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Overgeneralization and a lack of baseline data for microorganisms in high-latitude environments have restricted the understanding of the microbial response to climate change, which is needed to establish Antarctic conservation frameworks. To bridge this gap, we examined over 17,000 sequence variants of bacteria and microeukarya across the hyperarid Vestfold Hills and Windmill Islands regions of eastern Antarctica. Using an extended gradient forest model, we quantified multispecies response to variations along 79 edaphic gradients to explore the effects of change and wind-driven dispersal on community dynamics under projected warming trends. We also analyzed a second set of soil community data from the Windmill Islands to test our predictions of major environmental tipping points. Soil moisture was the most robust predictor for shaping the regional soil microbiome; the highest rates of compositional turnover occurred at 10-12% soil moisture threshold for photoautotrophs, such as Cyanobacteria, Chlorophyta, and Ochrophyta. Dust profiles revealed a high dispersal propensity for Chlamydomonas, a microalga, and higher biomass was detected at trafficked research stations. This could signal the potential for algal blooms and increased nonendemic species dispersal as human activities increase in the region. Predicted increases in moisture availability on the Windmill Islands were accompanied by high photoautotroph abundances. Abundances of rare oligotrophic taxa, such as Eremiobacterota and Candidatus Dormibacterota, which play a crucial role in atmospheric chemosynthesis, declined over time. That photosynthetic taxa increased as soil moisture increased under a warming scenario suggests the potential for competition between primary production strategies and thus a more biotically driven ecosystem should the climate become milder. Better understanding of environmental triggers will aid conservation efforts, and it is crucial that long-term monitoring of our study sites be established for the protection of Antarctic desert ecosystems. Furthermore, the successful implementation of an improved gradient forest model presents an exciting opportunity to broaden its use on microbial systems globally., (© 2024 The Authors. Conservation Biology published by Wiley Periodicals LLC on behalf of Society for Conservation Biology.)

Paleoclimate data provide important information about the character of natural climate variability. However, records with sufficient length and resolution to resolve high‐frequency (decadal‐scale) variability across the Holocene are scarce. We present a 10,800‐year reconstruction of spring and summer temperature at three‐year resolution based on biochemical varves from Lake Żabińskie, Poland. The reconstruction is based on Ca/Ti ratio, which are significantly correlated with instrumental spring and summer temperature spanning 240 years. Major climate events of the Holocene period are represented in the reconstruction, including the Holocene Thermal Maximum, 8.2 ka Event, Medieval Climate Anomaly, and Little Ice Age. A low‐frequency 8,000‐year decreasing trend in warm‐season temperatures is driven by declining summer insolation. Temperature variability is highest during the early Holocene, likely related to warmer and drier conditions. The rate of warming during the past 90 years is extremely unusual, if not unprecedented for the Holocene, based on our reconstruction. Plain Language Summary: Studying past climate change helps us understand how the climate system works. One aspect of past climate that is not well understood is how much temperatures changed from year to year and over decades during warm periods of Earth's history. In this study, we measured chemical properties of lake sediments from Poland and found that chemical changes were related to spring and summer temperature changes. We used this data to estimate spring and summer temperatures during the past 10,800 years. Relatively warm summers occurred around 9,000–7,500 years ago, a period known from other studies to be relatively warm in the northern hemisphere. We also found greater variability in temperatures during this warm period. Our long record of spring and summer temperatures shows that the warming rate of the past 90 years is most likely faster than any time during the past 10,800 years, showing that human‐caused global warming is more extreme than natural climate variations. Key Points: 10,800‐year‐long, 3‐year‐resolution, warm‐season temperature reconstruction from biochemical varves from Lake Żabińskie, PolandPeak summer temperatures occurred during the early Holocene with declining summer insolation driving cooling during the past 8,000 yearsThe rate of modern warming is highly unusual, at least 4 standard deviations above the mean temperature trend of the past 10,800 years [ABSTRACT FROM AUTHOR]

Introduction: Drainage for agricultural purposes is one of the main drivers of peatland degradation, leading to significant greenhouse gas (GHG) emissions, biodiversity loss, and soil eutrophication. Rewetting is a potential solution to restore peatlands, but it generally requires a land-use shift to paludiculture or nature areas. Methods: This study explored whether three different water level management techniques (subsoil irrigation, furrow irrigation, and dynamic ditch water level regulation) could be implemented on dairy grasslands to yield increases in essential ecosystem services (vegetation diversity and soil biogeochemistry) without the need to change the current land use or intensity. We investigated vegetation diversity, soil biogeochemistry, and CO2 emission reduction in fourteen agricultural livestock pastures on drained peat soils in Friesland (Netherlands). Results: Across all pastures, Shannon-Wiener diversity was below 1, and the species richness was below 5. The plant-available phosphorus (P) was consistently higher than 3 mmol L-1. None of the water level management (WLM) techniques enhanced vegetation diversity or changed soil biogeochemistry despite a notable increase in water table levels. The potential for CO2 emission reduction remained small or even absent. Indicators of land-use intensity (i.e., grass harvest and fertilization intensity), however, showed a strong negative correlation with vegetation diversity. Furthermore, all sites' total and plant-available P and nitrate exceeded the upper threshold for species-rich grassland communities. Discussion: In conclusion, our research suggests that incomplete rewetting (i.e., higher water tables while maintaining drainage) while continuing the current land use does neither effectively mitigate GHG emissions nor benefit vegetation diversity. Therefore, we conclude that combining WLM and reducing land-use intensity is essential to limit the degradation of peat soils and restore more biodiverse vegetation. [ABSTRACT FROM AUTHOR]

