively managed grassland using dynamic chambers
Authors: David M. , Loubet B. , Cellier P. , Mattsson M. , Schjoerring J. K. , Nemitz E. , Roche R. , Riedo M. , Sutton M. A.
Published: April 2010

Abstract. Grassland is a canopy with a complex structure where sources and sinks of ammonia may coexist at the plant level. Moreover, management practices such as mowing, hay production and grazing, may change the composition of the sward and hence the source-sinks relationship at the canopy level as well as the interaction with the atmosphere. There is therefore a need to better understand the exchanges of ammonia between grasslands and the atmosphere, especially regarding the locations of sources and sinks and their magnitudes. Fluxes of atmospheric ammonia (NH3) within a grassland canopy were assessed in the field and under controlled conditions using a dynamic chamber technique (cuvette). These cuvette measurements were combined with extraction techniques to estimate the ammonium (NH4+) concentration and the pH of a given part of the plant or soil, leading to an estimated ammonia compensation point (Cp). The combination of the cuvette and the extraction techniques was used to identify the potential sources and sinks of NH3 within the different compartments of the grassland: the soil, the litter or "litter leaves", and the functioning "green leaves". A set of 6 field experiments and 6 laboratory experiments were performed in which the different compartments were either added or removed from the cuvettes. This study shows that the cuvette measurements agree with the extraction technique in ordering the strength of compartment sources. It suggests that in the studied grassland the green leaves were mostly a sink for NH3 with a compensation point around 0.1–0.4 μg m−3 NH3 and an NH3 flux of 6 to 7 ng m−2 s−1 NH3. Cutting of the grass did not increase the NH3 fluxes of the green leaves. The litter was found to be the largest source of NH3 in the canopy, with a compensation point up to 1000 μg m−3 NH3 and an NH3 flux up to 90 ng m−2 s−1 NH3. The litter was found to be a much smaller NH3 source when dried (Cp=160 μg m−3 NH3 and FNH3=35 ng m−2 s−1 NH3). Moreover emissions from the litter were found to vary with the relative humidity of the air. The soil was a strong source of NH3 in the period immediately after cutting (Cp=320 μg m−3 NH3 and FNH3=60 ng m−2 s−1 NH3), although always relatively smaller than the litter source. The soil NH3 emissions were, however, not lasting more than one day, and were not observed with sieved soil. Soil emissions not be solely explained by xylem sap flow extruding NH4+. These results indicate that future research on grassland-ammonia relationships should focus on the post-mowing period and the role of litter in interaction with meteorological conditions.
Advection of NH3 over a pasture field, and its effect on gradient flux measurements
Authors: Loubet B. , Milford C. , Hensen A. , Daemmgen U. , Erisman J.-W. , Cellier P. , Sutton M. A.
Published: April 2010

Abstract. Deposition of atmospheric ammonia (NH3) to semi-natural ecosystems leads to serious adverse effects, such as acidification and eutrophication. A step in this quantification is the measurement of NH3 fluxes over semi-natural and agricultural land. However, measurement of NH3 fluxes over vegetation in the vicinity of strong NH3 sources is difficult, since NH3 emissions are highly heterogeneous. Indeed, under such conditions, local advection errors may alter the measured fluxes. In this study, local advection errors (Δ Fz,adv) were estimated over a 14 ha grassland field, which was successively cut and fertilised, as part of the GRAMINAE integrated Braunschweig experiment. The magnitude of Δ Fz,adv was determined up to 810 m downwind from farm buildings emitting between 6 and 12 kg NH3 day−1. The GRAMINAE experiment provided a unique opportunity to compare two methods of estimating Δ Fz,adv: (1) based on direct measurements of horizontal concentration gradients, and (2) based on inverse dispersion modelling. Two sources of local advection were clearly identified: the farm NH3 emissions leading to positive Δ Fz,adv, and field NH3 emissions, after cutting and fertilisation, which led to a negative Δ Fz,adv. The local advection flux from the farm was in the range 0 to 27 ng m−2 s−1 NH3 at 610 m from the farm, whereas Δ Fz,adv due to field emission was proportional to the local flux, and ranged between −209 and 13 ng m−2 s−1 NH3. The local advection flux Δ Fz,adv was either positive or negative depending on the magnitude of these two contributions. The modelled and measured advection errors agreed well, provided the modelled Δ Fz,adv was estimated at 2 m height. This study constitutes the first attempt to validate the inverse modelling approach to determine advection errors for NH3. The measured advection errors, relative to the vertical flux at 1 m height, were 121% on average, before the field was cut (when downwind of the farm), and less than 7% when the field was fertilised.
A process-based model to estimate gas exchange and monoterpene emission rates in the mediterranean maquis – comparisons between modelled and measured fluxes at different scales
Authors: Vitale M. , Matteucci G. , Fares S. , Davison B.
Published: April 2010

