Microbial Colonization Strategies and Resource Partitioning in Grassland Soils under Different Land-Use Intensities

Project phase 2017 - 2020

 

Scientific investigators:

Prof. Dr. Ellen Kandeler

Dr. Sven Marhan

Dr. Anna Abrahao

(Uni Hohenheim)

Background

Within this project we analyze small and large scale effects of land-use intensity on abundance and function of microorganisms in grassland soils. The current phase builds upon the three former project phases during the time period 2008–2017, in which an influence of land-use intensity on the spatial distribution of soil microorganisms on a 10 x 10 m scale was revealed. It was shown that spatial differences of soil microorganisms are only encompassed on a small (< 12 cm) or next larger (> 10 m) scale. Congruously to these results, the current project phase (term 2017–2020) analyzes the distribution and function of soil microorganisms at the smallest spatial scale and at regional level.


The research work consists of 4 major blocks:


1. Colonization of new surfaces (minerals, organo-mineral complexes and roots) by microorganisms.

2. Partitioning of nutrient resources between bacteria and fungi in detritusphere (litter decomposition layer) and rhizosphere (root surrounding zone).

3. Reactions of the microbial community towards changes in land-use intensity of grassland soils at regional scale.

4. Influence of physico-chemical soil properties on soil microbial communities in grassland soils under different land use intensity.

The investigations of the first two blocks are based on mineral cores – plastic rings filled with minerals that are enclosed with fine gauze (50 µm mesh size) at the top and bottom side. These prevent ingrowth of roots, but allows unhampered colonization by bacteria and fungi. The mineral cores are buried in 8 cm soil depth in five grassland sites with high and in five grassland sites with low land-use intensity within the exploratory Schwäbische Alb.

To give detailed statements about the chronology of colonization and nutrient use, mineral cores were sampled and analyzed after 1, 3, 6, 12, and 30 months.

The feeding preferences of bacteria and fungi as well as nutrient acquisition strategies of plants between newly introduced and already existing nutrient sources is analyzed. At this, a mineral-root mixture is introduced into the soil: minerals are mixed with isotopically labeled (13C and 15N) plant roots of orchard grass (Dactylis glomerata) and perennial rye-grass (Lolium perenne) and buried in the research sites.

These so called isotopic labels enable us to gain accurate insights into nutrient cycles, colonization strategies and food webs of soil microorganisms and plants. Phrasing it simple: we can determine who arrives at which time and who is eaten by whom in the soil.

In the third research block we analyze if and how microbial communities react to short term changes in land-use intensity at the regional scale. Within the framework of two big sampling campaigns, one in May 2011 and one in May 2014, soil samples were taken from the top 10 cm in 150 grassland sites in all three exploratories (Schwäbische Alb, Hainich-Dün and Schorfheide Chorin). The sampling of identical sites with a time lag of three years enables conclusions about the influence of region and land-use intensity on short- and longterm effects, so that following questions can be answered:

1) Which soil microbiological changes occurred between 2011 and 2014?

2) Which of these changes are due to changes in land-use intensity?

3) Are there short- and longterm effects of land-use intensity on microbial communities and their functions in grassland soils?

In the fourth research block we will deepen the existing knowledge on the influence of land-use intensity on soil microbial habitats colonized over time depending on physical and chemical soil characteristics. To achieve this, we will analyze the relationships between the physical habitat conditions (soil pore system) and the soil microorganisms (bacteria, fungi, protozoa).

 

Cooperation

Additionally to our central analyses, we cooperate intensively with the following projects and experiments within the Biodiversity Exploratories, in which we provide or receive analytical, staff or interpretative legwork:

Besides this, an intensive information exchange takes place with the following projects:

Soil Microbial Communities in Grasslands – Biogeography at the Local and Regional Scale

Project phase 2011-2017

Scientific investigators:

Prof. Dr. Ellen Kandeler

Dr. Sven Marhan

(University of Hohenheim, Stuttgart)

 

Goals

(University of Hohenheim, Stuttgart)
1. Plant community composition and seasonality in resource partitioning on a local scale
2. Climate, soil texture, and geology show more pronounced effects than land use intensity at a regional scale

 

Methods

 1. Spatial patterns of a following parameters are measured at a subplot of one experimental plot at the Exploratory Schwäbische Alb:

  •    Biogeochemical soil properties
  •    Recalcitrant organic compounds
  •    Metabolic profiling of DOC
  •    PLFA, ergosterol
  •    Abundance of bacteria, archaea, fungi
  •    Denitrifiers
  •    Enzyme activities (C-, N-, P-cycle)
  •    Geostatistics

 

 Working groups participating in this experiment:
Fischer (University of Bern) – plant community compostion, shoot biomass
Schloter (Research Center for Env. Health, Munich) – Archaeal and bacterial nitrifiers, N2 fixing microorganisms
Buscot/Wubet (UFZ Halle) – Ascomycetes, Basidiomycetes, AM mycorrhiza in soil
Bonkowski (University of Cologne) – Protozoa
Rillig, Hempel (FU Berlin) – AM mycorrhiza inside roots, root biomass
Overmann, Friedrich (German Collection of Microorganism and Cell Cultures, Braunschweig; University of Bremen) – Acidobacteria

 2. Sampling of denitrifiers, enzyme activities (C-, N-, P- cycle), PLFA, ergosterol, and biogeochemical soil properties studied at all 50 grassland EPs

 

 

 

Effect of Land-Use Intensity on Spatial Structure and Function of Soil Microbial Communities

Project phase 2008-2011

 

Scientific investigators:

Prof. Dr. Ellen Kandeler

Dr. Sven Marhan

Dr. Christian Poll

(University of Hohenheim, Stuttgart)

This project will clarify whether land-use intensity of grasslands influences functional diversity of soil microorganisms in the three exploratories. The focus will be on C- and N-cycling as key processes in terrestrial ecosystems. We hypothesize that grasslands of different land-use could be classified by general soil microbial properties similar to plant based classification approaches. Therefore, fuzzy modeling will be applied using 1200 reference values that were collected across Europe over the past 20 years. In a next step, we will apply geostatistical techniques on soil enzyme activities, which characterize microbial functioning in C- and N-cycling. We hypothesize that increasing land-use intensity will decrease the spatial heterogeneity of microbial processes by decreasing soil microhabitat and plant diversity. Similarly, we expect land-use to modify specific functions of the microbial community. The density and community structure of denitrifying bacteria as key players of the N-cycle will be assessed by analyzing functional genes (narG, nirK, nirS, nosZ). Linking density of functional genes with nitrate reductase activity will help to understand the regulation of N-cycling in terrestrial ecosystems. All data will be linked to above ground biodiversity and will further enlighten the relationship of ecosystem functioning and biotic diversity. Therefore, information on below-ground functional diversity at different resolution will help to understand the impact of land-use intensity on spatial patterns of grassland plant species.


Field work (soil sampling) and study design:

 

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