Interacting effects of leaf litter species and macrofauna on decomposition in different litter environments

Abstract

The leaf litter environment (single species versus mixed species), and interactions between litter diversity and macrofauna are thought to be important in influencing decomposition rates. However, the role of soil macrofauna in the breakdown of different species of leaf litter is poorly understood. In this study we examine the multiple biotic controls of decomposition – litter quality, soil macrofauna and litter environment and their interactions. The influence of soil macrofauna and litter environment on the decomposition of six deciduous tree species (Fraxinus excelsior L., Acer pseudoplatanus L., Acer campestre L., Corylus avellana L., Quercus robur L., Fagus sylvatica L.) was investigated in a temperate forest, Wytham Woods, Southern England. We used litterbags that selectively excluded macrofauna to assess the relative importance of macrofauna versus microbial, micro and mesofauna decomposition, and placed single species bags in either conspecific single species or mixed species litter environments. The study was designed to separate plant species composition effects on litter decomposition rates, allowing us to evaluate whether mixed species litter environments affect decomposition rates compared to single species litter environments, and if so whether the effects vary among litter species, over time, and with regard to the presence of soil macrofauna. All species had faster rates of decomposition when macrofauna were present, with 22–41% of the total mass loss attributed to macrofauna. Macrofauna were most important for easily decomposable species as soon as the leaves were placed on the ground, but were most important for recalcitrant species after nine months in the field. The mass loss rates did not differ between mixed and single species litter environments, indicating that observed differences between single species and mixed species litterbags in previous field studies are due to the direct contact of neighbouring species inside the litterbag rather than the litter environment in which they are placed.