Abstract. This paper concerns the application of a process-based model (MOCA, Modelling of Carbon Assessment) as an useful tool for estimating gas exchange, and integrating the empirical algorithms for calculation of monoterpene fluxes, in a Mediterranean maquis of central Italy (Castelporziano, Rome). Simulations were carried out for a range of hypothetical but realistic canopies of the evergreen Quercus ilex (holm oak), Arbutus unedo (strawberry tree) and Phillyrea latifolia. More, the dependence on total leaf area and leaf distribution of monoterpene fluxes at the canopy scale has been considered in the algorithms. Simulation of the gas exchange rates showed higher values for P. latifolia and A. unedo (2.39±0.30 and 3.12±0.27 gC m−2 d−1, respectively) with respect to Q. ilex (1.67±0.08 gC m−2 d−1) in the measuring campaign (May–June). Comparisons of the average Gross Primary Production (GPP) values with those measured by eddy covariance were well in accordance (7.98±0.20 and 6.00±1.46 gC m−2 d−1, respectively, in May–June), although some differences (of about 30%) were evident in a point-to-point comparison. These differences could be explained by considering the non uniformity of the measuring site where diurnal winds blown S-SW direction affecting thus calculations of CO2 and water fluxes. The introduction of some structural parameters in the algorithms for monoterpene calculation allowed to simulate monoterpene emission rates and fluxes which were in accord to those measured (6.50±2.25 vs. 9.39±4.5μg g−1DW h−1 for Q. ilex, and 0.63±0.207μg g−1DW h−1 vs. 0.98±0.30μg g−1DW h−1 for P. latifolia). Some constraints of the MOCA model are discussed, but it is demonstrated to be an useful tool to simulate physiological processes and BVOC fluxes in a very complicated plant distributions and environmental conditions, and necessitating also of a low number of input data.
Incorporation of crop phenology in Simple Biosphere Model (SiBcrop) to improve land-atmosphere carbon exchanges from croplands
Authors: Lokupitiya E. , Denning S. , Paustian K. , Baker I. , Schaefer K. , Verma S. , Meyers T. , Bernacchi C. , Suyker A. , Fischer M.
Published: April 2010

Abstract. Croplands are man-made ecosystems that have high net primary productivity during the growing season of crops, thus impacting carbon and other exchanges with the atmosphere. These exchanges play a~major role in nutrient cycling and climate change related issues. An accurate representation of crop phenology and physiology is important in land-atmosphere carbon models being used to predict these exchanges. To better estimate time-varying exchanges of carbon, water, and energy of croplands using the Simple Biosphere (SiB) model, we developed crop-specific phenology models and coupled them to SiB. The coupled SiB-phenology model (SiBcrop) replaces remotely-sensed NDVI information, on which SiB originally relied for deriving Leaf Area Index (LAI) and the fraction of Photosynthetically Active Radiation (fPAR) for estimating carbon dynamics. The use of the new phenology scheme within SiB substantially improved the prediction of LAI and carbon fluxes for maize, soybean, and wheat crops, as compared with the observed data at several AmeriFlux eddy covariance flux tower sites in the US mid continent region. SiBcrop better predicted the onset and end of the growing season, harvest, interannual variability associated with crop rotation, day time carbon uptake (especially for maize) and day to day variability in carbon exchange. Biomass predicted by SiBcrop had good agreement with the observed biomass at field sites. In the future, we will predict fine resolution regional scale carbon and other exchanges by coupling SiBcrop with RAMS (the Regional Atmospheric Modeling System).
Night-time ozone uptake by Mediterranean species
Authors: Mereu S. , Finco A. , Gerosa G. , Fusaro L. , Muys B. , Manes F.
Published: April 2010

Abstract. Due to the evident tropospheric ozone impact on plant productivity, an accurate ozone risk assessment for the vegetation has become an issue. There is a growing evidence that ozone stomatal uptake may also take place at night and that the night-time uptake may be more damaging than diurnal uptake. Estimation of night-time uptake in the field is complicated because of instrumental difficulties. Eddy covariance technology is not always reliable because of the low turbulence at night. Leaf level porometry is defective at relative humidity above 70% which often takes place at night. Improved sap flow technology allows to estimate also slow flows that usually take place at night and hence may be, at present, the most trustworthy technology to measure night-time transpiration and hence to derive canopy stomatal conductance and ozone uptake at night. Based on micrometeorological data and the sap flow of three Mediterranean woody species, the night-time ozone uptake of these species was evaluated during a summer season as drought increased. Night-time ozone uptake was 10% of the total when plants were exposed to a weak drought, but increased up to 24% as the drought became more pronounced. The percentage increase is due to a stronger reduction of diurnal stomatal conductance than night-time stomatal conductance.
The Sub-Saharan Africa carbon balance, an overview
Authors: Bombelli A. , Henry M. , Castaldi S. , Adu-Bredu S. , Arneth A. , de Grandcourt A. , Grieco E. , Kutsch W. L. , Lehsten V. , Rasile A. , Reichstein M. , Tansey K. , Weber U. , Valentini R.
Published: April 2010

