Species level differences in decomposition rates and deadwood carbon storage in the southeastern United States

The dynamics of nutrient cycling and longevity of carbon stored in deadwood varies across ecosystems and is frequently modeled as a function of climate. However, interspecific differences in physiochemical properties also influence decomposition. In diverse forests, particularly those in the southeastern United States, our understanding of species-specific rates of decomposition is limited. To investigate these decomposition pathways, including structural and chemical changes, we established a common garden experiment using eight common tree species (Acer rubrum, Carya ovata, Juniperus virginiana, Liriodendron styraciflua, Maclura pomifera, Pinus taeda, Quercus alba, Quercus pagoda) replicated across three forested sites in central Mississippi, USA. We measured changes in wood mass, carbon, nitrogen, and spectral properties via FTIR spectroscopy over two years. After 24 months, M. pomifera decomposed the slowest, with 89.0 ± 0.9 % mass remaining; L. styraciflua had the fastest decomposition with 27.4 ± 4.4 % mass remaining followed by A. rubrum (39.2 ± 5.6 %). Pinus taeda had the greatest carbon concentration in both fresh wood (50.7 ± 0.4 %) and after 24 months (52.5 ± 0.5; p < 0.001) although M. pomifera had the greatest increase in carbon relative to remaining mass (∆4.7 ± 0.6 %) highlighting the role these two species may play in long-term storage of carbon. Species with the fastest decomposition, L. styraciflua and A. rubrum, had the greatest change in spectral properties, indicating higher loss of cellulose through decomposition and exposure of lignin. In contrast, M. pomifera and Q. alba had the strongest structural stability, with minimal change in spectra. Results of this study demonstrate interspecific controls on deadwood decomposition in southeastern forests and highlight the variable response to multiple interacting drivers.