Soil Organic Layer Research Articles

Differential seasonal changes in soil enzyme activity along an altitudinal gradient in an alpine-gorge region

Information about the seasonal changes in soil enzyme activity along altitudinal gradients is key for understanding the responses of soil biochemical processes to ongoing climate change. Therefore, a 3-year in situ soil core incubation experiment was conducted along a 2431-m altitudinal gradient in an alpine-gorge region on the eastern Qinghai-Tibet Plateau, which includes dry valley shrubland, valley-mountain ecotone forest, subalpine coniferous forest, alpine coniferous forest and alpine meadow. The invertase, urease, and acid phosphatase activities in the soil organic layer (OL) and mineral layer (ML) were measured at five critical periods from 2013 to 2017. Higher soil enzyme activity was observed in the subalpine coniferous forest and alpine meadow, whereas lower activity was observed in the dry valley shrubland and valley-mountain ecotone forest. Overall, the seasonal sensitivity of soil enzyme activity decreased with increases in altitude. In the subalpine and alpine coniferous forests, the seasonal sensitivity of soil enzyme activity was significantly higher in the ML than in the OL. The key drivers of the seasonal variation in soil enzyme activity exhibited marked variation with changes in altitude, and these variations depended on the enzyme type and soil layer. Significant effects of temperature and precipitation on seasonal fluctuations in enzyme activities were observed at lower altitudes, whereas soil freeze-thaw cycles significantly affected the seasonal changes in acid phosphatase activity at higher altitudes. In addition, the seasonal variations in specific enzyme activities differed from those found for enzyme activities, which indicated that microorganisms might have mediated the effects of environmental factors on soil enzyme activity by altering the enzyme production efficiency. Briefly, the seasonal fluctuations in soil enzyme activity and their dominant drivers varied greatly among different altitudes in the alpine-gorge region, implying that soil biochemical processes will exhibit differential responses to ongoing climate change at different altitudes.

Effects of Fire on the Organic and Chemical Properties of Soil in a Pinus halepensis Mill. Forest in Rocallaura, NE Spain

The present study was conducted following a fire that took place in Rocallaura (NE Iberian Peninsula) in 23 June 2016 with the aim of analyzing the chemical properties of soil in burnt and unburnt areas in order to determine the short-term effects of fire on an ecosystem dominated by Pinus halepensis Mill. Transects were laid out in a control area and an adjacent burnt area. Laboratory analyses were performed to determine the chemical properties of the organic and mineral soil layers at 5 cm and 10 cm (total carbon, total nitrogen, organic and inorganic carbon, carbonates, pH, electrical conductivity, and major cations). The results show partial combustion of the organic substrate, with a significant increase in TC, OC, TN, EC and K+, and a slight decrease in pH in the post-fire area compared to the control area, demonstrating that the fire was of low intensity and did not generate significant short-term negative impacts on the soil. Soils of this type, with high organic matter content, tend to maintain their structure after a low-intensity fire and retain the nutrients necessary for ecosystem recovery and resilience.

Soil functional indicators in a mountain forest-rangeland mosaic of northern Iran

