Contribution of subsurface peat to CO₂ and CH₄ fluxes in a neotropical peatland

Abstract

Tropical peatlands play an important role in the global carbon cycling but little is known about factors regulating carbon dioxide (CO 2 ) and methane (CH 4 ) fluxes from these ecosystems. Here, we test the hypotheses that (i) CO 2 and CH 4 are produced mainly from surface peat and (ii) that the contribution of subsurface peat to net C emissions is governed by substrate availability. To achieve this, in situ and ex situ CO 2 and CH 4 fluxes were determined throughout the peat profiles under three vegetation types along a nutrient gradient in a tropical ombrotrophic peatland in Panama. The peat was also characterized with respect to its organic composition using 13 C solid state crosspolarization magic-angle spinning nuclear magnetic resonance spectroscopy. Deep peat contributed substantially to CO 2 effluxes both with respect to actual in situ and potential ex situ fluxes. CH 4 was produced throughout the peat profile with distinct subsurface peaks, but net emission was limited by oxidation in the surface layers. CO 2 and CH 4 production were strongly substrate-limited and a large proportion of the variance in their production (30% and 63%, respectively) was related to the quantity of carbohydrates in the peat. Furthermore, CO 2 and CH 4 production differed between vegetation types, suggesting that the quality of plant-derived carbon inputs is an important driver of trace gas production throughout the peat profile. We conclude that the production of both CO 2 and CH 4 from subsurface peat is a substantial component of the net efflux of these gases, but that gas production through the peat profile is regulated in part by the degree of decomposition of the peat. , 2010). In areas of the tropics which are expected to experience reduced rainfall and more prolonged drought (Meehl et al., 2007), peatlands may become less important sources of atmospheric methane (CH 4 ). However, this would be offset by greatly increased rates of aerobic decomposition and carbon dioxide (CO 2 ) release, with the result that their combined global warming potential would increase (Hirano et al., 2009;Couwenberg et al., 2010;Sjö gersten et al., 2010). It is also plausible that old C stored deep in the peat profile would be metabolized if climatic conditions become more favourable for decomposition, as has been reported for northern peatlands (e.g. Dorrepaal et al., 2009). In tropical environments, a substantial draw down of the water table would be required to impact deep peat layers. Considerable variation in C fluxes occurs between vegetation types in tropical wetland systems (Melling et al., 2005a, b;Sjö gersten et al., 2010), suggesting that C inputs from the vegetation (Sebacher et al., 1985;Joabsson & Christensen, 2001;Konnerup et al., 2010) are strong drivers of C fluxes in these systems. However, it is not known if these differences in C fluxes result mainly from surface processes or are maintained throughout the peat profile. Tropical peatlands may reach depths of up to 15 m (Phillips et al., 1997;Page et al., 1999Page...

Root oxygen loss from Raphia taedigera palms mediates greenhouse gas emissions in lowland neotropical peatlands

“…Moisture content was determined by gravimetric analysis of the water mass loss of 10 g fresh peat samples after oven drying peat samples at 70°C for 70 h (Wright et al 2011). Loss on ignition (LOI), as an indirect measurement of soil organic matter content (SOM), was measured by gravimetric analysis of mass loss from dry peat samples placed in the muffle furnace for 7 h at 550°C.…”

“…For example, the photosynthetic activity of trees is correlated strongly with soil respiration in temperate savannah and temperate peatlands (Mikkelä et al 1995;Tang et al 2005; Thomas et al 1996). The release of photosynthates through the rhizosphere provide labile substrate for decomposer organisms (Silvola et al 1996;Ström et al 2003;Wright et al 2011), influencing the diurnal pattern of CO 2 and CH 4 emissions in both temperate and tropical ecosystems (Bahn et al 2009;Wright et al 2013b). Therefore, it is important to measure greenhouse gas fluxes on a diurnal basis, as this allows investigation of biotic and abiotic controls on the temporal variation of greenhouse gas emissions (Armstrong 1971;Ström et al 2003;Wang and Han 2005).…”

“…(Myers 1981;Phillips et al 1997), or mixed forest composed of R. taedigera and evergreen broadleaved hardwood trees (Phillips et al 1997;Urquhart 1999). These forests emit both CO 2 and CH 4 , with seasonal and spatial variability in emissions being related to both substrate availability and CH 4 oxidation processes (Wright et al 2011;Wright et al 2013b), indicating that the vegetation activity may moderate greenhouse gas emissions in these forests.…”

Impact of Simulated Changes in Water Table Depth on Ex Situ Decomposition of Leaf Litter from a Neotropical Peatland

“…(c. 1 m tall sedge). The texture of the peat varies between the interior (coarse) and edge (fine) of the peatland (Phillips et al 1997;Wright et al 2011), indicating differing rates of decomposition and/or differences in the source of litter. The peat is shallower at the edge of the peatland than in the interior i.e.…”

Seasonal variability in methane and nitrous oxide fluxes from tropical peatlands in the western Amazon basin

“…Key factors include redox/water table depth (Couwenberg et al, 2010(Couwenberg et al, , 2011Silver et al, 1999;Teh et al, 2005;von Fischer and Hedin, 2007), plant productivity (von Fischer and Hedin, 2007;Whiting and Chanton, 1993), soil organic matter lability (Wright et al, 2011), competition for C substrates among anaerobes (Teh et al, 2008;von Fischer and Hedin, 2007), and presence of plants capable of facilitating atmospheric egress (Pangala et al, 2013). Of all these factors, fluctuation in soil redox conditions, as mediated by variations in water table depth, is perhaps most critical in regulating CH 4 dynamics (Couwenberg et al, 2010(Couwenberg et al, , 2011 because of the underlying physiology of the microbes that produce and consume CH 4 .…”