Peat Decomposition Research Articles

Response of peat decomposition to corn straw addition in managed organic soils

Drainage and land-use are key factors that trigger CO2 emissions from cultivated organic soils. Drainage enhances aeration, and land-use might affect peat decomposition due to the input of fresh organic matter (FOM). The effect of FOM addition on peat decomposition of agriculturally used organic soils has seldom been quantified experimentally. In this study, we i) incubated soil samples taken from three adjacent former peatland sites that were drained and managed as cropland, perennial grassland and forest, respectively, and measured CO2 release over 16months at 20°C. In a second experiment, ii) we incubated soil samples from the same three sites with and without adding corn straw as FOM (2% w/w) at 20°C over three weeks. The 13C and 14C signatures of soil organic carbon (SOC) and emitted CO2 enabled us to apportion the amount of decomposed corn, as well as to estimate relative effects of corn addition on the decomposition of SOC from old peat (SOCold) and from young soil organic carbon (SOCyoung). In the first experiment, samples lost between 0.03 and 0.09mg CO2-C mg SOC−1 in the order forest>grassland>cropland. The higher 14C values of the emitted CO2 vs. that of SOC indicated that SOCyoung was more easily decomposable. FOM addition induced negative (−14.8±5.2%), positive (+14.9±4.6%) and neutral priming (−14.2±30.0%) of SOC decomposition in the forest, grassland and cropland samples, respectively. Most importantly, we find that the relative contribution of SOCold to the overall CO2 release consistently decreased after FOM application, whereas decomposition of SOCyoung was rather stimulated. The latter finding is in line with previous studies on intact peat. Our results show that young and old C pools in managed organic soils respond differently to the addition of fresh plant residues, and FOM addition can effectively reduce the decomposition of old peat. Hitherto negative priming was never reported for agriculturally used organic soils and it might be caused by the overall poor decomposability of old peat.

Rate of warming affects temperature sensitivity of anaerobic peat decomposition and greenhouse gas production.

Temperature sensitivity of anaerobic carbon mineralization in wetlands remains poorly represented in most climate models and is especially unconstrained for warmer subtropical and tropical systems which account for a large proportion of global methane emissions. Several studies of experimental warming have documented thermal acclimation of soil respiration involving adjustments in microbial physiology or carbon use efficiency (CUE), with an initial decline in CUE with warming followed by a partial recovery in CUE at a later stage. The variable CUE implies that the rate of warming may impact microbial acclimation and the rate of carbon-dioxide (CO2 ) and methane (CH4 ) production. Here, we assessed the effects of warming rate on the decomposition of subtropical peats, by applying either a large single-step (10°C within a day) or a slow ramping (0.1°C/day for 100days) temperature increase. The extent of thermal acclimation was tested by monitoring CO2 and CH4 production, CUE, and microbial biomass. Total gaseous C loss, CUE, and MBC were greater in the slow (ramp) warming treatment. However, greater values of CH4 -C:CO2 -C ratios lead to a greater global warming potential in the fast (step) warming treatment. The effect of gradual warming on decomposition was more pronounced in recalcitrant and nutrient-limited soils. Stable carbon isotopes of CH4 and CO2 further indicated the possibility of different carbon processing pathways under the contrasting warming rates. Different responses in fast vs. slow warming treatment combined with different endpoints may indicate alternate pathways with long-term consequences. Incorporations of experimental results into organic matter decomposition models suggest that parameter uncertainties in CUE and CH4 -C:CO2 -C ratios have a larger impact on long-term soil organic carbon and global warming potential than uncertainty in model structure, and shows that particular rates of warming are central to understand the response of wetland soils to global climate change.

