Soil microorganisms are strongly impacted by anthropogenic activities and the ongoing global climate change [1]. Understanding the how microbial information may be used to support soil health assessments is crucial for both scientific and policy perspectives to anticipate the functional consequences of future climatic conditions or land use pressures on soil systems [2].
Measurements of soil biology are similar to soil physical and chemical properties in that the interpretation of what constitutes a "good" level for soil health is highly context-specific [3]. The taxonomic and functional diversity of soil microbiome is closely linked to soil health due to soil’s role in dynamic ecosystem processes and the biota’s sensitivity to land management practices [4]. Therefore, selecting microbial metrics to measure soil health depends on the specific soil, site, and aspects of interest.
Denmark is responding to the growing number of EU initiatives to protect soils and the environment by gathering data on complex soil properties that provide a richer picture of soil health. We collected over 7000 topsoil samples from natural and agricultural areas across Denmark, and analyzed their bacterial composition through a DNA metabarcoding approach. We calculated α-diversity and potential functions to bacterial communities. We used spatial layers of soil properties, climate, vegetation, geomorphology, and parent materials to map the α-diversity, and the relative abundance of denitrifiers, methanotrophs and nitrite-oxidizing bacteria.
We used spatialized soil health indicators namely, SOC concentration, bulk density, pH, EC, soil hydrophobicity, SOC sequestration potential, tillage erosion, water erosion, and nitrogen leaching to map the simultaneous presence of potential threats to soil health in Denmark. We considered potential threats to those soils characterized by below-typical SOC and pH values, and above-typical values of pH, BD, EC clay-to-SOC ratio, soil hydrophobicity, SOC loss, tillage erosion, water erosion, and nitrogen leaching. We did not directly include the soil microbial data as soil health indicator. Instead, we explored the relationship between potential threats and our microbial data to understand how taxonomical and functional diversity respond to different soil degradation conditions.
The α-diversity and the relative abundance of functional groups did not decrease as the potential threats to soil health increased. It is possible that threatening soil conditions, which may physically or chemically inhibit, injure, or eliminate certain microbial communities, create opportunities for other organisms to grow and reproduce, thereby increasing diversity in these areas.