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Soil respiration (CO2 effluxes) is a critical component for land-based greenhouse gas (GHG) monitoring, reporting and modelling. In organic matter-rich tropical peatlands, soil respiration magnitudes and variability are driven by belowground live root density (autotrophic) with substantial contribution of peat oxidation via microbial activity (heterotrophic). Moreover, other seasonally characterised environmental factors affect soil respiration dynamics such as hydrological condition, temperature and soil moisture. Yet, the respective contribution of autotrophic and heterotrophic to total soil respiration may vary between sites, vegetation covers, and microtopography profiles in tropical peatlands, leading to GHG reporting uncertainty. Clarifying the contribution heterotrophic activity will therefore provide a better understanding of the effect of peatland restoration or drainage on soil CO2 effluxes reduction or increase, respectively. Here, we present and discuss soil respiration measurements taken across two different microtopography (hummock and hollow) and three land covers (natural forest, retired Acacia plantation, and shrubland) in tropical peatlands of Tri Pupa Jaya, South Sumatra, Indonesia over wet and dry seasons of 2022. We used a trenching approach (live root free peat plot) and complementary with carbon stable isotope (13C-CO2) sampling across 27 paired measurement plots to determine the proportion of their autotrophic and heterotrophic contributions. Our preliminary findings suggest that autotrophic and heterotrophic soil respiration substantially vary across plots located in the hummock compared to hollow microtopography, with higher soil respiration observed at hummock compared to hollow microtopography, suggesting dominant root distribution forming higher elevations and generating higher autotrophic respiration in the hummock microtopography. Soil respiration from the trenched plots, was typically lower by 14–42% compared to untrenched plots and this pattern is consistent with the carbon stable isotope signatures. This study will help improve the current understanding of the driving mechanism and factors controlling magnitudes of soil respiration in tropical peatlands, particularly in assessing the impacts of both peatland restoration and drainage toward soil CO2 efflux dynamics.

The majority of tropical peatlands located in Southeast Asia are being affected by artificial drainage, which lowers the water table level (WTL) to provide conditions suitable for establishing profitable plantation crops, such as Acacia crassicarpa. Nevertheless, drawdown of the WTL also exposes peat organic matter to belowground heterotrophic microbial activity, subsequently generating greenhouse gas (GHG) emissions. Over the recent years, a consensus has emerged in the scientific community suggesting that reversing drainage effects through rewetting peatlands is the key to mitigating GHG emissions: higher WTLs lead to lower GHG emissions overall. In this study, we tested this emerging paradigm by constructing a mesocosm experiment comprising duplicates of three different WTLs in a degraded tropical peatland near Jambi, South Sumatra. Instead of directly controlling the WTL, peat surfaces were excavated to different depths (i.e., no removal as control, -25cm and -50cm of surface peat removed) with an area of 100 m2 for each plot. All plots were subject to similar seasonal WTL fluctuations but the respective WTL distance from the surface varied depending on how much peat was removed at each plot. A total of eight automated chambers monitored the carbon dioxide (CO2) and methane (CH4) soil fluxes at hourly intervals for the period August 1st 2022 to December 8th 2022. A Random Forest model was developed for each of the eight chambers to identify the driving environmental variables (including WTL) and gap-fill the missing data when technical problems prevented data collection. Our results show that the WTL-CO2 emissions relationship at our study site was close to linear with greater emissions (mean ± stdev; 3.85 ± 1.87 µmol m-2 s-1) at the plots where distance of WTL from the surface was lowest, and lower emission (1.44 ± 1.21 µmol m-2 s-1) at the control plots. The effect of WTL on CH4 fluxes was, however, more complex and ranged between -18.01 and 1692.36 nmol m-2 s-1, with the greatest mean emission rate and variability (0.88 ± 1.25 nmol m-2 s-1) in one of our control sites with standing Acacia. Differences in vegetation and root-mediated gas release thus seem to influence CH4 emissions at a greater rate than WTL at our study site. Additionally, our Random Forest model determined that soil surface temperature was a better explanatory variable than WTL in predicting both CO2 and CH4 spatial and temporal variability. Our results suggest that effectively managing GHGs from degraded peatlands may be more complicated than looking at WTL alone. Consequently, we recommend running long-term continuous time series and adding other environmental variables, such as soil temperature, in models to better understand, predict and manage GHGs exchange from tropical peatlands.

Tropical peatlands are among the greatest terrestrial carbon stores on Earth, able to influence the contemporary global carbon budget. Despite the necessity to protect those large carbon stocks, tropical peatlands are increasingly being exposed to degradation as a result of climate and land use change. Canal blocking is a prerequisite to restoring degraded peatlands. This physical action has the potential to increase water table level in the upstream catchment and minimize carbon loss along the aquatic continuum and toward the atmosphere. However, the impact of canal blocking on aquatic carbon exchange has yet to be quantified – and particularly so in tropical settings. Here, we compare the hydrodynamics, fluvial carbon concentrations and fluxes between a flowing and a stagnant (blocked) canal in a retired Acacia plantation in South Sumatra, Indonesia. The two canals were hydrologically and biogeochemically monitored using a combination of automated long-term sensors and manual discrete samples over the year 2022. Our results show that one direct consequence of canal blocking is the decrease in water flow and dissolved oxygen which enhanced dissolved CH4 concentrations and CH4 evasion, including from ebullition. No significant difference in dissolved organic carbon (DOC) and dissolved carbon dioxide (CO2) concentrations between the two canals was observed, which suggests that canal blocking does not alter the quantity of carbon available for mineralization. The evasion of CO2 was higher from the flowing canal, particularly from the spillways that were narrower and generated higher water flow. The main benefit of canal blocking was related to the absence of surface downstream carbon export. However, undocumented subsurface flow may still be occurring. Considering the ambivalence of these findings, we argue that a mass balance model that integrates the exchange of water and carbon at the catchment scale is the only way to accurately determine by how much canal blocking minimizes aquatic carbon losses. We conclude that the benefit of canal blocking on aquatic carbon losses from peatlands may be more complex than conventionally assumed, and recommend management responses aimed at minimising aquatic carbon losses from degraded and restored tropical peatlands.

