Greenhouse gas soil production and surface fluxes at a high arctic polar oasis
Arctic vegetation and soil biological communities interact with a range of biotic and abiotic factors to produce or consume the greenhouse gases (GHG) carbon dioxide, methane, and nitrous oxide. In Arctic environments the parameters controlling these processes are not well understood. We measured soil GHG concentrations and surface fluxes from six vegetation communities at a High Arctic polar oasis and adjacent polar deserts in order to identify regions within the soil profile of production and consumption of CO2, CH4, and N2O. Examined communities included two polar deserts differing in parent material and soil pH, and four lowland tundra communities: prostrate dwarf-shrub, herb tundra, prostrate/hemiprostrate dwarf-shrub tundra, nontussock sedge, dwarf-shrub, moss tundra and a sedge/grass, moss wetland, representative of large areas at lower Arctic latitudes. Polar desert soils were net producers of greenhouse gases during the brief High Arctic growing season, including at depths close to the permafrost layer, and effluxes from the surface were of a similar magnitude to nearby mesic and hydric tundra soils including for CO2, indicative of soil respiration in desert soils with few roots. Differences in water content, rather than calculated diffusivity, appear to drive gas transport in at least some soils, with all three GHG appearing to move rapidly through, for example, the soil at 10 cm above permafrost in the Prostrate (dominated by Dryas integrifolia) plant community. Such physical processes may obscure or falsely suggest biological processes in soil ecosystems.
A High Arctic soil ecosystem resists long-term environmental manipulations
We evaluated above‐ and belowground ecosystem changes in a 16 year, combined fertilization and warming experiment in a High Arctic tundra deciduous shrub heath (Alexandra Fiord, Ellesmere Island, NU, Canada). Soil emissions of the three key greenhouse gases (GHGs) (carbon dioxide, methane, and nitrous oxide) were measured in mid‐July 2009 using soil respiration chambers attached to a FTIR system. Soil chemical and biochemical properties including Q10 values for CO2, CH4, and N2O, Bacteria and Archaea assemblage composition, and the diversity and prevalence of key nitrogen cycling genes including bacterial amoA, crenarchaeal amoA, and nosZ were measured. Warming and fertilization caused strong increases in plant community cover and height but had limited effects on GHG fluxes and no substantial effect on soil chemistry or biochemistry. Similarly, there was a surprising lack of directional shifts in the soil microbial community as a whole or any change at all in microbial functional groups associated with CH4 consumption or N2O cycling in any treatment. Thus, it appears that while warming and increased nutrient availability have strongly affected the plant community over the last 16 years, the belowground ecosystem has not yet responded. This resistance of the soil ecosystem has resulted in limited changes in GHG fluxes in response to the experimental treatments.
How is nitrogen fixation in the high arctic linked to greenhouse gas emissions?
Background and aims Approximately 50 % of belowground organic carbon is present in the northern permafrost region and due to changes in climate there are concerns that this carbon will be rapidly released to the atmosphere. The release of carbon in arctic soils is thought to be intimately linked to the N cycle through the N cycle’s influence on microbial activity. The majority of new N input into arctic systems occurs through N2-fixation; therefore, N2-fixation may be the key driver of greenhouse gases from these ecosystems.
Methods At Alexandra Fjord lowland, Ellesmere Island, Canada concurrent measurements of N2-fixation, N mineralization and nitrification rates, dissolved organic soil N (DON) and C, inorganic soil N and surface greenhouse gas fluxes (CO2, N2O and CH4) were taken in two ecosystem types (Wet Sedge Meadow and Dryas Heath) over the 2009 growing season (June-August). Using Structural Equation Modelling we evaluated the hypothesis that CO2, CH4 and N2O flux are linked to N2-fixation via the N cycle.
Results The soil N cycle was linked to CO2 flux in the Dryas Heath ecosystem via DON concentrations, but there was no link between the soil N cycle and CO2 flux in the Wet Sedge Meadow. Methane flux was also not linked to the soil N cycle, nor surface soil temperature or moisture in either ecosystem. The soil N cycle was closely linked to N2O emissions but via nitrification in the Wet Sedge Meadow and inorganic N in the Dryas Heath, indicating the important role of nitrification in net N2O flux from arctic ecosystems.
Conclusions Our results should be interpreted with caution given the high variability in both the rates of the N cycling processes and greenhouse gas flux found in both ecosystems over the growing season. However, while N2-fixation and other N cycling processes may play a more limited role in instantaneous CO2 emissions, these processes clearly play an important role in controlling N2O emissions.
