bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of the pH/pCO2 control method on medium chemistry and phytoplankton growth
Authors: Shi D. , Xu Y. , Morel F. M. M.
Published: April 2010

Abstract. The control of key chemical parameters in phytoplankton cultures, such as pCO2, pH and Ω (the saturation state of calcium carbonate), is made difficult by the interdependence of these parameters and by the changes resulting from the growth of the organisms, such as CO2 fixation, nutrient uptake and, for coccolithophores, calcite precipitation. Even in cultures where pCO2 or pH is maintained constant, other chemical parameters change substantially at high cell densities. Experimentally we observed that various methods of adjustment of pCO2/pH – acid or base addition, use of buffers or pH-stats, or bubbling of CO2-enriched air – can be used, the choice of one or the other depending on the goals of the experiments. At seawater pH, we measured the same growth rates in cultures of the diatom Thalassiosira weissflogii where the pCO2/pH was controlled by these different methods. The pH/pCO2 control method also did not affect the rates of growth or calcification of the coccolithophore Emiliania huxleyi at seawater pH. At lower pH/higher pCO2, in the E. huxleyi strain PLY M219, we observed increases in rates of carbon fixation and calcification per cell, along with a slight increase in growth rate, except in bubbled cultures. In our hands, the bubbling of cultures seemed to induce more variable results than other methods of pCO2/pH control. While highly convenient, the addition of pH buffers to the medium apparently induces changes in trace metal availability and cannot be used under trace metal-limiting conditions.
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.
Coastal hypoxia and sediment biogeochemistry
Authors: Middelburg J. J. , Levin L. A.
Published: April 2010

Abstract. The intensity, duration and frequency of coastal hypoxia (oxygen concentration <63 μM) are increasing due to human alteration of coastal ecosystems and changes in oceanographic conditions due to global warming. Here we provide a concise review of the consequences of coastal hypoxia for sediment biogeochemistry. Changes in bottom-water oxygen levels have consequences for early diagenetic pathways (more anaerobic at expense of aerobic pathways), the efficiency of re-oxidation of reduced metabolites and the nature, direction and magnitude of sediment-water exchange fluxes. Hypoxia may also lead to more organic matter accumulation and burial and the organic matter eventually buried is also of higher quality, i.e. less degraded. Bottom-water oxygen levels also affect the organisms involved in organic matter processing with the contribution of metazoans decreasing as oxygen levels drop. Hypoxia has a significant effect on benthic animals with the consequences that ecosystem functions related to macrofauna such as bio-irrigation and bioturbation are significantly affected by hypoxia as well. Since many microbes and microbial-mediated biogeochemical processes depend on animal-induced transport processes (e.g. re-oxidation of particulate reduced sulphur and denitrification), there are indirect hypoxia effects on biogeochemistry via the benthos. Severe long-lasting hypoxia and anoxia may result in the accumulation of reduced compounds in sediments and elimination of macrobenthic communities with the consequences that biogeochemical properties during trajectories of decreasing and increasing oxygen may be different (hysteresis) with consequences for coastal ecosystem dynamics.
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 quantifying such effects 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 challenging, since NH3 emissions are highly heterogeneous. Indeed, under such conditions, local advection errors may alter the measured fluxes. In this study, local advection errors (ΔFz,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 ΔFz,adv was determined up to 810 m downwind from farm buildings emitting between 6.2 and 9.9 kg NH3 day−1. The GRAMINAE experiment provided a unique opportunity to compare two methods of estimating ΔFz,adv: one inference method based on measurements of horizontal concentration gradients, and one based on inverse dispersion modelling with a two-dimensional model. Two sources of local advection were clearly identified: the farm NH3 emissions leading to positive ΔFz,adv ("bias towards emissions") and field NH3 emissions, which led to a negative ΔFz,adv ("bias towards deposition"). The local advection flux from the farm was in the range 0 to 27 ng NH3 m−2 s−1 at 610 m from the farm, whereas ΔFz,adv due to field emission was proportional to the local flux, and ranged between −209 and 13 ng NH3 m−2 s−1. The local advection flux ΔFz,adv was either positive or negative depending on the magnitude of these two contributions. The modelled and inferred advection errors agreed well. The inferred advection errors, relative to the vertical flux at 1 m height, were 52% on average, before the field was cut, and less than 2.1% when the field was fertilised. The variability of the advection errors in response to changes in micrometeorological conditions is also studied. The limits of the 2-D modelling approach are discussed.
SURFATM-NH3: a model combining the surface energy balance and bi-directional exchanges of ammonia applied at the field scale
Authors: Personne E. , Loubet B. , Herrmann B. , Mattsson M. , Schjoerring J. K. , Nemitz E. , Sutton M. A. , Cellier P.
Published: April 2010

