Range-expansion effects on the belowground plant microbiome

Plant range expansion is occurring at a rapid pace, largely in response to human-induced climate warming. While the movement of plants along latitudinal and altitudinal gradients is well documented, effects on the belowground microbial communities remains largely unknown. Further, in range expansion not all plant species are equal: in a new range the relatedness between range-expanding plant species and native flora can influence plant-microbe interactions. Here we used a latitudinal gradient across Europe to examine bacterial and fungal communities in the rhizosphere and surrounding soils of range-expanding plant species. We selected range expanders with and without congeneric natives in the new range, and as a control, the congeneric natives, totaling 382 plant individuals collected across Europe. In general, a plant’s status as range expander was a weak predictor of bacterial and fungal community composition. However, microbial communities of range-expanding plant species became more similar to each other farther from their original range. Range expanders unrelated to the native community also experienced a decrease in the ratio of plant pathogens to symbionts, giving weak support to the enemy release hypothesis. Even at a continental scale the effects of plant range expansion on the belowground microbiome are detectable, though changes to specific taxa remain difficult to decipher.