Kahmen, Ansgar, Prof. Dr.

 

Research Interests

My research addresses the interface between plants and their biotic and abiotic environment. I investigate the physiological responses of plans to changes in the environment in order to understand the mechanisms that determine the composition, diversity and function of ecosystems in a changing world. As such, my research links plant ecophysiology to plant population dynamics and ecosystem biogeochemistry. Within this broad framework my research focuses on three specific topics:

• Biological control of biogeochemical cycles: In conceptual and process-based models the biogeochemistry of terrestrial ecosystems is typically described as a function of physicochemical control mechanisms. In my work, I attempt to expand this view by identifying how biological variables such as plant species composition and biodiversity influence the magnitude and stability of biogeochemical cycles beyond physicochemical factors.

• Stable isotopes as recorders of plant water relations: Stable isotopes analyses are a fundamentally important tool for my research. In my latest work I seek to resolve the mechanisms that determine the oxygen or hydrogen isotope composition of plant materials. The goal of this work is to establish the stable oxygen isotope ratio of plant cellulose or the hydrogen isotope composition of leaf wax n-alkanes as integrative recorders of plant water relations. If successful, this work will allow to employ stable oxygen isotopes from tree ring cellulose or hydrogen isotopes from n-alkanes in lake sediments to assess long-term and low-frequency responses of plant water relations to environmental change.

• Ecology of plant N nutrition: Nitrogen is a key nutrient that influences the physiological and biogeochemical properties of plants and ecosystems. Surprisingly, many critical ecological aspects of plant N nutrition remain unclear. In my research I address the ecological strategies that plants have evolved in order to compete with other plants or with microbes for different chemical forms of nitrogen in the soil. Based on this, I investigate how different N-use-strategies shape plant community dynamics and ecosystem-level biogeochemistry.

I use different approaches for my research, that range from greenhouse and mesocosm experiments to landscape-level observations and modelling. An indispensable tool for all three areas of my research is the analysis of stable C, N, O and HD isotopes that I use as tracers or in their natural abundance to characterize biogeochemical cycles and their biological or physicochemical drivers.

Education and Professional Experience

• 10/2011 - ongoing Assistant Professor for Physiological Plant Ecology. ETH Zurich, Switzerland.

• 01/2010 - 09/2011 Senior Scientist. Institute of Agricultural Sciences, ETH Zurich, Switzerland.

• 04/2006 – 12/2009 Schrödinger and Marie Curie Postdoctoral Fellow. Center for Stable Isotope Biogeochemistry, University of California at Berkeley, USA.

• 04/2005 – 03/2006 Postdoctoral Fellow. Institute for Plant Sciences, ETH Zurich, Switzerland.

• 01/2005 – 03/2005 Visiting Scientist. Forest Science Center, University of Melbourne, Australia.

• 03/2001 – 12/2004 Ph.D. Student. Max Planck Institute for Biogeochemistry, Jena, Germany.

• 10/1994 – 02/2001 Student in botany and plant ecology. University of Vienna, Austria and University of California at Santa Cruz, USA.

Publications

Peer Reviewed Journal Articles

• Sachse D, Chikaraishi Y, Dawson TE, Feakins SJ, Freeman KH, Magill C, McInerney FA, van der Meer M, Pedentchouk N, Polissar P, Robins R, Schmidt HL, Sessions AL, White JWC, West JB, Kahmen A (in press) The hydrogen-isotopic composition of organic biomarkers from photosynthesiting organisms. Annual Review of Earth and Planetary Sciences.

• Garcin Y, Schwab-Lavrič VF, Gleixner G, Kahmen A, Todou G, Séné O, Onana J-M, Achoundong G, Sachse D (2012) Hydrogen isotope ratios of lacustrine sedimentary n-alkanes as proxies of tropical African hydrology: insights from a calibration transect across Cameroon. Geochimica et Cosmochimica Acta, 79: 106-126.

• Kahmen A, Dawson TE, Vieth A, Sachse D (2011) Leaf wax n-alkane δD values are determined early in the ontogeny of deciduous Populus trichocarpa leaves. Plant, Cell & Environment, 34: 1639-1651.

• Kahmen A, Sachse D, Arndt SK, Tu KP, Farrington H, Vitousek PM, Dawson TE (2011) Cellulose δ18O is an index of the leaf to air vapor pressure difference (VPD) in tropical plants. Proceedings of the National Academy of Sciences (PNAS), 108: 1981-1986.

• Sachse D, Gleixner G, Wilkes H, Kahmen A (2010) Leaf wax n-alkane δD values of a field-grown barley reflect leaf water δD values at the time of leaf formation. Geochimica et Cosmochimica Acta, 74: 6741-6750.

• Stein C, Unsicker SB, Kahmen A, Wagner M, Audorff V, Auge H, Prati D, Weisser WW (2010) Impact of invertebrate herbivory in grasslands depends on plant diversity. Ecology, 91: 1639 – 1650.
  ➙ Highlighted in the Editors Choice of Science (2010) Driving diversity underground. Science, 329: 258.

• Kahmen A, Livesley SJ, Arndt SK (2009) High potential but low actual glycine uptake of dominant plant species in three Australian land-use types with intermediate N availability. Plant and Soil, 325: 109-121.

• Kahmen A, Simonin S, Tu KP, Goldsmith GR, Dawson TE (2009) The influence of species and growing conditions on the 18-O enrichment of leaf water and its impact on “effective path length”. New Phytologist, 184: 619-630.

