Search Results (6)

The decomposition rate of plant residues is determined by both abiotic (temperature, moisture) and biotic factors (biochemical composition). To separate the contribution of each factor to the decomposition process, long-term incubation experiments under controlled conditions are required. Two-year incubation experiments were conducted with various types of peat-forming plants (Sphagnum fuscum, Chamaedaphne calyculata, Eriophorum vaginatum, and a mixed sample consisting of 60% Sphagnum fuscum and 40% Chamaedaphne calyculata). The experiments were carried out at temperatures of 2, 12, and 22 °C, with varying moisture levels (W = 30, 60, and 90% of their water-holding capacity). In all plant samples, the highest rates of C(CO₂) emission (DecR) were observed in the initial stages of decomposition. The cumulative carbon loss (C_cum) during the experiment ranged from 45 to 196 mgC/g of plant material at 22 °C and 23 to 156 mgC/g of plant material at 2 °C. The decay constant (k) for all plant samples increased with rising temperature. The results of the three-way ANOVA showed that the influence of the examined factors on the cumulative losses of C(CO₂) decreased in the following order: the type of plant > temperature > moisture. Throughout the experiment, the influence of the type of plant and moisture on DecR increased, while the effect of temperature decreased. The highest temperature sensitivity (Q₁₀ = 0.71–6.19) was observed in the low-temperature range (2–12 °C) during months 4 to 6 of incubation. These results are relevant for modeling and predicting the rate of transformation of peat organic matter under changing climatic conditions. Full article

Few fires are known to have burned the tundra of the Arctic Slope north of the Brooks Range in Alaska, USA. A total of 90 fires between 1969 and 2022 are known. Because fire has been rare, old burns can be detected by the traces of thermokarst and distinct vegetation they leave in otherwise uniform tundra, which are visible in aerial photograph archives. Several prehistoric tundra burns have been found in this way. Detection of tundra fires in this sparsely populated and remote area has been historically inconsistent and opportunistic, relying on reports by aircraft pilots. Fire reports have been logged into an administrative database which, out of necessity, has been used to scientifically evaluate changes in the fire regime. To improve the consistency of the record, we completed a systematic search of Landsat Collection 2 for the Brooks Range Foothills ecoregion over the period 1972–2022. We found 57 unrecorded tundra burns, about 41% of the total, which now numbers 138. Only 15% and 33% of all fires appear in MODIS and VIIRS satellite-borne thermal anomaly products, respectively. The fire frequency in the first 37 years of the record is 0.89 y⁻¹ for natural ignitions that spread ≥10 ha. Frequency in the last 13 years is 2.5 y⁻¹, indicating a nearly three-fold increase in fire frequency. Full article

In this study, we describe the variation in δ¹³C value in the litter of two species of peat-forming plants: Sphagnum fuscum and Eriophorum vaginatum, during 3 years of field decomposition in oligotrophic bog ecosystems drained for the purpose of forest melioration and fire affected and at the stage of post-pyrogenic restoration. Litterbags were periodically retrieved in the autumn and the δ¹³C value in the residual litter was related to mass loss, litter chemistry, and hydrothermal conditions. Sph. fuscum decomposes much more slowly than E. vaginatum. Low rate of transformation for Sph. fuscum is observed in drained and post-pyrogenic sites, while for E. vaginatum minimal rate of transformation is observed in the native site. During the decomposition of Sphagnum residues, ¹³C enrichment occurs, and during the decomposition of E. vaginatum, we observed ¹²C enrichment. The changes in the isotope composition of carbon for investigation sites are insignificant for Sphagnum fuscum, but it was observed for E. vaginatum, the largest of ¹³C depletion is observed in the drained site (−28.3‰) and minimal in the postpyrogenic site (−27.4‰). Full article

