Partitioning of NEE and ecosystem respiration of a managed ...carboeurope.org/ceip/conference/files/Conference_Proceedings_PA_… · PA6 Poster Presentations 1 Partitioning of NEE

Session “Partitioning of ecosystem C fluxes”

PA6 Poster Presentations 1

Partitioning of NEE and ecosystem respiration of a managed temperate grassland based on eddy covariance and chamber measurements

C. Ammann, C. Flechard, A. Neftel, J. Fuhrer Agroscope ART, Federal Resarch Station, Air Pollution/Climate Group

Reckenholzstr. 191, CH-8046 Zürich, Switzerland [email protected]

Keywords flux partitioning, ecosystem respiration, soil respiration, static chambers

Abstract Managed agricultural ecosystems form a significant part of the European land cover. Greenhouse gas mitigation options like the conversion from arable land to permanent grassland and an optimized management could help to sequester carbon in agricultural soils. We have monitored the carbon cycle of a managed grassland site on the Swiss Central Plateau since 2002 as part of the FLUXNET and CarboEurope-IP network. The grassland field, used for producing hay and silage, was divided in two plots, one undergoing intensive management (high nitrogen input), the other extensive management (no fertilization). The net CO2 exchange of the two plots is monitored continuously be eddy covariance (EC) measurements. For a process-oriented analysis and interpretation of the CO2 exchange (also used for the gap-filling algorithm) the net EC fluxes were partitioned into assimilation and ecosystem respiration using mechanistic parameterisation functions. In order to account for the fast changing vegetation cover in a managed grassland (fast increase of LAI and up to 5 cuts per year) a adaptive temporal adjustment of the dominating functional parameters was necessary. The results showed that the annual ratio of respiration over assimilation strongly depended on the management intensity and the weather conditions during summer. For hot and dry summer conditions (like in the year 2003), the ratio was significantly enhanced. The extensively managed plot usually exhibited a similar annual assimilation but a higher respiration than the intensively managed plot. For a further partitioning of the ecosystem respiration, static chambers of different sizes were applied: larger chambers (covered areas of c. 0.1 m2 to 1 m2) for the dark ecosystem respiration and small chambers (0.007 m2) for the soil respiration excluding grass plants. On average the observed soil respiration accounted for 40-60% of the total respiration for both management systems.



Partitioning of sources of CO2 flush induced by freezing-thawing of arable and forest soils

Kuzyakov Y., Sapronov D.V. 1) Dep. of Agroecosystem Research, University of Bayreuth, Germany

2) Institute of Physicochemical and Biological Problems of Soil Science, Pushchino, Russia 1) Dep. of Agroecosystem Research, University of Bayreuth, 90544 Bayreuth, Germany

2) IPBSS RAS, Institutskaja 2, 142290 Pushchino, Russia [email protected]

Keywords CO2 partitioning, freezing-thawing, root respiration, microbial respiration

Abstract Freezing of soil and subsequent thawing is a common in autumn and spring in temperate and cold climates. Strong increases of CO2 efflux from soil after thawing (CO2 flush) were formerly explained by mineralization of microbial cells died by freezing by survived microorganisms. We hypothesized that not only microbial biomass but also living roots, which previously have been excluded from laboratory experiments, are an important C source for CO2 flush. We monitored the CO2 and 14CO2 efflux from rooted and root-free undisturbed soil cores taken from arable and forest soils subjected to a simulated freezing (-4 °C) and thawing (+5 °C) cycle. To trace various CO2 sources we added i) 14C labeled plant residues, or ii) 14C glucose injected immediately before freezing to label dissolved organic carbon (DOC), or iii) 14C glucose injected 2 weeks before freezing to label microbial biomass. The combination of various C sources with 14C labeling allowed us to distinguish between the CO2 efflux originating from soil organic matter, dead plant residues, DOC, microbial biomass and living roots. The CO2 flush during thawing was about 2 times higher in forest soil compared to arable soil. A significant part of the CO2 flush after thawing originated from root respiration per se, reaching 80% and 46% of total CO2 efflux from arable and forest soil, respectively. Contribution of C from microbial biomass died by freezing was the second most important source of the CO2 flush. In the root-free soil the contribution of labeled MB during the thawing period was 51% for arable soil and 34% for forest soil. The contribution of slowly decomposable C sources such plant residues and soil organic matter to the total CO2 efflux during the freezing-thawing cycle was marginal.



Carbon storage and soil CO2 flux partitioning in two stands of Pinus sylvestris and Quercus robur of the Belgian campine

1 Chiti T., 2 Sirignano C, 2 Neubert REM, 3 Janssens IA, 1 Certini G. 1: University of Florence; 2 Centrum voor IsotopenOnderzoek, (CIO); 3 University of

Antwerp 1 P.le Cascine 28, 50144 Firenze, Italy; 2 Nijenborgh 4, 9747 AG

Groningen, The Netherlands; 3 Univeriteitsplein 1, B-2610 Wilrijk, Belgium. [email protected]

Keywords Soil carbon, flux partitioning, 14C radiocarbon

Abstract Two neighboring stands (Brasschaat, 51° 18” 33’ N, 14° 31” 14’ E), developed on the same parental material since 80 years, one of pure Scots pine, the other of English oak, were compared in terms of total amount of carbon (C) stored in the mineral soil and in the litter layer. Besides we followed the variations in the 14C content of soil CO2 and atmospheric air, collecting samples once a season for the whole year 2003. The contribution of the different components to the total soil CO2 flux was calculated assuming that soil CO2 is produced by the contribution of two pools: a) fast decomposing pool (pool C1), b) slow decomposing pool (pool C2). The relative contribution of these two reservoirs (C1 and C2) to the total soil CO2 flux was calculated with a two component-mixing model knowing the 14C content of the respired CO2, atmospheric air and bulk SOM (Dörr, 1986). Scots pine stand appears to be richer in C both in the mineral soil and in the litter layer. The difference between the two stands appears to be confined in the mineral soil where the pine store more than twice (17.2 kgC m-2) the amount of the oak stand (7.1 kgC m-2). The annual 14C variation of soil CO2 is controlled by the seasonally varying contribution of root respiration and microbial decomposition of organic matter producing soil CO2. Dörr H, Münnich KO, 1986. Annual variations of the 14C content of soil CO2. Radiocarbon, Vol 28, N° 2A, pp 338-345.



Stable carbon dioxide isotopes for partitioning grassland fluxes: a comparison of Mass Spectrometric and Spectroscopic (FTIR and QCL) techniques.

Zeeman, M.J.(1*), Tuszon, B.(2), Mohn, J. (2), Eugster, W.(1), Werner, R.A.(1), Emmenegger, L. (2), Buchmann, N.(1)

1. ETH Zürich, Institute of Plant Sciences, Grassland Group 2. Swiss Federal Institute for Materials Science & Technology

1. Univeristätsstrasse 2, 8092 Zürich, Switzerland 2. Überlandstrasse 129, 8600 Dübendorf, Switzerland

* [email protected]

Keywords stable isotopes, CO2 fluxes, grassland, FTIR, QCL

Abstract Three research sites on elevations covering the relevant stages of the Swiss agricultural system (400, 1000, and 2000 m a.s.l.) have been established. This allows for in-situ investigation of the processes involved in green-house gas exchanges of grassland. A first assessment of stable carbon dioxide isotope analysis has provided valuable information on CO2 flux partitioning. For the first time a comparison of three independent measurement techniques for stable isotope ratios (13C/12C, 18O/16O) and green-house gas concentrations (CO2, CH4, N2O) was performed. During a three week period, air samples were collected at four height profiles (z = 0.055; 0.14; 0.40; 1.90 m) and in a regular two hours interval by automated air samplers connected to a switching inlet system. The isotopic ratios (13C/12C and 18O/16O) were measured in the laboratory with Isotope Ratio Mass Spectrometry (IRMS). Simultaneously, two additional optical techniques were used to continuously measure these stable isotope ratios in the field: (1) Fourier Transform Infrared (FTIR) and (2) Quantum Cascade Laser (QCL) spectroscopy. The time resolution was one minute and one second, respectively. Furthermore, the greenhouse gas concentrations were continuously monitored with an open path IR gas analyser (CO2) and a photo-acoustic gas analyser (CO2, CH4, N2O). The FTIR spectrometer also measured the concentration of CO2, CO, CH4 and N2O. The preliminary results show the added value of spectroscopic techniques that allow for continuous and high time resolution measurements, which can be used for the investigation of flux partitioning. The FTIR instrument achieved accuracy in δ13C ratios of +/- 0.4 ‰. The achieved temporal resolution of 1 second of the QCL system has significant potential in computation of eddy covariance isotopic fluxes.