Frequent fires in tropical Peat Swamp Forests (PSFs) that have been repurposed for forestry and agriculture result in substantial emissions of locked carbon. Fire-affected PSFs emit double the amount of CH4 compared to intact ones over extended periods of time. CH4 production is largely driven by communities of microorganisms (microbiomes – archaea in particular), thus, our ability to reduce emissions hinges on (i) identifying those with the capacity to generate CH4, (ii) ecological processes that shape their composition and functioning, and (iii) environmental variables which drive them. Ecological processes are particularly important as they determine our ability to predict the trajectory of communities and their functioning. Trajectories of communities shaped by deterministic processes can be predicted based on environmental variables as opposed to those shaped by stochastic processes whose trajectories are difficult to predict. We fill this knowledge gap by sequencing and comparing the ecological processes shaping peat microbiomes from a fire-impacted PSF to an intact PSF that occur within the same peat dome in Brunei. The composition of archaeal communities were significantly different between the fire-impacted and intact PSFs and strongly stratified by depth. The largest difference was observed between communities from the surface (0-5 cm) and those from below the water table (95-100 cm). In the fire-impacted PSF, archaea doubled in abundance in the anoxic zone compared to the surface, while, no such change was detected in the intact PSF. Archaeal communities occurring in the anoxic layers of the fire-impacted PSF were dominated by methanogens from the class Methanomicrobia and Bathyarchaeia, both of which occur in high-methane flux habitats. We determined ecological processes shaping the assembly of these methanogenic populations using bin-based phylogenetic null models. This showed that methanogenic populations in the fire-impacted PSF were largely shaped by stochastic processes, whereas, similar populations, albeit at lower abundances, were shaped by deterministic processes in the intact PSF. Changes in pH and dissolved oxygen correlated strongly with differences in assembly processes. Our work shows that changes in the environment resulting from fires can set methanogenic communities on unpredictable trajectories, which in turn correlate strongly with both increased and non-homogeneous CH4 emissions. Altering these key environmental correlates could form the basis for developing nature-based solutions for reducing emissions from fire-impacted peatlands.

Tropical peatlands in South-East Asia are some of the most carbon dense ecosystems in the world. Recurrent wildfires in repurposed peatlands release massive amounts of carbon and other greenhouse gases, strongly alter peat geochemistry and physicochemical conditions. However, little is known about the impact of fire on peat microbiome composition, microbial guilds contributing to greenhouse gas emissions, and their predictability based on environmental conditions. Here, we address this gap by studying peat microbiomes from fire-affected and intact areas of a tropical peatland in Brunei using high-throughput sequencing and ecological process modelling at the community and clade levels. We show that fire disrupts depth-stratification of peat microbiomes with the strongest effects observed at 1m below the surface. The enrichment of specific taxa and methanogenic archaea at such depths suggests an adaptation to low-energy conditions post-fire. Finally, fire shifts archaeal community composition and clades containing abundant methanogens in a homogeneous manner that can be predicted from environmental conditions and functional traits. Together, our findings provide a biological basis for earlier work which reported elevated methane flux 2-3 years post-fire and show that such changes follow predictable trajectories with important implications for post-fire microbiome forecasting and ecosystem recovery efforts.

Local communities can play a role in helping to restore tropical peatlands by using more sustainable agricultural practices. Enhancing this role would help to address interconnected crises such as climate change, food security and environmental degradation.

Fires and drainage are common disturbance factors in tropical peatlands (TP) in Southeast Asia. These disturbances alter the hydrology, vegetation composition, and peat biogeochemistry; thereby affecting the microbiome where microbial communities reside. Studies from northern peatlands have well established the role of vegetation composition in regulating the labile C, in the form of plant root exudates, and microbial community composition affecting the peat decomposition; however, for tropics, it remains unexplored. Recent studies have also established how these fire-degraded TP areas become a hot spot of sedge-mediated CH4 emission. To further our understanding of control mechanisms regulating CH4 dynamics, we investigated the composition of plant root exudates (n=3 per plant species) from sedges (Scleria sumatrensis) and ferns (Blechnum indicum, Nephrolepis hirsutula), the most commonly occurring plant species at our fire-degraded tropical peatland site in Brunei, Northwest Borneo, as well as microbial community composition in plant (n=9 for S. sumatrensis, and B. indicum, and n=5 for N. hirsutula) rhizo-compartments (rhizosphere, rhizoplane, endosphere). Using a targeted analysis, we found that the root exudates compounds secreted from sedge (Scleria sumatrensis) and one species of fern (Blechnum indicum) were significantly different (p4 emissions from fire-degraded TP. Our results provide fresh insights into the effects of post-fire vegetation composition in regulating the labile C and microbial community composition, and hence affecting CH4 emissions from fire-degraded TP. Further, our results can form an important basis for future CH4 dynamics studies as the emissions might increase with the expansion of degraded TPs as a consequence of frequent fire episodes and flooding