Enhanced silicon availability leads to increased methane production, nutrient and toxicant mobility in peatlands

Peatlands perform important ecosystem functions, such as carbon storage and nutrient retention, which are affected, among other factors, by vegetation and peat decomposition. The availability of silicon (Si) in peatlands differs strongly, ranging from <1 to >25 mg L−1. Since decomposition of organic material was recently shown to be accelerated by Si, the aim of this study was to examine how Si influences decomposition of carbon and nutrient and toxicant mobilization in peatlands. We selected a fen site in Northern Bavaria with naturally bioavailable Si pore water concentrations of 5 mg/L and conducted a Si addition experiment. At a fourfold higher Si availability, dissolved organic carbon, carbon dioxide, and methane concentrations increased significantly. Furthermore, dissolved nitrogen, phosphorus, iron, manganese, cobalt, zinc, and arsenic concentrations were significantly higher under high Si availability. This enhanced mobilization may result from Si competing for binding sites but also from stronger reducing conditions, caused by accelerated respiration. The stronger reducing conditions also increased reduction of arsenate to arsenite and thus the mobility of this toxicant. Hence, higher Si availability is suggested to decrease carbon storage and increase nutrient and toxicant mobility in peatland ecosystems.

Factors affecting oxidative peat decomposition due to land use in tropical peat swamp forests in Indonesia

The increasing frequency of fire due to drainage of tropical peatland has become a major environmental problem in Southeast Asia. To clarify the effects of changes in land use on carbon dioxide emissions, we measured oxidative peat decomposition (PD) at different stages of disturbance at three sites in Central Kalimantan, Indonesia: an undrained peat swamp forest (UF), a heavily drained peat swamp forest (DF), and a drained and burned ex-forest (DB).PD exhibited seasonality, being less in the wet season and greater in the dry season. From February 2014 to December 2015, mean PD (±SE) were 1.90±0.19, 2.30±0.33, and 1.97±0.25μmolm−2s−1 at UF, DF, and DB, respectively. The groundwater level (GWL) was a major controlling factor of PD at all sites. At UF and DF, PD and GWL showed significant quadratic relationships. At DB, PD and GWL showed significant positive and negative relationships during the dry and wet seasons, respectively. Using these relationships, we estimated annual PD from GWL data for 2014 and 2015 as 698 and 745gCm−2yr−1 at UF (mean GWL: −0.23 and −0.39m), 775 and 825gCm−2yr−1 at DF (−0.55 and −0.59m), and 646 and 748gCm−2yr−1 at DB (−0.22 and −0.62m), respectively. The annual PD was significantly higher in DF than in UF or DB, in both years. Despite the very dry conditions, the annual PD values at these sites were much lower than those reported for tropical peat at plantations (e.g., oil palm, rubber, and acacia). The differences in the relationship between PD and GWL indicate that separate estimations are required for each type of land. Moreover, our results suggest that PD can be enhanced by drainage both in forests and at burned sites.

The role of molecular weight in the enzyme-inhibiting effect of phenolics: the significance in peatland carbon sequestration

Northern peatlands store 455Pg of carbon–a third of the entire global carbon store. Carbon accumulates because phenolic inhibitors slow the rate of decomposition to below that of photosynthetic production. The disproportionate importance of phenolics in peatlands is related to the unique properties of waterlogged peat soils suppressing the activity of phenol oxidase; one of the few enzymes capable of breaking these inhibitors down (a role often referred to as the “enzymic latch”). This permits accumulation of phenolic compounds that are potent inhibitors of hydrolase enzymes–major agents in the breakdown of organic matter. In our study we investigate the importance of the molecular weight of phenolics on levels of inhibition of microbial decomposition in peat. We found the higher the molecular weight, of a phenolic compound, the greater its inhibitory effect on the breakdown of organic matter.

