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Determining the plant traits that best predict carbon (C) storage is increasingly important as global change drivers will affect plant species composition and ecosystem C cycling. Despite the critical role of peatlands in the global C cycle, trait-flux relationships in peatlands are relatively unknown., We assessed the ability of four non-destructive plant traits to predict carbon dioxide ( CO2) and methane ( CH4) fluxes over two growing seasons in a temperate peatland in Ontario, Canada. We examined relationships between C-fluxes and leaf area, leaf persistence (deciduous, evergreen), growth form (woody, herbaceous) and aerenchyma tissue. To explore potential inconsistencies between different scales of data aggregation, traits were analysed at the level of plots, species and microsites., CO2 fluxes showed a positive relationship with leaf area and leaf persistence, and a negative relationship with proportion of woody species. CH4 fluxes showed a positive relationship with aerenchyma and leaf area. The significance of trait-flux relationships differed based on whether data were averaged at the level of plot, species or microsite., We recommend applying leaf area as a non-destructive trait to other systems where it is not ideal to measure traits destructively. A better understanding of the relationships between above and below-ground traits is likely needed to further explain variation in ecosystem respiration and CH4 fluxes from plant traits., A is available for this article. [ABSTRACT FROM AUTHOR]

To identify the controls on dissolved organic carbon (DOC) production, we incubated soils from 18 sites, a mixture of 52 forest floor and peats and 41 upper mineral soil samples, at three temperatures (3, 10, and 22°C) for over a year and measured DOC concentration in the leachate and carbon dioxide (CO2) production from the samples. Concentrations of DOC in the leachate were in the range encountered in field soils (<2 to >50 mg l−1). There was a decline in DOC production during the incubation, with initial rates averaging 0.03–0.06 mg DOC g−1 soil C day−1, falling to averages of 0.01 mg g−1 soil C day−1; the rate of decline was not strongly related to temperature. Cumulative DOC production rates over the 395 days ranged from less than 0.01 to 0.12 mg g−1 soil C day−1 (0.5–47.6 mg g−1 soil C), with an average of 0.021 mg g−1 soil C day−1 (8.2 mg g−1 soil C). DOC production rate was weakly related to temperature, equivalent to Q10 values of 0.9 to 1.2 for mineral samples and 1.2 to 1.9 for organic samples. Rates of DOC production in the organic samples were correlated with cellulose (positively) and lignin (negatively) proportion in the organic matter, whereas in the mineral samples C and nitrogen (N) provided positive correlations. The partitioning of C released into CO2–C and DOC showed a quotient (CO2–C:DOC) that varied widely among the samples, from 1 to 146. The regression coefficient of CO2–C:DOC production (log10 transformed) ranged from 0.3 to 0.7, all significantly less than 1. At high rates of DOC production, a smaller proportion of CO2 is produced. The CO2–C:DOC quotient was dependent on incubation temperature: in the organic soil samples, the CO2–C:DOC quotient rose from an average of 6 at 3 to 16 at 22°C and in the mineral samples the rise was from 7 to 27. The CO2–C:DOC quotient was related to soil pH in the organic samples and C and N forms in the mineral samples. [ABSTRACT FROM AUTHOR]

We investigated the response of CO2 and CH4 production to a water table fluctuation and a SO42− pulse in a bog mesocosm. Net gas production rates in the mesocosm were calculated from concentration data by diffusive mass-balances. Incubation experiments were used to quantify the effect of SO42− addition and the distribution of potential CO2 and CH4 production rates. Flooding of unsaturated peat resulted in rapid depletion of O2 and complex patterns of net CH4, CO2, and H2S production. Methane production began locally and without a time lag at rates of 3–4 nmol cm−3 d−1 deeper in the peat. Similar rates were determined after a time lag of 10–60 days in the surface layers, whereas rates at lower depths declined. Net CO2 production was largest immediately after the water table position was altered (100–300 nmol cm−3 d−1) and declined to −50–50 nmol cm−3 d−1 after a few weeks. SO42− addition (500 mM) significantly increased potential CH4 production rates in the surface layer from an average of 132–201 nmol cm−3 d−1 and reduced it below from an average of 418–256 nmol cm−3 d−1. Our results suggest that deeper in the peat (40–70 cm) under in situ conditions, methanogenic populations are less impaired by unsaturated conditions than in the surface layers, and that at these depths after flooding the substrate availability for CH4 and DIC production is significantly enhanced. They also suggest that methanogenic and SO42−-reducing activity were non-competitive in the surface layer, which might explain contradictory findings from field studies. [Copyright &y& Elsevier]

