Decomposition is an important process in nutrient cycling in any ecosystem and is driven largely by activity of extracellular enzymes secreted by the microbial community. At edges between forest and field ecosystems, decomposition slows drastically with the sharp change in moisture regime. However, it is unclear how decomposition rates change at softer edges (e.g., between two forest types) where the change in environmental variables is not as steep as at forest-field edges. The goal of our study was to test decomposition rates across three forest-forest ecotones in temperate deciduous forests. We hypothesized that decomposition rate would be slower in ecotones than in ecosystem centers because of changes in abiotic soil variables leading to changes in microbial communities at ecotones. We tested this hypothesis using leaves that spanned a gradient of leaf recalcitrance (red oak, sugar maple, and shagbark hickory). We placed leaf litter bags in ecosystem centers and in ecotones between upland, bottomland, and riparian forests in December 2017. Collections occurred every six months for eighteen months; remaining leavers were dried, weighed, and ashed to measure decomposition. As a proxy for investment in acquisition of carbon, nitrogen, and phosphorus by the microbial community, we measured microbial extracellular enzyme activity.
Results/Conclusions
Among forest types, decomposition was faster in the center of the bottomland forest than the centers of upland and riparian forest for labile red maple and shagbark hickory leaves, but not red oak. Red oak decomposition was approximately the same across all three habitat types. Among ecotone types, decomposition rates in bottomland-upland ecotones was more rapid than for the bottomland-riparian or upland-riparian ecotones. We found that both ecotone type and leaf recalcitrance play critical roles in how much litter decomposition occurred over the course of the study in both ecotones and ecosystem centers. Overall, these preliminary results suggest that decomposition is fastest in the wettest parts of the forest and that mixing of forest abiotic factors in ecotones, as well as leaf chemistry, plays a role in how quickly litter breaks down. Upcoming analysis of enzyme activity will help us further identify factors that drive decomposition in these systems as well as an overall better understanding of shifting nutrient limitations between edges and ecosystem centers.