Changes in soil food web structure of the decomposer system with land use intensity in forest systems

 

Scientific investigators:

Prof. Dr. Stefan Scheu

Dr. Melanie Maraun

Dr. Kerstin Heidemann

Dr. Sarah Zieger

Melissa Jüds

(Uni Göttingen)

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 role we know little about these creatures and their interactions due to their small size, high diversity but also their cryptic life.

 

Goals

We investigate the effect of forest land-use on structure of soil animal communities and their trophic interactions. 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, diversity and biomass over time. We then use these data to study trophic relationships of key species, their trophic position and their food resources.

 

Monitoring and the effect of Forest Management

We are investigating inter-annual shifts in soil animal communities. Species fluctuate between years due to changing abiotic (temperature, precipitation) and biotic factors (changes in competition strength, predation or facilitation).

Hypotheses

  • Generally, dominance and trophic structure of the soil animal communities vary little in time, and variations with forest type / land-use intensity are consistent in time.

  • Temporal variations are more pronounced in larger soil animal taxa and increase with trophic level.

Methods

Soil fauna (Macrofauna (Fig. 1) and Mesofauna (Fig. 2)) will be extracted from litter and soil separately using a high gradient canister technique (Fig. 3A). Earthworms will be extracted by the mustard method. Soil animals will be identified to species level and abundance, diversity and biomass will be recorded.
Microbial parameters are essential for the analysis of trophic links of soil animal food webs. Therefore, microbial biomass will be measured by the substrate induced respiration (SIR) method and microbial PLFA patterns using biomarker fatty acids.

 

Diptera community

Dipteran larvae are major components of the decomposer food web and little is known about their feeding behavior and the effect of land use intensity on community structure.

Hypotheses

  • Similar to soil meso- and macrofauna the density of dipteran larvae increases with the thickness of organic layers but varies little with forest type / land-use intensity.
  • The trophic position of dipteran species varies significantly with the thickness of organic layers but little with forest type.

Methods

By using emergence traps (Fig. 3B) we capture Diptera direct after reaching maturity. Stable isotope signature of these individuals reflect the trophic position of larvae which are heavily understudied due to difficulty to identify Diptera larvae to species level.

 

Trophic structure and trophic links in the fungal energy channel as indicated by molecular gut content analyses

The project aims at filling this gap of knowledge of the fungal energy channel by focusing on links between fungi and fungivores. Collembola are a highly diverse group feeding mainly on fungi. We are focusing on species in which their diet has been investigated before in a comprehensive way (stable isotope signatures and fatty acid patterns).

Hypotheses

  • The use of general fungal primers allows to explore the range of fungi consumed by fungivores
  • Specific primers for representative saprotrophic and mycorrhizal fungi allows quantifying the role of saprotrophic vs. mycorrhizal fungi in the diet of fungivorous Collembola.
  • Molecular gut content analysis allows to unravel changes in trophic niches of fungal feeding soil mesofauna species with forest type / land-use intensity.

Methods

Primers for three saprotrophic and mycorrhizal fungi abundant at the study sites will be used.
Six Collembola species will be selected, three representing primary and three representing secondary decomposers. The six species of each of the four forest land-use systems of the three Exploratories will be screened for their fungal diet using specific primers for saprotrophic and mycorrhizal fungi.

Fig. 1: Diversity of soil macrofauna. (a, k): Isopoda; (b, c, d, f): Diplopoda; (e): Opilionida; (g,h): Chilopoda, (j): Gastropoda. © Sarah Zieger
Fig. 2: Diversity of soil mesofauna. (a): MacFayden soil sampler; (b, d, h): Oribatida (moss mites); (c, e, f, g, I, j: Collembola (springtails). © Sarah Zieger
Fig. 3: Sampling methods to extract soil animals; A: High gradient canister technique for soil samples; B: Emergence traps to obtain freshly hatched Diptera.

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