Maestre, F.T., Departamento de Biología y Geología, Física y Química Inorgánica, Universidad Rey Juan Carlos, Móstoles, Spain
Delgado-Baquerizo, M., Hawkesbury Institute for the Environment, Western Sydney University, Penrith, NSW, Australia
Jeffries, T.C., Hawkesbury Institute for the Environment, Western Sydney University, Penrith, NSW, Australia
Eldridge, D.J., School of Biological, Earth and Environmental Sciences, University of New South Wales, Sydney, NSW, Australia
Ochoa, V., Departamento de Biología y Geología, Física y Química Inorgánica, Universidad Rey Juan Carlos, Móstoles, Spain
Gozalo, B., Departamento de Biología y Geología, Física y Química Inorgánica, Universidad Rey Juan Carlos, Móstoles, Spain
Quero, J.L., Departamento de Ingeniería Forestal, Escuela Técnica Superior de Ingeniería Agronómica y de Montes, Universidad de Córdoba, Campus de Rabanales, Córdoba, Spain
García-Gómez, M., Departamento de Ingeniería y Morfología del Terreno, Escuela Técnica Superior de Ingenieros de Caminos, Canales y Puertos, Universidad Politécnica de Madrid, Madrid, Spain
Gallardo, A., Departamento de Sistemas Físicos, Químicos y Naturales, Universidad Pablo de Olavide, Sevilla, Spain
Ulrich, W., Department of Ecology and Biogeography, Nicolaus Copernicus University in Toruń, Lwowska 1, Toruń, Poland
Bowker, M.A., School of Forestry, Northern Arizona University, Flagstaff, AZ, United States
Arredondo, T., Division de Ciencias Ambientales, Instituto Potosino de Investigacion Cientifica y Tecnologica, San Luis Potosí, SLP, Mexico
Barraza-Zepeda, C., Departamento de Biología, Facultad de Ciencias, Universidad de La Serena, Benavente 980, Casilla 554, La Serena, Chile
Bran, D., Nacional de Tecnología Agropecuaria, Estación Experimental San Carlos de Bariloche, San Carlos de Bariloche, Río Negro, Argentina
Florentino, A., Instituto de Edafología, Facultad de Agronomía, Universidad Central de Venezuela, Campus UCVMaracay, Estado Aragua, Venezuela
Gaitán, J., Instituto de Suelos, Centro de Investigación en Recursos Naturales, Instituto Nacional de Tecnología Agropecuaria, Nicolas Repetto y de los Reseros Sin Número, Hurlingham, Buenos Aires, Argentina
Gutiérrez, J.R., Departamento de Biología, Facultad de Ciencias, Universidad de La Serena, Benavente 980, Casilla 554, La Serena, Chile, Centro de Estudios Avanzados en Zonas Áridas (CEAZA), La Serena, Chile, Instituto de Ecología y Biodiversidad, Facultad de Ciencias, Universidad de Chile, Las Palmeras 3425, Casilla 653, Ñuñoa, Santiago, Chile
Huber-Sannwald, E., Division de Ciencias Ambientales, Instituto Potosino de Investigacion Cientifica y Tecnologica, San Luis Potosí, SLP, Mexico
Jankju, M., Department of Range and Watershed Management, Ferdowsi University of Mashhad, Mashhad, Iran
Mau, R.L., Center for Ecosystem Science and Society, Northern Arizona University, Flagstaff, AZ, United States
Miriti, M., Department of Evolution, Ecology and Organismal Biology, Ohio State University, Columbus, OH, United States
Naseri, K., Department of Range and Watershed Management, Ferdowsi University of Mashhad, Mashhad, Iran
Ospina, A., Instituto de Edafología, Facultad de Agronomía, Universidad Central de Venezuela, Campus UCVMaracay, Estado Aragua, Venezuela
Stavi, I., Dead Sea and Arava Science Center, Yotvata, Israel
Wang, D., Institute of Grassland Science, Key Laboratory for Vegetation Ecology, Northeast Normal University, Changchun, Jilin, China
Woods, N.N., Department of Evolution, Ecology and Organismal Biology, Ohio State University, Columbus, OH, United States
Yuan, X., Institute of Grassland Science, Key Laboratory for Vegetation Ecology, Northeast Normal University, Changchun, Jilin, China
Zaady, E., Department of Natural Resources, Agriculture Research Organization, Ministry of Agriculture, Gilat Research Center, Mobile Post Negev, Israel
Singh, B.K., Hawkesbury Institute for the Environment, Western Sydney University, Penrith, NSW, Australia, Global Centre for Land-Based Innovation, Western Sydney University, Penrith, NSW, Australia

Soil bacteria and fungi play key roles in the functioning of terrestrial ecosystems, yet our understanding of their responses to climate change lags significantly behind that of other organisms. This gap in our understanding is particularly true for drylands, which occupy ∼ 41% of Earth's surface, because no global, systematic assessments of the joint diversity of soil bacteria and fungi have been conducted in these environments to date. Here we present results from a study conducted across 80 dryland sites from all continents, except Antarctica, to assess how changes in aridity affect the composition, abundance, and diversity of soil bacteria and fungi. The diversity and abundance of soil bacteria and fungi was reduced as aridity increased. These results were largely driven by the negative impacts of aridity on soil organic carbon content, which positively affected the abundance and diversity of both bacteria and fungi. Aridity promoted shifts in the composition of soil bacteria, with increases in the relative abundance of Chloroflexi and α-Proteobacteria and decreases in Acidobacteria and Verrucomicrobia. Contrary to what has been reported by previous continental and global-scale studies, soil pH was not a major driver of bacterial diversity, and fungal communities were dominated by Ascomycota. Our results fill a critical gap in our understanding of soil microbial communities in terrestrial ecosystems. They suggest that changes in aridity, such as those predicted by climatechange models, may reduce microbial abundance and diversity, a response that will likely impact the provision of key ecosystem services by global drylands.