Soil plays an essential role in providing ecosystem services, especially in mountain ecosystems which are often considered as fragile and sensitive systems and commonly consist of a mosaic of forest and rangeland plant communities. The relationship between above-ground plant cover and the properties of soil organic and mineral layers in mountain areas are rarely studied. This research aimed to assess the effect of different land covers (i.e. forest, forest-rangeland ecotone, and rangeland) on soil functional indicators, i.e. fertility and biological activities, in the Hyrcanian region of northern Iran. We hypothesized that (i) the presence of tree cover enhances soil fertility and biological activities and creates hot spots (islands) of soil functional indicators especially in the topsoil, (ii) litter quality and organic matter fractions are the drivers for activities of soil organisms, nutrient cycles and transformation processes in mountain ecosystems. Litter (O-horizon including L, F and H layers) and mineral soil samples (in two separate depths of 0–10 cm and 10–20 cm) were taken using iron frames (30 × 30 cm). In total, 45 litter and 90 soil samples were transferred to the laboratory. Soil characteristic especially in the 0–10 cm depth, litter carbon (C), nitrogen (N) and C/N ratio were significantly affected by different land covers showing the maximum of soil organic C and microbial activity under forest. Our findings showed that the studied land covers, as well as litter and soil properties can be separated by PCA output. The first and second axes, accounted more than 50% of the explained variance in each of the studied soil depths. Soils with a better quality of litter (i.e. lower C/N ratio), higher values for organic matter fractions, soil fertility indicators and soil biological activities can be attributed to the forest. In contrast, positions of low soil fertility indicator values and biota abundance were imposed by forest-rangeland ecotone and rangeland. Although each land cover plays a prominent ecological role and takes its place in the evolutionary process, forests are essential because of their capacity to store and transform carbon and nutrients and to create hotspots identified by functional soil indicators. Based on our findings, soil functions decreased ranked in the order forest > forest-rangeland ecotone > rangeland, which can be assigned to the lower density of trees, and the amount of litter mass and litter quality. It can be concluded that tree covers have a prominent role in increasing soil functions, which should be given special consideration in the restoration of degraded mountain ecosystems.

Soil Carbon Isotope Values and Paleoprecipitation Reconstruction

AbstractAnthropogenic climate change has significant impacts at the ecosystem scale including widespread drought, flooding, and other natural disasters related to precipitation extremes. To contextualize modern climate change, scientists often look to ancient climate changes, such as shifts in ancient precipitation ranges. Previous studies have used fossil leaf organic geochemistry and paleosol inorganic chemistry as paleoprecipitation proxies, but have largely ignored the organic soil layer, which acts as a bridge between aboveground biomass and belowground inorganic carbon accumulation, as a potential recorder of precipitation. We investigate the relationship between stable carbon isotope values in soil organic matter (δ13CSOM) and a variety of seasonal and annual climate parameters in modern ecosystems and find a statistically significant relationship between δ13CSOM values and mean annual precipitation (MAP). After testing the relationship between actual and reconstructed precipitation values in modern systems, we test this potential paleoprecipitation proxy in the geologic record by comparing precipitation values reconstructed using δ13CSOM to other reconstructed paleoprecipitation estimates from the same paleosols. This study provides a promising new proxy that can be applied to ecosystems post‐Devonian (∼420 Ma) to the Miocene (∼23 Ma), and in mixed C3/C4 ecosystems in the geologic record with additional paleobotanical and palynological information. It also extends paleoprecipitation reconstruction to more weakly developed paleosol types, such as those lacking B‐ horizons, than previous inorganic proxies and is calibrated for wetter environments.

The molecular composition of extractable soil microbial compounds and their contribution to soil organic matter vary with soil depth and tree species

Recent findings on soil organic matter (SOM) revealed that soil microorganisms are not only crucial for SOM formation through plant litter degradation but soil microbial biomass (SMB) may also directly contribute to SOM and its composition. However, the role and interactions of litter quality, microbial turnover and composition of SMB and SOM remain unclear. Hence, soil profiles (organic forest floor and mineral soil layers) at a recultivated and afforested post-mining site were investigated for the influence of litter quality from different tree species (Fagus sylvatica, Pseudotsuga menziesii, Pinus nigra) and soil depth – representing different degrees of organic matter (OM) turnover – on the molecular composition of chloroform fumigation extracted SMB-derived compounds in comparison with easily extractable (non-fumigated) SOM-derived compounds. The SMB extracts were analyzed for microbial biomass carbon (MBC), nitrogen (MBN) and phosphorus (MBP). The molecular composition of SMB and SOM compounds were determined by electrospray ionization Fourier transformation ion cyclotron resonance mass spectrometry (ESI-FT-ICR-MS) complemented by the determination of nine monosaccharides representing microbial or plant origin.Van Krevelen diagrams obtained from the ESI-FT-ICR mass spectra revealed the substantial contribution of microbial-derived compounds to extractable SOM that further increased with soil depth. Analysis of the easily extractable monosaccharides implied that >99% were of microbial origin. Microbial sugars as well as MBC, MBN and MBP explained best depth-related variations of extractable SMB compounds indicating that supply and availability of C-rich OM drive these parameters. Furthermore, the contribution of microbial sugar C to MBC increased with depth, suggesting that recycling of carbohydrates is an adaptation strategy of microorganisms in C-limited environments. The supply of tree species-specific substrates resulted in different chemical composition of SMB with largest differences between deciduous and coniferous stands and vice versa, microorganisms contributed to SOM resulting in large similarity in the composition of extractable SOM and SMB.

