OPERATING INSTITUTE: CNRS UPS 3248 Ecotron Européen de Montpellier.

MAIN PURPOSE: Submit ecosystem samples to environmental changes and measure processes.

ECOSYSTEM TYPE: Ecosystem to organism scale, natural or cultivated, sampled in situ or reconstructed.

EXPERIMENTAL TREATMENTS: Various simulated environmental conditions (CO2, temperature, precipitation, light, biodiversity…).

LOCALISATION: 43.681976839207195 3.8760852813720703

FACILITIES: The Montpellier Ecotron is devoted to the analysis of responses to environmental change by ecosystems, organisms and biodiversity. It is open to the international community through calls for proposals. Its principle is to confine samples of ecosystems or organisms in order to better simulate various environmental conditions and to accurately measure ecosystem and organism function. Three platforms allow studies at different scales (ecosystem to organism) on different types of ecosystem (“natural” or cultivated, sampled in situ or reconstructed). The Ecotron has the flexibility to simulate a wide range of climatic conditions (including sub-zero degree Celsius temperatures) and CO2 concen-trations. At Montpellier, ecosystem processes are measured at high temporal resolution, in particular the automated on-line flux measurements of H2O, CO2, CH4 and N2O. A specific emphasis is put on isotopic techniques (13C labeling of the organic matter and carbon dioxide 13C on line measure-ments). Real time access to the environ-mental conditions of each unit and to the on-line measurements via the internet allows authorised researchers to follow the experiment from any location. A staff of 8 research engineers and technicians runs the infrastructure and secures the online measurements.
Recently, a more powerful cooling system has been added to the macrocosms platform in order to allow the simulation of a larger range of climatic conditions with, in particular negative temperatures. It is now also possible to  work in totally controlled conditions in 6 of the macrocosms by blocking the sun’s radiation and using plasma lamps instead. A platform of 12 growth chambers with flexible light conditions (sun-like radiation spectrum with plasma lamps, of variable spectrum with LED lamps) has been installed.

CONTACT: J. ROY (This email address is being protected from spambots. You need JavaScript enabled to view it.)

‚óŹ Milcu, A., Roscher, C., Gessler, A., Bachmann, D., Gockele, A., Guderle, M., Landais, D., Piel, C., Escape, C., Devidal, S., Ravel, O., Buchmann, N., Gleixner, G., Hildebrandt, A., Roy, J. (2014) Functional diversity of leaf nitrogen concentrations drives grassland carbon fluxes. Ecology Letters, early view doi:10.1111/ele.12243.


TA PROJECTS: Genetic variability in tillering response of durum wheat to assimilate availability modulated by PPFD. TILLER.

TA User (visit): Fulvia Rizzi, Consiglio per la Ricerca e la sperimentazione in Agricoltura, Genomics Research Centre (CRA - GPG), Italy (February, 2015 – 05 days)
Project Description: The increase in biomass and grain production of 12 durum wheat varieties to elevated atmospheric CO2 (570 ppm vs. ambient) tested with two years of FACE (Free Air Carbon dioxide Enrichement) was mainly related to increased tillering (Badeck et al. 2013). Similar results have previously been obtained for other crops (Gifford, 1977; Ziska et al. 2004; Shimono et al. 2009; Thilakarathne et al. 2013, Tausz-Posch et al. 2015). As most effects of elevated CO2 have been shown to be mediated through variation of photosynthetic rates that cause downstream allocation changes, the most parsimonious hypothesis to explain the association between tillering response and biomass response, is that increased assimilate availability leads to increased numbers of tillers which provide an increased sink for further assimilates. The proposed experiment tests this hypothesis through variation of an other factor, the incident photon flux in a controlled environment and the related genotypic variability (Sanna et al. 2014).

Impact of CO2 fixation by PEPC on carbon isotope composition of root-respired CO2 in a C3 plant. (ISOPEP 2)

TA User (visit): Franz-W. Badeck, Consiglio per la Ricerca e la sperimentazione in Agricoltura, CRA-GPG , Italy (February, 2015 – 45 days)
Project Description: Carbon isotope composition of leaf bulk organic matter is often used as reference for photosynthetic discrimination in both plant and ecosystem level studies. However, we have shown that leaves are in general 13C-depleted compared to all other organs suggesting that post-photosynthetic discriminations do also occur. With an exploratory experiment (ExpeER fast track grant ISOPEP) we recently showed that one of the candidate mechanisms, i.e. a contribution of PEPc activity (re-fixation of CO2 by PEP carboxylase via anaplerotic pathway) in heterotrophic organs can be detected with online measurements. The aim of the present proposal is to apply the new measurement system for investigating the role of PEPc activity in roots.

