Waterlogged Peat Research Articles

Reversal in the drought stress response of the Scots pine forest ecosystem: Local soil water regime as a key to improving climate change resilience

In a changing climate, forest ecosystems have become increasingly vulnerable to continuously exacerbating heat and associated drought conditions. Climate stress resilience is governed by a complex interplay of global, regional, and local factors, with hydrological conditions being among the key players. We studied a Scots pine (Pinus sylvestris L.) forest ecosystem located near the southern edge of the boreal ecotone, which is particularly subjected to frequent and prolonged droughts. By comparing the dendrochronological series of pines growing in apparently contrasting hydrological conditions ranging from the waterlogged peat bog area to the dry soil at the surrounding elevations, we investigated how the soil water regime affects the climate response and drought stress resilience of the forest ecosystem. We found that in the dry land area, a significant fraction of the trees were replaced after two major climate extremes: prolonged drought and extremely low winter temperatures. The latter has also been followed by a three- to ten-fold growth reduction of the trees that survived in the next year, whereas no similar effect has been observed in the peat bog area. Multi-scale detrended partial cross-correlation analysis (DPCCA) indicated that tree-ring width (TRW) was negatively correlated with spring and summer temperatures and positively correlated with the Palmer drought severity index (PDSI) for the same year. For the elevated dry land area, the above effect extends to interannual scales, indicating that prolonged heatwaves and associated droughts are among the factors that limit tree growth. In marked contrast, in the waterlogged peat bog area, a reversed tendency was observed, with prolonged dry periods as well as warmer springs and summers over several consecutive years, leading to increasing tree growth with a one- to three-year time lag. Altogether, our results indicate that the pessimal conditions of a warming climate could become favorable through the preservation of the soil water regime.

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

A small imbalance in plant productivity and decomposition accounts for the carbon (C) accumulation capacity of peatlands. As climate changes, the continuity of peatland net C storage relies on rising primary production to offset increasing ecosystem respiration (ER) along with the persistence of older C in waterlogged peat. A lowering in the water table position in peatlands often increases decomposition rates, but concurrent plant community shifts can interactively alter ER and plant productivity responses. The combined effects of water table variation and plant communities on older peat C loss are unknown. We used a full-factorial 1-m3 mesocosm array with vascular plant functional group manipulations (Unmanipulated Control, Sedge only, and Ericaceous only) and water table depth (natural and lowered) treatments to test the effects of plants and water depth on CO2 fluxes, decomposition, and older C loss. We used Δ14 C and δ13 C of ecosystem CO2 respiration, bulk peat, plants, and porewater dissolved inorganic C to construct mixing models partitioning ER among potential sources. We found that the lowered water table treatments were respiring C fixed before the bomb spike (1955) from deep waterlogged peat. Lowered water table Sedge treatments had the oldest dissolved inorganic 14 C signature and the highest proportional peat contribution to ER. Decomposition assays corroborated sustained high rates of decomposition with lowered water tables down to 40 cm below the peat surface. Heterotrophic respiration exceeded plant respiration at the height of the growing season in lowered water table treatments. Rates of gross primary production were only impacted by vegetation, whereas ER was affected by vegetation and water table depth treatments. The decoupling of respiration and primary production with lowered water tables combined with older C losses suggests that climate and land-use-induced changes in peatland hydrology can increase the vulnerability of peatland C stores.

Minnesota peat viromes reveal terrestrial and aquatic niche partitioning for local and global viral populations

