Low‐severity fire as a mechanism of organic matter protection in global peatlands: Thermal alteration slows decomposition

Worldwide, regularly recurring wildfires shape many peatland ecosystems to the extent that fire‐adapted species often dominate plant communities, suggesting that wildfire is an integral part of peatland ecology rather than an anomaly. The most destructive blazes are smoldering fires that are usually initiated in periods of drought and can combust entire peatland carbon stores. However, peatland wildfires more typically occur as low‐severity surface burns that arise in the dormant season when vegetation is desiccated, and soil moisture is high. In such low‐severity fires, surface layers experience flash heating, but there is little loss of underlying peat to combustion. This study examines the potential importance of such processes in several peatlands that span a gradient from hemiboreal to tropical ecozones and experience a wide range of fire return intervals. We show that low‐severity fires can increase the pool of stable soil carbon by thermally altering the chemistry of soil organic matter (SOM), thereby reducing rates of microbial respiration. Using X‐ray photoelectron spectroscopy and Fourier transform infrared, we demonstrate that low‐severity fires significantly increase the degree of carbon condensation and aromatization of SOM functional groups, particularly on the surface of peat aggregates. Laboratory incubations show lower CO₂ emissions from peat subjected to low‐severity fire and predict lower cumulative CO₂ emissions from burned peat after 1–3 years. Also, low‐severity fires reduce the temperature sensitivity (Q₁₀) of peat, indicating that these fires can inhibit microbial access to SOM. The increased stability of thermally altered SOM may allow a greater proportion of organic matter to survive vertical migration into saturated and anaerobic zones of peatlands where environmental conditions physiochemically protect carbon stores from decomposition for thousands of years. Thus, across latitudes, low‐severity fire is an overlooked factor influencing carbon cycling in peatlands, which is relevant to global carbon budgets as climate change alters fire regimes worldwide.     

Decomposition and Organic Matter Quality in Continental Peatlands: The Ghost of Permafrost Past

Permafrost patterning in boreal peatlands contributes to landscape heterogeneity, as peat plateaus, palsas, and localized permafrost mounds are interspersed among unfrozen bogs and fens. The degradation of localized permafrost in peatlands alters local topography, hydrology, thermal regimes, and plant communities, and creates unique peatland features called internal lawns. I used laboratory incubations to quantify carbon dioxide (CO₂) production in peat formed under different permafrost regimes (with permafrost, without permafrost, melted permafrost), and explored the relationships among proximate organic matter fractions, nutrient concentrations, and decomposition. Peat within each feature (internal lawn, bog, permafrost mound) is more chemically similar than peat collected within the same province (Alberta, Saskatchewan) or within depth intervals (surface, deep). Internal lawn peat produces more CO₂ than the other peatland types. Across peatland features, acid-insoluble material (AIM) and AIM/nitrogen are significant predictors of decomposition. However, within each peatland feature, soluble proximate fractions are better predictors of CO₂ production. Permafrost stability in peatlands influences plant and soil environments, which control litter inputs, organic matter quality, and decomposition rates. Spatial patterns of permafrost, as well as ecosystem processes within various permafrost features, should be considered when assessing the fate of soil carbon in northern ecosystems.     

The disappearance of relict permafrost in boreal north America: Effects on peatland carbon storage and fluxes

Boreal peatlands in Canada have harbored relict permafrost since the Little Ice Age due to the strong insulating properties of peat. Ongoing climate change has triggered widespread degradation of localized permafrost in peatlands across continental Canada. Here, we explore the influence of differing permafrost regimes (bogs with no surface permafrost, localized permafrost features with surface permafrost, and internal lawns representing areas of permafrost degradation) on rates of peat accumulation at the southernmost limit of permafrost in continental Canada. Net organic matter accumulation generally was greater in unfrozen bogs and internal lawns than in the permafrost landforms, suggesting that surface permafrost inhibits peat accumulation and that degradation of surface permafrost stimulates net carbon storage in peatlands. To determine whether differences in substrate quality across permafrost regimes control trace gas emissions to the atmosphere, we used a reciprocal transplant study to experimentally evaluate environmental versus substrate controls on carbon emissions from bog, internal lawn, and permafrost peat. Emissions of CO₂ were highest from peat incubated in the localized permafrost feature, suggesting that slow organic matter accumulation rates are due, at least in part, to rapid decomposition in surface permafrost peat. Emissions of CH₄ were greatest from peat incubated in the internal lawn, regardless of peat type. Localized permafrost features in peatlands represent relict surface permafrost in disequilibrium with the current climate of boreal North America, and therefore are extremely sensitive to ongoing and future climate change. Our results suggest that the loss of surface permafrost in peatlands increases net carbon storage as peat, though in terms of radiative forcing, increased CH₄ emissions to the atmosphere will partially or even completely offset this enhanced peatland carbon sink for at least 70 years following permafrost degradation.     