Fire is the largest natural disturbance factor in the boreal forest and plays a critical role in the composition, structure, and succession of stands and landscapes. The island of Newfoundland, located in eastern Canada, is subjected to a greater maritime influence, which may result in longer fire return intervals. The limited data on the fire regime does not account for interactions between fire, vegetation, and climate throughout the Holocene. We used sediment cores from Arnold's Pond, Terra Nova National Park, which covered the last ~11,800 cal. yr BP, to investigate these interactions. We recognize 4 pollen zones and macroscopic charcoal analysis detected 45 local fire events. The 250-year mean fire return interval associated with the current vegetation is longer than a previous estimate for the park, but significantly shorter than other estimates for the island. Our mean fire return interval is within the range of fire estimates from Quebec with similar vegetation. Our results suggest that the fire regime was primarily influenced by vegetation and climate. The transition to an open forest from a shrub tundra resulted in increased fire activity and fire frequency, which were likely driven by additional fuel on the landscape, but could have also been influenced by unknown climatic factors. We identified several examples of changes in the fire frequencies and/or charcoal accumulation that coincided with regional climate shifts, but we also identified a non-synchronous change. The non-synchronous shift to drier conditions resulted in a ~500-year time lag between peak Pinus strobus abundance and maximum fire frequency. Synchronous shifts in fire activity and/or fire frequency coincided with the 8200 event, Medieval Climate Anomaly and Little Ice Age. We also noted a decrease in fire frequency between 2600-1500 cal. yr BP that coincided with similar changes in the fire frequency from ~3000-1000 cal. yr BP in Que bec. Our study highlights the complex interactions influencing the fire regime in our study area during the Holocene. [ABSTRACT FROM AUTHOR]

Wetlands are crucial components of the Earth's system, interacting with various processes such as the hydrological cycle, energy exchanges with the atmosphere, and global nitrogen and carbon cycles. The future trajectory of wetlands is anticipated to be influenced not only by direct human activities, but also by climate change. Here we present our assessment of climate‐driven global changes in wetlands extent, focusing on the main wetland complexes. We used an approach based on the Topographic Hydrological model (TOPMODEL) and soil liquid water content projections from 14 models of the Coupled Model Intercomparison Project Phase 6 (CMIP6). Our analysis reveals a consistent decrease in wetlands extent in the Mediterranean, Central America, and northern South America, with a substantial loss of 28% in the western Amazon Basin for the end of the 21st century (2081–2100) under the SSP370 scenario. Conversely, Central Africa exhibits an increase in wetlands extent, except in the Congo Basin. Nevertheless, most of the areas studied (80%) present uncertain results, due to conflicting projections of changes between the models. Notably, we show that there is significant uncertainty among CMIP6 models regarding liquid soil water content in high latitudes. By narrowing our focus to 10 models, which seem to better represent the thawing of permafrost, we obtain a better inter‐model agreement. We then find a modest declines in the overall global area (<5%), but an average loss of 13% beyond 50°N. Specific areas like the Hudson Bay Lowlands experiencing a 21% decrease and the Western Siberian Lowlands a 15% decrease. Plain Language Summary: Wetlands are vital ecosystems, that exchange matter and energy with other components of the Earth's system. They are expected to face changes in their functioning and extent due to both human activities and climate change. Our assessment using advanced models reveals consistent shrinking of wetlands extent in the Mediterranean, Central America, and parts of South America, with a significant loss projected in the western Amazon Basin. Conversely, Central Africa may see an increase, except in the Congo Basin. However, much of our findings carry uncertainty due to conflicting model projections, particularly regarding soil water content in high latitudes. Focusing on models better representing permafrost thawing, we find a modest global decline in wetland area, with notable decreases in specific regions like the Hudson Bay and Western Siberian Lowlands. Key Points: Projections of climate‐driven changes in wetlands extent are analyzed using the sixth phase of the Coupled Model Intercomparison ProjectConsistent decrease in wetlands extent are projected over the Mediterranean, Central America, and Amazon Basin in South AmericaThere is significant uncertainty among models in high latitudes, but a subsample of models indicate a decrease in boreal wetlands extent [ABSTRACT FROM AUTHOR]

"Global change" significantly alters organic matter and element cycling, but many of the underlying processes and consequences remain poorly understood. The interface of plants and soil plays a central role, coupling the atmosphere, hydrosphere, biosphere and lithosphere and integrating biological and geochemical processes. The contributions to this special issue address questions on both biotic and abiotic interactions underlying responses of terrestrial biogeochemical cycling to a range of global changes, including increases in atmospheric CO 2 concentrations, warming, drought and altered water regimes. In this overview, we synthesize key findings of the contributing empirical, conceptual and modelling-based studies covering responses of plants to elevated CO 2 ; the role of soil organisms in modulating responses to warming; impacts of global change on soil organic carbon, nitrogen, and mineral nutrient availability; and the influence of altered water-table depth caused by global change on greenhouse gas emissions. The showcased studies were conducted in regions from the Arctic to the tropics and highlight the manifold impacts of global change on various ecosystem components controlling biogeochemical processes occurring at the plant–soil interface. This multi-ecosystem interdisciplinary understanding is crucial for deciphering feedbacks of terrestrial ecosystems to the climate system. [ABSTRACT FROM AUTHOR]