Despite being an important terrestrial carbon (C) reserve, tropical peatlands (TP) have been heavily degraded through extensive drainage and fire, to an extent where degraded TP occupies one-tenth of the total peatland area in Southeast Asia (as in 2015). Consequently, repeated fires along with frequent flooding can alter the microtopography, vegetation composition as well as higher diurnal temperature variation due to open canopy, where each is known to influence C dynamics. However, assessing the importance of all these variables on-site can be challenging due to difficult site conditions; hence an incubation experiment approach may provide more useful insights in disentangling the complex interplay of these important variables in regulating GHG (CO2 and CH4) production and emissions from fire-degraded tropical peatland areas. Therefore, we conducted an incubation study to investigate the interactions of microtopography (creating water-saturation conditions: mesic, flooded oxic, and anoxic), labile C inputs (in form of root exudate secretion from ferns and sedges), as well as on-site diurnal temperature variation in regulating CO2 and CH4 production from fire-degraded tropical peat. We found that CO2 and CH4 production significantly varied among treatments and were strongly regulated by microtopography, labile C inputs, and temperature variation. Mesic (oxic) treatments acted as a strong source of CO2 (230.4 ± 29 µgCO2 g-1 hr-1) and mild sink for CH4 (-5.6 ± 0.2 ngCH4 g-1 hr-1) compared to anoxic treatments acting as a mild source of CO2 (61.3 ± 6.2 µgCO2 g-1 hr-1) and strong source of CH4 (591.9 ± 112.1 ngCH4 g-1 hr-1). The addition of labile C enhanced both the CO2 and CH4 production irrespective of the treatment conditions, whereas the effect of diurnal temperature variation was clearly pronounced in mesic (for CO2) and anoxic (for CH4) conditions. Q10 values for both CO2 and CH4 production varied significantly with higher values for CO2 in mesic treatments (1.21 ± 0.28) and higher for CH4 in anoxic treatments (1.56 ± 0.35). We also observed a gradient across conditions, where flooded oxic treatments showed in-between values both for CO2 and CH4 production and temperature sensitivity, further reflecting the importance of on-site peat water-saturation in regulating the GHG production and emission from the fire degraded tropical peatland areas. Overall, these findings highlight how the water-saturation conditions due to microtopographic variation in peat surface, quality, and quantity of labile C secreted from plant communities and temperature variation during a day can influence the GHGs production rates from the fire degraded tropical peat. More importantly, given the current state and extent of degraded tropical peatland areas and future climate and land-use changes as well as frequent fire episodes in the region, our results demonstrate the increasing trend in GHG production from the fire-degraded tropical peatlands in Southeast Asia.

Mangroves have been harvested for their wood by local communities and industries alike under three major silviculture regimes: plantation, small-scale and large-scale selective logging. A global review to evaluate and compare the impact of various logging practices on sediment dynamics in mangroves is yet to be done. Suggested variables to observe soil conditions in harvested mangroves globally are carbon (as soil organic carbon or total carbon), nitrogen (as NH4+ or total nitrogen), phosphorus (as available phosphorus or total phosphorus), soil bulk density, and salinity. This chapter provides global review and study case examining the impact of mangrove forest harvest on soil physicochemical indicators. Results show that under all silviculture regimes, there is a significant impact on the soil between 1–5 years post-harvest, which generally followed by a recovery conditions at similar level to primary forests within 25–30 years. The recovery rate depends on the level of disturbance and silviculture regimes, with plantation seemingly having a greater initial disturbance. Tidal regimes, elevation, and vegetation appear to be major physicochemical influences on soil dynamics in harvested mangroves. In the future, the major soil research issues to tackle for mangrove silviculture systems are the lack of long-term data and observations, and establishing comparative studies of different harvest regimes within the same mangrove site.

The magnitude of future emissions of greenhouse gases from the northern permafrost region depends crucially on the mineralization of soil organic carbon (SOC) that has accumulated over millennia in these perennially frozen soils. Many recent studies have used radiocarbon (14C) to quantify the release of this “old” SOC as CO2 or CH4 to the atmosphere or as dissolved and particulate organic carbon (DOC and POC) to surface waters. We compiled ~1,900 14C measurements from 51 sites in the northern permafrost region to assess the vulnerability of thawing SOC in tundra, forest, peatland, lake, and river ecosystems. We found that growing season soil 14C‐CO2 emissions generally had a modern (post‐1950s) signature, but that well‐drained, oxic soils had increased CO2 emissions derived from older sources following recent thaw. The age of CO2 and CH4 emitted from lakes depended primarily on the age and quantity of SOC in sediments and on the mode of emission, and indicated substantial losses of previously frozen SOC from actively expanding thermokarst lakes. Increased fluvial export of aged DOC and POC occurred from sites where permafrost thaw caused soil thermal erosion. There was limited evidence supporting release of previously frozen SOC as CO2, CH4, and DOC from thawing peatlands with anoxic soils. This synthesis thus suggests widespread but not universal release of permafrost SOC following thaw. We show that different definitions of “old” sources among studies hamper the comparison of vulnerability of permafrost SOC across ecosystems and disturbances. We also highlight opportunities for future 14C studies in the permafrost region., Key Points: We compiled ~1,900 14C measurements of CO2, CH4, DOC, and POC from the northern permafrost region. Old carbon release increases in thawed oxic soils (CO2), thermokarst lakes (CH4 and CO2), and headwaters with thermal erosion (DOC and POC). Simultaneous and year‐long 14C analyses of CO2, CH4, DOC, and POC are needed to assess the vulnerability of permafrost carbon across ecosystems., EC | H2020 | H2020 Priority Excellent Science | H2020 European Research Council (ERC) http://dx.doi.org/10.13039/100010663, Gouvernement du Canada | Natural Sciences and Engineering Research Council of Canada (NSERC) http://dx.doi.org/10.13039/501100000038, National Science Foundation (NSF) http://dx.doi.org/10.13039/100000001

