Anaerobic CO2 Production Research Articles

Salt marsh invasion reduces recalcitrant organic carbon pool while increases lateral export of dissolved inorganic carbon in a subtropical mangrove wetland

Mangrove wetlands are one of the most productive ecosystems and store large amounts of organic carbon (blue carbon). However, mangrove wetlands have been invaded by S. alterniflora-dominated salt marsh globally, the understanding of how this ecological invasion affects carbon cycling in mangroves remains limited. In this study, we conducted intensive investigations and measurements in a subtropical mangrove wetland (S.E. China) to evaluate the impacts of S. alterniflora invasion on sediment organic carbon (SOC) pools, sources, stability, and dissolved inorganic carbon (DIC) export. Results showed that S. alterniflora invasion increased sediment labile organic carbon (LOC) content and decreased the proportion of recalcitrant organic carbon (ROC) compared with other habitats (e.g., mudflat, mangrove, and marsh-mangrove transitional community). The δ13C values showed that mangroves can provide more SOC and ROC than S. alterniflora. The SOC provided by S. alterniflora mostly consisted of LOC, which was unstable and easily transformed, leading to the higher anaerobic mineralization rate and CO2 production. Different from the acidic environment of mangrove sediment, the alkaline environment of S. alterniflora sediment preserves more CO2 in the form of DIC in porewater, which could be transported during the movement of tides. Thus, S. alterniflora potentially exported more DIC to the estuary than mangroves. These findings suggested that S. alterniflora-dominated salt marsh invasion can substantially perturb the mangrove wetlands by reducing ROC pool and potentially increasing the lateral export of DIC.

Relationship between soil CO2 fluxes and soil moisture: Anaerobic sources explain fluxes at high water content

Soil moisture is a known environmental factor influencing carbon dioxide (CO2) emissions and therefore represents an important variable in predictive models. Establishing relationships between soil CO2 emissions and soil moisture has long focused on the role of soil organic carbon mineralization by aerobic respiration. This approach, which generally yields a bell-shaped relationship establishing maximum CO2 production at moderate soil moisture, ignores anaerobic processes as a potential source of CO2. To decouple the effects of soil moisture and O2, we conducted a factorial batch experiment by incubating soil samples at different imposed moisture contents (30%, 45%, 65%, 80%, and 100% water-filled pore space; WFPS) at 25 °C, under both oxic (normal air) and anoxic (N2 atmosphere) headspace conditions. Gas fluxes measured in the oxic incubations show that CO2 fluxes were maximal (31.2 ± 1.8 nmol cm−3 soil hr-1) at moderate moisture content (65% WFPS), as commonly reported. However, contrary to previous models that predict negligible CO2 fluxes under fully saturated conditions due to O2 limitation, substantial fluxes of CO2 (18.1 ± 2.2 nmol cm−3 soil hr-1) were measured at 100% WFPS. In the anoxic treatments, CO2 fluxes rose sharply when the moisture content exceeded 65% WFPS, with values at 100% saturation (21.8 ± 2.2 nmol cm−3 soil hr-1), close to the corresponding fluxes in the oxic incubations. Methane (CH4) fluxes in the anoxic incubations increased over time, ultimately reaching parity with the CO2 fluxes at 100% WFPS. To reproduce the soil moisture dependence of the CO2 fluxes, we propose a kinetic model representing both aerobic and anaerobic CO2 production. Together, the gas flux measurements, porewater geochemistry data, and modeling results indicated that at soil moisture contents approaching saturation (≥90%), anaerobic processes were the major source of CO2 in the oxic incubations. Overall, we conclude that existing models may underrepresent soil CO2 production at high soil moisture by not considering anaerobic reaction pathways releasing CO2.

