The rhizosphere microbiota of plant invaders: an overview of recent advances in the microbiomics of invasive plants

Abstract

Plants in terrestrial systems have evolved in direct association with microbes functioning as both agonists and antagonists of plant fitness and adaptability. As such, investigations that segregate plants and microbes provide only a limited scope of the biotic interactions that dictate plant community structure and composition in natural systems. Invasive plants provide an excellent working model to compare and contrast the effects of microbial communities associated with natural plant populations on plant fitness, adaptation, and fecundity. The last decade of DNA sequencing technology advancements opened the door to microbial community analysis, which has led to an increased awareness of the importance of an organism's microbiome and the disease states associated with microbiome shifts. Employing microbiome analysis to study the symbiotic networks associated with invasive plants will help us to understand what microorganisms contribute to plant fitness in natural systems, how different soil microbial communities impact plant fitness and adaptability, specificity of host-microbe interactions in natural plant populations, and the selective pressures that dictate the structure of above-ground and below-ground biotic communities. This review discusses recent advances in invasive plant biology that have resulted from microbiome analyses as well as the microbial factors that direct plant fitness and adaptability in natural systems.

Keywords: invasive plant; microbiome; plant–microbe interactions; rhizosphere; soil.

FIGURE 1

An overview of plant–microbe interactions that occur in rhizosphere and bulk soils beneath a plant. The soil environment has a direct effect on the plant, the rhizosphere microclimate, and the microbial community in the bulk soil. Root exudates from the plant direct chemical signaling between the plant and the microbial symbiotic network in the soil matrix. Rhizobiota recognize root exudate signals and are recruited to the rhizoplane or root interior. Bulk soil microbes compete for space to colonize the rhizosphere, which results in a rhizosphere microbial community that is derived from the total microbial population in the bulk soil. The microenvironment in the rhizosphere includes the rhizosphere microbiome (<3–5 mm of the root), rhizoplane microbiome (at root–soil interface), and the interior root microbiome. Common symbiotic interactions in the root zone include mycorrhizal fungi, bacterial endophytes, and symbiont nodules.

FIGURE 2

Factors that directly affect the soil microbiota associated with invasive plants and the positive feedbacks on the plant invasion derived from each major group (saprophytes, pathogens, and beneficials). Each of the seven factors directly affect the microbial community structure and function in the soil by imposing some degree of selective pressure wherein certain microbes are not capable of surviving. These seven factors dictate the relative abundance of saprophytes, pathogens, and beneficials that are able to associate with the plant. Two mechanisms of plant invasion that lead to positive feedbacks from these plant–microbe interactions are shown for each group of soil microbes.