Jun'Prof. Dr. Christiane Werner

• 1995 Diploma, University of Cologne: Water relations and photosynthesis on cork-oak (Quercus suber L.) with special reference to the effect of bark-stripping - a field study in Portugal

• 2000 PhD University of Bielefeld: Evaluation of structural and functional adaptations of Mediterranean macchia species to drought stress with emphasis on the effects of photoinhibition on whole-plant carbon gain - a modelling approach

• 1996-1999 scientific assistant at the University of Bielefeld

• 1998 research assistant Restoration project in Mediterranean degradated soils and ecosystems, University Lisbon

• 2000-2001 Post-doc EU-project NETCARB (Network for Ecophysiology in Closing Terrestrial CARbon Budget), University of Lisbon

• Since 2001: Scientific assistant at the University of Bielefeld

• Since 2003 Junior Professor of Plant Ecophysiology and Head of Stable Isotope Laboratory

Present Co-operations with:

• Matthias Cuntz, UFZ Leipzig

• Cristina Máguas, Otília Correia, University of Lisbon

• Joao Santos Pereira, Maria Caldeira, ISA, Technical University of Lisbon

• André Große-Stoltenberg, Tillmann Buttschardt, Universität Münster

• Jens Oldeland, Universität Hamburg

• Rolf Siegwolf, PSI, Schwitzerland

• Roland Werner, Nina Buchmann, ETH, Zurique

• Arthur Gessler, ZALF, Berlin

• Jana Jeglinski, Fritz Trillmich, University Bielefeld

• Kolby Jardine, Leif Abrell, Biosphere 2 Centre, Arizona

• Jaleh Ghashghaie, University of Paris-Sud, France

• Ron Ryel, University of Logan, USA
  
  

Grants:

• PhD-grant (DAAD)

• Research grant PRAXIS, FCT, Lisbon

• Post-doc Research grant, EU-Project NETCARB

Awards:

• “Dissertation 2000” of the Westfälisch Lippische Universitätsgesellschaft

• Karl Peter Grotemeyer-Award 2009 for outstanding achievements and personal engagement in teaching

Current Projects:

Disentangling seasonal vegetation effects on ecosystem evapotranspiration and water use efficiency of a Mediterranean savannah-type oak forest (WATERFLUX, DFG)

Water represents one of the key factors driving ecosystem productivity due to the tight coupling between ecosystem water and carbon fluxes. A functional understanding of evapotranspiration and photosynthesis is required to understand the development of water and carbon fluxes, particularly in water-limited ecosystems where global climate change is expected to intensify drought and alter precipitation patterns. The aim of this project is a detailed mechanistic evaluation of the water balance and water use efficiency of a typical Mediterranean savannah-type oak woodland. The project will focus on seasonal dynamics of over- and understorey vegetation of this two-component system and on the vegetation feedbacks on water and carbon fluxes. The study will combine (1) ecosystem and understorey measurements of net CO2 and H2O fluxes with (2) an experimental approach (trenching plot design) to disentangle major vegetation effects on water and carbon processes, and (3) a modelling approach to integrate the information gained from the different scales. Partitioning of net water fluxes into their individual components will be achieved by the use of stable isotopes. This project will deliver a process-based understanding of ecosystem water cycling and water use efficiency with a particular focus on the contribution of the understorey, which will be evaluated under consideration of future climate trends. Such improved understanding will help to develop appropriate management strategies and is needed for a risk assessment of climate change impact on Mediterranean ecosystems.

PhD-Student Maren Dubbert, in collaboration with Stefan Unger, Matthias Cuntz, Cristina Maguas, Joao S.Pereira

Changing ground water levels: the impact on an invasive species and native plant communities in a Mediterranean dune ecosystem (TransDune, DFG)