Peatland pools are unvegetated, inundated depressions that cover up to 30 % of the surface of many temperate and boreal peatlands and that are net carbon (C) sources within C-accumulating ecosystems. The emission of carbon dioxide (CO 2) and methane (CH 4) from peatland pools comes from the degradation of organic matter (OM) that comprises the surrounding matrix. It is, however, not clear how decomposition rates in pools, which define their function and distinguish them from other aquatic ecosystems, vary spatially and what mechanisms drive these variations. We first quantified rates of OM decomposition from fresh litter at different depths in six pools of distinct morphological characteristics in a temperate ombrotrophic peatland using litterbags of Sphagnum capillifolium and Typha latifolia over a 27-month period. Rates of decomposition were faster for T. latifolia than S. capillifolium and, overall, faster at the pool surface and decreased with increasing depth. We then measured potential CO 2 and CH 4 production from the sediments of the same six pools by performing 35 d laboratory incubations. Pool sediment chemistry was variable among pools and influenced the production of CH 4 and CO 2 from sediments, with decreasing CO 2 production with increasing OM humification and decreasing CH 4 production with increasing nitrogen-to-phosphorus ratio. Both CH 4 production and CO 2 production from pool sediments were higher in the 1 m deep pools but similar in the shallow < 1 and the > 1.5 m deep pools. When combining both experiments, our results indicate that OM decomposition in peatland pools is highly variable and mostly related to the environmental conditions in which it occurs as a function of general pool depth rather than to OM chemistry. Overall, we show that OM degradation and C emissions in peatland open-water pools may increase over time in warmer and drier climate conditions. [ABSTRACT FROM AUTHOR]

Ratios of glycerol dialkyl glycerol tetraethers (GDGT), which are membrane lipids of bacteria and archaea, are at the base of several paleoenvironmental proxies. They are frequently applied to soils as well as lake‐ and marine sediments to generate records of past temperature and soil pH. To derive meaningful environmental information from these reconstructions, high analytical reproducibility is required. Based on submitted results by 39 laboratories from across the world, which employ a diverse range of analytical and quantification methods, we explored the reproducibility of brGDGT‐based proxies (MBT′5ME, IR, and #ringstetra) measured on four soil samples and four soil lipid extracts. Correct identification and integration of 5‐ and 6‐methyl brGDGTs is a prerequisite for the robust calculation of proxy values, but this can be challenging as indicated by the large inter‐interlaboratory variation. The exclusion of statistical outliers improves the reproducibility, where the remaining uncertainty translates into a temperature offset from median proxy values of 0.3–0.9°C and a pH offset of 0.05–0.3. There is no apparent systematic impact of the extraction method and sample preparation steps on the brGDGT ratios. Although reported GDGT concentrations are generally consistent within laboratories, they vary greatly between laboratories. This large variability in brGDGT quantification may relate to variations in ionization efficiency or specific mass spectrometer settings possibly impacting the response of brGDGTs masses relative to that of the internal standard used. While ratio values of GDGT are generally comparable, quantities can currently not be compared between laboratories. Key Points: 39 laboratories participated in a round robin to determine the reproducibility of glycerol dialkyl glycerol tetraethers (GDGT) proxy values and quantitiesPeak selection impacts the ratio values and there is no apparent systematic impact of the extraction method and sample preparation stepsQuantification of GDGTs remains a problem, and comparison of GDGT concentrations between laboratories requires further method development [ABSTRACT FROM AUTHOR]

Higher-dimensional models of peatland development are required to analyse the influence of spatial heterogeneity and complex feedback mechanisms on peatland behaviour. However, the current models exclude the mechanical process that leads to uncertainties in simulating the spatial variability in the water table position, vegetation composition, and peat physical properties. Here, we propose MPeat2D, a peatland development model in two dimensions, which considers mechanical, ecological, and hydrological processes together with the essential feedback from spatial interactions. MPeat2D employs poroelasticity theory that couples fluid flow and solid deformation to model the influence of peat volume changes on peatland ecology and hydrology. To validate the poroelasticity formulation, the comparisons between numerical and analytical solutions of Mandel's problems for two-dimensional test cases are conducted. The application of MPeat2D is illustrated by simulating peatland growth over 5000 years above a flat and impermeable substrate with free-draining boundaries at the edges, using constant and variable climate. In both climatic scenarios, MPeat2D produces lateral variability in the water table depth, which results in the variation in the vegetation composition. Furthermore, the drop in the water table at the margin increases the compaction effect, leading to a higher value of bulk density and a lower value of active porosity and hydraulic conductivity. These spatial variations obtained from MPeat2D are consistent with the field observations, suggesting plausible outputs from the proposed model. By comparing the results of MPeat2D to a one-dimensional model and a two-dimensional model without the mechanical process, we argue that mechanical–ecohydrological feedbacks are important for analysing spatial heterogeneity, shape, carbon accumulation, and resilience of peatlands. [ABSTRACT FROM AUTHOR]