Interactive effects of vegetation and water table depth on belowground C and N mobilization and greenhouse gas emissions in a restored peatland
Aims: This study assesses the relative effects of hydrology and colonization by vascular plants on belowground C and N mobilization, and emission of CO2 and CH4 in an extracted bog under restoration in Alberta (Canada). Methods: A wet (high water table) and dry (low water table) area were identified at the site and plots with cottongrass (Eriophorum vaginatum) or bare peat were established in each area. Plant growth, peat and porewater dissolved C (DOC) and N (TDN), microbial biomass and the emissions of CO2 and CH4 were monitored at the plots throughout the growing season. Results: The largest concentrations of DOC were measured in dry and bare sites. Lower E2:E3 ratios suggested a higher aromaticity of the DOC at these sites that were net sources of CO2 and CH4. The concentration of TDN was greater in plots with cottongrass and high water table, supporting a more abundant microbial biomass. Cottongrass dominated plots also had larger gas emissions as compared to bare plots even though they were net C sinks due to their high photosynthetic rates. Conclusion: Maintaining a high water table is key to reducing peatland C losses. While vascular plant presence seems to prime the release of N and greenhouse gases, the inputs of C exceeded the losses and recovered the C sink function of the peatland ecosystem in the short term. Carbon inputs are maximized under high water table and plant presence.
Conservation of Synteny Between Guppy and Xiphophorus Genomes
The guppy and fish in the genus Xiphophorus have both been important model systems for the study of natural and sexual selection for over 50 years. Whereas the guppy is unique in the degree to which the environmental variables shaping phenotypic variation are known, Xiphophorus has the advantage that genomic resources have been developed due to the utility of this taxon for the study of melanoma. If linkage maps for the guppy and Xiphophorus are similar, genomic resources developed in Xiphophorus will be useful in the guppy. The authors used an F2 mapping cross of divergent populations of the guppy to construct partial female and male genetic linkage maps incorporating microsatellite markers derived from Xiphophorus mapping efforts. Flanking regions for a sample of microsatellites occurring in maps for both taxa were sequenced in the guppy and compared to published sequences from Xiphophorus. This confirmed that these loci were homologous and estimated the divergence in neutral nuclear DNA to be 0.21 substitutions per site. The female map comprises 16 linked markers on six linkage groups, and the male map comprises 24 markers on nine linkage groups. Linkage relationships among loci homologous in the guppy and Xiphophorus primarily show conservation of genetic architecture between species, but several major changes were detected.
Effects of invasion by birch on the growth of planted spruce at a post-extraction peatland
Planting forest on cutover peatlands may be regarded as a viable restoration technique in western Canada, where natural bogs are treed with a high density of Black Spruce, Picea mariana. Fertilizer is needed to promote P. mariana establishment on cutover peatlands; however, it also encourages spontaneous colonisation by non-peatland species such as Paper Birch, Betula papyrifera. This study aimed to assess the most appropriate fertilizer dose for P. mariana establishment and growth against the trade-off of birch invasion; consequently, we monitored the effect of B. papyrifera on P. mariana growth. Four levels of fertilizer dose were applied below-ground, but flooding of the site following planting allowed fertilizer to reach the surface and favoured the colonisation of B. papyrifera. Seven years after planting, fertilizer promoted P. mariana survival and the highest fertilizer dose improved both P. mariana and B. papyrifera growth, while the lowest fertilizer dose promoted spruce growth, to a lesser degree, without promoting birch growth as much as higher doses of fertilizer. Birch removal had a significant positive effect on the growth of P. mariana, possibly by allowing greater light penetration and higher near-surface soil moisture. Avoiding B. papyrifera colonisation on site is more effective than cutting due to the ability of birch to regenerate rapidly from stumps. In practice, if planting coniferous trees is the chosen restoration option, the risk of birch colonisation can be minimised by leaving a thicker remnant peat deposit, burying fertilizer near the planted seedlings, and planning planting to avoid flooding during the growing season post-planting whenever possible.
Tree restoration and ecosystem carbon storage in an acid and metal impacted landscape: Chronosequence and resampling approaches
Tree restoration on degraded land has been identified as an effective and affordable capture carbon strategy but it is unclear if carbon sequestration rates are comparable to rates on non-industrially impacted silvicultural forests. To this end, we resampled a jack pine (Pinus banksiana) and red pine (P. resinosa) chronosequence 16 years after the initial measurement to quantify carbon pools following ca. 40 years of regreening on an acid and metal impacted landscape. Measured carbon pools were then compared to those reported in an unpublished study to determine how carbon sequestration rates have changed over time and if repeated sampling at the stand level validates temporal trends estimated by the chronosequence. Total ecosystem carbon (TEC) within the stands ranged from 55 to 136 Mg ha−1 with a regional mean of 90.2 ± 9.6 Mg ha−1. On average, tree and soil organic pools (SOC) were the two largest carbon pools, representing 47% and 42% of TEC, respectively. Compared with unplanted sites, tree restoration resulted in a significant increase in the mean TEC among all sites of 54.4 ± 10.2 Mg ha−1 with a corresponding sequestration rate of 1.7 ± 0.3 Mg ha−1 yr−1. The chronosequence approach was only able to consistently detect a change in the tree carbon pool. In contrast, repeated sampling at the stand level identified changes in carbon sequestration rates within SOC, LFH and shrub carbon pools and showed that the chronosequence tree carbon sequestration rate was underestimated by a factor of 2.3. Chronosequence studies assume study sites have similar landscape history and environmental conditions, which may not be reasonable in highly degraded landscapes where past events (e.g., pollution, erosion, restoration) influence multiple landscape characteristics (e.g., local hydrology and topography). We conclude that tree restoration on impacted landscapes can sequester carbon at a rate comparable to silvicultural plantations in a similar climatic region and that reforestation of industrially damaged landscapes could be part of an effective carbon capture strategy.
