As non-native plant species invade grasslands, they form novel interactions and influence ecosystem functioning. Previous studies showed that exotic species affect soil microbiota, but the results were limited to changes in microbial abundance, and isolation/characterization of cultivable microorganisms. Advancement of molecular techniques, e.g. next-generation sequencing (NGS), allows detection of uncultured microorganisms constituting a large undescribed group that might play an important role in terrestrial processes and plant-microbe interactions. We tested for differences in soil microbial community structure and diversity in native vs. exotic plant communities using a common garden experiment in Central Texas. The plots (n=64) were mixtures of nine native or exotic plant species that were either exposed to summer irrigation or not in a 2 x 2 factorial design. Bulk soil samples were collected in 2009, 2014, and 2015 (2nd, 7th, and 8th year of the study). DNA extraction was followed by amplification and sequencing of V4 region of 16S rRNA gene and Internal Transcribed Spacer (ITS) region. The quality filtered sequences were assigned taxonomically and analyzed statistically to test differences in microbial communities between native and exotic plots. Plant composition, net primary productivity (NPP) were estimated annually. N mineralization with cation and anion exchange resin membranes was measured in 2015.
Exotic plots had higher NPP on average, low diversity with a greater proportion of C4 grasses, and lower N mineralization than native plots (all p < 0.05). Simpson’s and Shannon’s diversity measures, and Chao1 richness estimator of bacterial and fungal communities did not vary between four tested groups, however they showed variations across the sampling years. Native and exotic plant communities differed in fungal communities (perMANOVA, p < 0.05) while differences in bacterial communities were less pronounced. Summer precipitation did not cause any changes either in native or exotic plants but there was a significant interaction between the plant origin and irrigation in fungal community in 2015 (p=0.007). Some differentially abundant Operational Taxonomic Units (OTUs) caused differences in fungal community structure between native and exotic plots across years. Stagonospora (cereal fungal pathogen) and Humicola grisea (decomposer) were abundant in native plots, while exotic plots had higher abundance of OTUs from Hypocreales order (potential saprobes). Fungal composition was strongly correlated with plant composition in exotic but not in native plots, while bacterial composition was correlated in both. The exotic-dominated communities affect microbial communities significantly. The further study should address ecological relationships (e.g. determination of generalists/specialist among microbial phylotypes).