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See detailThe time after feeding alters methane emission kinet- ics in Holstein dry cows fed with various restricted diets
Blaise, Yannick ULiege; Andriamandroso, Andriamasinoro ULiege; Beckers, Yves ULiege et al

in Livestock Science (in press)

This study aims to investigate shifts in methane (CH4) emission in cattle in relation to the time after feeding, diet composition, and feed allowance. Four non-cannulated dry Holstein cows were equipped ... [more ▼]

This study aims to investigate shifts in methane (CH4) emission in cattle in relation to the time after feeding, diet composition, and feed allowance. Four non-cannulated dry Holstein cows were equipped with activity and infrared sensors to monitor feeding behavior and CH4 and carbon dioxide (CO2) levels in the breath, continuously and at a frequency of 4 Hz. The second goal pursued, was to assess the methane emission estimation (CH4, L/h) by the CO2-method based on the ratio between CH4 and CO2 in the exhaled air, using metabolic CO2 as a marker. All cows were fed twice a day at 12 h intervals with contrasting isoenergy diets in a cross-over design: LIN100 diet (5562 VEM, i.e. Voedereenheid Melk, Dutch energy unit for milk production, 1 VEM = 6.9 kJ net energy for lactation) composed of haylage, linseed and wheat, and HAY100 (5367 VEM) diet containing only haylage. After a 2 week adaptation period to the diets, 3 days were required for the measurements and immediately after, two additional experimental treatments were applied by reducing the feed allowance to 70% with the same diets to evaluate the impact of the dry matter intake, yielding the two additional treatments HAY70 and LIN70. In addition, two other rumen-cannulated cows were used to monitor time after feeding short-chain fatty acid concentrations in the rumen. On a daily basis, all indicators (daily CH4:CO2 ratio, eructation frequency and CH4 emission) followed the same trend and showed that cows on a hay-based diet produced more CH4 and feed restriction induced different production levels for the same type of diet. The average CH4 emission for the different diets were 6.86 L/h for HAY100 > 6.25 L/h for HAY70 > 4.26 L/h for LIN100 > 3.97 L/h LIN70 (P < 0.001). The LIN100 diet produced 38% lower daily CH4 emissions than HAY100 and reduced the eructation frequency by 44%. During feeding, the eructation frequency was higher (P<0.001) for HAY than LIN diets. This work underlines the daily CH4 emission dynamics observed using the CH4:CO2 ratio in the cow's exhaled air. Methane emissions (L/h) are strongly influenced by the time after feeding time (P < 0.001). They increased for up to 2 hours after the distribution of the meal, and then decreased until the next meal, with shifts between the maximum and the minimum emission of more than 100% for LIN100 and 22% for HAY100. Consistently, the acetate:proprionate ratio was smaller for the LIN100 diet between 2 to 5 hours after the meal (P < 0.001). [less ▲]

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See detailRestoring a worn-out pasture: what impact on N2O exchanges ?
Lognoul, Margaux ULiege; Gourlez de la Motte, Louis ULiege; Naiken, Alwin ULiege et al

Poster (2019, April 08)

A paired-flux tower experiment was set up in a 40 y-o grazed pasture managed by a local farmer. A parcel under restoration was compared to a control plot. In addition to N2O flux monitoring, soil mineral ... [more ▼]

A paired-flux tower experiment was set up in a 40 y-o grazed pasture managed by a local farmer. A parcel under restoration was compared to a control plot. In addition to N2O flux monitoring, soil mineral N content (ammonium and nitrate) was measured every 10-15 days. [less ▲]

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See detailHerd position habits can bias net CO2 ecosystem exchange estimates in free range grazed pastures.
Gourlez de la Motte, Louis ULiege; Dumortier, Pierre ULiege; Beckers, Yves ULiege et al

Conference (2019, April)

The eddy covariance (EC) technique has been widely used to quantify the net CO2 ecosystem exchange (NEE) of grasslands, which is an important component of grassland carbon and greenhouse gas budgets. In ... [more ▼]