Abstract. This study presents a summary overview of the carbon balance of Sub-Saharan Africa (SSA) by synthesizing the available data from national communications to UNFCCC and first results from the project CarboAfrica (net ecosystem productivity and emissions from fires, deforestation and forest degradation, by field and model estimates). According to these preliminary estimates the overall carbon balance of SSA varies from 0.43 Pg C y−1 (using in situ measurements for savanna NEP) to a much higher sink of 2.53 Pg C y−1 (using model estimates for savanna NEP). UNFCCC estimates lead to a moderate carbon sink of 0.58 Pg C y−1. Excluding anthropogenic disturbance and intrinsic episodic events, the carbon uptake by forests (0.98 Pg C y−1) and savannas (from 1.38 to 3.48 Pg C y−1, depending on the used methodology) are the main components of the SSA sink effect. Fires (0.72 Pg C y−1), deforestation (0.25 Pg C y−1) and forest degradation (0.77 Pg C y−1) are the main contributors to the SSA carbon emissions, while the agricultural sector contributes only with 0.12 Pg C y−1. Notably, the impact of forest degradation is higher than that caused by deforestation, and the SSA forest net carbon balance is close to equilibrium. Savannas play a major role in shaping the SSA carbon balance, due to their large areal extent, their fire regime, and their strong interannual NEP variability, but they are also a major uncertainty in the overall budget. This paper shows that Africa plays a key role in the global carbon cycle system and probably could have a potential for carbon sequestration higher than expected, even if still highly uncertain. Further investigations are needed, particularly to better address the role of savannas and tropical forests. The current CarboAfrica network of carbon measurements could provide future unique data sets for better estimating the African carbon balance.
Concentrations and fluxes of biogenic volatile organic compounds above a Mediterranean macchia ecosystem in Western Italy
Authors: Davison B. , Taipale R. , Langford B. , Misztal P. , Fares S. , Matteucci G. , Loreto F. , Cape J. N. , Rinne J. , Hewitt C. N.
Published: April 2010

Abstract. Emission rates and concentrations of biogenic volatile organic compounds (BVOCs) were measured at a Mediterranean coastal site at Castelporziano, approximately 25 km south-west of Rome, between 7 May and 3 June 2007, as part of the ACCENT-VOCBAS field campaign on biosphere-atmosphere interactions. Concentrations and emission rates were measured using the disjunct eddy covariance method utilizing three different proton transfer reaction mass spectrometers (PTR-MS) for BVOC mixing ratio measurements and sonic anemometers for three-dimensional high-frequency wind measurements. Depending on the measurement period and the instrument, the median volume mixing ratios were 1.6–3.5 ppbv for methanol, 0.4–1.5 ppbv for acetaldehyde, 1.0–2.5 ppbv for acetone, 0.10–0.17 ppbv for isoprene, and 0.18–0.30 ppbv for monoterpenes. A diurnal cycle in mixing ratios was apparent with daytime maxima for methanol, acetaldehyde, acetone, and isoprene. The median fluxes were 370–440 μg m−2 h−1 for methanol, 180–360 μg m−2 h−1 for acetaldehyde, 180–450 μg m−2 h−1 for acetone, 71–290 μg m−2 h−1 for isoprene, and 240–860 μg m−2 h−1 for monoterpenes.
Wetland restoration and methanogenesis: the activity of microbial populations and competition for substrates at different temperatures
Authors: Jerman V. , Metje M. , Mandić-Mulec I. , Frenzel P.
Published: April 2010

Abstract. Ljubljana marsh in Slovenia is a 16 000 ha area of partly drained fen, intended to be flooded to restore its ecological functions. The resultant water-logging may create anoxic conditions, eventually stimulating production and emission of methane, the most important greenhouse gas next to carbon dioxide. We examined the upper layer (~30 cm) of Ljubljana marsh soil for microbial processes that would predominate in water-saturated conditions, focusing on the potential for iron reduction, carbon mineralization (CO2 and CH4 production), and methane emission. Methane emission from water-saturated microcosms was near minimum detectable levels even after extended periods of flooding (>5 months). Methane production in anoxic soil slurries started only after a lag period and was inversely related to iron reduction, which suggested that iron reduction out-competed methanogenesis for electron donors, such as H2 and acetate. Methane production was observed only in samples incubated at 14–38°C. At the beginning of methanogenesis, acetoclastic methanogenesis dominated. In accordance with the preferred substrate, most (91%) mcrA (encoding the methyl coenzyme-M reductase, a key gene in methanogenesis) clone sequences could be affiliated to the acetoclastic genus Methanosarcina. No methanogens were detected in the original soil. However, a diverse community of iron-reducing Geobacteraceae was found. Our results suggest that methane emission can remain transient and low if water-table fluctuations allow re-oxidation of ferrous iron, sustaining iron reduction as the most important process in terminal carbon mineralization.
Effects of the pH/pCO2 control method in the growth medium of phytoplankton
Authors: Shi D. , Xu Y. , Morel F. M. M.
Published: April 2010