Oxygen as missing link to respiratory quotient: measurement tests in the ECOTRON large scale lysimeters

TA User (visit): Marian Kazda, Institute of Systematic Botany and Ecology, Ulm University, Germany (January, 2015 – 40 days)
Project Description: The 12 lysimeters of the ECOTRON macrocosms facility were filled with 2 m deep intact soil monoliths. Each six of them were planted with beans and cotton, respectively, and grown for 6 months. Previous measurements of CO2 dynamics in lysimeter soils showed diurnal cycles of CO2 concentrations. Such finding is supported by a recent study by Han et al. (2014) who found the daytime cycles of soil respiration being linearly correlated to plant photosynthesis with a lag of 1 to 1.5 hours. Therefore, our timely high-resolution measurements will provide a valuable information for both, the O2 and CO2 diurnal dynamics. Such high-resolution data can be used in a subsequent modeling of soil gas exchange processes.
After the cotton/bean experiment, the ECOTRON macrocosms lysimeters were harvested and the soil was not watered for 10 months during which maintenance and tests were done on the platform. These lysimeters are now in a rehydration phase and they will be planted with bean for a biological test of the heterogeneity within and between macrocosms. Such set-up also offers an unique possibility to test the various hypothesis related to CO2 and O2 dynamics in soil profiles while assessing the RQ. The planed CO2 and O2 measurements will test the following overall hypothesis: The soil respiratory activity and the oxygen consumption are directly related to the size of the plant pool (above-ground and below-ground biomass) and its metabolic activity. This approach will also offer a possibility for other projects, linking our results to the size and availability of plant-derived soil organic matter. The hypothesis will be tested using the following assumptions: - Soil CO2 concentrations and the differences between soil pO2 and pO2 in the ambient air will increase gradually after the establishment of the plants.
- Soon after the planting, the soil RQ starts to increase up to nearly 1 due to metabolic activity of plant roots and supply of root exudates (Bare soil at the beginning of the experiment has a low RQ due to low-level microbial respiration based mainly on internal reserves and the use of recalcitrant carbon.) - Plant stress (i.e. drought) impair carbon fixation and decreases the supply of carbohydrates to below-ground and the soil microbiota starts to degrade more recalcitrant organic matter leading to lower RQ. Plant harvest will at first lead to increasing RQ due to fast mineralisation of fine plant roots and to nitrification, the later consuming O2 without concomitant CO2 production.
- Modelling of short-time changes in CO2 and O2 concentration gradients will reveal new insights into soil gas exchange such as sorption/re-sorption and temporary sinks for CO2 and O2 in soils.

Oxygen as missing link to respiratory quotient: measurement tests in the Ecotron large scale lysimeters (RESP_O2).

TA User (visit): Marian Kazda, Ulm University, Germany (November, 2014 – 3 days)
Project Description: Soil respiration (the sum of root and heterotrophic respiration) is highly dependent on plant cover, soil temperature and humidity. However, there are only few experimental approaches examining the response of soil respiration and its sensitivity to combined environmental effects such as warming and drought (Suseela & Dukes, 2013). Even though, vast majority of the studies are investigating solely soil respiration as release of CO2 from the soil without considering oxygen consumption i.e. respiratory quotient (RQ=CO2 eliminated/O2 consumed). Direct oxygen measurements for estimation of respiratory quotients were done in comparatively few soil studies and moreover mainly in incubation experiments (Jenkins & Adams, 2011).
Furthermore, RQ is highly dependent on the origin of organic substances used by soil microbes. Readily degradable organic material gives a RQ ~ 1 but the degradation of more recalcitrant organic matter results in RQ < 1 (Dilly, 2003). In this respect RQ is also linked to the roots exudates, i.e. plant growth and metabolic activity. It is assumed, that about 20% of C assimilated by higher plants via photosynthesis is released by roots as exudates consisting of easily degradable hydrocarbons (Hinsinger et al. 2006).
It can be hypothesised, that soils with active and unstressed plants will have higher RQ but plants under severe stress such as prolonged drought will shut down the exudation of carbohydrates (c.f. Fuchslueger et al. 2014). Consequently, soil respiration will go back to less degradable organic compounds thus leading to a decline in RQ. However, drought stress-tolerant corn cultivars increased their root exudation under drought as a part of their stress acclimation (Song et al. 2012). Therefore, changes in the plant-soil-microbiota system under stress and their influence on soil respiration processes need further understanding.
The aim of the present study is to test the feasibility of implementing optical oxygen measurements into already existing assessment of soil CO2 within the Ecotron macrocosms facility. This should allow future tests of the hypothesis, that drought-induced changes in soil respiration also affect the respiratory quotient due to decreased input of root exudates.