2-1-3 In-situ decomposition of tropical peat from three representative vegetation of primary forest in Sarawak, Malaysia

2-1-3 In-situ decomposition of tropical peat from three representative vegetation of primary forest in Sarawak, Malaysia

Improved durability of lignocellulose-polypropylene composites manufactured using twin-screw extrusion

The objective of this study was to investigate the use of peat as a potential lignocellulose source in composites manufactured by twin-screw extrusion. The effects of peat decomposition rate and particle size on the mechanical properties and moisture resistance of peat-polypropylene (PP) composites under cyclic conditions were evaluated. The properties of the peat-PP composites were compared to commercial lignocellulosic fibre products, namely wood-plastic composite (WPC), medium density fibreboard (MDF) and hardboard (HB). The results show that prior cyclic freeze-thaw testing peat-PP composites had properties equal to commercial WPC, but their mechanical permanence was better after freeze-thaw conditioning. When moderately decomposed, smaller particle–size peat was used, peat-PP composites had better dimensional stability, though particle size did not affect as much as the decomposition degree. Thus, the chemical structure of peat has a greater influence on composite durability, as better water and weather resistance are achieved with peat that is more decomposed.

Nitrous Oxide Emission of a Tropical Peat Soil Grown with Pineapple at Saratok, Malaysia

Draining of peatland for agriculture could affect the release of nitrous oxide into the atmosphere. Presently, there is dearth of information on soil nitrous oxide emission from tropical peat soils cultivated with pineapples. Lysimeter and closed chamber methods were used to quantify nitrous oxide emission from root respiration, microbial respiration, and oxidative peat decomposition under controlled water table condition. Treatments evaluated were: peat soil grown with pineapple, uncultivated peat soils, and bare peat soil fumigated with chloroform. Cultivation of Moris pineapple on drained peat soils resulted in the higher release of nitrous oxide emission (15.7 t N2O ha/yr), followed by fumigated peat soil with chloroform (14.3 t N2O ha/yr), and uncultivated peat soil (10.2 t N2O ha/yr). Soil nitrous oxide emission was affected by nitrate fertilization but emission was not affected by soil temperature nor soil moisture.

Methane Emission from Pineapple Cultivation on a Tropical Peatland at Saratok, Malaysia

Information on methane emission in pineapple cultivation on peatlands is scarce. Methane emission in pineapple cultivation is important as 90% of pineapples are grown on the peat soils of Malaysia. It is essential to determine methane emission in pineapple cultivation because pineapples are Crassulacean acid metabolism plants whose effects on methane could be different from other crops grown on tropical peat soils. Methane emissions from root respiration, microbial respiration, and oxidative peat decomposition were determined in a lysimeter experiment. There were three treatments: peat soil cultivated with pineapple, bare peat soil, and bare peat soil fumigated with chloroform. Methane emissions from peat soil cultivated with pineapple, bare peat soil, and bare peat soil fumigated with chloroform were 0.65 t/ha/yr, 0.75 t/ha/yr, and 0.75 t/ha/yr, respectively. The lower methane emissions are consistent with the general believe that methane emission from cultivated peat soils is lower than those of anaerobic or water logged peat soils. Soil methane emission was affected by nitrogen fertilization under pineapple cultivation but the converse was true for soil temperature nor soil moisture.

Cotton-Grass and Blueberry have Opposite Effect on Peat Characteristics and Nutrient Transformation in Peatland

Peatlands are large repositories of carbon (C). Sphagnum mosses play a key role in C sequestration, whereas the presence of vascular plants is generally thought to stimulate peat decomposition. Recent studies stress the importance of plant species for peat quality and soil microbial activity. Thus, learning about specific plant–microbe–soil relations and their potential feedbacks for C and nutrient cycling are important for a correct understanding of C sequestration in peatlands and its potential shift associated with vegetation change. We studied how the long-term presence of blueberry and cotton-grass, the main vascular dominants of spruce swamp forests, is reflected in the peat characteristics, soil microbial biomass and activities, and the possible implications of their spread for nutrient cycling and C storage in these systems. We showed that the potential effect of vascular plants on ecosystem functioning is species specific and need not necessarily result in increased organic matter decomposition. Although the presence of blueberry enhanced phosphorus availability, soil microbial biomass and the activities of C-acquiring enzymes, cotton-grass strongly depleted phosphorus and nitrogen from the peat. The harsh conditions and prevailing anoxia retarded the decomposition of cotton-grass litter and caused no significant enhancement in microbial biomass and exoenzymatic activity. Therefore, the spread of blueberry in peatlands may stimulate organic matter decomposition and negatively affect the C sequestration process, whereas the potential spread of cotton-grass would not likely change the functioning of peatlands as C sinks.

