Contrasting environmental preferences of photosynthetic and non-photosynthetic soil cyanobacteria across the globe

Aim: Cyanobacteria have shaped the history of life on Earth and continue to play important roles as carbon and nitrogen fixers in terrestrial ecosystems. However, their global distribution and ecological preferences remain poorly understood, particularly for two recently discovered non-photosynthetic cyanobacterial classes (Sericytochromatia and Melainabacteria). Location: Two hundred and thirty-seven locations across six continents encompassing multiple climates (arid, temperate, tropical, continental and polar) and vegetation types (forests, grasslands and shrublands). Time period: Sampling was carried out between 2003 and 2015. Major taxa studied: Photosynthetic and non-photosynthetic cyanobacterial taxa. Methods: We conducted a field survey and used co-occurrence network analysis and structural equation modelling to evaluate the distribution and environmental preferences of soil cyanobacteria across the globe. These ecological preferences were used to create a global atlas (predictive distribution maps) of soil cyanobacteria. Results: Network analyses identified three major groups of cyanobacterial taxa, which resembled the three main cyanobacterial classes: the photosynthetic Oxyphotobacteria-dominated cluster, which were prevalent in arid and semi-arid areas, and the non-photosynthetic Sericytochromatia- and Melainabacteria-dominated clusters, which preferred hyper-arid oligotrophic and acidic/humid environments, respectively. Main conclusions: This study provides new insights into the environmental preferences of non-photosynthetic cyanobacteria in soils globally. Our findings highlight the contrasting environmental preferences among the three clusters of cyanobacteria and suggest that alterations in environmental conditions linked to climate change might result in important changes in the ecology and biogeography of these functionally important microorganisms.