Impact of CO2 fixation by PEPc on carbon isotope composition of root-respired CO2 in a C3 plant (ISOPEP).

TA User (visit): Franz-W. Badeck, Consiglio per la Ricerca e la sperimentazione in Agricoltura, Genomics research centre (CRA - GPG), Italy (September, 2014 - 5 days).
Project Description: Carbon isotope composition of leaf bulk organic matter is often used as reference for photosynthetic discrimination in both plant and ecosystem level studies. However, we have shown that leaves are in general 13C-depleted compared to all other organs (Badeck et al. 2005, see also Cernusak et al. 2009) suggesting that post-photosynthetic discriminations do also occur. Two of several hypotheses to explain this between-organ isotopic difference, are (1) opposite respiratory fractionation between leaves and heterotrophic organs, (2) higher PEPc activity (re-fixation of CO2 by PEP carboxylase via anaplerotic pathway) in heterotrophic organs compared to leaves, etc. (see our recent review Ghashghaie & Badeck 2014). We have already validated hypothesis 1 (see references below) and the aim of the present proposal is to investigate hypothesis 2 on the role of PEPc activity mainly in roots.
An exploratory experiment to examine if CO2-fixation by roots can be measured in situ will be conducted in September in the ECOTRON. Our model plant French bean will be used for these experiments for which we have already demonstrated the opposite apparent respiratory isotope discrimination between leaves and roots. The bean plants will be grown in small pots specially made for these experiments (pots have the inlet and outlet tubes allowing gas exchange measurements and isotope labelling of roots). The culture will be done in vermiculite with nutrient solution and the pots will be placed in one growth chamber of the Microcosmes platform in the Montpellier ECOTRON under standard environmental conditions. At the end of September, during a 5-days  measurement period  (the length of the Transnational access visit), on 3 week old plants, the top of the pots will be sealed to avoid exchange with the ambient air. Respiration rate and 13C exchange will be measured using the Ecotron CO2 and 13C analyser with different inlet air to the root compartment for 3 different sets of plants (4 plants for each set): (i) CO2 free air, (ii) air with normal CO2 isotope composition at –8 per mil, and (iii) air with industrial CO2 at –40 per mil. Del13C of net root respired CO2 is expected to be invariable with changing ambient rooting volume CO2 concentration and del13C if there is no CO2 fixation via carboxylation reactions. Plants will be harvested at the end of the experiments for carbon isotope composition on root metabolites (malate, AOA, sugars) involved in the anaplerotic pathway and respiration and organic mass by Prof. Jaleh Ghashghaie (at the platform “metabolism-métabolome” of the IFR87, Université Paris-Sud, Orsay).
The proposed 4 week exploratory experiment serves to evaluate the feasibility of the use of the ECOTRON facility for online measurements (Barbour et al. 2007) of the 13C isotopic signature of root-respired CO2 under varying concentration and del13C of air supplied to the rooting volume. Del13C of net root respired CO2 is expected to be invariable with changing ambient rooting volume CO2 concentration and del13C if there is no CO2 fixation via carboxylation reactions. Variation of root-space gas composition will be used to separate CO2 release during respiration from CO2 fixation during anaplerotic carboxylation reactions. In case of a positive outcome it is envisaged to subsequently propose a full experiment to be done on the Microcosms platform. This full experiment will serve to study the role of anaplerotic root metabolism under variable N nutrition (Raven & Farquhar, 1990) for apparent fractionation of 13C in root respiration. The results of the experiment and of a potential full experiment on the successful test contribute to better characterize plant root gas exchange in the frame of studies of belowground gas fluxes (Brüggemann et al., 2011).

