Divergent response of plant-derived lipids and fire-derived organic matter to warming and elevated CO2 in a boreal peatland.

Peatlands occupy ~3% of the land surface, yet they store more than one-third of global terrestrial carbon. However, there is growing concern that the decomposition of this vast carbon bank in the face of climate change could alter peatlands from a carbon sink to a carbon source, but experimental data is scarce. Here, we examine peatland carbon stability after four years of whole-ecosystem warming (+0, +2.25, +4.5, +6.75 and +9 °C) and two years of elevated CO₂ manipulation (500 ppm above ambient). We use solvent-extractable (alkanoic acids, alkanols and alkanes) and hydrolysable lipids (cutin and suberin) and benzene polycarboxylic acids (BPCA) as tracers for fire-derived organic matter and investigate their degree of decomposition in a boreal forested peatland.

We found fire-derived organic matter stemming from past fires, either nearby or long-distance atmospheric transport. Warming alone or when combined with elevated CO₂ did not affect the quantity and quality of fire-derived organic matter stemming from past fires, as indicate by the molecular markers BPCA. The wet conditions probably helped to preserve these slowly degrading aromatic compounds. Molecular markers for leaf- (cutin) and root‐derived biomass (suberin), showed that with warming more new plant biomass came from roots, at the expense of leaf-derived compounds under both, ambient and elevated CO₂ treatments, implying dynamic alterations to leaf and root carbon incorporation and sequestration with environmental changes. These responses were more pronounced in the surface aerobic acrotelm, highlighting that the aerobic layer responded surprisingly fast, within a few seasons to changing environmental conditions.