Hydrological regimes in a tropical valley of New Caledonia (SW Pacific): Impacts of wildfires and invasive fauna

AbstractIn New Caledonia wildfires and invasive mammals (deer and wild pigs) constitute the major agents of land surface degradation. Our study reveals the linkage between land cover and water balance on the northeast coast of New Caledonia (2400 mm annual rainfall) located on a micaschist basement. The hydrological regime of characteristic and representative land surfaces is assessed using a 1‐year record from three 100 m2 plots each, located in a forest area degraded by an invasive fauna, in a woody savannah which is regularly burned, and in a healthy forest area. The three plots present highly contrasting hydrological regimes, with annual and maximum runoff/rain ratios during a rain event of, respectively, 0.82, 0.16, 0.03, and 2.7, 0.7, 0.2, for the degraded forest, the savannah and the healthy forest. Such results suggest that subsurface flow originating from the contributing area above the degraded forest plot should exfiltrate inside the plot. A conceptual model for the degraded forest plot shows that water exfiltrating inside the plot represents 61% of the observed runoff. In savannahs, water should mainly be transferred downstream by subsurface flow within a thick organic soil layer limited by an impervious clay layer at a 20–30 cm depth. Savannahs are generally located above forests and generate the transfer of rainwater to downslope forests. Exfiltration into the forests can be the result of this transfer and depends on the thickness and permeability of the forest topsoils and on topographic gradients. Water exfiltration in forest areas highly degraded by pigs and deer enhances erosion and increases further degradation. It probably also limits percolation in the areas located downstream by increasing the amount of superficial runoff concentrated in gullies.

Foxes fertilize the subarctic forest and modify vegetation through denning

Ecosystem engineers modify habitats through processes other than trophic interactions, such as by regulating soil nutrients, and can influence resource availability and quality for other organisms. Predator-mediated elemental cycling may be especially important in determining plant diversity and growth in ecosystems where soil fertility and primary productivity are low. Red foxes (Vulpes vulpes L.), top predators in the Subarctic, could engineer local ecosystems through denning, which could create biogeochemical hotspots of nutrients due to continual input of feces, urine and prey remains. We examined soil and vegetation characteristics on red fox dens and paired control sites in woodland habitats near the Arctic treeline in Manitoba, Canada. The organic soil layer on den sites had 81% more inorganic nitrogen and 250% more extractable phosphorus than in control areas. Denning also increased soil respiration and pH in the organic layer, suggesting improved soil quality and nutrient availability for plants. By enriching nutrients and disturbing soils through digging, den sites had a higher plant species ß-diversity and a greater cover of erect woody shrubs (Salix spp.), grasses (Leymus mollis (Trinius) Pilger) and weedy ephemerals compared to control sites, resulting in a regional increase in plant species richness. Our research highlights the importance of considering impacts of predators other than through their consumption of prey, and provides insight into the role of red foxes in modifying plant diversity and productivity in the Subarctic.

Permafrost Promotes Shallow Groundwater Flow and Warmer Headwater Streams

AbstractThe presence of permafrost influences the flow paths of water through Arctic landscapes and thereby has the potential to impact stream discharge and thermal regimes. Observations from 11 headwater streams in Alaska showed that July water temperatures were higher in catchments with more near‐surface permafrost. We apply a fully coupled cryohydrology model to investigate if the impact of permafrost on flow path depth could cause the same pattern in temperatures of groundwater discharging from hillslopes to streams. The model simulates surface energy and water balances, snow, and subsurface water and energy balances for two‐dimensional hillslope model cases with varying permafrost extent. We find that hillslopes with continuous permafrost have more shallow flow paths and twice as high rates of evapotranspiration, compared to hillslopes with no permafrost. For our simulated cases, 6.7% of the horizontal water flux moves through the top organic soil layers when there is continuous permafrost, while only 0.5% moves through organic layers without permafrost. The deeper flow paths in permafrost‐free simulations buffer seasonal temperature extremes, so that summer groundwater discharge temperatures are highest with continuous permafrost. Our results suggest that permafrost thawing alters groundwater flow paths and can lead to decreases in summer stream temperatures and reductions in evapotranspiration in headwater catchments. These changes are of potential importance for stream biotic components of ecosystems, however, the full impact remains unknown.