BackgroundPeatlands are expected to experience sustained yet fluctuating higher temperatures due to climate change, leading to increased microbial activity and greenhouse gas emissions. Despite mounting evidence for viral contributions to these processes in peatlands underlain with permafrost, little is known about viruses in other peatlands. More generally, soil viral biogeography and its potential drivers are poorly understood at both local and global scales. Here, 87 metagenomes and five viral size-fraction metagenomes (viromes) from a boreal peatland in northern Minnesota (the SPRUCE whole-ecosystem warming experiment and surrounding bog) were analyzed for dsDNA viral community ecological patterns, and the recovered viral populations (vOTUs) were compared with our curated PIGEON database of 266,125 vOTUs from diverse ecosystems.ResultsWithin the SPRUCE experiment, viral community composition was significantly correlated with peat depth, water content, and carbon chemistry, including CH4 and CO2 concentrations, but not with temperature during the first 2 years of warming treatments. Peat vOTUs with aquatic-like signatures (shared predicted protein content with marine and/or freshwater vOTUs) were significantly enriched in more waterlogged surface peat depths. Predicted host ranges for SPRUCE vOTUs were relatively narrow, generally within a single bacterial genus. Of the 4326 SPRUCE vOTUs, 164 were previously detected in other soils, mostly peatlands. None of the previously identified 202,371 marine and freshwater vOTUs in our PIGEON database were detected in SPRUCE peat, but 0.4% of 80,714 viral clusters (VCs, grouped by predicted protein content) were shared between soil and aquatic environments. On a per-sample basis, vOTU recovery was 32 times higher from viromes compared with total metagenomes.ConclusionsResults suggest strong viral “species” boundaries between terrestrial and aquatic ecosystems and to some extent between peat and other soils, with differences less pronounced at higher taxonomic levels. The significant enrichment of aquatic-like vOTUs in more waterlogged peat suggests that viruses may also exhibit niche partitioning on more local scales. These patterns are presumably driven in part by host ecology, consistent with the predicted narrow host ranges. Although more samples and increased sequencing depth improved vOTU recovery from total metagenomes, the substantially higher per-sample vOTU recovery after viral particle enrichment highlights the utility of soil viromics.3EUUqCyiCvMAAvxFuvvQVmVideo abstract The importance of Minnesota peat viromes in revealing terrestrial and aquatic niche partitioning for viral populations

Сезонный рост сосны обыкновенной на заболоченных почвах Севера

The seasonal rhythm of height growth of young shoots of Scots pine growing in a 33-year-old shrubby-sphagnum pine forest of the northern taiga natural-climatic zone has been studied in a complex with the main physiological processes. The possibility of regulating their intensity by additional introduction of nitrogen fertilizer has been determined. It has been found that on hydromorphic excessively wet soils of the North, seasonal height growth of pine occurs with a maximum rate in late June and early July, when air temperature rises and the root system is released from excessive moisture. Unlike lichen pine forests, in which pine roots are not affected by flooding, on hydromorphic peat soils pine grows much slower and during the growing season has less intensive physiological processes. The low rate of shoot growth and physiological processes in pine in sphagnum forest site conditions is explained by dysfunction of its root system as a result of soil anoxia caused by flooding, as well as by insufficient supply of growing shoots with acronutrients from the crown as a result of violation of their normal outflow and movement in the tree. Nitrogen fertilizers positively affect growth and physiological processes in pine trees in sphagnum forest types. However, their effect in these forest site conditions is much weaker than in the dry lichen forests of the Far North. On water-logged peat soils under the influence of nitrogen fertilizer seasonal height growth of pine trees increases by 20 %, the duration of seasonal shoot growth increases by 8–10 days, the intensity of photosynthesis increases significantly, and, as a result of reduced water onsumption for transpiration, the tree water regime normalizes and the transpiration productivity increases. These positive nitrogen-induced changes ultimately improve the viability and productivity of sphagnum pine forests. For citation: Zarubina L.V., Khamitov R.S. Seasonal Growth of Scots Pine under the Conditions of Water-Logged Soils of the North. Lesnoy Zhurnal [Russian Forestry Journal], 2021, no. 3, pp. 86–100. DOI: 10.37482/0536-1036-2021-3-86-100

Production of hydroxyl radicals following water-level drawdown in peatlands: A new induction mechanism for enhancing laccase activity in carbon cycling

