The rise of plant–soil feedback in ecology and evolution

Over the last two decades, a growing literature examining the interactions, mechanisms and players in plant–microbial–soil dynamics has provided key insight into a host of ecological phenomena from succession to plant invasion to community organization (van der Putten et al. 2013). These studies have shown that legacy effects of plant–soil interactions are largely driven by shifts in soil microbial communities that have both short- and long-term effects for future plant populations. Ecological feedbacks occur when interactions at one time determine (either positively or negatively) the performance or interactions of organisms at another time. Feedbacks may have evolutionary consequences when variation in fitness, and thus natural selection, is mediated by these past interactions. Plant–soil feedback research recognizes and reveals complex above- and belowground interactions, mediated by microbial communities, which are far greater than the sum of their parts. Previous collections on the topic of plant–soil feedbacks reviewed the state of knowledge of the field and highlighted important research gaps, largely focusing on ecological process and not evolutionary process. Yet, it becomes clear that ecological and evolutionary processes interact, and recognition of such interactions can provide novel insights and understanding into process and pattern in a variety of contexts. This special feature advances our knowledge of plant–soil feedback research, focusing on three key areas: (i) evolutionary mechanisms and consequences, (ii) plant–microbial interaction mechanisms and predictive models and (iii) plant–soil feedback and global change. Together these papers show, with reviews and empirical data, that we are making great strides in understanding the evolutionary mechanisms and consequences of plant–soil feedback at local and macroscales, with new methods and models enabling us to better predict when and how plant–soil feedbacks will occur, and that by understanding plant–soil feedbacks, we may gain greater insight into plant and soil responses to climate change and better inform restoration efforts. Very little work to date has focused on the evolutionary mechanisms and consequences of plant–soil feedback. Because populations are individuals that vary genetically, and because individuals respond differently to the environmental conditions created by feedbacks, evolution is inevitable. This special feature focuses on this topic and highlights important new directions in plant–soil feedback that are just beginning to be examined. In the lead article, Van Nuland et al. (2016) highlight how plant–soil feedback research has the potential to link evolution and ecosystem ecology like never before and shows the importance and feasibility of this approach. terHorst & Zee (2016) describe how genetically based interactions between plants and soil microbes offer a promising direction for future research as strong selection plus their short generation times allow for rapid evolution and tight coevolutionary dynamics. As an empirical test, Evans et al. (2016) identify components of an eco-evolutionary feedback operating in the invasive garlic mustard, where heritable phenotypic variation of an allelopathic compound drives plant–soil interactions that feedback to alter demographic rates. Wooliver et al. (2016) demonstrate large-scale evolutionary effects of plant–soil linkages by examining phylogenetic responses of plants to soil nitrogen, thus showing macroevolutionary consequences of plant–soil feedbacks. Herrera Paredes & Lebeis's review (2016) show how new methods and statistical approaches are making it easier to test the microbial mechanisms of plant–soil feedback, such as sequencing and bioinformatic tools that link plant and microbial phenotypes with functional gene content. Revillini, Gehring & Johnson (2016) use a novel approach with optimal resource allocation models to characterize species interactions and predict plant–soil feedback outcomes across resource gradients. In a global change context, van der Putten et al. (2016) present a plant–soil feedback triangle that balances symbiont, decomposer and enemy contributions to net plant–soil feedback values under human-induced global changes, demonstrating how climate change may shift species interactions and feedback responses. Lastly, de la Pena et al. (2016) show how the legacy of soil changes due to plant–soil interactions impacts plant community assembly and should be considered to improve the success of restoration efforts. These advances in plant–soil feedback research, along with ongoing mathematical/theoretical advances, further demonstrate how important plant–soil feedback research is for understanding not only the ecology, but also the evolution of complex interactions – as well as showing us how much we still have to learn (Van Nuland et al. 2016). We are confident that researchers in this field are up to the challenge. We are grateful to all of the contributions of the authors and reviewers that made this special feature possible. We value all of the insight provided on this topic and are excited to see what this collection of papers inspires in future work on this important topic. Special thanks to Chuck Fox and Jennifer Meyer at Functional Ecology for allowing us to put together this special feature and for all of their guidance and support throughout the process.