Management strategies for medically unexplained symptoms in general practice: A qualitative study

Northern peatlands store 455 Pg of carbon–a third of the entire global carbon store. Carbon accumulates because phenolic inhibitors slow the rate of decomposition to below that of photosynthetic production. The disproportionate importance of phenolics in peatlands is related to the unique properties of waterlogged peat soils suppressing the activity of phenol oxidase; one of the few enzymes capable of breaking these inhibitors down (a role often referred to as the “enzymic latch”). This permits accumulation of phenolic compounds that are potent inhibitors of hydrolase enzymes–major agents in the breakdown of organic matter. In our study we investigate the importance of the molecular weight of phenolics on levels of inhibition of microbial decomposition in peat. We found the higher the molecular weight, of a phenolic compound, the greater its inhibitory effect on the breakdown of organic matter.

MOLECULAR-MASS DISTRIBUTION OF HUMIC SUBSTANCES AND HYMATOMELANIC ACIDS FROM DIF-FERENT ORIGIN PEATS OF THE TULA REGION

Humic substances were isolated from different origin peats of the Tula region: reed fen peat (RFP), sphagnum high-moor peat (SHP), black alder fen peat (BFP), sphagnum transition peat (STP) by water-alkaline extraction. The yield of humic substances from reed fen peat is maximal and comes in at 11,1±0,2%; The minimum yield is from sphagnum transition peat 7,4±0,2%, which is explained by the degree of transformation of the initial biomaterial and the conditions of occurrence of peats. Analyzed peats are in a row according to the content of humic substances: RFP&gt;SHP&gt;BFP&gt;STP. The yields of hymatomelanic acids come in at 23,3–25,3%. Polydispersity of humic substances and monodispersity of hymatomelanic acids have been proved by gel-penetrating chromatography. Four fractions differing in their molecular masses and relative content were obtained from humic substances of peats regardless of their origin. Values of the molecular masses of the fractions of HS of BFP are dominant and 25% higher than of the fractions of HS of RFP. Sphagnum peats have a similar qualitative composition and, as a consequence, have similar molecular masses of isolated humic substances correlating with the degree of peat decomposition and with the yields of humic substances. Hymatomelanic acids are one fraction: the molecular weight of GMAs of BFP is 42 kDa, which is 44% higher than of GMAs STP. The correlation between the degree of humification and peat's genesis was revealed. It was shown that the amount of hymatomelanic acids in humic substances of peats can be marker of phases of humification of peats.

Organic composition and multiphase stable isotope analysis of active, degrading and restored blanket bog

Here we used organic composition and stable isotopic analysis to evaluate the effects of drainage and restoration at an ombrotrophic peatland, to assess whether rewetting of blanket bogs will reverse degradation. The organic composition of the peat and the isotopic fractionation between the solid (peat), liquid (pore water) and gas (soil gas) phases on actively accumulating, degrading and restored locations are compared. Fourier Transform Infrared Spectroscopy (FTIR) analysis of the organic material has shown a high level of humification (low decomposition) in the active peat. Stable isotope analysis in the solid, liquid and gas phases has corresponded with this and indicated that the active location is enriched in 13C in the solid and gas phases, 15N in the solid phase, 18O in the liquid and gas phases and D in the liquid phase, suggesting a closed system with limited isotopic fractionation and thus limited water movement and decomposition. The degrading location has a lower level of humification, and is depleted in 13C in the solid phase due to ingression of vascular plants. The restored location has high humification and enrichment of 13C and 15N in the solid phase, and D in the liquid phase suggesting increased microbial activity. 13C and 18O in the gas phase and 18O in the liquid phase are depleted, as a result of microbial mediated gas production and rewetting. FTIR analysis has also indicated a subsurface zone of increased decomposition between the acrotelm and catotelm in both the active and degrading peat. This is due to a stable water table and is not present within the restored location, which we attribute to water table fluctuation associated with rewetting. This zone of increased decomposition adds to the complexity of blanket bog peatlands and the assumption that all systems can be generalized under one conceptual model.