The hydroxyl radical (•OH) is the most powerful reactive oxygen species that plays a critical role in the fate of redox-active substances. Peatlands are carbon-rich ecosystems with highly reduced substances and ubiquitous redox interfaces. However, little is known about the production of •OH during the reoxidation of peatlands under waterlogged conditions. Here, we conduct a set of reoxidation experiments using waterlogged peat soil dominated by various vegetation species and monitored •OH production. The results show that the cumulative concentrations of •OH produced within 24 h upon oxygenation of waterlogged peat samples are 307–840 mmol g−1. The main factors affecting the production of •OH include an acidic environment, abundant reduced dissolved organic matter and Fe(II). In addition, •OH production enhances laccase activity (the largest class of phenol oxidases in the soil) by 7.7% ~ 20.4% and increases soil respiration by 3.17% ~ 23.67% during the reoxidation of the waterlogged peat samples. In addition, the simulation experiments confirm that •OH can promote laccase activity directly by serving as an electron acceptor and indirectly by oxidizing substrates. Both mechanisms are greater than the effect of oxygen (O2) alone on laccase activity. Our results indicate a new induction mechanism for enhancing laccase activity by •OH when subjected to anoxic-oxic interface fluctuations, which is particularly important for carbon cycling in peatlands because it can break the decomposition latch and can further promote soil organic carbon mineralization.

The Construction Of Roadbeds on Permafrost and in Swamps from Reinforced Soils of Increased Strength

The paper presents the history of the transport infrastructure of the West-Siberian oil and gas complex in the last century and ways to solve the problems of road construction in the twenty-first century. The development of the territory of Siberia and the North in the present period is constrained by the low rates of development of the transport structure. One of the reasons for this lag is the lack of regulatory documents to substantiate transport structures in the harsh climatic and difficult soil and geological conditions based on the use of new modern road-building materials. The development of new resource-saving materials, structures and technologies based on local building materials, products and industrial waste using modern methods and research methods in materials science is an aim of current study. The general research methodology consisted of theoretical, laboratory and field studies. The developed designs and technologies for the construction of embankments in permafrost and in swamps using geotechnical holders filled with unsuitable soils (thawed and frozen waterlogged peat and clay soils) can reduce the volume of work and the cost of construction by one and a half to two times while increasing the service life of structures. The experimental sites of embankments constructed between 1995 and 2009 in the wetlands of the Uvat Group of deposits in the Tyumen Region and in permafrost in the areas of Novy Urengoy have been observed for more than ten years. The artificial stone material tested in Murmansk and Surgut based on the strengthening of local soils with inorganic binders with polymer additives using modern technologies allows it to be used instead of imported stone materials and reinforced concrete slabs for the construction of structural layers of road pavements, reinforcing slopes, as well as in hydraulic structures. The new artificial stone material is characterized by high strength and durability in areas with a temperature gradient of the external environment of more than 100 (from +50 to -50 °C).

Dynamics of fine-root production and mortality of Scots pine in waterlogged peat soil during the growing season

Excess water in the rooting zone critically reduces tree growth and may even kill trees; however, the relative importance of damage to roots versus aboveground parts and the time course of damage are not well understood. We studied the dynamics of fine-root growth and mortality of 7-year-old Scots pine (Pinus sylvestris L.) saplings affected by a 5-week period of waterlogging (WL) during the growing season. Two out of six WL-exposed saplings survived the treatment. After 1–2 weeks of WL, the mortality of the first-order short roots (usually mycorrhizas) started to increase and the production of these roots started to decrease. WL decreased the longevity of short and long roots. Total root length (especially of fine roots with a diameter < 0.5 mm), specific fine-root length, total root dry mass (including stump), and reverse-flow root hydraulic conductance were lower in WL saplings than in control saplings at the end of the experiment; however, several root traits were similar in control and surviving WL saplings. Because of the high importance of fine roots for tree growth and carbon sequestration, their responses to elevated water tables should be considered in sustainable use and management of boreal peatland forests, for example, by continuous cover forestry and (or) ditch network maintenance.

Are the wooden remains of the Lusatian culture settlement at Biskupin safe? Decomposition of archaeological oak wood samples during a 10-year experiment

A study was made of the decomposition of oak wood samples deposited in different environments on the Lusatian culture site in Biskupin, Poland. Waterlogged archaeological wood samples were examined after 10 years of deposition in peat, sand or mineral soil or in a water-filled trench. Wood decay was evaluated on the basis of wood mass loss, sample volume loss, physical properties (maximum water content, basic density, porosity) with and without mineral compounds, chemical composition (holocellulose, cellulose, pentosans, lignin, substances soluble in 1% NaOH, 95% ethanol and hot and cold water, and ash content) and microscopic observations. The oak wood was found to be least degraded in the strongly reducing waterlogged peat in which the preserved remains of wooden constructions of the Biskupin settlement are deposited. Nevertheless, even in this near-anaerobic environment, wood decomposition was significant. The loss of wood mass was about 8–10%, whilst the decrease in the cellulose content ranged from 14 to 16%. To preserve the remains of the Biskupin settlement for future generations, it is proposed to consider excavating some of the wood for conservation and exhibition under controlled museum conditions.