Partitioning of CO2 fluxes from fertilized and unfertilized soil: The comparison of split-root and root exclusion techniques

A.S. Tulina1, Y.V. Kuzyakov2, V.M. Semenov1

1Institute of Physicochemical and Biological Problems in Soil Science, 142290 Russia, Pushchino

2Institute of Soil Science, Hohenheim University, 70593 Stuttgart, Germany [email protected]

Keywords: CO2 flux partitioning, split-root, root exclusion

Abstract For the separation of rhizosphere respiration (RR) and soil organic matter (SOM) microbial decomposition the method with balk soil – so-called "root exclusion technique" is widely used. However, as SOM decomposition is different in soil with and without plants because sizes and activity of microbial biomass are not equal, it seems more appropriate to evaluate this CO2 flux by means of method taking into account influence of growing plants on SOM, e.g. split-root technique. The aim of this study was to compare the two methods. The investigations were carried out on the old-arable loamy Halpic Luvisol with organic carbon of 1.3%. For the split-root technique two-compartment pots were used. Root systems of Zea mays 14-days-old seedlings were divided into two halves. The first half was placed into the compartment contained soil, and the second one was placed into the compartment contained washed and tempered sand with nitrogen fertilizer. As a control, unfertilized plants were used. Calculations: A (Total efflux) = CO2 emission from soil; B (RR) = CO2 emission from sand; C (SOM decomposition) = A–B. For the comparison with split-root system, we apply root exclusion technique. The share of SOM decomposition in total CO2 emission from soil estimated by root exclusion technique made 69%, and that estimated by split-root system amounted for 54%. Nitrogen fertilization increased RR, determined via both methods, in 1.7 times, and SOM decomposition remained constant, so that share of SOM decomposition decreased to 57% and 31% evaluated by root exclusion and split-root system, correspondingly. Thus, rate of SOM decomposition under plants was smaller than in the balk soil so this part of CO2 flux evaluated by root exclusion technique was overestimated. N-fertilization decreased the share of SOM decomposition, since RR increased and organic matter of the studied soil was stable against decomposition under nitrogen application. This work was supported by RFBR, Project No 04-04-48670-а and DAAD, Kennziffer: A/01/10600



A novel approach for partitioning root and microbial respiration in soil

I. Yevdokimov*, A. Larionova*, M. Bahn** *Institute of Physicochemical and Biological Problems in Soil Science, RAS, Russia

**Institute of Ecology, University of Innsbruck, Austria *Institutskaya 2, 142290, Pushchino, Moscow region, Russia

**Sternwartestr. 15, 6020 Innsbruck, Austria [email protected]; [email protected]

Keywords root respiration, microbial respiration, CO2 emission, partitioning

Abstract Partitioning of CO2 efflux from the soil surface to microbial (MR) and root respiration (RR) is urgent for estimations whether terrestrial ecosystem is a net sink or a net source for atmospheric CO2. This research was aimed to estimate MR and RR contributions on different ecosystems (arable land, forest , meadow) of Russian soils (Dystric Podzoluvisol and Humic Podzoluvisol) and Austrian (Dystric Cambisol and Phleic Cambisol) soils and to test a new methodological approach combining the substrate-induced respiration (SIR) and the component integration (CI) methods (“combined method”, CM). Both methods tested were found to give similar estimates RR under laboratory conditions. When applied in situ on a high productivity meadow, CM demonstrated higher RR values (40% of total CO2 emission from soil) than those obtained in parallel by CM and CI in laboratory experiment (24%). Root/microbial contributions determined on low productivity meadows revealed opposite tendency – with percentage of 11% and 32% for RR contribution as determined by field and laboratory methods, respectively. The reason of these discrepancies are changes in MR fraction connected to the decomposition of soil detritus. CM application on Dystric Podzoluvisol and Humic Podzoluvisol revealed one more methodological problem - stimulating effect of added moisture on RR when glucose solution is applied. Therefore RR contributions determined by CM using water glucose solution (31 – 38%) were higher than those obtained by CI (29%). At the same time, laboratory experiments with glucose application as mixture of dry glucose with sand or talc demonstrated the RR contributions similar to those obtained by CI technique – 25%. Thus, CM was calibrated by the component integration method. Applicability of CM for in situ determinations of RR and MR contributions depends on the extent to which the soil microbial community is sensible to watering and changes in microbial respiration related to detritus decomposition.



Partitioning of Soil CO2 Fluxes in Italian Mountain Grasslands under Different Management

Gavrichkova Olga1, Moscatelli Cristina2, Valentini Riccardo1. 1Department of Forest Environment and Resources (DISAFRI), University of Tuscia,

01100 Viterbo, Italy 2Department of Agrobiology and Agrochemistry (DABAC), University of Tuscia,

01100 Viterbo, Italy [email protected]

Keywords respiration, partitioning, heterotrophic and autotrophic components, grasslands

Abstract Soil respiration is an important component of the carbon cycle and is representing about 60-80% of the ecosystem respiration. It consists of an autotrophic component associated with roots plus the rhizosphere and heterotrophic component associated with soil microorganisms. The main objective of this study is to characterize the contribution of the heterotrophic and autotrophic components of soil respiration in differently managed grassland in Italian mountains. The study is conducted in Amplero - a Mediterranian grasslands site, located in central Italy at 900 m a.s.l. Amplero is managed by once-a-year mowing during the peak of the growing season and the rest of the year is used as a pasture. Five fence areas (2x2 m were established in the territory in the year 2002. For the partitioning of soil respiration we have used a root exclusion technique. Roots were removed from the soil cores; half of the sampled soil was placed to the nylon meshes and returned to the study site. Meshes with 1mc openings were used to prevent the roots growing inside the core and to maintain the same conditions as an exterior soil. Another half of the samples were placed back without any barriers for the roots growing. The difference between these two treatments ((bulk soil respiration + root respiration) – bulk soil respiration) will allow getting the value of autotrophic contribution to the soil CO2 efflux. Measurements of total soil respiration started at the end of April 2006; the separation experiment was established in the first days of May. Preliminary analysis of total soil respiration did not show a significant difference between the territories in spring months; from early June soil respiration was larger inside the fences, despite the fact that soil temperature there was generally 4-5 degrees and soil moisture 2-3% lower than outside. This suggests that vegetation-induced differences in microclimate (shading of the soil surface by the uncut canopy in fences) are not the main controlling factors of soil respiration between the two management types. Fluxes were poorly correlated with soil temperature; on the contrary, linear regression of soil moisture vs. soil respiration explained 42% of the variability in soil respiration inside and 78 % outside the fences (data for june-july). In a dry summer season we also did not find any differences in heterotrophic respiration between the treatments, but contribution of autotrophic respiration was significantly higher in fences (34%) than in managed areas (14%). To find an answer on the question what factors could be responsible for the observed and expected differences in soil respiration rate some additional measurements will be done (belowground and aboveground biomass, microbial biomass C, potential soil respiration rate and some other characteristics of soil).



