CO2 Production Potentials Research Articles

Moderate increase of precipitation stimulates CO2 production by regulating soil organic carbon in a saltmarsh.

Saltmarsh is widely recognized as a blue carbon ecosystem with great carbon storage potential. Yet soil respiration with a major contributor of atmospheric CO2 can offset its carbon sink function. Up to date, mechanisms ruling CO2 emissions from saltmarsh soil remain unclear. In particular, the effect of precipitation on soil CO2 emissions is unclear in coastal wetlands, due the lack of outdoor data in real situations. We conducted a 7-year field manipulation experiment in a saltmarsh in the Yellow River Delta, China. Soil respiration in five treatments (-60%, -40%, +0%, +40%, and + 60% of precipitation) was measured in the field. Topsoils from the last 3 years (2019-2021) were analyzed for CO2 production potential by microcosm experiments. Furthermore, quality and quantity of soil organic carbon and microbial function were tested. Results show that only the moderate precipitation rise of +40% induced a 66.2% increase of CO2 production potential for the microcosm experiments, whereas other data showed a weak impact. Consistently, soil respiration was also found to be strongest at +40%. The CO2 production potential is positively correlated with soil organic carbon, including carbon quantity and quality. But microbial diversity did not show any positive response to precipitation sizes. r-/K-strategy seemed to be a plausible explanation for biological factors. Overall, our finding reveal that a moderate precipitation increase, not decrease or a robust increase, in a saltmarsh is likely to improve soil organic carbon quality and quantity, and bacterial oligotroph:copiotroph ratio, ultimately leading to an enhanced CO2 production.

Assessment of Carbon Stock and СO<sub>2</sub> Production Potential for Soils of Coniferous-Broad-Leaved Forests

Within the territory of MSU Agrobiostation “Chashnikovo”, assessment of carbon stock for soil, typical for coniferous-broad-leaved forests subzone – coniferous forests, small-leaved forests, agrocenoses, fallow lands and floodplain meadows – was given. The next indexes were studied for litters: typology, stock, detritus content and ratio of sub-horizons thickness (deposit) – these indexes are indicators of organic matter decomposition intensity. For mineral soil profile, the assessment of general organic carbon stock in 0–30 and 0–100 cm layers, as well as stock of biologically active carbon in 0–20 cm layer (by calculation according to the content of total carbon), are given. Maximum organic matter accumulation in litters and moderate accumulation – in mineral profile, was obtained for coniferous forests soddy-podzolic soils. The litter carbon stock value in spruce forests differ by almost 10 times, depending on location in tessera. Minimal carbon accumulation by litters is obtained for meadow ecosystem soils – upland meadows as well as flood-plain meadows. Alluvial soils of flood-plain meadows are characterized by highest stock of general carbon, as well as carbon of biologically active soil organic matter. Potential of CO2 production by soil, determined by data, including structural and functional litter indexes and organic matter biologically active carbon stock (0–20 cm layer), depends on combination of row of factors: vegetation type, hydromorphism degree, and agricultural use character in present or past. Coniferous forest soils comparing with small-leaved forest soils are characterized by less rate of litter decomposing due to plant remains biochemical features, thereby these soils are assumed to less CO2 production potential. Soils of natural grass ecosystems, especially flood-plain meadows, are characterized by maximal potential production of carbon dioxide, resulting from intensive plant residues decomposition and high stock of biologically active organic matter carbon.

