Drivers of decomposition and the detrital invertebrate community differ across a hummock-hollow microtopology in Boreal peatlands

Background/Question/Methods

In boreal peatlands, low decomposition rates are the underlying cause of carbon sequestration. Decomposition of litter can be affected by factors relating to soil moisture and temperature, litter quality, and the biotic decomposer community, among others. Exploring how these drivers interact will provide a better understanding of carbon dynamics in boreal peatlands. We measured the decomposition of three common peatland plant functional types (Sphagnum moss, Carex sedge, and Chamaedaphne shrub), and associated oribatid mite communities (Acari: Oribatida) using litterbags placed in hollows (wet depressions) and hummocks (dry, raised areas) of a boreal peatland near White River, Ontario, Canada. After one year of litterbags staying in the field, we looked for a correlation between oribatid mite species composition and litter mass loss, and subsequently asked whether plant type or microtopology drives oribatid mite community and decomposition rates. We predicted oribatid mite communities to be more diverse in hollows than on hummocks due to the higher moisture levels of this microhabitat and that Sphagnum mosses would have the lowest decomposition rates due to their lowest carbon quality.

Results/Conclusions

Decomposition was significantly different between all plant litter types, and greatest in sedge, but was not significantly different between hummock and hollow microhabitats. The decomposer community displayed an opposite pattern, significantly affected by microhabitat where richness and abundance of oribatid mites were greater in hollows than on hummocks. Plant litter type did not affect oribatid mite community structure in hollows but was a determinant of oribatid dominance in hummocks. These results suggest that abiotic environmental conditions are the main drivers of community structure for decomposers, while plant litter quality is a more important determinant of decomposition dynamics in boreal peatlands.