Abstract. A new biophysical model SURFATM-NH3, simulating the ammonia (NH3) exchange between terrestrial ecosystems and the atmosphere is presented. SURFATM-NH3 consists of two coupled models: (i) an energy budget model and (ii) a pollutant exchange model, which distinguish the soil and plant exchange processes. The model describes the exchanges in terms of adsorption to leaf cuticles and bi-directional transport through leaf stomata and soil. The results of the model are compared with the flux measurements over grassland during the GRAMINAE Integrated Experiment at Braunschweig, Germany. The dataset of GRAMINAE allows the model to be tested in various meteorological and agronomic conditions: prior to cutting, after cutting and then after the application of mineral fertilizer. The whole comparison shows close agreement between model and measurements for energy budget and ammonia fluxes. The major controls on the ground and plant emission potential are the physicochemical parameters for liquid-gas exchanges which are integrated in the compensation points for live leaves, litter and the soil surface. Modelled fluxes are highly sensitive to soil and plant surface temperatures, highlighting the importance of accurate estimates of these terms. The model suggests that the net flux depends not only on the foliar (stomatal) compensation point but also that of leaf litter. SURFATM-NH3 represents a comprehensive approach to studying pollutant exchanges and its link with plant and soil functioning. It also provides a simplified generalised approach (SVAT model) applicable for atmospheric transport models.
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. F. , 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. The maps have been computed using a neural network technique which reconstructs the non-linear relationships between three biogeochemical parameters and marine pCO2. A self organizing map (SOM) neural network has been trained using 389 000 triplets of the SeaWiFS-MODIS chlorophyll-a concentration, the NCEP/NCAR reanalysis sea surface temperature, and the FOAM mixed layer depth. The trained SOM was labelled with 137 000 underway pCO2 measurements collected in situ during 2004, 2005 and 2006 in the North Atlantic, spanning the range of 208 to 437 μatm. The root mean square error (RMSE) of the neural network fit to the data is 11.6 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 estimates of the interannual variability in the major biogeochemical provinces are presented and discussed. High resolution combined with basin-wide coverage makes the maps a useful tool for several applications such as the 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.
Improved understanding of drought controls on seasonal variation in Mediterranean forest canopy CO2 and water fluxes through combined in situ measurements and ecosystem modelling
Authors: Keenan T. , García R. , Friend A. D. , Zaehle S. , Gracia C. , Sabate S.
Published: April 2010

Abstract. Water stress is a defining characteristic of Mediterranean ecosystems, and is likely to become more severe in the coming decades. Simulation models are key tools for making predictions, but our current understanding of how soil moisture controls ecosystem functioning is not sufficient to adequately constrain parameterisations. Canopy-scale flux data from four forest ecosystems with Mediterranean-type climates were used in order to analyse the physiological controls on carbon and water flues through the year. Significant non-stomatal limitations on photosynthesis were detected, along with lesser changes in the conductance-assimilation relationship. New model parameterisations were derived and implemented in two contrasting modelling approaches. The effectiveness of two models, one a dynamic global vegetation model ("ORCHIDEE"), and the other a forest growth model particularly developed for Mediterranean simulations ("GOTILWA+"), was assessed and modelled canopy responses to seasonal changes in soil moisture were analysed in comparison with in situ flux measurements. In contrast to commonly held assumptions, we find that changing the ratio of conductance to assimilation under natural, seasonally-developing, soil moisture stress is not sufficient to reproduce forest canopy CO2 and water fluxes. However, accurate predictions of both CO2 and water fluxes under all soil moisture levels encountered in the field are obtained if photosynthetic capacity is assumed to vary with soil moisture. This new parameterisation has important consequences for simulated responses of carbon and water fluxes to seasonal soil moisture stress, and should greatly improve our ability to anticipate future impacts of climate changes on the functioning of ecosystems in Mediterranean-type climates.
Intercomparison and assessment of turbulent and physiological exchange parameters of grassland
Authors: Nemitz E. , Hargreaves K. J. , Neftel A. , Loubet B. , Cellier P. , Dorsey J. R. , Flynn M. , Hensen A. , Weidinger T. , Meszaros R. , Horvath L. , Dämmgen U. , Frühauf C. , Löpmeier F. J. , Gallagher M. W. , Sutton M. A.
Published: April 2010