Consistent centennial-scale change in European sub-Arctic peatland vegetation toward Sphagnum dominance—Implications for carbon sink capacity

Climate warming is leading to permafrost thaw in northern peatlands, and current predictions suggest that thawing will drive greater surface wetness and an increase in methane emissions. Hydrology largely drives peatland vegetation composition, which is a key element in peatland functioning and thus in carbon dynamics. These processes are expected to change. Peatland carbon accumulation is determined by the balance between plant production and peat decomposition. But both processes are expected to accelerate in northern peatlands due to warming, leading to uncertainty in future peatland carbon budgets. Here, we compile a dataset of vegetation changes and apparent carbon accumulation data reconstructed from 33 peat cores collected from 16 sub-arctic peatlands in Fennoscandia and European Russia. The data cover the past two millennia that has undergone prominent changes in climate and a notable increase in annual temperatures toward present times. We show a pattern where European sub-Arctic peatland microhabitats have undergone a habitat change where currently drier habitats dominated by Sphagnum mosses replaced wetter sedge-dominated vegetation and these new habitats have remained relatively stable over the recent decades. Our results suggest an alternative future pathway where sub-arctic peatlands may at least partly sustain dry vegetation and enhance the carbon sink capacity of northern peatlands.     

Carbon storage dynamics in peatlands: Comparing recent‐ and long‐term accumulation histories in southern Patagonia

Peatlands have been important terrestrial carbon (C) reservoirs throughout the Holocene, yet whether these ecosystems will become stronger or weaker C sinks in the future remains debated. While surface peat layers (acrotelm) have a greater apparent rate of C accumulation than deeper, millennial‐aged peat (catotelm), it is difficult to project how much more aerobic decomposition will take place before the younger surface cohorts join the older deeper ones. Studies have suggested that warming could lead to weakened C accumulation in peatlands due to enhanced aerobic decay in the acrotelm, which would lead to a slower transfer of peat into the catotelm, if any. Conversely, other studies have suggested increased C accumulation in the acrotelm and thus, larger long‐term C transfer into the catotelm under warming conditions because of greater plant productivity and faster peat accumulation. Improving our predictions about the rate of present and future peatland development is important to forecast feedbacks on the global C cycle and help inform land management decisions. In this study, we analyzed two peat cores from southern Patagonia to calculate their long‐ versus short‐peat C accumulation rates. The acrotelm rates were compared to the catotelm peat C legacies using an empirical modeling approach that allows calculating the future catotelm peat storage based on today's acrotelm characteristics, and thus predict if those recent rates of C accumulation will lead to greater or weaker long‐term C storage in the future. Our results indicate that, depending on local bioclimatic parameters, some peatlands may become stronger C sinks in the future, while others may become weaker. In the case of this study, the wetter site is expected to increase its C sink capacity, while our prediction for the drier site is a net decrease in C sequestration in the coming decades to centuries.     

Soil organic matter molecular composition and state of decomposition in three locations of the European Arctic