 
The introduction of non-native species and its spread are recognized to be one of the major threats to biodiversity and ecosystem functioning. Climate change is expected to enhance ecosystem invasibility through changes in resource availability (e.g. water) and the risks of desertification in Mediterranean areas, however scientific studies are rare. This project will evaluate specific traits of a characteristic invader towards competition for limited resources and the consequent alteration of community functioning under decreasing ground water availability. We selected a protected Mediterranean costal dune system of high ecological value, where large-scale extraction of ground water provides excellent experimental conditions to study changes in the competitive balances among invasive and native species. We will analyse the effects i) at the seedling level to evaluate changes in plant establishment; ii) at the plant level to gain major insights on the spatial and temporal partitioning of water sources and regulating mechanisms of selected species and iii) at the community level to evaluate changes in water flow, competition and facilitation (e.g. hydraulic lift), community functioning, and changes in invasibility of the system. The aim is the identification of key processes controlling the competitive balances between invasive neophytes and native species and invasibility of semi-arid systems to contribute to a risk assessment under global change scenarios.


Katie Rascher, Tine Hellmann in collaboration with Cristina Maguas

Ecological relevance of carbon isotope fractionation during dark respiration (ECORES, DFG)

Stable isotopes provide a powerful diagnostic tool to analyze carbon pools and fluxes, which along with the isotopic composition of ecosystem respiration (δ¹³C_R) are now measured in ecosystems world-wide. Recently, a mechanistic understanding on isotopic fractionation during dark respiration has been achieved on the physiological scale, while much less is known on its impact at larger scales, under natural conditions or in different functional groups. This project aims to close the gap between recent advances on mechanisms of fractionation during dark respiration and its ecological significance by combining metabolic, whole-plant and ecosystem approaches. Our innovative and low-cost technique enables a high-time resolved assessment of dark respired δ¹³CO₂ (δ¹³C_res) (Werner et al 2007).
Starting with a wide species survey of diurnal courses of δ¹³C_res, this study will focus on the analysis of these short-term variations in selected functional groups considering leaf, shoot and root diurnal dynamics of metabolite pools and partitioning. Possible involvement in larger temporal and spatial scales will be assessed by evaluating their respective contribution first at the “whole-plant” and second at the ecosystem scale using a component mass balance approach in a natural Mediterranean ecosystem. Understanding the dynamics of δ¹³C_R has significant implications for the evaluation of ecosystem response to global change.

PhD-Student Frederik Wegener, In collaboration with Pierrick Priault, Cristina Maguas, Joao S.Pereira, Jaleh Gashghaie

Partitioning of N-sources in different successional stages in a nutrient poor sandy grassland by¹⁵N-labelling-experiments.

Open sandy grasslands are characteristic nutrient poor habitats with extreme microclimatic conditions. Because of land use change and atmospheric nutrient input these ecosystems become more and more endangered. In order to better understand the mechanisms of succession, competition and co-existence in these ecosystems, we are presently investigating the influence of different nitrogen sources on N-partitioning between species by ¹⁵NO₃^- and ¹⁵NH₄⁺ labelling under natural conditions. Particularly, causes for the disappearance of early successional species during succession are investigated. In these nutrient poor systems niche differentiation in respect to differential N-source utilization (e.g. NO₃^- ; NH₄⁺) may play a major role.
We tested the hypothesis of changes in N-source utilization from the most available nitrogen source (NO₃^-) to less available NH₄⁺ with ongoing succession occurs to coexist with other species in later successional stages with higher competition. Particullarly, we compared two typical pioneer species with different strategies - R. acetosella and C. canescens. The latter is a pioneer species characteristic for open sand areas, e.g. after disturbance, whereas the former shows a longer presence in succession. Therefore we hypothesised that C. canescens has a lower benefit from increased nitrogen availability than R. acetosella.

PhD-student: Vanessa M. Stahl, co-orientated by: Wolfram Beyschlag, Tom Steinlein

Further Project Cooperation:

Invasive Species Evaluation, ConTrol & Education (EU-Marie-Currie IRSES)

coordinated by Tillmann Buttschardt (University of Münster), with Tine Hellmann (University Bielefeld), Cristina Máguas (University of Lisbon), Joao Meiro (University Federal de Viçosa, Brazil)

DeInvader project EUFAR hyperspectral LIDAR-flight

André Große-Stoltenberg, T. Buttschardt, (University Münster)

Shrub invasion in Mediterranean Cork oak woodlands (MEDshrub, DAAD) with Maria Caldeira, Instituto Superior de Agronomia, Lisbon

