Establishing peat-forming plant communities: A comparison of wetland reclamation methods in Alberta's oil sands region

The Sandhill Wetland (SW) and Nikanotee Fen (NF) are two wetland research projects designed to test the viability of peatland reclamation in the Alberta oil sands post-mining landscape. To identify effective approaches for establishing peat-forming vegetation in reclaimed wetlands, we evaluated how plant introduction approaches and water level gradients influence species distribution, plant community development, and the establishment of bryophyte and peatland species richness and cover. Plant introduction approaches included seeding with a Carex aquatilis-dominated seed mix, planting C. aquatilis and Juncus balticus seedlings, and spreading a harvested moss layer transfer. Establishment was assessed 6 years after the introduction at SW and 5 years after the introduction at NF. In total, 51 species were introduced to the reclaimed wetlands, and 122 species were observed after 5 and 6 years. The most abundant species in both reclaimed wetlands was C. aquatilis, which produced dense canopies and occupied the largest water level range of observed plants. Introducing C. aquatilis also helped to exclude marsh plants such as Typha latifolia that has little to no peat accumulation potential. Juncus balticus persisted where the water table was lower and encouraged the formation of a diverse peatland community and facilitated bryophyte establishment. Various bryophytes colonized suitable areas, but the moss layer transfer increased the cover of desirable peat-forming mosses. Communities with the highest bryophyte and peatland species richness and cover (averaging 9 and 14 species, and 50%-160% cover respectively) occurred where the summer water level was between -10 and -40 cm. Outside this water level range, a marsh community of Typha latifolia dominated in standing water and a wet meadow upland community of Calamagrostis canadensis and woody species established where the water table was deeper. Overall, the two wetland reclamation projects demonstrated that establishing peat-forming vascular plants and bryophytes is possible, and community formation is dependent upon water level and plant introduction approaches. Future projects should aim to create microtopography with water tables within 40 cm of the surface and introduce vascular plants such as J. balticus that facilitate bryophyte establishment and support the development of a diverse peatland plant community.

Rewetting increases vegetation cover and net growing season carbon uptake under fen conditions after peat-extraction in Manitoba, Canada

The moss layer transfer technique has been developed to restore the carbon sequestration function and typical vegetation of Sphagnum-dominated peatlands after peat extraction in North America. However, the technique does not lead to successful bryophyte establishment when applied to peatlands with a richer residual fen peat. Therefore, we evaluated an alternative method of active rewetting and passive vegetation establishment using vegetation surveys and carbon dioxide and methane (CH4) flux measurements at a post-extracted fen in southern Manitoba, Canada. After one growing season post-rewetting, wetland vegetation established and the site was a net carbon sink over the growing season. However, high abundance of Carex lasiocarpa 10 years post-treatment led to higher CH4 emissions than the reference ecosystem. Successful establishment of wetland vegetation is attributed to the area being surrounded by undisturbed fens that can provide a local source of plant propagules. Bryophyte expansion was less successful than vascular plants, likely due to episodic flooding and shading from the sedge communities. Therefore, careful management of water levels to just below the peat surface is needed if reference vegetation community recovery is the goal of restoration. Water level management will also play a key role in controlling CH4 emissions to maximize carbon sequestration potential.

Rising temperature modulates pH niches of fen species

Rising temperatures may endanger fragile ecosystems because their character and key species show different habitat affinities under different climates. This assumption has only been tested in limited geographical scales. In fens, one of the most endangered ecosystems in Europe, broader pH niches have been reported from cold areas and are expected for colder past periods. We used the largest European-scale vegetation database from fens to test the hypothesis that pH interacts with macroclimate temperature in forming realized niches of fen moss and vascular plant species. We calibrated the data set (29,885 plots after heterogeneity-constrained resampling) with temperature, using two macroclimate variables, and with the adjusted pH, a variable combining pH and calcium richness. We modelled temperature, pH and water level niches for one hundred species best characterizing European fens using generalized additive models and tested the interaction between pH and temperature. Fifty-five fen species showed a statistically significant interaction between pH and temperature (adj p ˂ .01). Forty-six of them (84%) showed a positive interaction manifested by a shift or restriction of their niche to higher pH in warmer locations. Nine vascular plants and no moss showed the opposite interaction. Mosses showed significantly greater interaction. We conclude that climate significantly modulates edaphic niches of fen plants, especially bryophytes. This result explains previously reported regional changes in realized pH niches, a current habitat-dependent decline of endangered taxa, and distribution changes in the past. A warmer climate makes growing seasons longer and warmer, increases productivity, and may lower the water level. These effects prolong the duration and intensity of interspecific competition, support highly competitive Sphagnum mosses, and, as such, force niches of specialized fen species towards narrower high-pH ranges. Recent anthropogenic landscape changes pose a severe threat to many fen species and call for mitigation measures to lower competition pressure in their refugia.

