Measuring N2 and N2O fluxes and related processes at high sensitivity and resolution in the field using advanced stable isotopic tools as a basis for model evaluation

点击翻译按钮获取中文摘要

Field scale denitrification data suitable to validate N2 fluxes in denitrification models are cur-rently missing due to previous methodical limitations and the extreme spatio-temporal hetero-geneity of denitrification. Until now, it was thus not possible to evaluate accuracy of models to predict denitrification at the field scale. Therefore, it is necessary to obtain activity data at this scale to better understand denitrification control and as a basis to support the evaluation and upscaling of modelling concepts developed in phase I of our research unit. We will use new and improved stable isotope approaches to provide denitrification data sets comprising as much detail on activity and regulation as possible as a basis to evaluate existing and new de-nitrification models that are applied and/or developed by DASIM subprojects (P7, P8, PC). During phase I our current work focussed on establishing lab and field methods and included controlled lab incubations. For the current application of phase II we will focus at the field scale and propose to work on the following tasks: Tasks 1 and 2 will complete work that was fore-seen for phase I and include determination of (Task 1) the minimum averaging soil volume for N2 and N2O fluxes from arable soils, and (Task 2) the anaerobic soil volume fraction of DASIM soils. Tasks 3 to 5 will cover preparatory work for subsequent field flux studies, including fur-ther development and field-scale testing of the 15N gas flux method (Task 3), establishing a field measurement system (Task 4), and calibrating the isotopocule mapping approach to iden-tify fungal denitrification based on natural abundance isotopic signatures of N2O (Task 5). Task 6 will include field experiments to quantify N2 and N2O fluxes, contributing processes and control factors in cropped soils to elucidate field-scale denitrification dynamics and as a basis for calibration and validation of existing as well as new models developed by DASIM partners. Finally, Task 7 is foreseen to use the data obtained from Task 6 to evaluate selected existing biogeochemical models. The work program will be realised in collaboration with five partners supplying support in field infrastructure and experimentation, modelling of diffusive gas fluxes, continuous in situ measurement of soil nitrate, stable isotope analysis and evaluation of bio-geochemical models.