Abstract. To study the effects of ocean acidification on the physiology of phytoplankton requires that the key chemical parameters of the growth medium, pCO2, pH and Ω (the saturation state of calcium carbonate) be carefully controlled. This is made difficult by the interdependence of these parameters. Moreover, in growing batch cultures of phytoplankton, the fixation of CO2, the uptake of nutrients and, for coccolithophores, the precipitation of calcite all change the inorganic carbon and acid-base chemistry of the medium. For example, absent pH-buffering or CO2 bubbling, a sizeable decrease in pCO2 occurs at a biomass concentration as low as 50 μM C in non-calcifying cultures. Even in cultures where pCO2 or pH is maintained constant, other chemical parameters change substantially at high cell densities. The quantification of these changes is facilitated by the use of buffer capacities. Experimentally we observe that all methods of adjustment of pCO2/pH can be used, the choice of one or the other depending on the specifics of the experiments. The mechanical effect of bubbling of cultures seems to induce more variable results than other methods of pCO2/pH control. While highly convenient, the addition of pH buffers to the medium induces changes in trace metal availability and cannot be used under trace metal-limiting conditions.
Simultaneous measurements of CO2 and water exchanges over three agroecosystems in South-West France
Authors: Stella P. , Lamaud E. , Brunet Y. , Bonnefond J.-M. , Loustau D. , Irvine M.
Published: April 2010

Abstract. During the last few decades, many studies have been performed to determine water and carbon budgets of broadleaf and deciduous forests, crops and grasslands. However, since most measurements have been made in different regions and at different periods, it is difficult to compare the results directly. In order to evaluate accurately the respective contribution of various agroecosystems to global water and carbon exchanges, it is necessary to compare data obtained in similar climatic and weather conditions. To address this question, we present the results from simultaneous measurements carried out from 31 March 2007 to 3 March 2008 over three typical agroecosystems of the Les Landes region in South-West France: an agricultural field with maize from 29 May to 18 October, a young (5 year-old) pine forest and a mature (37 year-old) pine forest. All measurements were collected as part of the Regional Experiment component of the CarboEurope-IP project. During most of the year, the agricultural field without vegetation is a source of CO2, but from late June to early September the maize crop becomes a stronger carbon sink than the forests. Over the whole measurement period the three agroecosystems behave as CO2 sinks with carbon storage of about 500, 330 and 230 gC m−2 for the young forest, the mature forest and the agricultural field, respectively. Daily Water Use Efficiencies (WUE) of the three ecosystems were evaluated and expressed as functions of the mean daily vapour pressure deficit (VPD). Similar trends were observed for the two forests, which suggests that for a given species WUE is independent of stand age. The WUE of the maize crop at maturity was also found to depend upon VPD, but it is about twice as large as for the forests, owing to the physiological advantages of C4 species.
Short term variability of dissolved lipid classes during summer to autumn transition in the Ligurian sea (NW Mediterranean)
Authors: Goutx M. , Guigue C. , Aritio D. , Ghiglione J. , Pujo-Pay M. , Andersen V.
Published: April 2010

Abstract. Changes in concentration and composition of dissolved lipid classes (Iatroscan TLC/FID) were examined at daily to month scale, in relation to the hydrological and biological situation at a central site of the Ligurian sea, NW Mediterranean during the PECHE-DYNAPROC 2 experiment (14 September to 17 October). Dissolved lipid concentrations (TLd) and lipid to DOC ratios varied in the range 5.3–48.5 μ g l−1 and 0.01 to 0.08 respectively, along the 0–1000 m water column. The highest TLd concentration values were found in the 0–150 m surface layer coinciding with phytoplankton biomass. Lipid class composition provided valuable information on the origin of DOM, and the changes that occurred during the period investigated. The significant correlations (p<0.01, n=87) between glycolipids from chloroplast membrane (MGDG) (38.7±8.5% of TLd, n=166), and various phytoplankton pigments (chlorophyll cs-170, violaxanthin, diadinoxanthin, zeaxanthin, and lutein), suggested that picoeucaryotes were the major source of dissolved lipids. Lipid metabolites (37.6±11.1%, n=166), the second most important compounds in TLd, showed a greater degree of degradation of lipids in this transition period than previously observed earlier in the year. A contribution of lipids to DOM in the mesopelagic zone was observed before the winter mixing: At mid time of the cruise (4–6 October), zooplankton wax esters biomarkers (WE, 5.5–13.6 μg L−1) appeared in the 0–150 m surface layer. WE were observed later and deeper in the mesopelagic layer (6 to 11 October), accompanied by re-increases of hydrocarbons (6–8 October) and phospholipids concentrations (12 October) in the 400–1000 m depth layer. Zooplankton migration and/or fecal pellets egestion, followed by DOM release from POM, were likely responsible for the appearance of these lipid signatures in the mesopelagic layer, which occurred during the period of low wind (<15 knots) (28 September–12 October). The low salinity water lenses that appeared twice during the cruise in the 40–80 m surface layer had little effect on total biogenic lipid concentrations. Lower concentrations in phosphoglycerides and hydrocarbons than the nearby sea water suggested different microbial assemblages and different level of HC contamination in this less-salted water.
Impact of anthropogenic ocean acidification on thermal tolerance of the spider crab Hyas araneus
Authors: Walther K. , Sartoris F. J. , Bock C. , Pörtner H. O.
Published: April 2010

