High Q10 Values Research Articles

Diurnal and seasonal variations in carbon dioxide exchange in ecosystems in the Zhangye oasis area, Northwest China.

Quantifying carbon dioxide exchange and understanding the response of key environmental factors in various ecosystems are critical to understanding regional carbon budgets and ecosystem behaviors. For this study, CO2 fluxes were measured in a variety of ecosystems with an eddy covariance observation matrix between June 2012 and September 2012 in the Zhangye oasis area of Northwest China. The results show distinct diurnal variations in the CO2 fluxes in vegetable field, orchard, wetland, and maize cropland. Diurnal variations of CO2 fluxes were not obvious, and their values approached zero in the sandy desert, desert steppe, and Gobi ecosystems. Additionally, daily variations in the Gross Primary Production (GPP), Ecosystem Respiration (Reco) and Net Ecosystem Exchange (NEE) were not obvious in the sandy desert, desert steppe, and Gobi ecosystems. In contrast, the distributions of the GPP, Reco, and NEE show significant daily variations, that are closely related to the development of vegetation in the maize, wetland, orchard, and vegetable field ecosystems. All of the ecosystems are characterized by their carbon absorption during the observation period. The ability to absorb CO2 differed significantly among the tested ecosystems. We also used the Michaelis-Menten equation and exponential curve fitting methods to analyze the impact of Photosynthetically Active Radiation (PAR) on the daytime CO2 flux and impact of air temperature on Reco at night. The results show that PAR is the dominant factor in controlling photosynthesis with limited solar radiation, and daytime CO2 assimilation increases rapidly with PAR. Additionally, the carbon assimilation rate was found to increase slowly with high solar radiation. The light response parameters changed with each growth stage for all of the vegetation types, and higher light response values were observed during months or stages when the plants grew quickly. Light saturation points are different for different species. Nighttime Reco increases exponentially with air temperature. High Q10 values were observed when the vegetation coverage was relatively low, and low Q10 values occurred when the vegetables grew vigorously.

Substantial net N mineralization during the dormant season in temperate forest soils

AbstractIn temperate forest soils, N net mineralization has been extensively investigated during the growing season, whereas N cycling during winter was barely addressed. Here, we quantified net ammonification and nitrification during the dormant season by in situ and laboratory incubations in soils of a temperate European beech and a Norway spruce forest. Further, we compared temperature dependency of N net mineralization in in situ field incubations with those from laboratory incubations at controlled temperatures. From November to April, in situ N net mineralization of the organic and upper mineral horizons amounted to 10.9 kg N (ha · 6 months)–1 in the spruce soil and to 44.3 kg N (ha · 6 months)–1 in the beech soil, representing 65% (beech) and 26% (spruce) of the annual above ground litterfall. N net mineralization was largest in the Oi/Oe horizon and lowest in the A and EA horizons. Net nitrification in the beech soil [1.5 kg N (ha · 6 months)–1] was less than in the spruce soil [5.9 kg N (ha · 6 months)–1]. In the range of soil temperatures observed in the field (0–8°C), the temperature dependency of N net mineralization was generally high for both soils and more pronounced in the laboratory incubations than in the in situ incubations. We suggest that homogenization of laboratory samples increased substrate availability and, thus, enhanced the temperature response of N net mineralization. In temperate forest soils, N net mineralization during the dormant season contributes substantially to the annual N cycling, especially in deciduous sites with large amounts of litterfall immediately before the dormant season. High Q10 values of N net mineralization at low temperatures suggest a huge effect of future increasing winter temperature on the N cycle in temperate forests.

Temperature sensitivity of soil carbon mineralization and nitrous oxide emission in different ecosystems along a mountain wetland-forest ecotone in the continuous permafrost of Northeast China