Effects of conversion of coastal marshes to aquaculture ponds on sediment anaerobic CO2 production and emission in a subtropical estuary of China

The extensive conversion of carbon-rich coastal wetland to aquaculture ponds in the Asian Pacific region has caused significant changes to the sediment properties and carbon cycling. Using field sampling and incubation experiments, the sediment anaerobic CO2 production and CO2 emission flux were compared between a brackish marsh and the nearby constructed aquaculture ponds in the Min River Estuary in southeastern China over a three-year period. Marsh sediment had a higher total carbon and lower C:N ratio than aquaculture pond sediment, suggesting the importance of marsh vegetation in supplying labile organic carbon to the sediment. Conversion to aquaculture ponds significantly decreased sediment anaerobic CO2 production rates by 69.2% compared to the brackish marsh, but increased CO2 emission, turning the CO2 sink (−490.8 ± 42.0 mg m−2 h−1 in brackish marsh) into a source (6.2 ± 3.9 mg m−2 h−1 in aquaculture pond). Clipping the marsh vegetation resulted in the highest CO2 emission flux (382.6 ± 46.7 mg m−2 h−1), highlighting the critical role of marsh vegetation in capturing and sequestering carbon. Sediment anaerobic CO2 production and CO2 uptake (in brackish marsh) and emission (in aquaculture ponds) were highest in the summer, followed by autumn, spring and winter. Redundancy analysis and structural equation modeling showed that the changes of sediment temperature, salinity and total carbon content accounted for more than 50% of the variance in CO2 production and emission. Overall, the results indicate that vegetation clearing was the main cause of change in CO2 production and emission in the land conversion, and marsh replantation should be a primary strategy to mitigate the climate impact of the aquaculture sector.

Electron Accepting Capacities of a Wide Variety of Peat Materials From Around the Globe Similarly Explain CO2 and CH4 Formation

AbstractIn organic soils, the availability of terminal electron acceptors (TEAs) determines the ratio of CO2 to CH4 formation under anoxic conditions. While the importance of electron accepting capacities (EACs) of organic matter is increasingly acknowledged, redox properties of organic matter have only been investigated in a limited set of peat and reference materials. Therefore, we incubated 60 peat samples from 15 sites covering a variety of both bog and poor to intermediate fen samples and characterized their capacities to serve as TEA for anaerobic CO2 formation. We quantified CO2 and CH4 formation and changes in available EAC in anoxic incubations of 56 days. In our experiment, on average 36.5% of CO2 could be attributed to CH4 formation, assuming an CO2:CH4 ratio for methanogenesis of 1:1. Regarding the remaining CO2 formed, for which a corresponding TEA would be needed, we could on average explain 70.8% by corresponding consumption of EAC from both organic and inorganic TEAs, the latter contributing less than 0.1%. When the initial EAC was high, CO2 formation from the apparent consumption of EAC was high and outweighed CO2 formation from methanogenesis. Rapid depletion of available EAC, especially in reactive peat, resulted in a higher share of CO2 from CH4 formation. Our study demonstrates that EAC provides the most important redox buffer for competitive suppression of methanogenesis in peat soils, particularly under fluctuating water table levels, when EAC is repeatedly regenerated. Moreover, electron budgets including EAC of organic matter could largely explain anaerobic CO2 production.

Effect of tidal hydrology on soil anaerobic CO2 production of freshwater marsh in the Yellow River estuary wetland, China

Tidal hydrology has an important effect on anaerobic carbon decomposition in estuary wetlands. However, it remains unclear how soil anaerobic CO2 production responds to change in tidal hydrology. We differentiated anaerobic CO2 production of freshwater marsh soil exposed to different tidal hydrology in the Yellow River estuary wetland. For this purpose, soil cores of a freshwater marsh with no-tidal hydrology were translocated to and cultured in the three tidal salt marshes with different tidal hydrology, respectively. Over 16-month culture, change in tidal hydrology significantly affected properties and anaerobic CO2 production of freshwater marsh soil. Exposure to tidal hydrology had increased pH and electrical conductivity (EC) of freshwater marsh soil, while decreased organic carbon (TOC), dissolved organic carbon (DOC) and C:N ratios. Anaerobic CO2 production of freshwater marsh soil showed a significantly reduction after exposed to different tidal hydrology conditions, with the corresponding mean decreasing from 2.53 μgC·g−1·d−1 under the no-tidal hydrology to 1.09–2.10 μgC·g−1·d−1 under the different tidal hydrology. Soil anaerobic CO2 production were negatively correlated with pH and EC, and positively correlated with TOC, DOC and C:N ratios, with a total 92.6% explanation of soil properties for the change in anaerobic CO2 production. The results suggest that soil anaerobic CO2 production of freshwater marsh soil might be inhibited when exposed to seawater intrusion due to the rise of salt and the decrease of substrate quality.