High-resolution paleoclimate records from tropical continental settings are greatly needed to advance understanding of global climate dynamics. The International Continental Scientific Drilling Program (ICDP) project DeepCHALLA recovered a 214.8 m long sediment sequence from Lake Chala, a deep and permanently stratified (meromictic) crater lake in eastern equatorial Africa, covering the past ca. 250 000 years (250 kyr) of continuous lacustrine deposition since the earliest phase of lake-basin development. Lipid biomarker analyses on the sediments of Lake Chala can provide quantitative records of past variation in temperature and moisture balance from this poorly documented region. However, the degree to which climate proxies derived from aquatically produced biomarkers are affected by aspects of lake developmental history is rarely considered, even though it may critically influence their ability to consistently register a particular climate variable through time. Modern-system studies of Lake Chala revealed crucial information about the mechanisms underpinning relationships between proxies based on isoprenoid (iso-) and branched (br-) glycerol dialkyl glycerol tetraethers (GDGTs) and the targeted climate variables, but the persistence of these relationships in the past remains unclear. Here we assess the reliability of long-term climate signals registered in the sediments of Lake Chala by comparing downcore variations in GDGT distributions with major phases in lake-system evolution as reflected by independent proxies of lake depth, mixing regime and nutrient dynamics: seismic reflection data, lithology and fossil diatom assemblages. Together, these records suggest that during early lake history (before ca. 180–200 ka) the distinct mixing-related depth zones with which specific GDGT producers are associated in the modern-day lake were not yet formed, likely due to more open lake hydrology and absence of chemical water-column stratification. Consequently absolute GDGT concentrations dating to this period are relatively low, proxies sensitive to water-column stratification (e.g., branched versus isoprenoid tetraether (BIT) index) display highly irregular temporal variability, and correlations between proxies are dissimilar to expectations based on modern-system understanding. A sequence of lake-system changes between ca. 180–200 and ca. 80 ka first established and then strengthened the chemical density gradient, promoting meromictic conditions despite the overall decrease in lake depth due to the basin gradually being filled up with sediments. From ca. 180 ka onward some GDGTs and derived proxies (e.g., crenarchaeol concentration, BIT index and Ipage2878R6Me) display strong ∼ 23 kyr periodicity, likely reflecting the predominantly precession-driven insolation forcing of Quaternary climate variability in low-latitude regions. Our results suggest that GDGT-based temperature and moisture-balance proxies in Lake Chala sediments reflect the climate history of eastern equatorial Africa from at least ca. 160 ka onwards, i.e., covering the complete last glacial–interglacial cycle and the penultimate glacial maximum. This work confirms the potential of lacustrine GDGTs for elucidating the climate history of tropical regions at Quaternary timescales, provided they are applied to suitably high-quality sediment archives. Additionally, their interpretation should incorporate a broader understanding of the extent to which lake-system evolution limits the extrapolation back in time of proxy-climate relationships established in the modern system. [ABSTRACT FROM AUTHOR]

Branched glycerol dialkyl glycerol tetraethers (brGDGTs) are bacterial lipids that have been widely used as environmental proxies in continental paleorecords. Another group of related lipids, branched glycerol monoalkyl glycerol tetraethers (brGMGTs), has recently been proposed as a potential paleotemperature proxy. Nevertheless, the sources and environmental dependencies of both brGDGTs and brGMGTs along the river–sea continuum are still poorly understood, complicating their application as paleoenvironmental proxies in some aquatic settings. In this study, the sources of brGDGTs and brGMGTs and the potential factors controlling their distributions are explored across the Seine River basin (NW France), which encompasses the freshwater-to-seawater continuum. BrGDGTs and brGMGTs were analyzed in soils, suspended particulate matter (SPM), and sediments (n=237) collected along the land–sea continuum of the Seine basin. Both types of compounds (i.e., brGDGTs and brGMGTs) are shown to be produced in situ, in freshwater and saltwater, based on their high concentrations and distinct distributions in aquatic settings (SPM and sediments) vs. soils. Redundancy analysis further shows that both salinity and nitrogen dominantly control the brGDGT distributions. Furthermore, the relative abundance of 6-methyl vs. that of 5-methyl brGDGTs (the IR 6Me ratio), the total nitrogen (TN), the δ15 N, and the chlorophyll a concentration co-vary in a specific geographical zone with low salinity, suggesting that 6-methyl brGDGTs are preferentially produced under low-salinity and high-productivity conditions. In contrast to brGDGTs, the brGMGT distribution appears to be primarily regulated by salinity, with a distinct influence on the individual homologues. Salinity is positively correlated with homologues H1020a and H1020b and negatively correlated with compounds H1020c and H1034b in SPM. This suggests that bacteria living in freshwater preferentially produce compounds H1020c and H1034b, whereas bacteria that primarily grow in saltwater appear to be predominantly responsible for the production of homologues H1020a and H1020b. Based on the abundance ratio of the freshwater-derived compounds (H1020c and H1034b) vs. their saltwater-derived homologues (H1020a and H1020b), a novel proxy, the Riverine IndeX (RIX), is proposed to trace riverine organic matter inputs, with high values (>0.5) indicating a higher riverine contribution. We successfully applied RIX to the Godavari River basin (India) and a paleorecord across the upper Paleocene and lower Eocene from the Arctic Coring Expedition at Lomonosov Ridge, showing its potential applicability to both modern samples and paleorecords. [ABSTRACT FROM AUTHOR]