The eddy covariance (EC) technique has been widely used to quantify the net CO2 ecosystem exchange (NEE) of grasslands, which is an important component of grassland carbon and greenhouse gas budgets. In free range grazed pastures, NEE estimations are supposed to also include cattle respiration. However, cattle respiration measurement by an EC system is challenging as animals act as moving points emitting CO2 that are more or less captured by the EC tower depending on their presence in the footprint. Often it is supposed that, over the long term, cattle distribution in the pasture is homogeneous so that fluctuations due to moving sources are averaged and NEE estimates are reasonably representative of cattle respiration. In this study, we test this hypothesis by comparing daily cow respiration rate per livestock unit (LU) estimated by postulating a homogeneous cow repartition over the whole pasture with three other estimates based on animal localization data, animal scale carbon budget and confinement experiments. We applied these methods to an intensively managed free range grassland and showed that the NEE estimate based on a homogeneous cow repartition was systematically lower than the three other estimates. Consequently, in order to allow estimating the validity of this hypothesis but also to improve inter site comparisons, we advocate to compute separately pasture NEE and grazer’s respiration. In the presentation, we will propose a method based on cattle presence detection using CH4 fluxes, elimination of data with cattle and gap filling on the basis of data without cattle. For the second we propose three independent methods (animal localization with GPS, animal scale carbon budget, confinement experiments) to estimate the cattle respiration rate and discuss their use depending on site specificities. [less ▲]

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See detailÉchanges de Composés Organiques Volatils entre les agrosystèmes et l'atmosphère
Buysse, Pauline; Kammer, Julien; Heinesch, Bernard ULiege

Conference (2019, March 21)

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See detailChangements climatiques et agriculture
Heinesch, Bernard ULiege

Conference given outside the academic context (2019)

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See detailHerd position habits can bias net CO2 ecosystem exchange estimates in free range grazed pastures.
Gourlez de la Motte, Louis ULiege; Dumortier, Pierre ULiege; Beckers, Yves ULiege et al

in Agricultural and Forest Meteorology (2019), 268

The eddy covariance (EC) technique has been widely used to quantify the net CO2 ecosystem exchange (NEE) of grasslands, which is an important component of grassland carbon and greenhouse gas budgets. In ... [more ▼]

The eddy covariance (EC) technique has been widely used to quantify the net CO2 ecosystem exchange (NEE) of grasslands, which is an important component of grassland carbon and greenhouse gas budgets. In free range grazed pastures, NEE estimations are supposed to also include cattle respiration. However, cattle respiration measurement by an EC system is challenging as animals act as moving points emitting CO2 that are more or less captured by the EC tower depending on their presence in the footprint. Often it is supposed that, over the long term, cattle distribution in the pasture is homogeneous so that fluctuations due to moving sources are averaged and NEE estimates are reasonably representative of cattle respiration. In this study, we test this hypothesis by comparing daily cow respiration rate per livestock unit (LU) estimated by postulating a homogeneous cow repartition over the whole pasture with three other estimates based on animal localization data, animal scale carbon budget and confinement experiments. We applied these methods to an intensively managed free range grassland and showed that the NEE estimate based on a homogeneous cow repartition was systematically lower than the three other estimates. The bias was about 60 g C m–2 yr–1, which corresponded to around 40% of the annual NEE. The sign and the importance of this bias is site specific, as it depends on cow location habits in relation to the footprint of the EC measurements which highlight the importance of testing the hypothesis of homogeneity of cattle distribution on each site. Consequently, in order to allow estimating the validity of this hypothesis but also to improve inter site comparisons, we advocate to compute separately pasture NEE and grazer’s respiration. For the former we propose a method based on cattle presence detection using CH4 fluxes, elimination of data with cattle and gap filling on the basis of data without cattle. For the second we present and discuss three independent methods (animal localization with GPS, animal scale carbon budget, confinement experiments) to estimate the cattle respiration rate. [less ▲]

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See detailChangements climatiques… Agir pour empêcher ?
Heinesch, Bernard ULiege