Abstract. Commonly, the micrometeorological parameters that underline the calculations of surface atmosphere exchange fluxes (e.g. friction velocity and sensible heat flux) and parameters used to model exchange fluxes with SVAT-type parameterisations (e.g. latent heat flux and canopy temperature) are measured with a single set of instrumentation and are analysed with a single methodology. This paper evaluates uncertainties in these measurements with a single instrument, by comparing the independent results from nine different institutes during the international GRAMINAE integrated field experiment over agricultural grassland near Braunschweig, Lower Saxony, Germany. The paper discusses uncertainties in measuring friction velocity, sensible and latent heat fluxes, canopy temperature and investigates the energy balance closure at this site. Although individual 15-min flux calculations show a large variability between the instruments, when averaged over the campaign, fluxes agree within 2% for momentum and 11% for sensible heat. However, the spread in estimates of latent heat flux (λE) is larger, with standard deviations of averages of 18%. The dataset averaged over the different instruments fails to close the energy budget by 20%, significantly larger than the uncertainties in the individual flux corrections. However, if the largest individual turbulent flux estimates are considered, energy closure can be achieved, indicating that the closure gap is within the spread of the measurements. The uncertainty in λE feeds results in an uncertainty in the bulk stomatal resistance, which further adds to the uncertainties in the estimation of the canopy temperature that controls the exchange. The paper demonstrated how a consensus dataset was derived, which is used by the individual investigators to calculate fluxes and drive their models.
Spatial trends in leaf size of Amazonian rainforest trees
Authors: Malhado A. C. M. , Malhi Y. , Whittaker R. J. , Ladle R. J. , ter Steege H. , Phillips O. L. , Butt N. , Aragão L. E. O. C. , Quesada C. A. , Araujo-Murakami A. , Arroyo L. , Peacock J. , Lopez-Gonzalez G. , Baker T. R. , Anderson L. O. , Almeida S. , Higuchi N. , Killeen T. J. , Monteagudo A. , Neill D. , Pitman N. , Prieto A. , Salomão R. P. , Vásquez-Martínez R. , Laurance W. F.
Published: April 2010

Abstract. Leaf size influences many aspects of tree function such as rates of transpiration and photosynthesis and, consequently, often varies in a predictable way in response to environmental gradients. The recent development of pan-Amazonian databases based on permanent botanical plots has now made it possible to assess trends in leaf size across environmental gradients in Amazonia. Previous plot-based studies have shown that the community structure of Amazonian trees breaks down into at least two major ecological gradients corresponding with variations in soil fertility (decreasing from southwest to northeast) and length of the dry season (increasing from northwest to south and east). Here we describe the geographic distribution of leaf size categories based on 121 plots distributed across eight South American countries. We find that the Amazon forest is predominantly populated by tree species and individuals in the mesophyll size class (20.25–182.25 cm2). The geographic distribution of species and individuals with large leaves (>20.25 cm2) is complex but is generally characterized by a higher proportion of such trees in the northwest of the region. Spatially corrected regressions reveal weak correlations between the proportion of large-leaved species and metrics of water availability. We also find a significant negative relationship between leaf size and wood density.
Using satellite-derived backscattering coefficients in addition to chlorophyll data to constrain a simple marine biogeochemical model
Authors: Kettle H.
Published: April 2010

Abstract. Biogeochemical models of the ocean carbon cycle are frequently validated by, or tuned to, satellite chlorophyll data. However, ocean carbon cycle models are required to accurately model the movement of carbon, not chlorophyll, and due to the high variability of the carbon to chlorophyll ratio in phytoplankton, chlorophyll is not a robust proxy for carbon. Using inherent optical property (IOP) inversion algorithms it is now possible to also derive the amount of light backscattered by the upper ocean (bb) which is related to the amount of particulate organic carbon (POC) present. Using empirical relationships between POC and bb, a 1-D marine biogeochemical model is used to simulate bb at 490 nm thereby allowing the model to be compared with both remotely-sensed chlorophyll or bb data. Here I investigate the possibility of using bb in conjunction with chlorophyll data to help constrain the parameters in a simple 1-D NPZD model. The parameters of the biogeochemical model are tuned with a genetic algorithm, so that the model is fitted to either chlorophyll data or to both chlorophyll and bb data at three sites in the Atlantic with very different characteristics. Several inherent optical property (IOP) algorithms are available for estimating bb, three of which are used here. The effect of the different bb datasets on the behaviour of the tuned model is examined to ascertain whether the uncertainty in bb is significant. The results show that the addition of bb data does not consistently alter the same model parameters at each site and in fact can lead to some parameters becoming less well constrained, implying there is still much work to be done on the mechanisms relating chlorophyll to POC and bb within the model. However, this study does indicate that including bb data has the potential to significantly effect the modelled mixed layer detritus and that uncertainties in bb due to the different IOP algorithms are not particularly significant.
After trees die: quantities and determinants of necromass across Amazonia
Authors: Chao K.-J. , Phillips O. L. , Baker T. R. , Peacock J. , Lopez-Gonzalez G. , Vásquez Martínez R. , Monteagudo A. , Torres-Lezama A.
Published: April 2010