Over the past few decades, tropical peatlands in Southeast Asia have been heavily degraded for multiple land uses, mainly by employing drainage and fire. More importantly, the extent of these degraded areas, primarily covered with ferns and sedges, have increased to almost 10% of the total peatland area in Southeast Asia. In particular, the role of sedges in plant-mediated gas transport to the atmosphere has been recognized as a significant CH4 pathway in northern peatlands, however, in the Tropics this is still unknown. Within this context, we adopted an integrated approach using on-site measurements (CH4, porewater physicochemical characteristics) with genomics to investigate the role of hydrology, vegetation structure, and microbiome on CH4 emission from fire-degraded tropical peatland in Brunei. We found for the first time that in degraded tropical peatlands of Southeast Asia, sedges transported 70-80% of the total CH4 emission and significantly varied with values ranging from 1.22±0.13 to 6.15±0.57 mg CH4 m-2 hr-1, during dry and wet period, respectively. This variation was mainly attributed to water table position along with changes in sedge cover and porewater properties, which created more optimal methanogenesis conditions. Total emissions via this process might increase in the future as the extent of degraded tropical peatlands expands due to more frequent fire episodes and flooding. Further, we used 16S rRNA high-throughput sequencing to investigate the microbiomes in peat profile (above and below water table) as well as rhizo-compartments (Rhizosphere, Rhizoplane, Endosphere) of sedges. We found that the peat profile as well as rhizo-compartments of sedge harboured a higher number of methanogenic archaea in the order Methanomicrobiales and Methanobacteriales, compared to non-burnt and bulk soil, which further explains our findings of higher CH4 emission from degraded tropical peatland areas covered with sedges. These insights into the impact of fire on hydrology, vegetation structure, and microbial community composition on CH4 emissions provide an important basis for future studies on CH4 dynamics in degraded tropical peatland areas.

Tropical peat swamp forests hold about 15–19% of the global organic carbon (C) pool of which 77% is found in Southeast Asia. Nonetheless, these ecosystems have been drained, exploited for timber and land for agriculture, leading to frequent fires in the region. Fire alters the physico-chemical characteristics of peat as well as the hydrology, which may convert these ecosystems into a source of C for decades as C emissions to the atmosphere exceeds photosynthesis.To understand the long-term impacts of fire on C cycling, we investigated C emissions in intact and degraded PSFs in Brunei Darussalam, which has experienced 7 fires over the last 40 years. We quantified the magnitude and patterns of C loss (CO2, CH4, and Dissolved Organic carbon) and soil-water quality characteristics along with continuous monitoring of soil temperature and water table level from June 2017 to January 2019. To investigate the age and sources of C contributing to ecosystem respiration (Reco) and CH4, we used natural tracers such as 14C.We observed a major difference in the physico-chemical parameters, which in turn affected C dynamics, especially CH4. In burnt areas (7.8±2.2 mg CH4 m-2 hr-1) the CH4 emission was approximately twice compared to the intact peat swamp forest (4.0±2.0 mg CH4 m-2 hr-1) due to prolonged higher water table creating optimum methanogenesis conditions. On the contrary, Reco did not show a significant difference between burnt (432±83 mg CO2 m-2 hr-1) and intact areas (359±76 mg CO2 m-2 hr-1). Further, radiocarbon (14C) analysis showed an overall modern signature for both CO2 and CH4 fluxes implying a microbial preference for the more labile C fraction in solution.With frequent fires and more flooding in the future, these degraded tropical peat swamp forests areas may remain a hot spot of C emissions as suggested by our findings.

Over the last decades we are seeing an increase in forest fires due to deforestation and climate change. In Southeast Asia, tropical peatland forest fires are a major environmental issue having a significant effect on the climate and causing extensive social, health and economical impacts. As a result, forest fire prediction has emerged as a key challenge in computational sustainability. Existing forest fire prediction systems, such as the Canadian Forest Fire Danger Rating System (Natural Resources Canada), are based on handcrafted features and use data from instruments on the ground. However, data from instruments on the ground may not always be available. In this work, we propose a novel machine learning approach that uses historical satellite images to predict forest fires in Indonesia. Our prediction model achieves more than 0.86 area under the receiver operator characteristic(ROC) curve. Further evaluations show that the model's prediction performance remains above 0.81 area under ROC curve even with reduced data. The results support our claim that machine learning based approaches can lead to reliable and cost-effective forest fire prediction systems.

Southeast Asia is a region where forest clearance, drainage of peatlands for agriculture, and ongoing use of fire to ‘manage’ land leads to extensive emissions of greenhouse gases to the atmosphere, and significant disturbance to peatland soils. While recent campaigns investigating tropical peatland fire emissions have improved our knowledge and understanding of ‘direct’ greenhouse gas emissions during fires, there remains a significant gap in our knowledge of the immediate post-fire impacts on peat respiration and methanogenesis. Ongoing research shows that peatland microbial communities (responsible for respiration), including methanogens and methanotrophs (responsible for controlling net methane emissions), are considerably altered following fire disturbance. As such, we hypothesise that peatland fires will lead to significant alterations to GHG emissions, compared to sites that have not burned. Further, we also hypothesise that the magnitude of this post-fire effect will be predictably interrelated to different forms of peatland degradation and land-use history.Here we present results from seven fire locations (recently burnt) and their corresponding neighbouring control sites (not recently burnt), three of our fire locations were associated with forest clearance fires, while the other four locations were slash fires on oil palm plantations. We characterize the post-fire disturbance emissions of carbon dioxide (CO2) and methane (CH4) in situ, in the immediate aftermath of a fire (within days or weeks), and in the subsequent months following a fire at our burn sites. For comparison, we also measure CO2 and CH4 emissions from neighbouring control sites that remained unburnt. We find substantial, significant differences in CH4 emissions between the burn sites and control sites for all seven of our measurement locations. We suggest a number of mechanisms responsible for this post-fire effect, including disturbance to the methanotroph microbial communities at the burn sites, as well as reduced elevation at the burn sites, leading to higher water tables.