Speech/Talk (2018)

À l’occasion du film « Woman at War » au cinéma Sauvenière, Réjouisciences vous propose une rencontre avec des intervenants de l’Université de Liège autour du thème « Changements climatiques… Agir pour ... [more ▼]

À l’occasion du film « Woman at War » au cinéma Sauvenière, Réjouisciences vous propose une rencontre avec des intervenants de l’Université de Liège autour du thème « Changements climatiques… Agir pour empêcher ? ». Halla est grande. Elle est cette belle quinquagénaire en pleine forme qui tend la corde de son arc pour s’attaquer aux lignes électriques. Traits concentrés, regard d’acier, sourire en coin, elle a la carrure d’une amazone. Pourtant, dans la vie d’Halla, point d’aventures à dos de cheval, son ennemi c’est la finance. Quand l’industrie de l’aluminium contamine son pays, souille sa nature virginale, Halla s’en va saborder les pylônes électriques qui alimentent ses usines. Peu importe que son combat soit celui du pot de terre contre le pot de métal. De petits en grands sabotages, la voilà devenue, pour l’opinion publique, l’insaisissable et énigmatique « Femme des montagnes ». La projection du film sera suivie d’une rencontre : « Changements climatiques… Agir pour empêcher ? » avec Bernard HEINESCH, enseignant-chercheur à Gembloux Agro-Bio Tech, Caroline GLORIE, philosophe (ULiège), et Frédéric CLAISSE, sociologue (ULiège). Rencontre organisée dans le cadre de la COP24 en partenariat avec Les Grignoux. [less ▲]

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See detailRotational and continuous grazing does not affect the total net ecosystem exchange of a pasture grazed by cattle but modifies CO2 exchange dynamics
Gourlez de la Motte, Louis ULiege; Mamadou, Ossenatou; Beckers, Yves ULiege et al

in Agriculture, Ecosystems and Environment (2018), 253

Grassland carbon budgets are known to be greatly dependent on management. In particular, grazing is known to directly affect CO2 exchange through consumption by plants, cattle respiration, natural ... [more ▼]

Grassland carbon budgets are known to be greatly dependent on management. In particular, grazing is known to directly affect CO2 exchange through consumption by plants, cattle respiration, natural fertilisation through excreta, and soil compaction. This study investigates the impact of two grazing methods on the net ecosystem exchange (NEE) dynamics and carbon balance, by measuring CO2 fluxes using eddy covariance in two adjacent pastures located in southern Belgium during a complete grazing season. Rotational (RG) grazing consists of an alternation of rest periods and short high stock density grazing periods. Continuous grazing (CG) consists of uninterrupted grazing with variable stocking rates. To our knowledge, this is the first study to assess the impact of these grazing methods on total net ecosystem exchange and CO2 exchange dynamics using eddy covariance. The results showed that NEE dynamics were greatly impacted by the grazing method. Following grazing events on the RG parcel, net CO2 uptake on the RG parcel was reduced compared to the CG parcel. During the following rest periods, this phenomenon progressively shifted towards a higher assimilation for the RG treatment. This behaviour was attributed to sharp biomass changes in the RG treatment and therefore sharp changes in plant photosynthetic capacity. We found that differences in gross primary productivity at high radiation were strongly correlated to differences in standing biomass. In terms of carbon budgets, no significant difference was observed between the two treatments, neither in cumulative NEE, or in terms of estimated biomass production. The results of our study suggest that we should not expect major benefits in terms of CO2 uptake from rotational grazing management when compared to continuous grazing management in intensively managed temperate pastures. [less ▲]

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See detailRestoring a worn-out pasture : What impact on greenhouse gas exchanges ?
Lognoul, Margaux ULiege; Gourlez de la Motte, Louis ULiege; Debacq, Alain ULiege et al

Poster (2018, September 12)

The restoration of permanent pastures is often required in order to restore a productive state and the palatability of the grass. The restoration process consists on destroying the former vegetation using ... [more ▼]