Assessment of Carbon Stock and CO2 Production Potential for Soils of Coniferous-Broadleaved Forests

—The assessment of carbon stocks in soils of coniferous and broadleaved forests, agrocenoses, fallow lands, and floodplains has been performed for the territory of the Chashnikovo Agrobiological Station of Moscow State University. The typology of litter horizons, the contents of plant detritus in the them, and the ratio of the thicknesses of litter subhorizons have been determined as indicators of the organic matter decomposition intensity. For mineral soil profile, total organic carbon stocks in the layers of 0–30 and 0–100 cm layers and the stock of biologically active carbon in the layer of 0–20 cm layer have been determined. Maximum organic matter accumulation in litters and moderate accumulation in mineral profile is typical of soddy-podzolic soils (Retisols) under coniferous forests. The litter carbon stocks in spruce forests differ by almost an order of magnitude depending on the position in the tessera. Minimum carbon accumulation in litters is characteristic of the soils of upland and floodplain meadows. Alluvial soils of floodplain meadows are characterized by the highest stock of total carbon, as well as carbon of biologically active soil organic matter. The potential of CO2 production by soil determined the structural and functional litter characteristics and the stock of biologically active organic matter in the upper (0–20 cm) soil layer depend on several factors: vegetation type, hydromorphism degree, and agricultural use at present and in the past. Soils of coniferous forests in comparison with soils of broadleaved forests are characterized by lower rates of litter decomposition due to the biochemical features of plant remains and are assumed to have a lower potential for CO2 production. Soils of natural herbaceous ecosystems, especially floodplain meadows, are characterized by the maximum potential production of carbon dioxide due to intense decomposition of plant residues and high stock of biologically active organic matter carbon.

Duration of extraction determines CO2and CH4emissions from an actively extracted peatland in eastern Quebec, Canada

Abstract. Draining and extracting peat alters the conditions that control CO2 and CH4 emissions. Carbon (C) emissions from peatlands undergoing horticultural peat extraction are not well constrained due to a lack of measurements. We determine the effect that production duration (years of extraction) has on the CO2 and CH4 emissions from an actively extracted peatland over 3 years of measurements (2018–2020). We studied five sectors identified by the year when extraction began (1987, 2007, 2010, 2013, 2016). Greater average CO2 and CH4 emissions were measured from the drainage ditches (CO2: 2.05 ± 0.12 g C m−2 d−1; CH4: 72.0 ± 18.0 mg C m−2 d−1) compared to the field surface (CO2: 0.9 ± 0.06 g C m−2 d−1; CH4: 9.2 ± 4.0 mg C m−2 d−1) regardless of sector. For peat fields, CO2 fluxes were highest in the youngest sector, which opened in 2016 (1.5 ± 0.2 g C m−2 d−1). The four older sectors all had similar mean CO2 fluxes (∼ 0.65 g C m−2 d−1) that were statistically different from the mean 2016 CO2 flux. A spatial effect on CO2 fluxes was observed solely within the 2016 sector, where CO2 emissions were highest from the centre of the peat field and declined towards the drainage ditches. These observations occur due to operators contouring surfaces to facilitate drainage. The domed shape and subsequent peat removal resulted in a difference in surface peat age hence different humification and lability. In addition, 14C dating confirmed that the peat contained within the 2016 sector was younger than peat within the 2007 sector and that peat age is younger toward the centre of the field in both sectors. Humification indices derived from mid-infrared spectrometry (MIRS) (1630/1090 cm−1) indicated that peat humification increases with increasing years of extraction. Laboratory incubation experiments showed that CO2 production potentials of surface peat samples from the 2016 sector increased toward the centre of the field and were greater than for samples taken from the 1987 and 2007 sectors. Our results indicate that peatlands under extraction are a net source of C, where emissions are high in the first few years after opening a field for extraction and then decline to about half the initial value and remain at this level for several decades, and the ditches remain a 2 to 3 times greater source than the fields but represent <3.5 % of the total area of a field.

