Latitude, Elevation, and Mean Annual Temperature Predict Peat Organic Matter Chemistry at a Global Scale

Abstract

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.

Variation in carbon and nitrogen concentrations among peatland categories at the global scale

“…Previous studies have shown that Sphagnum -derived peat that is more typical in acidic northern peatlands has a lower C:OM ratio than peat derived primarily from herbaceous vegetation and woody plants [ 20 , 39 ]. Indeed, Verbeke [ 33 ] used FTIR to show that concentrations of carbohydrates decreased relative to aromatics in samples taken from the same sites as those used in our study. This would result in a loss of organic O and C and a relative increase in C-C bonding resulting in more C relative to OM in deeper peat.…”

“…We quantified global variation in peatland C and N concentrations and organic matter content in 1226 individual peat samples at different depths, from 436 cores, collected across 24 countries and six continents ( Fig 1 ). The samples are part of a larger project characterizing the geochemistry and microbial communities in global peatlands ([ 33 ], Global Peatland Microbiome Project). An important aim of the overall project was to generate a common data set across peatlands that was robust enough to allow global-scale comparisons but was also flexible enough to be useful for local-scale research projects at each site.…”

Evidence for older carbon loss with lowered water tables and changing plant functional groups in peatlands

“…Lower water tables consistently increase ecosystem respiration (ER) in the short term, but whether these increases are compensated for by primary production depends on plant community changes (Bubier et al, 2003; Chimner et al, 2017; Juszczak et al, 2012; Laiho, 2006; Riutta et al, 2007; Zhong et al, 2020). Hypoxic conditions below the water table depress peatland decomposition rates, indicating that persistent labile organic material in peatland C sinks may be readily decomposed when not waterlogged (Laiho, 2006), especially in colder northern sites (Verbeke et al, 2022). Hydrology influences redox conditions, gas diffusion, and nutrient availability (Holden, 2005).…”

“…Hypoxic conditions below the water table depress peatland decomposition rates, indicating that persistent labile organic material in peatland C sinks may be readily decomposed when not waterlogged (Laiho, 2006), especially in colder northern sites (Verbeke et al, 2022). Hydrology influences redox conditions, gas diffusion, and nutrient availability (Holden, 2005).…”

Organochemical Characterization of Peat Reveals Decomposition of Specific Hemicellulose Structures as the Main Cause of Organic Matter Loss in the Acrotelm

“…This indicates that hemicellulose content and composition play an essential role in the stability of surface peat. Increased temperatures and latitudinal gradients were found to influence the carbohydrate content of peat, − indicating that differences in specific carbohydrate linkages are important for peat stability. Moreover, it was found that CO 2 releases were twice as high in surface peat (2.5–5 cm) than in older peat (10–12.5 cm) .…”