Alternative afforestation options on sandy heathland result in minimal long-term changes in mineral soil layers

Extensive afforestation is currently being widely promoted as a key nature-based solution for climate change mitigation. Fundamental to this strategy is the sequestration of carbon into long-term stable storage, either in wood products or the soil. However, the long-term effects of tree planting on soil carbon, or other soil properties, has rarely been examined. Importantly, afforestation can take many different forms, with differing effects on soil properties. Here, we evaluate how the historical afforestation of sandy heathland adopting a range of management options – including different combinations of conifers and broadleaves in monocultures and mixtures – have affected soil pH, total carbon and nitrogen concentrations, the C:N ratio, and carbon and nitrogen stocks almost a century later. We analyse these properties at a range of soil depths through the organic (litter, F and grass layers) and upper mineral (0–5 cm, 5–10 cm and 10–20 cm depth) soil layers. In comparison to the historical heathland sites, afforestation decreased soil pH, most dramatically under conifers, and increased the C:N ratio. However, there was overall little difference in carbon and nitrogen concentrations between alternative management options. While the total carbon and nitrogen concentrations were much higher in the organic layers of the forest options compared to the open sites, this did not translate into differences in the mineral layers. Furthermore, although we found some evidence of the transferral of carbon and nitrogen into the uppermost soil mineral layers, this was minimal in comparison to the concentrations of the organic layers. The soils at our study site are low quality and sandy, and are therefore unfavourable for incorporating organic matter, but it is still notable how little was incorporated after nearly a century of afforestation. Given the current emphasis on tree planting as a means to tackle climate change, these results demonstrate the fundamental importance of the appropriate consideration of both the afforestation management option and underlying soil type.

Long‐term, amplified responses of soil organic carbon to nitrogen addition worldwide

Soil organic carbon (SOC) is the largest carbon sink in terrestrial ecosystems and plays a critical role in mitigating climate change. Increasing reactive nitrogen (N) in ecosystems caused by anthropogenic N input substantially affects SOC dynamics. However, uncertainties remain concerning the effects of N addition on SOC in both organic and mineral soil layers over time at the global scale. Here, we analysed a large empirical data set spanning 60years across 369 sites worldwide to explore the temporal dynamics of SOC to N addition. We found that N addition significantly increased SOC across the globe by 4.2% (2.7%-5.8%). SOC increases were amplified from short- to long-term N addition durations in both organic and mineral soil layers. The positive effects of N addition on SOC were independent of ecosystem types, mean annual temperature and precipitation. Our findings suggest that SOC increases largely resulted from the enhanced plant C input to soils coupled with reduced C loss from decomposition and amplification was associated with reduced microbial biomass and respiration under long-term N addition. Our study suggests that N addition will enhance SOC sequestration over time and contribute to future climate change mitigation.

Understory plant diversity and composition across a postfire tree density gradient in a Siberian Arctic boreal forest

Cajander larch (Larix cajanderi Mayr.) forests of the Siberian Arctic are experiencing increased wildfire activity in conjunction with climate warming. These shifts could affect postfire variation in the density and arrangement of trees and understory plant communities. To better understand how understory plant composition, abundance, and diversity vary with tree density, we surveyed understory plant communities and stand characteristics (e.g., canopy cover, active layer depth, and soil organic layer depth) within 25 stands representing a density gradient of similarly-aged larch trees that established following a 1940 fire near Cherskiy, Russia. Understory plant diversity and mean total plant abundance decreased with increased canopy cover. Canopy cover was also the most important variable affecting individual species’ abundances. In general, tall shrubs (e.g., Betula nana subsp. exilis) were more abundant in low-density stands with high light availability, and mosses (e.g., Sanionia spp.) were more abundant in high-density stands with low light availability. These results provide evidence that postfire variation in tree recruitment affects understory plant community composition and diversity as stands mature. Therefore, projected increases in wildfire activity in the Siberian Arctic could have cascading impacts on forest structure and composition in both overstory and understory plant communities.

