Global projections of the soil microbiome in the Anthropocene

Soil microbes are essential for maintaining life-supporting ecosystem services, but projections of how these microbes will be affected by global change scenarios are lacking. Therefore, we aim to provide projections of future soil microbial distribution using multiple global change scenarios. We used a global database of soil microbial communities across six continents to estimate past and future trends of the soil microbiome. To do so, we used structural equation models to include the direct and indirect effects of climate and land-use change in our predictions, using current climate (temperature and precipitation) and land-use projections between 1950 and 2090. Local bacterial richness will increase in all scenarios of climate and land-use change considered, although this increase will be followed by a generalized community homogenization process affecting more than 85% of terrestrial ecosystems. Changes in the relative abundance of functional genes associated with the increases in bacterial richness are also expected. Based on an ecological cluster analysis our results suggest that phylotypes such as Geodermatophilus sp. (typical desert bacteria), Mycobacterium sp. (which are known to include important human pathogens), Streptomyces mirabilis (major producers of antibiotic resistance genes), or potential fungal soil-borne plant pathogens belonging to Ascomycota fungi (Venturia sp, Devriesia sp), will become more abundant in their communities. Local bacterial richness will increase in all scenarios of climate and land-use change considered, although this increase will be followed by a generalized community homogenization process affecting more than 85% of terrestrial ecosystems. Changes in the relative abundance of functional genes associated with the increases in bacterial richness are also expected. Based on an ecological cluster analysis our results suggest that phylotypes such as Geodermatophilus sp. (typical desert bacteria), Mycobacterium sp. (which are known to include important human pathogens), Streptomyces mirabilis (major producers of antibiotic resistance genes), or potential fungal soil-borne plant pathogens belonging to Ascomycota fungi (Venturia sp, Devriesia sp), will become more abundant in their communities. Our results provide evidence that climate change has a stronger influence on soil microbial communities than land-use change (often including deforestation and agricultural expansion), although most of the climate effects are indirect through other environmental variables (e.g., changes in soil pH). The same was found for microbial functions such as the prevalence of phosphate transport genes. We provide reliable predictions about the changes in the global distribution of microbial communities, showing an increase in alpha diversity and a homogenization of soil microbial communities in the Anthropocene.