Abstract. The Amazon basin, one of the most substantial biomass carbon pools on earth, is characterised by strong macroecological gradients in biomass, mortality rates, and wood density from west to east. These gradients could affect necromass stocks, but this has not yet been tested. This study aims to assess the stocks and determinants of necromass across Amazonian forests. Field-based and literature data were used to find relationships between necromass and possible determinants. Furthermore, a simple model was applied to estimate and extrapolate necromass stocks across terra firma Amazonian forests. In eight northwestern and three northeastern Amazonian permanent plots, volumes of coarse woody debris (≥10 cm diameter) were measured in the field and the density of each decay class was estimated. Forest structure and historical mortality data were used to determine the factors controlling necromass. Necromass is greater in forests with low stem mortality rates (northeast) rather than in forests with high stem mortality rates (northwest) (58.5±10.6 and 27.3±3.2 Mg ha−1, respectively). Using all published necromass values, we find that necromass across terra firma forests in Amazonia is positively related to both forest dynamics (mortality mass inputs and a surrogate for decomposition rate (average wood density of living trees)) and forest structure (biomass), but is better explained by forest dynamics. We propose an improved method to estimate necromass for plots where necromass has not been measured. The estimates, together with other actual measurements of necromass, were scaled-up to project a total Amazonian necromass of 9.6±1.0 Pg C. The ratio of necromass (on average weighted by forest region) to coarse aboveground biomass is 0.127. Overall, we find (1) a strong spatial trend in necromass in parallel with other macroecological gradients and (2) that necromass is a substantial component of the carbon pool in the Amazon.
Ignoring detailed fast-changing dynamics of land use overestimates regional terrestrial carbon sequestration
Authors: Zhao S. Q. , 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 the local to global scales.
Growth phase dependent hydrogen isotopic fractionation in alkenone-producing haptophytes
Authors: Wolhowe M. D. , Prahl F. G. , Probert I. , Maldonado M.
Published: April 2010

Abstract. Recent works have investigated use of the hydrogen isotopic composition of C37 alkenones (δDK37s, lipid biomarkers of certain haptophyte microalgae, as an independent paleosalinity proxy. We discuss herein the factors impeding the success of such an application and identify the potential alternative use of δDK37s measurements as a proxy for non-thermal, physiological stress impacts on the U37K' paleotemperature index. Batch-culture experiments with the haptophyte Emiliania huxleyi (CCMP 1742) were conducted to determine the magnitude and variability of the isotopic contrasts between individual C37 alkenones. Further experiments were conducted with Emiliania huxleyi (CCMP 1742) andGephyrocapsa oceanica (PZ3-1) to determine whether, and to what extent, δDK37s varies between the physiological extremes of nutrient-replete exponential growth and nutrient-depleted senescence. Emiliania huxleyi was observed to exhibit an isotopic contrast between di- and tri-unsaturated C37 alkenones (αK37:3-K37:2≈0.97) that is nearly identical to that reported recently by others for environmental samples. Furthermore, this contrast appears to be constant with growth stage. The consistency of the offset across different growth stages suggests that a single, well-defined value for αK37:3-K37:2 may exist and that its use in an isotope mass-balance will allow accurate determination of δD values for individual alkenones without having to rely on time- and labor-intensive chemical separations. The isotopic fractionation between growth medium and C37 alkenones was observed to increase dramatically upon the onset of nutrient-depletion-induced senescence, suggesting that δDK37s may serve as an objective tool for recognizing and potentially correcting, at least semi-quantitatively, for the effects of nutrient stress on U37K' temperature records.
Biodiversity for multifunctional grasslands: equal productivity in high-diversity low-input and low-diversity high-input systems
Authors: Weigelt A. , Weisser W. W. , Buchmann N. , Scherer-Lorenzen M.
Published: April 2010