Does fire always accelerate shrub expansion in Arctic tundra? Examining a novel grass-dominated successional trajectory on the Seward Peninsula

ABSTRACT Over the last century in the circumpolar north, notable terrestrial ecosystem changes include shrub expansion and an intensifying wildfire regime. Shrub invasion into tundra may be further accelerated by wildfire disturbance, which creates opportunities for establishment where recruitment is otherwise rare. The Seward Peninsula currently experiences more frequent and larger fires than other tundra regions in Alaska. There are areas of overlapping burn scars dating back to the 1950s. Using a chronosequence approach, we examined vegetation and ecosystem dynamics in tussock tundra. Increasing burn severity and fire frequency corresponded with an increase in grass cover and a decrease in shrub basal area. We used multivariate ordination analysis to create a single integrator variable of fire effect that accounted for time after fire, burn severity, and number of times burned. This fire effect was significantly associated with decreases in soil organic layer thickness and overall plant biomass. Unlike previous studies in Arctic Alaska tundra, we found that increases in fire frequency and severity did not increase shrub cover and biomass. Instead, intensifying fire disturbance, and particularly repeat fires, led to grass dominance. Our findings support the hypothesis that intensifying tundra fire regimes initiate alternative post-fire trajectories that are not shrub dominated and that are structurally and functionally quite different from sedge or shrub-dominated tundra.

Long-term stabilization of 15N-labeled experimental NH4+ deposition in a temperate forest under high N deposition

High nitrogen (N) deposition levels, currently present in many industrial and agricultural regions of the world, can strongly affect the functioning of forest ecosystems. In a pine forest with strong N leaching, located in the Netherlands, we studied the long-term fate of a year-long NH4+ deposition cohort labeled with 15N. A high ambient and a low N deposition treatment had been established at the site by means of a roof and sprinklers. Resampling the N pools 19 years after labeling and 11 years after the last sampling, we found similar 15N deltas in needles, twigs and the LF1 organic soil layer of each treatment, indicating intensive N cycling among these pools. In the last 11 years, label recovery decreased in these labile pools, while recovery remained constant in wood and increased in bark. Together these aboveground vegetation pools retained less than 3% of the labeled N. In the organic layers, label recovery after 19 years decreased to 23% in both treatments, while in the mineral soil it increased from 4% to 13% (high N) and from 3% to 29% (low N treatment). Within the mineral soil of the high N treatment the labeled N was mainly found in fine roots, while in the low N treatment most N was incorporated in the two soil density fractions, shifting to the high density fraction with depth. This suggests a low capacity of the mineral soil at high N deposition to incorporate N. After the labeled N had been lost substantially in previous years, especially in the first, its presence remained constant in the last 11 years at 38% (high N) and 54% (low N treatment). Apparently, even in this strongly N leaching ecosystem, N once incorporated, was retained well and did not affect the input-output fluxes of the system.

Methane-Oxidizing Communities in Lichen-Dominated Forested Tundra Are Composed Exclusively of High-Affinity USCα Methanotrophs.