Is bog water chemistry affected by increasing N and S deposition from oil sands development in Northern Alberta, Canada?

Nitrogen and sulfur emissions from oil sands operations in northern Alberta, Canada have resulted in increasing deposition of N and S to the region's ecosystems. To assess whether a changing N and S deposition regime affects bog porewater chemistry, we sampled bog porewater at sites at different distances from the oil sands industrial center from 2009 to 2012 (10-cm intervals to a depth of 1 m) and from 2009 to 2019 (top of the bog water table only). We hypothesized that: (1) as atmospheric N and S deposition increases with increasing proximity to the oil sands industrial center, surface porewater concentrations of NH₄⁺, NO₃^-, DON, and SO₄^2- would increase and (2) with increasing N and S deposition, elevated porewater concentrations of NH₄⁺, NO₃^-, DON, and SO₄^2- would be manifested increasingly deeper into the peat profile. We found weak evidence that oil sands N and S emissions affect bog porewater NH₄⁺-N, NO₃^--N, or DON concentrations. We found mixed evidence that increasing SO₄^2- deposition results in increasing porewater SO₄^2- concentrations. Current SO₄^2- deposition, especially at bogs closest to the oil sands industrial center, likely exceeds the ability of the Sphagnum moss layer to retain S through net primary production, such that atmospherically deposited SO₄^2- infiltrates downward into the peat column. Increasing porewater SO₄^2- availability may stimulate dissimilatory sulfate reduction and/or inhibit CH₄ production, potentially affecting carbon cycling and gaseous fluxes in these bogs.

Niche modelling of marsh plants based on occurrence and abundance data

The information of species' response (optimum or critical limits along environmental gradients) is a key to understanding ecological questions and to design management plans. A large number of plots (762) from 70 transects of 13 wetland sites in Northeast China were sampled along flooding gradient from marsh to wet meadow. Species response (abundance and occurrence) to flooding were modelled with Generalized Additive Models for 21 dominant plant species. We found that 20 of 21 species showed a significant response to flooding for the occurrence and abundance models, and four types of response were found: monotonically increasing, monotonically decreasing, skewed unimodal and symmetric unimodal. The species with monotonically increasing response have the deepest flooding optimum and widest niche width, followed by those with unimodal curve, and the monotonically decreasing ones have the smallest values. The optima and niche width (whether based on occurrence or abundance models) both significantly correlated with the frequency, but not with mean abundance. Abundance models outperformed occurrence models based on goodness of fit. The abundance models predicted a rather sharp shift from dominance of helophytes (Carex pseudo-curaica and C. lasiocarpa) to wet meadow species (Calamagrostis angustifolia and Carex appendiculata) if water levels drop from about 10cm above soil surface to below the surface. The defined optima and niche width based on the abundance models can be applied to better instruct restoration management. Given the time required to collect abundance data, an efficient strategy could be to monitor occurrence in many plots and abundance in a subset of these.

Organellar phylogenomics of an emerging model system: Sphagnum (peatmoss)

BACKGROUND AND AIMS

Sphagnum-dominated peatlands contain approx. 30 % of the terrestrial carbon pool in the form of partially decomposed plant material (peat), and, as a consequence, Sphagnum is currently a focus of studies on biogeochemistry and control of global climate. Sphagnum species differ in ecologically important traits that scale up to impact ecosystem function, and sequencing of the genome from selected Sphagnum species is currently underway. As an emerging model system, these resources for Sphagnum will facilitate linking nucleotide variation to plant functional traits, and through those traits to ecosystem processes. A solid phylogenetic framework for Sphagnum is crucial to comparative analyses of species-specific traits, but relationships among major clades within Sphagnum have been recalcitrant to resolution because the genus underwent a rapid radiation. Herein a well-supported hypothesis for phylogenetic relationships among major clades within Sphagnum based on organellar genome sequences (plastid, mitochondrial) is provided.