Soil organic matter decomposition under global warming has a potential to alter soil carbon and nitrogen storages in permafrost. The objectives of this study were to investigate the temperature sensitivity of greenhouse gas emissions from soil samples along a mountain wetland-forest ecotone in the continuous permafrost and determine its influencing mechanisms. The CO2, N2O and carbon, nitrogen substrates were measured at 5, 15 and 25°C. The relation between greenhouse gas emission rates and temperature depended on substrate quality in the three ecosystems. Soil DOC, MBC, NH4+ and NO3− concentrations determined the higher CO2 and N2O emission rates in the thicket peatland and the surface soil layer. During the incubation period, the degrees of soil carbon and nitrogen losses in the thicket peatland were 0.6–4.7% and 1.0–14.3 (1000×%), approximately 1.6 and 1.2 times higher than those in the forest and fen, respectively. The highest degrees of soil carbon and nitrogen losses in the thicket peatland indicated that more greenhouse gases would emit from soils when permafrost degradation induced the succession from wetlands or forest to the wetland-forest ecotone. Although the gas emission rates presented significant differences in the three ecosystems, the Q10 values with 2.0 to 2.2 for CO2 and 2.4 to 3.0 for N2O, did not change significantly, indicating that the temperature sensitivity of gas emissions would not fluctuate much in the ecosystems along the mountain wetland-forest ecotone. However, the higher Q10 values in the deeper soil layer in our study indicated that the decomposition of soil C and N in the deeper active layer of the permafrost region is more impressionable to global warming. As laboratory results could not actually reflect the situation in the field, more field work about temperature sensitivity of soil organic matter decomposition in different ecosystems should be encouraged in the future.

Characterization of the temperature-sensitive reaction of F1-ATPase by using single-molecule manipulation.

F1-ATPase (F1) is a rotary motor protein that couples ATP hydrolysis to mechanical rotation with high efficiency. In our recent study, we observed a highly temperature-sensitive (TS) step in the reaction catalyzed by a thermophilic F1 that was characterized by a rate constant remarkably sensitive to temperature and had a Q10 factor of 6–19. Since reactions with high Q10 values are considered to involve large conformational changes, we speculated that the TS reaction plays a key role in the rotation of F1. To clarify the role of the TS reaction, in this study, we conducted a stall and release experiment using magnetic tweezers, and assessed the torque generated during the TS reaction. The results indicate that the TS reaction generates the same amount of rotational torque as does ATP binding, but more than that generated during ATP hydrolysis. Thus, we confirmed that the TS reaction contributes significantly to the rotation of F1.

Foliar respiration and its temperature sensitivity in trees and lianas: in situ measurements in the upper canopy of a tropical forest

Leaf dark respiration (R) and its temperature sensitivity are essential for efforts to model carbon fluxes in tropical forests under current and future temperature regimes, but insufficient data exist to generalize patterns of R in species-rich tropical forests. Here, we tested the hypothesis that R and its temperature sensitivity (expressed as Q10, the proportional increase in R with a 10 °C rise in temperature) vary in relation to leaf functional traits, and among plant functional types (PFTs). We conducted in situ measurements of R of 461 leaves of 26 species of tree and liana in the upper canopy of a tropical forest in Panama. A construction crane allowed repeated non-destructive access to measure leaves kept in the dark since the previous night and equilibrated to the ambient temperature of 23-31 °C in the morning. R at 25 °C (R25) varied among species (mean 1.11 μmol m(-2) s(-1); range 0.72-1.79 μmol m(-2) s(-1)) but did not differ significantly among PFTs. R25 correlated positively with photosynthetic capacity, leaf mass per unit area, concentrations of nitrogen and phosphorus, and negatively with leaf lifespan. Q10 estimated for each species was on average higher than the 2.0 often assumed in coupled climate-vegetation models (mean 2.19; range 1.24-3.66). Early-successional tree species had higher Q10 values than other functional types, but interspecific variation in Q10 values was not correlated with other leaf traits. Similarity in respiration characteristics across PFTs, and relatively strong correlations of R with other leaf functional traits offer potential for trait-based vegetation modeling in species-rich tropical forests.

Temperature and Moisture Effects on Microbial Biomass and Soil Organic Matter Mineralization

Concern over climate change has stimulated interest in the temperature and moisture dependence of soil organic matter decomposition. In particular, there has been intense debate in relation to the factors that determine the temperature dependence of C mineralization. We examined temperature and moisture responses of C and N mineralization in an 85‐d laboratory incubation (factorial combination of four temperatures [5, 12, 18, 25°C] and five moisture treatments [matric potential from −5 to −1200 kPa]) using three agriculturally important New Zealand soils (soils with a history of pasture, arable, or vegetable cropping). Mineralization was linearly related to gravimetric moisture content, except in the high‐C pasture soil where O2 supply apparently limited mineralization at high (25°C) temperature–moisture combinations. Temperature responses were adequately described by a Q10 function (Q10 values for C mineralization ranged 1.9–2.8). The pool of mineralizable C, estimated using a first‐order kinetic model, increased as temperature and moisture increased, whereas the rate constant did not show a consistent trend with either temperature or moisture. Part of the C mineralized during the incubation was from the microbial biomass (post‐incubation biomass C decreased by an average of 0.22–0.31 mg kg−1 for each 1 mg kg−1 CO2–C evolved). Microbial biomass C (MBC) was particularly sensitive to temperature (post‐incubation biomass C decreased 18–35% between 5–25°C). The decline in MBC between 5 and 12°C represented an average of 40% of the C mineralization increase in that temperature interval. Between 18 and 25°C, the decline in MBC was equivalent to only 20% (on average) of the C mineralized in that temperature interval. High Q10 values reported in laboratory incubations at low temperature may be partly due to mineralization of microbial C.