The effective light response curve for estimating the canopy uptake of carbon dioxide

Dellwik E., Mikkelsen T., Ibrom A., Pilegaard K. Risø National Laboratory 4000 Roskilde, Denmark [email protected]

Keywords canopy uptake, light response, empirical

Abstract This study concerns a simple model for estimating the uptake of carbon dioxide by a temperate beech forest. A new concept, the effective light response curve (ELRC), is introduced and discussed. The ELRC is based on an ensemble of leaf measurements taken at ambient conditions in the forest. By integrating along the ELRC, the uptake of carbon dioxide by the canopy is estimated. The integration also requires parameters concerning clumping, leaf angle and light extinction. These are decided from PAR profile and LAI measurements taken in the forest. The ELRC takes into account the non-linearity in the light response as discussed by de Pury and Farquhar (1997). Implicit in the concept of this model is that the canopy to some degree is self-organised. For example, we assume that a sunny spot in the middle of the canopy receives more resources in terms of nitrogen than a corresponding shady spot. The estimated uptake is compared to eddy-flux data, where the respiration has been deducted. The respiration is estimated from night time eddy-flux data. The proposed estimation of ecosystem respiration is compared to measurements of soil respiration and a model for woody tissue respiration. We find a good correlation between the modelled canopy uptake and eddy covariance measurements by this very simple method. The method may serve as a base for the inclusion of the optimal stomatal conductance concept as formulated by Hari et al. (1986) into a single layer model. It is labour intensivet to take measurements for estimation of an ELRC. The possibility of converting data from multi-layer models to receive the same curve is discussed.



NPP drives Rh in forest ecosystems: an analysis across different biomes, stand ages and management.

I. Inglima§, S. Luyssaert†, J.-A. Subke‡, M.F. Cotrufo§ and I. Janssens† §Dept. of Environmental Science, Second University of Naples

†Dept. of Biologiy, Universiteit Antwerpen ‡Stockholm Environmental Institute, University of York

§Via Vivaldi 43, 81100 Caserta, Italy †Campus Drie Eiken D.C16 Universiteitsplein 1 2610 Wilrijk, Antwerpen, Belgium

‡Heslington, York, YO10 5DD, UK [email protected]

Keywords C balance, heterotrophic respiration, net primary productivity

Abstract Future changes in atmospheric CO2 concentration and climate are likely to affect NPP and C storage of terrestrial ecosystems. NPP consists of the net input of C to ecosystems by plant growth and it represents ecosystem C assimilation over short term periods. Most of the C taken up and allocated to growth of plant material is then decomposed by soil microbes and released to the atmosphere over longer time scales. Depending on the balance between uptake (NPP) and release though heterotrophic respiration (Rh), ecosystems can act as sinks or sources of C over longer time periods. In the contests of the Carboeurope project, a very large dataset has been put together on NPP and Rh, collected from studies conducted in forest ecosystems distributed all over the world, which represent a powerful tool for the study of the ecosystem C balance. The two fluxes are here summarised and compared according to latitudinal distribution, biome, mean annual temperature and precipitation, by means of meta-analysis. Moreover, the effect of management and stand age on the two fluxes is being assessed.



Photosynthesis drives interannual variability in net carbon-exchange of pine forests at different latitudes

S. Luyssaert (1), I.A. Janssens (1), M. Sulkava (2), D. Papale (3), A.J. Dolman (4), M. Reichstein (5), T. Suni (6), J. Hollmén (7), T. Vesala (8), D. Lousteau (9), B. Law (10) and

E.J. Moors (11) (1)Department of Biology, University of Antwerp, Universiteitsplein 126 2610 Wilrijk,

Belgium (2) Helsinki Univ Technol, Lab Comp & Informat Sci, POB 5400, Helsinki, FI-02015 Finland

(3) University of Tuscia, Via S. Camillo de Lellis, s.n.c., 01100 Viterbo, Italy (4) Vrije Univ. Amsterdam, Dept. Geo-Environm. Sciences, De Boelelaan 1085, 1081 HV

Amsterdam, The Netherlands (5) Max Planck Institute for Biogeochemistry, PO Box 100164, 07701 Jena, Germany (6) CSIRO Atmosph. Sciences, Pye Laboratory, GPO Box 1666, Canberra, ACT 2601,

Australia (7) Helsinki Univ Technol, Lab Comp & Informat Sci, POB 5400, Helsinki, FI-02015 Finland

(8) University of Helsinki, P.O. Box 64, FIN-00014, Helsinki, Finland (9) INRA, UR 1263 EPHYSE, 71 avenue Edouard Bourlaux, 33883 , Villenave d'Ornon,

France (10) 328 Richardson Hall, Oregon State University, Corvallis, OR 97331, USA

(11) Alterra, Droevendaalsesteeg 3, PO Box 47, 6700 AA Wageningen, The Netherlands [email protected]

Abstract The atmospheric carbon dioxide growth rate exhibits large interannual variations which are largely influenced by year-to-year fluctuations in land-atmosphere fluxes which are in turn driven by large-scale biomass burning and climatic variability. Various studies of terrestrial ecosystem fluxes have sometimes shown conflicting results regarding climate influences on interannual variability in gross photosynthesis and net carbon uptake. The conflicting results are at least partly caused by differences in methodologies or limited length of time over which measurements were made. This study introduces an observation-driven methodology that provides insights to the interannual variability of the ecosystem carbon exchange and relation to climatic conditions. The methods were applied on 9-years of near continues eddy-covariance measurements in boreal, temperate and maritime pine forests. The data from all three sites were collected, processed and quality-checked in a consistent manner. At all three sites, the net ecosystem exchange of carbon dioxide (NEE, net of photosynthesis and respiration) was a stronger sink than the long-term mean, on days characterized by low incident radiation, low vapor pressure deficit and high precipitation. Annual anomalies in NEE were dominated by anomalies in GPP that were correlated with incident radiation and vapor pressure deficit. Although temperature generally showed little direct effect on NEE, it became important when the mean daily air temperature exceeded 25 °C. On such days the mean global radiation exceeded 250 Wm-2 but gross photosynthesis (GPP) decreased likely because the maximal vapor pressure deficit exceeded 2 kPa inhibiting photosynthetic uptake. However, the high temperature also stimulated respiration and as result positive anomalies in NEE occurred. At the boreal site, extreme climatic conditions in summer rarely met the criteria to inhibit photosynthesis. Climatic extremes in summer were more severe in the South than in the North, and had larger effects in the South. At the moment we are moving from a



daily resolution towards an event based resolution which should allow to better understand the effect of climatic interactions on the carbon fluxes.



A comparison between gas exchange at canopy and leaf level in field-grown maize plants in Southern Italy.

*L. Vitale1,2, P. Di Tommasi1, C. Arena1, M. Riondino1,2, T. Bertolini1, F. Nacca3, P. Carillo3, C. Cozzolino3, A. Fierro2, A. Virzo De Santo2, A. Fuggi3, V. Magliulo1.