Abstract. Future scenarios project combined developments of elevated CO2 concentrations and global warming and their impact on marine ecosystems. The synergistic impact of both factors was addressed by studying the effect of CO2 accumulation on thermal tolerance of the cold-eurythermal spider crab Hyas araneus. Animals were exposed to present day normocapnia (380 ppm CO2), CO2 levels expected towards 2100 (710 ppm) and beyond (3000 ppm). Heart rate and haemolymph PO2 (PeO2) were measured during progressive short term cooling from 10 to 0°C and during warming from 10 to 25°C. An increase of PeO2 occurred during cooling with highest values reached at 0°C under all three CO2 levels. Heart rate increased during warming until a critical temperature (Tc) was reached. The putative Tc under normocapnia was presumably >25°C, from where it fell to 23.5°C under 710 ppm and then 21.1°C under 3000 ppm. At the same time, thermal sensitivity, as seen in the Q10 values of heart rate, rose with increasing CO2 concentration in the warmth. Our results suggest a narrowing of the thermal window of Hyas araneus under moderate increases in CO2 levels by exacerbation of the heat or cold induced oxygen and capacity limitation of thermal tolerance.
Modelling basin-wide variations in Amazon forest productivity – Part 1: Model calibration, evaluation and upscaling functions for canopy photosynthesis
Authors: Mercado L. M. , Lloyd J. , Dolman A. J. , Sitch S. , Patiño S.
Published: April 2010

Abstract. Given the importance of Amazon rainforest in the global carbon and hydrological cycles, there is a need to parameterize and validate ecosystem gas exchange and vegetation models for this region in order to adequately simulate present and future carbon and water balances. In this study, a sun and shade canopy gas exchange model is calibrated and evaluated at five rainforest sites using eddy correlation measurements of carbon and energy fluxes. Results from the model-data evaluation suggest that with adequate parameterisation, photosynthesis models taking into account the separation of diffuse and direct irradiance and the dynamics of sunlit and shaded leaves can accurately represent photosynthesis in these forests. Also, stomatal conductance formulations that only take into account atmospheric demand fail to correctly simulate moisture and CO2 fluxes in forests with a pronounced dry season, particularly during afternoon conditions. Nevertheless, it is also the case that large uncertainties are associated not only with the eddy correlation data, but also with the estimates of ecosystem respiration required for model validation. To accurately simulate Gross Primary Productivity (GPP) and energy partitioning the most critical parameters and model processes are the quantum yield of photosynthetic uptake, the maximum carboxylation capacity of Rubisco, and simulation of stomatal conductance. Using this model-data synergy, we developed scaling functions to provide estimates of canopy photosynthetic parameters for a~range of diverse forests across the Amazon region, utilising the best fitted parameter for maximum carboxylation capacity of Rubisco, and foliar nutrients (N and P) for all sites.
Ignoring detailed fast-changing dynamics of land use overestimates regional terrestrial carbon sequestration
Authors: Zhao S. , Liu S. , Li Z. , Sohl T. L.
Published: April 2010

Abstract. Land use change is critical in determining the distribution, magnitude and mechanisms of terrestrial carbon budgets at the local to global scales. To date, almost all regional to global carbon cycle studies are driven by a static land use map or land use change statistics with decadal time intervals. The biases in quantifying carbon exchange between the terrestrial ecosystems and the atmosphere caused by using such land use change information have not been investigated. Here, we used the General Ensemble biogeochemical Modeling System (GEMS), along with consistent and spatially explicit land use change scenarios with different intervals (1 yr, 5 yrs, 10 yrs and static, respectively), to evaluate the impacts of land use change data frequency on estimating regional carbon sequestration in the southeastern United States. Our results indicate that ignoring the detailed fast-changing dynamics of land use can lead to a significant overestimation of carbon uptake by the terrestrial ecosystem. Regional carbon sequestration increased from 0.27 to 0.69, 0.80 and 0.97 Mg C ha−1 yr−1 when land use change data frequency shifting from 1 year to 5 years, 10 years interval and static land use information, respectively. Carbon removal by forest harvesting and prolonged cumulative impacts of historical land use change on carbon cycle accounted for the differences in carbon sequestration between static and dynamic land use change scenarios. The results suggest that it is critical to incorporate the detailed dynamics of land use change into local to global carbon cycle studies. Otherwise, it is impossible to accurately quantify the geographic distributions, magnitudes, and mechanisms of terrestrial carbon sequestration at local to global scales.
Effects of long-term flooding on biogeochemistry and vegetation development in floodplains – a mesocosm experiment to study interacting effects of land use and water quality
Authors: Banach A. M. , Banach K. , Peters R. C. J. H. , Jansen R. H. M. , Visser E. J. W. , Stępniewska Z. , Roelofs J. G. M. , Lamers L. P. M.
Published: April 2010