N2O flux from plant-soil systems in polar deserts switch between sources and sinks under different light conditions
Production and consumption of greenhouse gases such as CO2, CH4 and N2O are key factors driving climate change. While CO2 sinks are commonly reported and the mechanisms relatively well understood, N2O sinks have often been overlooked and the driving factors for these sinks are poorly understood. We examined CO2, CH4 and N2O flux in three High Arctic polar deserts under both light (measured in transparent chambers) and dark (measured in opaque chambers) conditions. We further examined if differences in soil moisture, evapotranspiration, Photosynthetically Active Radiation (PAR), and/or plant communities were driving gas fluxes measured in transparent and opaque chambers at each of our sites. Nitrous oxide sinks were found at all of our sites suggesting that N2O uptake can occur under extreme polar desert conditions, with relatively low soil moisture, soil temperature and limited soil N. Fluxes of CO2 and N2O switched from sources under dark conditions to sinks under light conditions, while CH4 fluxes at our sites were not affected by light conditions. Neither evapotranspiration nor PAR were significantly correlated with CO2 or N2O flux, however, soil moisture was significantly correlated with both gas fluxes. The relationship between soil moisture and N2O flux was different under light and dark conditions, suggesting that there are other factors, in addition to moisture, driving N2O sinks. We found significant differences in N2O and CO2 flux between plant communities under both light and dark conditions and observed individual communities that shifted between sources and sinks depending on light conditions. Failure of many studies to include plant-mediated N2O flux, as well as, N2O soil sinks may account for the currently unbalanced global N2O budget.
Using the Tea Bag Index to characterize decomposition rates in restored peatlands
Peatlands characteristically accumulate organic matter due to low decomposition rates, but peatland disturbance alters local physicochemical conditions often resulting in loss of soil organic matter and emission of CO2. Restoration may reduce peat oxidation, but traditional measurements of decomposition are time-consuming. The Tea Bag Index (TBI) is a simple, standardized method to measure decomposition rates in soils. We used the TBI to measure decomposition rate at four restored peatland sites across Canada that were used for peat extraction or disturbed by oil extraction (former well-sites), comparing to undisturbed and unrestored sites. We measured environmental conditions including soil temperature, water table position and peat pH from May to August 2016. Litter bags were buried for one year alongside tea bags at one site for a direct comparison of decomposition rates between the methods. There were no significant differences for TBI decay constant (kTBI) between treatments of restored, unrestored or undisturbed sites across the whole data set, but some differences were found among treatments within the same peatland site for sections restored at different times in the past. Soil temperature, pH, and water table were not significantly related to kTBI, but were negatively correlated with the stabilization factor (S). The kTBI and litter bag k were significantly different but positively correlated. The TBI is not easily comparable to traditional litter bags, but is less costly in both time and money, and may be used in conjunction with additional parameters to determine decomposition patterns with potential for use as a metric for evaluating restoration outcomes.
The influence of Carex aquatilis and Juncus balticus on methane dynamics: A comparison with water sourced from a natural and a constructed fen
As fen peatlands have been heavily disturbed by resource extraction in northeastern Alberta, Canada, fen construction has been completed. In order to optimize biogeochemical function of future constructed fens, it is beneficial to understand methane (CH₄) cycling of newly constructed fens, and how revegetation strategies influence CH₄ dynamics. Here, we investigate the effects of two vascular species used for fen construction on CH₄ dynamics. A factorial greenhouse experiment using peat columns and a laboratory incubation experiment were used to understand differences in CH₄ production, emissions, pore water concentration, and oxidation between Carex aquatilis Wahlenb. and Juncus balticus Willd. The experiment also considered how water sourced from the constructed fen influenced CH₄ dynamics compared to natural rich fen water. Higher pore water CH₄ concentration and potential CH₄ production were found at C. aquatilis columns, possibly associated with higher labile carbon throughout the column. In columns with J. balticus, evidence to support radial oxygen loss reducing CH₄ concentration and production was found. Water sampled from peat columns with constructed fen water had higher Fe (all cation forms), Mn (all cation forms), SO₄²−, and NO₃− compared to columns with rich fen water, which corresponded to lower CH₄ emissions and pore water concentration. Results from this study could be used to inform revegetation designs of future constructed fens that consider greenhouse gas emissions, including CH₄, as a reclamation goal.