Under future climate change scenarios, boreal peatlands can expect warmer, longer growing seasons and alterations to the already fluctuating water tables. With combined increases in atmospheric CO2 concentrations and temperature, we can further expect increased sphagnum growth in these peatlands, and thus, the potential for increased, labile root exudates during the growing season. Root exudates are commonly found as low molecular weight carbon compounds (LMWCC), such as the simple sugar glucose. Increased availability of LMWCC may stimulate an increase in microbial biomass and, indirectly, microbial cell turnover, which provides bio-available carbon (C) and nitrogen (N) compounds for microbial degradation and assimilation. Working at the Spruce and Peatland Responses Under Climatic and Environmental Change (SPRUCE) site in northern Minnesota, we are interested in how the soil microbial community in this system is responding to changes in temperature and moisture. Using experimental microcosms, we explore how the interaction between belowground labile carbon compound inputs and altered climate will impact C and N cycles. This is tested in two simulated phases: an initial warming/drying phase (early summer), and LMWCC pulse with subsequent respiration (late summer). The four substrate additions include two LMWCC (glucose + citrate and glycine) plus chitin and a control (DI).
Results/Conclusions
Cumulative carbon mineralization varied by temperature × moisture manipulation and substrate addition. There was a significant interaction between moisture and temperature, with the greatest C mineralized at high temperature but low moisture. However, the magnitude of the response to climate varied by substrate. For example, glycine-amended communities had the greatest cumulative carbon mineralized at low temperatures, but the lowest at high temperatures. In addition, three of the substrate amendments followed consistent temporal dynamics across temperatures. The glycine addition demonstrated a unique response whereby the timing of peak C mineralization varied by temperature with the warmest temperatures producing the earliest maximum respiration. Glycine treatments also sustained high levels of respiration across the duration of the study resulting in the most narrow differences in cumulative mineralization among climate treatments. From the cumulative carbon mineralization values, peat communities amended with glycine would appear least sensitive to temperature. Collectively, our results indicate that moisture alone, through potential future alterations in the water table, does not alter decomposition. An interaction between increased temperatures and moisture fluctuations may cause future increases in decomposition, and thus, CO2 respiration from peatland ecosystems, but this may be tempered by belowground LMWCC.