Enrichment of lignin reveals consistent anaerobic degradation and persistent vegetation signatures in the organic matter of diverse lowland tropical peatland profiles

Abstract. Tropical peatlands store a significant amount of carbon but are also one of the most vulnerable carbon stocks due to anthropogenic pressures and climate change. The stability and accumulation of the organic carbon stored in tropical peat systems, and its sensitivity to changing temperature and/or hydrology, is intrinsically linked to the organic matter (OM) character. However, we currently lack a detailed understanding of the OM characteristics in tropical peatlands, hindering the accurately prediction of tropical peatland stability during the 21st century.
In this study, we therefore characterise the macromolecular composition of peatland vegetation, leaf litter, and across peat depth profiles using a range of tropical (n = 7) and temperate (n = 2) peatland ecosystems that serve as comparison. This characterisation is achieved primarily via Pyrolysis Gas Chromatography Mass Spectrometry (Py-GC-MS), complemented by Fourier-Transform Infrared Spectroscopy (FTIR) but silicate mineral interference make FTIR not applicable in some of our sites. Our results show that all sites exhibit distinct pools of putatively labile and recalcitrant (plant) organic matter, with both shared and distinct downcore degradation features. Most sites exhibit a downcore enrichment in aromatic pyrolysates vs polysaccharide pyrolysates following logarithmic decline, even in the anoxic horizons. Regardless of the decomposition of the peat, however, a pyrolytic fingerprint of the original vegetation persists. This unique fingerprint is likely a driver behind the microbial community’s speciality to degrade the OM in its specific peatland, an effect known as the home advantage theory. The predicable preferential loss of polysaccharides at depth and consistent aromaticity of the leaf litter in the tropical sites can aid peatland accumulation modelling and enable more accurate predictions of peatland dynamics under future climate change.