• Craine JM, Elmore AJ , Aidar MPM, Bustamante M, Dawson TE, Hobbie EA, Kahmen A, Mack MC, McLauchlan KK, Michelsen A, Nardoto GB, Pardo LH, Peñuelas J, Reich PB, Schuur EAG, Stock WD, Templer PH, Virginia RA, Welker JM, Wright IJ (2009) Global patterns of foliar nitrogen isotopes and their relationships with climate, mycorrhizal fungi, foliar nutrient concentrations, and nitrogen availability. New Phytologist, 183: 980-992.

• Sachse D, Kahmen A, Gleixner G (2009) Significant seasonal variation in the hydrogen isotopic composition of leaf-wax lipids for two deciduous ecosystems (Fagus sylvatica and Acer pseudoplananus). Organic Geochemistry, 40: 732-742.

• Tylianakis JM, Rand TA, Kahmen A, Klein AM, Buchmann N, Perner J, Tscharntke T (2008) Resource heterogeneity moderates the biodiversity-function relationship in real world ecosystems. PLoS Biology, 6(5): 947-956.

• Kahmen A, Wanek W, Buchmann N (2008) Foliar δ¹⁵N values characterize soil N cycling and reflect nitrate or ammonium preference of plants along a temperate grassland gradient. Oecologia, 156: 861-870.

• Kahmen A, Simonin K, Tu KP, Merchant A, Callister A, Siegwolf R, Dawson TE, Arndt SK (2008) Effects of environmental parameters, leaf physiological properties and leaf water relations on leaf water δ¹⁸O enrichment in different Eucalyptus species. Plant, Cell & Environment, 31: 738-751.

• Wagner M, Kahmen A, Schlumprecht H, Audorff V, Perner J, Buchmann N, Weisser W (2007) Prediction of herbage yield in grassland: How well do Ellenberg N-values perform in comparison with other approaches? Journal of Applied Vegetation Science, 10: 15-24.

• Unsicker SB, Baer N, Kahmen A, Wagner M, Buchmann N, Weisser WW (2006) Invertebrate herbivory along a gradient of plant species diversity in extensively managed grasslands. Oecologia, 150: 233-246.

• Kahmen A, Renker C, Unsicker SB, Buchmann N (2006) Niche complementarity for nitrogen use - An explanation for the biodiversity and ecosystem functioning relationship in grasslands? Ecology, 87: 1244-1255.

• Börstler B, Renker C, Kahmen A, Buscot F (2006) Species composition of arbuscular mycorrhizal fungi in two mountain meadows with differing management types and levels of plant biodiversity. Biology and Fertility of Soils, 42: 286-298.

• Kahmen A, Perner J, Buchmann N (2005) Diversity dependent productivity in semi-natural grasslands following climate perturbations. Functional Ecology, 19: 594-601.
  ➙ Highlighted in Nature News and Views by Moore, PD (2005) Roots of stability. Nature, 437: 959-960.

• Unsicker SB, Renker C, Kahmen A, Spindler S, Buchmann N, Weisser W (2005) Testing the efficiency of three 15N-labeled nitrogen compounds for indirect labeling of grasshoppers via plants in the field. Entomologia Experimentalis et Applicata, 116: 219-226.

• Perner J, Wytrykush C, Kahmen A, Buchmann N, Egerer I, Creutzburg S, Odat N, Audorff V, Weisser W (2005) Effects of plant diversity, plant productivity and habitat parameters on arthropod abundance in montane European grasslands. Ecography, 28: 429-442.

• Kahmen A and Jules ES (2005) Assessing the recovery of a long lived herb following logging: Trillium ovatum across a 424-year chronosequence. Forest Ecology and Management, 210: 107-116.

• Kahmen A, Perner J, Audorff J, Weisser W, Buchmann N (2005) Effects of plant diversity, community composition and environmental parameters on productivity in semi-natural montane European grasslands. Oecologia, 142: 606-615.

• Arndt SK, Kahmen A, Arampatsis C, Popp M, Adams M (2004) Nitrogen metabolism and importance of nitrogen fixation in perennial plants in a hyperarid desert with a constant groundwater table. Oecologia, 141: 385-394.

Book Chapters

• Kahmen A and Buchmann N (2007) Addressing the value of biodiversity for ecosystem functioning using stable isotopes. In: Dawson TE and Siegwolf R (Editors) Isotopes as indicators of ecological change. Elsevier Academic Press, San Diego, USA, pp. 347-359.

• 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: Dawson TE, Siegwolf R (Editors) Isotopes as indicators of ecological change. Elsevier Academic Press, San Diego, USA, pp. 399-405.

• Kahmen A (2005) Biodiversity and functioning of selected terrestrial ecosystems: Grasslands. In: Bartlott W, Porembski S, Linsenmair KE (Editors) Biodiversity: Structure and Function. Encyclopedia of Life Support Systems (EOLSS), Developed under the auspices of the UNESCO, Eolss Publishers, Oxford, UK, [http://www.eolss.net].

• Kahmen A, Arampatsis C, Arndt SK (2004) Nutrient supply and nitrogen metabolism of perennial plant species in the Taklimakan desert. In: Runge M and Ximing Z (Editors) Ecophysiology and habitat requirements of perennial plant species in the Taklimakan desert. ISBN 3-8322-2582-X, Shaker Verlag, Aachen, pp. 135-146.

• Buchmann N, Knohl A, Hahn V, Soe A, Kahmen A, Temperton V (2003) Stoffkreisläufe und Biodiversität in terrestrischen Ökosystemen. In: Jahrbuch 2003 der Max-Planck-Gesellschaft. ISBN 3-598-24930-6, K.G. Saur Verlag, München.