While Si influences nutrient stoichiometry and decomposition of graminoid litter, it is still unclear how Si influences anoxic litter decomposition and CH₄ formation in graminoid dominated fen peatlands. First, Eriophorum vaginatum plants were grown under different Si and P availabilities, then shoots and roots were characterized regarding their proportions of C, Si, N and P and regarding C quality. Subsequently the Eriophorum shoots were subjected to anoxic decomposition. We hypothesized; that (I) litter grown under high Si availability would show a higher Si but lower nutrient mass fractions and a lower share of recalcitrant carbon moieties; (II) high-Si litter would show higher CH₄ and CO₂ production rates during anoxic decomposition; (III) methanogenesis would occur earlier in less recalcitrant high-Si litter, compared to low-Si litter. We found a higher Si mass fraction that coincides with a general decrease in C and N mass fractions and decreased share of recalcitrant organic moieties. For high-Si litter, the CH₄ production rate was higher, but there was no long-term influence on the CO₂ production rate. More labile high-Si litter and a differential response in nutrient stoichiometry led to faster onset of methanogenesis. This may have important implications for our understanding of anaerobic carbon turnover in graminoid-rich fens. Full article

Bogs, as nutrient-poor ecosystems, are particularly sensitive to atmospheric nitrogen (N) deposition. Nitrogen deposition alters bog plant community composition and can limit their ability to sequester carbon (C). Spectroscopy is a promising approach for studying how N deposition affects bogs because of its ability to remotely determine changes in plant species composition in the long term as well as shorter-term changes in foliar chemistry. However, there is limited knowledge on the extent to which bog plants differ in their foliar spectral properties, how N deposition might affect those properties, and whether subtle inter- or intraspecific changes in foliar traits can be spectrally detected. The objective of the study was to assess the effect of N deposition on foliar traits and spectra. Using an integrating sphere fitted to a field spectrometer, we measured spectral properties of leaves from the four most common vascular plant species (Chamaedaphne calyculata, Kalmia angustifolia, Rhododendron groenlandicum and Eriophorum vaginatum) in three bogs in southern Québec and Ontario, Canada, exposed to different atmospheric N deposition levels, including one subjected to a 18-year N fertilization experiment. We also measured chemical and morphological properties of those leaves. We found detectable intraspecific changes in leaf structural traits and chemistry (namely chlorophyll b and N concentrations) with increasing N deposition and identified spectral regions that helped distinguish the site-specific populations within each species. Most of the variation in leaf spectral, chemical, and morphological properties was among species. As such, species had distinct spectral foliar signatures, allowing us to identify them with high accuracy with partial least squares discriminant analyses (PLSDA). Predictions of foliar traits from spectra using partial least squares regression (PLSR) were generally accurate, particularly for the concentrations of N and C, soluble C, leaf water, and dry matter content (<10% RMSEP). However, these multi-species PLSR models were not accurate within species, where the range of values was narrow. To improve the detection of short-term intraspecific changes in functional traits, models should be trained with more species-specific data. Our field study showing clear differences in foliar spectra and traits among species, and some within-species differences due to N deposition, suggest that spectroscopy is a promising approach for assessing long-term vegetation changes in bogs subject to atmospheric pollution. Full article

The use of Remotely Piloted Aircraft Systems (RPAS) as well as newer automated unmanned aerial vehicles is becoming a standard method in remote sensing studies requiring high spatial resolution (<1 m) and very precise temporal data to capture phenological events. In this study we use a low cost rotorcraft to map Eriophorum vaginatum at Mer Bleue, an ombrotrophic bog located east of Ottawa, ON, Canada. We focus on E. vaginatum because this sedge plays an important role in methane (CH₄) gas exchange in peatlands. Using the remote controlled rotorcraft we were able to record, process, and mosaic 11.1 hectares of 4.5 cm spatial resolution imagery extracted from individual frames of video recordings (post georegistration RMSE 4.90 ± 4.95 cm). Our results, based on a supervised classification (96% accuracy) of the red, green, blue image planes, indicate a total tussock cover of 2,417 m². Because the basal area of the plant is more relevant for calculating its contribution to the CH₄ flux, the tussock area was related to the basal area from field data (R² = 0.88, p < 0.0001). Our final results indicate a total basal area of 1,786 ± 62.8 m². Based on temporal measurements of CH₄ flux from the peatland as a whole that vary over the growing season, we estimate the E. vaginatum contribution to range from 3.0% to 17.3% of that total. Overall, our low cost approach was an effective non-destructive way to derive E. vaginatum coverage and estimate CH₄ exchange over the growing season. Full article