Mircoclimate versus plant effects on relationships between soil CO2 concentrations and efflux.

TA User (visit): David Reinthaler, Institute of Ecology, University of Innsbruck, Austria (October, 2013 – 21 days).
Project Description: Terrestrial ecosystems are an important component of the global carbon cycle whereas more than thirty percent of the CO2 in the atmosphere is exchanged annually with the terrestrial biosphere (e.g. Ciais et al 1997). The two most important fluxes which regulate the carbon balance of terrestrial ecosystems are canopy photosynthesis and ecosystem respiration. The largest source of CO2 from terrestrial ecosystems is soil CO2 efflux that includes heterotrophic and autotrophic CO2 (Schlesinger and Andrews, 2000, Bond-Lamberti & Thomson 2010). The role of soil CO2 efflux from ecosystems in the terrestrial carbon cycle and its feedbacks to climate change is well known and has been shown to be influenced both by climatic conditions and plant activity (Janssens et al. 2001, Reichstein et al. 2003, Hibbard et al. 2005, Bahn et al. 2008). More recently it has been shown that the knowledge of CO2 concentrations and CO2 diffusion across the soil profile adds importantly to out understanding of mechanisms underlying soil CO2 production and efflux (Pumpanen et al. 2008, Vargas et al. 2010, 2011), though a separation of plant-derived and microclimate-derived effects of soil CO2 efflux is still not well resolved and requires further attention (Subke & Bahn 2010, Philipps et al. 2011).
The main aims of the of the project are 1) to test and validate a soil CO2-profile-based system for assessing CO2 production and diffusion across the soil profile and the resulting total soil surface CO2 efflux in the large lysimeters of the Montpellier Ecotron, and 2) to separate effects of microclimate, soil physics and plant-related activity on soil CO2 production and efflux and consequences for the net ecosystem exchange of CO2.
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Circadian regulation of leaf water fluxes (CIRFLUX).

TA User (visit): Juan Pedro Ferrio Diaz, Dpt. Crop and Forest Sciences-AGROTECNIO Center, University of Lleida, Spain (September, 2013 – 23 days).
Project Description: Act locally, think globally: do circadian rhythms in leaf mesophyll hydraulics affect terrestrial water fluxes?
Terrestrial water fluxes are largely dominated by transpiration, however, large uncertainties on the controls of stomatal conductance lead to poorly constrained global estimates of transpiration (Jasechko et al. 2013). At the diurnal scale, one of the major assumptions underlying studies of the exchange of water between terrestrial ecosystems and the atmosphere is that daily fluctuations in transpiration are driven almost exclusively by direct physiological responses to changes in irradiance, temperature, humidity and other meteorological factors. However, it is increasingly recognized that transpiration may also vary over time in the absence of variation in external forcing because of endogenous control from the circadian clock (Resco de Dios et al. in press; Resco et al. 2009). On the other hand, transpiration and stomatal conductance are tightly controlled by the hydraulic conductivity of the leaf (Tyree and Zimmerman 2002). Previous work from the applicant has shown that short-term changes in leaf hydraulics is mediated by the interplay between mesophyll conductance and the “scaled effective path length”, or the water pathway from the xylem to the site of evaporation, a key parameter in models describing isotopic enrichment of leaf water (Ferrio et al. 2009, 2012; Flexas et al. 2012). This regulation is likely to be at least in part determined by changes in aquaporin expression (Flexas et al. 2012).
In this context, the ExpeER stay, planned for two weeks, will allow to participate to an on-going experiment on cotton and bean mesocosms in the Ecotron, coordinated by V. Resco de Dios (Sidney University) and A. Gessler (Leibniz Institute Berlin), and aiming at testing for a circadian regulation of daytime transpiration at the leaf level that scales up to affect whole ecosystem water fluxes, and to disentangle the underlying mechanisms. More specifically, the aim of the stay is to:
1) Disentangling whether the mechanism by which the circadian clock controls stomatal conductance also influence the expression of different aquaporin families in the mesophyll, thus affecting either mesophyll conductance for CO2 and H2O, or both ;
2) Compare circadian rhythms of leaf lamina hydraulic conductance and the scaled effective path length, as proxies for mesophyll conductance for H2O, with the time-pattern of transpiration, mesophyll conductance for CO2 and aquaporin expression, which will be determined by the other participants in the experiment.

