Das Projekt "Der Einfluss von Tauniederschlag auf den Wasser- und Nährstoffhaushalt der Vegetation von Stipa tenacissima dominierten Hängen unterschiedlicher Exposition im semi-ariden Südosten Spaniens" wird vom Umweltbundesamt gefördert und von Albert-Ludwigs-Universität Freiburg, Institut für Biologie II, Lehrstuhl für Geobotanik durchgeführt. In vielen Lebensräumen ist Wasser der bedeutendste limitierende Faktor für das Wachstum und die Verbreitung der Pflanzen. Neuere Arbeiten zeigen, dass auch Arten, die nicht über spezielle Blattorgane zur Aufnahme von Wasser verfügen, auf Tau mit einer Erhöhung des Wasserpotentials und der Photosynthese sowie mit gesteigertem Wurzelwachstum reagieren. Das Ziel des Projekts ist die Evaluierung des Einflusses und die Untersuchung der Wirkungsweise von Tau auf die Vegetation von Stipa tenacissima dominierten Hängen entlang eines Niederschlags-Tauniederschlags-Transekts in SO-Spanien. An S. tenacissima und an ausgewählten annuellen Arten wird der Einfluss von Tau auf den Wasserhaushalt, die Photosynthese und die Fähigkeit der Wurzeln zur Wasseraufnahme im Freiland und im Gewächshaus bestimmt. Seine Wirkungsweise, eventuelle Aufnahmewege, Verlagerungen im Boden sowie sein Einfluss auf die Nährstoffverfügbarkeit werden untersucht. Die Bestimmung der Taumenge und -häufigkeit, verbunden mit Mikroklimamessungen, ermöglicht eine Abschätzung des Beitrags von Tau zur Wasserbilanz der untersuchten Hänge. Das Projekt wird Fragen des Wasser- und Nährstoffhaushalts der Vegetation in ariden und semi-ariden Gebieten beantworten. Dies trägt zu einem besseren Verständnis der Ökologie und der Verbreitung der Pflanzen dieser Gebiete bei, welches für die zukünftige Bewirtschaftung und Rehabilitation von degradierten Flächen in diesen Ökosystemen wichtig ist.
Das Projekt "Controls of plant biodiversity on water flux partitioning in grassland ecosystems" wird vom Umweltbundesamt gefördert und von Eidgenössische Technische Hochschule Zürich, Institut für Agrarwissenschaften, Departement Biologie durchgeführt. Global environmental change is predicted to result in increased frequency and intensity of extreme climatic events, including severe droughts and intense precipitation events (IPCC, 2001; IPCC, 2007). The determination and partitioning of water use of entire ecosystems will thus gain increasing importance under future climatic conditions (IPCC 2007). Studying the effects of plant diversity on ecosystem water fluxes is also a crucial aspect of our understanding of the mechanisms underlying the response of ecosystems to global change as well as the direction and magnitude of potential feedback effects of ecosystems on the hydrological cycle and the atmosphere. However, up to now, biodiversity-ecosystem functioning studies have neglected the water cycle almost completely. In the proposed project, the controls of plant diversity (i.e., species richness and functional group richness) on ecosystem water fluxes, their partitioning into soil evaporation and transpiration as well as plant water uptake patterns will be assessed in grassland ecosystems with the following objectives: - To quantify water losses from grassland ecosystems of varying plant diversity to the atmosphere (evapotranspiration fluxes); - To partition the evapotranspiration flux into its soil evaporative and vegetation transpiration components; - to identify the environmental constraints of plant water sources as a function of plant diversity. The study will be carried out at The Jena Experiment, a large biodiversity experiment in which experimental plant community plots of varying species composition, but also species and functional group richness are studied since 2002. We propose to use micrometeorological techniques to measure the ecosystem evapotranspiration flux (ET) and partition it into vegetation transpiration (T) and soil evaporation (E) at the ecosystem level, as well as to use stable isotope analyses to identify the source water of transpiration during intensive field campaigns at times of different water availability. The expected outcomes of the project proposed are manyfold. Using an innovative combination of techniques, we can provide a proof-of-concept to a scientific community (e.g. biodiversity, population biology, plant ecology communities) that typically has little to no knowledge about the great potential of such methodology. We will obtain highly relevant data on the relationships between plant diversity and water fluxes, their component fluxes and environmental drivers, information that does not exist at the moment. Moreover, we then can assess land surface-atmosphere coupling and the impact of climate change on grassland ecosystems, one of the major land use types in Europe and globally.
Das Projekt "Wasserverhaeltnisse in einer reifen gemeinen Fichte" wird vom Umweltbundesamt gefördert und von Eidgenössische Forschungsanstalt für Wald, Schnee und Landschaft durchgeführt. Water relations of mature Picea abies tree in the Seehornwald (1640m a.s.l.) near Davos, Switzerland, are under investigation. In the soil, temperature and soil matric water potential are being measured. As micrometeorological parameters we measure solar radiation, air temperature, water vapour pressure deficit, wind speed and evaporation throughout the canopy. Precipitation is measured at the top of the canopy only. To estimate the water relations of lichens in the tree crown, the electrical resistance of lichens growing on the twigs is measured. To estimate tree water relations transpiration of selected twigs is measured using climatized gas exchange chambers, xylem sap flow in the stem and some branches using sap flow meters, and the water potential and the osmotic values of the needle tissue is estimated using the pressure bomb technique and cryoscopy respectively. Leading Questions: How does the quantity of water evaporated from a mature Picea abies tree in a subalpine forest vary with different micro-meteorological conditions?Is drought a problem for a tree in a subalpine forest, and what are the reactions of the tree to this stress? Do different parts of the crown (in the sun and in the shade) react to water stress in the same manner? What drought conditions cause needle fall?
Das Projekt "Gasaustausch in Aesten erwachsener Nadelbaeume im subalpinen Bereich, beeinflusst durch erhoehte CO2-Konzentration in der Luft" wird vom Umweltbundesamt gefördert und von Eidgenössische Forschungsanstalt für Wald, Schnee und Landschaft durchgeführt. Over several years, photosynthesis and transpiration in shoots of mature coniferous trees at natural subalpine sites (Seehornwald and Stillberg, Davos) have been measured using thermoelectrically climatized gas exchange chambers with different CO2 concentrations (ambient and ambient + 350ppm CO2). Maximum photosynthetic capacity of the shoots has been estimated periodically. In addition to the gas exchange measurements at ambient CO2 concentration, past measurements, taken at the same places, will serve as controls. Leading Questions: Are the photosynthetic rates of mature coniferous trees different at elevated CO2 concentrations? Are there changes in the water relations (transpiration, stomatal conductance) of shoots of mature coniferous trees exposed to elevated CO2 concentrations? In short-term experiments with elevated CO2 concentration, an increase in CO2 assimilation is observed. Is there, with time, an adaptation back to the present photosynthetic rates? Is the temperature optimum in shoots grown under elevated CO2 concentration different?