Abstract. Modern grassland management seeks to provide many ecosystem services and experimental studies in resource-poor grasslands have shown a positive relationship between plant species richness and a variety of ecosystem functions. Thus, increasing species richness might help to enhance multifunctionality in managed grasslands if the relationship between species richness and ecosystem functioning is equally valid in high-input grassland systems. We tested the relative effects of low-input to high-input management intensities and low to high plant species richness. Using a combination of mowing frequencies (1, 2 or 4 cuts per season) and fertilisation levels (0, 100 and 200 kg N ha−1 a−1), we studied the productivity of 78 experimental grassland communities of increasing plant species richness (1, 2, 4, 8 or 16 species with 1 to 4 functional groups) in two successive years. Our results showed that in both years higher diversity was more effective in increasing productivity than higher management intensity: the 16-species mixtures had a surplus of 449 g m−2 y−1 in 2006 and 492 g m−2 y−1 in 2007 over the monoculture yields whereas the high-input management resulted in only 315 g m−2 y−1 higher productivity in 2006 and 440 g m−2 y−1 in 2007 than the low-input management. In addition, high-diversity low-input grassland communities had similar productivity as low-diversity high-input communities. The slopes of the biodiversity – productivity relationships significantly increased with increasing levels of management intensity in both years. We conclude that the biological mechanisms leading to enhanced biomass production in diverse grassland communities are as effective for productivity as a combination of several agricultural measures. Our results demonstrate that high-diversity low-input grassland communities provide not only a high diversity of plants and other organisms, but also ensure high forage yields, thus granting the basis for multifunctional managed grasslands.
Temporal variability in bioassays of the stomatal ammonia compensation point in relation to plant and soil nitrogen parameters in intensively managed grassland
Authors: Mattsson M. , Herrmann B. , David M. , Loubet B. , Riedo M. , Theobald M. R. , Sutton M. A. , Bruhn D. , Neftel A. , Schjoerring J. K.
Published: April 2010

Abstract. The exchange of ammonia between crop canopies and the atmosphere depends on a range of plant parameters and climatic conditions. However, little is known about effects of management factors. We have here investigated the stomatal ammonia compensation point in response to cutting and fertilization of a grass sward dominated by Lolium perenne. Tall grass had a very low NH3 compensation point (around 1 nmol mol−1), reflecting the fact that leaf nitrogen (N) concentration was very low. During re-growth after cutting, leaf tissue concentrations of NO3−, NH4+, soluble N and total N increased along with apoplastic NH4+ concentrations. In contrast, apoplastic pH decreased resulting in largely unaltered NH3 compensation points. Nitrogen fertilization one week after cutting caused the apoplastic NH4+ concentration of the newly emerging leaves to increase dramatically. The NH3 compensation point peaked between 15 and 25 nmol mol−1 the day after the fertiliser was applied and thereafter decreased over the following 10 days until reaching the same level as before fertilisation. Ammonium concentrations in leaf apoplast, bulk tissue and litter were positively correlated (P=0.001) throughout the experimental period. Bulk tissue NH4+ concentrations, total plant N and soil NH4+ concentrations also showed a positive correlation. A very high potential for NH3 emission was shown by the plant litter.
Net community production of oxygen derived from in vitro and in situ 1-D modeling techniques in a cyclonic mesoscale eddy in the Sargasso Sea
Authors: Mouriño-Carballido B. , Anderson L. A.
Published: April 2010

Abstract. It has been proposed that the disagreement traditionally reported between in vitro incubation and in situ estimates of oxygen net community production (NCP) could be explained, at least partially, by undersampling episodic pulses of net autotrophy associated with mesoscale dynamics. In this study we compare in vitro incubation estimates of net community production with in situ estimates, derived from oxygen profiles and a 1-D model, within a cyclonic eddy investigated in the Sargasso Sea in summer 2004. The in vitro NCP rates measured at the center of the eddy showed a shift from net autotrophy (7±3 mmol O2 m−2 d−1) to net heterotrophy (−25±5 mmol O2 m−2 d−1) from late June to early August. The model-derived NCP rates also showed a temporal decline (19±6 to −3±7 and 11±8 mmol O2 m−2 d−1), but they were systematically higher than the in vitro estimates and reported net autotrophy or balance for the sampling period. In this comparison episodic pulses in photosynthesis or respiration driven by mesoscale eddies can not explain the discrepancy between the in vitro and in situ estimates of NCP. This points to methodological artefacts or temporal or submesoscale variability as the mechanisms responsible for the disagreement between the techniques, at least in this dataset.
Applying biomass and stem fluxes to quantify temporal and spatial fluctuations of an old-growth forest in disturbance
Authors: Liu S. , Li Y.-L. , Zhou G.-Y. , Wenigmann K. O. , Luo Y. , Otieno D. , Tenhunen J.
Published: April 2010