Changes in oak wood buried in waterlogged peat: shrinkage as a complementary indicator of the wood degradation rate

A study was made on the degradation of contemporary heartwood of oak (Quercus sp.) buried in waterlogged peat on the archaeological site at Biskupin (Poland). The state of wood preservation was evaluated after 2, 4, 6, 8 and 10 years of deposition of samples in conditions similar to anaerobic. The changes that occurred in the wood were assessed on the basis of microscopic examinations, chemical composition, mass loss and selected physical properties of the wood. Despite a distinct mass loss of the samples (7.4% after 10 years of the experiment), only the initial phase of cell wall degradation and almost unchanged contents of major chemical components were observed in the examined wood. Greater changes were recorded in the content of water-soluble extractives, maximum water content, basic density and wood porosity, as well as in the total tangential and the total radial shrinkage. Wood mass loss resulted mainly from the loss of substances soluble in water (up to 70.8% after 10 years of the experiment) and less from the biological degradation of cell walls (loss of major chemical components of wood). A close relationship was observed between content of substances soluble in water, mass loss, and wood shrinkage. It was concluded that tangential and radial shrinkage may serve as a simple complementary indicator of the state of preservation of wood decomposing in the conditions of a monitored archaeological site.

Toward a mechanistic understanding of "peat collapse" and its potential contribution to coastal wetland loss.

Coastal wetlands are susceptible to loss in both health and extent via stressors associated with global climate change and anthropogenic disturbance. Peat collapse may represent an additional phenomenon contributing to coastal wetland loss in organic‐rich soils through rapid vertical elevation decline. However, the term “peat collapse” has been inconsistently used in the literature, leading to ambiguities regarding the mechanisms, timing, and spatial extent of its contribution to coastal wetland loss. For example, it is unclear whether peat collapse is distinct from general subsidence, or what biogeochemical changes or sequence of events may constitute peat collapse. A critical analysis of peer‐reviewed literature related to peat collapse was supplemented with fundamental principles of soil physics and biogeochemistry to develop a conceptual framework for coastal wetland peat collapse. We propose that coastal wetland peat collapse is a specific type of shallow subsidence unique to highly organic soils in which a loss of soil strength and structural integrity contributes to a decline in elevation, over the course of a few months to a few years, below the lower limit for emergent plant growth and natural recovery. We further posit that coastal wetland peat collapse is driven by severe stress or death of the vegetation, which compromises the supportive structure roots provide to low‐density organic soils and shifts the carbon balance of the ecosystem toward a net source, as mineralization is no longer offset by sequestration. Under these conditions, four mechanisms may contribute to peat collapse: (1) compression of gas‐filled pore spaces within the soil during dry‐down conditions; (2) deconsolidation of excessively waterlogged peat, followed by transport; (3) compaction of aerenchyma tissue in wetland plant roots, and possibly collapse of root channels; and (4) acceleration of soil mineralization due to the addition of labile carbon (dying roots), oxygen (decreased flooding), nutrients (eutrophication), or sulfate (saltwater intrusion). Scientists and land managers should focus efforts on monitoring vegetation health across the coastal landscape as an indicator for peat collapse vulnerability and move toward codifying the term “peat collapse” in the scientific literature. Once clarified, the contribution of peat collapse to coastal wetland loss can be evaluated.