Abstract. The frequent occurrence of summer floods in Eastern Europe, possibly related to climate change, urges the need to understand the consequences of combined water storage and nature rehabilitation as an alternative safety measure instead of raising and reinforcing dykes, for floodplain biogeochemistry and vegetation development. We used a mesocosm design to investigate the possibilities for the creation of permanently flooded wetlands along rivers, in relation to water quality (nitrate, sulphate) and land use (fertilization). Flooding resulted in severe eutrophication of both sediment pore water and surface water, particularly for more fertilized soil and sulphate pollution. Vegetation development was mainly determined by soil quality, resulting in a strong decline of most species from the highly fertilized location, especially in combination with higher nitrate and sulphate concentrations. Soils from the less fertilized location showed, in contrast, luxurious growth of target Carex species regardless water quality. The observed interacting effects of water quality and agricultural use are important in assessing the consequences of planned measures for ecosystem functioning (including peat formation) and biodiversity in river floodplains.
Carbon-nitrogen interactions regulate climate-carbon cycle feedbacks: results from an atmosphere-ocean general circulation model
Authors: Thornton P. E. , Doney S. C. , Lindsay K. , Moore J. K. , Mahowald N. , Randerson J. T. , Fung I. , Lamarque J.-F. , Feddema J. J. , Lee Y.-H.
Published: April 2010

Abstract. Inclusion of fundamental ecological interactions between the terrestrial carbon and nitrogen cycles in the land component of an atmosphere-ocean general circulation model (AOGCM) leads to increased carbon storage on land under radiatively-forced anthropogenic climate change, and an overall negative climate-carbon cycle feedback. The primary mechanism responsible for increased land carbon storage is shown to be fertilization of plant growth by increased mineralization of nitrogen directly associated with increased decomposition of soil organic matter under a warming climate. Results from the fully-coupled AOGCM also confirm a previously reported pattern of significantly reduced CO2-fertilization of terrestrial carbon uptake compared to simulations without an explicit nitrogen cycle. Our results show a significant growth in the airborne fraction of anthropogenic CO2 emissions over the coming century, attributable in part to a steady decline in the ocean sink fraction. Comparison to experimental studies on the fate of radio-labeled nitrogen tracers in temperate forests indicates that the model representation of competition between plants and microbes for new mineral nitrogen resources is reasonable. Our results suggest a weaker dependence of net land carbon flux on soil moisture changes in tropical regions, and a stronger positive growth response to warming in those regions, than predicted by a similar AOGCM implemented without land carbon-nitrogen interactions. We expect that the between-model uncertainty in predictions of future atmospheric CO2 concentration and associated anthropogenic climate change will be reduced as additional climate models introduce carbon-nitrogen cycle interactions in their land components.
Estimating the monthly pCO2 distribution in the North Atlantic using a self-organizing neural network
Authors: Telszewski M. , Chazottes A. , Schuster U. , Watson A. J. , Moulin C. , Bakker D. C. E. , González-Dávila M. , Johannessen T. , Körtzinger A. , Lüger H. , Olsen A. , Omar A. , Padin X. A. , Ríos A. , Steinhoff T. , Santana-Casiano M. , Wallace D. W. R. , Wanninkhof R.
Published: April 2010

Abstract. Here we present monthly, basin-wide maps of the partial pressure of carbon dioxide (pCO2) for the North Atlantic on a 1° latitude by 1° longitude grid for years 2004 through 2006 inclusive, constructed using a neural network technique which reconstructs the non-linear relationships between 3 biogeochemical parameters and marine pCO2. A self organizing map (SOM) neural network has been trained using the SeaWiFS-MODIS chlorophyll a concentration, the NCEP/NCAR reanalysis sea surface temperature, and the FOAM mixed layer depth. 389 000 such triplets were used. The trained SOM was labelled with 137 000 underway pCO2 measurements collected in situ during 2004, 2005 and 2006 in the North Atlantic, which span the range of 208 and 437 μatm. The root mean square (RMS) deviation of the neural network fits from the data is 11.55 μatm, which equals to just above 3 per cent of an average pCO2 value in the in situ dataset. The seasonal pCO2 cycle as well as the interannual variability estimates in the major biogeochemical provinces is presented and spatial and temporal variability of the estimated fields is discussed. High resolution combined with basin-wide cover makes the maps a useful tool for several applications such as monitoring of basin-wide air-sea CO2 fluxes or improvement of seasonal and interannual marine CO2 cycles in future model predictions. The method itself is a valuable alternative to traditional statistical modelling techniques used in geosciences.
Basin-wide variations in foliar properties of Amazonian forest: phylogeny, soils and climate
Authors: Fyllas N. M. , Patiño S. , Baker T. R. , Bielefeld Nardoto G. , Martinelli L. A. , Quesada C. A. , Paiva R. , Schwarz M. , Horna V. , Mercado L. M. , Santos A. , Arroyo L. , Jiménez E. M. , Luizão F. J. , Neill D. A. , Silva N. , Prieto A. , Rudas A. , Silviera M. , Vieira I. C. G. , Lopez-Gonzalez G. , Malhi Y. , Phillips O. L. , Lloyd J.
Published: April 2010