Abstract. A subtropical old-growth forest was studied over a twelve-year period to investigate temporal and spatial fluctuations of biomass and stem fluxes under disturbances. Vegetations were categorized into three types according to disturbances caused by biotic and abiotic factors, including Castanopsis chinensis population, insect direct-influenced population, and insect indirect-influenced population according to disturbance scenarios. The biomass fluxes (growth and mortality) and stem fluxes (stem recruitment and mortality) were used to quantify population fluctuations. Annual average biomass growth rate was stable throughout the study while annual biomass mortality and stem fluxes increased consistently. C. chinensis population predominantly contributed to biomass fluxes of the community. Biomass and stem mortalities of insect direct-influenced population increased significantly during the whole study period (1992–2004). Results of indirect-influenced population showed that (1) the increase in biomass of the dominant species was well correlated between different intervals. Similar relationships were found in stem fluxes; (2) higher stem mortality occurred within the DBH range of 1 to 10 cm; (3) stem fluxes in the canopy gaps were remarkably higher than those in closed canopy.
Influence of elevated CO2 concentrations on cell division and nitrogen fixation rates in the bloom-forming cyanobacterium Nodularia spumigena
Authors: Czerny J. , Barcelos e Ramos J. , Riebesell U.
Published: April 2010

Abstract. The surface ocean absorbs large quantities of the CO2 emitted to the atmosphere from human activities. As this CO2 dissolves in seawater, it reacts to form carbonic acid. While this phenomenon, called ocean acidification, has been found to adversely affect many calcifying organisms, some photosynthetic organisms appear to benefit from increasing [CO2]. Among these is the cyanobacterium Trichodesmium, a predominant diazotroph (nitrogen-fixing) in large parts of the oligotrophic oceans, which responded with increased carbon and nitrogen fixation at elevated pCO2. With the mechanism underlying this CO2 stimulation still unknown, the question arises whether this is a common response of diazotrophic cyanobacteria. In this study we therefore investigate the physiological response of Nodularia spumigena, a heterocystous bloom-forming diazotroph of the Baltic Sea, to CO2-induced changes in seawater carbonate chemistry. N. spumigena reacted to seawater acidification/carbonation with reduced cell division rates and nitrogen fixation rates, accompanied by significant changes in carbon and phosphorus quota and elemental composition of the formed biomass. Possible explanations for the contrasting physiological responses of Nodularia compared to Trichodesmium may be found in the different ecological strategies of non-heterocystous (Trichodesmium) and heterocystous (Nodularia) cyanobacteria.
Impact of ocean acidification on a key Arctic pelagic mollusc (Limacina helicina)
Authors: Comeau S. , Gorsky G. , Jeffree R. , Teyssié J.-L. , Gattuso J.-P.
Published: April 2010

Abstract. Thecosome pteropods (shelled pelagic molluscs) can play an important role in the food web of various ecosystems and play a key role in the cycling of carbon and carbonate. Since they harbor an aragonitic shell, they could be very sensitive to ocean acidification driven by the increase of anthropogenic CO2 emissions. The impact of changes in the carbonate chemistry was investigated on Limacina helicina, a key species of Arctic ecosystems. Pteropods were kept in culture under controlled pH conditions corresponding to pCO2 levels of 350 and 760 μatm. Calcification was estimated using a fluorochrome and the radioisotope 45Ca. It exhibits a 28% decrease at the pH value expected for 2100 compared to the present pH value. This result supports the concern for the future of pteropods in a high-CO2 world, as well as of those species dependent upon them as a food resource. A decline of their populations would likely cause dramatic changes to the structure, function and services of polar ecosystems.
The influence of hypercapnia and the infaunal brittlestar Amphiura filiformis on sediment nutrient flux – will ocean acidification affect nutrient exchange?
Authors: Wood H. L. , Widdicombe S. , Spicer J. I.
Published: April 2010

Abstract. Rising levels of atmospheric carbon dioxide and the concomitant increased uptake of this by the oceans is resulting in hypercapnia-related reduction of ocean pH. Research focussed on the direct effects of these physicochemical changes on marine invertebrates has begun to improve our understanding of impacts at the level of individual physiologies. However, CO2-related impairment of organisms' contribution to ecological or ecosystem processes has barely been addressed. The burrowing ophiuroid Amphiura filiformis, which has a physiology that makes it susceptible to reduced pH, plays a key role in sediment nutrient cycling by mixing and irrigating the sediment, a process known as bioturbation. Here we investigate the role of A. filiformis in modifying nutrient flux rates across the sediment-water boundary and the impact of CO2- related acidification on this process. A 40 day exposure study was conducted under predicted pH scenarios from the years 2100 (pH 7.7) and 2300 (pH 7.3), plus an additional treatment of pH 6.8. This study demonstrated strong relationships between A. filiformis density and cycling of some nutrients;
Coccolithophore response to climate and surface hydrography in Santa Barbara Basin, California, AD 1917–2004
Authors: Grelaud M. , Schimmelmann A. , Beaufort L.
Published: April 2010

