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.
Highlights
Plant inputs of leaf and stem material and rhizodeposits are important in regulating greenhouse gas (GHG) emissions from tropical peat (Hoyos-Santillan et al 2016b)
Tropical peats derived from different botanical origins have distinct organic matter chemistries which results in different decomposition rates and GHG production (Hoyos-Santillan et al 2015), in comparison to temperate and boreal peatlands where peat formation is predominantly driven by graminoid and moss inputs (Turetsky et al 2014)
Peats derived from C. panamensis and R. taedigera display significant heterogeneity of biogeochemical properties within the rooting zone
Summary
Plant inputs of leaf and stem material and rhizodeposits are important in regulating greenhouse gas (GHG) emissions from tropical peat (Hoyos-Santillan et al 2016b). Land use and climate change can significantly alter plant community composition, which may alter peat chemistry through changes in species-specific carbon inputs (Tonks et al 2017; Girkin et al 2018a, b). The consequences of this change are likely to be pronounced as peatlands contain an estimated 15–19% of the global peat carbon stock, and are a significant source of carbon dioxide (CO2) and methane (CH4) (Page et al 2011; Dargie et al 2017). Differences in vegetation can affect the balance of these emissions through changes in substrate inputs, organic matter composition, microbial communities (Ayres et al 2009; Keiser et al 2014), root release of oxygen (Hoyos-Santillan et al 2016a), and physical properties of the peat (Wright et al 2013b), and through providing a significant pathway for GHG transport (Pangala et al 2017)
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