Increased mineralization of the organic matter (OM) stored in permafrost is expected to constitute the largest additional global warming potential from terrestrial ecosystems exposed to a warmer climate. Chemical composition of permafrost OM is thought to be a key factor controlling the sensitivity of decomposition to warming. Our objective was to characterise OM from permafrost soils of the European Arctic: two mineral soils—Adventdalen, Svalbard, Norway and Vorkuta, northwest Russia—and a “palsa” (ice-cored peat mound patterning in heterogeneous permafrost landscapes) soil in Neiden, northern Norway, in terms of molecular composition and state of decomposition. At all sites, the OM stored in the permafrost was at an advanced stage of decomposition, although somewhat less so in the palsa peat. By comparing permafrost and active layers, we found no consistent effect of depth or permafrost on soil organic matter (SOM) chemistry across sites. The permafrost-affected palsa peat displayed better preservation of plant material in the deeper layer, as indicated by increasing contribution of lignin carbon to total carbon with depth, associated to decreasing acid (Ac) to aldehyde (Al) ratio of the syringyl (S) and vanillyl (V) units, and increasing S/V and contribution of plant-derived sugars. By contrast, in Adventdalen, the Ac/Al ratio of lignin and the Alkyl C to O-alkyl C ratio in the NMR spectra increased with depth, which suggests less oxidized SOM in the active layer compared to the permafrost layer. In Vorkuta, SOM characteristics in the permafrost profile did not change substantially with depth, probably due to mixing of soil layers by cryoturbation. The composition and state of decomposition of SOM appeared to be site-specific, in particular bound to the prevailing organic or mineral nature of soil when attempting to predict the SOM proneness to degradation. The occurrence of processes such as palsa formation in organic soils and cryoturbation should be considered when up-scaling and predicting the responses of OM to climate change in arctic soils.     

Ecosystem state shifts during long‐term development of an Amazonian peatland

The most carbon (C)‐dense ecosystems of Amazonia are areas characterized by the presence of peatlands. However, Amazonian peatland ecosystems are poorly understood and are threatened by human activities. Here, we present an investigation into long‐term ecohydrological controls on C accumulation in an Amazonian peat dome. This site is the oldest peatland yet discovered in Amazonia (peat initiation ca. 8.9 ka BP), and developed in three stages: (i) peat initiated in an abandoned river channel with open water and aquatic plants; (ii) inundated forest swamp; and (iii) raised peat dome (since ca. 3.9 ka BP). Local burning occurred at least three times in the past 4,500 years. Two phases of particularly rapid C accumulation (ca. 6.6–6.1 and ca. 4.9–3.9 ka BP), potentially resulting from increased net primary productivity, were seemingly driven by drier conditions associated with widespread drought events. The association of drought phases with major ecosystem state shifts (open water wetland–forest swamp–peat dome) suggests a potential climatic control on the developmental trajectory of this tropical peatland. A third drought phase centred on ca. 1.8–1.1 ka BP led to markedly reduced C accumulation and potentially a hiatus during the peat dome stage. Our results suggest that future droughts may lead to phases of rapid C accumulation in some inundated tropical peat swamps, although this can lead ultimately to a shift to ombrotrophy and a subsequent return to slower C accumulation. Conversely, in ombrotrophic peat domes, droughts may lead to reduced C accumulation or even net loss of peat. Increased surface wetness at our site in recent decades may reflect a shift towards a wetter climate in western Amazonia. Amazonian peatlands represent important carbon stores and habitats, and are important archives of past climatic and ecological information. They should form key foci for conservation efforts.     

Effects of disturbances on the carbon balance of tropical peat swamp forests

Tropical peatlands have accumulated huge soil carbon over millennia. However, the carbon pool is presently disturbed on a large scale by land development and management, and consequently has become vulnerable. Peat degradation occurs most rapidly and massively in Indonesia, because of fires, drainage, and deforestation of swamp forests coexisting with tropical peat. Peat burning releases carbon dioxide (CO₂) intensively but occasionally, whereas drainage increases CO₂ emission steadily through the acceleration of aerobic peat decomposition. Therefore, tropical peatlands present the threat of switching from a carbon sink to a carbon source to the atmosphere. However, the ecosystem‐scale carbon exchange is still not known in tropical peatlands. A long‐term field experiment in Central Kalimantan, Indonesia showed that tropical peat ecosystems, including a relatively intact peat swamp forest with little drainage (UF), a drained swamp forest (DF), and a drained burnt swamp forest (DB), functioned as net carbon sources. Mean annual net ecosystem CO₂ exchange (NEE) (± a standard deviation) for 4 years from July 2004 to July 2008 was 174 ± 203, 328 ± 204 and 499 ± 72 gC m^?2 yr^?1, respectively, for the UF, DF, and DB sites. The carbon emissions increased according to disturbance degrees. We found that the carbon balance of each ecosystem was chiefly controlled by groundwater level (GWL). The NEE showed a linear relationship with GWL on an annual basis. The relationships suggest that annual CO₂ emissions increase by 79–238 gC m^?2 every 0.1 m of GWL lowering probably because of the enhancement of oxidative peat decomposition. In addition, CO₂ uptake by vegetation photosynthesis was reduced by shading due to dense smoke from peat fires ignited accidentally or for agricultural practices. Our results may indicate that tropical peatland ecosystems are no longer a carbon sink under the pressure of human activities.     

