GRK 1086 The Role of Biodiversity for Biogeochemical Cycles and Biotic Interactions in Temperate Deciduous Forests

Project description A4

Scientific advisor
Prof. Dr. S. Scheu

Project

Mechanisms determining effects of tree species diversity on soil fauna in the rhizosphere and the soil litter interface

The project focuses on the biodiversity and activity of soil meso- and macrofauna in the Hainich National Park (Thuringia, Germany). The effects of different broad-leaved tree species and species mixtures on the soil food web are analyzed. To separate the effect of single tree species from the effect of tree diversity, a new approach of small-scale clusters is used. A cluster consists of three trees arranged in a triangle. Species include beech (Fagus sylvatica,), ash (Fraxinus excelsior), lime (Tilia cordata and T. platyphyllos), hornbeam (Carpinus betulus) and maple (Acer pseudoplatanus), the dominating tree species in the research area. One, two and three-species clusters were set up resulting in 25 combinations of tree species. In these clusters soil and litter samples of 20 and 5 cm diameter were taken in May 2008 and the fauna was extracted by heat.
To analyze the trophic structure of the soil food web, we analyze natural variations in stable isotope ratios (13C/12C and 15N/14N) and use stable isotopes as tracers. For the latter, beech and ash seedlings were labelled with 13C and 15N in a greenhouse using 13C enriched CO2 and 15N labelled nutrient solution.
In a laboratory experiment the flux of root derived carbon and nitrogen into the soil food web is investigated. Therefore, young beech and ash trees were excavated from the the Hainich forest and placed into mesocosms including natural soil core, leaf litter and soil fauna. The systems were incubated in the greenhouse for five months and labelled with 13C enriched CO2 and 15N labelled nutrient solution. The soil fauna was extracted by heat and determined to species level. The species that incorporated the label reflect the flux of carbon, respectively nitrogen, into the soil food web. By following both the 13C and 15N signal, we expect to be able to separate the trophic pathway via root resources from that via detritus (and associated saprotrophic fungi) resources. To separate species that feed on mycorrhizal vs saprotrophic fungi, 13C signatures in microbial PLFAs and animal NLFAs will be analyzed in cooperation with Carolin Fornaçon (Project B6). An in-situ 13C labelling experiment with young trees will be conducted together with the other subprojects of the graduate program to determine the fate of root-derived carbon in soil.
An interdisciplinary field experiment is conducted in the Hainich National Park. Mesocosms with the 13C and 15N labelled leaf litter are used to determine the effects of litter quality and litter mixtures on the partitioning of litter carbon and nitrogen. Together with the subprojects A1 (Jasmin Weiße), B5 (Christina Langenbruch) and B6 (Andrea Scheibe), we will follow the flux of litter C and N into mycorrhizae, bacteria, saprotrophic fungi and macro and mesofauna food web components.


Methods


  • Heat extraction of the soil fauna from litter and soil samples
  • Production of 13C and 15N labelled tree seedlings (beech and ash) in a greenhouse using 13C enriched CO2 and 15N labelled nutrient solution
  • Incubation of labelled and unlabelled leaf and root litter in different combinations
  • Analysis of stable isotopes (15N, 13C) of the soil fauna
  • Pulse labelling of tree seedlings and following the label into the soil food web