The restoration of permanent pastures is often required in order to restore a productive state and the palatability of the grass. The restoration process consists on destroying the former vegetation using herbicides followed by tillage and reseed. The short term and long term impacts of such operations on the carbon cycle and N2O emissions are not well defined for old permanent pastures. Therefore, a paired flux tower measurement campaign was started in March 2018 at the Dorinne Terrestrial Observatory in Southern Belgium, with the aim to study the impact of pasture restoration on CO2 and N2O fluxes exchanged by the ecosystem. The site is a 100-year-old intensively managed grassland which last restoration was performed more than 40 years ago. It is grazed by Belgian blue beef cattle and fertilized with around 120 kgN ha-1 per year on average, reflecting common practices in the area. A former study carried out at the same site, showed that the pasture acted as significant carbon sink before the start of experiment. Two adjacent parcels belonging to the same farm were both equipped with identical instrumentation including eddy covariance measurements of CO2 (LICOR 7000) and N2O/CH4 (Aerodyne Inc. quantum cascade laser) exchanges to allow the comparison between a control and a restored plot subject to identical pedo-climatic conditions. Preliminary results of greenhouse gas fluxes will be presented in relation to climatic conditions and management operations and the evolution of soil ammonium and nitrate. [less ▲]

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See detailN2O flux short-term response to meteorological solicitations and farming practices in a fertilized crop
Lognoul, Margaux ULiege; Debacq, Alain ULiege; Manise, Tanguy ULiege et al

Poster (2018, September 11)

Using the eddy covariance technique, half-hourly N2O fluxes were measured over a sugar beet crop (Terrestrial Observatory of Lonzée, BE, ICOS site level 2) between March and October 2016. Several ... [more ▼]

Using the eddy covariance technique, half-hourly N2O fluxes were measured over a sugar beet crop (Terrestrial Observatory of Lonzée, BE, ICOS site level 2) between March and October 2016. Several parameters of data quality control tests were modified to suit the characteristics of N2O. The u* filtering threshold was determined based on CO2 data as the procedure could not be implemented using N2O fluxes. The uncertainty on N2O fluxes was assessed for several aspects of data treatment (total random uncertainty, spectral correction, u* filtering, gap-filling), which were combined to determine the uncertainty on the budget. N2O flux variability was characterized by three peak episodes during the experiment, interspersed with background fluxes. These events were driven by several variables, depending on the time-scale. The more time had passed after fertilization, the lower the potential for high fluxes was, and by the end of the crop season, only background flux was recorded. The soil water content at 5 cm was identify as the single trigger of N2O emission bursts, while intraday oscillations were positively correlated to the variations of surface temperature. For the first time, an inhibiting effect of surface soil disturbance (seed-bed preparation) on N2O fluxes was observed, which delayed the start of the following emission peak. This observation combined to the synchronicity between surface temperature and the oscillations of N2O fluxes supports the hypothesis of a N2O producing microbial community located in the topmost soil layer. Between fertilization and harvest, the crop emitted 6520 (± 908) μmol N2O m-2 which corresponds to an EF of 1.3 % - slightly above the IPCC estimate. Our results stress the importance of measuring N2O exchanges in fertilized crops, as it weighed for 20% of the GHG budget. [less ▲]

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See detailAntarctic landfast sea ice: autotrophy vs heterotrophy, sink vs source of CO2
Van der Linden, Fanny ULiege; Moreau, Sébastien; Champenois, Willy ULiege et al

Conference (2018, June 20)

Sea ice is a biome actively participating in the regional cycling of CO2 as both a source and a sink at different times of the year depending on its trophic status (autotrophic vs heterotrophic). In the ... [more ▼]

