N2O emissions from soils

This project is part of the large multidisciplinary CCES project RECORD-Catchment, which investigates various aspects of river corridor management in the River Thur catchment. This SNF funded sub-project investigates factors on the microscale that govern the greenhouse gas potential of floodplain and related gleyic forest soils. This includes soil aggregation, plant - soil - microbe interactions and litter accumulations.

Background

This project closely follows up the soil related investigations within the previous CCES project RECORD. In particular, it relates to the observations in the course of this former project and many other studies, that in soils of restored and natural floodplains nitrogen pools, transformation rates and fluxes vary strongly in space and time. More specifically, zones in floodplains that are frequently disturbed by flooding can be considered "hot spots", and the drying phases after major floods "hot moments" of nitrogen cycling and related nitrous oxide emissions (Fig. 2, 3). For more details and references see the predecessor project.

Objectives

The over-arching research question is "what are the driving factors for "hot spots" and "hot moments" of nitrogen cycling in floodplain soils on the micro scale?

To this end we plan

• laboratory experiments assessing the effects of different "micro habitats" on the production and emission of nitrous oxide from floodplain soils and gleyic soils. The "micro habitat effects" include the effects of soil aggregation on the small-scale variability of oxygen availability, of plant root exudation on heterotrophic microbial processes such as nitrogen mineralisation or denitrification, of root induced aeration of the rhizosphere, and of leaf or root litter accumulations on local carbon and oxygen availability. The experiments will be carried out in dedicated microcosms (Fig.  4). This is the topic of a SNF funded Ph.D. project starting in 2014 and involves innovative isotopic approaches to measure gross nitrous oxide production and nitrous oxide source partitioning.
• Test the relevance of the laboratory results in field experiments at the restored section of the Thur River at Niederneunforn (Fig. 1). Experimental treatments are planned to involve treching/clipping to exclude effects of root - soil interactions, and exclusion of aggregate forming soil biota.