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.     

Permafrost Distribution Drives Soil Organic Matter Stability in a Subarctic Palsa Peatland

Palsa peatlands, permafrost-affected peatlands characteristic of the outer margin of the discontinuous permafrost zone, form unique ecosystems in northern-boreal and arctic regions, but are now degrading throughout their distributional range due to climate warming. Permafrost thaw and the degradation of palsa mounds are likely to affect the biogeochemical stability of soil organic matter (that is, SOM resistance to microbial decomposition), which may change the net C source/sink character of palsa peatland ecosystems. In this study, we have assessed both biological and chemical proxies for SOM stability, and we have investigated SOM bulk chemistry with mid-infrared spectroscopy, in surface peat of three distinct peatland features in a palsa peatland in northern Norway. Our results show that the stability of SOM in surface peat as determined by both biological and chemical proxies is consistently higher in the permafrost-associated palsa mounds than in the surrounding internal lawns and bog hummocks. Our results also suggest that differences in SOM bulk chemistry is a main factor explaining the present SOM stability in surface peat of palsa peatlands, with selective preservation of recalcitrant and highly oxidized SOM components in the active layer of palsa mounds during intense aerobic decomposition over time, whereas SOM in the wetter areas of the peatland remains stabilized mainly by anaerobic conditions. The continued degradation of palsa mounds and the expansion of wetter peat areas are likely to modify the bulk SOM chemistry of palsa peatlands, but the effect on the future net C source/sink character of palsa peatlands will largely depend on moisture conditions and oxygen availability in peat.     

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.     

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.     

Ecosystem carbon response of an Arctic peatland to simulated permafrost thaw

Permafrost peatlands are biogeochemical hot spots in the Arctic as they store vast amounts of carbon. Permafrost thaw could release part of these long‐term immobile carbon stocks as the greenhouse gases (GHGs) carbon dioxide (CO₂) and methane (CH₄) to the atmosphere, but how much, at which time‐span and as which gaseous carbon species is still highly uncertain. Here we assess the effect of permafrost thaw on GHG dynamics under different moisture and vegetation scenarios in a permafrost peatland. A novel experimental approach using intact plant–soil systems (mesocosms) allowed us to simulate permafrost thaw under near‐natural conditions. We monitored GHG flux dynamics via high‐resolution flow‐through gas measurements, combined with detailed monitoring of soil GHG concentration dynamics, yielding insights into GHG production and consumption potential of individual soil layers. Thawing the upper 10–15 cm of permafrost under dry conditions increased CO₂ emissions to the atmosphere (without vegetation: 0.74 ± 0.49 vs. 0.84 ± 0.60 g CO₂–C m^?2 day^?1; with vegetation: 1.20 ± 0.50 vs. 1.32 ± 0.60 g CO₂–C m^?2 day^?1, mean ± SD, pre‐ and post‐thaw, respectively). Radiocarbon dating (¹⁴C) of respired CO₂, supported by an independent curve‐fitting approach, showed a clear contribution (9%–27%) of old carbon to this enhanced post‐thaw CO₂ flux. Elevated concentrations of CO₂, CH₄, and dissolved organic carbon at depth indicated not just pulse emissions during the thawing process, but sustained decomposition and GHG production from thawed permafrost. Oxidation of CH₄ in the peat column, however, prevented CH₄ release to the atmosphere. Importantly, we show here that, under dry conditions, peatlands strengthen the permafrost–carbon feedback by adding to the atmospheric CO₂ burden post‐thaw. However, as long as the water table remains low, our results reveal a strong CH₄ sink capacity in these types of Arctic ecosystems pre‐ and post‐thaw, with the potential to compensate part of the permafrost CO₂ losses over longer timescales.     

Effect of water table drawdown on peatland nutrient dynamics: implications for climate change