Long-term carbon and nitrogen dynamics at SPRUCE revealed through stable isotopes in peat profiles

Abstract. Peatlands encode information about past vegetation dynamics, climate, and microbial processes. Here, we used δ15N and δ13C patterns from 16 peat profiles to deduce how the biogeochemistry of the Marcell S1 forested bog in northern Minnesota responded to environmental and vegetation change over the past ∼ 10 000 years. In multiple regression analyses, δ15N and δ13C correlated strongly with depth, plot location, C ∕ N, %N, and each other. Correlations with %N, %C, C ∕ N, and the other isotope accounted for 80 % of variance for δ15N and 38 % of variance for δ13C, reflecting N and C losses. In contrast, correlations with depth and topography (hummock or hollow) reflected peatland successional history and climate. Higher δ15N in plots closer to uplands may reflect upland-derived DON inputs and accompanying shifts in N dynamics in the lagg drainage area surrounding the bog. The Suess effect (declining δ13CO2 since the Industrial Revolution) lowered δ13C in recent surficial samples. High δ15N from −35 to −55 cm probably indicated the depth of ectomycorrhizal activity after tree colonization of the peatland over the last 400 years, as confirmed by the occasional presence of wood down to −35 cm depth. High δ13C at ∼ 4000 years BP (−65 to −105 cm) could reflect a transition at that time to slower rates of peat accumulation, when 13C discrimination during peat decomposition may increase in importance. Low δ13C and high δ15N at −213 and −225 cm ( ∼ 8500 years BP) corresponded to a warm period during a sedge-dominated rich fen stage. The above processes appear to be the primary drivers of the observed isotopic patterns, whereas there was no clear evidence for methane dynamics influencing δ13C patterns.

Comparison of plant litter and peat decomposition changes with permafrost thaw in a subarctic peatland

Organic matter decomposition in response to thawing permafrost has critical implications for carbon release. This study examined how thaw induced plant community and environmental changes influenced litter and peat decomposition in a subarctic peatland. We conducted laboratory incubations under current site pre-thaw (dry and large oxic peat layer) and thawed (wet and small oxic peat layer) conditions, and mimiced pond thaw conditions (water saturated and anoxic) at 4 and 22 °C. Carbon dioxide (CO2) and methane (CH4) releases from ground surface plant litter and top 1 m peat samples at permafrost area (Palsa) and wet thawed lawn (WL) were quantified under current site conditions. Dissolved organic carbon (DOC) released from litter was additionally quantified under pond thaw conditions. Plant litter mass significantly increased from Palsa to WL. Under current site conditions, litter in WL had significantly higher CO2 and CH4 production rates than litter in Palsa. Pond thaw conditions changed litter carbon loss partitioning into lower CO2 but higher DOC and CH4 production, and increased total carbon release. Whole peat decomposition was restricted from Palsa to WL with thaw. Estimated growing season gas carbon loss (CO2 and CH4) in WL was greater than that in Palsa due to significantly increased litter carbon loss after thaw. Changes in organic matter decomposition, especially litter decomposition, enlarged carbon losses from this subarctic peatland with permafrost thaw.

Phylogenetic or environmental control on the elemental and organo-chemical composition of Sphagnum mosses?