Abstract. The varved sedimentary AD 1917–2004 record from the depositional center of the Santa Barbara Basin (SBB, California) was analyzed with monthly to triannual resolution to yield relative abundances of six coccolithophore species representing at least 96% of the coccolithophore assemblage. Seasonal/annual relative abundances respond to climatic and surface hydrographic conditions in the SBB, whereby (i) the three species G. oceanica, H. carteri and F. profunda are characteristic of the strength of the northward flowing warm California Counter Current, (ii) the two species G. ericsonii and G. muellerae are associated with the cold equatorward flowing California Current, (iii) and E. huxleyi appears to be endemic to the SBB. Spectral analyses on relative abundances of these species show that all are influenced by the El Niño Southern Oscillation (ENSO) and/or by the Pacific Decadal Oscillation (PDO). Increased relative abundances of G. oceanica and H. carteri are associated with warm ENSO events, G. muellerae responds to warm PDO events and the abundance of G. ericsonii increases during cold PDO events. Morphometric parameters measured on E. huxleyi, G. muellerae and G. oceanica indicate increasing coccolithophore shell carbonate mass from ~1917 until 2004 concomitant with rising pCO2 and sea surface temperature in the region of the SBB.
Technical Note: Approaches and software tools to investigate the impact of ocean acidification
Authors: Gattuso J.-P. , Lavigne H.
Published: April 2010

Abstract. Although future changes in the seawater carbonate chemistry are well constrained, their impact on marine organisms and ecosystems remains poorly known. The biological response to ocean acidification is a recent field of research as most purposeful experiments have only been carried out in the late 1990s. The potentially dire consequences of ocean acidification attract scientists and students with a limited knowledge of the carbonate chemistry and its experimental manipulation. Hence, some guidelines on carbonate chemistry manipulations may be helpful for the growing ocean acidification community to maintain comparability. Perturbation experiments are one of the key approaches used to investigate the biological response to elevated pCO2. They are based on measurements of physiological or metabolic processes in organisms and communities exposed to seawater with normal or altered carbonate chemistry. Seawater chemistry can be manipulated in different ways depending on the facilities available and on the question being addressed. The goal of this paper is (1) to examine the benefits and drawbacks of various manipulation techniques and (2) to describe a new version of the R software package seacarb which includes new functions aimed at assisting the design of ocean acidification perturbation experiments. Three approaches closely mimic the on-going and future changes in the seawater carbonate chemistry: gas bubbling, addition of high-CO2 seawater as well as combined additions of acid and bicarbonate and/or carbonate.
Long term changes in the ecosystem in the northern South China Sea during 1976–2004
Authors: Ning X. , Lin C. , Hao Q. , Liu C. , Le F. , Shi J.
Published: April 2010

Abstract. Physical and chemical oceanographic data were obtained by seasonal monitoring along a transect (Transect N) in the northern South China Sea (nSCS) during 1976–2004. Fluctuations of DIN (dissolved inorganic nitrogen), seawater temperature (SST and Tav – average temperature of the water column), N:P ratio and salinity (Sav and S200 – salinity at the 200 m layer) exhibited an increasing trend, while those of T200, DO, P, Si, Si:N and SSS exhibited a decreasing trend. The annual rates of change in DIN, DO, T and S revealed pronounced changes, and the climate trend coefficients, which was defined as the correlation coefficient between the time series of an environmental parameter and the nature number (namely 1,2,3,......n), were 0.38 to 0.89 and significant (p≤0.01 to 0.05). Our results also showed that the ecosystem has obviously been influenced by the positive trends of both SST and DIN, and negative trends of both DO and P. For example, before 1997, DIN concentrations in the upper layer were very low and N:P ratios were less than half of the Redfield ratio of 16, indicating potential N limitation. However after 1997, all Si:P ratios were >22 and the Nav:Pav was close to the Redfield ratio, indicating potential P limitation, and therefore N limitation has been reduced after 1997. Ecological investigation shows that there have been some obvious responses of the ecosystems to the long-term environmental changes in the nSCS. Chlorophyll-a concentration, primary production, phytoplankton abundance, benthic biomass, cephalopod catch and demersal trawl catch have increased. But phosphorus depletion in upper layer may be related to the shift in the dominant species from diatoms to dinoflagellates and cyanophytes. The ecosystem response was induced by not only anthropogenic activities, but also global climate change, e.g. ENSO. The effects of climate change on the nSCS were mainly through changes in the monsoon winds, and physical-biological oceanography coupling processes. In this study physical-chemical parameters were systemic maintained, but the contemporaneous biological data were collected from various sources. Regional response to global climate change is clearly a complicated issue, which is far from well understood. This study was made an attempt to tackle this important issue. For the aim these data were valuable.
Biosphere-atmosphere exchange of CO2 in relation to climate: a cross-biome analysis across multiple time scales
Authors: Stoy P. C. , Richardson A. D. , Baldocchi D. D. , Katul G. G. , Stanovick J. , Mahecha M. D. , Reichstein M. , Detto M. , Law B. E. , Wohlfahrt G. , Arriga N. , Campos J. , McCaughey J. H. , Montagnani L. , Paw U K. T. , Sevanto S. , Williams M.
Published: April 2010