Quantifying the inhibitory impact of soluble phenolics on anaerobic carbon mineralization in a thawing permafrost peatland.

The mechanisms controlling the extraordinarily slow carbon (C) mineralization rates characteristic of Sphagnum-rich peatlands ("bogs") are not fully understood, despite decades of research on this topic. Soluble phenolic compounds have been invoked as potentially significant contributors to bog peat recalcitrance due to their affinity to slow microbial metabolism and cell growth. Despite this potentially significant role, the effects of soluble phenolic compounds on bog peat C mineralization remain unclear. We analyzed this effect by manipulating the concentration of free soluble phenolics in anaerobic bog and fen peat incubations using water-soluble polyvinylpyrrolidone ("PVP"), a compound that binds with and inactivates phenolics, preventing phenolic-enzyme interactions. CO2 and CH4 production rates (end-products of anaerobic C mineralization) generally correlated positively with PVP concentration following Michaelis-Menten (M.M.) saturation functions. Using M.M. parameters, we estimated that the extent to which phenolics inhibit anaerobic CO2 production was significantly higher in the bog-62 ± 16%-than the fen-14 ± 4%. This difference was found to be more substantial with regards to methane production-wherein phenolic inhibition for the bog was estimated at 54 ± 19%, while the fen demonstrated no apparent inhibition. Consistent with this habitat difference, we observed significantly higher soluble phenolic content in bog vs. fen pore-water. Together, these findings suggest that soluble phenolics could contribute to bogs' extraordinary recalcitrance and high (relative to other peatland habitats) CO2:CH4 production ratios.

Microbial communities reveal impacts of unconventional oil and gas development on headwater streams

The demand for natural gas has led to the development of techniques used to access unconventional oil and natural gas (UOG) resources, due to the novelty of UOG, the potential impacts to freshwater ecosystems are not fully understood. We used a dual pronged approach to study the effects of UOG development on microbial biodiversity and function via a laboratory microcosm experiment and a survey study of streams with and without UOG development within their watersheds. The microcosm experiment simulated stream contamination with produced water, a byproduct of UOG operations, using sediment collected from one high water-quality stream and two low water-quality streams. For the survey study, biofilm and sediment samples were collected from streams experiencing varying levels of UOG development. In the microcosm experiment, produced water decreased microbial aerobic and anaerobic CO2 production in the high water-quality stream sediment but had a positive effect on this microbial activity in the lower water-quality stream sediments, suggesting habitat degradation alters the response of microbes to contaminants. Results from the stream survey indicate UOG development alters stream water temperature, chemistry, sediment aerobic and anaerobic CO2 production, and microbial community biodiversity in both sediments and biofilms. Correlations among UOG associated land use, environmental, and microbial variables suggest increases in light availability and sediment delivery to streams, due to deforestation and land disturbance, impact stream microbial communities and their function. Consistent changes in the relative abundance of bacterial taxa suggest microorganisms may be good indicators of the environmental changes associated with UOG development. The observed impacts of UOG development on microbial community composition and carbon cycling could have cascading effects on stream health and broader ecosystem function.