Abstract. We analysed 1040 individual trees, positioned in sixty three plots across the Amazon Basin for leaf mass per area (MA), leaf carbon isotope composition (δ13C) and leaf level concentrations of C, N, P, Ca, Mg, K and Al. All trees were identified to the species with the dataset containing 58 families, 236 genera and 508 species, distributed across a wide range of soil types and precipitation regimes. Some foliar characters such as MA, [C], [N] and [Mg] emerge as highly constrained by the taxonomic affiliation of tree species, but with others such as [P], [K], [Ca] and δ13C also strongly influenced by site growing conditions. By removing the environmental contribution to trait variation, we find that intrinsic values of most trait pairs coordinate, although different species (characterised by different trait suites) are found at discrete locations along a common axis of coordination. Species that tend to occupy higher fertility soils are characterised by a lower MA and have a higher intrinsic [N], [P], [K], [Mg] and δ13C than their lower fertility counterparts. Despite this consistency, different scaling patterns were observed between low and high fertility sites. Inter-relationships are thus substantially modified by growth environment. Analysing the environmental component of trait variation, we found soil fertility to be the most important predictor, influencing all leaf nutrient concentrations and δ13C composition and reducing MA. Mean annual temperature was negatively associated with leaf level [N], [P] and [K] concentrations. Total annual precipitation positively influences MA, [C] and δ13C, but with a negative impact on [Mg]. These results provide a first basis for understanding the relationship between the physiological functioning and distribution of tree species across Amazonia.
Seasonal and mesoscale variability of oceanic transport of anthropogenic CO2
Authors: Lachkar Z. , Orr J. C. , Dutay J.-C.
Published: April 2010

Abstract. Estimates of the ocean's large-scale transport of anthropogenic CO2 are based on one-time hydrographic sections, but the temporal variability of this transport has not been investigated. We have evaluated this variability with the aid of an eddy-permitting version of the coupled ocean sea-ice model ORCA-LIM. As for heat transport, the seasonally varying transport of anthropogenic CO2 is largest within 20° of the Equator and shows secondary maxima in the subtropics. Ekman transport generally drives most of the seasonal variability, but the contribution of the vertical shear becomes important near the Equator and in the Southern Ocean. Mesoscale variabilty contributes to the annual-mean transport of both heat and anthropogenic CO2 with strong poleward transport in the Southern Ocean and equatorward transport in the tropics. This "rectified" eddy transport is largely baroclinic in the tropics and barotropic in the Southern Ocean due to a larger contribution from standing eddies. Our analysis revealed that most previous hydrographic estimates of meridional transport of anthropogenic CO2 are severely biased because they neglect temporal fluctuations due to non-Ekman velocity variations. In each of the three major ocean basins, this bias is largest near the Equator and in the high southern latitudes. In the subtropical North Atlantic, where most of the hydrographic-based estimates have been focused, this uncertainty represents up to 20% and 30% of total meridional transport of heat and CO2. Generally though, outside the tropics and Southern Ocean, there are only small variations in meridional transport due to seasonal variations in tracer fields and time variations in eddy transport. For the North Atlantic, eddy variability accounts for up to 10% and 15% of the total transport of heat and CO2. This component is not accounted for in coarse-resolution hydrographic surveys.
Non-additive effect of day and night warming on soil respiration in a temperate steppe
Authors: Xia J. , Han Y. , Zhang Z. , Zhang Z. , Wan S.
Published: April 2010

Abstract. This study was conducted to examine potentially differential effects of day and night warming on soil respiration in a temperate steppe in northern China. A full factorial design with day and night warming was used in this study, including control (C), day (6 a.m.–6 p.m., local time; D) warming, night (6 p.m.–6 a.m.; N) warming, and diurnal warming (W). Day warming showed neutral effect on soil respiration, whereas night warming significantly increased soil respiration by 7.1% over the first 3 growing seasons. The insignificant effect of day warming on soil respiration could be attributable to the offset of the direct positive effects by the indirect negative effects via aggravating water limitation and suppressing ecosystem C assimilation. The positive effects of night warming on soil respiration were largely due to the stimulation of ecosystem C uptake and substrate supply via over-compensation of plant photosynthesis. In addition, day and night warming showed antagonistic effects on soil respiration, which could be ascribed to their contrasting effects on ecosystem C assimilation. The results suggest differential and non-additive effects of day and night warming on soil respiration, which was driven by the treatment-induced changes in substrate supply.
Physiological basis for high CO2 tolerance in marine ectothermic animals: pre-adaptation through lifestyle and ontogeny?
Authors: Melzner F. , Gutowska M. A. , Langenbuch M. , Dupont S. , Lucassen M. , Thorndyke M. C. , Bleich M. , Pörtner H.-O.
Published: April 2010

