Microbial Ecology Meets Macroecology: Developing a Process‐Based Understanding of the Microbial Role in Global Ecosystems

Microorganisms inhabit all biomes on Earth. The terrestrial microbiome spans from leaf to soil, including all surrounding organisms, and microbial effects extend across ecological, spatial, and temporal scales. The terrestrial microbiome mediates plant invasions, plant succession, nutrient cycling, and even ecosystem carbon feedback to the atmosphere. Yet, for far too long, a lack of data constrained the elucidation of macroecological phenomena of terrestrial microbial communities over space and time. However, during the 2000s, breakthroughs in DNA sequencing technology were co‐opted by environmental microbiologists to look deeper into the terrestrial microbiome than ever before possible. Rapid declines in the cost of DNA sequencing technology spurred more than a decade of work to understand spatial patterns of microbial communities (Fierer and Jackson 2006, Amend et al. 2012, Tedersoo et al. 2014, Davison et al. 2015). This accumulation of knowledge has enabled new global analyses of microbial communities (Ramirez et al. 2018) and their associated functions (Bahram et al. 2018) in both space (Tedersoo et al. 2014) and time (Averill et al. 2019). While discovery science remains an essential and important part of microbial ecology, these data are pushing the field of microbial macroecology toward process‐ and hypothesis‐driven science. For example, species distribution models of microbial species (Kivlin et al. 2017) and dominant functional groups (Delgado‐Baquerizo et al. 2018) allow us to explicitly include microbial guilds into process‐based ecosystem models of carbon and nutrient cycling (Sulman et al. 2019). Furthermore, combining microbial distribution data with that of plants, animals, and humans reveals that microbial associations can influence ecosystem‐level processes such as plant nutrient cycling (Mushinski et al. 2019, Averill et al. 2019) and litter decomposition (Steidinger et al. 2019), as well as plant community response to global change (Averill et al. 2018, Jo et al. 2019). These studies, among others, demonstrate the critical influence of microorganisms over entire ecosystems and highlight the need to incorporate microbial interactions with other components of ecosystems if we intend to fully appreciate the fate of global ecological populations, communities, and ecosystems. At the Ecological Society of America 2019 Annual Meeting, we convened a symposium to synthesize strides made toward a process‐driven understanding of microbial communities at large scales and subsequent impacts on ecosystem functions. Here, we provide an overview