Vascular plant‐mediated controls on atmospheric carbon assimilation and peat carbon decomposition under climate change

Climate change can alter peatland plant community composition by promoting the growth of vascular plants. How such vegetation change affects peatland carbon dynamics remains, however, unclear. In order to assess the effect of vegetation change on carbon uptake and release, we performed a vascular plant‐removal experiment in two Sphagnum‐dominated peatlands that represent contrasting stages of natural vegetation succession along a climatic gradient. Periodic measurements of net ecosystem CO₂ exchange revealed that vascular plants play a crucial role in assuring the potential for net carbon uptake, particularly with a warmer climate. The presence of vascular plants, however, also increased ecosystem respiration, and by using the seasonal variation of respired CO₂ radiocarbon (bomb‐¹⁴C) signature we demonstrate an enhanced heterotrophic decomposition of peat carbon due to rhizosphere priming. The observed rhizosphere priming of peat carbon decomposition was matched by more advanced humification of dissolved organic matter, which remained apparent beyond the plant growing season. Our results underline the relevance of rhizosphere priming in peatlands, especially when assessing the future carbon sink function of peatlands undergoing a shift in vegetation community composition in association with climate change.     

北方泥炭地氮素有效性的变化及其对碳汇功能的影响

北方泥炭地是典型的氮限制性生态系统,对全球气候变化及人类活动响应敏感。气候变暖导致内源有效氮增加以及人类活动引起的大量外源氮输入,改变了北方泥炭地氮素有效性,对泥炭地碳氮循环过程及碳汇功能产生了深远影响。本文综述了北方泥炭地碳积累速率和碳汇功能的影响因素,分析了氮沉降、冻融、火烧等因素对北方泥炭地氮素有效性的影响,分别从碳固定和碳排放过程阐述了植物及土壤微生物对氮素有效性变化的响应,并对全球变化影响下泥炭生态系统碳汇功能相关研究进行了展望,以期助力“双碳”目标的实施。     

Holocene Carbon Accumulation of Fen Peatlands in Boreal Western Canada: A Complex Ecosystem Response to Climate Variation and Disturbance

Understanding the long-term ecological dynamics of northern peatlands is essential for assessment of the possible responses and feedbacks of these carbon-rich ecosystems to climate change and natural disturbance. I used high-resolution macrofossil and lithological analyses of a fen peatland in western Canada to infer the Holocene developmental history of the peatland, to document the temporal pattern of long-term peat accumulation, and to investigate ecosystems responses to climate changes in terms of species composition and carbon accumulation. The peatland has been dominated by sedges and brown mosses during its 10,000-year history, despite interruption by tephra deposition. Peat accumulation rates vary by more than an order of magnitude and decline from 5500 to 1300 cal BP, resulting in a convex depth–age curve, which contrasts with the carbon accumulation patterns documented for oceanic peatlands. The synthesis of regional data from continental western Canada indicates that fens tend to accumulate more carbon than bogs of the same ages. These data suggest that the carbon sink potential of northern peatlands has varied dramatically in the past, so estimates of the present and projected carbon sink strengths of these peatlands need to take this temporal variation into consideration. Widespread slowdown of peat accumulation over the last 4000 years may have resulted from climate cooling in northern latitudes after the Holocene insolation maximum. The findings indicate that long-term peatland dynamics are modified by many local and regional factors and that gradual environmental change may be capable of triggering abrupt shifts and jumps in ecosystem states.     

