Print PageThe projected increase in biodiversity loss worldwide has prompted the need to understand the role of diversity in ecosystem functioning. The decomposition of plant litter is an example of such a key function with important implications for nutrient cycling within ecosystems. In a pan-European project (BioCycle), we investigated whether mechanisms behind diversity effects on decomposition are common to litter mixing experiments across five biomes (subarctic, boreal, temperate, Mediterranean and tropical) and across terrestrial (forest floors) and aquatic (forest streams) systems. We conducted ten concerted experiments using a common protocol. Leaf litter from four native tree species in each biome, belonging to one of four functional groups (N-fixer, rapidly decomposing deciduous, slowly decomposing deciduous, evergreen), was exposed in field microcosms in all possible single-species and multiple-species combinations. Mesh size of microcosms was varied to allow access of three different decomposer communities (microorganisms, mesofauna and/or macrofauna) in both terrestrial and aquatic systems. Litter mass loss was quantified to a defined decomposition stage (about 60% of the initial litter mass lost). C and N loss was determined for each individual species in all litter mixtures.
Results/Conclusions
Both biome (representing species identity effects and local environmental conditions) and system (aquatic/ terrestrial) and their interaction explained one quarter of the variation associated with decomposition rates. However, the type of decomposer community also had a highly significant effect on litter mass loss across the ten experiments. Decomposer community type interacted strongly with biome and to a lesser extent with system, but in general, access to the litter by meso- and macrofaunal communities accelerated decomposition, particularly when a N-fixer was present in the litter mixture. We observed no overall species richness effects on litter mass loss across biomes or systems, although there was an overall net positive diversity effect of litter mixing. The presence of each functional group significantly accelerated (N-fixer or rapidly decomposing deciduous litter) or slowed down (slowly decomposing deciduous or evergreen litter) decomposition of litter mixtures. Similarly, the combination of a N-fixer and rapidly decomposing deciduous litter or of a rapidly and slowly decomposing deciduous litter resulted in overall faster decomposition (i.e. a positive net diversity effect) across biomes and systems. Our results suggest that although species identity effects are important, the type of decomposer community present and the occurrence of litter from particular plant functional types and their interactions may provide insight into general mechanisms behind net diversity effects observed in litter mixing experiments.
