Canopy cycling of carbon dioxide, water vapour and reactive trace gases: Measurement of fluxes and plan exological modelling

• Applicant: Professor Dr. Franz X. Meixner
• Subject Area: Atmospheric Science
• Term: from 2006 to 2009
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 31825550

The ability of vegetation canopies to absorb trace gases, which are biogenically emitted by the plants and/or by the soil below, became recently known to be an important aspect of atmospheric budgets of trace gases. The amount of absorbed/escaping trace gases is controlled by (a) physiological and/or surface characteristics of vegetation and soils and (b) interaction of turbulent transport with processes of trace gas exchange, and (c) interaction of turbulent transport with atmospheric chemical transformations. In this respect, a better understanding of de-coupling of in-canopy layers, and coupling between vegetation and atmospheric boundary layer is of crucial importance. Distinct differences between the net vertical transport of H²O and that of CO² or reactive trace gases (NO, NO², O³, NH³, HONO, HNO³) are expected. Therefore, the sub-project aims at measuring and modeling of water fluxes and bi-directional trace gas exchange, as well as interactive coupling of the processes involved; long-term and campaign-wise field measurements are complemented by laboratory studies. Biogenic NO emission from soils will be determined by laboratory experiments. During EGER s Intensive Observation Periods, fluxes from and to soils will be quantified by measurements of the soil air profile and by soil chambers. For the investigation of in-canopy storage, canopy cycling, and whole ecosystem exchange of non-reactive and reactive trace gases vertical profiles of concentrations will be measured as well as in-canopy and above canopy fluxes of reactive trace gases (by eddy covariance and modified Bowen-ratio techniques). In the model, canopy structure is represented by 3D (inhomogeneous) distribution of individual plants, resulting in detailed (m-scale) probability density functions for in- and below canopy scalars and fluxes. In-canopy recycling of matter will be treated by extending the decoupling approach for water vapor (¿-reformulation of the Penman-Monteith equation) to other fluxes (e.g., CO², NO, NO², etc.). Effects of surface heterogeneities and de-coupling on net fluxes during the up-scaling process will be included by (a) solving the EGER P3 Reactive trace gases and plant ecology Meixner/Falge respective equations either analytically for the parameter distributions or using Taylor expansions, and (b) constructing effective 1D model parameterizations based on detailed probability density functions.

• DFG Programme: Research Grants