Modelling past and future peatland carbon dynamics across the pan‐Arctic

The majority of northern peatlands were initiated during the Holocene. Owing to their mass imbalance, they have sequestered huge amounts of carbon in terrestrial ecosystems. Although recent syntheses have filled some knowledge gaps, the extent and remoteness of many peatlands pose challenges to developing reliable regional carbon accumulation estimates from observations. In this work, we employed an individual‐ and patch‐based dynamic global vegetation model (LPJ‐GUESS) with peatland and permafrost functionality to quantify long‐term carbon accumulation rates in northern peatlands and to assess the effects of historical and projected future climate change on peatland carbon balance. We combined published datasets of peat basal age to form an up‐to‐date peat inception surface for the pan‐Arctic region which we then used to constrain the model. We divided our analysis into two parts, with a focus both on the carbon accumulation changes detected within the observed peatland boundary and at pan‐Arctic scale under two contrasting warming scenarios (representative concentration pathway—RCP8.5 and RCP2.6). We found that peatlands continue to act as carbon sinks under both warming scenarios, but their sink capacity will be substantially reduced under the high‐warming (RCP8.5) scenario after 2050. Areas where peat production was initially hampered by permafrost and low productivity were found to accumulate more carbon because of the initial warming and moisture‐rich environment due to permafrost thaw, higher precipitation and elevated CO₂ levels. On the other hand, we project that areas which will experience reduced precipitation rates and those without permafrost will lose more carbon in the near future, particularly peatlands located in the European region and between 45 and 55°N latitude. Overall, we found that rapid global warming could reduce the carbon sink capacity of the northern peatlands in the coming decades.     

Biotic and Abiotic Drivers of Peatland Growth and Microtopography: A Model Demonstration

Peatlands are important carbon reserves in terrestrial ecosystems. The microtopography of a peatland area has a strong influence on its carbon balance, determining carbon fluxes at a range of spatial scales. These patterned surfaces are very sensitive to changing climatic conditions. There are open research questions concerning the stability, behaviour and transformation of these microstructures, and the implications of these changes for the long-term accumulation of organic matter in peatlands. A simple two-dimensional peat microtopographical model was developed, which accounts for the effects of microtopographical variations and a dynamic water table on competitive interactions between peat-forming plants. In a case study of a subarctic mire in northern Sweden, we examined the consequences of such interactions on peat accumulation patterns and the transformation of microtopographical structure. The simulations demonstrate plausible interactions between peatland growth, water table position and microtopography, consistent with many observational studies, including an observed peat age profile from the study area. Our model also suggests that peatlands could exhibit alternative compositional and structural dynamics depending on the initial topographical and climatic conditions, and plant characteristics. Our model approach represents a step towards improved representation of peatland vegetation dynamics and net carbon balance in Earth system models, allowing their potentially important implications for regional and global carbon balances and biogeochemical and biophysical feedbacks to the atmosphere to be explored and quantified.     

Evidence for older carbon loss with lowered water tables and changing plant functional groups in peatlands

A small imbalance in plant productivity and decomposition accounts for the carbon (C) accumulation capacity of peatlands. As climate changes, the continuity of peatland net C storage relies on rising primary production to offset increasing ecosystem respiration (ER) along with the persistence of older C in waterlogged peat. A lowering in the water table position in peatlands often increases decomposition rates, but concurrent plant community shifts can interactively alter ER and plant productivity responses. The combined effects of water table variation and plant communities on older peat C loss are unknown. We used a full-factorial 1-m³ mesocosm array with vascular plant functional group manipulations (Unmanipulated Control, Sedge only, and Ericaceous only) and water table depth (natural and lowered) treatments to test the effects of plants and water depth on CO₂ fluxes, decomposition, and older C loss. We used Δ¹⁴C and δ¹³C of ecosystem CO₂ respiration, bulk peat, plants, and porewater dissolved inorganic C to construct mixing models partitioning ER among potential sources. We found that the lowered water table treatments were respiring C fixed before the bomb spike (1955) from deep waterlogged peat. Lowered water table Sedge treatments had the oldest dissolved inorganic ¹⁴C signature and the highest proportional peat contribution to ER. Decomposition assays corroborated sustained high rates of decomposition with lowered water tables down to 40 cm below the peat surface. Heterotrophic respiration exceeded plant respiration at the height of the growing season in lowered water table treatments. Rates of gross primary production were only impacted by vegetation, whereas ER was affected by vegetation and water table depth treatments. The decoupling of respiration and primary production with lowered water tables combined with older C losses suggests that climate and land-use-induced changes in peatland hydrology can increase the vulnerability of peatland C stores.     