Influence of biodiversity on soil water flow.

TA User (visit): Marcus Guderle, Friedrich-Schiller-University Jena, Germany (February, 2013).
Project Description: Besides comprising an essential resource for plants soil water acts as a transport medium for dissolved matter and mediates microbial activity. Thus soil water fluxes and resulting redistribution of soil water provide important information for understanding, besides resource use strategies, other biological and abiotic processes. Up to know it is not possible to measure soil water flow directly (Vereecken et al., 2008), and our knowledge about changes of ecosystem root water uptake profiles with plant diversity is rudimentary. Soil water fluxes can only be estimated either (i) through inverse modelling or (ii) directly for a large soil column with lysimeters like in the ECOTRON, where with the drainage flux a closed water balance can be recorded. The aim of this research is to investigate (1) whether root water uptake profiles differ significantly between ecosystems of different diversity (2) how plant diversity influence vertical soil water fluxes and redistribution of soil water over the growing season and (3) how plant diversity contributes to groundwater recharge or to what extent they use groundwater for transpiration. Furthermore, we will (4) prepare data for validation of an inverse model, which shall be applied to the original plots in the Jena Experiment. This task can only be achieved with data from a lysimeter, such as the ECOTRON. In order to investigate the questions, we will analyse time series of soil matric potential, soil moisture, groundwater table, drainage, evapotranspiration as well as irrigation recorded in a measurement campaign on 12 lysimeters in the ECOTRON facility from April to August 2012. These lysimeters from the Jena Experiment field site cover two diversity levels (4 and 16 species). We will (1) close the water balance of each of the macrocosms, and (2) apply data-driven methods on lysimeters with different diversities to estimate root water uptake profiles and soil water fluxes based on the short term fluctuations of soil moisture.
The visit in Montpellier is needed to exploit with inputs from the Ecotron personnel who collected the data, the Ecotron data base related to the Ecotron-Jena experiment which was run from March to August 2012. The visit is planned from February 1st to April 5th 2013.
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Extreme event effects on grassland soil respiration.

TA User (visit): Angela Augusti, CNR IBAF, Porano, ITALY (September, 2011).
Project Description: Extreme events (e.g. heat waves and severe summer drought), are forecasted to be more frequent in the coming future. Moreover, it is interesting to study the effects of extremes events in a future climate context, meaning warmer and drier conditions than present, and with an increased atmospheric CO2 concentration. The responses of terrestrial ecosystems to such extreme events will clarify, among the other things, the role of biosphere as sink for atmospheric CO2.
The total size of terrestrial soil organic carbon, 1m depth, has been estimated to be 1500 Pg of C, with a potential global rate of soil C sequestration between 68 and 80 Pg/year. This depends on several factors that act on the equilibrium between ecosystem photosynthesis and respiration, among which include climate factors such as temperature, precipitation and atmospheric CO2 concentration.
In particular, my interest is focused on the combined effects of such climate factors on CO2 efflux from soil as a result of autotrophic and heterotrophic respiration. To disentangle the different components of CO2 soil efflux my approach involves separate analysis of total soil, heterotrophic and root respiration.
At the ECOTRON of Montpellier, there are portions of mid-altitude grassland, originating from central France, which are exposed to a future climate scenario reproducing air temperature and precipitation for the period 2040-2060 (air temperature 2.3 °C higher and precipitation 11% lower than current climate). Out of the 12 macrocosms present at the ECOTRON, 6 are exposed to ambient CO2 and 6 to a CO2 concentration of 520 ppm. During summer, a heat wave and a drought stress will be applied. During this period, air temperature will be increased by 3.5 °C, compared to the temperature predicted for the period 2040-2060; at the same time a drought stress (0 mm precipitation) will also be applied.
Results from this experiment will shed light on the potentially positive effect of increasing atmospheric CO2 concentration on the effect of drought stress on soil respiration. In other words, results will contribute to clarifying the role grassland ecosystems will have on C sequestration in the coming years.