Tropical peatland biogeochemistry along an ecological transect: the enigmatic fate of organic matter

Abstract

Peatlands play a pivotal role in the global carbon cycle. Despite only covering 3% of the world’s surface, peatlands hold 500–700 Gt of carbon (Page & Baird, 2016). These dense carbon stocks are sensitive to direct and/or indirect human intervention and can quickly turn from carbon sink to carbon source when perturbed. Additionally, peat deposits are crucial for our understanding of terrestrial environmental change by recording environmental parameters such as temperature and biogeochemical cycling through geological time (Naafs et al., 2019). Constraining the magnitude and rate of change during past periods of climatic change in the terrestrial realm is essential for accurately predicting the effects of anthropogenic global warming.

Most peatland studies have focussed on reconstructing environmental parameters such as water table depth, temperature, vegetation, and pH, because those are readily available through quick observation or meteorological data. However, changes in the nature of the organic matter (OM) is often harder to characterize but is imperative to the tight balance between accumulation and degradation of peat. Especially in tropical peatlands, the nature of OM is largely understudied. Tropical peats are more carbon-dense compared to boreal peatlands, have a more active methane cycle, and can have a wider range of vegetation, which makes understanding their biogeochemistry vitally important.

We investigated the biogeochemistry of a tropical peat along an ecological transect consisting of 5 sites: mangrove, mixed tropical forest, hardwood tropical forest, stunted forest with sawgrass and ombrotrophic (i.e., rain-fed) sawgrass bog. From each site, a 1–2 meter core was collected and analysed by pyrolysis-GC/MS, GC/MS (of apolar and polar fractions), 16S rRNA genomic profiling and, UPLC-QToF-MS. Our unique dataset allows for a direct comparison of the biogeochemistry of tropical peats under different vegetation and nutrient concentrations, but constant temperature.