Lauren C. Cline, Jonathan S. Schilling, Jon Menke, Emily Groenhof, Peter G. Kennedy
Decomposition represents an important process in the global carbon (C) cycle, as C locked into plant tissues is released as CO2 into the atmosphere by microorganisms. Because wood makes up a substantial amount of both living and dead plant tissue, the rate of wood decay has important implications for the amount of C entering the atmosphere. While rates of wood decay are often estimated by temperature and precipitation at regional scales (i.e., hundreds of kilometers), mounting evidence suggests that the diversity and identity of fungal decomposers may be an important governor of wood decomposition at smaller spatial scales (i.e., meters). For example, endophytes – a group of fungi that colonize living plant tissues without causing plant harm – may gain a ‘home field advantage’ during initial stages of wood decomposition. Specifically, arriving first may allow certain endophytes to immediately begin wood decomposition following plant death and increase in abundance in the absence of other microbial decomposers. The rapid growth of DNA-based technologies provides an exciting opportunity to investigate whether fungal endophytes have long-term effects on decomposition as colonists of living plant tissues. Over a period of four years, we compared birch log decomposition when endophytes were absent (endophytes removed via wood sterilization) versus present (un-sterilized wood) in a field experiment in a Minnesota forest. Quantifying the types of fungi in wood using DNA-based sequencing, as well as the rate and type of wood decay, we found that endophyte presence changed the identity of fungi that colonized wood in the first two years of the experiment and also increased rates of wood decay. These results indicate that certain fungal endophytes serve as important initiators of wood decomposition and also deter other fungi from colonizing wood in the early stages of decomposition. However, the presence or absence of endophytes did not influence the types of wood components that were decayed, suggesting that other environmental factors influence wood rot types. Together, these results suggest that endophytes may shape the initial stages of wood decomposition, and that understanding the conditions that increase the strength and duration of their home field advantage has implications for rates of decomposition and ultimately terrestrial C cycles.
Image caption: A wood sample harvested after 42 months of decomposition on the forest floor at the Cloquet Forestry Center in Minnesota.