Tropical peatland degradation due to oil palm plantation development has reduced peat's ability to naturally regulate floods. In turn, more severe and frequent flooding on peatlands could seriously impair plantation productivity. Understanding the roles of peatland ecosystems in regulating floods has become essential given the continued pressure on land resources, especially in Southeast Asia. However, the limited knowledge on this topic has resulted in the oversimplifications of the relationships between floods, commercial plantations and peatland sustainability, creating major disagreement among policymakers at different levels in governments, companies, NGOs and society. Hence, this study identifies whether flood policies are integrated within peatland management through a qualitative policy analysis of publicly available papers, government reports, and other official documents that discuss flooding, and/or more in general, hydrology in peatlands. Document analysis was then triangulated with data obtained from several semi-structured discussions. The analysis indicates that the industry on peatlands and the peatland's environmental sustainability could be threatened by increased flooding. We show that, in spite of this, flood policies in SE Asian countries like Malaysia and Indonesia have not been well-integrated into peatland management. We also discuss how the countries could move forward to overcome this problem.

Author(s): Lupascu, M; Czimczik, CI; Welker, MC; Ziolkowski, LA; Cooper, EJ; Welker, JM | Abstract: Currently, there is a lack of understanding on how the magnitude and sources of carbon (C) emissions from High Arctic tundra are impacted by changing snow cover duration and depth during winter. Here we investigated this issue in a graminoid tundra snow fence experiment on shale-derived gelisols in Svalbard from the end of the growing season and throughout the winter. To characterize emissions, we measured ecosystem respiration (Reco) along with its radiocarbon (14C) content. We assessed the composition of soil organic matter (SOM) by measuring its bulk-C and nitrogen (N), 14C content, and n-alkane composition. Our findings reveal that greater snow depth increased soil temperatures and winter Reco (25nmg C m−2 d−1 under deeper snow compared to 13nmg C m−2 d−1 in ambient conditions). At the end of the growing season, Reco was dominated by plant respiration and microbial decomposition of C fixed within the past 60nyears (Δ14Cn=n62n±n8‰). During winter, emissions were significantly older (Δ14Cn=n−64n±n14‰), and likely sourced from microorganisms decomposing aged SOM formed during the Holocene mixed with biotic or abiotic mineralization of the carbonaceous, fossil parent material. Our findings imply that snow cover duration and depth is a key control on soil temperatures and thus the magnitude of Reco in winter. We also show that in shallow Arctic soils, mineralization of carbonaceous parent materials can contribute significant proportions of fossil C to Reco. Therefore, permafrost-C inventories informing C emission projections must carefully distinguish between more vulnerable SOM from recently fixed biomass and more recalcitrant ancient sedimentary C sources.

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.

Peatlands are both responding to and influencing climate change. While numerous studies on peatland carbon dynamics have been published in boreal and temperate regions for decades, a much smaller yet growing body of scientific articles related to tropical peatlands has recently been published, including from previously overlooked regions such as the Amazonian and Congo basins. The recent recognition of tropical peatlands as valuable ecosystems because of the organic carbon they accumulate in their water-saturated soils has occurred after most of them have been drained and degraded in Southeast Asia. Under disturbed conditions, their natural carbon storage function is shifted to an additional carbon source to the atmosphere. Understanding the effect of land-use change and management practices on peatlands can shed light on the driving variables that influence carbon emissions and can model the magnitude of emissions in future degraded peatlands. This is of primary importance as other peatland-covered regions in the tropics are at risk of land-use and land-cover changes. A systematic review that synthesizes the general understanding of tropical peatland carbon dynamics based on the published literature is much needed to guide future research directions on this topic. Moreover, previous studies of biogeochemical cycling in tropical peatlands have largely focused on terrestrial stocks and fluxes with little attention given to document lateral and downstream aquatic export through natural and artificial drainage channels. Here, we present a systematic review protocol to describe terrestrial and aquatic carbon dynamics in tropical peatlands and identify the influence of land-use change on carbon exchange. We described a set of literature search and screening steps that lay the groundwork for a future synthesis on tropical peatlands carbon cycling. Such an evidence-based synthesis using a systematic review approach will help provide the research community and policymakers with consistent science-based guidelines to set and monitor emissions reduction targets as part of the forestry and land-use sector.

Recent warming in the Arctic, which has been amplified during the winter1–3, greatly enhances microbial decomposition of soil organic matter and subsequent release of carbon dioxide (CO2)4. However, the amount of CO2 released in winter is not known and has not been well represented by ecosystem models or empirically based estimates5,6. Here we synthesize regional in situ observations of CO2 flux from Arctic and boreal soils to assess current and future winter carbon losses from the northern permafrost domain. We estimate a contemporary loss of 1,662 TgC per year from the permafrost region during the winter season (October–April). This loss is greater than the average growing season carbon uptake for this region estimated from process models (−1,032 TgC per year). Extending model predictions to warmer conditions up to 2100 indicates that winter CO2 emissions will increase 17% under a moderate mitigation scenario—Representative Concentration Pathway 4.5—and 41% under business-as-usual emissions scenario—Representative Concentration Pathway 8.5. Our results provide a baseline for winter CO2 emissions from northern terrestrial regions and indicate that enhanced soil CO2 loss due to winter warming may offset growing season carbon uptake under future climatic conditions. Winter warming in the Arctic will increase the CO2 flux from soils. A pan-Arctic analysis shows a current loss of 1,662 TgC per year over the winter, exceeding estimated carbon uptake in the growing season; projections suggest a 17% increase under RCP 4.5 and a 41% increase under RCP 8.5 by 2100.