Differential effects of redox conditions on the decomposition of litter and soil organic matter

Soil redox conditions exert substantial influence on biogeochemical processes in terrestrial ecosystems. Humid tropical forest soils are often characterized by fluctuating redox, yet how these dynamics affect patterns of organic matter decomposition and associated CO2 fluxes remains poorly understood. We used a 13C-label incubation experiment in a humid tropical forest soil to follow the decomposition of plant litter and soil organic matter (SOM) in response to four redox regimes—static oxic or anoxic, and two oscillating treatments. We used high-resolution mass spectrometry to characterize the relative composition of organic compound classes in the water extractable OM. CO2 production from litter and SOM showed different responses to redox treatments. While cumulative production of SOM-derived CO2 was positively correlated with the length of oxic exposure (r = 0.89, n = 20), cumulative 13C-litter-derived CO2 production was not linked to oxygen availability. Litter-derived CO2 production was highest under static anoxic conditions in the first half of the experiment, and later dropped to the lowest rate amongst the treatments. In anoxic soils, we observed depletion of more oxidized water-extractable OM (especially amino sugar-, carbohydrate-, and protein-like compounds) over the second half of the experiment, which likely served as substrates for anaerobic CO2 production. Results from two-pool kinetic modeling showed that more frequent anoxic exposure limited decomposition of a slow-cycling C pool, but not a fast-cycling pool. These results suggest that aerobic and anaerobic heterotrophs were equally effective at degrading labile substrates released from fresh plant litter in this humid tropical forest soil, while aerobic decomposers were more effective in breaking down the potentially refractory compounds found in SOM.

Temperature sensitivity of anaerobic CO2 production in soils of Phragmites australis marshes with distinct hydrological characteristics in the Yellow River estuary

Temperature sensitivity (Q10) is important to reveal carbon decomposition responding to climate change. It’s remains limited to understand how Q10 of anaerobic soil organic matter (SOM) decomposition is regulated by soil property in various wetlands with distinct hydrological characteristics. In the present study, samples of soil at the depths of 0–10 cm, 10–20 cm and 20–30 cm were collected in three typical Phragmites australis marshes, including a freshwater marsh (FPa), a no-tidal salt marsh (NTPa) and a tidal salt marsh (TPa), in the Yellow River estuary. The soil samples were incubated at 10 °C, 20 °C and 30 °C, respectively, to determine the rates of anaerobic CO2 production, Q10 values, and their relations to soil properties. Over 70-d incubation, temperature rise significantly increased the mean rates by 70%–136% (from 10 °C to 20 °C) and 64%–142% (from 20 °C to 30 °C) among the marshes, with the mean Q10 values ranging from 1.61 to 2.66. The rates of CO2 production and Q10 values were significantly affected by wetland type and soil depth. Among marshes, the Q10 of the FPa and NTPa soils was higher than that of the TPa soil (for 0–10 cm and 10–20 cm but for 20–30 cm); along soil depths, the Q10 of the top soil was higher than that of the subsoil (for FPa and NTPa but for TPa). Q10 was affected by total organic carbon (TOC), salinity and pH, and the effects were different with marshes. TOC was a main factor regulating Q10 for the freshwater and the no-tidal salt marshes, while salinity and pH were main factors for the tidal salt marsh. The findings highlight an interactive mechanism of soil property and tidal underlying the response of SOM decomposition to temperature change in estuarine wetlands.

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.

Disentangling the effects of methanogen community and environment on peatland greenhouse gas production by a reciprocal transplant experiment