Abstract. The net ecosystem exchange of CO2 (NEE) varies at time scales from seconds to years and longer via the response of its components, gross ecosystem productivity (GEP) and ecosystem respiration (RE), to physical and biological drivers. Quantifying the relationship between flux and climate at multiple time scales is necessary for a comprehensive understanding of the role of climate in the terrestrial carbon cycle. Orthonormal wavelet transformation (OWT) can quantify the strength of the interactions between gappy eddy covariance flux and micrometeorological measurements at multiple frequencies while expressing time series variance in few energetic wavelet coefficients, offering a low-dimensional view of the response of terrestrial carbon flux to climatic variability. The variability of NEE, GEP and RE, and their co-variability with dominant climatic drivers, are explored with nearly one thousand site-years of data from the FLUXNET global dataset consisting of 253 eddy covariance research sites. The NEE and GEP wavelet spectra were similar among plant functional types (PFT) at weekly and shorter time scales, but significant divergence appeared among PFT at the biweekly and longer time scales, at which NEE and GEP were relatively less variable than climate. The RE spectra rarely differed among PFT across time scales as expected. On average, RE spectra had greater low frequency (monthly to interannual) variability than NEE, GEP and climate. CANOAK ecosystem model simulations demonstrate that "multi-annual" spectral peaks in flux may emerge at low (4+ years) time scales. Biological responses to climate and other internal system dynamics, rather than direct ecosystem response to climate, provide the likely explanation for observed multi-annual variability, but data records must be lengthened and measurements of ecosystem state must be made, and made available, to disentangle the mechanisms responsible for low frequency patterns in ecosystem CO2 exchange.
Carbon emissions from deforestation in the Brazilian Amazon Region
Authors: Potter C. , Klooster S. , Genovese V.
Published: April 2010

Abstract. A simulation model based on satellite observations of monthly vegetation greenness from the Moderate Resolution Imaging Spectroradiometer (MODIS) was used to estimate monthly carbon fluxes in terrestrial ecosystems of Brazilian Amazon and Cerrado regions over the period 2000–2002. The NASA-CASA (Carnegie Ames Stanford Approach) model estimates of annual forest production were used for the first time as the basis to generate a prediction for the standing pool of carbon in above-ground biomass (AGB; g C m−2) for forested areas of the Brazilian Amazon region. Plot-level measurements of the residence time of carbon in wood in Amazon forest from Malhi et al. (2006) were interpolated by inverse distance weighting algorithms and used with CASA to generate a new regional map of AGB. Data from the Brazilian PRODES (Estimativa do Desflorestamento da Amazônia) project were used to map deforested areas. Results show that net primary production (NPP) sinks for carbon varied between 4.25 Pg C yr−1 (1 Pg=1015 g) and 4.34 Pg C for the region and were highest across the eastern and northern Amazon areas, whereas deforestation sources of CO2 flux from decomposition of residual woody debris were higher and less seasonal in the central Amazon than in the eastern and southern areas. Increased woody debris from past deforestation events was predicted to alter the net ecosystem carbon balance of the Amazon region to generate annual CO2 source fluxes at least two times higher than previously predicted by CASA modeling studies. Variations in climate, land cover, and forest burning were predicted to release carbon at rates of 0.5 to 1 Pg C yr−1 from the Brazilian Amazon. When direct deforestation emissions of CO2 from forest burning of between 0.2 and 0.6 Pg C yr−1 in the Legal Amazon are overlooked in regional budgets, the year-to-year variations in this net biome flux may appear to be large, whereas our model results implies net biome fluxes had actually been relatively consistent from year to year during the period 2000–2002. This is the first study to use MODIS data to model all carbon pools (wood, leaf, root) dynamically in simulations of Amazon forest deforestation from clearing and burning of all kinds.