Background and aimsPlant litter chemistry is a key driver of decomposition in peatlands. This study explored the relative contributions of phylogeny and environment to litter chemistry of peat mosses (Sphagnum), the key peat-forming plants on earth.MethodsFifteen Sphagnum species, representing three taxonomic sections ACUTIFOLIA, CUSPIDATA and SPHAGNUM, were sampled across a wide range of hydro-geochemical conditions. For all species we characterised chemical composition within (i) inorganic elements, (ii) carbohydrate polymers (iii) non-carbohydrates.ResultsThe variation in carbohydrates was mostly explained by taxonomic section, suggesting phylogenetic conservation of carbohydrate composition. ACUTIFOLIA species invested relatively more in pectins, whereas CUSPIDATA and SPHAGNUM species invested more in hemicellulose. The composition of non-carbohydrates was mainly influenced by environment, except for some constituents for which the variation was more correlated to phylogeny. Finally, the variation in inorganic element concentrations mostly reflected hydro-geochemical conditions within and between peatlands.ConclusionsThe separation into an environmentally independent, phylogenetically conserved group of compounds (structural carbohydrates) and an environmentally dependent, variable group of compounds (inorganic elements, non-carbohydrates) has important implications both for understanding patterns in and for upscaling of spatially variable ecosystem processes associated with peat decomposition such as carbon sequestration, nutrient cycling and greenhouse gas emissions.

Transport, anoxia and end-product accumulation control carbon dioxide and methane production and release in peat soils

Anaerobic respiration and methanogenesis have been found to slow-down in water saturated peat soils with accumulation of metabolic end-products, i.e. dissolved inorganic carbon (DIC) and methane (CH4), due to a lack of solute and gas transport. So far it is not well understood how solute and gas transport may control this effect. We conducted a column experiment with homogenized ombrotrophic peat over a period of 300 days at 20 °C. We specifically evaluated the effects of diffusive flux as control, downward advective water flux, intensified ebullition by conduit gas transport and diffusive oxygen supply on controlling anaerobic decomposition rates and carbon (C) turnover. To simulate advective flux, water and solutes were recirculated downward through the column after stripping of dissolved gases. We analyzed DIC and CH4 concentrations, production rates and fluxes, gas filled porosity, oxygen profiles (O2) and microbial C biomass over time. DIC residence time thereby served as proxy to characterize transport. A slowdown of anaerobic respiration and methanogenesis evolved with the accumulation of the end-products DIC and CH4 and set in after 150 days. This slow-down was accompanied by a decrease in the distribution of microbial biomass C with depths. Anaerobic DIC and CH4 production rates were fastest close to the water table and sharply slowed with depth. Accumulation of DIC and CH4 in the homogeneous peat material throughout the column decreased decomposition constants from about 10−5 near the surface to 10−9 year−1 deeper in the profile. Advective water transport extended the zone of active methanogenesis compared to a diffusive system; experimental enhancement of ebullition had little or no effect as well as strictly anoxic conditions. DIC residence time was negatively correlated to anaerobic respiration suggesting this parameter to be a predictor of anaerobic peat decomposition in peatlands. Overall, this study suggests that burial of peat and accumulation of metabolic end-products effectively slows decomposition and that this effect needs to be considered to explain peat accumulation and the response of peat mineralization rates to changes in environmental conditions.

Amount and stability of recent and aged plant residues in degrading peatland soils

Peatlands store large amounts of soil organic carbon (SOC). Drainage, required for agriculture, aerates these organic soils and triggers rapid peat decomposition. In turn, cultivation of organic soils is also accompanied by input of young organic carbon (YOC) from plant residues. The extent to which YOC inputs compensate for oxidative peat loss is unknown. Furthermore, the lability of YOC in organic soils introduced by cultivation has never been examined. Here we studied the amount and lability of YOC in two adjacent drained organic soils by a combined 13C and 14C approach. Soils have been under intensive arable use for several decades and were both cultivated, inter alia, with corn, a C4 plant. In 1995, one soil was converted from annual cropping to permanent cultivation with Miscanthus x giganteus, another C4 plant, while the other was converted to permanent C3 grassland in 2009. Using δ13C signatures, we analysed the fractions of C4 derived carbon in the soil and in CO2, during one month of soil incubation. This enabled us i) to estimate C4-C accumulation in both soils, and ii) to assess the lability of C4-C carbon that accumulated either at least five years prior to sampling (current grassland soil) or until sampling (current Miscanthus soil). The fraction of C4-C derived SOC in the Miscanthus soil was 0.19 ± 0.024 in the top 30 cm, corresponding to an accumulation rate of 1.6 ± 0.2 t C4-C ha−1 yr−1. This accumulation rate is in the range of rates found for fertile mineral soils cultivated with Miscanthus. Yet, this C4-C accumulation rate is below average C-losses of agriculturally used organic soils. The grassland soil contained a smaller fraction of 0.08 ± 0.002 C4-C in SOC. The rates of total CO2 emitted from the two soils did not differ, but the fraction of CO2 derived from C4-C was significantly higher in the Miscanthus soil (0.53 ± 0.05) than in the grassland (0.29 ± 0.04) soil. Hence, in both soils YOC was more labile than bulk SOC. The ratio between the fraction of decomposing C4-C and C4-C in SOC was the same for both soils indicating a similar lability of currently accumulated and aged C4-C. In both soils, the 14C age of emitted CO2 was younger than that of SOC, confirming an increased lability of YOC over old SOC.

