Changes in soil food web structure of the decomposer system with land use intensity in forest systems
Prof. Dr. Stefan Scheu
Dr. Melanie Maraun
Dr. Kerstin Heidemann
Dr. Sarah Zieger
In our project “LitterLinks“, we investigate the effect of forest land-use on structure of soil animal communities and their trophic interactions. Soil food webs are an essential part of terrestrial ecosystems and closely linked to aboveground systems. In soil, animals act as decomposer of dead organic matter, as root feeders or as ecosystem engineers, which improve soil structure by mixing soil layers. Despite their important roles we know little about these creatures and their interactions, much due to their small size, high diversity but also their opaque lifestyle.
The goals of this project are two-fold: First, we characterize the animal communities of the soil and litter layer in differently managed forests and record shifts in abundance and diversity over time. We then use these data to study trophic relationships of key species, their trophic position and their food resources.
In our “trenching-experiment”, we want to investigate the importance of above-ground processes for structure of the soil food web. By cutting tree roots we stopped flow of root exsudates into soil, thereby reducing an important nutrient resource for mycorrhizal fungi and bacteria which will eventually alter the microbial and animal community.
1. Land-use change alters composition of animal decomposer community in a predictable way.
2. Land-use change has only little effect on type and strength of trophic interaction between decomposer animals and their food resources.
We record abundance and diversity of soil animals using heat extraction of soil cores. To characterize land-use types we also record biotic and abiotic factors, such as microbial biomass, soi pH and litter mass.
To analyse trophic interactions we employ three different methods, which allow us to illustrate the soil food web in unmatched detail: We use stable isotope analysis (ratios of 13C/12C- and 15N/14N) to identify trophic level and basal resources of soil animals. Fatty acid analysis shows if a consumer is linked to the bacterial or fungal pathway in soil. PCR-based molecular gut content analysis detects prey DNA in the guts of animal consumers and allows species-specific tracking of trophic interactions. This method will also be used to screen guts of collembolan and oribatid mites for mycorrhizal fungi, soil algae and nematode prey and to assess their respective importance in differently managed forests. All these data will then be used to model whole food webs and to assess effect of land-use on structure and dynamcis of soil animal communities.
Changes in the trophic structure of soil animal communities in response to forest management
Prof. Dr. Stefan Scheu
Dr. Melanie Maraun
PD Dr. Liliane Rueß
(Humboldt Universität Berlin)
- Species composition of the decomposer community changes in a predictable and consistent manner with forest management.
- Links between decomposers and their food resources change little with intensity and type of land use.
LitterLinks investigates changes in the structure of soil animal communities with forest type and land use intensity. Soil animals form an integral and essential part of terrestrial ecosystems and are closely linked to the aboveground system. Decomposer animals process dead organic matter including plant leaf litter root deposits, root feeders directly influences plant growth and soil engineers such as earthworms alter the structure of the soil thereby enhancing nutrient mineralization and plant nutrient capture. The services of the soil animal community provided for the functioning of ecosystems and for humans are diverse, nevertheless, the interactions and regulatory forces in decomposer systems are poorly understood. This is due to methodological difficulties including the opaqueness of the soil, the small size of soil organisms making their identification difficult and the fact that the assessment of density, biomass and species richness is laborious.
The work of our project intends to identify key taxa in litter and soil of forest sites with different land use type and to investigate changes in community composition and species diversity. For this purpose soil animals are extracted from soil cores by heat and determined to species level. The determination is done by the PhD, master and bachelor students. Contributions of other projects complement the work. Oribatid mites are investigated by Georgia Erdmann (Frass), protozoa by Jan Weinert (NanoFauna) and woodlice by Roswitha Ehnes (ModelWeb).
Data on additional biotic and abiotic factors including microbial respiration, acidity of soil and litter and the thickness of the litter layer have been measured allowing the characterization of land use types and interpretation of site specific differences.
After the determination of species we will analyze the food relationships between representative soil animal taxa, their trophic position and basal food resource by employing three methodologies complementing each other:
- Stable isotope analysis (13C/12C and 15N/14N ratios) of soil animals and potential resources (e.g. leaf litter) allows evaluating the basal resources of food webs and the trophic position of species in food web.
- Fatty acid analysis traces the incorporation of fatty acids from food into the body tissue of an organism. By analyzing fatty acid patterns bacterial and fungal food chains are separated.
- Molecular gut content analysis detects DNA fragments of prey in the gut of predators and allows to trace prey species.
Data on density, biomass and trophic interrelationships of key taxa will be used to establish empirically based food web models by the project ModelWeb. This will allow to uncover the structure of decomposer communities in European beech forest soils in unprecedented detail and to evaluate the impact of forest management on the structure and functioning of decomposer systems.