Sea ice is a biome actively participating in the regional cycling of CO2 as both a source and a sink at different times of the year depending on its trophic status (autotrophic vs heterotrophic). In the frame of the YROSIAE project (Year-Round survey of Ocean-Sea-Ice-Atmosphere Exchanges), carried out at Cape Evans in McMurdo Sound (Antarctica) from Nov. 2011 to Dec. 2012, ice cores, seawater, and brines were collected at regular time intervals. We used dissolved inorganic carbon (DIC) and chlorophyll-a (chl-a) as proxies of net community production and autotrophic biomass, respectively. From spring, very high chl-a concentrations (>2400𝜇𝑔.𝐿!!) were observed at the bottom of the ice. This suggests high primary production. Strikingly, at the same time, nutrients increased significantly indicating strong remineralization at the bottom. In the ice interior, evolution of DIC was marked by a succession of autotrophic and heterotrophic phases. The overall increase of DIC suggests that the ice interior was rather heterotroph. Such sea ice system should expel CO2. Yet, strong under-saturation in CO2 and DIC depletion appeared at the ice surface, suggesting that sea ice should take up CO2 from the atmosphere. On the whole, land fast sea ice in McMurdo Sound appears as a puzzling ecosystem. High primary production and remineralization develop simultaneously at the bottom while the top of the ice is rather heterotrophic but still able to pump CO2 from the atmosphere. [less ▲]

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See detailRotational and continuous grazing does not affect the total net ecosystem exchange of a pasture grazed by cattle but modifies CO2 exchange dynamics
Gourlez de la Motte, Louis ULiege; Beckers, Yves ULiege; Bodson, Bernard ULiege et al

Conference (2018, April)

Grassland carbon budgets are known to be greatly dependent on management. In particular, grazing is known to directly affect CO2 exchange through consumption by plants, cattle respiration, natural ... [more ▼]

Grassland carbon budgets are known to be greatly dependent on management. In particular, grazing is known to directly affect CO2 exchange through consumption by plants, cattle respiration, natural fertilisation through excreta, and soil compaction. This study investigates the impact of two grazing methods on the net ecosystem exchange (NEE) dynamics and carbon balance, by measuring CO2 fluxes using eddy covariance in two adjacent pastures located in southern Belgium during a complete grazing season. Rotational (RG) grazing consists of an alternation of rest periods and short high stock density grazing periods. Continuous grazing (CG) consists of uninterrupted grazing with variable stocking rates. To our knowledge, this is the first study to assess the impact of these grazing methods on total net ecosystem exchange and CO2 exchange dynamics using eddy covariance. The results showed that NEE dynamics were greatly impacted by the grazing method. Following grazing events on the RG parcel, net CO2 uptake on the RG parcel was reduced compared to the CG parcel. During the following rest periods, this phenomenon progressively shifted towards a higher assimilation for the RG treatment. This behaviour was attributed to sharp biomass changes in the RG treatment and therefore sharp changes in plant photosynthetic capacity. We found that differences in gross primary productivity at high radiation were strongly correlated to differences in standing biomass. In terms of carbon budgets, no significant difference was observed between the two treatments, neither in cumulative NEE, or in terms of estimated biomass production. The results of our study suggest that we should not expect major benefits in terms of CO2 uptake from rotational grazing management when compared to continuous grazing management in intensively managed temperate pastures. [less ▲]

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See detailImpact of CO2 storage flux sampling uncertainty on net ecosystem exchange measured by eddy covariance
Nicolini, G.; Aubinet, Marc ULiege; Feigenwinter, C. et al

in Agricultural and Forest Meteorology (2018), 248

Complying with several assumption and simplifications, most of the carbon budget studies based on eddy covariance (EC) measurements quantify the net ecosystem exchange (NEE) by summing the flux obtained ... [more ▼]

