A new experimental approach that accounts for a larger number of environmental variables can better capture how soil ecosystems around the world may respond to anthropogenic pressures. "This new approach provides a promising avenue for understanding the impact of multiple, simultaneous drivers in the heavily modified ecosystems that are becoming increasingly common across the globe," writes Peter Manning in a related Perspective. Soils form the foundation of most terrestrial ecosystems: they serve as pools of critical nutrients and microbial life for plants and animals alike. However, soils worldwide face growing pressure from changes in environmental factors such as temperature and precipitation, which are largely linked to human activity. Despite the complexity of global environmental change, most studies of soil function only examine the impact of one to two environmental factors at a time. These single-factor studies can uncover important mechanisms, but new approaches are needed to better grasp how changes in multiple variables will affect soils and the ecosystems they underpin. Inspired by previous studies of species biodiversity, Matthias Rillig and colleagues adopted a new design that uses a pool of up to ten global change factors, including temperature, soil aggregation, and microplastics. The new approach revealed major shifts in the properties of soil and the microbial community; for example, accounting for more factors led to a lower observed genetic diversity among soil fungi. At the highest factorial levels, the authors also saw "ecological surprises" such as a large change in soil water repellency, which was barely affected in single-factor experiments. Although Rillig et al. tested their design in small, relatively simple microcosms, Manning notes that the results could one day help identify dangerous factor combinations and tipping points for soil ecosystems in the future.
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Science