Elevated CO2 affects the rhizosphere microbial community and the growth of two invader plant species differently in semiarid Mediterranean soils.
The rise in atmospheric CO2 levels is foreseen to enhance the growth of exotic invasive plants and potentially alter the rhizosphere microbial community, which in turn could enhance the risk of colonization by such invaders. This response could be determined by the plant type and the features of invaded soil. The goal of this investigation was to compare the effects of elevated CO2 on the rhizosphere bacterial and fungal communities of two invaders with distinct degrees of invasiveness, Nicotiana glauca and Mirabilis jalapa, by growing the plants in five different semiarid soils at ambient (410 ppm) or elevated (760 ppm) CO2. The changes in soil physicochemical, biochemical, and biological features mediated by the invaders were also evaluated. The effect of CO2 supply on shoot dry biomass was only significant for N. glauca, the shoot and root biomass of plants grown under elevated CO2 being approximately 53% and 14% greater, respectively, than those of the plants grown under ambient CO2. Elevated CO2 only promoted shifts in the rhizosphere bacterial community composition and enhanced the bacterial functional potential related to nucleoside and nucleotide biosynthesis and N-cycling in N. glauca. Among the bacterial indicator species, the genera Sphingomonas, Stenotrophobacter, and Gaiella were more abundant in the rhizosphere of N. glauca plants grown under elevated CO2. This study demonstrates that the responses of aboveground and belowground biomass of invasive plants to CO2 enrichment, as well as those of the composition and functioning of soil microbial communities, are dependent on their degree of invasiveness.