Peat fires in the northern high latitudes have the potential to burn vast amounts of carbon-rich organic soil, releasing large quantities of long-term stored carbon to the atmosphere. Due to anthropogenic activities and climate change, peat fires are increasing in frequency and intensity across the high latitudes. However, at present they are not explicitly included in most fire models. Here we detail the development of INFERNO-peat, the first parameterization of peat fires in the JULES-INFERNO (Joint UK Land Environment Simulator INteractive Fire and Emission algoRithm for Natural envirOnments) fire model. INFERNO-peat utilizes knowledge from lab and field-based studies on peat fire ignition and spread to be able to model peat burnt area, burn depth, and carbon emissions, based on data of the moisture content, inorganic content, bulk density, soil temperature, and water table depth of peat. INFERNO-peat improves the representation of burnt area in the high latitudes, with peat fires simulating on average an additional 0.305×106 km 2 of burn area each year, emitting 224.10 Tg of carbon. Compared to Global Fire Emissions Database version 5 (GFED5), INFERNO-peat captures ∼ 20 % more burnt area, whereas INFERNO underestimated burning by 50 %. Additionally, INFERNO-peat substantially improves the representation of interannual variability in burnt area and subsequent carbon emissions across the high latitudes. The coefficient of variation in carbon emissions is increased from 0.071 in INFERNO to 0.127 in INFERNO-peat, an almost 80 % increase. Therefore, explicitly modelling peat fires shows a substantial improvement in the fire modelling capabilities of JULES-INFERNO, highlighting the importance of representing peatland systems in fire models. [ABSTRACT FROM AUTHOR]

Investigating the relationship between plants and soils is important for environmental management. This study looked at how measures of plant biomass correlated with soils under bush mango and lowland rainforest. The study adopted quasi experimental design, and applied stratified random sampling to subdivide the study area into 10 strata. Two sampling sites each was chosen from each strata (being bush mango stand and adjacent rainforest) thus, made up 20 sampling sites. Data collected were tree heights, tree diameters, and soil samples. Abney level was used to determine tree heights, girthing tape for tree diameters, and core sampler for soil samples collected from 0-15cm and 15cm-30cm soil depths. Laboratory analyses of the soil samples maintained standard procedures to obtain the concentrations of soil elements. Data generated were analysed with Pearson’s bivariate correlation statistics. Findings showed that biomass of the standing bush mango and adjacent rainforest trees correlated positively with soil elements under their stands. From the stands of bush mango, tree heights correlated positively with soil bulk density (0.135), porosity (0.151), water holding capacity (0.256) and sand (0.438); while tree diameters correlated positively with total organic matter (0.20), potassium (0.457), bulk density (0.592), water holding capacity (0.473), silt (0.562) and clay (0.072). Within the rainforest, tree heights positively correlated with total organic matter (0.302), potassium (0.613), bulk density (0.064), porosity (0.122), silt (0.755*), and clay (0.183); while tree diameters positively correlated with total nitrogen (0.325), porosity (0.036), water holding capacity (416), sand (0.548) and clay (0.191). Since measures of plant biomass of the stands of bush mangoes positively correlated with soil properties, their conservation as rainforest species is encouraged for proper ecosystem functioning and management. [ABSTRACT FROM AUTHOR]

Northern fens, that host unique biota and form a remarkable carbon stock, are sensitive to changes in the moisture balance and, therefore, may be strongly affected by climatic fluctuations. However, long‐term monitoring and palaeoecological studies of fens are relatively rare and, as a result, their responses to past and current climatic fluctuations are poorly known. In this study, we examined the recent vegetation change as well as changes in testate amoeba communities in the mire margin of a subarctic fen in Finnish Lapland with four peat profiles. Testate amoebae were used as indicators of past fluctuations in water table depth. The vegetation showed a drastic shift from sedge‐dominated fen to Sphagnum‐dominated communities during the late 20th and the early 21st centuries. This shift was accompanied by a turnover in the testate amoeba community. Testate amoeba‐based water table reconstructions indicated recent drying. This may be due to the lowering of the water table either from accelerated Sphagnum increment or enhanced evaporation. The observed hummock establishment concurs with the documented hemisphere‐wide expansion trend of hummock communities in fens. This change may strengthen the carbon sink and storage capacity of these peatlands, which could be viewed as a welcome negative feedback process to the ongoing climate warming. However, the change also poses a threat to biodiversity since fens are not only species‐rich habitats but are also endangered ecosystems. [ABSTRACT FROM AUTHOR]

Millennial-scale climate variations during the last glacial period, such as Dansgaard–Oeschger (DO) cycles and Heinrich events, have been extensively studied using ice core and marine proxy records. However, there is a limited understanding of the magnitude of these temperature fluctuations in continental regions, and questions remain about the seasonal signal of these climate events. This study presents a 60 000-year-long temperature reconstruction based on branched glycerol dialkyl glycerol tetraethers (brGDGTs) extracted from lake sediments from the Eifel Volcanic Field, Germany. brGDGTs are bacterial membrane-spanning lipids that are known to have a strong relationship with temperature, making them suitable for temperature reconstructions. We test several temperature calibration models on modern samples taken from soils and multiple maar lakes. We find a negative bias in brGDGT-based temperature estimates associated with water depth and anoxic conditions that can be corrected for by accounting for a brGDGT isomer that is only produced in anoxic conditions. The corrected temperature reconstruction correlates with proxy and climate model estimates of temperature spanning the same time period, validating the calibration approach we selected. However, millennial-scale variability is significantly dampened in the brGDGT record, and in contrast to other Northern Hemisphere climate records, during several Heinrich stadials, temperatures actually increase. We demonstrate that these apparent discrepancies can be explained by the unique seasonal response of the brGDGT paleothermometer to temperatures of months above freezing (TMAF). Our data support the view that warm-season temperatures in Europe varied minimally during the last glacial period and that abrupt millennial-scale events were defined by colder, longer winters. Our continuous high-resolution temperature reconstruction provides important information about the magnitude of seasonal climate variability during the last glacial period that can be used to test climate models and inform studies of paleoecological change. [ABSTRACT FROM AUTHOR]