Foraging strategies of sea lion populations in Galapagos

Jana Jeglinski, Fritz F. Trillmich (University Bielefeld), National Geographic

Mechanisms of isotope fractionation during respiration

Marco Lehmann, Roland Werner and Nina Buchmann (ETH Zürich) Rolf Siegwolf (Paul Scherer Institut, Schweiz), Arthur Gessler (ZALF Berlin)

Former Projects:

Partitioning seasonal changes in carbon fluxes of a Mediterranean woodland into photosynthetic and respiratory components by stable isotope analysis (ISOFLUX, DFG)

A functional understanding of carbon fixation by terrestrial ecosystems and atmosphere/biosphere gas exchange is particularly important regarding global climate change. However, a mechanistic understanding of changes in photosynthetic carbon fixation and respiratory CO2 release is difficult to achieve from the analysis of net ecosystem exchange rates (NEE). Naturally abundant stable isotopes provide a unique way to partition these opposing fluxes. We will analyse the seasonal changes in the photosynthetic and respiratory carbon fluxes in a Mediterranean evergreen woodland (at the Euroflux site in Portugal). This well characterized system provides unique conditions for a functional analysis of the temporal dynamics and environmental parameters, since the natural changes in climate conditions result in large seasonal variations in net ecosystem fluxes. The temporal dynamics of ecosystem and soil respiration (Keeling-plot approach) will be assessed, as well as the contribution of hetero- and autotrophic respiration. Furthermore, the contribution of different functional plant groups (grass-, shrub, and tree-layer) to the net fluxes will be analysed. Model approaches will be used, first, to estimate ecosystem fluxes from isotope gradient measurements (isofluxes) and analyse fractionation processes at the ecosystem level; and second, to evaluate the contribution of different functional groups to ecosystem productivity and seasonal changes carbon source/sink strength. By identifying critical factors for ecosystem functioning, a risk assessment of climate changes effects for this semi-arid ecosystem can be developed. 

PhD-student: PhD-Student Stephan Unger, in collaboration with Cristina Maguas, Joao S. Pereira

Publications:

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Peer-reviewed Journals

Rascher K.G., Hellmann C., Máguas C., Werner C (2012) Community scale 15N isoscapes: tracing the spatial impact of an exotic N2-fixing invader. Ecology Letters, in press, doi10.1111/j.1461-0248.2012.01761.x

Jeglinski J.W.E., Werner C., Robinson P., Costa D.P. & Trillmich F. (2012). Age, mass and environmental variation shape the foraging ontogeny of Galapagos sea lions. Mar Ecol Progr Ser in press

Unger S., Máguas C., Pereira J.S., David T.S. & Werner C. (2012) Interpreting post-drought rewetting effects on soil and ecosystem carbon dynamics in a Mediterranean oak savannah. Agricultural and Forest Meteorology. 154-155: 9-18. doi: 10.1016/j.agrformet.2011.10.007

Máguas C., Rascher K.G., Martins-Loução A., Carvalho P., Pinho P., Ramos M., Correia O. & Werner C. (2011) Responses of woody species to spatial and temporal ground water changes in coastal sand dune systems. Biogeosciences 8, 3823–3832, doi:10.5194/bg-8-3823-2011, www.biogeosciences.net/8/3823/2011/

Werner C., F. Badeck, E. Brugnoli, B. Cuntz, T. Dawson, A. Gessler, J. Ghashghaie, T.E.E. Grams, Z. Kayler, C. Keitel, M. Lakatos, X. Lee, C. Máguas, J. Ogée, K.G. Rascher, H. Schnyder, R. Siegwolf, S. Unger, J. Welker, L. Wingate, M.J. Zeeman. Linking carbon and water cycles using stable isotopes across scales: progress and challenges. Submitted to Biogeosciences Discuss., 8, 2659–2719, 2011 doi:10.5194/bgd-8-2659-2011, www.biogeosciences-discuss.net/8/2659/2011/

