Modeling a spring wheat crop under elevated CO\u3csub\u3e2\u3c/sub\u3e and drought

• The simulation model DEMETER was used here to investigate which mechanisms led to a larger CO2 effect on biomass production and yield of a spring wheat crop under drought compared with unlimited water supply. • Field data of the free-air CO2enrichment (FACE) wheat experiments in Arizona (1993–94) were used to test the model. The influence of a particular mechanism leading to a higher CO2effect under drought was investigated by eliminating the influence of the other causes on the simulation results on selected days during the growing seasons. • A larger CO2effect under drought was caused in the model by the lower potential transpiration rate, higher root biomass and the nonlinear functional dependence of net assimilation rate on leaf internal CO2concentration. The contribution of the different mechanisms changed in significance during the growing season depending on the degree of soil water limitation. The model successfully described the qualitative and quantitative behavior of the crop under elevated CO2. • A well-tested simulation model can be a useful tool in understanding the complex interactions underlying observed ecosystem responses to stress under elevated CO2

The BAYSOFI Campaign - Measurements Carried out during the Total Solar Eclipse of August 11, 1999

The total solar eclipse of August 11, 1999 provided a unique opportunity to observe the input of fast day-night and night-day transitions, under high solar elevation around noon, on the earth-atmosphere-biosphere system. Within the interdisciplinary field campaign BAYSOFI, measurements of radiation, boundary layer micrometeorology and photochemistry, photosynthesis and transpiration were carried out at Freising-Weihenstephan and several locations nearby focusing on short-term effects of the eclipse. Although the overall grosswetterlage on August 11 was not favourable for viewing the eclipse, with clouds covering most of central Europe, observational conditions at Weihenstephan were fair due to a large hole in the cloud layer which appeared just half hour before totality lasting for more than one hour. Thus significant effects of the eclipse on radiation, photolysis rates, OH, the temperature, wind, turbulence structure and stratification, ozone and CO2 fluxes, photosynthesis, transpiration and sap flow of trees could be observed which are reported and discussed in the following sequence of papers

Effects of Elevated Atmospheric CO{sub 2} on Canopy Transpiration in Senescent Spring Wheat

The seasonal course of canopy transpiration and the diurnal courses of latent heat flux of a spring wheat crop were simulated for atmospheric CO{sub 2} concentrations of 370 {micro}mol mol{sup {minus}1} and 550 {micro}mol mol{sup {minus}1}. The hourly weather data, soil parameters and the irrigation and fertilizer treatments of the Free-Air Carbon Dioxide Enrichment wheat experiment in Arizona (1992/93) were used to drive the model. The simulation results were tested against field measurements with special emphasis on the period between anthesis and maturity. A model integrating leaf photosynthesis and stomatal conductance was scaled to a canopy level in order to be used in the wheat growth model. The simulated intercellular CO{sub 2} concentration, C{sub i} was determined from the ratio of C{sub i} to the CO{sub 2} concentration at the leaf surface, C{sub s} the leaf to air specific humidity deficit and a possibly unfulfilled transpiration demand. After anthesis, the measured assimilation rates of the flag leaves decreased more rapidly than their stomatal conductances, leading to a rise in the C{sub i}/C{sub s} ratio. In order to describe this observation, an empirical model approach was developed which took into account the leaf nitrogen content for the calculation of the C{sub i}/C{sub s} ratio. Simulation results obtained with the new model version were in good agreement with the measurements. If changes in the C{sub i}/C{sub s} ratio accorded to the decrease in leaf nitrogen content during leaf senescence were not considered in the model, simulations revealed an underestimation of the daily canopy transpiration of up to 20% and a decrease in simulated seasonal canopy transpiration by 10%. The measured reduction in the seasonal sum of canopy transpiration and soil evaporation owing to CO{sub 2} enrichment, in comparison, was only about 5%

Untersuchung der Auswirkungen erhoehter atmosphaerischer CO_2-Konzentrationen auf Weizenbestaende des Free-Air Carbondioxid Enrichment (FACE)-Experimentes Maricopa (USA) Abschlussbericht

A version of the demeter model was developed which describes both the quantitative and qualitative effects of elevated atmospheric CO_2 on a wheat crop under conditions of limited water and/or nitrogen supply. In the model's photosynthesis and energy balance modules, first versions of components were developed which it should be possible to apply in further ecosystem models (starting with the cereals models of the demeter family). Experimental data from the Maricopa FACE wheat experiments 1992-1996, in which scientists from PIK were involved, were used for the development and testing of the model. Model solutions obtained were applied for the first time of central European climatic and site conditions as part of a regional yield study for the Federal State of Brandenburg. (orig.)Available from TIB Hannover: RR 5801(37) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEBundesministerium fuer Bildung, Wissenschaft, Forschung und Technologie, Bonn (Germany)DEGerman