Summary 1Above-ground biomass was measured at bog hummock, bog hollow and poor-fen sites in Mer Bleue, a large, raised ombrotrophic bog near Ottawa, Ont., Canada. The average above-ground biomass was 587 g m-2 in the bog, composed mainly of shrubs and Sphagnum capitula. In the poor fen, the average biomass was 317 g m-2 , comprising mainly sedges and herbs and Sphagnum capitula. Vascular plant above-ground biomass was greater where the water table was lower, with a similar but weaker relationship for Sphagnum capitula and vascular leaf biomass. 2Below-ground biomass averaged 2400 g m-2 at the bog hummock site, of which 300 g m-2 was fine roots (< 2 mm diameter), compared with 1400 g m-2 in hollows (fine roots 450 g m-2 ) and 1200 g m-2 at the poor-fen site. 3Net Ecosystem Exchange (NEE) of CO2 was measured in chambers and used to derive ecosystem respiration and photosynthesis. Under high light flux (PAR of 1500 µmol m-2 s-1 ), NEE ranged across sites from 0.08 to 0.22 mg m-2 s-1 (a positive value indicates ecosystem uptake) in the spring and summer, but fell to –0.01 to –0.13 mg m-2 s-1 (i.e. a release of CO2 ) during a late-summer dry period. 4There was a general agreement between a combination of literature estimates of photosynthetic capacity for shrubs and mosses and measured biomass and summer-time CO2 uptake determined by the eddy covariance technique within a bog footprint (0.40 and 0.35–0.40 mg m-2 s-1 , respectively). 5Gross photosynthesis was estimated to be about 530 g m-2 year-1 , total respiration 460 g m-2 year-1 , and export of DOC, DIC and CH4 10 g m-2 year-1 , leaving an annual C sequestration rate of 60 g m-2 year-1 . Root... [ABSTRACT FROM AUTHOR]

Abstract: We investigate the relationships between CO2 and CH4 fluxes across space and time at a temperate ombrotrophic bog in Canada to assess the coupling between plant production and CH4 emissions. Based on periodic manual chamber measurements, we show that maximum net ecosystem CO2 exchange (NEEmax) was a good predictor of the spatial variations in CH4 flux among the wetter Eriophorum and lawn sites (r 2 = 0.61–0.88), but not the drier hummock sites (r 2 = 0.04–0.49). Also, we observed large interannual variability in the NEEmax-CH4 relationship at the Eriophorum and lawn sites, with a smaller regression slope in 2010 that had a seasonal mean water table 8 cm lower than in 2009. Results of cross-correlation of instantaneous gross ecosystem production (GEP) and CH4 flux from autochambers show a moderate relationship (σ = −0.31) in the Eriophorum community at a lag of 9–12 h, suggesting a rapid turnover of recent photosynthate for methanogenesis. On the other hand, we found in two Maianthemum-dominated chambers that the temperature-independent residuals of daily mean CH4 flux lagged behind GEP by 18–26 days at the seasonal scale. The lagged correlations between GEP and CH4 flux by month were particularly strong in the late growing season in the Eriophorum and Maianthemum/Ledum communities. Our results suggest the presence of spatial and temporal coupling of plant production and CH4 emissions in this bog, whose strength varies with species composition, water table position, and plant phenology. [Copyright &y& Elsevier]

