Barking up the right tree: ecological insights into the microbiome of bald cypress tree bark

Trees and their associated microbes provide numerous ecosystem services including carbon sequestration, nutrient cycling and phytoremediation. Tree bark represents a large and seasonably stable habitat for microbial communities. However, the tree bark microbiome remains largely understudied, particularly for wetland tree species. In the Lower Mississippi River Basin, bald cypress (Taxodium distichum) are the predominant tree species in many wetlands, including lakes and streams connected to large agroecosystems dominated by row-crop agriculture. These water bodies are often managed for irrigation and drainage needs and are subject to agrochemical runoff from adjacent fields. Thus, we sought to understand how hydrology affects the bald cypress bark microbiome.

We collected 278 bark samples over six months from 18 trees located in three different lakes. Using 16S rRNA gene sequencing, we found that the bald cypress tree bark microbiome was largely consistent between trees within a lake as well as between different lakes, with a core microbiome that includes bacterial taxa that were present in over 95% of samples collected. Hydrology had a significant influence on microbiome structure, with different sections of bark having distinct bacterial communities depending on if the bark was submerged, just above the water, or dry. Water quality was significantly correlated with alpha diversity of wet bark, which was more diverse than dry bark and had higher relative abundances of bacteria that may be providing relevant ecosystem services such as denitrification, methane oxidation, and pollutant degradation.

Wetlands are important for nutrient cycling and water quality regulation. Our study provides insights into microbial dynamics of these ecosystems and how hydrology can impact the microbial communities present, which in turn may be impacting water quality. This work is the first to the describe the bark microbiome of a wetland tree species and lays the groundwork for future studies assessing the functional role of the microbiome in wetland ecosystem services.