Do bacterial diversity and structure respond to diversity of native and exotic-dominated plant communities exposed to irrigation

Background/Question/Methods

In many systems, exotic-dominated plant communities are replacing native plant communities, with subsequent declines in biodiversity and potential impacts on ecosystem functioning.  Given the widespread recognition of plant-microbe interactions, we tested the extent to which bacterial diversity and structure are affected by the origin (native vs. exotic) of plant communities. Further, climate change impacts on plant-microbe interactions were investigated via irrigation treatments.  Using deep sequencing of 16S rRNA, we explored the sensitivity of bacterial community composition to changes in plant diversity and climate.  Our working hypothesis is that through differences in substrate inputs, plant origin and irrigation will affect the diversity and structure of bacterial communities. We predict that bacterial diversity will be greatest under native communities, while exotic communities that have lost plant diversity will host bacterial communities dominated by fewer taxa. Alternatively, soil microbial communities may not respond to changes mediated by plant communities, in which case the direct effects of irrigation on the soil habitat may affect bacterial diversity and structure. Overall, this study will reveal the role of plant-microbe interactions in grassland ecosystems in the face of global change.

Results/Conclusions

Plant diversity was 41% greater in native compared to exotic plots (P < 0.05), yet no significant differences in bacterial diversity were detected.  RDA analysis with Monte-Carlo permutation test revealed that plant origin explained only a small proportion (3.5%) of the variability in bacterial beta-diversity (P < 0.006). No significant main or interaction effects of irrigation on bacterial diversity were detected.  Nonetheless the relative composition of the bacterial communities varied among treatments.  Our results suggest that over short time scales (4 years) soil bacterial diversity has not been measurably affected by native vs. exotic plant origin in the Blackland Prairie region of Texas, nor by the main or interaction effects of altered precipitation.  Instead, the soil habitat appears to regulate the structure of microbial communities over short time scales.