Abstract Northern peatlands consist of a mosaic of peatland types that vary spatially and temporally and differ in their methane (CH4) production. Microbial community composition and environment both potentially control the processes that release carbon from anoxic peat either as CH4 or as carbon dioxide (CO2), a less potent greenhouse gas than CH4. However, the respective roles of these controls remain unclear, which prevents incorporating microbes in the predictions of peatland CH4 emissions. Here, a reciprocal transplant experiment was carried out to separate the influences of microbial community and environment in CH4 and anaerobic CO2 production. Peat from an acidic Sphagnum bog and a sedge fen with higher pH was enclosed in membrane bags with a pore size of 0.2 µm, preventing microbial colonization from the outside, and transplanted in the field for 2 months. Potential CH4 production was primarily controlled by the environment. The conditions in the bog suppressed the initially higher activity of fen methanogens and reduced CH4 production by 79%. Against expectations, the inhibition was not specific to acetate‐using Methanotrichaceae. Reciprocal transplantation favoured Methanosarcinaceae and potentially methylotrophic methanogenesis in general. Bog methanogens, mostly hydrogenotrophic Methanoregulaceae, retained their community structure and activity in the fen with a slight increase (+37%) in CH4 production. Anaerobic CO2 production was controlled by both the microbial community and the environment. Transplantation led to increased CO2 production in both bog (+50%) and fen peat (+57%) with distinct bacterial community, showing that the new environment directed more carbon to other anaerobic processes than methanogenesis. Taken together, these results relate differences in CH4 production of bogs and fens to ecophysiology of specific methanogen groups. The sensitiveness of fen methanogens to the acidic conditions in Sphagnum bogs can help explain the decrease in CH4 emission in the typical boreal peatland succession from young fens to older bogs. Increase in anaerobic CO2 versus CH4 production with transplantation shows that disturbances of boreal peatlands can activate poorly defined pathways of anaerobic decomposition. A free Plain Language Summary can be found within the Supporting Information of this article.

Methanogenic response to long-term permafrost thaw is determined by paleoenvironment.

ABSTRACTMethane production in thawing permafrost can be substantial, yet often evolves after long lag phases or is even lacking. A central question is to which extent the production of methane after permafrost thaw is determined by the initial methanogenic community. We quantified the production of methane relative to carbon dioxide (CO2) and enumerated methanogenic (mcrA) gene copies in long-term (2–7 years) anoxic incubations at 4 °C using interglacial and glacial permafrost samples of Holocene and Pleistocene, including Eemian, origin. Changes in archaeal community composition were determined by sequencing of the archaeal 16S rRNA gene. Long-term thaw stimulated methanogenesis where methanogens initially dominated the archaeal community. Deposits of interstadial and interglacial (Eemian) origin, formed under higher temperatures and precipitation, displayed the greatest response to thaw. At the end of the incubations, a substantial shift in methanogenic community composition and a relative increase in hydrogenotrophic methanogens had occurred except for Eemian deposits in which a high abundance of potential acetoclastic methanogens were present. This study shows that only anaerobic CO2 production but not methane production correlates significantly with carbon and nitrogen content and that the methanogenic response to permafrost thaw is mainly constrained by the paleoenvironmental conditions during soil formation.

Invention of Artificial Rice Field Soil: A Tool to Study the Effect of Soil Components on the Activity and Community of Microorganisms Involved in Anaerobic Organic Matter Decomposition.

Soils are characterized by diverse biotic and abiotic constituents, and this complexity hinders studies on the effects of individual soil components on microorganisms in soil. Although artificial soils have been used to overcome this issue, anoxic soils have not yet been examined. We herein aimed to create artificial soil that reproduces anaerobic methane production by soil from a rice field. Organic materials and mineral particles separated from rice field soil were mixed to prepare an artificial soil matrix; the matrix was added with a small volume of a soil suspension as a microbial inoculum. When the microbial inoculum was added immediately after matrix preparation, anaerobic decomposition was markedly less than that by original soil. When the inoculum was added 9–15 days after soil matrix preparation, anaerobic CO2 and methane production was markedly activated, similar to that by original soil after 40 days of incubation, which suggested that the maturation of the soil matrix was crucial for the reproduction of anaerobic microbial activities. The diversity of the microbial community that developed in artificial soil was markedly less than that in original soil, whereas their predicted functional profiles were similar. Humic substances altered the composition and network patterns of the microbial community. These results suggested that the functional redundancy of soil microorganisms was sustained by different microbial sub-communities. The present study demonstrated that artificial soil is a useful tool for investigating the effects of soil components on microorganisms in anoxic soil.