nthropogenic nitrogen (N) loading has the potential to affect plant community structure and function, and the carbon dioxide (CO) sink of peatlands. Our aim is to study how vegetation changes, induced by nutrient input, affect the CO exchange of a nutrient-limited bog. We conducted 9- and 4-year fertilization experiments at Mer Bleue bog, where we applied N addition levels of 1.6, 3.2, and 6.4 g N m a, upon a background deposition of about 0.8 g N m a, with or without phosphorus and potassium (PK). Only the treatments 3.2 and 6.4 g N m a with PK significantly affected CO fluxes. These treatments shifted the Sphagnum moss and dwarf shrub community to taller dwarf shrub thickets without moss, and the CO responses depended on the phase of vegetation transition. Overall, compared to the large observed changes in the vegetation, the changes in CO fluxes were small. Following Sphagnum loss after 5 years, maximum ecosystem photosynthesis (Pg) and net CO exchange (NEE) were lowered (−19 and −46%, respectively) in the highest NPK treatment. In the following years, while shrub height increased, the vascular foliar biomass did not fully compensate for the loss of moss biomass; yet, by year 8 there were no significant differences in Pg and NEE between the nutrient and the control treatments. At the same time, an increase (24–32%) in ecosystem respiration (ER) became evident. Trends in the N-only experiment resembled those in the older NPK experiment by the fourth year. The increasing ER with increasing vascular plant and decreasing Sphagnum moss biomass across the experimental plots suggest that high N deposition may lessen the CO sink of a bog. [ABSTRACT FROM AUTHOR]

Abstract: Small angle scattering techniques (SAXS and SANS) have been used to investigate the microstructural properties of the subbituminous coals (R max 0.42–0.45%) from the Huntly Coalfield, New Zealand. Samples were collected from the two thick (>5 m) coal seams in the coalfield and have been analysed for methane and carbon dioxide sorption capacity, petrography, pore size distribution, specific surface area and porosity. Specific surface area (SSA) available for carbon dioxide adsorption, extrapolated to a probe size of 4 Å, ranged from 1.25×106 cm−1 to 4.26×106 cm−1 with total porosity varying from 16% to 25%. Porosity was found to be predominantly composed of microporosity, which contributed the majority of the available SSA. Although considerable variation was seen between samples, the results fit well with published rank trends. Gas holding capacity at the reservoir pressure (approximately 4 MPa) ranged from 2.63 to 4.18 m3/t for methane on a dry, ash-free basis (daf) and from 22.00 to 23.72 m3/t daf for carbon dioxide. The resulting ratio of CO2:CH4 ranged from 5.7 to 8.6, with an average of 6.7:1. Holding capacities for both methane and carbon dioxide on a dry ash free basis (daf) were found to be correlated with sample microporosity. However, holding capacities for the two gases on an as analysed (aa) basis (that is including mineral matter and moisture), showed no such correlation. Carbon dioxide (aa) does show a negative correlation with both specific surface area and microporosity. As the coals have low inorganic matter content, the reversal is thought to be related to moisture which is likely concentrated in the pore size range 12.5–125 Å. Methane holding capacity, both daf and aa, correlates with macroporosity, thus suggesting that the holding capacity of micropores is diminished by the presence of moisture in the pores. [Copyright &y& Elsevier]

