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Evidence is mounting that the immense diversity of microorganisms and animals that live belowground contributes significantly to shaping aboveground biodiversity and the functioning of terrestrial ecosystems. Our understanding of how this belowground biodiversity is distributed, and how it regulates the structure and functioning of terrestrial ecosystems, is rapidly growing. Evidence also points to soil biodiversity as having a key role in determining the ecological and evolutionary responses of terrestrial ecosystems to current and future environmental change. Here we reviewrecent progress and propose avenues for further research in this field.
T he last two decades have witnessed an enormous research effort directed at understanding how biodiversity loss impacts ecosystem functioning, and the influence of this on the goods and services that ecosystems provide1. This research has led to the general consensus that biodiversity loss reduces most ecosystem functions and impairs their sta- bility over time, and that functional traits of species have a major role in determining diversity effects1. The majority of research on this topic, how- ever, has had an aboveground focus; as a result, our understanding of the functional consequences of biodiversity loss belowground is less well developed. This lack of knowledge hampers our ability to predict the con- sequences of realistic scenarios of diversity change, especially since below- ground biodiversity represents one of the largest reservoirs of biological diversity on Earth2,3.
Soil communities are extremely complex and diverse, with millions of species and billions of individual organisms being found within a single ecosystem (Table 1 ), ranging from microscopic bacteria and fungi, through to larger organisms, such as earthworms, ants and moles (Fig. 1). Our under- standing of this hidden biodiversity is limited, at least compared to what is known about aboveground diversity. But the last decade has witnessed a growing number of studies testing how belowground communities are distributed in space and time, how they respond to global change and what the consequences of biodiversity change are for plant community dynamics, aboveground trophic interactions, and biogeochemical cycles. Moreover, soil biodiversity research is now entering a new era: awareness is growing among scientists and policy makers of the importance of soil biodiversity for the supply of ecosystem goods and services to human society4; and a new generation of tools are available to...