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Biological soil crusts are complex communities consisting of photosynthetically active green algae, cyanobacteria, bryophytes and lichens, heterotrophic fungi, protozoa and bacteria, which cover the top few millimetres of soil.

The organisms and their by-products create a micro-ecosystem, whose ecological function is of great importance in particular on bare soils (e.g., nitrogen fixation by cyanobacteria, primary production, water retention, soil stabilisation or allocation of plant-available nutrients).

Although soil crusts are ecologically important, to date research has mainly focussed on arid and semi-arid habitats. In the first phase, we focused on the biodiversity in soil crusts and their function in biogeochemical phosphorus turnover. These correlations were analysed in greater depth during the second phase. In the current phase, spatial distribution of nutrient turnover in biocrusts will be examined as well as their recovery after ecosystem disturbance.

Picture: The photo looking down shows a close-up of a soil crust.
Bottom crust

We will link the turnover of phosphorus and nitrogen within soil crusts to the abundance and diversity of genes encoding N and P transformation processes. These data will then be linked to crustal organism structure and compared to other microbial hotspots such as the rhizosphere and detritus sphere to understand interactions among all organisms in soil crusts from exploratory forest plots.

A combination of metagenomic and fatty acid profiling of the community structure of bacteria, archaea, fungi, cyanobacteria and algae will be evaluated for the first time in taxonomic depth (what is there in what numbers?). Further, we will use stable isotopes to identify nutrient hotspots in biocrusts and combine this with transcription analyses of microbial groups involved in N and P turnover (What happens where?).

The abundance and functional composition of biocrusts will be evaluated after severe surface disturbances due to tree felling will be analysed. The recovery of biocrusts will be related to their organismic diversity, the land-use intensity of the forest and biogeochemistry of P and N. The concentrations and chemical species of these elements will indicate whether BSCs act as sink or source for P-and N-compounds after disturbance (which does what?).


1. Biocrust communities play a key ecological role in the biogeochemical, often interlinked cycles of N, P and C in forests. Biocrust communities are involved in transformation from inorganic to organic fractions in the biogeochemical cycling of P and N.

2. Biocrust microorganisms prefer organic N molecules. A high availability of N will also increase the mobilisation of P in order to maintain intracellular N:P homeostasis of microorganisms.

3. Functional pattern of biocrusts depend less on the level of disturbance than on site-specific properties. Strong disturbance at plots with low silvicultural management intensity will result in a faster development of biocrusts.

4. Functional pattern of biocrusts differ from those of the rhizosphere and detritusphere at the same site (all microbial hotspots).

Picture: The photo shows pieces of soil crusts lined up on an open palm, wrist, and parts of a forearm.
Soil crust

  • Metagenomic and transcriptomic analyses
  • Amplicon Sequencing of 16S rRNA and 18S rRNA genes
  • qPCR targeting specific genes for N- and P-turnover
  • Fatty acids analyses
  • Total C, N, P determination
  • NanoSIMS and stable isotopes

We found biocrusts especially at disturbed places in the forests, such as skid trails, at slopes and after wind fall or clear cutting. This indicates the important role of biocrusts as first (pioneer) colonisers of free soil and their protective role against erosion. Biocrusts in forests inherit a high diversity of algae with filamentous species being most abundant. Further, we observed a specific bacterial community in the biocrust compared to bulk soil. In particular, the abundance of cellulose-degrading and bacterivore bacteria was higher in biocrusts than in bulk soil.

Biocrusts were described to accumulate carbon and nitrogen in the top soil layer. We could confirm this finding within the exploratories and further extend the current knowledge: biocrusts also enrich phosphorus, especially the organic fraction of P is enhanced. All genes involved in the P-cycling were found in higher abundance, indicating a faster biogeochemical P-turnover in the biocrust compared to bulk soil.


Doc
Glaser K., Albrecht M., Baumann K., Overmann J., Sikorski J. (2022): Biological Soil Crust From Mesic Forests Promote a Specific Bacteria Community. Frontiers for Microbiology 13, 769767. doi: 10.3389/fmicb.2022.769767
More information:  doi.org
Doc
Eigenschaften der Tonfraktion und Grünlandbewirtschaftung beeinflussen die Zusammensetzung und Stabilität der organischen Bodensubstanz auf molekularer Ebene
Baumann K., Eckhardt K.-U., Schöning I., Schrumpf M., Leinweber P. (2022): Clay fraction properties and grassland management imprint on soil organic matter composition and stability at molecular level. Soil Use and Management, doi: 10.1111/sum.12815
More information:  doi.org
Doc
Phosphorus Turnover in Biological Soil Crusts under Drought Stress
Phosphatkreislauf in biologischen Bodenkrusten unter Dürrestress
Zimmer M. (2022): Phosphorus Turnover in Biological Soil Crusts under Drought Stress. Master thesis, Technical University Munich
Doc
Gall C., Ohan J., Glaser K., Karsten U., Schloter M., Scholten T., Schulz S., Seitz S., Kurth J. K. (2022): Biocrusts: Overlooked hotspots in managed mesic soils. Journal of Plant Nutrition and Soil Science 185 (6), 745-751. doi: 10.1002/jpln.202200252
More information:  doi.org

Project in other funding periods

Picture: The photo shows a close-up of liverwort.
Crustfunction I (Contributing project)
#Soil biology & Element cycling  #2014 – 2017  #Drought tolerance […]
Picture: The photo shows a close-up of liverwort.
Crustfunction II (Contributing project)
#Soil biology & Element cycling  #2017 – 2020  #Bacteria […]

Scientific assistants

Jun.-Prof. Dr. Karin Glaser
Project manager
Jun.-Prof. Dr. Karin Glaser
Technische Universität Freiberg
Prof. Dr. Ulf Karsten
Project manager
Prof. Dr. Ulf Karsten
Universität Rostock
Dr. Stefanie Schulz
Project manager
Dr. Stefanie Schulz
Helmholtz Zentrum München
Juliette Ohan
Alumni
Juliette Ohan
Prof. Dr. Peter Leinweber
Employee
Prof. Dr. Peter Leinweber
Universität Rostock
Dr. Karen Baumann
Employee
Dr. Karen Baumann
Universität Vechta
Prof. Dr. Michael Schloter
Employee
Prof. Dr. Michael Schloter
Technische Universität München (TUM)
Dr. Julia Kurth
Employee
Dr. Julia Kurth
Helmholtz Zentrum München
Oluwaseun Ishola
Oluwaseun Ishola
Sandra Kammann
Employee
Sandra Kammann
Universität Rostock
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