Epsilon Open Archive

Abstract

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.