Changes of water table position influence carbon cycling in peatlands, but effects on the sources and sinks of carbon are difficult to isolate and quantify in field investigations due to seasonal dynamics and covariance of variables. We thus investigated carbon fluxes and dissolved carbon production in peatland mesocosms from two acidic and oligotrophic peatlands under steady state conditions at two different water table positions. Exchange rates and CO2, CH4 and DOC production rates were simultaneously determined in the peat from diffusive-advective mass-balances of dissolved CO2, CH4 and DOC in the pore water. Incubation experiments were used to quantify potential CO2, CH4, and DOC production rates. The carbon turnover in the saturated peat was dominated by the production of DOC (10–15 mmol m-2 d-1) with lower rates of DIC (6.1–8.5 mmol m-2 d-1) and CH4 (2.2–4.2 mmol m-2 d-1) production. All production rates strongly decreased with depth indicating the importance of fresh plant tissue for dissolved C release. A lower water table decreased area based rates of photosynthesis (24–42%), CH4 production (factor 2.5–3.5) and emission, increased rates of soil respiration and microbial biomass C, and did not change DOC release. Due to the changes in process rates the C net balance of the mesocosms shifted by 36 mmol m-2 d-1. According to our estimates the change in C mineralization contributed most to this change. Anaerobic rates of CO2 production rates deeper in the peat increased significantly by a factor of 2–3.5 (DOC), 2.9–3.9 (CO2), and 3–14 (CH4) when the water table was lowered by 30 cm. This phenomenon might have been caused by easing an inhibiting effect by the accumulation of CO2 and CH4 when the water table was at the moss surface. [ABSTRACT FROM AUTHOR]

We measured net ecosystem exchange of carbon dioxide (CO2) (NEE) during wet and dry summers (2000 and 2001) across a range of plant communities at Mer Bleue, a large peatland near Ottawa, southern Ontario, Canada. Wetland types included ombrotrophic bog hummocks and hollows, mineral-poor fen, and beaver pond margins. NEE was significantly different among the sites in both years, but rates of gross photosynthesis did not vary spatially even though species composition at the sites was variable. Soil respiration rates were very different across sites and dominated interannual variability in summer NEE within sites. During the dry summer of 2001, net CO2 uptake was significantly smaller, and most locations switched from a net sink to a source of CO2 under a range of levels of photosynthetically active radiation (PAR). The wetter areas—poor fen and beaver pond margin—had the largest rates of CO2 uptake and smallest rates of respiratory loss during the dry summer. Communities dominated by ericaceous shrubs (bog sites) maintained similar rates of gross photosynthesis between years; by contrast, the sedge-dominated areas (fen sites) showed signs of early senescence under drought conditions. Water table position was the strongest control on respiration in the drier summer, whereas surface peat temperature explained most of the variability in the wetter summer. Q 10 temperature-respiration quotients averaged 1.6 to 2.2. The ratio between maximum photosynthesis and respiration ranged from 3.7:1 in the poor fen to 1.2:1 at some bog sites; it declined at all sites in the drier summer owing to greater respiration rates relative to photosynthesis in evergreen shrub sites and a change in both processes in sedge sites. Our ability to predict ecosystem responses to changing climate depends on a more complete understanding of the factors that control NEE across a range of peatland plant communities. [ABSTRACT FROM AUTHOR]

The inundation of boreal forests and peatlands through the construction of hydroelectric reservoirs can increase carbon dioxide (CO 2 ) and methane (CH 4 ) emission. To establish controls on emission rates, we incubated samples of forest and peat soils, spruce litter, forest litter and peatland litter collected from boreal ecosystems in northern Quebec for 16 weeks and measured CO 2 and CH 4 production rates under flooded or non-flooded conditions and varying oxygen concentration and temperature. CO 2 production under flooded conditions was less than under non-flooded conditions (5–71 vs. 5–85 mg C g − 1 C), but CH 4 production under flooded conditions was larger than under non-flooded conditions (1–8158 vs. 0–86 μg C g − 1 C). The average CO 2 and CH 4 production rate factor for flooded:non-flooded conditions was 0.76 and 1.32, respectively. Under flooded conditions, high oxygen concentrations increased CO 2 production in peat soils but decreased CH 4 production in forest and peat soils and spruce litter. Warmer temperatures (from 4 to 22 °C) raised both CO 2 production in peat soils and peatland litter, and CH 4 production in peat soils and spruce litter. This study shows that the direction and/or strength of CO 2 and CH 4 fluxes change once boreal forests and peatlands are inundated. [ABSTRACT FROM AUTHOR]