Werner C. & Gessler A. (2011) Diel variations in the carbon isotope composition of respired CO2 and associated carbon sources: a review of dynamics and mechanisms. Biogeosciences 8, 2437–2459, doi:10.5194/bg-8-2437-2011 www.biogeosciences.net/8/2437/2011/

Stahl V., Beyschlag W. & Werner C. (2011) Dynamic niche sharing in dry acidic grasslands - a 15N labelling approach. Plant and Soil, 344, 389-400. doi:10.1007/s11104-011-0758-2. http://dx.doi.org/10.1007/s11104-011-0758-2

Kueffer C., Niinemets Ü., Drenovsky R., Kattge J., Milberg P., Poorter H., Reich P., Werner C., Westoby M. & Wright I. (2011). Fame, glory and neglect in meta-analysis. Letter, Trends in Ecology and Evolution, doi:10.1016/j.tree.2011.07.007

Reyers M., Krüger A., Werner C., Pinto J.G., Zacharias S., & Kerschgens M. (2011) The Simulation of the Opposing Fluxes of Latent Heat and CO2 over Various Land-Use Types: Coupling a Gas Exchange Model to a Mesoscale Atmospheric Model. Boundary Layer Meteorology 139:121-141. doi:10.1007/s10546-010-9574-0 http://www.springerlink.com/content/h66758m462572524/

Hellmann C., Sutter R., Rascher K., Máguas C., Correia O. & Werner C. (2011) Influence of an exotic N2-fixing Acacia on community composition and N status of native Mediterranean species. Acta Oecologia 37: 43-50. (doi:10.1016/j.actao.2010.11.005)

Rascher K.G., Große-Stoltenberg A., Máguas C., Werner C. (2011) Understory invasion by Acacia longifolia alters the water balance and carbon gain of a Mediterranean pine forest. Ecosystems 14: 904–919 (doi:10.1007/s10021-011-9453-7)

Rascher K.G., Große-Stoltenberg A., Máguas C., Meira J. & Werner C. (2011) Acacia invasion impacts vegetation structure and regeneration dynamics in open dunes and pine forests. Biological Invasions 13: 1099-1113. (doi 10.1007/s10530-011-9949-2)

Rascher K.G., Máguas C. & Werner C. (2010) On the use of phloem sap 13C as an indicator of canopy carbon discrimination. Tree Physiology 30: 1499-1514. doi:10.1093/treephys/tpq092

Wegener F., Beyschlag W. & Werner C. (2010) The magnitude of diurnal variation in carbon isotopic composition of leaf dark respired CO2 correlates with the difference between δ13C of leaf and root material. Functional Plant Biology 37: 849–858. (doi: 10.1071/FP09224)

Werner C. (2010) Do isotopic respiratory signals trace changes in metabolic fluxes? New Phytologist 186: 569–571. (doi 10.1111/j.1469-8137.2010.03248.x)

Unger S., Máguas C., Pereira J.S., David T.S. & Werner C. (2010) The influence of precipitation pulses on soil respiration – Assessing the “Birch Effect” by stable carbon isotopes. Soil Biology and Biochemistry 42: 1800-1810. (doi: 10.1016/j.soilbio.2010.06.01)

Unger S., Máguas C., Pereira J.S., Aires L.M., David T.S. & Werner C. (2010) Disentangling drought-induced variation in ecosystem and soil respiration by stable isotope partitioning. Oecologia 163:1043–1057. (doi 10.1007/s00442-010-1576-6)

Werner C. & Máguas C. (2010) Carbon isotope discrimination as a tracer of functional traits in a Mediterranean macchia plant community. Functional Plant Biology 2010, 37, 467–477. (doi 10.1071/FP09081)

Werner C., Zumkier U., Beyschlag W. & Máguas C. (2010) High competitiveness of a resource demanding invasive acacia under low resource supply. Plant Ecology, 206: 83-96. (doi 10.1007/s11258-009-9625-0)

Priault P., Wegener F., Werner C. (2009) Pronounced differences in diurnal variation of carbon isotope composition of leaf respired CO2 among functional groups. New Phytologist, 181, 400-412.