It is anticipated that a lowering of the water table and reduced soil moisture levels in peatlands may increase peat decomposition rates and consequently affect nutrient availability. However, it is not clear if patterns will be consistent across different peatland types or within peatlands given the natural range of ecohydrological conditions within these systems. We examined the effect of persistent drought on peatland nutrient dynamics by quantifying the effects of an experimentally lowered water table position (drained for a 10-year period) on peat KCl-extractable total inorganic nitrogen (ext-TIN), peat KCl-extractable nitrate (ext-NO₃ ^?), and water-extractable ortho-phosphorus (ext-PO₄ ^3?) concentrations and net phosphorus (P) and nitrogen (N) mineralization and nitrification rates at natural (control) and drained microforms (hummocks, lawns) of a bog and poor fen near Québec City, Canada. Drainage (water table drawdown) decreased net nitrification rates across the landscape and increased ext-NO₃ ^? concentrations, but did not affect net N and P mineralization rates or ext-TIN and ext-PO₄ ^3? concentrations. We suggest that the thick capillary fringe at the drained peatland likely maintained sufficient moisture above the water table to limit the effects of drainage on microbial activity, and a 20 cm lowering of the water table does not appear to have been sufficient to create a clear difference in nutrient dynamics in this peatland landscape. We found some evidence of differences in nutrient concentrations with microforms, where concentrations were greater in lawn than hummock microforms at control sites indicating some translocation of nutrients. In general, the same microtopographic differences were not observed at drained sites. The general spatial patterns in nutrient concentrations did not reflect net mineralization/immobilization rates measured at our control or drained peatlands. Rather, the spatial patterns in nutrient availability may be regulated by differences in vegetation (mainly Sphagnum moss) cover between control and drained sites and possibly differences in hydrologic connection between microforms. Our results suggest that microform distribution and composition within a peatland may be important for determining how peatland nutrient dynamics will respond to water table drawdown in northern peatlands, as some evidence of microtopographic differences in nutrient dynamics was found.     

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.     

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。     

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.     

Towards sustainable management of Indonesian tropical peatlands

Large areas of Indonesian peatlands have been converted for agricultural and plantation forest purposes. This requires draining with associated CO₂ emissions and fire risks. In order to identify alternative management regimes for peatlands, it is important to understand the sustainability of different peatland uses as well as the economic benefits peatlands supply under different land uses. This study explores the key sustainability issues in Indonesian peatlands, the ecosystem services supplied by peatlands, and potential responses to promote more sustainable peatland use. A literature review and spatial analysis were conducted. Based on predominantly government data, we estimate the amount of Indonesian peatlands that has been converted between 2000 and 2014. We quantify increases in oil palm and plantation forest crop production in this period, and we analyse key sustainability issues, i.e. peat fires and smoke-haze, soil subsidence and flood risk, CO₂ emissions, loss of habitat (in protected areas), and social conflicts that influence sustainability of Indonesian peatlands management. Among others we show that CO₂ emissions from peatlands in Indonesia can be estimated at between 350 and 400 million ton CO₂ per year, and that encroachment of oil palm and plantation forestry (acacia, rubber) has taken place on 28% of protected areas. However, as we examine, the uncertainties involved are substantial. Based on our findings, we distil several implications for the management of the peatlands.     

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.     

Rapid carbon loss and slow recovery following permafrost thaw in boreal peatlands

Permafrost peatlands store one‐third of the total carbon (C) in the atmosphere and are increasingly vulnerable to thaw as high‐latitude temperatures warm. Large uncertainties remain about C dynamics following permafrost thaw in boreal peatlands. We used a chronosequence approach to measure C stocks in forested permafrost plateaus (forest) and thawed permafrost bogs, ranging in thaw age from young (<10 years) to old (>100 years) from two interior Alaska chronosequences. Permafrost originally aggraded simultaneously with peat accumulation (syngenetic permafrost) at both sites. We found that upon thaw, C loss of the forest peat C is equivalent to ~30% of the initial forest C stock and is directly proportional to the prethaw C stocks. Our model results indicate that permafrost thaw turned these peatlands into net C sources to the atmosphere for a decade following thaw, after which post‐thaw bog peat accumulation returned sites to net C sinks. It can take multiple centuries to millennia for a site to recover its prethaw C stocks; the amount of time needed for them to regain their prethaw C stocks is governed by the amount of C that accumulated prior to thaw. Consequently, these findings show that older peatlands will take longer to recover prethaw C stocks, whereas younger peatlands will exceed prethaw stocks in a matter of centuries. We conclude that the loss of sporadic and discontinuous permafrost by 2100 could result in a loss of up to 24 Pg of deep C from permafrost peatlands.     

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.     

Permafrost condition determines plant community composition and community‐level foliar functional traits in a boreal peatland

