Soil fauna as drivers of the architecture of forest floors

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Soil animals are major driving factors of the structure and dynamics of forest floors. We use state-of-the-art methodologies to investigate which soil detritivore taxa contribute to the processing of forest litter material. Analysing natural variations in stable isotope ratios, compound specific lipid and amino acid analyses in detritivore consumers combined with labelling approaches and experimental manipulations will allow understanding their role in the formation and dynamics of forest floors in unprecedented detail. We will focus on three meso- (Collembola, Oribatida, Enchytraeidae) and macrofauna detritivore taxa (Lumbricidae, Diplopoda, Isopoda). Following the overall design of the Research Unit 12 sites dominated by beech but interspersed with maple and spruce will be investigated. The project comprises three work packages: In work package 1, we will study the energy channelling through major detritivore taxa as affected by temperature and nutrient status of forest stands. As basis of the food web microbial communities will be studied using phospholipid fatty acid markers. Trophic niches of detritivores will be investigated by natural variations in stable isotopes as well as compound specific amino acid analysis. Combined with measurements of body size the channelling of basal resources (litter, bacteria, fungi) into detritivore taxa as affected by temperature and nutrient status of forest stands will be evaluated.In work package 2, mesocosms allowing to manipulate access by meso- and macrofauna will be used to evaluate the long-term effects of these detritivore guilds for the formation and dynamics of forest floors. The use of 13C and 15N labelled litter will allow to follow the processing of litter material by and incorporation into detritivore taxa. Compound specific lipid analyses will provide insight into the pathways litter materials are incorporated into detritivore consumers and into long-term effects of major soil detritivore taxa for the dynamics of forest floors as affected by temperature and nutrient status of the forest stands. In work packages 3, we will investigate the role of detritivore soil animals for the spatial spread litter materials. Using 15N labelled litter and measuring its incorporation into detritivore taxa will provide insight into the horizontal and vertical spread of litter materials and its temporal dynamics. Overall, the proposed project will allow novel insights into the functioning of soil detritivore communities and their role in the formation and dynamics of forest floors, and their variation with temperature and nutrient status of forest stands.