Rhizosphere Priming and Methane Oxidation in Agricultural Soil - Effect of Land Use on Atmospheric Concentrations of CO2 and CH4 and Climate Change

Sammanfattning: Rhizosphere interactions have high influence on the fluxes of carbon to and from terrestrial ecosystems. One very important part of the rhizosphere interactions is the rhizosphere priming effect (RPE) which is defined as changes in the decomposition rate of soil organic matter (SOM) in response to labile organic carbon input from plant roots. Changes in decomposition of SOM affect nutrient availability and nutrient cycling, and does also bring changes in emissions of CO2 from soil. Therefore, changes in the RPE can have a crucial impact in the ecosystems of soil and on the atmospheric concentrations of CO2. Oxidation of methane in soil is another component affecting carbon fluxes in soil and global climate. The aim of this study was to test whether differences in priming could be observed in soil of different agricultural land uses; arable land, pasture and ley, and at the same time measuring methane oxidation to test if any differences occurred between the three different land uses. According to the microbial mining hypothesis, it was hypothesized that the highest levels of priming would occur in pasture soil with low availability of nitrogen. Due to expected low concentrations of nitrogen and especially ammonium, methane oxidation was also expected to be highest in pasture. Priming was observed as significant changes in SOM decomposition due to glucose amendments. No significant differences were found between arable land, pasture and ley in terms of SOM respiration, priming or methane oxidation. However, a pattern supporting the stoichiometric decomposition theory was observed, as pasture on average had the lowest priming effect. At the same time, the highest methane oxidation rate was observed on pasture. This indicate low emissions of greenhouse gasses from pasture relative to arable land and ley. However, this pattern is not significantly evident and does need more research.