Werner C., Wegener F., Unger S., Nogués S. & Priault P. (2009) Short-term dynamics of isotopic composition of leaf respired CO2 upon darkening: measurements and implications. Rapid Communication in Mass Spectrometry, 23: 2428-2438. (doi: 10.1002/rcm.4038)

Unger S., Máguas C., Pereira J.S., Aires L.M., David T.S. & Werner C. (2009). Partitioning carbon fluxes in a Mediterranean oak forest to disentangle changes in ecosystem sink strength during drought. Agricultural and Forest Meteorology, 149: 949–961. (doi:10.1016/j.agrformet.2008.11.013)

Rascher K.G., Máguas C., Correia O. & Werner C. (2009) Tracing Seasonal Changes in Water Use of an Invasive Acacia and a Native Pine in Southern Portugal by Measurement of Sap Flow. Acta Horticulturae (ISHS) 846:209-216

Beyschlag W., Hanisch S., Friedrich S., Jentsch A. & Werner C. (2009) 15N Natural Abundances during Early and Late Succession in a Middle-European Dry Acidic Grassland. Plant Biology 11:713-724 (doi:10.1111/j.1438-8677.2008.00173.x)

Werner C., Hasenbein N., Maia R., Beyschlag W., Máguas C. (2007) Evaluating high time-resolved changes in carbon isotope ratio of respired CO2 by a rapid in-tube incubation technique. Rapid Communication in Mass Spectrometry, 21:1352-1360.

Werner C., Unger S., Pereira J.S., Maia R., Kurz-Besson C., David T.S., David J.S. & Máguas C. (2006) Importance of short-term dynamics in carbon isotope ratios of ecosystem respiration (δ13CR) in a Mediterranean oak woodland and linkage to environmental factors. New Phytologist, 172, 330-346.

Peperkorn R., Werner C. & Beyschlag W. (2005) Phenotypic Plasticity of an Invasive Acacia versus Two Native Mediterranean Species. Functional Plant Biology, 32, 933-944.

Clemente A.S., Werner C. Máguas C., Cabral M.S., Martins-Louçao M.A., and Correia O. (2004) Restoration of a Limestone Quarry: Effect of Soil Amendments on the Establishment of Native Mediterranean Sclerophyllous Shrubs. Restoration Ecology, 12, 20-28.

Werner C., Correia O. & Beyschlag W. (2002) Characteristic patterns of chronic and dynamic photoinhibition of different functional groups in a Mediterranean ecosystem. Functional Plant Biology, 29, 999-1011.

Werner C., Correia O., Ryel R.J. & Beyschlag W (2001) Effects of photoinhibition on whole-plant carbon gain assessed with a photosynthesis model. Plant, Cell & Environment 24: 27-40.

Werner C., Ryel R.J., Correia O. & Beyschlag W. (2001) Structural and functional variability within the canopy and its relevance for carbon gain and stress avoidance. Acta Oecologica 22: 1-10.

Werner C., Correia O. & Beyschlag W. (1999) Two different strategies of Mediterranean macchia plants to avoid photoinhibitory damage by excessive radiation levels during summer drought. Acta Oecologia 20: 15-35

Werner C., Correia O., Ryel J.R. & Beyschlag W. (1998) Modelling whole-plant primary production of macchia species: assessing the effects of photoinhibition and foliage orientation. Revista de Biologia (Lisboa) 16: 247-257

Werner C. & Correia O. (1996) Photoinhibition in cork-oak leaves under stress: influence of the bark-stripping on the chlorophyll fluorescence emission in Quercus suber L. Trees 10: 288-292

Oliveira G., Werner C. & Correia O. (1996) Are ecophysiological responses influenced by crown position in cork-oak? Ann Sci For 53: 235-241

Peer-reviewed book chapters

Beyschlag W. and Werner C. Kohlenstoffhaushalt von Ökosystemen. In: W. Schröder, O. Fränzle, F. Müller (eds.) Handbuch der Umweltwissenschaften, Wiley-VCH Verlag, Weinheim, accepted

Werner C., Peperkorn R., Máguas C., Beyschlag, W. (2008) Competitive balance between the alien invasive Acacia longifolia and native Mediterranean species. In: Plant Invasions: Human perception, ecological impacts and management. Eds. B. Tokarska-Guzik, J. Brock, G. Brundu, L. Child, C. Daehler, P. Pyšek, Backhuys Publishers, Leiden, The Netherlands, pp. 261-275

Werner C., Unger S., Pereira J.S., Ghashghaie J. & Máguas C. (2007) Temporal dynamics in d¹³C of ecosystem respiration in response to environmental changes. In: Isotopes as Tracers of Ecological Change. T. Dawson & R. Siegwolf. (eds.) Elsevier Academic Press, San Diego, pp.193-210.

