The interaction between carbon and nitrogen during litter decomposition
Sammanfattning: Litter decomposition is essential for the cycling of elements in ecosystems. How carbon (C) and nitrogen (N) interact during litter decomposition is, however, not yet fully understood. This thesis studies litter decomposition with the aim of increasing our understanding of the interactions between C and N. The areas in focus are litter mixtures, mycorrhizal fungi, and various N:C ratios. The decomposition rate of litter mixtures can differ from that expected on the basis of the decomposition rate of the single components. This thesis shows that changed decomposition rates in litter mixtures can be linked to a transfer of N between the litters. Besides the typical decomposers, the saprotrophs, also mycorrhizal fungi can decompose organic matter. This thesis explores how mycorrhizal fungi interact with their plant partner under different N availabilities to modify the C and N dynamics of the plant and in the soil. The results indicate that in order to understand how decomposition is influenced by a changing N availability, we need an increased understanding of the decomposer ability of the mycorrhizal fungi and the plant–fungus relation in mycorrhizal associations. It is problematic to estimate the parameters describing the relation between C and N during decomposition. This thesis shows that the key parameter to estimate is the critical N:C ratio, i.e. the litter N:C ratio at which N immobilisation switches to mineralisation.
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