Tropical peatlands hold about 15%-19% of the global peat carbon (C) pool of which 77% is stored in the peat swamp forests (PSFs) of Southeast Asia. Nonetheless, these PSFs have been drained, exploited for timber and land for agriculture, leading to frequent fires in the region. The physico-chemical characteristics of peat, as well as the hydrology of PSFs are affected after a fire, during which the ecosystem can act as a C source for decades, as C emissions to the atmosphere exceed photosynthesis. In this work, we studied the longer-term impact of fires on C cycling in tropical PSFs, hence we quantified the magnitude and patterns of C loss (CO

Peatlands cover approximately 4.2 million km2 of terrestrial land surface and store up to 700 Pg of terrestrial carbon. Preserving the carbon stocks in peatland is therefore crucial for climate change mitigation. Under natural conditions, peatland carbon storage is maintained by moist peat conditions, which decreases decomposition and encourages peat formation. However, conversion of peatlands to drainage-based agriculture in the form of industrial plantations and smallholder farming has resulted in globally significant greenhouse gas emissions. Paludiculture, loosely conceptualized as biomass production on wet peatlands with the potential to maintain carbon storage, is proposed as a sustainable, non-drainage-based agriculture alternative for peatland use. However, while the concept of paludiculture was developed in temperate ecoregions, its application in the tropics is poorly understood. In this review, we examine common definitions of paludiculture used in literature to derive key themes and future directions. We found three common themes: ecosystem services benefits of paludiculture, hydrological conditions of peatlands, and vegetation selection for planting. Ambiguities surrounding these themes have led to questions on whether paludiculture applications are sustainable in the context of carbon sequestration in peat soil. This review aims to evaluate and advance current understanding of paludiculture in the context of tropical peatlands, which is especially pertinent given expanding agriculture development into Central Africa and South America, where large reserves of peatlands were recently discovered.

A meta-analysis of soil incubation studies from the permafrost zone suggests that thawing under aerobic conditions, which releases CO2, will strengthen the permafrost carbon feedback more than waterlogged systems, which releases CO2 and CH4. Increasing temperatures in northern high latitudes are causing permafrost to thaw1, making large amounts of previously frozen organic matter vulnerable to microbial decomposition2. Permafrost thaw also creates a fragmented landscape of drier and wetter soil conditions3,4 that determine the amount and form (carbon dioxide (CO2), or methane (CH4)) of carbon (C) released to the atmosphere. The rate and form of C release control the magnitude of the permafrost C feedback, so their relative contribution with a warming climate remains unclear5,6. We quantified the effect of increasing temperature and changes from aerobic to anaerobic soil conditions using 25 soil incubation studies from the permafrost zone. Here we show, using two separate meta-analyses, that a 10 °C increase in incubation temperature increased C release by a factor of 2.0 (95% confidence interval (CI), 1.8 to 2.2). Under aerobic incubation conditions, soils released 3.4 (95% CI, 2.2 to 5.2) times more C than under anaerobic conditions. Even when accounting for the higher heat trapping capacity of CH4, soils released 2.3 (95% CI, 1.5 to 3.4) times more C under aerobic conditions. These results imply that permafrost ecosystems thawing under aerobic conditions and releasing CO2 will strengthen the permafrost C feedback more than waterlogged systems releasing CO2 and CH4 for a given amount of C.

Undergraduate teaching assistants (UTAs) have long been shown to support student learning in higher education, but most of the research on UTAs has been done in Western contexts. The aim of this study was to pilot a UTA programme within a first-year, interdisciplinary, team-based qualitative research methods course with fieldwork component at a large university in Singapore and evaluate the overall UTA experience. The findings pinpoint the UTAs’ motivations to serve, self-assessed contributions to student learning, expected and realized challenges, personal benefits both sought and gained, and post-course reflections as well as suggestions for improvement in future programmes. These UTAs, like their Western counterparts, are committed and capable peer mentors who can collaborate meaningfully with instructors to enhance undergraduate learning. Nanyang Technological University This project was supported by the EdeX Grant from the Teaching, Learning, and Pedagogy Division, Nanyang Technological University, Singapore.

Author(s): Crowther, TW; Machmuller, MB; Carey, JC; Allison, SD; Blair, JM; Bridgham, SD; Burton, AJ; Dijkstra, FA; Elberling, B; Estiarte, M; Larsen, KS; Laudon, H; Lupascu, M; Marhan, S; Mohan, J; Niu, S; J Penuelas, J; Schmidt, IK; Templer, PH; Kroel-Dulay, G; Frey, S; Bradford, MA

14C-CO2 measurement is an unique tool to quantify source-based emissions of CO2 for both the urban and natural environments. Acquiring a sample that temporally integrates the atmospheric 14C-CO2 signature that allows for precise 14C analysis is often necessary, but can require complex sampling devices, which can be difficult to deploy and maintain, especially for multiple locations. Here we describe our progress in developing a diffusive atmospheric CO2 molecular sieve trap, which requires no power to operate. We present results from various cleaning procedures, and rigorously tested for blank and memory effects. Traps were tested in the environment along-side conventional sampling flasks for accuracy. Results show that blank and memory effects can be minimized with thorough cleaning and by avoiding overheating, and that diffusively collected air samples agree well with traditionally canister-sampled air.