Response of peat biogeochemistry and soil organic matter quality to rewetting in bogs and spruce swamp forests

Various peatland restoration strategies developed during the last two decades have aimed to stop degradation and bring back the original hydrology, biodiversity and other peatland functions. This study evaluated progress 6–15 years after rewetting in vegetation development, physicochemical properties of peat, soil organic matter (SOM) quality and microbial activity in previously long-term drained bogs and spruce swamp forests (SSF) in comparison with pristine and long-term drained sites in the Bohemian Forest, Czech Republic.Long-term drainage led to overall ecosystem degradation, indicated by a change in vegetation composition, reduced decomposability of peat, with high content of recalcitrant compounds and decreased pH, and reduced soil microbial biomass and activity. The degradation was more pronounced in SSF, while bogs seemed to be relatively resistant to environmental changes caused by drainage. Post-rewetting progress has occurred with regard to vegetation composition, peat pH, microbial biomass and potential anaerobic CO2 and CH4 production, all of which tending towards characteristics of the pristine sites. However, overall SOM quality has not yet responded significantly, indicating that some peat properties and functions, such as C accumulation, need much longer periods of time to return to the original level.

No evidence for trace metal limitation on anaerobic carbon mineralization in three peatland soils

Peatlands store roughly one-third of the terrestrial soil carbon and release the potent greenhouse gas methane (CH4) to the atmosphere, making these wetlands among the most important ecosystems in the global carbon cycle. Despite their importance, the controls of anaerobic decomposition of organic matter to carbon dioxide (CO2) and CH4 within peatlands are not well understood. It is known, however, that the enzymes responsible for CH4 production require cobalt, iron and nickel, and there is a growing appreciation for the potential role of trace metal limitation in anaerobic decomposition. To explore the possibility of trace metal limitation in peatlands, we washed 3 peat soils with either PbCl2, to remove available trace metals, or distilled water. Following these washes, we added trace metals (as CoCl2, CuCl2, FeCl2, PbCl2 and NiCl2) to each soil. We measured anaerobic CH4 and CO2 production in laboratory incubations over 4weeks before adding glucose as a labile carbon source and measuring CH4 and CO2 production for an additional 4weeks. In all 3 soils, neither CH4 nor CO2 production were limited by individual trace metals, even following the wash with PbCl2 to remove available metals. Further, in response to the addition of a labile carbon substrate, all soils supported increased rates of CH4 and CO2 production without progressive trace metal limitation. Taken together, our findings suggest that individual trace metals may not be limiting to anaerobic decomposition in many peatland soils.

The Urgent Compelling Need to Swap on a Global Scale from Indirect Mouse Calorimetry (IMC) Towards Direct Mouse Calorimetry (DMC) in Determining the Basal Metabolic Rate (BMR): A Principle of Proof Study

Mouse models are important in Biomedical- and Life Sciences. Recently it has been stated that the genetically engineered mouse models for contemporary Obesity and/or Type-2 diabetes (DM2) will in most cases deliver heavily metabolically abnormal animals due to changed gut microbiotics with increased anaerobic CO2 production. Therefore, it can be questioned if indirect calorimetry which it at this moment “the golden standard” in all mouse laboratories over the world, still can be practiced because it is dependent on the conversion factor Respiratory-Quotient (RQ-value: CO2/O2) for expressing energy expenditure into Heat production (HP) in [mW]. Direct calorimetry, however, can accurately quantify HP and thus Basal Metabolic Rate (BMR) in both metabolically normal and abnormal states. In this first manuscript we determined physical properties and characteristics of a former aquatic flow-through twin detection Setaram calorimeter used for measuring Basal Metabolic Rate of fish under adverse environmental conditions (anoxic-, hypoxic-, acid- environmental water). Our objective of this study was to determine if this Setaram calorimetric system with stainless steel vessel of 1 liter could be used in the physical medium air in order to measure energy expenditure in mouse models. This first [Technical note] describes the physical properties and characteristics in the medium water and air of this calorimetric set up. Characteristics of the calorimetric system in air were for the initial baseline over 80 minutes a heat flow of 13.44 ± 1.611 (mW) and for the end baseline over 175 minutes 14.95 ± 1.79 (mW) so the A¢ÂˆÂ†-Baseline (initial –end) was 13.44-14.95 = -1.51 (mW). The drifting baseline over the total experiment of 33h was (14.95 / 13.44) * 100% = 1.1124% with a drifting baseline per hour was 0.035 % per hour which are common values for twin detection Calvin calorimeters. We calculated based on the heat transfer characteristics from water to stainless steel (aquatic calorimeter) in combination with the specific heat capacity of water Cp-water of 4,1884 [kJ K-1] vs Cp-air is 0.001293 [kJ K-1] an aquatic time-constant τwater of 30.48 min vs τair or = 0.019605 min. Because the τair was so small deconvolution techniques (earlier successfully applied in water), correcting for the lag time of the system had no effect. This study also includes the first successful “principle of proof” pilot-experiment with one single mouse locked up for ≈ 14 h proves that measuring the energy expenditure with a single mouse in the 1 liter stainless steel calorimetric vessel in the medium air corresponds to measured values of wild strain mouse used in indirect calorimetry (IMC) (of ≈10 mW/g). A precondition was that in order to prevent suffocating of the mouse in the one liter vessel both vessel (Measurement and Reference: twin detection measurement were supplied with one liter of air per minute- with this former aquatic flow-through twin detection Setaram calorimeter. Although there is in Bio-calorimetry a switch to cell-, (sub)cellular, molecular and biomolecular interactions, this study with “whole animal” calorimetry proves that at the organismal level important fundamental questions are still unanswered and open related to the pathogenesis of human diseases like Obesity and metabolic related disorders like Type-2 Diabetes and more fundamental Life Sciences related processes like ‘ageing’. In addition, also the research area of nutraceuticals can be tested with DMC.