Impacts of thinning activities on boreal peatland forests

Boreal peatland forests are an important source of timber. Recently, timber harvesting has been extended to warmer months, resulting in machinery traffic over unfrozen soils, and leading to higher levels of soil disturbance, such as deeper ruts. Despite this, our knowledge of the impact of soil disturbance on peat physical properties and soil biochemistry is still limited. To address this gap, I conducted a study to examine the effects of soil disturbance caused by harvesting machinery during thinning operations on the soil physical, chemical, and biological properties and vegetation of drained boreal peatland forests. To assess the rate of recovery, I sampled six sites that formed a chronosequence covering 15 years since thinning. The results showed that soil disturbance caused an increase in the bulk density and field capacity of peat, along with a decrease in total porosity. In the vegetation, moss biomass and root production were reduced, but sedge cover increased. Furthermore, recently disturbed areas exhibited greater soil CO2 production potential, as well as higher soil CO2 and CH4 concentrations compared to control areas. However, CO2 and CH4 emissions, microbial communities, and cellulose decomposition rate were not impacted. Although the rate of recovery varied, all studied properties impacted by disturbance were fully recovered within 15 years. As the water retention characteristic (WRC) describes soil structure and its alterations, it a useful for disturbance assessment. Thus, I propose how WRC can be predicted using artificial neural networks. Overall, the study demonstrated that while drained boreal peatlands are sensitive to disturbance, they are also resilient to mechanical soil disturbance caused by thinnings.

Space-for-time substitution leads to carbon emission overestimation in eutrophic lakes

Lacustrine eutrophication is generally considered as an important contributor of carbon emissions to the atmosphere; however, there is still a huge challenge in accuracy estimating carbon emissions from lakes. To test the effect of widely used space-for-time substitution on lake carbon emissions, this study monitored different processes of carbon emissions, including the carbon production potential, dissolved carbon concentrations, and carbon release fluxes in eight lakes along the trophic gradients on a spatial scale and the typical eutrophic Lake Taihu for one year on a temporal scale. Eutrophication promoted carbon production potential, dissolved carbon concentrations, and carbon release fluxes, especially for CH4. Trophic lake index (TLI) showed positive correlations with the CH4 production potential, dissolved CH4 concentrations, and CH4 release fluxes, and also positive correlations with the CO2 production potential, dissolved CO2 concentrations, and CO2 release fluxes. The space-for-time substitution led to an overestimation for the influence of eutrophication on carbon emissions, especially the further intensification of lake eutrophication. On the spatial scale, the average CH4 production potential, dissolved CH4 concentrations and CH4 release fluxes in eutrophic lakes were 268.6, 0.96 μmol/L, and 587.6 μmol m−2·h−1, respectively, while they were 215.8, 0.79 μmol/L, and 548.6 μmol m−2·h−1 on the temporal scale. Obviously, CH4 and CO2 emissions on the spatial scale were significantly higher than those on the temporal scale in eutrophic lakes. The primary influencing factors were the seasonal changes in the physicochemical environments of lake water, including dissolved oxygen (DO) and temperature. The CH4 and CO2 release fluxes showed negative correlations with DO, while temperature displayed positive correlations, respectively. These results suggest that the effects of DO and temperature on lake carbon emissions should be considered, which may be ignored during the accurate assessment of lake carbon budget via space-for-time substitution in eutrophic lakes.

Potential greenhouse gases emissions by different plant communities in maritime Antarctica

Antarctic plant communities show a close relationship with soil types across the landscape, where vegetation cover changes, biological influence, and soil characteristics can affect the dynamic of greenhouse gases emissions. Thus, the objective of this study was to evaluate greenhouse gases emissions in lab conditions of ice-free areas along a topographic gradient (from sea level up to 300 meters). We selected 11 distinct vegetation compositions areas and assessed greenhouse gases production potentials through 20 days of laboratory incubations varying temperatures at -2, 4, 6, and 22 °C. High N2O production potential was associated with the Phanerogamic Community under the strong ornithogenic influence (phosphorus, nitrogen, and organic matter contents). Seven different areas acted as N2O sink at a temperature of -2 °C, demonstrating the impact of low-temperature conditions contributing to store N in soils. Moss Carpets had the highest CH4 emissions and low CO2 production potential. Fruticose Lichens had a CH4 sink effect and the highest values of CO2. The low rate of organic matter provided the CO2 sink effect on the bare soil (up to 6 °C). There is an overall trend of increasing greenhouse gases production potential with increasing temperature along a toposequence.