We compared the amount and composition of different aboveground biomass (BM) fractions of four mires with their net ecosystem CO2 exchange (NEE) measured by eddy covariance. We found clear differences in response of green biomass (GBM) of plant functional types (PFTs) to water table (WT), which resulted in larger spatial variation in GBM within a mire than variation between mires. GBM varied between mires from 126 ± 7 to 336 ± 16 g·m-2 (mean ± SE), while within mire variation at largest was from 157 ± 17 to 488 ± 20 g·m-2 (mean ± SE). GBM of dominant PFTs appeared to be better in explaining the peak growing season NEE than the total BM or GBM of a mire. The differences in photosynthetic capacity between PTFs had a major role, and thus a smaller GBM with different species composition could result in higher NEE than larger GBM. Vascular plant GBM, especially that of sedges, appeared to have a high impact on NEE. Eleven PFTs, defined here, appeared to capture well the internal variation within mires, and the differences in GBM between communities were explained by the water table response of PFTs. Our results suggest the use of photosynthesizing BM, separated into PFTs, in modelling ecosystem carbon exchange instead of using just total BM. [ABSTRACT FROM AUTHOR]

We investigated soil carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) exchanges in an age-sequence (4, 17, 32, 67 years old) of eastern white pine ( Pinus strobus L.) forests in southern Ontario, Canada, for the period of mid-April to mid-December in 2006 and 2007. For both CH4 and N2O, we observed uptake and emission ranging from −160 to 245 μg CH4 m−2 h−1 and −52 to 21 μg N2O m−2 h−1, respectively (negative values indicate uptake). Mean fluxes from mid-April to mid-December across the 4, 17, 32, 67 years old stands were similar for CO2 fluxes (259, 246, 220, and 250 mg CO2 m−2 h−1, respectively), without pattern for N2O fluxes (−3.7, 1.5, −2.2, and −7.6 μg N2O m−2 h−1, respectively), whereas the uptake rates of CH4 increased with stand age (6.4, −7.9, −10.8, and −23.3 μg CH4 m−2 h−1, respectively). For the same period, the combined contribution of CH4 and N2O exchanges to the global warming potential (GWP) calculated from net ecosystem exchange of CO2 and aggregated soil exchanges of CH4 and N2O was on average 4%, <1%, <1%, and 2% for the 4, 17, 32, 67 years old stand, respectively. Soil CO2 fluxes correlated positively with soil temperature but had no relationship with soil moisture. We found no control of soil temperature or soil moisture on CH4 and N2O fluxes, but CH4 emission was observed following summer rainfall events. LFH layer removal reduced CO2 emissions by 43%, increased CH4 uptake during dry and warm soil conditions by more than twofold, but did not affect N2O flux. We suggest that significant alternating sink and source potentials for both CH4 and N2O may occur in N- and soil water-limited forest ecosystems, which constitute a large portion of forest cover in temperate areas. [ABSTRACT FROM AUTHOR]