Tu KP, Bowen G, Hemming D, Kahmen A, Knohl A, Lai C-T, Werner C. (2007). Stable isotopes as indicators, tracers and recorders of ecological change: synthesis and outlook. In: Isotopes as Indicators of Ecological Change. T. Dawson & R. Siegwolf (eds.), Elsevier Academic Press, San Diego, pp. 399-405

Werner C., Clemente A.S., Correia P.M., Lino P., Máguas C., Correia A.I. and Correia O. (2000) Restoration of disturbed areas in the Mediterranean - a case study in a limestone quarry, In: Sustainable Land-Use in Deserts. Breckle, S.-W., Veste, M. & Wucherer, W. (eds.), Springer-Verlag Berlin, Heidelberg, pp. 368-376.

Werner C., Correia O., Ryel J.R. & Beyschlag W. (1998) Evaluation of photoinhibition on single-leaf and whole-plant photosynthesis of mediterranean macchia species. In: Photosynthesis: Mechanisms and Effects, G. Garab (ed), vol V, Kluwer Academic Publishers. Dortrecht, Netherlands, pp. 4011-4014

Conference Proceedings, Books etc.

Máguas, C., Ferreira, J., Pereira, A., Martins-Loução, M.A., Marchante, H., Marchante, E., Scheck, C., Freitas, H., Ramos, M., Werner, C. & Correia, O. (2007). Acacia longifolia invasiveness on Portuguese coastal dune systems: Environmental and plant community changes. In Proceedings: MEDECOS XI – The International Mediterranean Ecosystems Conference. CSIRO Publishing, Melbourne, Australia.

Pereira, A., Correia, O., Ramos, M., Werner, C. & Máguas, C. (2007). Different responses to water stress of the invasive Acacia longifolia versus native Mediterranean dune species. In Proceedings: MEDECOS XI – The International Mediterranean Ecosystems Conference. CSIRO Publishing, Melbourne, Australia.

Unger S, Pereira J.S., Máguas C. & Werner C. (2007) Carbon-flux partitioning of ecosystem respiration in a Mediterranean oak forest in response to drought. In 'MEDECOS IX' Proceedings: 9th International Mediterranean ecosystems conference, CSIRO Publishing: Melbourne, Australia.

Werner C., A. Loichot, G. Oliveira, A. Nunes, A.S. Clemente & O. Correia (2005) Ecological restoration of limestone quarries: a case study. Proceedings of the 1^st international Forum on ecological construction of Beijing (FECB2005), Beijing, China. pp. 152-163.

Werner C., Maia R. & Máguas C. (2001) Are carbon and oxygen isotope compositions of bulk leaf material reliable predictors of water use efficiency in slow-growing drought-adapted species? PS2001 Proceedings: 12th International Congress on Photosynthesis. CSIRO Publishing: Melbourne, Australia, 2001.

Unger S., Werner C. & Máguas C. (2001) Evaluation of water use efficiency: the contribution of structural vs. functional adaptations to drought stress. PS2001 Proceedings: 12th International Congress on Photosynthesis. CSIRO Publishing: Melbourne, Australia, 2001. S28-029

Werner C. (2000) Evaluation of structural and functional adaptations of Mediterranean macchia species to drought stress with emphasis on the effects of photoinhibition on whole-plant carbon gain – a modelling approach. PhD-thesis, Bielefeld.

Oliveira G., Werner C., Mertens C. & Correia O. (1993) Influencia de la posición de la copa sobre la fenología y las relaciones hídricas en alcornoque (Quercus suber). Proceedings of the Congresso florestal Español Lourizán, Vol.I, pp. 277-282

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