The Effects of Peatland Restoration on Water‐Table Depth,Elemental Concentrations,and Vegetation: 10 Years of Changes

We studied the effects of restoration on water‐table depth (WTD), element concentrations of peat and vegetation composition of peatlands drained for forestry in southern Finland. The restoration aimed to return the trajectory of vegetation succession toward that of undisturbed systems through the blockage of ditches and the removal of trees. Permanent plots established on a bog and a fen were sampled 1 year before, and 1, 2, 3, and 10 years after the restoration. The restoration resulted in a long‐term rise of the water‐table in both peatlands. Ten years after restoration, the mineral element concentrations (Ca, K, Mg, Mn, and P) of peat corresponded to those reported from comparable pristine peatlands. In particular, the increase of K and Mn concentrations at both sites suggests the recovery of ecosystem functionality in terms of nutrient cycling between peat and plants. The restoration resulted in the succession of plant communities toward the targeted peatland vegetation of wetter condition at both sites. This was evident from the decreased abundance of species benefiting from drainage and the corresponding increase of peatland species. However, many species typical of pristine peatlands were missing 10 years after restoration. We conclude that the restoration led to a reversal of the effects of drainage in vegetation and studied habitat conditions. However, due to the slow recovery of peatland ecosystems and the possibility that certain failures in the restoration measures may become apparent only after extended time periods, long‐term monitoring is needed to determine whether the goals of restoration will be met.     

Patterns of Fungal and Bacterial Carbon Mineralization Across Northern European Peatlands

The fungal and bacterial activity was determined in 20 northern European peatlands ranging from ombrotrophic bogs to eutrophic fens with key differences in degree of humification, pH, dry bulk density, carbon (C) content and vegetation communities using the selective inhibition (SI) technique. These peatlands were partly disturbed and the respective water tables lowered below the surface layer. Basal respiration ranged from 24 to 128 µg CO₂-C g^?1 dry peat d^?1. Bacterial contributions to CO₂ production were high in most peatlands and showed the following pattern: eutrophic >> transitional ≥ mesotrophic >> ombrotrophic peatland types. The fungal-to-bacterial (F:B) ratios varied substantially within peatland type, and this was mainly attributed to differences in peat botanical compositions and chemistry. The computed mean Inhibitor Additivity Ratio (IAR) was quite close to 1 to suggest that the SI techniques can be used to partition eukaryotic and prokaryotic activity in wide range of peatlands. Overall, basal respiration, microbial biomass-C, fungal and bacterial activities varied across the studied peatland types, and such differences could have consequences for C- and nutrient-cycling as well as how bogs and fens will respond to environmental changes.     

Status and restoration of peatlands in northern Europe

Environmental management of peatlands,landscape ecology and protection of keybiotopes have created needs and pressure torestore drained peatlands to natural mireecosystems. Here, we summarize differentapproaches and restoration techniquesdeveloped for peatland management inEstonia, Sweden, and Finland wherepeatlands are abundant. Without rewetting,plant colonisation on abandoned cut-awayareas is slow due to harsh hydrological andmicroclimatic conditions. However, after restoration, cut-away peatlands may returnto a functional state close to that ofpristine mires, and therefore restore a netcarbon sink function within a few years. Inaddition, restoration techniques can helpto create buffer zones between terrestrialand limnic ecosystems that reduces thenutrient loading imposed on watercourses byforestry operations. Restoration may alsobe important for peatland conservationprograms as drained peatlands are part ofpresent and future conservation areas.Finally, restoration actions in themselvescan have negative environmental impacts.For instance, inundation of peat surfacesresulting from the rewetting process oftenincreases phosphorus leaching. Efforts onpeatland restoration should focus onenvironmental monitoring, research onrestoration and its environmental impact aswell as public relations activities. Inthat respect, knowledge transfer betweenacademics and managers should generatesynergy benefits.     