Response of vegetation and soil biological properties to soil deformation in logging trails of drained boreal peatland forests

In the boreal region, peatland forests are a significant resource of timber. Under pressure from a growing bioeconomy and climate change, timber harvesting is increasingly occurring over unfrozen soils. This is likely to cause disturbance in the soil biogeochemistry. We studied the impact of machinery-induced soil disturbance on the vegetation, microbes, and soil biogeochemistry of drained boreal peatland forests caused by machinery traffic during thinning operations. To assess potential recovery, we sampled six sites that ranged in time since thinning from a few months to 15 years. Soil disturbance directly decreased moss biomass and led to an increase in sedge cover and a decrease in root production. Moreover, soil CO2 production potential, and soil CO2 and CH4 concentrations were greater in recently disturbed areas than in the control areas. In contrast, CO2 and CH4 emissions, microbial biomass and structure, and the decomposition rate of cellulose appeared to be uncoupled and did not show signs of impact. While the impacted properties varied in their rate of recovery, they all fully recovered within 15 years covered by our chronosequence study. Conclusively, drained boreal peatlands appeared to have high biological resilience to soil disturbance caused by forest machinery during thinning operations.

The influence of lipid content and taxonomic affiliation on methane and carbon dioxide production from phytoplankton biomass in lake sediment

AbstractThe greenhouse gases methane (CH4) and carbon dioxide (CO2) are end products of microbial anaerobic degradation of organic matter (OM) in lake sediments. Although previous research has shown that phytoplankton lipid content influences sediment methanogenesis, current understanding on how OM quality affects methanogenesis is still limited. Such information is needed to more accurately assess how lake greenhouse gas emissions may change in response to anthropogenic activities. We cultured 11 phytoplankton species from five classes and studied how taxonomic identity, C : N ratio, lipid content, and fatty acid composition of phytoplankton biomass affects the CH4 and net CO2 production in anaerobic lake sediments with an incubation experiment that lasted > 100 d. The carbon‐normalized potential CH4 (0.09–0.23 μmol mg C−1 d−1) and net CO2 (0.09–0.28 μmol mg C−1 d−1) production rates were not related to phytoplankton taxonomic affiliation (e.g., class, species), C : N ratio, or fatty acid composition of algal biomass. Methane or net CO2 production potentials did not increase with higher lipid content (10–30%); however, total fatty acid content had a weak correlation with CH4 production potential. In contrast to previous research, our results suggest that lipid content is of minor importance in determining methanogenesis rates from the biomass of multispecies phytoplankton communities settling on sediments. The decrease in CO2 concentration and the correlation between stable carbon isotope signatures of CH4 and molar ratio of CH4 and CO2 at the end of the experiment may indicate that importance of hydrogenotrophic methanogenesis, which uses CO2 when other substrates become limiting, increased during the long incubation.

Effects of Land Use Types on CH4 and CO2 Production Potentials in Subtropical Wetland Soils

Changes in land use types can alter the soil and environmental characteristics of wetlands, which in turn influence the magnitude of greenhouse gas production by soil microbes. However, the effects of land use change on the production potential of methane (CH4) and carbon dioxide (CO2) in subtropical wetland soils and the underlying controls are still largely unknown. In this study, we examined the soil CH4 and CO2 production potentials under five different land use types (natural mangrove, Gei Wai water channel, Gei Wai forest, reedbed, and freshwater pond) and their relationships with soil physico-chemical properties in a subtropical wetland in Hong Kong using aerobic and anaerobic laboratory incubation experiments. Our results showed an overall decreasing trend of CH4 and CO2 production potentials down the soil profile at all sites, which could be attributed to a reduction in the concentrations of soil organic matter (SOM), total Kjeldahl nitrogen (TKN) and ammonium nitrogen (NH4+-N). Moreover, the soil CH4 and CO2 production potentials varied significantly in the surface soils among land use types, but were more similar across the sites in the deeper soils. The conversion of natural mangrove to other land use types significantly reduced both the aerobic and anaerobic CO2 production potentials in the top 10 cm soils, except for Gei Wai forest, which demonstrated significantly higher CO2 production rates (61.15–97.91 μg g−1 day−1). Meanwhile, the mean CH4 production potential in the surface soils of natural mangrove (0.05 μg g−1 d−1) was significantly lower than that in the Gei Wai forest and Gei Wai channel (0.26–0.27 μg g−1 day−1) but slightly higher than that in the freshwater pond and reedbed (0.00–0.02 μg g−1 day−1). The high soil CH4 and CO2 production potentials observed in the Gei Wai forest could be explained by the high soil concentrations of SOM, TKN and NH4+-N. On the other hand, the lower anaerobic CH4 and aerobic CO2 productions observed in the reedbed could be attributed to the lower concentrations of NH4+-N and available phosphorus. Our findings highlighted the significant impacts of land use types on the CH4 and CO2 production potentials of subtropical wetland soils, which had practical implications for wetland management for climate change mitigation.

