Microbe-mediated plant-soil feedback and its roles in a changing world

Plants affect soil conditions, which in turn alter plant growth and interspecific competition, forming plant-soil feedback (PSF) systems. PSF is a good example of bidirectional interactions between biomes and the non-living environments, acting as a major driving force of community structure and ecosystem function. Among the major types of PSF mediated by various soil components, there are many holes in our knowledge of the interactions between PSF mediated by plant species-specific litter and PSF mediated by soil microbes. Here I discuss the role of the functional diversity of microbial decomposers in litter-mediated PSF and also propose new hypotheses on the role of microbial diversity in PSF mediated by pathogenic and mutualistic soil microbes. I also review how PSF interacts with human-induced environmental change, i. e., direct drivers of change in the ecosystem (e. g. climate change and the invasion of alien species). Many authors have suggested that the impact of alien plant species on ecosystems is mediated by PSF, which also interacts with other direct drivers, such as climate change. Using a simple model of litter-mediated PSF with microbial decomposers, I confirm that the interactions between PSF and other direct drivers affect the invasion process of alien species. The model also demonstrates that the functional diversity of microbial decomposers accelerates or decelerates the speed of the invasion depending on the environmental change scenarios. Further theoretical and empirical studies are needed to derive general predictions on how exogenous environmental change induced by human activities alters communities and ecosystems through disturbance or modification of endogenous community-ecosystem interactions, such as the functioning of PSF. © 2012 The Ecological Society of Japan.