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).
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:
Further project contribution of Prof. Dr. Ellen Kandeler: MicroSYSteM II
Further project contribution of Dr. Sven Marhan: BE_CH4