Examining CO2 and N2O pollution and reduction from forestry application of pure and mixture forest

Greenhouse gases (GHGs) carbon dioxide (CO2) and nitrous oxide (N2O), contribute significantly to global warming, and they have increased substantially over the years. Reforestation is considered as an important forestry application for carbon sequestration and GHGs emission reduction, however, it remains unknown whether reforestation may instead produce too much CO2 and N2O contibuting to GHGs pollution. This study was performed to characterize and examine the CO2 and N2O emissions and their controlling factors in different species and types of pure and mixture forest used for reforestation. Five soil layers from pure forest Platycladus orientalis (PO), Robinia pseudoacacia (RP), and their mixed forest P-R in the Taihang mountains of central China were sampled and incubated aerobically for 11 days. The P-R soil showed lower CO2 and N2O production potentials than those of the PO soils (P < 0.01). The average reduction rate of cumulative CO2 and N2O was 31.63% and 14.07%, respectively. If the mixed planting pattern is implemented for reforestation, the annual CO2 reduction amounts of China’s plantation can be achieved at 8.79 million tonnes. With the increase of soil depths, cumulative CO2 production in PO and RP soils decreased, whereas CO2 and N2O production in P-R soil did not show similar pattern. Soil particle size fraction was the main factor influencing GHGs emissions, and the clay fraction showed negative correlation with cumulative CO2 and N2O production. In summary, compared with PO pure artificial forests, the mixture plantation mode can not only reduce GHGs pollution but also improve soil fertility, which is conducive to sustainable management of artificial forests.

Long-term fertilizer management in NERICA cultivated upland affects on soil bio-chemical properties

ABSTRACT This study aims to characterize soil chemical properties and microbial biomass, greenhouse gas production, and organic matter dynamics in upland rice field as affected by the long-term fertilizer managements in Uganda. Soil total C (TC) and N (TN) contents were in the relatively smaller range under different fertilizer treatments, even after 20 crop seasons. However, available phosphate contents showed positive correlation with average yield of upland rice. Incubation experiments were conducted under aerobic or under flooding conditions to measure CO2, methane, and nitrous oxide productions. After the incubation, soil samples were extracted to quantify nitrification rate for aerobic condition and ammonification rate for flooding condition. Soil microbial biomass carbon (MBC) and nitrogen were measured. Stable isotope ratio of 13C and 15N were also determined for the soil samples. CO2 production potential under aerobic condition was higher than the flooding condition. The qCO2 (CO2/MBC) in the treatment applied with compost tended to be higher than the other treatments. Positive correlation between nitrous oxide production and nitrification was found. The delta 13C values of the soil samples indicated that the effect of C4 plants before rice cultivation still remained, while the contribution of biological N2 fixation was little according to delta 15N values. These results indicate that soil microbial biomass in upland rice field of the long-term fertilizer experiment in Uganda was characterized with higher qCO2. Greenhouse gas production was affected by fertilizer management, while soil organic C before the long-term experiment still remained in the experiment.

