Plant-soil feedbacks: a meta-analytical review

Recent studies suggest that plant-soil feedbacks (PSFs) may provide mechanisms for plant diversity, succession, and invasion. To determine whether there is general support for these hypotheses, we conducted a meta-analysis of PSF experiments, determining effect sizes among plant types, ecosystems, and experimental approaches. Overall, PSFs had a medium negative effect size, indicating that most plants create soils that decrease growth of conspecifics. PSFs were very large and negative for annual and early-successional species, supporting the hypothesis that PSFs maintain diversity by accelerating species replacement (e.g., succession). Across all studies, non-native plants did not benefit from PSFs; however, in studies that measured non-native and native PSFs in the same study system, non-natives did benefit from PSFs. In a comparison of life-forms, grasses demonstrated more negative PSFs than forbs, shrubs, and trees. A review of PSF methodologies showed that experiments using sterilized/inoculated soils, greenhouse conditions, and manipulative experiments to cultivate soils exaggerated PSFs compared to experiments that used whole field soils, field conditions, and natural experiments to cultivate soils, respectively. Our findings provide broad support for the role of PSFs in plant community assembly, but also underscore the need for expanded testing under field conditions.