A new study shows that the way land is used determines the types and diversity of predatory soil microorganisms. A researcher says that, from a conservation perspective, clearing woodlands to make way for agricultural cropland or converting cropland into woodlands changes the microbial composition of the soil.
Soil is a complex ecosystem. In addition to minerals and other inorganic material, soil also comprises thousands of strains of bacteria, viruses and fungi as well as protists: single-celled organisms that are more closely related to humans than they are to bacteria.
Scientists have studied viruses, bacteria and fungi in soil for many years but have not focused much on soil protists and their role in the overall planetary ecosystem.
However, this is changing now that researchers have conducted a major study on the prevalence of soil protists in various locations in Europe. The research shows that the composition of soil protist communities varies between woodlands, croplands and grasslands.
These differences can affect biodiversity, which becomes crucial when woodlands are cleared to create cropland or when cropland is converted to woodland.
“Like all other organisms, protists have an important role in the global ecosystem. Learning more about their prevalence in different types of soil is therefore important, since this knowledge can potentially be used to understand differences in biochemical processes in cropland soil versus woodland soil,” explains a researcher behind the study, Leho Tedersoo, Professor, Institute of Science and Technology, University of Tartu, Estonia.
The research has been published in Soil Biology and Biochemistry.
Protists – overlooked but everywhere
Although protists are unknown to many people, they are among the most abundant organisms on Earth.
Viruses are the most abundant, followed by bacteria and then protists.
Soil contains about 1,000 times more bacteria than protists, but the number of protists is still incredibly large.
Protists have many roles in terrestrial and aquatic ecosystems. Some predate on bacteria or fungi, and as the main predators of pathogenic fungi or bacteria, they naturally control microorganisms that can harm humans.
Analysed soil from 1,000 sites in Europe
Leho Tedersoo and colleagues aimed to investigate differences in the prevalence and diversity of protist communities in various types of soil across Europe.
To investigate the biodiversity of soil organisms on the European scale and understand their function across grassland, woodlands and cropland, the European Union Joint Research Centre site in Ispra, Italy initiated the European Commission’s Land Use and Coverage Area Frame Survey (LUCAS).
The researchers analysed 1,000 soil samples for the prevalence of protists and investigated variation between the soil samples.
“The study is part of a larger study characterising how land use and other microorganisms influence biodiversity. This can enhance knowledge on the development of antimicrobial resistance, factors that promote the development of pathogens in soil and other topics,” says Leho Tedersoo.
Land use changes the composition of microbial communities
The study found huge differences in the composition of protists between the soil types examined, especially between cropland and woodland.
Leho Tedersoo compares the findings to what happens when land is cleared of all vegetation.
The first thing is the emergence of pioneer species that start to grow because there is now room for them. In the plant kingdom, this refers to plants with small leaves that do not tolerate shade especially well.
Similarly, the researchers found that cropland was dominated by pioneering protist species that seize the opportunity in an ecosystem with less competition.
Important from a conservation perspective
The researchers found several types of protists in cropland soil, but the various samples of cropland soil were quite homogeneous.
This means that there may have been greater variation in species in each cropland soil sample. Conversely, the composition of protists between the samples from woodlands differed more. Cropland soil also had more pathogenic protists.
“This provides fundamental knowledge about protists, but determining what this knowledge can be used for is not easy,” notes Leho Tedersoo, adding that an obvious difference between cropland and woodland soils is that cropland is human-made.
This means that changing land use from woodland to cropland or from grassland to woodland changes the biodiversity underfoot.
“This can be important from a conservation perspective. Changing land use from cropland to woodland reduces the abundance of protists in the soil. Conversely, the change from woodland to cropland can mean more pathogenic protists. This changes the function of the overall microbiological ecosystem,” concludes Leho Tedersoo.
