SG: Understanding local controls on wood decomposition in a regional context

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A critical determinant of the carbon balance of forests is the rate at which dead wood decays. This is determined by the rate at which dead wood is formed and the rate at which it breaks down, or decomposes. Dead wood is also a hotspot for other nutrients to accumulate and it is a home for many species of animals, plants and microbes. Because trees contain a lot of carbon, our understanding of how the carbon cycle might be changing requires a better understanding of the wood decomposition process. With that in mind, this project will decompose logs from five common US tree species across a gradient spanning northeastern to southeastern US temperate forests. Potential controls on wood decomposition rates will be manipulated experimentally, such as the density of dead wood and the types of wood-decomposing fungi growing on the logs. Other factors, such as soil nutrient content, temperature and moisture will be monitored. The tree logs will be collected after a year of decay in the field and brought into the laboratory to assess their decomposition extent and associated wood-decaying fungi. The data will then be analyzed to determine wood decomposition rates under the different conditions. Information from this project will be used to refine predictions of carbon-cycle changes and the effects of environmental change on forests. The results will also provide guidance to the forest industry on management of dead wood stocks in forest.The importance of natural wood decay will be communicated through a collaborative effort with the Peabody Museum of Natural History, by creating "living" dead wood exhibits for public display and use in educating visiting middle-school students. The project will also train both graduate and undergraduate students in research, and will work with high-school summer interns from groups of students that are underrepresented in science. Understanding the processes governing the decomposition of dead wood is essential for forest management, especially to mitigate negative effects of declining dead wood stocks on forest productivity, biodiversity and carbon storage. Controls on decomposition of leaf litter are better resolved, with climate and litter quality considered predominant regulators of decomposition rates at global and regional scales. These factors also regulate decomposition of dead wood, but additional unidentified controls mean that wood decomposition rates at regional scales are hard to predict with reasonable certainty. The objective of this work is to identify important, additional controls, which can then be used to formulate and parameterize carbon cycle models, where wood decomposition is a critical uncertainty. In single site studies, the primary factor affecting wood decomposition rates appears to be fungal community structure. Indeed, the species, strain and interactions of wood-rot fungi are strong determinants of decay rates. In particular, those fungi that aggregate their hyphae into thick mycelial cords are considered dominant agents of decomposition. These hyphal-aggregating fungi are termed non-unit-restricted fungi because their mycelia proliferate and interconnect discrete pieces of wood. The connectivity confers a strong competitive advantage, allowing fungi to rapidly colonize dead wood by accessing a broad suite of nutrient sources. As such, the working hypothesis of our project is: The decomposition of downed dead wood proceeds rapidly when non-unit restricted wood-rot fungi can colonize efficiently. A primary control on colonization, and hence fungal-mediated decomposition rates, is the proximity and abundance of coarse woody material (CWM). The working hypothesis will be tested with observational transects and common-garden experiments across five sites spanning a regional climate gradient in eastern US temperate forests. Transect studies will assess the decomposition of logs of five tree species, across pronounced microclimate gradients, either next to or away from natural CWM. Four common gardens at each site will comprise zero, medium and high levels of CWM, crossed with replicates that use plastic edging to disrupt foraging by non-unit restricted fungi. Competing hypotheses to explain the observed patterns of decomposition will be evaluated using field and laboratory assays estimating abiotic factors and the functional abilities of the decomposer communities. The project will engage high school students through an internship program, where graduating students who have college offers to pursue STEM majors, and who are from backgrounds under-represented in higher education, will pursue a paid, summer research position. The goal is to help redress the low (10%) college matriculation rate of this group. The project will also involve training at the graduate and undergraduate levels. Lastly, public outreach to 6th graders will be developed in collaboration with the Peabody Museum of Natural History, to expand their educational toolkit for school-visit programs, and to promote public interest in fungi, CWM and decomposition.