Soil biota and plant diversity: Soil biota, including symbionts such as mycorrhizal fungi and nitrogen-fixing bacteria, as well as fungal and bacterial pathogens, affect terrestrial plant diversity and growth patterns (see the Perspective by van der Putten). Teste et al. monitored growth and survival in Australian shrubland plant species paired with soil biota from plants of the same species and from other plants that use different nutrient acquisition strategies. Plant-soil feedbacks appear to drive local plant diversity through interactions between the different types of plants and their associated soil biota. Bennett et al. studied plant-soil feedbacks in soil and seeds from 550 populations of 55 species of North American trees. Feedbacks ranged from positive to negative, depending on the type of mycorrhizal association, and were related to how densely the same species occurred in natural populations. Science , this issue p. 134 , p. 173 ; see also p. 181

The factors that influence a plant's ability to invade are not well understood. Many mechanisms are involved and the relative importance of different mechanisms depends on the specific invasion. Here we consider one factor—mycorrhizal symbioses. These symbioses are ubiquitous interactions involving the plants and soil fungi of most terrestrial ecosystems. We develop a conceptual framework for considering mycorrhizal symbioses in plant species invasions. The most critical aspects of this framework are: (a) the mycorrhizal status and (b) the growth response of the invading plant, (c) the ability of the plant to associate with different fungi, (d) the quality of the plant as a host for local fungi and feedback dynamics, (e) the biogeography and dispersal of the fungi, (f) the introduction and spread of the fungi, and (g) the ecological consequences of the creation of novel mycorrhizas. These aspects can critically influence the trajectory of a plant invasion, and this symbiosis deserves more attention in plant invasion biology.

John Klironomos, Martin Zobel, Mark Tibbett, William D. Stock, Matthias C. Rillig, Jeri L. Parrent, Mari Moora, Alexander M. Koch, José M. Facelli, Evelina Facelli, Ian A. Dickie and James D. Beve