Assessing nutrient responses and biomass quality for selection of appropriate paludiculture crops

Tall wetland graminoids with rapid growth, high productivity and wide tolerance of biotic and abiotic stresses are potentially valuable bioenergy crops, especially when grown in rewetted peat soils for biomass (paludiculture). Using wetland plants as renewable bioenergy crops instead of fossil fuels has the ecological benefits of reducing greenhouse gas (GHG) emissions, improving water quality and conserving peat soils. As these potential crops will grow in peat that differs in nutrient availability, not only will their biomass productivity be affected, but also the biomass quality for bioenergy may be altered. We set up five different nutrient availability treatments in waterlogged peat soil to simulate different nutrient environments for wetland plant cultivation. Seven wetland plants suitable for paludiculture (Typha latifolia, Arundo plinii, Arundo donax and four distinct genotypes of Phragmites australis from Denmark, The Netherlands, Romania and Italy) were selected to test responses of biomass production and tissue quality to different nutrient availability. Due to their high biomass productivity, T. latifolia, A. donax, Dutch (NL) and Romanian (RO) P. australis had the greatest potential to produce bioenergy feedstock. All taxa survived when cultivated with very low nutrient availability, especially NL and RO P. australis and T. latifolia. Moreover, biomass quality was both species-specific and element-specific, affected by increasing nutrient availability. Overall, T. latifolia had the lowest tissue concentrations of S and Si as well as high concentrations of Ca, and therefore the best tissue quality for combustion both at low and high nutrient availability. These results will provide crucial information for choosing appropriate crops and managements and promote the success of culturing wetland plants as bioenergy feedstock.

The Fate of 15N Tracer in Waterlogged Peat Cores from Two Central European Bogs with Different N Pollution History

Under low nitrogen (N) input into rain-fed peat bogs, Sphagnum moss efficiently filters incoming N, preventing invasion of vascular plants and peat oxygenation. Elevated atmospheric N deposition, in combination with climatic warming, may cause retreat of bryophytes and degradation of peat deposits. There are concerns that higher emissions of greenhouse gases, accompanying peat thinning, will accelerate global warming. Breakthrough of deposited N below living moss has been quantified for two Central European peat bogs dominated by Sphagnum magellanicum. In the 1990s, the northern site, ZL, received three times more atmospheric N (> 40 kg ha−1 year−1) than the southern site, BS. Today, atmospheric N inputs at both sites are comparable (15 and 11 kg ha−1 year−1, respectively). Replicated peat cores were collected from the wet central segments of both study sites, 15N-NO3− tracer was applied on the moss surface, and the peat cores were incubated under water-logged conditions. After 40 weeks, the rate of downcore leaching of the 15N tracer was assessed. The recent history of high N pollution at ZL did not accelerate 15N penetration into deeper peat layers, relative to BS. At both sites, less than 3% of the 15N tracer reached the shallow depth of 9 cm. Analysis of control peat cores, along with a 210Pb chronology, revealed removal of the “excess” N from the ZL peat profiles prior to sampling. Following a decrease of atmospheric N pollution in the past two decades, efficient filtering of atmospheric N by Sphagnum at ZL has been renewed.

МЕТАН В ПОЧВАХ ЕВРОПЕЙСКОЙ РОССИИ, "Известия Российской академии наук. Серия географическая"

The authors compiled and analyzed experimental data on the distribution of methane content in the soils of the lower Don steppe province (the south of Rostov oblast) and the subzone of typical (average) taiga (Karelia), forest-bog landscapes of Arkhangelsk, Pskov and Moscow oblasts. The data from the literature were also involved. Investigations revealed relatively low concentrations of methane (average of 0.18 µg/g of sample) in drained soils of tundra, taiga forest and steppe zones, and transition zones between forest and steppe, with a trend of increasing its amount from steppe zone to taiga with increasing soil moisture. Higher concentrations of methane (1–2 orders of magnitude higher) are typical for soils of waterlogged sites and peat deposits of bogs. The distribution along the vertical profile of methane in dry and temporarily flooded soils is characterized by a reduction of its concentrations from the surface to the lower horizons, while in peat deposits of bogs, the concentration of gas, by contrast, increases significantly with depth.