A pan-Arctic synthesis of CH4 and CO2 production from anoxic soil incubations.

Permafrost thaw can alter the soil environment through changes in soil moisture, frequently resulting in soil saturation, a shift to anaerobic decomposition, and changes in the plant community. These changes, along with thawing of previously frozen organic material, can alter the form and magnitude of greenhouse gas production from permafrost ecosystems. We synthesized existing methane (CH4 ) and carbon dioxide (CO2 ) production measurements from anaerobic incubations of boreal and tundra soils from the geographic permafrost region to evaluate large-scale controls of anaerobic CO2 and CH4 production and compare the relative importance of landscape-level factors (e.g., vegetation type and landscape position), soil properties (e.g., pH, depth, and soil type), and soil environmental conditions (e.g., temperature and relative water table position). We found fivefold higher maximum CH4 production per gram soil carbon from organic soils than mineral soils. Maximum CH4 production from soils in the active layer (ground that thaws and refreezes annually) was nearly four times that of permafrost per gram soil carbon, and CH4 production per gram soil carbon was two times greater from sites without permafrost than sites with permafrost. Maximum CH4 and median anaerobic CO2 production decreased with depth, while CO2 :CH4 production increased with depth. Maximum CH4 production was highest in soils with herbaceous vegetation and soils that were either consistently or periodically inundated. This synthesis identifies the need to consider biome, landscape position, and vascular/moss vegetation types when modeling CH4 production in permafrost ecosystems and suggests the need for longer-term anaerobic incubations to fully capture CH4 dynamics. Our results demonstrate that as climate warms in arctic and boreal regions, rates of anaerobic CO2 and CH4 production will increase, not only as a result of increased temperature, but also from shifts in vegetation and increased ground saturation that will accompany permafrost thaw.

Linking tree species identity to anaerobic microbial activity in a forested wetland soil via leaf litter decomposition and leaf carbon fractions

