Forest Soils - Source or Sink for Atmospheric Trace Gases? : Biogenic emissions of greenhouse gases caused by arable and animal agriculture - measurement technologies and emission factors

1998

S. 94-104

Bandaufführung

102312

Two years ago a new soil biology working group was established at the Austria Federal Forest Research Centre, which focuses on the production and decomposition of trace gases in forest soils. Three projects were conducted or are still in progress: 1. N2O emissions from Alpine pastures and pastured woodlands. 2. Factors affecting methane and ethylene decomposition in forest soils. 3. N2O, CH4 and CO2 fluxes in beech forests affected by moderate nitrogen loads Results from our first project indicate that afforestation of Alpine pastures, which now occurs in many parts of the Alps, does not neccessarily reduce N2O emissions from the soils. We try to relate these observations to changes in the internal nitrogen cycle. Secondly, we want to extend the current discussion of trace gases to the potential airpollution due to ethylene emissions. Ethylene reacts with OH radicas and hence reduces the sink capacity of the atmosphere for methane. Like methane, ethylene can effectively be decomposed in forest soils but it can also be produced by microbes under anaerobic soil conditions. Although different groups of microorganisms seem to be involved, both ethylene and methane uptake in soils are negatively affected by the addition of mineral nitrogen and by enhanced CO2 concentrations. In our third project we observed that N2O osses from beech forest soils can be substantial when the microbial release of nitrogen is temporarily decoupled from tree development. N2O emissions proved to be lower on a forested wetland in comparison to upland plots. Forests are known as sinks for greenhouse gases as trees assimilate CO2. However, the impact of forest soils on the global budget of greenhouse gases is less clear and I wandt to discuss the question whether the release of CO2 and N2O, and the decomposition of methane mediated by soil bacteria are of any relevance compared to the amounts of CO2 fixed in tree biomass.