Upland soils of tundra function as a constant sink for atmospheric CH4 but the identity of methane oxidizers in these soils remains poorly understood. Methane uptake rates of −0.4 to −0.6 mg CH4-C m−2 day−1 were determined by the static chamber method in a mildly acidic upland soil of the lichen-dominated forested tundra, North Siberia, Russia. The maximal CH4 oxidation activity was localized in an organic surface soil layer underlying the lichen cover. Molecular identification of methanotrophic bacteria based on retrieval of the pmoA gene revealed Upland Soil Cluster Alpha (USCα) as the only detectable methanotroph group. Quantification of these pmoA gene fragments by means of specific qPCR assay detected ~107 pmoA gene copies g−1 dry soil. The pmoA diversity was represented by seven closely related phylotypes; the most abundant phylotype displayed 97.5% identity to pmoA of Candidatus Methyloaffinis lahnbergensis. Further analysis of prokaryote diversity in this soil did not reveal 16S rRNA gene fragments from well-studied methanotrophs of the order Methylococcales and the family Methylocystaceae. The largest group of reads (~4% of all bacterial 16S rRNA gene fragments) that could potentially belong to methanotrophs was classified as uncultivated Beijerinckiaceae bacteria. These reads displayed 96–100 and 95–98% sequence similarity to 16S rRNA gene of Candidatus Methyloaffinis lahnbergensis and “Methylocapsa gorgona” MG08, respectively, and were represented by eight species-level operational taxonomic units (OTUs), two of which were highly abundant. These identification results characterize subarctic upland soils, which are exposed to atmospheric methane concentrations only, as a unique habitat colonized mostly by USCα methanotrophs.

Production of Fungal Mycelia in a Temperate Coniferous Forest Shows Distinct Seasonal Patterns.

In temperate forests, climate seasonality restricts the photosynthetic activity of primary producers to the warm season from spring to autumn, while the cold season with temperatures below the freezing point represents a period of strongly reduced plant activity. Although soil microorganisms are active all-year-round, their expressions show seasonal patterns. This is especially visible on the ectomycorrhizal fungi, the most abundant guild of fungi in coniferous forests. We quantified the production of fungal mycelia using ingrowth sandbags in the organic layer of soil in temperate coniferous forest and analysed the composition of fungal communities in four consecutive seasons. We show that fungal biomass production is as low as 0.029 µg g−1 of sand in December–March, while it reaches 0.122 µg g−1 in June–September. The majority of fungi show distinct patterns of seasonal mycelial production, with most ectomycorrhizal fungi colonising ingrowth bags in the spring or summer, while the autumn and winter colonisation was mostly due to moulds. Our results indicate that fungal taxa differ in their seasonal patterns of mycelial production. Although fungal biomass turnover appears all-year-round, its rates are much faster in the period of plant activity than in the cold season.

Carbon budgets for soil and plants respond to long-term warming in an Alaskan boreal forest

The potential consequences of global warming for ecosystem carbon stocks are a major concern, particularly in high-latitude regions where soil carbon pools are especially large. Research on soil and plant carbon responses to warming are often based on short-term (< 10 year) warming experiments. Furthermore, carbon budgets from boreal forests, which contain at least 10–20% of the global soil carbon pool, have shown mixed responses to warming. In this study, we measured carbon and nitrogen budgets (i.e., soil and understory vegetation carbon and nitrogen stocks) from a 13-year greenhouse warming experiment in an Alaskan boreal forest. Although there were no differences in total aboveground + belowground pools, the carbon in the moss biomass and in the soil organic layer significantly decreased with the warming treatment (− 88.3% and − 19.1%, respectively). Declines in moss biomass carbon may be a consequence of warming-associated drying, while shifts in the soil microbial community could be responsible for the decrease in carbon in the soil organic layer. Moreover, in response to warming, aboveground plant biomass carbon tended to increase while root biomass carbon tended to decrease, so carbon allocation may shift aboveground with warming. Overall these results suggest that permafrost-free boreal forests are susceptible to soil carbon loss with warming.

Generalized models to estimate carbon and nitrogen stocks of organic soil horizons in Interior Alaska

Abstract. Boreal ecosystems comprise one-tenth of the world's land surface and contain over 20 % of the global soil carbon (C) stocks. Boreal soil is unique in that its mineral soil is covered by what can be quite thick layers of organic soil. These organic soil layers, or horizons, can differ in their state of decomposition, source vegetation, and disturbance history. These differences result in varying soil properties (bulk density, C concentration, and nitrogen concentration) among soil horizons. Here we summarize these soil properties, as represented by over 3000 samples from Interior Alaska, and examine how soil drainage and stand age affect these attributes. The summary values presented here can be used to gap-fill large datasets when important soil properties were not measured, provide data to initialize process-based models, and validate model results. These data are available at https://doi.org/10.5066/P960N1F9 (Manies, 2019).

