The influence of agricultural management practices on microbial functions and networks in biological soil crusts
Microbial Ecology and Applied Microbiology
Final Report Abstract
Biological soil crusts (BSCs) have been identified as hotspots with spatial accumulation of soil microorganisms and nutrients in oligotrophic environments like deserts but they can also be found in agricultural soils especially with a low quality assessment rating. In contrast to desert BSC, BSC of agricultural soils are strongly influenced by land management like physical disturbance, fertilization and plant coverage and thus have to re-assemble frequently. It was the aim of this project to investigate the influence of three management practices (tillage, organic fertilization and mineral fertilization amount) on chemical properties and the microbial community in BSC as well as the potential to produce exo- (EPS) and lipopolysaccharides (LPS), which strongly influence surface wettability and soil aggregate stability. Therefore, samples (BSCs and bulk soil as control) were taken from a field with a low average soil quality within an international organic and mineral nitrogen fertilization experiment conducted by the LUFA Speyer, Germany, to describe the microbial community composition (bacteria, archaea, fungi), abundance and nutrient contents. Moreover, a pot experiment was performed, which tested how the EPS/LPS producing community resembled during BSC development. Our data revealed that: (i) The BSCs on the agricultural soils cover huge parts of the surface of the investigated agricultural site preferably in wheel tracks and close to decaying litter. Based on the high nutrient contents and microbial abundance BSC were classified as copiotroph and are therefore comparable to the trophic level in the rhizosphere. Most of the microorganisms found were heterotrophic bacteria like Actinobacteria, Bacteroidetes, Planctomycetes, Proteobacteria, and Verrucomicrobia and fungi like Ascomycota and Basidiomycota, but also pathogenic fungi were detected in higher amounts, which should be considered for the management strategy after years with severe disease outbreaks. (ii) Cyanobacteria, which are prominent pioneer organisms in BSC development, were detected even in high amounts in BS samples, which might point to initial BSC development stages across the whole agricultural field. (iii) Tillage had a much stronger effect on the bacterial community composition of BSC compared to the bulk soil community, most likely because the BSC assemblage is severely disturbed by the tillage event. The management effect was similar on the BS and BSC fungal community. (iv) The production of EPS and LPS is a central function of BSC, independent of the soil substrate they are growing on. Even if the bacterial community changes during BSC development functionally redundant bacteria take over the production of EPS and LPS. This might have two consequences for agricultural management. Firstly, a good coverage with BSC might protect the soil surface against erosion and desiccation and secondly, the ploughing in BSC material might improve soil aggregate stability by distributing EPS/LPS producing bacteria in the soil.
Publications
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(2018) „Biological Soil Crusts are Nutrient and Microbial Hotspots on Agricultural Soil Surfaces” (ISME17 Conference 2018)
Krawczyk J., Schmid C., Vestergaard G., Albrecht M., Karsten U., Armbruster M., Schloter M., Schulz S.