1CNR-ISAFoM; 2Università Federico II;

3SUN, Caserta, Italy 1 Via Patacca, 85-80056Ercolano (Na), Italy;

2 Via Cinzia, Complesso di Monte S.Angelo-80100Napoli, Italy; *e-mail: [email protected]

Keywords maize; gas exchange; Mediterranean ecosystem

Abstract In the Mediterranean region, maize crops are often exposed to stress conditions that may limit CO2 uptake. Climate change could exacerbate summer drought leading to a reduction of crop productivity especially when water supply is a limiting factor. The present study aims to evaluate the behaviour of an high productive mediterranean agroecosystem in relation to environmental factors by measurements of CO2 exchange both at leaf and canopy scales. The study was conducted in the IT-Bci site (Eboli, Italy) part of the CarboEurope-IP and NitroEurope-IP European Networks. Net CO2 and H2O fluxes from the canopy were measured continuously using the eddy covariance technique while leaf gas exchange was measured on a campaign basis by an IRGA system during the early and middle vegetative stages and at the beginning of the anthesis. Ecosystem gas exchange was lower than leaf gas exchange during the early and middle canopy vegetative stages, whereas an inversion of the trend was observed in concomitance with the anthesis. No hysteretic loop and midday depression of photosynthesis due to stomatal limitations was observed during campaign measurements. The lower leaf and canopy gas exchange rates were measured at the beginning of the anthesis and could be attributable to an increase of respiratory rates with start of reproductive stages. In addition, there was no indication of canopy CO2 uptake limitations when water supply was adequate.



Ecosystem respiration depends strongly on photosynthesis in a temperate heath

Klaus S. Larsen§, Andreas Ibrom§, Claus Beier§, Sven Jonasson* , Anders Michelsen* §Biosystems Department, Risø National Laboratory

*Dept. of Terrestrial Ecology, Institute of Biology, University of Copenhagen §Building BIO-309, P.O. Box 49, Frederiksborgvej 399, DK-4000 Roskilde, Denmark.

*O. Farimagsgade 2D, DK-1353 Copenhagen K., Denmark. [email protected]

Keywords Calluna heath, carbon balance, modelling ecosystem respiration, photosynthesis-related respiration, Q10

Abstract We measured net ecosystem CO2 flux (Fn, ambient light) and ecosystem respiration (RE, darkened chamber), and estimated gross ecosystem photosynthesis (Pg) by difference, for two years in a temperate heath ecosystem using a chamber method. Model fit of RE of a classic, first-order exponential equation related to temperature (second year; R2 = 0.65) was improved when incorporating a linear relationship between RE and Pg (second year; R2 = 0.79), suggesting that daytime RE increased with increasing photosynthesis. The model introduces Rphoto as a measure of the instant respiratory costs of photosynthesis. It increases the reference value of RE by 5% per unit assimilated carbon dioxide flux at 0ºC and by 35% at 20 ºC implying a high sensitivity of respiration to photosynthesis during summer. The simple model provides an easily applied, non-intrusive tool for investigating seasonal trends in the relationship between ecosystem carbon sequestration and respiration. Rphoto showed a seasonal pattern with very low rates from November to February (5 % of RE). It increased strongly from March to September, peaking with up to 38 % of RE in June. Annually, it accounted for 24 % of RE. Furthermore, the temperature sensitivity of RE decreased from apparent Q10 values of 3.3 to 3.9 by the classic equation to a more realistic Q10 of 2.5 by the modified model. These findings may also be relevant for the derivation of Pg and RE from net fluxes in other ecosystems, i.e. from eddy covariance flux data.



CO2 balance of Scots pine seedlings determined with a novel laboratory system

Pumpanen Jukka 1), Heinonsalo Jussi 2), Rasilo Terhi 3) and Ilvesniemi Hannu 4) 1)Department of Forest Ecology, P.O. Box 27, FI-00014 University of Helsinki, Finland

2)Department of Applied Chemistry and Microbiology, P.O.Box 27, FI-00014 University of Helsinki, Finland

3)Department of Biological and Environmental Sciences, P.O. Box 56, FI-00014 University of Helsinki, Finland

4)Finnish Forest Research Institute, Vantaa Research Center, P.O.Box 18, FI-01301 Vantaa, Finland

[email protected]

Keywords CO2 exchange, photosynthesis, root and rhizosphere respiration, Scots pine

Abstract The processes underlying photosynthesis and respiration and their regulating factors are relatively difficult to study in detail in the field. Here, we describe a differential flow-through system for measuring gas exchange at individual plant level in controlled laboratory conditions. We used the measurement system to study the carbon balance of the above and below ground parts and the contribution of root and rhizosphere respiration in 19 six-month-old Scots pine seedlings. The seedlings were grown in microcosms filled with forest humus and allowing the gas exchange measurements of the root system and shoot separately at different temperature, moisture and light conditions. We measured the photosynthesis of the seedlings at 500 µmol m-2s-1 light intensity and 20-25ºC temperature and root microcosms at constant 15ºC temperature representing the average light and temperature conditions in Southern Finland between May and September. In addition, we studied the temperature response of respiration in the root microcosms using 3 ºC temperature intervals starting from 15 ºC and going down to 3ºC. The contribution of root and rhizosphere respiration was obtained by measuring the respiration in microcosms containing no plant, otherwise similarly as described above, and then subtracting the respiration value of the rootless microcosm from that of root filled microcosm. The photosynthetic rate in the seedlings was in average 46 µg CO2 min-1 and the dark respiration 1.42 µg CO2 min-1 per gram of dried needles. The contribution of root and rhizosphere respiration was between 40% and 55% of the total respiration in the root filled microcosms. The Q10 values measured in the root microcosms ranged from 3.77 in the root filled microcosms to 4.72 in the humus microcosms. The results indicated that this laboratory apparatus could be used for studying the environmental responses of photosynthesis and respiration at individual plant level with high accuracy.



Chamber technique versus eddy covariance method

Dalibor Janous, Manuel Acosta, Radek Czerny, Marian Pavelka Institute of Systemns Biology and Ecology, Academy of Sciences of the Czech Republic

Porici 3 b, Brno 603 00, Czech Republic [email protected]

Keywords CO2 efflux, chamber technique, eddy covariance

Abstract Poster - Eddy-covariance is a very useful method for measuring ecosystem CO2 fluxes. Its main advantages are no impact to any of the studied object and homogenized information for desired level (predominantly ecosystem level). Nevertheless, there is a major problem in using of measured data: difficult identification and quantification of advection occurrence. The advection can underestimate or somewhere overestimate, especially the night time fluxes. Chamber technique senses entire CO2 efflux, but it is impacted by chamber effects: crypt-climate and moving CO2 concentration. Chamber technique allows identifying individual components of CO2 fluxes but a very high number of measured points are needed to sufficiently describe an ecosystem level. Eddy covariance measurements are running above Norway spruce forest stand and above grassland on sites in the Beskydy Mts. (the Czech Republic). Soil and stem CO2 effluxes within the forest, soil and ecosystem effluxes at the grassland site are concurrently measured using automated chamber technique systems. The results of comparison of the chamber and eddy covariance technique showed underestimation of CO2 fluxes by eddy covariance method during night time period on the both forest and grassland sites. It was substantial especially at the forest stand due to existence of subcanopy advection. The chamber technique can hardly substitute eddy covariance measurements, it is practically unfeasible in cases of mature forest stands, but data from chamber measurement can realize partitioning of ecosystem fluxes and help to correct interpretation of eddy covariance measurements.