METHODS

We obtained nucleotide sequences (273 753 nucleotides in total) from the two organellar genomes from 38 species (including three outgroups). Phylogenetic analyses were conducted using a variety of methods applied to nucleotide and amino acid sequences. The Sphagnum phylogeny was rooted with sequences from the related Sphagnopsida genera, Eosphagnum and Flatbergium

KEY RESULTS

Phylogenetic analyses of the data converge on the following subgeneric relationships: (Rigida (((Subsecunda) (Cuspidata)) ((Sphagnum) (Acutifolia))). All relationships were strongly supported. Species in the two major clades (i.e. Subsecunda + Cuspidata and Sphagnum + Acutifolia), which include >90 % of all Sphagnum species, differ in ecological niches and these differences correlate with other functional traits that impact biogeochemical cycling. Mitochondrial intron presence/absence are variable among species and genera of the Sphagnopsida. Two new nomenclatural combinations are made, in the genera Eosphagnum and Flatbergium

CONCLUSIONS

Newly resolved relationships now permit phylogenetic analyses of morphological, biochemical and ecological traits among Sphagnum species. The results clarify long-standing disagreements about subgeneric relationships and intrageneric classification.

Evolution of niche preference in Sphagnum peat mosses

Peat mosses (Sphagnum) are ecosystem engineers-species in boreal peatlands simultaneously create and inhabit narrow habitat preferences along two microhabitat gradients: an ionic gradient and a hydrological hummock-hollow gradient. In this article, we demonstrate the connections between microhabitat preference and phylogeny in Sphagnum. Using a dataset of 39 species of Sphagnum, with an 18-locus DNA alignment and an ecological dataset encompassing three large published studies, we tested for phylogenetic signal and within-genus changes in evolutionary rate of eight niche descriptors and two multivariate niche gradients. We find little to no evidence for phylogenetic signal in most component descriptors of the ionic gradient, but interspecific variation along the hummock-hollow gradient shows considerable phylogenetic signal. We find support for a change in the rate of niche evolution within the genus-the hummock-forming subgenus Acutifolia has evolved along the multivariate hummock-hollow gradient faster than the hollow-inhabiting subgenus Cuspidata. Because peat mosses themselves create some of the ecological gradients constituting their own habitats, the classic microtopography of Sphagnum-dominated peatlands is maintained by evolutionary constraints and the biological properties of related Sphagnum species. The patterns of phylogenetic signal observed here will instruct future study on the role of functional traits in peatland growth and reconstruction.

Fine-scale vegetation distribution in a cool temperate peatland

Carbon (C) modeling and carbon dioxide (CO2) flux measurements in peatlands are dependent on the distribution and productivity of vegetation in a system with a high degree of spatial variability, often linked to the position of the water table. We tested the hypothesis that at a fine-scale (tens of metres) water table position exerts a strong control on species abundance, plant biomass, particularly photosynthetically active tissues, leaf area index (LAI), and areal foliar N and chlorophyll at Mer Bleue, a cool temperate peatland in eastern Canada. Total aboveground biomass ranged from 147 to 1011 g·m–2, with shrubs contributing between 42% and 72% of the total in the transects. We found significant (P < 0.05) positive relationships between foliar and total vascular plant biomass and mean water table position, and significant decreases in the shrub foliar:woody biomass ratio and moss biomass with a lower water table. However, there was no significant relationship between water table position and photosynthetically active tissues (vascular plant leaves and moss capitulum), ranging from 114 to 672 g·m–2) and the areal mass of N in these tissues, ranging from 1.5 to 6.7 g·m–2. Multivariate analyses of vegetation and environmental data showed that species distribution could be explained by both water table and chemistry gradients and that unimodal rather than linear responses best described the species and water table relationships. LAI ranged from 0.1 to over 3 and was correlated with both water table position and with vascular foliar biomass. Percent cover of shrubs was correlated with foliar biomass and LAI. Our results suggest that the less labour-intensive estimates of percent cover can be used to predict the vascular plant foliar biomass and LAI measurements. The lack of relationship between photosynthetically active tissues, tissue N concentrations, and water table may also explain the surprising lack of spatial variability in peak growing season eddy flux net ecosystem CO2 exchange in three different areas of the peatland.