Plant and microbial impacts of an invasive species vary across an environmental gradient

Invasive plants often successfully occupy large areas encompassing broad environmental gradients in their invaded range, yet how invader dominance and effects on ecological communities vary across the landscape has rarely been explored. Furthermore, while impacts of invasion plant are well studied, it is not understood whether responses above-ground (plant) below-ground (microbial) coupled. Here we test patterns Phragmites australis (common reed) a field survey eight sites situated salinity gradient, ranging from freshwater to saline marsh, Southeast Louisiana. At each site, surveyed composition used metabarcoding methods assess soil fungal bacterial plots within dense stand, transition zone ~50:50 Phragmites:native plants, native-only areas. We hypothesized that Phragmites' abundance impact above- would gradient be found weak evidence varied gradient: stem densities increased slightly with salinity, litter accumulation more fresh compared brackish. stronger microbial salinity. strongly reduced native density greater reductions Plant species richness displayed consistent decreases gradient; however, sharply only brackish sites. effect community became as increased. Plants microbes exhibited coupled magnitude compositional shifts brought by Phragmites, but were Synthesis. Overall, variability particularly impacts, suggests may difficult generalize single-site or single-ecosystem studies. However, showed some Phragmites; thus understanding gives insight into occurring below-ground.