Spatial variability of organic matter properties determines methane fluxes in a tropical forested peatland

Abstract

Tropical peatland ecosystems are a significant component of the global carbon cycle and feature a range of distinct vegetation types, but the extent of links between contrasting plant species, peat biogeochemistry and greenhouse gas fluxes remains unclear. Here we assessed how vegetation affects small scale variation of tropical peatland carbon dynamics by quantifying in situ greenhouse gas emissions over 1 month using the closed chamber technique, and peat organic matter properties using Rock-Eval 6 pyrolysis within the rooting zones of canopy palms and broadleaved evergreen trees. Mean methane fluxes ranged from 0.56 to 1.2 mg m −2 h −1 and were significantly greater closer to plant stems. In addition, pH, ranging from 3.95 to 4.16, was significantly greater closer to stems. A three pool model of organic matter thermal stability (labile, intermediate and passive pools) indicated a large labile pool in surface peat (35–42%), with equivalent carbon stocks of 2236–3065 g m −2 . Methane fluxes were driven by overall substrate availability rather than any specific carbon pool. No peat properties correlated with carbon dioxide fluxes, suggesting a significant role for root respiration, aerobic decomposition and/or methane oxidation. These results demonstrate how vegetation type and inputs, and peat organic matter properties are important determinants of small scale spatial variation of methane fluxes in tropical peatlands that are affected by climate and land use change. Electronic supplementary material The online version of this article (10.1007/s10533-018-0531-1) contains supplementary material, which is available to authorized users.

Root oxygen mitigates methane fluxes in tropical peatlands

“…Taken together, these results indicate broad scale differences in organic chemistry between peat types, reflecting previously identified differences between dominant vegetation types [7,20]. Moreover, the relatively limited differences in organic chemistry between treatments supports recovery following mesocosm installation, with the exception of increased root necromass in the root-accessible and closed mesocosms (table 1).…”

“…First, differences in root oxygen input between species and the interaction with contrasting organic matter properties are likely to be strong drivers of peat decomposition. This interaction is also likely to explain part of the previously reported small scale variation in organic matter properties [20]. While some previous studies at Changuinola have reported significant differences in CH 4 flux from peats under contrasting plant communities [15], fluxes display a high variability and differences have not been consistently reported [8,20].…”

“…The hydrogen index (HI), a measure of released hydrocarbons relative to TOC RE6 , also decreased in both treatment mesocosms. Changes in HI and OI indicate the extent of organic matter decomposition and have previously been applied to tropical peats [20,39]. There were, however, significant differences in I (p < 0.01) and R (p < 0.05) indices between peat types, which describe the preservation of thermally labile and highly thermostable organic matter respectively.…”

“…CH 4 concentrations were measured using gas chromatography (GC) and flame ionization. Calculations of gas fluxes assumed linear accumulation over time within the chamber and were calculated using the ideal gas law [20].…”

Impact of forest plantation on methane emissions from tropical peatland

“…Variation in soil redox conditions driven by GWL fluctuation plays an essential role in influencing not only the quantity but also the quality of organic substrate used by the methanogenic archaea for CH 4 production (Girkin et al, 2018;Hoyos-Santillan et al, 2016;Reiche, Gleixner, & Küsel, 2010;Winton et al, 2017). Higher GWLs promote CH 4 production in a relatively large portion of the peat column and restrict the zone in which aerobic CH 4 oxidation can occur (Moore & Roulet, 1993;Moore et al, 2011;Strack et al, 2004).…”