Eddy covariance measurements as a tool to identify geochemical CO2 exchange

Penélope Serrano-Ortiz(1), Andrew S. Kowalski(1), Ivan A. Janssens(2), Sergio Sánchez-Moral(3), Soledad Cuezva(3), Antonio Delgado(5) Francisco Domingo(4), Borja Ruiz(1) and

Lucas Alados-Arboledas(1) (1) Department of Applied Physics, University of Granada

(2) Department of Biology, University of Antwerpen (3) Department of Geology, Museo Nacional Ciencias Naturales CSIC

(4) Estación Experimental de Zonas Áridas, CSIC (5) Estación Experimental del Zaidín (CSIC)

(1) C/ Fuentenueva s/n 18071 Granada, Spain (2) Universiteitsplein 1, B-2610, 7 Wilrijk, Belgium

(3) C/ Jose Gutierrez Abascal, 2, E-28006 Madrid, Spain (4) C/ General Segura, 04001 Almería, Spain

(5) C/ Profesor Albareda 1, 18008 Granada, Spain [email protected]

Keywords karstic systems, net ecosystem exchange, global carbon cycle

Abstract We examine the hypothesis that surface-atmosphere exchange of CO2 in terrestrial ecosystems always can be interpreted purely in terms of biological processes, neglecting geochemical cycling by karst systems that characterize 22 million km2 in the world. Eddy covariance data of net CO2 fluxes are presented for two ecosystems over karstic substrates in contrasting climates in the North and South of Spain. A semi-arid matorral is found to behave similarly to previously studied ecosystems when well watered, and with appropriate flux partitioning via empirical ecophysiological models. However, sizeable mid-day CO2 emissions during extended drought and plant senescence are found to be incompatible with ecophysiological interpretations of the flux. For a temperate pasture overlying an accessible cave, afternoon CO2 emissions in summer are likewise inexplicable in a biological context, but coincide with periods when ventilation is observed inside the subterranean cavity. Isotopic analysis of air samples from above (and sometimes within) these karst systems are used to help interpret the eddy fluxes. The results suggest direct linkages at times in CO2 exchanges among atmosphere, ecosystems, and carbonate substrates which represent more than a tenth of the Earth’s land surface.



Bridging the gap between eddy covariance data and ecological theory: Simple explanations for long-term C flux observations the Duke Forest, NC, USA

Paul C. Stoy1,* Gabriel G. Katul,1,2 Mario B.S. Siqueira,1,3 Jehn-Yih Juang,1 Kimberly A. Novick,1 and Ram Oren1

1 Nicholas School of the Environment and Earth Sciences, Box 90328, Duke University, Durham, North Carolina

2 Department of Civil and Environmental Engineering, Pratt School of Engineering, Duke University, Durham, North Carolina, USA

3 Departamento de Engenharia Mecânica, Universidade de Brasília, Brazil Nicholas School of the Environment and Earth Sciences, Box 90328, Duke University,

Durham, NC 27708-0328. *[email protected]

Keywords Eddy Covariance, Old Field, Pine Forest, Hardwood Forest, Ecological Theory

Abstract The length of continuous eddy covariance (EC) data records is beginning to approach time scales of ecological succession, often decades or longer. Contemporary understanding of carbon (C) exchange at successionary time scales is dominated by E.P. Odum’s ‘Strategy of Ecosystem Development’. This theory suggests that ecosystem respiration (RE) is primarily a function of biomass, net C flux is small upon ecosystem establishment, and early and late-successional ecosystems maximize productivity and ‘protection’, i.e. ecological resistance, respectively. We test these expectations using 18 site-years of EC data in three adjacent ecosystems that model a typical post agricultural successionary sequence in the southeastern US. In agreement with Odum’s theory, we show that the net ecosystem exchange of CO2 (NEE) over at least 5 years of measurements was near zero in early successional old field vegetation. However, NEE was nearly equal at an early successional planted pine forest and a late successional hardwood forest due to the sensitivity of the former to drought and ice storm damage. These observations can be explained by the relationships between gross ecosystem productivity (GEP), RE and canopy conductance, and by long-term shifts in ecosystem physiology in response to climate. A practical consequence suggests that plantation forestry may confer no net benefit over the conservation of mature forests for C sequestration.



Multiple constrained NEP assessment of a natural steppe of Hakasia (Russia)

Belelli Marchesini Luca, Papale Dario,Vuichard Nicolas (1), TCHebakova Nadja (2) and Valentini Riccardo (1)

(1) Department of Forest Environment and Resources, University of Tuscia. (2) Sukachev Institute of Forest, RAS-SB.

(1) Via S. Camillo de Lellis - 01100 Viterbo, ITALY (2) Russia, 660036, Krasnoyarsk, Academgorogok

[email protected]

Keywords eddy covariance, steppe, net primary productivity, heterotrophic respiration.

Abstract Steppe ecosystems represent an interesting case in which the assessment of carbon balance may be performed through a cross validation of the eddy covariance measurements against ecological inventory estimates of carbon exchanges (Ehman, 2002; Curtis, 2002) Indeed, the widespread presence of ideal conditions for the applicability of the eddy covariance technique, as vast and homogeneous grass vegetation cover over flat terrains (Baldocchi, 2003), make steppes a suitable ground to ensure a constrain to flux estimates with independent methodological approaches. We report about the analysis of the carbon cycle of a true steppe ecosystem in southern Siberia during the growing season of 2004 in the framework of the TCOS-Siberia project activities performed by continuous monitoring of CO2 fluxes at ecosystem scale by the eddy covariance method, fortnightly samplings of phytomass, and ingrowth cores extractions for NPP assessment, and weekly measurements of heterotrophic component of soil CO2 effluxes obtained by an experiment of root exclusion. The carbon balance of the monitored natural steppe was, according to micrometeorological measurements, a sink of carbon of 144.9±17.3 gC, cumulated during the growing season from May to September. This result was in agreement with the independent estimate through ecological inventory which yielded a sink of 150.1 gC (∆=5.2 gC) although this method was characterized by a large uncertainty (±130%) considering the 95% confidence interval of the estimate. Belowground processes in steppe ecosystems account for a preeminent part of the carbon exchange: in particular efforts to better quantify the dynamics of root biomass (growth and turnover) have to be undertaken in order to reduce the uncertainties in the assessment of NPP. This assessment should be preferably based on the application of multiple methods, each one characterized by its own merits and flaws.



Exchange of CO2 and water fluxes at two levels in a maritime pine forest

N. Jarosz, Y. Brunet, E. Lamaud, M. Irvine, D. Loustau INRA-EPHYSE

BP 81, 33883 Villenave d'Ornon cedex, France [email protected]

Keywords CO2, H20, fluxes, forest, understorey, partitioning

Abstract Forests extend over large areas and therefore have a major contribution to total energy and mass fluxes. Many studies have been conducted to evaluate these exchanges. However forests have often been considered as a whole and the contribution of the understorey has rarely been separated from the forest canopy, whereas the fluxes from the bottom layers may constitute a significant part of the overall forest fluxes. In this study CO2 and water vapour fluxes were measured above and below a maritime pine forest canopy in South West of France (Le Bray site). The understorey is mainly constituted of Molinia coerulea (L.) (Moench grass), representing up to 40% of the total leaf area index. Since 2001 fluxes have been measured by eddy covariance at 7 and 41 m above ground. The present study focusses on year 2002. The aim is to quantify the relative contribution of the trees and the understorey to the overall CO2 and water vapour fluxes. The data analysis shows that the understorey canopy is responsible for a varying part of the H2O and CO2 exchanges between the forest and the atmosphere, depending on the climatic conditions and the phenological and physiological status of the two ecosystem components. During periods with significant soil water deficit, the H2O fluxes of the understorey may be as large as 50% of the overall fluxes. The annual contribution of the understorey is 38% (154 mm) of the overall evaporation (245 mm). As for CO2 fluxes, the contribution of the understorey is generally less than for water fluxes but may be as large as 50% around midday during stressed summer periods as well.



