Decomposition of eucalyptus leaves in litter mixtures

Leaf litter from Eucalyptus globulus was decomposed alone and in mixture with either oak (Quercus petraea), ash (Fraxinus excelsior) or birch (Betula pendula) leaf litter under laboratory conditions. Decomposition was monitored as CO2 release and leaching of inorganic N over 13 weeks. At the end of the experiment, litters were separated into their species components and analyzed for mineral composition (K, Ca, Mg, P and N) and mass loss. Differences between expected and measured rates of decomposition were evaluated, based on a comparison between the results from the pure litters and the mixtures. Mixing eucalyptus litter with oak litter resulted in enhanced total CO2 release from the litter mixture when compared with the pure components. Similar, but less marked, positive interactions were observed in mixtures with eucalyptus + birch and eucalyptus + ash. Decomposition of eucalyptus litter in the presence of the other litters also influenced N mineralisation, resulting in greater net N retention in the mixtures with eucalyptus + oak and eucalyptus + birch, but a decrease in mixture with ash. The results support the conclusion that the decomposition of litters in mixtures cannot be readily predicted from the behaviour of the component litters decomposing in isolation. We suggest that mixtures of eucalyptus with other litters could be one mechanism by which the high productivity rates of eucalyptus plantations may be maintained, and that manipulation of litter mixtures could assist in synchronising nutrient release and plant uptake.