Peatland Organic Matter Chemistry Trends over a Global Latitudinal Gradient

Peatlands contain a significant amount of the global soil carbon, but the climate feedback affecting carbon stability within these peatland systems is still relatively unknown. Organic matter composition of peatlands plays a major role in determining carbon storage, and while high latitude peatlands seem to be the most sensitive to climate change, a global picture of peat organic matter chemistry is required to gauge overall peatland stability and to improve models of greenhouse gas emissions fueled by soil carbon decomposition. The goal of this research is to test the hypothesis that carbohydrate content, an indicator of soil organic matter lability or reactivity, will be lower in carbon deposits near the equator and greater in high latitude peatlands. Conversely we hypothesize that peat aromatic content will be higher at low latitudes relative to higher latitudes. As a part of the Global Peatland Microbiome Project (GPMP), around 1400 samples of peat across a latitudinal gradient from 79N to 65S were measured with Fourier transform infrared spectroscopy (FTIR) to examine the organic matter functional groups of peat. Carbohydrate and aromatic content, as determined by FTIR, are useful proxies of decomposition potential and recalcitrance, respectively. A highly significant relationship was observed between carbohydrate and aromatic content, latitude, and elevation. Carbohydrate contents of high latitude sites were significantly greater than at sites near the equator, in contrast to aromatic content which showed the opposite trend. It was also clear that at locations with similar latitudes but different elevations, the carbohydrate content was higher and aromatic content was lower at higher elevations. Higher carbohydrate content at higher latitudes indicates a greater potential for lability and resultant mineralization to form the greenhouse gases, carbon dioxide and methane, whereas the composition of low latitude peatlands is consistent with their apparent stability in the face of greater temperatures. The combination of low carbohydrates and high aromatics at warmer locations near the equator could foreshadow the organic matter composition of high latitude peat transitioning to a more recalcitrant form with a warming climate accompanying the evolution of greenhouse gases.