| The proposed study wants to evaluate the effects of increased temperature and enrichment with nitrogen on the accumulation of organic matter in soils. Knowledge on these effects is important because soils worldwide encompass a very large amount of organic carbon. Should the rate of formation and decay of this organic matter be affected, then this would influence atmospheric CO2 concentrations. If global warming in combination with nitrogen enrichment would accelerate organic matter decay, then there would be a positive feedback mechanism. Enrichment of terrestrial ecosystems with nitrogen occurs in densely populated areas as a consequence of intensive agriculture and industry. This environmental disturbance might also influence climate change through its effects on the terrestrial soil carbon. This project encompasses a study of the production and decay of dead plant material in grasslands, with an emphasis on the more refractory, ?recalcitrant? part of the material, which has not received much attention yet because of methodological constraints, but is of the utmost importance for long-term accumulation of soil carbon. Through field studies in Iceland where geothermal activity has created naturally heated sites close to unheated sites, long-term effects of temperature increase can be identified. In addition, experiments will be carried out in climate-controlled growth chambers, where plants will be cultivated under conditions of a 13CO2 atmosphere and 15N nutrition. The recalcitrant part of the plant material will be used for decomposition experiments in conditions of different temperature and N availability. The stable isotope signatures will enable testing of the effect of root exudates on the decay of the recalcitrant components. Further, the importance of fungi versus bacteria during the breakdown process will be investigated by using PFLA techniques. |