Molecular Characterization of Fermenting Yeast Species from Fermented Teff Dough during Preparation of Injera Using ITS DNA Sequence.

Identification of the yeast responsible for Injera fermentation is important in order to be more consistent and for scale-up of Injera production. In this study, yeast were isolated and identified from fermenting teff dough sample collected from household, hotels, and microenterprises, Addis Ababa. Initially, the yeast obtained from fermenting teff dough of different sources were selected on the basis of their CO2 production potentials. Its DNA sequencing of isolated yeast identified Pichia fermentans, Pichia occidentalis, Candida humilis, Saccharomyces cerevisiae, and Kazachstania bulderi. The association of identified yeast to their sources indicated the presence of Pichia fermentans in fermenting dough samples collected from all sources whereas Kazachstania bulderi, Saccharomyces cerevisiae, and Candida humilis were shown to be present in samples collected from households, hotels, and microenterprises, respectively. The phenotypes and CO2 production potentials of this yeast were also documented. This study has confirmed the presence of different yeast species in the fermentation of teff dough and hinted the complex nature of Injera dough fermentation.

Soil Greenhouse Gases: Relations to Soil Attributes in a Sugarcane Production Area

Core Ideas The production of the main soil greenhouse gases (CO2, CH4 and N2O) is influenced by agricultural practices. The soil bulk density and micropores showed negative correlation with soil CO2 emission. The factor analysis showed the formation of two independent processes that explained almost 72% of the total variance observed in the data. The soil moisture is a controlling factor of soil CO2 emission. The production of the main soil greenhouse gases (GHG: carbon dioxide [CO2], methane [CH4,] and nitrous oxide [N2O]) is influenced by agricultural practices that cause changes in soil physical, chemical, and biological attributes, directly affecting their emission to the atmosphere. The aim of this study was to investigate the infield soil carbon dioxide emissions (FCO2) and soil CO2, methane, and nitrous oxide production potentials (PCO2, PCH4, and PN2O, respectively) under laboratory conditions and their relationship to soil attributes in a mechanically harvested sugarcane area. Soil carbon dioxide emissions presented an infield average emission value of 1.19 µmol CO2 m‐2 s‐1, while GHG production in the laboratory was 2.34 µg C–CO2 g‐1 soil d‐1 and 0.20 ng N–N2O g‐1 soil d‐1 for PCO2 and PN2O, respectively. No significant production or oxidation was observed for CH4. Factor analysis showed the formation of two independent processes that explained almost 72% of the total variance observed in the data. The first process was related to FCO2 transport and its relation to soil physical attributes such as microporosity, macroporosity, the C/N ratio, soil moisture, and soil bulk density, showing the dependence between FCO2 and soil porosity. The second process was related to soil CO2 and N2O production potentials under laboratory conditions and their relation to soil chemical attributes such as the sum of bases, pH, and available phosphorus, which affect microbial activity and contribute to GHG production. Although presented as independent, these processes are coupled and occur simultaneously in the soil, in addition to providing information about their variability and showing if the infield emissions are due to gas transport processes or soil carbon levels and their quality.

CH4 and CO2 production below two contrasting peatland micro-relief forms: An inhibitor and δ13C study.