Mineralization and Decomposition Rates in Restored Pine Fens

Growing public interest in conserving peatlands has created a need for restoration and rapid indicators of progress in peat formation. Vegetation and hydrological indicators are commonly assessed, but changes in mineralization and decomposition rates might better indicate when peat formation is underway in restored peatlands. In Finland, we investigated differences in mineralization and decomposition in the upper peat layer of five undrained and eight drained Pinus‐dominated fens from 2006 to 2009. Forestry‐drained fens were restored in 2007 by harvesting either whole trees or only stems, and by damming and filling ditches. Before restoration, net N mineralization rate was slightly higher in the drained than in undrained fens, whereas soil pH and Betula leaf litter decomposition rate were lower. After restoration, net N mineralization rate was similar for the undrained and restored fens, except near ditches after stem harvest. Also, soil pH and decomposition rate of Betula leaf litter became similar for undrained and restored fens. We conclude that whole tree harvest is a more suitable method for peatland restoration than stem harvest and that mineralization and decomposition rates are suitable indicators for peat formation after restoration.     

15000年以来若尔盖高原泥炭地发育及其碳动态

高海拔泥炭地是维护高原气候环境稳定的重要生态系统,由于其兼具高海拔和高寒的特点,对气候变化尤为敏感。若尔盖高原泥炭地是中国高海拔泥炭地集中分布区,碳储量丰富,由于方法学差异及数据缺乏,其碳储量估算仍存在一定程度的不确定性,对长时间尺度碳通量的模拟研究还较为匮乏。因此,以若尔盖高原泥炭地为研究对象,基于若尔盖高原泥炭地每千年的面积变化和碳累积速率重新评估若尔盖高原泥炭地碳储量,并利用泥炭分解模型和碳通量重建模型探讨了15000年以来若尔盖高原泥炭地碳通量动态。研究结果表明,若尔盖高原泥炭地约从15000年开始发育,发育高峰期在12000-10000年和7000-5000年,泥炭累积速率范围为0.22-1.31 mm/a,平均值为0.56 mm/a;碳累积速率范围为13.4-77.2 g C m^-2 a^-1,平均碳累积速率为33.5 g C m^-2 a^-1,3000年至今碳累积速率最高,7000-6000年是碳累积速率次峰值时期;15000年以来若尔盖高原泥炭地碳储存量达1.4 Pg（1 Pg=10¹⁵ g）,碳累积输入和碳累积释放分别为5.6 Pg和4.2 Pg;净碳平衡平均值为0.087 Tg（1 Tg=10¹² g）C/a,峰值出现在11000-10000年为0.295 Pg;在6000-2000年若尔盖泥炭地出现微弱碳源,最大值出现在5000-4000年,约为-0.034 Pg,净碳平衡在15000-11000年和4000年至今呈现上升趋势,而10000-4000年整体呈现下降趋势。总体而言,若尔盖高原泥炭地碳储量丰富,是青藏高原东部重要的陆地生态系统碳库和碳汇,本研究将为我国高海拔泥炭地碳库保育提供一定的理论和数据支撑。     

A Tropical Freshwater Wetland: II. Production,Decomposition, and Peat Formation

As much as 10% of the total carbon stored in peatlands occurs in the tropics. Although tropical peatlands are poorly understood scientifically, they are increasingly exploited for a variety of human uses. Our objective was to measure baseline carbon cycling data in one type of tropical peatland in order to understand better how peat accumulates in these ecosystems. Average plant production for two study sites on the island of Kosrae in the Federated States of Micronesia over 2 year was 1122 g C m⁻² year⁻¹, of which 1058 g C m⁻² year⁻¹ was aboveground plant production (bole, buttress and litterfall). Although leaves contributed a high proportion of total plant productivity, their rapid decomposition left little carbon for peat accumulation. In contrast, fine roots only contributed 10% to plant productivity, but their slow decomposition allowed them to accumulate as peat. Wood (branches and stems) probably contributed the most carbon to the formation of peat. Despite being on the soil surface, small branches decomposed more slowly than leaves because of their high C:N and lignin:N ratios. In summary, we suggest that tropical peatlands in Micronesia accumulate peat not because of high plant production but rather because of slow decomposition of roots and wood under anaerobic conditions that result from nearly constant high water levels.