Peatlands contain a significant fraction of global soil carbon, but how these reservoirs will respond to the changing climate is still relatively unknown. A global picture of the variations in peat organic matter chemistry will aid our ability to gauge peatland soil response to climate. The goal of this research is to test the hypotheses that (a) peat carbohydrate content, an indicator of soil organic matter reactivity, will increase with latitude and decrease with mean annual temperatures, (b) while peat aromatic content, an indicator of recalcitrance, will vary inversely, and (c) elevation will have a similar effect to latitude. We used Fourier Transform Infrared Spectroscopy to examine variations in the organic matter functional groups of 1034 peat samples collected from 10 to 20, 30–40, and 60–70 cm depths at 165 individual sites across a latitudinal gradient of 79°N–65°S and from elevations of 0–4,773 m. Carbohydrate contents of high latitude peat were significantly greater than peat originating near the equator, while aromatic content showed the opposite trend. For peat from similar latitudes but different elevations, the carbohydrate content was greater and aromatic content was lower at higher elevations. Higher carbohydrate content at higher latitudes indicates a greater potential for mineralization, whereas the chemical composition of low latitude peat is consistent with their apparent relative stability in the face of warmer temperatures. The combination of low carbohydrates and high aromatics at warmer locations near the equator suggests the mineralization of high latitude peat until reaching recalcitrance under a new temperature regime.

Peatlands account for 15 to 30% of the world’s soil carbon (C) stock and are important controls over global nitrogen (N) cycles. However, C and N concentrations are known to vary among peatlands contributing to the uncertainty of global C inventories, but there are few global studies that relate peatland classification to peat chemistry. We analyzed 436 peat cores sampled in 24 countries across six continents and measured C, N, and organic matter (OM) content at three depths down to 70 cm. Sites were distinguished between northern (387) and tropical (49) peatlands and assigned to one of six distinct broadly recognized peatland categories that vary primarily along a pH gradient. Peat C and N concentrations, OM content, and C:N ratios differed significantly among peatland categories, but few differences in chemistry with depth were found within each category. Across all peatlands C and N concentrations in the 10–20 cm layer, were 440 ± 85.1 g kg -1 and 13.9 ± 7.4 g kg -1 , with an average C:N ratio of 30.1 ± 20.8. Among peatland categories, median C concentrations were highest in bogs, poor fens and tropical swamps (446–532 g kg -1 ) and lowest in intermediate and extremely rich fens (375–414 g kg -1 ). The C:OM ratio in peat was similar across most peatland categories, except in deeper samples from ombrotrophic tropical peat swamps that were higher than other peatlands categories. Peat N concentrations and C:N ratios varied approximately two-fold among peatland categories and N concentrations tended to be higher (and C:N lower) in intermediate fens compared with other peatland types. This study reports on a unique data set and demonstrates that differences in peat C and OM concentrations among broadly classified peatland categories are predictable, which can aid future studies that use land cover assessments to refine global peatland C and N stocks.

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Core IdeasSoil organic matter chemical composition highlighted the inputs of varied vegetation communities in the past.Soil N is an indicator of peat decomposition based on relationship of functional group C and total N.Future surveys of soil organic matter biogeochemical parameters and C chemical composition should be pursued.Climate change in the subarctic region has increased the rate of inundation of peatlands due to increased temperatures, precipitation, and permafrost thaw. Increased inundation may result in vegetation community shifts, as documented in a subarctic mire near Abisko, Sweden. The wet fen communities have established in former sphagnum areas, and sphagnum colonized in degraded palsa hummocks. At Stordalen mire, we studied the influence of vegetation community on chemical composition of peat soil organic matter (SOM). Vegetation and soil samples were obtained along a hydrologic gradient with representative communities: palsa, sphagnum, and fen. Soil organic matter chemical composition indicated shifts in vegetative communities. Total N and N isotope signatures in fen soils showed characteristics of sphagnum and palsa communities at >6‐cm depth, and sphagnum soil profile signatures shifted from sphagnum to palsa properties at a 20‐cm depth. Soil chemical composition measured by Fourier Transform Infrared (FTIR) spectroscopy and13C Nuclear Magnetic Resonance (NMR) spectroscopy showed increasing recalcitrant C (alkyl and aromatic) in palsa soil. Sphagnum soil profiles sustained labile organic C (O‐alkyl) until 15 cm then shifted to humified soil, and fen soil profiles showed areas of sphagnum and palsa signatures. Furthermore, the strong relationship between functional group C (O‐alkyl and alkyl) and total N demonstrated that soil N is an effective indicator of peat decomposition. Our results identified change points in soil chemical composition in regards to N content and C functional group which highlights the importance of historic vegetation community on chemical composition of peat soils.

Soil organic carbon (C) is a key component regulating grazing land ecosystem production and sustainability. In this study, we investigated the impacts of wet vs. dry physical separation of soil C fractions in representative sandy Coastal Plain Spodosols subjected to different levels of management intensification. X-ray diffraction and solid-state 13C nuclear magnetic resonance (NMR) spectroscopy were used to characterize the structural composition of the fine (< 53 μm) particle size. Dry sieving resulted in ~ 10–15% greater total C recovery as compared to wet sieving. Sieving method also affected the proportion of soil C associated with the various size fractions. In general, dry sieving resulted in greater proportion of soil C (48 to 73% of the total C in the 0 to 10 and 10 to 20 cm, respectively) associated with the 150–53 and < 53 μm fractions. Conversely, the proportion of C associated with large aggregates (2000–250 and 250–150 μm fractions) increased 1.5 to 2-fold when wet sieving was performed. X-ray diffraction demonstrated that mineral composition of the fine (< 53 μm) fraction was dominated by quartz and, thus, offers limited protection against mineralization. Results also demonstrated that alkyl C and total O-alkyl C dominated soil C chemical composition of both whole soils and < 53 μm fractions. In whole soils, abundance of alkyl C and total O-alkyl C decreased while methoxyl, carboxylic, and total aromatic-C increased with management intensification (native rangeland < silvopasture < sown pasture). However, in the < 53 μm fraction, total O-alkyl C abundance was greater in native rangeland than that in the silvopasture and sown pasture ecosystems. Both sieving methods were sensitive tools to evaluate the long-term impacts of grazing land intensification on soil C distribution among aggregate size fractions. However, because dry sieving is easier to perform and preserves more C than wet sieving, dry sieving can be a reliable method of soil C separation for determining the impacts of land use management on soil C dynamics in sandy soils.