We examined aerobic and anaerobic microbial carbon dioxide (CO2) and methane (CH4) exchange in peat samples representing different profiles at natural, mined, mined-abandoned, and restored northern peatlands and characterized the nutrient and substrate chemistry and microbial biomass of these soils. Mining and abandonment led to reduced nutrient and substrate availability and occasionally drier conditions in surface peat resulting in a drastic reduction in CO2 and CH4 production, in agreement with previous studies. Owing mainly to wetter conditions, CH4 production and oxidation were faster in restored block-cut than natural sites, whereas in one restored site, increased substrate and nutrient availability led to much more rapid rates of CO2 production. Our work in restored block-cut sites compliments that in vacuum-harvested peatlands undergoing more recent active restoration attempts. The sites we examined covered a large range of soil C substrate quality, nutrient availability, microbial biomass, and microbial activities, allowing us to draw general conclusions about controls on microbial CO2 and CH4 dynamics using stepwise regression analysis among all sites and soil depths. Aerobic and anaerobic decomposition of peat was constrained by organic matter quality, particularly phosphorus (P) and carbon (C) chemistry, and closely linked to the size of the microbial biomass supported by these limiting resources. Methane production was more dominantly controlled by field moisture content (a proxy for anaerobism), even after 20 days of anaerobic laboratory incubation, and to a lesser extent by C substrate availability. As methanogens likely represented only a small proportion of the total microbial biomass, there were no links between total microbial biomass and CH4 production. Methane oxidation was controlled by the same factors influencing CH4 production, leading to the conclusion that CH4 oxidation is primarily controlled by substrate (that is, CH4) availability. Although restoring hydrology similar to natural sites may re-establish CH4 dynamics, there is geographic or site-specific variability in the ability to restore peat decomposition dynamics. [ABSTRACT FROM AUTHOR]

The effects of peat bog harvesting and restoration on dissolved organic matter (DOM) are poorly known although DOM represents the most mobile part of organic matter in peat. The aims of our study were: (i) to determine concentrations and properties of DOM in a series of natural, harvested, and restored peatlands in eastern Que´bec and (ii) to relate DOM to CO2 efflux from these bogs. We sampled pore waters at eight peat bogs and determined dissolved organic carbon (DOC) concentrations, humification indices derived from synchronous fluorescence spectra (humification index (HIX), ratio of intensities at 470 and 400 nm), specific absorption at 280 nm, and the humic acid (HA) content. DOC concentrations ranged from 35 to 625 mg C l−1. The highest values were observed at a block-cut (BC) site where the ditches had been closed to stimulate restoration. This resulted in limited external drainage, DOM accumulation in deeper horizons, and an enrichment of the poorly biodegradable humic acids to about 60% of the bulk DOM. DOC concentrations increased immediately during harvesting up to 188 mg C l−1 as a result of this ecosystem disturbance. Afterwards, DOC concentrations decreased which might be due to a low content of potential DOM of the remaining little oxidised peat. The enhanced decomposition of the remaining peat during the restoration process seems to be important for a new build-up of potential DOM, which is indicated by reincreasing DOC concentration during the restoration process. We could not relate spectroscopic properties of DOM to peat harvesting and restoration. The portion of humic acids was inversely related to CO2 efflux, indicating low substrate quality of humic acids in pore waters. The seasonal average humification indices of DOM where humic acids had been removed were positively correlated with the seasonal CO2 efflux from the eight sites, indicating that high respiration results in an enrichment of more aromatic and complex DOM molecules. The relationships suggest that DOM composition affects CO2 efflux from peat bogs and is also driven by respiration and CO2 efflux. [Copyright &y& Elsevier]

Abstract We measured net ecosystem CO2 exchange (NEE) in Panamá over C4 pasture plots that varied in grazing intensity. After adjusting for variation in light, there were noticeable effects of grazing-related variables on CO2 exchange that were largely dependent on the developmental stage of the plant canopy. Above-ground productivity was positively related to grazing intensity (r 2 =0.30). Two experimentally grazed fields had significantly lower standing crop biomass but no significant difference in CO2 uptake (24.2 μmol/m2 /s) compared with two ungrazed fields (20.3 μmol/m2 /s). Grazed fields had significantly lower ecosystem respiration rates (10.3 μmol/m2 /s) than did ungrazed fields (17.6 μmol/m2 /s). These results suggest that, although these pastures were possible sources of CO2 during the time intervals sampled, the size of the sources tended to be dampened by cattle grazing through reductions in ecosystem respiration. Thus, it appears that disturbance caused by cattle grazing will not always result in an increase in CO2 release from tropical pastures to the atmosphere. [ABSTRACT FROM AUTHOR]