Boreal peatlands are critical ecosystems globally because they house 30%–40% of terrestrial carbon (C), much of which is stored in permafrost soil vulnerable to climate warming‐induced thaw. Permafrost thaw leads to thickening of the active (seasonally thawed) layer and alters nutrient and light availability. These physical changes may influence community‐level plant functional traits through intraspecific trait variation and/or species turnover. As permafrost thaw is expected to cause an efflux of carbon dioxide (CO₂) and methane (CH₄) from the soil to the atmosphere, it is important to understand thaw‐induced changes in plant community productivity to evaluate whether these changes may offset some of the anticipated increases in C emissions. To this end, we collected vascular plant community composition and foliar functional trait data along gradients in aboveground tree biomass and active layer thickness (ALT) in a rapidly thawing boreal peatland, with the expectation that changes in above‐ and belowground conditions are indicative of altered resource availability. We aimed to determine whether community‐level traits vary across these gradients, and whether these changes are dominated by intraspecific trait variation, species turnover, or both. Our results highlight that variability in community‐level traits was largely attributable to species turnover and that both community composition and traits were predominantly driven by ALT. Specifically, thicker active layers associated with permafrost‐free peatlands (i.e., bogs and fens) shifted community composition from slower‐growing evergreen shrubs to faster‐growing graminoids and forbs with a corresponding shift toward more productive trait values. The results from this rapidly thawing peatland suggest that continued warming‐induced permafrost thaw and thermokarst development alter plant community composition and community‐level traits and thus ecosystem productivity. Increased productivity may help to mitigate anticipated CO₂ efflux from thawing permafrost, at least in the short term, though this response may be swamped by increase CH₄ release.     

Mineralization rates of peat from eroding peat islands in reservoirs

Reservoirs are sources of greenhouses gases to the atmosphere, primarily due to organic carbon mineralization in flooded plants and soils to carbon dioxide (CO₂) and methane (CH₄). Floating peat islands are common in reservoirs that inundated peatlands. These islands can decompose on mass, or small pieces of peat can erode from islands to decompose in the water column or on the bottom of reservoirs. Here we used large 450 liter sealed enclosures to measure mineralization rates of small peat pieces and larger peat blocks collected from floating peat islands. Mineralization rates were calculated by quantifying dissolved inorganic carbon (DIC), CO₂ and CH₄ accumulation within the water and headspace of the enclosures over time. We found that peat did decompose under water, but rates of mineralization of peat pieces were not different than rates of mineralization of larger peat blocks. Mineralization rates ranged between 59 and l40 g C g^–1 d^–1. Peat pieces acidified the water, shifting the bicarbonate equilibrium to almost exclusively dissolved CO₂, which was then readily able to flux to the atmosphere. We estimated that 2.4–5.6% of peat carbon was mineralized annually, suggesting that fluxes of CO₂ and CH₄ from reservoirs that flood peatlands could last at minimum 18–42 years from this carbon source alone.     

Permafrost thaw causes large carbon loss in boreal peatlands while changes to peat quality are limited

Rapid, ongoing permafrost thaw of peatlands in the discontinuous permafrost zone is exposing a globally significant store of soil carbon (C) to microbial processes. Mineralization and release of this peat C to the atmosphere as greenhouse gases is a potentially important feedback to climate change. Here we investigated the effects of permafrost thaw on peat C at a peatland complex in western Canada. We collected 15 complete peat cores (between 2.7 and 4.5 m deep) along four chronosequences, from elevated permafrost peat plateaus to saturated thermokarst bogs that thawed up to 600 years ago. The peat cores were analysed for peat C storage and peat quality, as indicated by decomposition proxies (FTIR and C/N ratios) and potential decomposability using a 200-day aerobic laboratory incubation. Our results suggest net C loss following thaw, with average total peat C stocks decreasing by ~19.3 ± 7.2 kg C m⁻² over <600 years (~13% loss). Average post-thaw accumulation of new peat at the surface over the same period was ~13.1 ± 2.5 kg C m⁻². We estimate ~19% (±5.8%) of deep peat (>40 cm below surface) C is lost following thaw (average 26 ± 7.9 kg C m⁻² over <600 years). Our FTIR analysis shows peat below the thaw transition in thermokarst bogs is slightly more decomposed than peat of a similar type and age in permafrost plateaus, but we found no significant changes to the quality or lability of deeper peat across the chronosequences. Our incubation results also showed no increase in C mineralization of deep peat across the chronosequences. While these limited changes in peat quality in deeper peat following permafrost thaw highlight uncertainty in the exact mechanisms and processes for C loss, our analysis of peat C stocks shows large C losses following permafrost thaw in peatlands in western Canada.     

Holocene radiative forcing impact of northern peatland carbon accumulation and methane emissions

Throughout the Holocene, northern peatlands have both accumulated carbon and emitted methane. Their impact on climate radiative forcing has been the net of cooling (persistent CO₂ uptake) and warming (persistent CH₄ emission). We evaluated this by developing very simple Holocene peatland carbon flux trajectories, and using these as inputs to a simple atmospheric perturbation model. Flux trajectories are based on estimates of contemporary CH₄ flux (15–50 Tg CH₄ yr⁻¹), total accumulated peat C (250–450 Pg C), and peatland initiation dates. The contemporary perturbations to the atmosphere due to northern peatlands are an increase of ∼100 ppbv CH₄ and a decrease of ∼35 ppmv CO₂. The net radiative forcing impact northern peatlands is currently about −0.2 to −0.5 W m⁻² (a cooling). It is likely that peatlands initially caused a net warming of up to +0.1 W m⁻², but have been causing an increasing net cooling for the past 8000–11 000 years. A series of sensitivity simulations indicate that the current radiative forcing impact is determined primarily by the magnitude of the contemporary methane flux and the magnitude of the total C accumulated as peat, and that radiative forcing dynamics during the Holocene depended on flux trajectory, but the overall pattern was similar in all cases.     