In the context of the accelerating impacts of climate change on permafrost landscapes, we use Unpiloted Aerial Vehicle (UAV) LiDAR technology to investigate seasonal terrain changes in palsas – mounds of frozen peat – since other remote sensing methods have struggled to capture the full dynamics of these landforms. We investigated two palsas (4–5 m in height) in Sweden's largest palsa mire complex, where we performed five field campaigns between September 2022 and September 2023 to track intra-annual frost heave and thaw subsidence. Our approach allowed us to create digital terrain models (DTMs) from high density point clouds (>1,000 points/m²) and analyze elevation changes over time. We found that both palsas heaved on average 0.15 m (and up to 0.30 m) from September to April and subsided back to their height from the previous year, or slightly below, over the course of the following summer. At one of the palsas, we observed notable lateral degradation over the study period in a 300 m2 area, with 0.5–2.0 m height loss, likely initiated during the preceding warm and wet summer months. Part of this degradation occurred between September 2022 and April 2023, suggesting that the degradation of these palsas is not limited to the summer months. Our study shows the substantial value of using UAV LiDAR for understanding how permafrost areas are changing. It helps in tracking the ongoing effects of climate change and highlights palsa dynamics that would not be captured by annual measurements alone. [ABSTRACT FROM AUTHOR]

The Canadian Fire Weather Index (FWI) system, even though originally developed and calibrated for an upland Jack pine forest, is used globally to estimate fire danger for any fire environment. However, for some environments, such as peatlands, the applicability of the FWI in its current form, is often questioned. In this study, we replaced the original moisture codes of the FWI with hydrological estimates resulting from the assimilation of satellite-based L-band passive microwave observations into a peatland-specific land surface model. In a conservative approach that maintains the integrity of the original FWI structure, the distributions of the hydrological estimates were first matched to those of the corresponding original moisture codes before replacement. The resulting adapted FWI, hereafter called FWI peat , was evaluated using satellite-based information on fire presence over boreal peatlands from 2010 through 2018. Adapting the FWI with model- and satellite-based hydrological information was found to be beneficial in estimating fire danger, especially when replacing the deeper moisture codes of the FWI. For late-season fires, further adaptations of the fine fuel moisture code show even more improvement due to the fact that late-season fires are more hydrologically driven. The proposed FWI peat should enable improved monitoring of fire risk in boreal peatlands. [ABSTRACT FROM AUTHOR]

Earth's climate largely depends on carbon and nitrogen exchange between the atmosphere and tropical peatland ecosystems. Permanently wet peatlands take up carbon dioxide in plants and accumulate organic carbon in soil but release methane. Man-made drainage releases carbon dioxide from peat soils. Carbon and nitrous gas exchange and their relationships with tropical peatland conditions are poorly understood. We analysed natural peat swamp forests and fens, moderately drained and dry peatlands under a wide variety of land uses. The tropical peat swamp forests were large greenhouse gas sinks while tropical peatlands under moderate and low soil moisture levels emitted carbon dioxide and nitrous oxide. Carbon dioxide uptake of 160 mg m–2 h–1 dominated the net greenhouse gas budgets overall, while nitrous oxide emission of 90 mg CO2-equivalent m–2 h–1 on average was the second most important contributor (ahead of average methane emissions of 36 mg CO2-equivalent m–2 h–1) across the whole tropical peat moisture range. [ABSTRACT FROM AUTHOR]

Wetland methane responses to temperature and precipitation were studied in a boreal wetland-rich region in Northern Europe using ecosystem process models. Six ecosystem models (JSBACH-HIMMELI, LPX-Bern, LPJ-GUESS, JULES, CLM4.5 and CLM5) were compared to multi-model mean of ecosystem models and atmospheric inversions from the Global Carbon Project and up-scaled eddy covariance flux results for their temperature and precipitation responses and seasonal cycles of the regional fluxes. Two models with contrasting response patterns, LPX-Bern and JSBACH-HIMMELI, were used as priors in atmospheric inversions with Carbon Tracker Europe – CH4 in order to find out how the inversion attempts to change the prior fluxes in the posterior and how this alters the interpretation of the flux responses to temperature and precipitation. The inversion attempted to move emissions of both models in posterior towards co-limitation by temperature and precipitation. In general high temperature and/or high precipitation periods often resulted in high posterior emissions. This was not the case for the warm and dry period of summer 2018. The process models showed strong temperature as well as strong precipitation responses for the region (51–91 % of the variance explained by both), and the month of maximum emissions varied from May to September. However, multi-model means, inversions and up-scaled eddy covariance flux observations agreed on the month of maximum emissions, and had rather balanced temperature and precipitation responses. The set-up of different emission components (peatland emissions, mineral land fluxes) had a significant role in building up the response patterns. Considering the significant differences among the models, it is essential to pay more attention to the magnitude, composition, annual cycle and climate driver responses of wetland emissions in different regions. [ABSTRACT FROM AUTHOR]