Net primary and ecosystem productivities in an apple (Malus domestica) orchard

Panzacchi P., G. Tonon, F. Scandellari, M. Ventura, C. Ceccon, M.Zibordi, L. Corelli Grappadelli and M. Tagliavini

Dipartimento di Colture Arboree, Alma Mater Studiorum University of Bologna, Italy Viale Fanin 46, 40127, Bologna, Italy

[email protected]

Keywords apple, heterotrophic respiration, photosynthesis, root respiration, tree growth

Abstract To be ecologically sustainable, productive tree ecosystems should be managed in order to enhance their potential to fix atmospheric C. In this study we report one year data (from May 2005 to May 2006) of fluxes of C from the atmosphere to apple (Malus domestica) trees and from the tree-soil system to the atmosphere. The experimental orchard (2632 tree of cv. Gala per hectare, planted in 1996/1997) was located in the Po Valley (Northern Italy), managed according to integrated fruit production guidelines. The soil was alluvial and fertile while the climate temperate (~650 mm rain/year); trees were irrigated. The CO2 exchange of the whole canopy of six trees was monitored using a custom-built open system mounted for periods of around one week per month. Allometric relationships between tree size and biomass were obtained after excavations. Above ground productivity of trees during 2005 was assessed by measuring the biomass of abscised leaves, harvested fruits, shoot lengths and estimating tree framework biomass increase. Soil respiration was measured in plots where the presence of tree roots was avoided (by trenching) and in control plots to assess the contribution of roots to total soil respiration (33% on average), which was detracted from data of canopy exchange to obtain NPP of trees. NEP of the orchard area where trees insisted was quantified. Fine root density, assessed by soil cores excavation, did not vary during the season, so the experimental approach will also attempt to quantify the carbon flux from roots to soil by from data of NPP, ANPP and coarse root growth increment.



Carbon balance of two Belgian crops

C. Moureaux (1), A. Debacq (1), A. Vilret (1), M. Suleau (1), V. Dehaes (1), J. Hoyaux (1), B. Bodson (2), M. Culot (3) and M. Aubinet (1)

(1) Unité de Physique des Biosystèmes, Faculté universitaire des Sciences agronomiques de Gembloux, Belgique, (2) Unité de Phytotechnie tempérée, Faculté universitaire des Sciences agronomiques de Gembloux, Belgique, (3) Laboratoire d’écologie microbienne et d’écologie

des eaux, Faculté universitaire des Sciences agronomiques de Gembloux, Belgique Faculté universitaire des Sciences agronomiques de Gembloux - Unité de Physique des

Biosystèmes - 8, Avenue de la Faculté - B-5030 Gemloux - Belgique [email protected]

Keywords carbon balance, cropland, NEE, GPP, eddy covariance

Abstract In order to establish a crop carbon balance, the CO2 fluxes exchanged by a cropland situated at the CarboEurope-IP site of Lonzée (Belgium) have been measured for two years at different spatial and temporal scales. The crop is cultivated following a rotation. Sugar beet (SB) and winter wheat (WW) were cultivated during the first two years. The different terms of the carbon balance that were analysed and compared are:

− The Net Ecosystem Exchange (NEE), the Gross Primary Production (GPP) and the Total Ecosystem Respiration (TER) at the whole crop scale, measured by or inferred from eddy covariance measurements.

− The GPP extrapolated at the field scale from the leaf net assimilation measurements using a portable photosynthesis measurement system.

− The Total Soil Respiration (TSR) extrapolated from soil chamber measurements. − The Net Primary Productivity (NPP) extrapolated from crop sampling.

Between seedling and harvest (6 and 9 months for sugar beet crop and winter wheat crop respectively), the NEE amounted to 0.77 ± 0.1 kg C m-2 for the sugar beet crop and 0.62 ± 0.1 kg C m-2 for the winter wheat crop. The GPP inferred from these measurements was around 1.4 and 1.5 kg C m-2 for sugar beet and winter wheat crop respectively. These results were found in good agreement with those extrapolated from leaf chamber measurements. Both eddy covariance and soil chamber measurements revealed an enhanced respiration rate during the wheat development that was attributed to the autotrophic respiration. The ratio of autotrophic to heterotrophic respiration was found larger for the winter wheat crop than for the sugar beet crop. The uncertainty analysis is discussed for each procedure and suggestions are made in order to reduce the uncertainty in future measurements.



Abstract: Comparison of CO2 and energy fluxes over Rapeseed and Triticale fields in South-West France

Authors: E. Ceschia, P Beziat, Institute: CESBIO - 18 Avenue Edouard Belin 31401 Toulouse Cedex 9 - FRANCE.

e-mail: [email protected]

Keywords : Cropland, Eddy covariance, Net ecosystem exchange, Triticale, Rapeseed

Abstract From March 2005 till March 2006 CO2, water and energy fluxes were measured by means of the eddy-covariance method on two cultivated plots near Toulouse (South-West France). The Auradé and Lamasquère plots were cultivated with Rapeseed (+ Wheat since December 2005) and Triticale, respectively. Both plots received mineral fertilisation but Lamasquère also received organic fertilisation during this period. Data acquisition, processing and gapfilling followed CarboEurope-IP recommendations and net CO2 fluxes (NEE) were partitioned in Gross Primary Production (GPP) and Ecosystem Respiration (RE). In 2005, for Rapeseed and Triticale, respectively, maximum net assimilations were -35.9 µmol m-2 s-1 and -40.8 µmol m-

2 s-1, maximum GPP were -14.3 gC m-2 j-1 and -16.5 gC m-2 j-1 and maximum RE were 7.2 gC m-2 j-1 was 6.8 gC m-2 j-1. At full stand development, Light Use Efficiency ((LUE) and Water Use Efficiency (WUE) were 1.3 and t 1.5 gC MJ-1 and 4.2 and 4.3 gC Kg-1

water for Rapeseed and Triticale, respectively. Annual cumulated NEE were -242 and -315 gC m-2 y-1 at Auradé (Rapeseed and Lamasquère, respectively. Part of the difference in cumulated NEE can be explained by a stronger LUE throughout the season for the Triticale site. However, when considering carbon exportation following the harvest (168 and 568 gC m-2 at Auradé and Lamasquère, respectively) and carbon importation via organic fertilisation at Lamasquère, Auradé is a carbon sink (-74 gC m-2 yr-1) whereas Lamasquère becomes a net source of carbon (143 gC m-

2 yr-1).



Turbidity enhances methane oxidation in an estuary

Gwenaël Abril, Marc-Vincent Commarieu and Frédéric Guérin Environnement et Paléoenvironnement OCéaniques (EPOC), Université Bordeaux 1, CNRS-

UMR 5805. Avenue des Facultés, F 33405 Talence. France.

[email protected]

Keywords aquatic systems, suspended clays, methane oxidation

Abstract Microbial oxidation at the Earth surface is a large methane sink that may exceeds the oxidation by OH radicals in the troposphere. Besides few exceptions, methane oxidation occurs in majority in aerobic habitats and micro-habitats of wetland and aquatic systems, at or close to the site of methane production. Several controlling factors of methane oxidation have been elucidated yet in wetlands and rice paddies soils. Here we demonstrate the occurrence in an estuary of a strong, and yet undocumented, control of methane oxidation by the total solids suspended in the water. Methane and suspended particulate matter (SPM) concentrations, monitored bi-monthly during one hydrological year (2003-2004) along 70 km transects in the tidal regions of the Garonne and Dordogne rivers (SW France), showed a significant negative correlation, both spatially and temporally. During spring in clear waters (SPM~10 mg L-1), methane production was first evidenced by a net increase in concentrations, in parallel with temperature and a decrease in river flow. In summer, when the estuarine turbidity maximum (ETM) appeared and SPM concentrations exceeded 100 mg L-1, methane concentrations decreased from ~600 to ~30 nmol L-1 in one month. More downstream in the turbid Gironde Estuary, methane concentrations were occasionally below atmospheric equilibrium. In dark microcosms, high methane consumption was observed in samples from the ETM with SPM concentrations >2 000 mg L-1, but not after removing the SPM by settling (SPM=16 mg L-1), nor in a sample collected few km upstream the ETM, with SPM=3 mg L-1. Methane oxidation was also able to draw down methane concentration below half the atmospheric equilibrium value in an ETM sample. Suspended clays enhance methane oxidation in aquatic systems and strongly reduce methane fluxes to the atmosphere.



