Where, when and how plant–soil feedback matters in a changing world

It is increasingly acknowledged that plant–soil feedbacks may play an important role in driving the composition of plant communities and functioning of terrestrial ecosystems. However, the mechanistic understanding of plant–soil feedbacks, as well as their roles in natural ecosystems in proportion to other possible drivers, is still in its infancy. Such knowledge will enhance our capacity to determine the contribution of plant–soil feedback to community and ecosystem responses under global environmental change. Here, we review how plant–soil feedbacks may develop under extreme drought and precipitation events, CO₂ and nitrogen enrichment, temperature increase, land use change and plant species loss vs. gain. We present a framework for opening the ‘black box of soil’ considering the responses of the various biotic components (enemies, symbionts and decomposers) of plant–soil feedback to the global environmental changes, and we discuss how to integrate these components to understand and predict the net effects of plant–soil feedbacks under the various scenarios of change. To gain an understanding of how plant–soil feedback plays out in realistic settings, we also use the framework to discuss its interaction with other drivers of plant community composition, including competition, facilitation, herbivory, and soil physical and chemical properties. We conclude that understanding the role that plant–soil feedback plays in shaping the responses of plant community composition and ecosystem processes to global environmental changes requires unravelling the individual contributions of enemies, symbionts and decomposers. These biotic factors may show different response rates and strengths, thereby resulting in different net magnitudes and directions of plant–soil feedbacks under various scenarios of global change. We also need tests of plant–soil feedback under more realistic conditions to determine its contribution to changes in patterns and processes in the field, both at ecologically and evolutionary relevant time-scales.