14 C measurements of CH 4 in environmental samples (e.g. soil gas, lake water, gas hydrates) can advance understanding of C cycling in terrestrial and marine systems. The measurements are particularly useful for detecting the release of old C from climate sensitive environments such as peatlands and hydrate fields. However, because 14 C CH 4 measurements tend to be complex and time consuming, they are uncommon. Here, we describe a novel vacuum line system for the preparation of CH 4 and CO 2 from environmental samples for 14 C analysis using accelerator mass spectrometry (AMS). The vacuum line is a flow-through system that allows rapid preparation of samples (1 h for CH 4 and CO 2 , 30 min for CH 4 alone), complete separation of CH 4 and CO 2 and is an easy addition to multipurpose CO 2 vacuum lines already in use. We evaluated the line using CH 4 and CO 2 standards with different 14 C content. For CH 4 and CO 2 , respectively, the total line blank was 0.4 ± 0.2 and 1.4 ± 0.6 μg C, the 14 C background 51.1 ± 1.2 and 48.4 ± 1.5 kyr and the precision (based on pooled standard deviation) 0.9‰ and 1.3‰. The line was designed for sample volumes of ca. 180 ml containing 0.5–1% CH 4 and CO 2 , but can be adjusted to handle lower concentration and larger volume samples. This rapid and convenient method for the preparation of CH 4 and CO 2 in environmental samples for 14 C AMS analysis should provide more opportunities for the use of 14 C CH 4 measurements in C cycle studies.

The first International Peat Congress (IPC) held in the tropics – in Kuching (Malaysia) – brought together over 1000 international peatland scientists and industrial partners from across the world (“International Peat Congress with over 1000 participants!,” 2016). The congress covered all aspects of peatland ecosystems and their management, with a strong focus on the environmental, societal and economic challenges associated with contemporary large-scale agricultural conversion of tropical peat.

Permafrost peatlands are both an important source of atmospheric CH4 and a substantial sink for atmospheric CO2. Climate change can affect this balance, with higher temperatures resulting in the conversion of permafrost soils to wetlands and associated accelerated mineralisation and increased CH4 emission. To better understand the impact of such processes on methanogen populations, we investigated the anaerobic decay of soil carbon in a low Arctic, discontinuous permafrost peatland. Cores were collected monthly from sedge and Sphagnum mires in north Sweden during the summer of 2006. We determined CH4 concentrations and production potentials, together with variations in the size of the methanogenic community as indicated by concentrations of archaeal lipid biomarkers (phosphorylated archaeol, archaeol and hydroxyarchaeol). Concentrations of methanogen biomarkers generally were higher at the sedge site, increased with depth for all sites and months, and were usually below the detection limits in shallow (

This study investigates how warming and changes in precipitation may affect the cycling of carbon (C) in tundra soils, and between high Arctic tundra and the atmosphere. We quantified ecosystem respiration (Reco) and soil pore space CO2 in a polar semi-desert in northwestern Greenland under current and future climate conditions simulated by long-term experimental warming (+2 °C, +4 °C), water addition (+50% summer precipitation), and a combination of both (+4 °C × +50% summer precipitation). We also measured the 14C content of Reco and soil CO2 to distinguish young C cycling rapidly between the atmosphere and the ecosystem from older C stored in the soil for centuries to millennia. We identified changes in the amount and timing of precipitation as a key control of the magnitude, seasonality and sources of Reco in a polar semi-desert. Throughout each summer, small (4 mm), more winter snow and experimental irrigation were associated with higher Reco fluxes and the release of recently fixed (young) C. Warmer summers and experimental warming also resulted in higher Reco fluxes (+2 °C > +4 °C), but coincided with losses of older C. We conclude that in high Arctic, dry tundra systems, future magnitudes and patterns of old C emissions will be controlled as much by the summer precipitation regime and winter snowpack as by warming. The release of older soil C is of concern, as it may lead to net C losses from the ecosystem. Therefore, reliable predictions of precipitation amounts, frequency, and timing are required to predict the changing C cycle in the high Arctic.

The amount and timing of snow cover control the cycling of carbon (C), water, and energy in arctic ecosystems. The implications of changing snow cover for regional C budgets, biogeochemistry, hydrology, and albedo due to climate change are rudimentary, especially for the High Arctic. In a polar semidesert of NW Greenland, we used a ~10-year old snow manipulation experiment to quantify how deeper snow affects magnitude, seasonality, and 14C content of summer C emissions. We monitored ecosystem respiration (Reco), soil CO2, and their 14C contents over three summers in vegetated and bare areas. Additional snowpack, elevated soil water content (SWC), and temperature throughout the growing season in vegetated, but not in bare, areas. Daily Reco was positively correlated to temperature, but negatively correlated to SWC; consequently, we found no effect of increased snow on daily flux. Cumulative summertime Reco was not related to annual snowfall, but to water year precipitation (winter snow plus summer rain). Experimentally increased snowpack shortened the growing season length and reduced summertime Reco up to 40%. Soil CO2 was older under increased snow. However, we found no effect of snow depth on the R eco age because older C emissions were masked by younger CO 2 produced from the litter layer or plant respiration. In the High Arctic, anticipated changes in precipitation regime associated with warming are a key uncertainty for understanding future C cycling. In polar semideserts, water year precipitation is an important driver of summertime Reco. Permafrost C is vulnerable to changes in snowpack, with a deeper snowpack-promoting decomposition of older soil C. ©2014. American Geophysical Union. All Rights Reserved.