Gas exchange of CO2 in a turbulent and eutrophic river

Gwenaël Abril(1), Denis Maro(2), Michel Fontugne(3), Florentina Moatar(4), Françoise Siclet(5), Marc-Vincent Commarieu(1), Frédéric Guérin(1) and Didier Herbert(2)

(1)Environnement et Paléoenvironnement OCéaniques (EPOC), Université Bordeaux 1, CNRS-UMR 5805; (2) IRSN, Laboratoire de Radioécologie de Cherbourg-Octeville; (3)

Laboratoire des Sciences du Climat et de l'Environnement, UMR 1572-CEA/CNRS; (4)Laboratoire de géologie des environnements aquatiques continentaux (GéEAC), UPRES EA 2100, Université de Tours. (5)Laboratoire National d’Hydraulique et Environnement,

Electricite de France. (1)Avenue des Facultés, F 33405 Talence. France; (2) 50130 Cherbourg-Octeville, France; (3) Domaine du CNRS, 91198 Gif-sur-Yvette, France; (4) parc de Grandmont, 37200 Tours,

France; (5) 6 quai Watier, 78401 Chatou, France. [email protected]

Keywords River, photosyntesis, respiration, air-water CO2 fluxes, gas transfer velocity.

Abstract Rivers are well documented in terms of lateral carbon fluxes but poorly in terms of vertical carbon fluxes (CO2 water-air exchanges). Although the general average CO2 supersaturation of river waters is well known, a rigorous up-scaling of CO2 emissions by world rivers is hampered by large spatial and temporal variations in water pCO2 due to export from watersheds and in-stream processes and by a lack of an adequate parameterization of the gas transfer velocity (K600). Here, we report direct field measurements of water and air pCO2 and water-air CO2 fluxes during four seasons in an eutrophic and turbulent river. CO2 fluxes and gas transfer velocities were estimated with three different techniques: the floating chamber, the eddy covariance and the “delta” method, the latter based on diurnal pCO2 records with an equilibrator. The eutrophic Loire River behaved as a source of atmospheric CO2 during fall (Nov 2005: F(CO2) = +30mmol.m-2.d-1) and winter (Feb. 2003: F(CO2) = +80mmol.m-2.d-1) and as a sink of CO2 in spring (May 2005 F(CO2) = -30mmol.m-2.d-1) and summer (Sept 2004: F(CO2) = -60mmol.m-2.d-1). Strong diurnal variations in water pCO2, due to photosynthesis and respiration were observed, except in winter. The three methods used gave consistent CO2 fluxes and gas transfer velocities, the later being very high, in the range of 20-50 cm.h-1. The spring and summer CO2 uptake generates a lateral transport of algal carbon to the estuary. Previous works show however that this material is further totally mineralized, leading to a very high summer CO2 degassing in the estuary (F(CO2) = 280mmol.m-2.d-1). Throughout the year, the river-estuary continuum is a net CO2 source, with a magnitude similar to the organic carbon net export to the Atlantic Ocean.



Horizontal and vertical integration of CO2 concentration fields and wind fields in a 3D setup in connection with the computation of the non turbulent advective

CO2 fluxes

C. Feigenwinter (1,7), M. Yernaux (1), C. Bernhofer (2), U. Eichelmann (2), R. Queck (2), O. Kolle (3), M. Hertel (3), A. Lindroth (4), M. Mölder (4), L. Montagnani (5), S. Minerbi (5), D.

Janous (6), M. Aubinet (1) 1) Gembloux Agricultural University, Physique des Biosystèmes, Gembloux, Belgium (2) TU Dresden, Inst. of Hydrology and Meteorology, Dpt. of Meteorology, Dresden,

Germany (3) Max Planck Institute for Biogeochemistry, Jena, Germany

(4) University of Lund, Physical Geography and Ecosystems Analysis, Lund, Sweden (5) Autonomous Province of Bolzano, Forest Service, Agency of Environment, Bolzano, Italy

(6) Inst. of Systems Biol. and Ecol., Lab. of Plants Ecological Physiology, Brno, Czech Republic

(7) University of Basel, Inst. of Meteorol., Climatology and Remote Sensing, Basel, Switzerland

C. Feigenwinter, FUSAGx, Physique des Biosystèmes, 8, Av. de la faculté, B-5030 Gembloux [email protected]

Keywords Advection, Net Ecosystem Exchange, forest micrometeorology

Abstract During the last years the problem of advection has attracted many research groups to design and perform experimental approaches to measure simultaneously all the mass conservation equation terms (i.e.turbulent flux, storage change, vertical and horizontal advection, horizontal flux divergence). The CarboEurope-IP ADVEX advection group realised extensive campaigns at three different CE sites in 2005 and 2006. ADVEX data from the 2005 campaign in Renon, Italy, are analysed with regard to the non turbulent advective fluxes of CO2. A triangulation method based on profile functions for horizontal wind velocity and CO2 concentration is presented for the horizontal and vertical integration of the measurements over the whole control volume. It is shown that advective fluxes are highly dependent on the dominating meteorological and synoptic conditions. Mean diurnal courses of horizontal advection show high positive fluxes at night and zero to slightly negative fluxes during daytime. However, for a certain meteorological situation, horizontal advective flux may also disappear. A deeper analysis of the flux patterns shows regions of positive and negative contributions to the total flux caused by the changing direction of the horizontal [CO2] gradient and/or changing wind direction. This is observed in the horizontal as well as in the vertical layers of the control volume. The mean vertical wind component needed for the computation of the vertical advection term was calculated by the planar fit method. Results show in general positive vertical advective fluxes at night and zero fluxes during the day. However, due to our experience, the estimation of the mean vertical wind component (and thus the vertical advection term) is highly dependent on the chosen method. In the extreme case, the vertical advective flux may even change its sign. These findings are confirmed by a recent publication (Vickers and Mahrt, AFM 2006) and leave some open questions about this topic.



Two drainage flow situations on a sloping forested site and their impact on the CO2 concentration field

Heinesch B., Yernaux M., Aubinet M. Unité de Physique des Biosystèmes

Faculté des Sciences Agronomiques de Gembloux 8, avenue de la Faculté, 5030, Gembloux, BELGIQUE

[email protected]

Keywords Advection, CO2, drainage flow, forest

Abstract Two typical situations of drainage flows are analysed on the gently sloping forested site of Vielsalm (Belgium). The first is a situation of vertical convergence associated, as expected by the continuity equation, with an acceleration of the horizontal flow in the trunk-space. The second is an equilibrium situation with a constant horizontal flow in the trunk-space and no vertical motion. The causes of these distinct flow patterns occuring in stable atmospheric conditions are analysed. Moreover, its shown how these flows affect the CO2 concentration field in the forest. Particularly, the sign of the horizontal CO2 concentration gradient is shown to be negative in the situation of vertical convergence (i.e. depletion of CO2 concentration for a parcel of air flowing downslope) and slightly positive in the equilibrium situation.