This paper describes the rationale and the protocol of the first component of the third simulation round of the Inter-Sectoral Impact Model Intercomparison Project (ISIMIP3a, http://www.isimip.org , last access: 2 November 2023) and the associated set of climate-related and direct human forcing data (CRF and DHF, respectively). The observation-based climate-related forcings for the first time include high-resolution observational climate forcings derived by orographic downscaling, monthly to hourly coastal water levels, and wind fields associated with historical tropical cyclones. The DHFs include land use patterns, population densities, information about water and agricultural management, and fishing intensities. The ISIMIP3a impact model simulations driven by these observation-based climate-related and direct human forcings are designed to test to what degree the impact models can explain observed changes in natural and human systems. In a second set of ISIMIP3a experiments the participating impact models are forced by the same DHFs but a counterfactual set of atmospheric forcings and coastal water levels where observed trends have been removed. These experiments are designed to allow for the attribution of observed changes in natural, human, and managed systems to climate change, rising CH 4 and CO 2 concentrations, and sea level rise according to the definition of the Working Group II contribution to the IPCC AR6. [ABSTRACT FROM AUTHOR]

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Drained wetlands are thought to be carbon (C) source hotspots, and rewetting is advocated to restore C storage in drained wetlands for climate change mitigation. However, current assessments of wetland C balance mainly focus on vertical fluxes between the land and atmosphere, frequently neglecting lateral carbon fluxes and land-use effects. Here, we conduct a global synthesis of 893 annual net ecosystem C balance (NECB) measures that include net ecosystem exchange of CO 2 , along with C input via manure fertilization, and C removal through biomass harvest or hydrological exports of dissolved organic and inorganic carbon, across wetlands of different status and land uses. We find that elevating water table substantially reduces net ecosystem C losses, with the annual NECB decreasing from 2579 (95% interval: 1976 to 3214) kg C ha -1  year -1 in drained wetlands to -422 (-658 to -176) kg C ha -1  year -1 in natural wetlands, and to -934 (-1532 to -399) kg C ha -1  year -1 in rewetted wetlands globally. Climate, land-use history, and time since water table changes introduce variabilities, with drainage for (sub)tropical agriculture or forestry uses showing high annual C losses, while the net C losses from drained wetlands can continue to affect soil C pools for several decades. Rewetting all types of drained wetlands is needed, particularly for those formerly agriculture-used (sub)tropical wetlands where net ecosystem C losses can be largely reduced. Our findings suggest that elevating water table is an important initiative to reduce C losses in degraded wetlands, which could contribute to policy decisions for managing wetlands to enhance their C sequestration., (© 2024 John Wiley & Sons Ltd.)

Measurements of net primary productivity (NPP) and litter decomposition from tropical peatlands are severely lacking, limiting our ability to parameterise and validate models of tropical peatland development and thereby make robust predictions of how these systems will respond to future environmental and climatic change. Here, we present total NPP (i.e., above- and below-ground) and decomposition data from two floristically and structurally distinct forested peatland sites within the Pastaza Marañón Foreland Basin, northern Peru, the largest tropical peatland area in Amazonia: (1) a palm (largely Mauritia flexuosa) dominated swamp forest and (2) a hardwood dominated swamp forest (known as 'pole forest', due to the abundance of thin-stemmed trees). Total NPP in the palm forest and hardwood-dominated forest (9.83 ± 1.43 and 7.34 ± 0.84 Mg C ha -1  year -1 , respectively) was low compared with values reported for terra firme forest in the region (14.21-15.01 Mg C ha -1  year -1 ) and for tropical peatlands elsewhere (11.06 and 13.20 Mg C ha -1  year -1 ). Despite the similar total NPP of the two forest types, there were considerable differences in the distribution of NPP. Fine root NPP was seven times higher in the palm forest (4.56 ± 1.05 Mg C ha -1  year -1 ) than in the hardwood forest (0.61 ± 0.22 Mg C ha -1  year -1 ). Above-ground palm NPP, a frequently overlooked component, made large contributions to total NPP in the palm-dominated forest, accounting for 41% (14% in the hardwood-dominated forest). Conversely, Mauritia flexuosa litter decomposition rates were the same in both plots: highest for leaf material, followed by root and then stem material (21%, 77% and 86% of mass remaining after 1 year respectively for both plots). Our results suggest potential differences in these two peatland types' responses to climate and other environmental changes and will assist in future modelling studies of these systems., (© 2024 The Author(s). Global Change Biology published by John Wiley & Sons Ltd.)

Water-logged peatlands store tremendous amounts of soil carbon (C) globally, accumulating C over millennia. As peatlands become disturbed by human activity, these long-term C stores are getting destabilized and ultimately released as greenhouse gases that may exacerbate climate change. Oxidation of the dissolved organic carbon (DOC) mobilized from disturbed soils to streams and canals may be one avenue for the transfer of previously stored, millennia-aged C to the atmosphere. However, it remains unknown whether aged peat-derived DOC undergoes oxidation to carbon dioxide (CO 2 ) following disturbance. Here, we use a new approach to measure the radiocarbon content of CO 2 produced from the oxidation of DOC in canals overlying peatland soils that have undergone widespread disturbance in Indonesia. This work shows for the first time that aged DOC mobilized from drained and burned peatland soils is susceptible to oxidation by both microbial respiration and photomineralization over aquatic travel times for DOC. The bulk radiocarbon age of CO 2 produced during canal oxidation ranged from modern to ~1300 years before present. These ages for CO 2 were most strongly influenced by canal water depth, which was proportional to the water table level where DOC is mobilized from disturbed soils to canals. Canal microbes preferentially respired older or younger organic C pools to CO 2 , and this may have been facilitated by the use of a small particulate organic C pool over the dissolved pool. Given that high densities of canals are generally associated with lower water tables and higher fire risk, our findings suggest that peatland areas with high canal density may be a hotspot for the loss of aged C on the landscape. Taken together, the results of this study show how and why aquatic processing of organic C on the landscape can enhance the transfer of long-term peat C stores to the atmosphere following disturbance., (© 2024 John Wiley & Sons Ltd.)

