Carbon storage dynamics in peatlands: comparing recent- and long-term accumulation histories in southern Patagonia.

Peatlands have been important terrestrial carbon reservoirs throughout the Holocene, yet whether these ecosystems will become stronger or weaker carbon sinks in the future remains debated. While surface peat layers (acrotelm) have a greater apparent rate of carbon accumulation than deeper, millennial-aged peat (catotelm), it is difficult to project how much more aerobic decomposition will take place before the younger surface cohorts join the older deeper ones. Studies have suggested that warming could lead to weakened carbon accumulation in peatlands due to enhanced aerobic decay in the acrotelm, which would lead to a slower transfer of peat into the catotelm, if any. Conversely, other studies have suggested increased C accumulation in the acrotelm and thus, larger long-term carbon transfer into the catotelm under warming conditions because of greater plant productivity and faster peat accumulation. Improving our predictions about the rate of present and future peatland development is important to forecast feedbacks on the global carbon cycle and help inform land management decisions. In this study, we analyzed two peat cores from southern Patagonia to calculate their long- vs. short-peat carbon accumulation rates. The acrotelm rates were compared to the catotelm peat carbon legacies using an empirical modeling approach that allows calculating the future catotelm peat storage based on today's acrotelm characteristics, and thus predict if those recent rates of carbon accumulation will lead to greater or weaker long-term carbon storage in the future. Our results indicate that, depending on local bioclimatic parameters, some peatlands may become stronger carbon sinks in the future, while others may become weaker. In the case of this study, the wetter site is expected to increase its carbon-sink capacity, while our prediction for the drier site is a net decrease in carbon sequestration in the coming decades to centuries.