The role of molecular weight in the enzyme-inhibiting effect of phenolics: the significance in peatland carbon sequestration

Northern peatlands store 455Pg of carbon–a third of the entire global carbon store. Carbon accumulates because phenolic inhibitors slow the rate of decomposition to below that of photosynthetic production. The disproportionate importance of phenolics in peatlands is related to the unique properties of waterlogged peat soils suppressing the activity of phenol oxidase; one of the few enzymes capable of breaking these inhibitors down (a role often referred to as the “enzymic latch”). This permits accumulation of phenolic compounds that are potent inhibitors of hydrolase enzymes–major agents in the breakdown of organic matter. In our study we investigate the importance of the molecular weight of phenolics on levels of inhibition of microbial decomposition in peat. We found the higher the molecular weight, of a phenolic compound, the greater its inhibitory effect on the breakdown of organic matter.

Management strategies for medically unexplained symptoms in general practice: A qualitative study

Northern peatlands store 455 Pg of carbon–a third of the entire global carbon store. Carbon accumulates because phenolic inhibitors slow the rate of decomposition to below that of photosynthetic production. The disproportionate importance of phenolics in peatlands is related to the unique properties of waterlogged peat soils suppressing the activity of phenol oxidase; one of the few enzymes capable of breaking these inhibitors down (a role often referred to as the “enzymic latch”). This permits accumulation of phenolic compounds that are potent inhibitors of hydrolase enzymes–major agents in the breakdown of organic matter. In our study we investigate the importance of the molecular weight of phenolics on levels of inhibition of microbial decomposition in peat. We found the higher the molecular weight, of a phenolic compound, the greater its inhibitory effect on the breakdown of organic matter.

Canada: Titan International – carbon black ex-scrap tyres

Northern peatlands store 455 Pg of carbon–a third of the entire global carbon store. Carbon accumulates because phenolic inhibitors slow the rate of decomposition to below that of photosynthetic production. The disproportionate importance of phenolics in peatlands is related to the unique properties of waterlogged peat soils suppressing the activity of phenol oxidase; one of the few enzymes capable of breaking these inhibitors down (a role often referred to as the “enzymic latch”). This permits accumulation of phenolic compounds that are potent inhibitors of hydrolase enzymes–major agents in the breakdown of organic matter. In our study we investigate the importance of the molecular weight of phenolics on levels of inhibition of microbial decomposition in peat. We found the higher the molecular weight, of a phenolic compound, the greater its inhibitory effect on the breakdown of organic matter.

Invasion of the Alien MossCampylopus introflexusin Cutaway Peatlands

Priede, A. & Mežaka, A. 2016. Invasion of the alien moss Campylopus introflexus in cutaway peatlands. — Herzogia 29: 35–51.Campylopus introflexus is an invasive alien moss in Europe and North America considered as a threat to biodiversity, especially in dune habitats. In this study, we found that C. introflexus is a common pioneer species in vacuumharvested peatlands in Latvia occurring on dry peat substrates and peat substrates with highly fluctuating water tables, but not on waterlogged peat surfaces. The spread of this species is limited by dense vegetation cover, shading and high water table, but it is tolerant of different peat substrate properties and a wide range of pH values. The invaded plant communities do not represent a species composition typical of natural bogs and fens. C. introflexus can be considered as a successful pioneer invader on cutaway peatlands with minor impacts on vegetation diversity or particular native species and cannot be considered as a threat to peatlands. In cutaway peatlands, the vegetation recovery toward formation of bog or fen communities is hindered by lowered water table, not by invasion of C. introflexus.

Short-Term Summer Inundation as a Measure to Counteract Acidification in Rich Fens.