Microbes affect the global carbon cycle that influences climate change and are in turn influenced by environmental change. Here, we use data from a long-term whole-ecosystem warming experiment at a boreal peatland to answer how temperature and CO 2 jointly influence communities of abundant, diverse, yet poorly understood, non-fungi microbial Eukaryotes (protists). These microbes influence ecosystem function directly through photosynthesis and respiration, and indirectly, through predation on decomposers (bacteria and fungi). Using a combination of high-throughput fluid imaging and 18S amplicon sequencing, we report large climate-induced, community-wide shifts in the community functional composition of these microbes (size, shape, and metabolism) that could alter overall function in peatlands. Importantly, we demonstrate a taxonomic convergence but a functional divergence in response to warming and elevated CO 2 with most environmental responses being contingent on organismal size: warming effects on functional composition are reversed by elevated CO 2 and amplified in larger microbes but not smaller ones. These findings show how the interactive effects of warming and rising CO 2 levels could alter the structure and function of peatland microbial food webs-a fragile ecosystem that stores upwards of 25% of all terrestrial carbon and is increasingly threatened by human exploitation., (© 2024 John Wiley & Sons Ltd.)

Permafrost degradation in peatlands is altering vegetation and soil properties and impacting net carbon storage. We studied four adjacent sites in Alaska with varied permafrost regimes, including a black spruce forest on a peat plateau with permafrost, two collapse scar bogs of different ages formed following thermokarst, and a rich fen without permafrost. Measurements included year-round eddy covariance estimates of net carbon dioxide (CO 2 ), mid-April to October methane (CH 4 ) emissions, and environmental variables. From 2011 to 2022, annual rainfall was above the historical average, snow water equivalent increased, and snow-season duration shortened due to later snow return. Seasonally thawed active layer depths also increased. During this period, all ecosystems acted as slight annual sources of CO 2 (13-59 g C m -2  year -1 ) and stronger sources of CH 4 (11-14 g CH 4  m -2 from ~April to October). The interannual variability of net ecosystem exchange was high, approximately ±100 g C m -2  year -1 , or twice what has been previously reported across other boreal sites. Net CO 2 release was positively related to increased summer rainfall and winter snow water equivalent and later snow return. Controls over CH 4 emissions were related to increased soil moisture and inundation status. The dominant emitter of carbon was the rich fen, which, in addition to being a source of CO 2 , was also the largest CH 4 emitter. These results suggest that the future carbon-source strength of boreal lowlands in Interior Alaska may be determined by the area occupied by minerotrophic fens, which are expected to become more abundant as permafrost thaw increases hydrologic connectivity. Since our measurements occur within close proximity of each other (≤1 km 2 ), this study also has implications for the spatial scale and data used in benchmarking carbon cycle models and emphasizes the necessity of long-term measurements to identify carbon cycle process changes in a warming climate., (Global Change Biology© 2024 The Authors. Global Change Biology published by John Wiley & Sons Ltd.)

Mosses of the genus Sphagnum are the dominant vegetation in most pristine peatlands in temperate and high-latitude regions. They play a crucial role in carbon sequestration, being responsible for ca. 50% of carbon accumulation through their active participation in peat formation. They have a significant influence on the dynamics of CO 2 emissions due to an efficient maximum potential photosynthetic rate, lower respiration rates, and the production of a recalcitrant litter whose decomposition is gradual. However, various anthropogenic disturbances and land use management actions that favor its reestablishment have the potential to modify the dynamics of these CO 2 emissions. Therefore, the objective of this review is to discuss the role of Sphagnum in CO 2 emissions generated in peatland ecosystems, and to understand the impacts of anthropogenic practices favorable and detrimental to Sphagnum on these emissions. Based on our review, increased Sphagnum cover reduces CO 2 emissions and fosters C sequestration, but drainage transforms peatlands dominated by Sphagnum into a persistent source of CO 2 due to lower gross primary productivity of the moss and increased respiration rates. Sites with moss removal used as donor material for peatland restoration emit twice as much CO 2 as adjacent undisturbed natural sites, and those with commercial Sphagnum extraction generate almost neutral CO 2 emissions, yet both can recover their sink status in the short term. The reintroduction of fragments and natural recolonization of Sphagnum in transitional peatlands, can reduce emissions, recover, or increase the CO 2 sink function in the short and medium term. Furthermore, Sphagnum paludiculture is seen as a sustainable alternative for the use of transitional peatlands, allowing moss production strips to become CO 2 sink, however, it is necessary to quantify the emissions of all the components of the field of production (ditches, causeway), and the biomass harvested from the moss to establish a final closing balance of C., (Global Change Biology© 2023 The Authors. Global Change Biology published by John Wiley & Sons Ltd.)