Abstract. Future ocean acidification has the potential to adversely affect many marine organisms. A growing body of evidence suggests that many species could suffer from reduced fertilization success, decreases in larval- and adult growth rates, reduced calcification rates, metabolic depression and even mortality when being exposed to near-future levels (year 2100 scenarios) of ocean acidification. Little research focus is currently placed on those organisms/taxa that might be less vulnerable to the anticipated changes in ocean chemistry; this is unfortunate, as the comparison of more vulnerable to more tolerant physiotypes could provide us with those physiological traits that are crucial for ecological success in a future ocean. Here, we attempt to summarize some ontogenetic and lifestyle traits that lead to an increased tolerance towards high environmental pCO2. In general, marine ectothermic metazoans with an extensive extracellular fluid volume may be less vulnerable to future acidification as their cells are already exposed to much higher pCO2 values (0.1 to 0.4 kPa, 1000 to 4000 μatm) than those of unicellular organisms and gametes, for which the ocean (0.04 kPa, 400 μatm) is the extracellular space. A doubling in environmental pCO2 therefore only represents a 10% change in extracellular CO2 in some marine teleosts. High extracellular pCO2 values are to some degree related to high metabolic rates, as diffusion gradients need to be high in order to excrete an amount of CO2 that is directly proportional to the amount of O2 consumed. In active metazoans, such as teleost fish, cephalopods and many brachyuran crustaceans, exercise induced increases in metabolic rate require an efficient ion-regulatory machinery for CO2 excretion and acid-base regulation, especially when anaerobic metabolism is involved and metabolic protons leak into the extracellular space. These ion-transport systems, which are located in highly developed gill epithelia, form the basis for efficient compensation of pH disturbances during exposure to elevated environmental pCO2. Compensation of extracellular acid-base status in turn may be extremely important in avoiding metabolic depression. So far, maintained "performance" at higher seawater pCO2 (>0.3 to 0.6 kPa) has only been observed in adults/juveniles of active, high metabolic species with a powerful ion regulatory apparatus. However, while some of these taxa are adapted to cope with elevated pCO2 during their regular embryonic development, unicellular gametes, which lack specialized ion-regulatory epithelia, may be the true bottleneck for ecological success – even of the more tolerant taxa.
Short-term response of the coccolithophore Emiliania huxleyi to abrupt changes in seawater carbon dioxide concentrations
Authors: Barcelos e Ramos J. , Müller M. N. , Riebesell U.
Published: April 2010

Abstract. The response of the coccolithophore Emiliania huxleyi to rising CO2 concentrations is well documented in acclimated cultures where cells are exposed to the CO2 treatments for several generations prior to the experiment. Extended acclimation times have generally been applied because of the lack of information about time required to reach a new physiological "equilibrium" (acclimation) in response to CO2-induced changes in seawater carbonate chemistry. Here we show that Emiliania huxleyi's short-term response (hours to 1 day) to increasing CO2 is similar to that obtained with acclimated cultures under comparable conditions in earlier studies. At CO2 concentrations ranging from glacial (190 μatm) to projected year 2100 (750 μatm) levels, calcification decreased and organic carbon fixation increased within 8 h after exposing the cultures to the changed CO2 conditions. This led to a decrease in the ratio of CaCO3 to organic carbon production. Our results show that Emiliania huxleyiapidly alters the rates of various essential processes in response to changes in seawater carbonate chemistry, establishing a new physiological (acclimation) "state" within a matter of hours. If this relatively rapid response applies to other phytoplankton species, it may simplify interpretation of studies with natural communities (e.g. mesocosm studies and ship-board incubations), where often it is not feasible to allow for a pre-conditioning phase before starting experimental incubations.
Soil and plant contributions to the methane flux balance of a subalpine forest under high ultraviolet irradiance
Authors: Bowling D. R. , Miller J. B. , Rhodes M. E. , Burns S. P. , Monson R. K. , Baer D.
Published: April 2010

Abstract. Recent studies have demonstrated direct methane emission from plant foliage under aerobic conditions, particularly under high ultraviolet (UV) irradiance. We examined the potential importance of this phenomenon in a high-elevation conifer forest using micrometeorological techniques. Vertical profiles of methane and carbon dioxide in forest air were monitored every 2 h for 6 weeks in summer 2007. Day to day variability in above-canopy CH4 was high, with observed values in the range 1790 to 1910 nmol mol−1. High CH4 was correlated with high carbon monoxide and related to wind direction, consistent with pollutant transport from an urban area by a well-studied mountain-plain wind system. Soil moisture was moderately dry during the study. Vertical gradients of CH4 were small but detectable day and night, both near the ground and within the vegetation canopy. Gradients near the ground were consistent with the forest soil being a net CH4 sink. Using scalar similarity with CO2, the magnitude of the summer soil CH4 sink was estimated at ~1.7 mg CH4 m−2 h−1, which is similar to other temperate forest upland soils. The high-elevation forest was naturally exposed to high UV irradiance under clear sky conditions, with observed peak UVB irradiance >2 W m−2. Gradients and means of CO2 within the canopy under daytime conditions showed net uptake of CO2 due to photosynthetic drawdown as expected. No evidence was found for a significant foliar CH4 source in the vegetation canopy, even under high UV conditions. While the possibility of a weak foliar source cannot be excluded given the observed soil sink, overall this subalpine forest was a net sink for atmospheric methane during the growing season.