An international study involving the Consejo Superior de Investigaciones Científicas (CSIC) has shown that changes in land use are favoring the expansion of soil protists —key unicellular microorganisms in soil food webs— from temperate regions towards subtropical areas, beyond their natural distribution.
This displacement generates profound ecological alterations and contributes to the loss of microbial diversity in soils at a continental scale, a phenomenon known as biological homogenization.
Invisible microorganisms, visible impacts
While there has been extensive research on how land use affects plant and animal species, soil microbiota —especially protists— has received less attention.
This research reveals that human activities are facilitating the dispersion of generalist protists, which are colonizing new habitats in subtropical regions, displacing native communities.
This transregional species flow creates microbial invasions hotspots, especially in poorly studied tropical and subtropical areas, where the introduction of exotic species could reconfigure ecological balances and reduce soil functional diversity.
Metabarcoding and biogeography: studying the phenomenon
To understand this expansion, researchers applied metabarcoding techniques in different ecosystems in China: agricultural lands, residential areas, urban parks, and natural forests, in temperate and subtropical regions.
The study allowed tracking the distribution of protists and their relationships with microbial prey and hosts.
The results show that human-dominated land use systems expand the distribution range of generalist protists compared to forests, especially in their displacement from temperate zones to subtropical regions.
pH as a gateway: environmental factors facilitating expansion
One of the most relevant findings is that the increase in soil pH, associated with human practices, decreases the typical acidity of subtropical ecosystems, which eliminates natural barriers and allows temperate protist species to establish in new territories.
However, conversely, the expansion of subtropical species into temperate zones seems limited by a drier climate and even higher pH, restricting their colonization capacity.
Expanding phagotrophs: codispersion and ecological specialization
The research also reveals that interregional spread was more pronounced in phagotrophic protists —those that feed on other microorganisms— than in phototrophs or parasites.
This suggests an ecological codispersion with their prey, especially bacteria, based on specialized predator-prey relationships or similar responses to environmental changes.
Soil biodiversity: a forgotten dimension in land planning
This study highlights that changes in land use not only affect visible biodiversity, but also invisible microbial diversity, with profound ecological consequences.
The biological homogenization driven by the expansion of generalist protists could alter key soil functions, such as nutrient cycling, ecological resilience, and species interactions.
In tropical and subtropical regions, where soil microbiota has been poorly studied, these changes could have irreversible impacts if not integrated into conservation and land planning strategies.