Carbon emissions from South‐East Asian peatlands will increase despite emission‐reduction schemes

Carbon emissions from drained peatlands converted to agriculture in South‐East Asia (i.e., Peninsular Malaysia, Sumatra and Borneo) are globally significant and increasing. Here, we map the growth of South‐East Asian peatland agriculture and estimate CO₂ emissions due to peat drainage in relation to official land‐use plans with a focus on the reducing emissions from deforestation and degradation (REDD+)‐related Indonesian moratorium on granting new concession licences for industrial agriculture and logging. We find that, prior to 2010, 35% of South‐East Asian peatlands had been converted to agriculture, principally by smallholder farmers (15% of original peat extent) and industrial oil palm plantations (14%). These conversions resulted in 1.46–6.43 GtCO₂ of emissions between 1990 and 2010. This legacy of historical clearances on deep‐peat areas will contribute 51% (4.43–11.45 GtCO₂) of projected future peatland CO₂ emissions over the period 2010–2130. In Indonesia, which hosts most of the region's peatland and where concession maps are publicly available, 70% of peatland conversion to agriculture occurred outside of known concessions for industrial plantation development, with smallholders accounting for 60% and industrial oil palm accounting for 34%. Of the remaining Indonesian peat swamp forest (PSF), 45% is not protected, and its conversion would amount to CO₂ emissions equivalent to 0.7%–2.3% (5.14–14.93 Gt) of global fossil fuel and cement emissions released between 1990 and 2010. Of the peatland extent included in the moratorium, 48% was no longer forested, and of the PSF included, 40%–48% is likely to be affected by drainage impacts from agricultural areas and will emit CO₂ over time. We suggest that recent legislation and policy in Indonesia could provide a means of meaningful emission reductions if focused on revised land‐use planning, PSF conservation both inside and outside agricultural concessions, and the development of agricultural practices based on rehabilitating peatland hydrological function.     

The carbon content characteristics of tropical peats in Central Kalimantan, Indonesia: Estimating their spatial variability in density

Clarification of carbon content characteristics, on their spatial variability in density, of tropical peatlands is needed for more accurate estimates of the C pools and more detailed C cycle understandings. In this study, the C density characteristics of different peatland types and at various depths within tropical peats in Central Kalimantan were analyzed. The peatland types and the land cover types were classified by land system map and remotely sensed data of multi-temporal AVHRR composites (1-km pixel size), respectively. Differences in the mean values of volumetric C density (CD_V) were found among peatland types owing to the variability in physical consolidation from peat decomposition or nutrient inputs, although no vertical trends of CD_V were found. Using a step-wise regression technique, geographic variables and the categories of peatland type and land cover type were found to explain 54% of the variability of CD_V within tropical peatlands in some conditions.     

Legume inoculant application methods: effects on nodulation patterns,nitrogen fixation,crop growth and yield in narrow-leaf lupin and faba bean

Aims

Plant growth forms can influence carbon cycling, particularly in carbon-rich ecosystems like northern peatlands; however, mechanistic evidence of this relationship is limited. Our aim was to determine if northern peatland plant growth forms alter belowground dissolved carbon chemistry and enhance carbon release through stimulated microbial metabolism.

Methods

We used replicated, peat monoliths populated exclusively by Sphagnum mosses, graminoids, or bare peat and quantified changes in belowground dissolved organic carbon chemistry, microbial metabolism, as well as respired CO₂.

Results

The graminoid growth form was significantly distinct in belowground dissolved organic carbon chemistry with carbon compound lability 20 % and 11 % greater than bare peat and Sphagnum moss respectively. The labile dissolved organic carbon stimulated the microbial community, as indicated by greater microbial metabolic activity and richness values in conjunction with 50 % higher respired CO₂ fluxes under the graminoid treatment.

Conclusions

Our results provide mechanistic evidence that peatland plant growth forms can drive carbon cycling processes by altering dissolved organic carbon chemistry to prompt cascading effects on the microbial community and carbon release — trends suggestive of microbial priming effects. Should climate change increase graminoid prevalence at the expense of Sphagnum moss northern peatland carbon store stability may be threatened by this mechanism.