This chapter presents an overview of the steps required to prepare a sample for radiocarbon (14C) measurement by accelerator mass spectrometry (AMS). These include: (1) collection of an appropriate sample that can answer the question being asked; (2) pretreatment of samples to isolate a the most representative fraction of the bulk carbon (C) or to separate total C into different components; (3) conversion of C in the sample to CO2 and/or graphite for measurement by AMS; and (4) assessing errors, especially those associated with 14C contamination that occur during processing.

Relationships were determined between methane (CH4) production and in situ conditions within the permafrost active layer during a single melt season at Stordalen, Sweden, with a specific emphasis on temperature sensitivity of methanogenesis. In situ temperature, moisture, pH, dissolved organic carbon, and CH4 concentration data were measured at three contrasting active layer sites (sedge mire, Sphagnum mire, and ombrotrophic bog), and laboratory incubations of active layer material were subsequently employed to determine the sensitivity of CH4 production to temperature. Q10 values, describing the CH4 production response of peat to a temperature change of 10 °C, ranged from 1.9 to 3.5 and 2.4 to 5.8 for the sedge and Sphagnum mire sites, respectively. A wider review of the literature on Q10 responses of methanogenesis in northern peatlands shows similar features to the temperature response of CH4 production in the active layer at Stordalen. In general, Q10 values are not significantly different in...

Carbon fixed by vegetated coastal ecosystems (blue carbon) can mitigate anthropogenic CO 2 emissions, though its effectiveness differs with the spatial scale of interest. A literature review compiling carbon sequestration rates within key ecosystems confirms that blue carbon ecosystems are the most efficient natural carbon sinks at the plot scale, though some overlooked biogeochemical processes may lead to overestimation. Moreover, the limited spatial extent of coastal habitats minimizes their potential at the global scale, only buffering 0.42% of the global fossil fuel carbon emissions in 2014. Still, blue carbon plays a role for countries with moderate fossil fuel emissions and extensive coastlines. In 2014, mangroves mitigated greater than 1% of national fossil fuel emissions for countries such as Bangladesh, Colombia and Nigeria. Considering that the Paris Agreement is based on nationally determined contributions, we propose that mangrove blue carbon may contribute to climate change mitigation at this scale in some instances alongside other blue carbon ecosystems.

In this Brief Communications Arising Reply, the affiliation for author P. H. Templer was incorrectly listed as 'Department of Ecology & Evolutionary Biology, University of California Irvine, Irvine, California 92697, USA' instead of 'Department of Biology, Boston University, Boston, Massachusetts 02215, USA'. This has been corrected online.

Permafrost thaw can alter the soil environment through changes in soil moisture, frequently resulting in soil saturation, a shift to anaerobic decomposition, and changes in the plant community. These changes, along with thawing of previously frozen organic material, can alter the form and magnitude of greenhouse gas production from permafrost ecosystems. We synthesized existing methane (CH

International audience; The carbon (C) balance of permafrost regions is predicted to be extremely sensitive to climatic changes(1-3). Major uncertainties exist in the rate of permafrost thaw and associated C emissions (33-508 Pg C or 0.04-1.69 degrees C by 2100; refs 2,3) and plant C uptake. In the High Arctic, semi-deserts retain unique soil-plant-permafrost interactions(4,5) and heterogeneous soil C pools(6) (>12 Pg C; ref. 7). Owing to its coastal proximity, marked changes are expected for High Arctic tundra(8). With declining summer sea-ice cover(9), these systems are simultaneously exposed to rising temperatures(9), increases in precipitation(10) and permafrost degradation(11). Here we show, using measurements of tundra-atmosphere C fluxes and soil C sources (C-14) at a long-term climate change experiment in northwest Greenland, that warming decreased the summer CO2 sink strength of semi-deserts by up to 55%. In contrast, warming combined with wetting increased the CO2 sink strength by an order of magnitude. Further, wetting while relocating recently assimilated plant C into the deep soil decreased old C loss compared with the warming-only treatment. Consequently, the High Arctic has the potential to remain a strong C sink even as the rest of the permafrost region transitions to a net C source as a result of future global warming.

© 2016 Macmillan Publishers Limited. All rights reserved. The majority of the Earth's terrestrial carbon is stored in the soil. If anthropogenic warming stimulates the loss of this carbon to the atmosphere, it could drive further planetary warming. Despite evidence that warming enhances carbon fluxes to and from the soil, the net global balance between these responses remains uncertain. Here we present a comprehensive analysis of warming-induced changes in soil carbon stocks by assembling data from 49 field experiments located across North America, Europe and Asia. We find that the effects of warming are contingent on the size of the initial soil carbon stock, with considerable losses occurring in high-latitude areas. By extrapolating this empirical relationship to the global scale, we provide estimates of soil carbon sensitivity to warming that may help to constrain Earth system model projections. Our empirical relationship suggests that global soil carbon stocks in the upper soil horizons will fall by 30 ± 30 petagrams of carbon to 203 ± 161 petagrams of carbon under one degree of warming, depending on the rate at which the effects of warming are realized. Under the conservative assumption that the response of soil carbon to warming occurs within a year, a business-as-usual climate scenario would drive the loss of 55 ± 50 petagrams of carbon from the upper soil horizons by 2050. This value is around 12-17 per cent of the expected anthropogenic emissions over this period. Despite the considerable uncertainty in our estimates, the direction of the global soil carbon response is consistent across all scenarios. This provides strong empirical support for the idea that rising temperatures will stimulate the net loss of soil carbon to the atmosphere, driving a positive land carbon-climate feedback that could accelerate climate change.