1. ¹Department of Multitrophic Interactions, Netherlands Institute of Ecology, Heteren, The Netherlands
2. ²Laboratory of Nematology, Wageningen University, Wageningen, The Netherlands
3. ³Department of Integrative Biology, University of Guelph, Guelph, Ontario, Canada
4. ⁴Department of Forest Vegetation Ecology, Swedish University of Agricultural Sciences, Umeå, Sweden
5. ⁵Landcare Research, Lincoln, New Zealand

Correspondence: Professor WH van der Putten, Department of Multitrophic Interactions, Netherlands Institute of Ecology, PO Box 40, Boterhoeksestraat 48, 6666 ZG Heteren, The Netherlands. E-mail: w.vanderputten@nioo.knaw.nl

Received 5 February 2007; Revised 21 February 2007; Accepted 21 February 2007.

Abstract

Invasive microbes, plants and animals are a major threat to the composition and functioning of ecosystems; however, the mechanistic basis of why exotic species can be so abundant and disruptive is not well understood. Most studies have focused on invasive plants and animals, although few have considered the effects of invasive microbes, or interactions of invasive plant and animal species with microbial communities. Here, we review effects of invasive plants on soil microbial communities and discuss consequences for plant performance, plant community structure and ecosystem processes. In addition, we briefly discuss effects of invasive soil microbes on plant communities, which has been less well studied, and effects of invasive animals on soil decomposers and ecosystem functioning. We do this by considering each of three important functional groups of microbes, namely soil microbial parasites and pathogens, mutualistic symbionts and decomposers. We conclude that invasive plants, pathogenic and symbiotic soil microbes will have strongest effects on the abundance of individual species, community diversity and ecosystem functioning. Invasive decomposer microbes probably have little impact, because of limited specificity and great functional redundancy. However, invasive plants and animals can have major effects on microbial decomposition in soil. We propose that understanding, predicting and counteracting consequences of enhanced global homogenization of natural communities through introducing exotic plants, animals and microbes will require future studies on how pathogenic, symbiotic and decomposer soil microbes interact, how they are influenced by higher trophic level organisms and how their combined effects are influencing the composition and functioning of ecosystems.