Complying with several assumption and simplifications, most of the carbon budget studies based on eddy covariance (EC) measurements quantify the net ecosystem exchange (NEE) by summing the flux obtained by EC (FC) and the storage flux (SC). SC is the rate of change of a scalar, CO2 molar fraction in this case, within the control volume underneath the EC measurement level. It is given by the difference in the quasi-instantaneous profiles of concentration at the beginning and end of the EC averaging period, divided by the averaging period. The approaches used to estimate SC largely vary, from measurements based on a single sampling point usually located at the EC measurement height, to measurements based on profile sampling. Generally a single profile is used, although multiple profiles can be positioned within the control volume. Measurement accuracy reasonably increases with the spatial sampling intensity, however limited resources often prevent more elaborated measurement systems. In this study we use the experimental dataset collected during the ADVEX campaign in which turbulent and non-turbulent fluxes were measured in three forest sites by the simultaneous use of five towers/profiles. Our main objectives are to evaluate both the uncertainty of SC that derives from an insufficient sampling of CO2 variability, and its impact on concurrent NEE estimates.Results show that different measurement methods may produce substantially different SC flux estimates which in some cases involve a significant underestimation of the actual SC at a half-hourly time scales. A proper measuring system, that uses a single vertical profile of which the CO2 sampled at 3 points (the two closest to the ground and the one at the lower fringe of the canopy layer) is averaged with CO2 sampled at a certain distance and at the same height, improves the horizontal representativeness and reduces this (proportional) bias to 2–10% in such ecosystems. While the effect of this error is minor on long term NEE estimates, it can produce significant uncertainty on half-hourly NEE fluxes. © 2017 [less ▲]

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See detailStandardisation of eddy-covariance flux measurements of methane and nitrous oxide
Nemitz, E.; Mammarella, I.; Ibrom, A. et al

in International Agrophysics (2018), 32(4), 517-549

Commercially available fast-response analysers for methane (CH4) and nitrous oxide (N2O) have recently become more sensitive, more robust and easier to operate. This has made their application for long ... [more ▼]

Commercially available fast-response analysers for methane (CH4) and nitrous oxide (N2O) have recently become more sensitive, more robust and easier to operate. This has made their application for long-Term flux measurements with the eddy-covariance method more feasible. Unlike for carbon dioxide (CO2) and water vapour (H2O), there have so far been no guidelines on how to optimise and standardise the measurements. This paper reviews the state-of-The-Art of the various steps of the measurements and discusses aspects such as instrument selection, setup and maintenance, data processing as well as the additional measurements needed to aid interpretation and gap-filling. It presents the methodological protocol for eddy covariance measurements of CH4 and N2O fluxes as agreed for the ecosystem station network of the pan-European Research Infrastructure Integrated Carbon Observation System and provides a first international standard that is suggested to be adopted more widely. Fluxes can be episodic and the processes controlling the fluxes are complex, preventing simple mechanistic gap-filling strategies. Fluxes are often near or below the detection limit, requiring additional care during data processing. The protocol sets out the best practice for these conditions to avoid biasing the results and long-Term budgets. It summarises the current approach to gap-filling. © 2018 Eiko Nemitz et al., published by Sciendo 2018. [less ▲]

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See detailTowards long-term standardised carbon and greenhouse gas observations for monitoring Europe´s terrestrial ecosystems: a review
Franz, D; Acosta; Altimir et al

in International Agrophysics (2018)

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See detailInter-annual variability of Net Ecosystem Productivity for a temperate mixed forest: A predominance of carry-over effects?
Aubinet, Marc ULiege; Hurdebise, Quentin ULiege; Chopin, Henri ULiege et al

in Agricultural and Forest Meteorology (2018), 262

This study presents twenty years of Net Ecosystem Productivity estimations obtained using eddy covariance in a mixed forest, dominated by beech with sparse conifers, at the Vielsalm station, in the ... [more ▼]

