Temperature, oxygen, and vegetation controls on decomposition in a James Bay peatland

Abstract

The biochemical composition of a peat core from James Bay Lowland, Canada, was used to assess the extent of peat decomposition and diagenetic alteration. Our goal was to identify environmental controls on peat decomposition, particularly its sensitivity to naturally occurring changes in temperature, oxygen exposure time, and vegetation. All three varied substantially during the last 7000 years, providing a natural experiment for evaluating their effects on decomposition. The bottom 50 cm of the core formed during the Holocene Climatic Optimum (~7000-4000 years B.P.), when mean annual air temperature was likely 1-2°C warmer than present. A reconstruction of the water table level using testate amoebae indicated oxygen exposure time was highest in the subsequent upper portion of the core between 150 and 225 cm depth (from~2560 to 4210 years B.P.) and the plant community shifted from mostly Sphagnum to vascular plant dominance. Several independent biochemical indices indicated that decomposition was greatest in this interval. Hydrolysable amino acid yields, hydroxyproline yields, and acid:aldehyde ratios of syringyl lignin phenols were higher, while hydrolysable neutral sugar yields and carbon:nitrogen ratios were lower in this zone of both vascular plant vegetation and elevated oxygen exposure time. Thus, peat formed during the Holocene Climatic Optimum did not appear to be more extensively decomposed than peat formed during subsequent cooler periods. Comparison with a core from the West Siberian Lowland, Russia, indicates that oxygen exposure time and vegetation are both important controls on decomposition, while temperature appears to be of secondary importance. The low apparent sensitivity of decomposition to temperature is consistent with recent observations of a positive correlation between peat accumulation rates and mean annual temperature, suggesting that contemporary warming could enhance peatland carbon sequestration, although this could be offset by an increasing contribution of vascular plants to the vegetation.

Modeled CO2 Emissions from Coastal Wetland Transitions to Other Land Uses: Tidal Marshes, Mangrove Forests, and Seagrass Beds

“…However, sensitivity of decomposition to variation in temperature may be mediated by other factors. For example, Philben et al (2014Philben et al ( , 2015 reported that peat formed at equatorial latitudes during the Holocene Climatic Optimum did not appear to be any more decomposed than peat formed at higher, cooler latitudes, or during subsequent cooler periods in more recent sections of the peat cores. They suggested that decomposition in peatlands was regulated primarily by oxygen-exposure time, and not by temperature.…”

Source, composition, and environmental implication of neutral carbohydrates in sediment cores of subtropical reservoirs, South China

“…After 9 mL of Milli-UV + water were added (1.2 M H 2 SO 4 , final concentration of acid), the ampules were flame-sealed and the samples were stirred and hydrolyzed in a 100 • C water bath for 3 h. The hydrolysis was terminated by placing the ampules in an ice bath for 5 min. Then, the deoxyribose was added as the internal standard (Philben et al, 2015). Before instrumental analysis, the samples were run through a mixed bed of anion (AG 2-X8, 20-50 meshes, Bio-Rad) and cation (AG 50W-X8, 100-200 meshes, Bio-Rad) exchange resins (Philben et al, 2015).…”

“…Then, the deoxyribose was added as the internal standard (Philben et al, 2015). Before instrumental analysis, the samples were run through a mixed bed of anion (AG 2-X8, 20-50 meshes, Bio-Rad) and cation (AG 50W-X8, 100-200 meshes, Bio-Rad) exchange resins (Philben et al, 2015). Self-absorbed AG11 A8 resin was utilized to remove the acid.…”

“…Self-absorbed AG11 A8 resin was utilized to remove the acid. The volume of resin needed for complete neutralization depended on the amount of acid used for hydrolysis (Philben et al, 2015). After purification with a mixture of cation and anion exchange resins, neutral sugars were isocratically separated with 25 mM NaOH on a PA 1 column in a Dionex 500 ion chromatography system, which was equipped with a pulsed amperometric detector (PAD, model ED40) (Philben et al, 2015).…”

Fungal Communities in Ancient Peatlands at Sanjiang Plain, China

“…Despite covering only 6-8% of the terrestrial ecosystems, northern peatlands store ~550 Pg C [2], which accounts for between one-quarter and one-third of the world's soil carbon [3]. The sequestration of C arises of northern peatlands is a result of high productivity rates rather than low decomposition.…”