In regions with intensive agriculture, water level fluctuation in wetlands has generally become constricted within narrow limits. Water authorities are, however, considering the re-establishment of fluctuating water levels as a management tool in biodiverse, base-rich fens (‘rich fens’). This includes temporary inundation with surface water from ditches, which may play an important role in counteracting acidification in order to conserve and restore biodiversity. Inundation may result in an increased acid neutralizing capacity (ANC) for two reasons: infiltration of base-rich inundation water into peat soils, and microbial alkalinity generation under anaerobic conditions. The main objectives of this study were to test whether short-term (2 weeks) summer inundation is more effective than short-term winter inundation to restore the ANC in the upper 10 cm of non-floating peat soils, and to explain potential differences. Large-scale field experiments were conducted for five years in base-rich fens and Sphagnum-dominated poor fens. Winter inundation did not result in increased porewater ANC, because infiltration was inhibited in the waterlogged peat and evapotranspiration rates were relatively low. Also, low temperatures limit microbial alkalinity generation. In summer, however, when temperature and evapotranspiration rates are higher, inundation resulted in increased porewater Ca and HCO3 - concentrations, but only in areas with characteristic rich fen bryophytes. This increase was not only due to stronger infiltration into the soil, but also to higher microbial alkalinity generation under anaerobic conditions. In contrast, porewater ANC did not increase in Sphagnum-plots as a result of the ability of Sphagnum spp. to acidify their environment. In both rich and poor fens, flooding-induced P-mobilization remained sufficiently low to safeguard P-limited vegetation. NO3 - and NH4 + dynamics showed no considerable changes either. In conclusion, short-term summer inundation with base-rich and nutrient-poor surface water is considered beneficial in the management of non-floating rich fens, and much more effective than winter inundation.

Release of nitrous oxide and dinitrogen from a transition bog under drained and rewetted conditions due to denitrification: results from a [15N]nitrate–bromide double-tracer study

Denitrification is well known being the most important nitrate-consuming process in water-logged peat soils, whereby the intermediate compound nitrous oxide (N2O) and the end product dinitrogen (N2) are ultimately released. The present study was aimed at evaluating the release of these gases (due to denitrification) from a nutrient-poor transition bog ecosystem under drained and three differently rewetted conditions at the field scale using a 15N-tracer approach ([15N]nitrate application, 30 kg N ha−1) and a common closed-chamber technique. The drained site is characterized by a constant water table (WT) of –30 cm (here referred to as D30), while rewetted sites represent a constant WT of –15 cm, a constant WT of 0 cm (i.e. waterlogged), and an initial WT of 0 cm (which decreased slightly during the experiment), respectively, (here referred to as R15, R0, and R0d, respectively). The highest N2O emissions were observed at D30 (291 µg N2O–N m−2 h−1) as well as at R0d (665 µg N2O–N m−2 h−1). At the rewetted peat sites with a constant WT (i.e. R15 and R0), considerably lower N2O emissions were observed (maximal 37 µg N2O–N m−2 h−1). Concerning N2 only at the initially water-logged peat site R0d considerable release rates (up to 3110 µg N2–N m−2 h−1) were observed, while under drained conditions (D30) no N2 emission and under rewetted conditions with a constant WT (R15 and R0) significantly lower N2 release rates (maximal 668 µg N2–N m–2 h−1) could be detected. In addition, it has been found that natural WT fluctuations at rewetted peat sites, in particular a rapid drop down of the WT, can induce high emission rates for both N2O and N2.

The transition zones (ecotone) between boreal forests and peatlands: Ecological controls on ecosystem productivity along a transition zone between upland black spruce forest and a poor forested fen in central Saskatchewan

Forest productivity declines along the transition zones (ecotone) occupying the elevational gradient from upland boreal forest to peatlands. This decline is associated with water table rise and increasing peat depth from upper to lower topographic positions. We hypothesize that in boreal transition zones to poor fens, phosphorus limitations to plant growth are imposed by low pH, rising water table and increasing depth to mineral soil in the waterlogged peat. These phosphorus limitations, together with O2 limitations to root growth, cause sharp decline of productivity down to the fen. The ecosys model was applied to test these hypotheses in a boreal transition zone in central Saskatchewan, Canada. This zone extended from an upland black spruce forest down to a poor forested fen over an organic–mineral soil gradient with peat depth increasing from 60cm to 160cm. Model output was compared with field-derived tree carbon stocks, leaf area indexes, and moss net primary productivities at upper, middle, and lower undisturbed ecotone positions. Model results suggest that root contact with mineral soil through shallow peat over a deep water table at the upper ecotone sustained phosphorus uptake and plants did not experience phosphorus limitations. However deep peat and shallow water table towards the fen prevented root contact with mineral soil, imposing phosphorus limitations to plants growing in the poor, acidic peat, causing productivity decline by ∼75–80%, and tree biomass decline from ∼6900 to 2100gCm−2 in the model vs. ∼6600 to 800gCm−2 observed along the ecotone.