Application of a mass consistent model to study advective CO2 fluxes in an alpine forest (Renon site)

Leonardo Montagnani 1, Giovanni Manca 2, Elisa Canepa 3, Emilia Georgieva 4 1 Agency for the Environment, Forest Services, Autonomous Province of Bolzano (Italy)

2 European Commission, JRC, Institute for Environment and Sustainability, Climate Change Unit, Ispra (Italy)

3 CNR-INFM-CNISM, Department of Physics, University of Genoa (Italy) 4 Department of Physics, University of Genoa (Italy)

1 Autonomous Province of Bolzano, Servizi Forestali, Via Brennero 6, Bolzano (Italy) 2 TP 050, 21020 Ispra (VA) - Italy

3, 4 Via Dodecaneseo 33, I-16146 Genova, Italy [email protected]

Keywords CO2, advective flux, wind field, ecosystem carbon balance

Abstract A key problem in using eddy correlation technique for estimating the carbon budget of terrestrial ecosystem is the potential bias caused by advective fluxes of CO2. Advective fluxes are often not considered because difficult to identify and to quantify, especially in complex mountainous terrain with highly variable wind patterns and drainage flow. We propose a methodology to estimate these fluxes based on a full 3D experimental approach implemented at the topographically complex alpine forest site of Renon. The measurements at Renon carried out during 2005, in the framework of the CarboEurope-IP activity 1.2, included vertical profiles of wind, air temperature and CO2 concentration measured at five masts in order to get the full 3D resolution of airflows and concentration fields in the study area. The WIND mass – consistent model of University of Genoa, Italy, was used for physical interpolation of observed winds. The model had to be modified to take into account boundary layer processes in a forest canopy. Overall CO2 advective fluxes were calculated on the basis of interpolated 3D wind fields, 3D air density and CO2 concentration fields using the equation that describes the scalar flow crossing a closed surface. For final validation, the fluxes calculated with this approach were compared to measured soil CO2 fluxes and turbulent fluxes above the canopy for a biological validation. Results from this comparison are promising for the achievement of more accurate ecosystem carbon balances obtained from eddy correlation technique.



Influence of mesoscale transport processes of CO2 on flux measurements at complex terrain

Corinna Rebmann (1), Olaf Kolle (1), Werner Kutsch (1), Christian Feigenwinter (2,3), and the ADVEX group of CarboEurope-IP

(1) Max-Planck-Institute for Biogeochemistry; (2) Faculté universitaire des sciences agronomiques, Unité de Physique des Biosystèmes (3) University of Basel, Institute of

Meteorology, Climatology and Remote Sensing (1) Hans-Knöll-Str. 10, D-07745 Jena, Germany; (2) B-5030 Gembloux, Belgium; (3) Basel,

Switzerland [email protected]

Keywords turbulent fluxes, NEE, advection, complex terrain

Abstract Eddy covariance measurements are performed at the Wetzstein site in Thuringia, Germany since 2002. As many other sites in the CarboEurope framework, this spruce forest site is not an ‘ideal’ flux site because of the complicated or even complex orography. This became obvious through apparently non-realistic high night-time fluxes of CO2 under specific circumstances. To deal with these shortcomings, a number of additional measurements are currently performed at the site. The site was also selected for the advection experiment ADVEX as part of CarboEurope-IP. For more than 2 months in spring 2006 four additional towers were equipped with profile measurements for CO2-concentrations and wind components to determine advective processes. Additional flux measurements were performed on one of the ADVEX towers and on 2 towers at the slopes of the ridge for the main wind directions. It could be seen already that wind direction and atmospheric stability have a strong influence on the difference of fluxes measured at nearby locations even though the vegetation itself is more or less homogenous. This presentation will focus on CO2-flux and -concentration measurements along a transect across the ridge of the Wetzstein site. Preliminary analyses have shown that CO2 is often accumulated in the surrounding valleys during night-time and then transported upslope and measured as high respiration by the main tower flux system. The net ecosystem uptake measured at the slope tower is larger than at the main tower and will therefore compare better with inventory data. After careful analyses a set of selected data could probably be prepared for the main tower, which then may be used to determine annual sums of the net carbon exchange of the site. But we conclude that measurements from the slope tower are most probably more representative for this spruce ecosystem.



Planar-fitting based vertical advection as a remedy for the night-time problem

T. Vesala1, Ivan Mammarella1, Janne Rinne1, Petri Keronen1, Samuli Launiainen1, Üllar Rannik1, Pasi Kolari2, Juha-Pekka Tuovinen3 and Tuomas Laurila3

1University of Helsinki, Department of Physical Sciences, Helsinki, Finland 2University of Helsinki, Department of Forest Ecology, Helsinki, Finland

3Climate and Global Change Research, Finnish Meteorological Institute, Helsinki, Finland [email protected]

Keywords Advection, planar fitting, nighttime measurements, Socts pine, ozone

Abstract In night-time the importance of advection processes to full carbon balance estimate by micrometeorological methods is pronounced. The vertical advection needs the determination of mean vertical velocity which can be indirectly obtained from planar fitting, which is the determination of mean local streamline co-ordinates based on the measured statistics of the wind field over longer periods. Planar-fitting based estimate of vertical velocity may be biased due to several reasons. However, we tested the utilization of planar-fitting based vertical advection using long-term eddy covariance and very accurate concentration gradient data on Hyytiälä pine forest in Southern Finland. The vertical-advection corrected carbon balance, without any friction velocity filtering, agrees very well with those by filtering and gap-filling procedure, by gradient method and similarity theory and by chamber and ecosystem model. The agreement is good also for similar ozone deposition estimates. Although no direct measurements for horizontal advection is available, the results indicate minor significance of horizontal advection in the studied cases.



Turbulent conditions of high ecosystem respiration in a spruce ecosystem site located on a hill

Zeri, M.(1), Rebmann, C.(1), Kutsch, W.(1), Belcher, S.(2), Foken, T.(3), Schulze, E-D.(1) (1) Max Planck Institute for Biogeochemistry, Jena, Germany

(2) Department of Meteorology, University of Reading, UK (3) Department of Micrometeorology, University of Bayreuth, Bayreuth, Germany

(1) Marcelo Zeri, Hans-Knoell Strasse, 10, 07745, Jena, Germany [email protected]

Keywords Eddy-covariance, ecosystem respiration, micrometeorology, forest, flow over hills

Abstract In contrast to many other flux sites where night-time CO2 fluxes are usually lower than expected, at the Wetzstein site in Thuringia, Germany, unusual high respiratory fluxes are measured by the eddy covariance technique. A detailed inspection of turbulent fluxes and climatic data led to the identification of special situations that are associated with the majority of the fluxes that exceed the expected nocturnal respiration. At this site specific micrometeorological conditions cause disturbances in the flow field when the air is passing the hill. Under these situations a pressure gradient between the hill crest and slope promotes the transport of scalars and energy upslope. As a result, the tower at the hill crest most probably measures fluxes that are representative of a much larger area, leading to a deficient energy balance closure and disagreement between annual sums of net ecosystem exchange of CO2 and biomass inventory. A 2D model that predicts some features of such scenario was applied to the topography of the Wetzstein site. The model developed at the University of Reading, UK, simulates the vertical profiles of wind speed along the hill in the presence of a canopy. The model predictions were tested with data from additional measurements that were performed as part of the CARBO-EUROPE-IP advection experiment, ADVEX, carried out between April and June, 2006. The expected speed-up above the canopy at the top of the hill was observed, as well as the higher wind speed under the canopy at the slope tower. It was found that anomalous respiration cases lie inside a region in the u* - z/L plane, when u* is higher than 0.4 m/s and z/L is inside the neutral range. The distance of the footprint and wind direction, among other parameters, also characterize the micrometeorological conditions causing anomalous respiration rates.

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