Two peatland micro-relief forms (microforms) - hummocks and hollows - differ by their hydrological characteristics (water table level, i.e. oxic-anoxic conditions) and vegetation communities. We studied the CH4 and CO2 production potential and the localization of methanogenic pathways in both hummocks and hollows at depths of 15, 50, 100, 150 and 200cm in a laboratory incubation experiment. For this purpose, we measured CH4 and CO2 production rates, peat elemental composition, as well as δ13C values of gases and solids; the specific inhibitor of methanogenesis BES (2-bromo-ethane sulfonate, 1mM) was aimed to preferentially block the acetoclastic pathway. The cumulative CH4 production of all depths was almost one fold higher in hollows than in hummocks, with no differences in CO2. With depth, CO2 and CH4 production decreased, and the relative contribution of the hydrogenotrophic pathway of methanogenesis increased. The highest methanogenic activity among all depths and both microforms was measured at 15cm of hollows (91%) at which the highest relative contribution of acetoclastic vs. hydrogenotrophic pathway (92 and 8%, respectively) was detected. For hummocks, the CH4 production was the highest at 50cm (82%), where relative contribution of acetoclastic methanogenesis comprised 89%. The addition of 1mM BES was not selective and inhibited both methanogenic pathways in the soil. Thus, BES was less efficient in partitioning the pathways compared with the δ13C signature. We conclude that the peat microforms - dry hummocks and wet hollows - play an important role for CH4 but not for CO2 production when the effects of living vegetation are excluded.

Aerobic decomposition of food waste with different ratios of solids at ambient temperatures and evaluation of CO2 emissions

The aim of this study was to investigate the recycling of organic matter in the food waste by degrading aerobically and evaluation of the CO2 emissions. With this aim, food waste with the content of 5–7–10 % TS was degraded aerobically. The pH in all the reactors was observed within the range of 6.5–7. The highest CO2 production rate was obtained from 5 % TS. Removal was achieved at the rates of 5 % TS and 57 % in COD and TOC. CO2 production rate was calculated as 38.53 g CO2/h/kg TOCw. Moreover, CO2 production potential of the food waste was identified. A batch, single-stage reactor was used to determine the food waste pre-treatment. Finally, food waste in landfill areas was recycled and evaluated by without taking.

Changes in peat chemistry associated with permafrost thaw increase greenhouse gas production

Carbon release due to permafrost thaw represents a potentially major positive climate change feedback. The magnitude of carbon loss and the proportion lost as methane (CH4) vs. carbon dioxide (CO2) depend on factors including temperature, mobilization of previously frozen carbon, hydrology, and changes in organic matter chemistry associated with environmental responses to thaw. While the first three of these effects are relatively well understood, the effect of organic matter chemistry remains largely unstudied. To address this gap, we examined the biogeochemistry of peat and dissolved organic matter (DOM) along a ∼40-y permafrost thaw progression from recently- to fully thawed sites in Stordalen Mire (68.35°N, 19.05°E), a thawing peat plateau in northern Sweden. Thaw-induced subsidence and the resulting inundation along this progression led to succession in vegetation types accompanied by an evolution in organic matter chemistry. Peat C/N ratios decreased whereas humification rates increased, and DOM shifted toward lower molecular weight compounds with lower aromaticity, lower organic oxygen content, and more abundant microbially produced compounds. Corresponding changes in decomposition along this gradient included increasing CH4 and CO2 production potentials, higher relative CH4/CO2 ratios, and a shift in CH4 production pathway from CO2 reduction to acetate cleavage. These results imply that subsidence and thermokarst-associated increases in organic matter lability cause shifts in biogeochemical processes toward faster decomposition with an increasing proportion of carbon released as CH4. This impact of permafrost thaw on organic matter chemistry could intensify the predicted climate feedbacks of increasing temperatures, permafrost carbon mobilization, and hydrologic changes.

Effect of type and quality of two contrasting plant residues on CO2 emission potential of Ultisol soil: Implications for indirect influence of temperature and moisture