Our aim was to examine the linkage between tree species and anaerobic microbial activity in a forested wetland. If plant species have a unique influence on soil microorganisms, then knowing plant species identity has tremendous potential to predict rates of microbial activity belowground. We expected the linkage to occur via leaf litter decay rate and differences in leaf litter carbon (C) fractions. We used leaf litter from 10 tree species (angiosperm and gymnosperm, deciduous and evergreen) and soil from a forested wetland in New York State. We quantified leaf litter decay on the soil surface and correlated variation in rates with leaf mass per area (LMA) and several C fractions. We extracted water-soluble compounds from green leaves and leaf litter and tested their ability to fuel anaerobic carbon dioxide (CO2) production and methane (CH4) production. We also added leaf litter directly to soil to examine how the residue might influence anaerobic microbial activity. Leaf decay rates exhibited a negative linear relationship with LMA. Variations in rates of soil methane (CH4) production were species specific and greater with gymnosperms (mean = 8.6 μmol g−1 d−1) than angiosperms (mean = 3.7 μmol g−1 d−1). Rates of anaerobic CO2 production were less affected by plant species. Pectin and hemicellulose in leaf litter was particularly conducive to anaerobic decomposition and CH4 production. The influence of plant species on soil microbial activity will become clearer when we can better quantify leaf C fractions and understand the decomposability of each fraction in relationship to others.

Conifer litter identity regulates anaerobic microbial activity in wetland soils via variation in leaf litter chemical composition

Plant litter is a crucial source of energy and nutrients for soil microorganisms, and thus plant species identity may help account for variation in rates of soil microbial activity via species dependent differences in litter chemistry. This may be particularly important in forested wetlands where the composition of conifer tree species can vary. We explored the relationship between conifer litter identity and anaerobic microbial activity by adding fresh needle litter from nine conifer species to soils from two contrasting forested wetlands and quantifying rates of anaerobic respiration (CO2 production) and methanogenesis (CH4 production). We characterized litter chemistry as the amounts of structural polysaccharides and polymers (cellulose, hemicellulose, pectin, lignin) and examined changes in these fractions during incubation. Litter from Pinus species supported the largest rates of CH4 production, whereas litter from Picea species supported the lowest rates. Litter from two deciduous conifers (Metasequoia, Larix) supported intermediate rates of CH4 production. Tree species identity had less impact on rates of anaerobic CO2 production. Rates of CH4 production correlated with hemicellulose and with covalently bonded pectin, whereas rates of anaerobic CO2 production showed a positive correlation with initial acid-detergent lignin concentration and with pectin. Gaining a better understanding of how hemicellulose and pectin in decomposing plant litter promote anaerobic microbial activity, especially specialized methanogenesis in soil provides insight that links plant litter identity and leaf traits to anaerobic microbial activity in the underlying soil.

Stoichiometry and temperature sensitivity of methanogenesis and CO2 production from saturated polygonal tundra in Barrow, Alaska.

Arctic permafrost ecosystems store ~50% of global belowground carbon (C) that is vulnerable to increased microbial degradation with warmer active layer temperatures and thawing of the near surface permafrost. We used anoxic laboratory incubations to estimate anaerobic CO2 production and methanogenesis in active layer (organic and mineral soil horizons) and permafrost samples from center, ridge and trough positions of water-saturated low-centered polygon in Barrow Environmental Observatory, Barrow AK, USA. Methane (CH4 ) and CO2 production rates and concentrations were determined at -2, +4, or +8 °C for 60 day incubation period. Temporal dynamics of CO2 production and methanogenesis at -2 °C showed evidence of fundamentally different mechanisms of substrate limitation and inhibited microbial growth at soil water freezing points compared to warmer temperatures. Nonlinear regression better modeled the initial rates and estimates of Q10 values for CO2 that showed higher sensitivity in the organic-rich soils of polygon center and trough than the relatively drier ridge soils. Methanogenesis generally exhibited a lag phase in the mineral soils that was significantly longer at -2 °C in all horizons. Such discontinuity in CH4 production between -2 °C and the elevated temperatures (+4 and +8 °C) indicated the insufficient representation of methanogenesis on the basis of Q10 values estimated from both linear and nonlinear models. Production rates for both CH4 and CO2 were substantially higher in organic horizons (20% to 40% wt. C) at all temperatures relative to mineral horizons (<20% wt. C). Permafrost horizon (~12% wt. C) produced ~5-fold less CO2 than the active layer and negligible CH4 . High concentrations of initial exchangeable Fe(II) and increasing accumulation rates signified the role of iron as terminal electron acceptors for anaerobic C degradation in the mineral horizons.