Widespread tree mortality is occurring globally due to factors such as climatic change, the introduction of invasive pests, and habitat degradation. As foundation tree species die, an influx of carbon enters the soil and has the potential to alter carbon cycling and the microbial communities responsible for this process. A short-term increase in carbon loss from the soil could exacerbate climatic change as this carbon enters the atmosphere. Further, loss of foundation plant species could have lasting effects on microbial communities and carbon cycling, as novel plant communities establish thus altering the influx of carbon substrates entering the soil. To date, there has been little progress in understanding how microbial community structure and function respond to the loss of a foundational tree species. Using hemlock (Tsuga canadensis) as a model system, this study was focused to understand how tree stress and mortality impacts soil microbial community structure, potential function, and ecosystem carbon cycling in an eastern deciduous forest.
In October of 2015, a long-term manipulation was established in central Tennessee. Twenty plots were established centered around an individual mature hemlock tree. In ten plots, the hemlock tree was girdled to induce stress and eventual tree mortality. Soil bacterial and fungal community composition were assessed using amplicon sequencing, and shotgun metagenomic sequencing was employed to understand potential functional shifts in the community. Standard substrate decomposition was assessed over the course of the year.
Results/Conclusions
After just six months, girdling hemlock trees resulted in an ~ 10% increase in standard substrate decomposition, and an increase in the relative abundance of a saprotrophic fungal species demonstrating that a shifting soil microbial community may drive increases in carbon release as a result of tree mortality. Current work is focused to understand how the soil metagenome changes in response to tree stress and if genes involved in carbon degradation increase in abundance as decomposition rates speed up in the girdled plots.