The emission of CO2 from soil to the atmosphere is a major challenge throughout the world in both developed and developing countries, due to its critical role in the intensification of global warming. An incubation experiment was conducted to investigate CO2 emission potentials of Ultisol soils under residues of peanut (green manure) and rice (rice straw) and moisture regimes 60% (W1) and 120% (W2) of water holding capacity at different temperature ranges i.e. low to medium 5–20°C (T1 to T4), medium to high 25–30°C (T5 to T6) and very high 35–45°C (T7 to T9). Comparing two contrasting plant residues, we found that the incorporation of GM (green manure) residue significantly (P<0.05) increased the CO2 emission potential of Ultisol soils at both moisture regimes and all temperature ranges, and this increase tended to improve with the increase of temperature ranges. Conversely, RS residue mixed treatments showed significantly low production and emission of CO2, at all temperature ranges and both water regimes. This indicated that type and quality of plant residues have significant impact on the CO2 production and emission capacity of soils and plant residues with low decomposition, high stability and high lignin, cellulose and hemicelluloses compounds can be successfully used as an organic amendment to control the emission and production of CO2 from soil to atmosphere, by converting soils from CO2–C sources to sinks. We revealed that moisture and temperature also had a significant (P<0.05) effect on the CO2 production and emission potential of Ultisol soils, but this effect was indirect through influencing the rate of decomposition of the organic inputs. Our results suggested that applied amendments e.g. addition or incorporation of plant residues are in fact major factors which control the CO2 emission potential of soils by converting soils from CO2–C sources to sinks. On the other hand, other abiotic factors like temperature and moisture are indirect regulator of CO2 production and emission by influencing decomposition of these incorporated organic inputs.

Effects of land-use type and nitrogen addition on nitrous oxide and carbon dioxide production potentials in Japanese Andosols

Land-use type and nitrogen (N) addition strongly affect nitrous oxide (N2O) and carbon dioxide (CO2) production, but the impacts of their interaction and the controlling factors remain unclear. The aim of this study was to evaluate the effect of both factors simultaneously on N2O and CO2 production and associated soil chemical and biological properties. Surface soils (0–10 cm) from three adjacent lands (apple orchard, grassland and deciduous forest) in central Japan were selected and incubated aerobically for 12 weeks with addition of 0, 30 or 150 kg N ha–1 yr–1. Land-use type had a significant (p < 0.001) impact on the cumulative N2O and CO2 production. Soils from the apple orchard had higher N2O and CO2 production potentials than those from the grassland and forest soils. Soil net N mineralization rate had a positive correlation with both soil N2O and CO2 production rates. Furthermore, the N2O production rate was positively correlated with the CO2 production rate. In the soils with no N addition, the dominant soil properties influencing N2O production were found to be the ammonium-N content and the ratio of soil microbial biomass carbon to nitrogen (MBC/MBN), while those for CO2 production were the content of nitrate-N and soluble organic carbon. N2O production increased with the increase in added N doses for the three land-use types and depended on the status of the initial soil available N. The effect of N addition on CO2 production varied with land use type; with the increase of N addition doses, it decreased for the apple orchard and forest soils but increased for the grassland soils. This difference might be due to the differences in microbial flora as indicated by the MBC/MBN ratio. Soil N mineralization was the major process controlling N2O and CO2 production in the examined soils under aerobic incubation conditions.

Testing the stability of carbon pools stored in tussock sedge meadows

Tussocks formed by Carex stricta are a relatively large carbon (C) pool in sedge meadows, but the stability of organic matter in these ecosystems is not well understood. We initiated year-long incubation experiments (22.5°C) to evaluate the CO2 and CH4 production potentials of sedge meadow substrates under field moist and inundated treatments from five sites in the Upper Midwest, USA (4 reference, 1 restored). C mineralization potentials decreased with depth (tussocks>underlying soil), and were positively correlated with macro-organic matter content and negatively with lignin. Across sites, C stored in tussocks and soil at the restoration was the least stable, suggesting that the restoration of C-storage function may take decades. Mineralization potentials were similar between field moist and inundated treatments, but inundation resulted in higher methane production, accounting for 24–51% of total carbon mineralized from tussocks. In the field however, C. stricta tussocks emitted less methane (393±76mgCH4m−2d−1) than tussock interspaces (1362±371mgCH4m−2d−1) early in the growing season; we suggest that tussock tops oxidized methane produced from deeper anoxic horizons. Our results highlight the importance of considering how microtopography modulates greenhouse gas flux from wetlands and suggests that the C stored in the older, more decomposed C. stricta tussock sedge meadow substrates (both within and between sites) is relatively stable.