Evaluation on the decomposability of tropical forest peat soils after conversion to an oil palm plantation

To understand the variations in the decomposability of tropical peat soil following deforestation for an oil palm plantation, a field incubation experiment was conducted in Sarawak, Malaysia. Peat soils collected from three types of primary forest, namely Mixed Peat Swamp (MPS; Gonystylus-Dactylocladus-Neoscrotechinia association), Alan Batu (ABt; Shorea albida-Gonstylus-Strenonurus association), and Alan Bunga (ABg; Shorea albida association), were packed in polyvinyl chloride pipes and installed in an oil palm plantation. Carbon dioxide (CO2) and methane (CH4) fluxes from soil were monthly measured for 3years. Environmental variables including soil temperature, soil moisture content, and groundwater table were also monitored. The pH, loss on ignition, and total carbon (C) content were similar among the three soils, while total N content was larger in the MPS than in the ABg soils. Based on 13C nuclear magnetic resonance (NMR) spectroscopy, C composition of the MPS and ABg soils was characterized by the largest proportion of C present as alkyl C and O-alkyl C, respectively. The C composition of the ABt soil was intermediate between the MPS and ABg soils. The CO2 fluxes from the three soils ranged from 78 to 625mgCm−2h−1 with a negative correlation to groundwater level. The CH4 fluxes ranged from −67 to 653μgCm−2h−1. Both total CO2 and CH4 fluxes were larger in the order ABg>ABt>MPS (P<0.05). Annual rate of peat decomposition as was estimated from cumulative C loss differed up to 2 times, and the rate constant in exponential decay model was 0.033y−1 for the MPS soil and 0.066y−1 for the ABg soil. The field incubation results of the three forest peat soils seem to reflect the difference in the labile organic matter content, represented by polysaccharides.

Characteristics of peat humification, magnetic susceptibility and trace elements of Hani peatland, northeastern China: paleoclimatic implications

AbstractA high‐resolution peat humification record is obtained from Hani peatland, northeastern China to study climate change. An absorbance value time series from alkali‐extraction is used as a peat humification indicator. In addition, Hani peat magnetic susceptibility and trace elements have also been investigated. There is a sensitive response to abrupt climate changes when comparing a high‐resolution peat humification record with a Hani δ18O temperature proxy record and a drift ice record from the North Atlantic Ocean. Based on analyses of factors that affect peat decomposition, we suggest similar paleoclimate significance between the Hani and Dajiuhu peat on the degree of humification with a higher peat humification indicating colder and drier climate conditions. In contrast, a warm and moist climate provides a deoxidized condition that results in lower peat humification. Moreover, the Rb/Sr ratios and χlf in Hani peatland also indicate different climate conditions, especially in late Holocene. According to the Hani peat data, regional paleoclimate variations can be divided into the following five phases: 11.5–10.0 cal. kyr BP with warm climate conditions; 10.0–8.8 cal. kyr BP with sharply cooling and warming climate conditions; 8.8–4.8 cal. kyr BP with alternating cooling and warming climate conditions; 4.8–1.6 cal. kyr BP with warm climate conditions overall and 1.6–0 cal. kyr BP with cold climate conditions.