Biological invasions have significant impacts on ecosystems across the Earth, making their mechanisms of great importance. Many recent studies have focused on the plant-associated microbiome as a potential invasion mechanism. It has been hypothesized that by cultivating their own microbial community, invasive plants may dominate a community through escape from native pathogens coupled with unfettered interactions with generalist mutualists. Further, because site nutrients could impact the abundance of mutualists, such as mycorrhizae, and pathogen associates, the balance between mutualist and pathogen associates may depend on nutrient content.
We surveyed the native and non-native lineages of Phragmites australis to test this hypothesis. We collected root samples from populations of both lineages at eight sites across Michigan, USA that differed with respect to nutrient availability. Root tissues were surface sterilized and freeze dried prior to genomic DNA extraction. The internal transcribed spacer (ITS) of fungal rDNA was amplified and sequenced to identify the fungal taxa in roots. Bacterial 16s rRNA gene was amplified and sequenced to identify bacterial taxa. Roots of each lineage were also stained and examined for fungal hyphae presence using microscopy.
Results/Conclusions
Hyphal counts indicate that colonization was higher for the non-native (18 ± 3%) lineage than the native (7 ± 1%) across all sites (P < 0.0001). Site was also a significant predictor of variation in colonization percentage (P = 0.0005), although total soil N was not. Community analysis from amplified DNA revealed that site was a significant predictor of variation in root fungal communities (P = 0.001), but plant lineage and total soil N were not. Ascomycota was by far the most abundant phylum, making up 91% of the sequences recovered whereas Glomeromycota composed only 0.2%. This suggests that many of the hyphae counted via microscopy were likely endophytes or pathogens.
A comparison of phylotype taxonomy to FUNGuild determined 48% of fungal taxa were pathogenic. Another 33% were determined to be saprotrophic and ~10% were described as symbionts. When grouped by trophic mode, site was still a significant predictor of community variation (P = 0.005) while lineage and nutrient status were not. This suggests that, contrary to the hypothesized relationship, non-native and native Phragmites have similar internal fungal mutualist and pathogen communities. Additionally, while the compositions may differ by site, they do not seem to be impacted by soil nitrogen.