Decadal‐Scale Recovery of Carbon Stocks After Wildfires Throughout the Boreal Forests

AbstractBoreal forests store 30% of the world's terrestrial carbon (C). Consequently, climate change mediated alterations in the boreal forest fire regime can have a significant impact on the global C budget. Here we synthesize the effects of forest fires on the stocks and recovery rates of C in boreal forests using 368 plots from 16 long‐term (≥100 year) fire chronosequences distributed throughout the boreal zone. Forest fires led to a decrease in total C stocks (excluding mineral soil) by an average of 60% (range from &lt;10% to &gt;80%), which was primarily a result of C stock declines in the living trees and soil organic layer. Total C stocks increased with time since fire largely following a sigmoidal shape Gompertz function, with an average asymptote of 8.1 kg C m−2. Total C stocks accumulated at a rate of 2–60 g m−2 yr−1 during the first 100 years. Potential evapotranspiration (PET) was identified as a significant driver of C stocks and their post‐fire recovery, likely because it integrates temperature, radiation, and the length of the growing season. If the fire return interval shortens to ≤100 years in the future, our findings indicate that many boreal forests will be prevented from reaching their full C storage potential. However, our results also suggest that climate warming‐induced increases in PET may speed up the post‐fire recovery of C stocks.

Boreal blazes: biomass burning and vegetation types archived in the Juneau Icefield

The past decade includes some of the most extensive boreal forest fires in the historical record. Warming temperatures, changing precipitation patterns, the desiccation of thick organic soil layers, and increased ignition from lightning all contribute to a combustive combination. Smoke aerosols travel thousands of kilometers, before blanketing the surfaces on which they fall, such as the Juneau Icefield. However, many aerosols found in smoke plumes are also produced by other processes and therefore can be ambiguous indicators of fire activity. Here, we use the monosaccharide anhydrides levoglucosan, mannosan, and galactosan as specific indicators of biomass burning to unambiguously demonstrate that fire aerosols reach the Juneau Icefield and are integrated into the snowpack. Back trajectories and satellite observations demonstrate that smoke plumes originating in central Alaska and eastern Siberia affect the Juneau Icefield. These regional sources of fire differ from other combustion aerosols deposited on the Juneau Icefield, such as black carbon, that originate from local fossil fuel burning. Ratios of levoglucosan/mannosan (L/M) and levoglucosan/(mannosan + galactosan) (L/(M + G)) demonstrate that while the majority of fire aerosols reaching the Juneau Icefield originate from softwood burning, grasslands and hardwood forests are also sources. The presence of these hardwoods suggests that fire aerosols may reach the Juneau Icefield from locations as far away as East Asia.

Compressibility behaviour and properties of peaty soils from Dian-Chi Lake area, China

Peat deposits are widely encountered in many parts of the world and present various challenges for the geotechnical engineering community because of their low bearing capacity and very high compressibility and creep potential. This paper describes extensive index and oedometer testing to investigate the compressibility behaviour/properties of deep, strongly to completely humified peat and highly organic fine-grained soil layers at the northeast shore of Dian-Chi Lake in Kunming, southwest China; a region that recently is experiencing significant infrastructure construction. Compared to surficial peat deposits, the peaty soil layers investigated, with organic contents ranging 23.5–80.0%, have been subjected to a 6.7-m depth of inorganic soil overburden, such that they have substantially lower water content and void ratio and higher preconsolidation stress. Nevertheless, with deduced Cα/Cc = 0.04–0.07, Cr/Cc = 0.14–0.18 and Ck/e0 = 0.23, the Dian-Chi peaty soils exhibit similarities with surficial fibrous peats from other countries/regions. Unlike fibrous peats, however, the Dian-Chi peaty soils have extremely low permeability, with deduced kv values of the order of 1 × 10−9 to 1 × 10−10 m/s, consistent with their hunification level. Existing linear Cc – w0 correlations were found inadequate for the Dian-Chi peaty soils, such that a new Cc – w0 correlation is proposed from curve-fitting of the gathered experimental data to better capture their non-linear relationship.