This study presents twenty years of Net Ecosystem Productivity estimations obtained using eddy covariance in a mixed forest, dominated by beech with sparse conifers, at the Vielsalm station, in the Belgian Ardennes. First the quality and reliability of the data set is discussed. An uncertainty analysis showed that if, on one hand, the site heterogeneity and set-up changes may strongly affect yearly NEP estimates, questioning thus the total carbon budget relevance, on the other hand, robust inter-annual anomalies may be obtained as long as a site dedicated data treatment is carefully applied. A validation of the anomalies by comparison with a growth index derived from tree ring measurements is given. The resulting anomalies (range: [−206; + 123] g C m−2 yr−1, standard deviation: 93 g C m−2 yr−1) being larger than their own uncertainty (∼30 g C m−2 yr−1), an inter-annual variability analysis is possible. This analysis shows that the sources of NEP inter-annual variability at the Vielsalm station are multiple but the most prominent causes are biotic processes driven by carry-over effects of preceding meteorological events. The lowest observed NEP, in 2000, resulted from a bark beetle attack probably prompted by an early frost event in 1998. Besides, the robust lagged correlation between NEP anomalies and mean vapor pressure deficit during the preceding vegetation season also suggests a carry-over effect of water limitation during the previous year on the beech NEP. Mechanisms driving this carry-over effect are supposedly linked to tree physiology, which is confirmed by a dependency of canopy photosynthetic capacity to previous year water limitation. Some hypotheses, involving biomass allocation and bud formation, are proposed to explain its lagged impact on canopy photosynthetic capacity. Other causes of NEP inter-annual variability are the radiation during the current vegetation season and the temperature at the end of the winter but the latter variable rather indicates an effect on the conifers interspersed in the plot. Overall, the photosynthetic capacity combined with these two factors explained about 75% of NEP inter-annual variability. © 2018 Elsevier B.V. [less ▲]

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See detailRecent past (1979-2014) and future (2070-2099) isoprene fluxes over Europe simulated with the MEGAN-MOHYCAN model
Bauwens, Maite; Stavrakou, Trissevgeni; Müller, Jean-François et al

in Biogeosciences (2018), 15(12), 3673-3690

Isoprene is a highly reactive volatile organic compound emitted by vegetation, known to be a precursor of secondary organic aerosols and to enhance tropospheric ozone formation under polluted conditions ... [more ▼]

Isoprene is a highly reactive volatile organic compound emitted by vegetation, known to be a precursor of secondary organic aerosols and to enhance tropospheric ozone formation under polluted conditions. Isoprene emissions respond strongly to changes in meteorological parameters such as temperature and solar radiation. In addition, the increasing CO2 concentration has a dual effect, as it causes both a direct emission inhibition as well as an increase in biomass through fertilization. In this study we used the MEGAN (Model of Emissions of Gases and Aerosols from Nature) emission model coupled with the MOHYCAN (Model of HYdrocarbon emissions by the CANopy) canopy model to calculate the isoprene fluxes emitted by vegetation in the recent past (1979-2014) and in the future (2070-2099) over Europe at a resolution of 0.1° × 0.1°. As a result of the changing climate, modeled isoprene fluxes increased by 1.1%yr-1 on average in Europe over 1979-2014, with the strongest trends found over eastern Europe and European Russia, whereas accounting for the CO2 inhibition effect led to reduced emission trends (0.76%yr-1). Comparisons with field campaign measurements at seven European sites suggest that the MEGAN-MOHYCAN model provides a reliable representation of the temporal variability of the isoprene fluxes over timescales between 1h and several months. For the 1979-2014 period the model was driven by the ECMWF ERA-Interim reanalysis fields, whereas for the comparison of current with projected future emissions, we used meteorology simulated with the ALARO regional climate model. Depending on the representative concentration pathway (RCP) scenarios for greenhouse gas concentration trajectories driving the climate projections, isoprene emissions were found to increase by +7% (RCP2.6), +33% (RCP4.5), and +83% (RCP8.5), compared to the control simulation, and even stronger increases were found when considering the potential impact of CO2 fertilization: +15% (RCP2.6), +52% (RCP4.5), and +141% (RCP8.5). However, the inhibitory CO2 effect goes a long way towards canceling these increases. Based on two distinct parameterizations, representing strong or moderate inhibition, the projected emissions accounting for all effects were estimated to be 0-17% (strong inhibition) and 11-65% (moderate inhibition) higher than in the control simulation. The difference obtained using the two CO2 parameterizations underscores the large uncertainty associated to this effect. © Author(s) 2018. [less ▲]

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