Metabolic Thermal Sensitivity Optimizes Sea Krait Amphibious Physiology

Abstract Yellow-lipped Sea Kraits (Laticauda colubrina) are tropical amphibious snakes that divide their time between land and sea. When moving between habitats, the kraits experience rapid and sometimes extreme shifts in body temperature that can have profound metabolic effects. We quantified cutaneous and pulmonary oxygen uptake in sea kraits from Hoga Island, southeast Sulawesi, Indonesia, at temperatures commonly encountered in aquatic (27.6°C) and aerial (35.2°C) habitats. Total oxygen uptake rate was 49.14 mL Kg−1 h−1 at 27.6°C and 115.27 mL Kg−1 h−1 at 35.2°C. Pulmonary and cutaneous uptake rates were 44.58 and 104.70, and 4.56 and 10.57 mL Kg−1 h−1, at 27.6 and 35.2°C, respectively. Sea kraits had a temperature coefficient (Q10) of approximately 3, suggesting that metabolic rates triple with every 10°C temperature increase. High Q10 values may minimize time on land by increasing digestion and nutrient absorption rates as well as promoting faster healing and injury recovery times. Cooler reef tempe...

The effect of temperature on mitochondrial respiration in permeabilized cardiac fibres from the freshwater turtle, Trachemys scripta

Ectothermic animals regularly experience fluctuations in body temperature, which have profound effects on biochemical and metabolic processes. To cope with cold environments, the freshwater turtle, Trachemys scripta, exhibits inverse thermal compensation, where physiological processes exhibit exaggerated Q10 effects and are actively downregulated to limit energy requirements. The present study aimed to identify potential sites of temperature sensitivity in mitochondria from the turtle heart. The effect of acute temperature change on ADP sensitivity and respiratory flux through different components of the electron transport chain (Complexes I, II and IV) was analysed in permeabilized cardiac fibres from the turtle ventricle. An acute decrease in temperature significantly reduced the acceptor control ratio and maximum respiration rate (ṀO2) through all complexes of the electron transport chain. Calculated Q10 values for ṀO2across the three experimental temperatures tested (5, 13 and 21°C) were in the range of 1.19–3.65, and although there was a tendency for exaggerated Q10 values in the lower temperature range (5–13°C), there were no significant differences in Q10 between any temperatures or complexes examined. These results suggest the large-scale reductions in turtle cardiac function and high Q10 values at acutely low temperatures are likely due to a reduction in energy demand (contractile function), rather than supply (mitochondrial respiration).

Seasonal acclimation in metabolism reduces light requirements of eelgrass (Zostera marina)

We investigated the ability of eelgrass (Zostera marina) to adjust light requirements to seasonal changes in temperature, light and nutrient conditions through changes in metabolism, pigment and nutrient content. In agreement with expectations we found that rates of respiration and light saturated photosynthesis of summer acclimated plants peaked at higher temperatures (5°C and 2°C higher, respectively), and were lower than of winter acclimated plants, both at sub- and supra-optimal temperatures. Moreover respiration rates were generally more sensitive to increasing temperatures than photosynthetic rates, especially so for cold acclimated plants in February (36% higher Q10-values). These changes were accompanied by a reduction in chlorophyll a and nitrogen concentrations in leaves by 35% and 60% respectively from February to August. The critical light requirement (EC) of Z. marina to maintain a positive carbon balance increased exponentially with increasing temperature but less so for summer-acclimated than for winter-acclimated plants. However, combining EC vs temperature models for whole-plants with data on daily light availability showed that seasonal acclimation in metabolism increased the annual period, when light requirements were meet at the 2–5m depth interval, by 32–66days. Hence, acclimation is an important mechanism allowing eelgrass to grow faster and penetrate to deeper waters. Critical depth limits estimated for different combinations of summer temperatures and water clarity in a future climate scenario, suggested that expected increases in temperature and nutrient run-off have synergistic negative effects, especially in clear waters, stressing the importance of continued efforts to improve water clarity of coastal waters.

Comparison of Soil CO2 Efflux from a Secondary Forest and Tea Plantations in Taiwan

Soil CO2 efflux, soil temperatures, and soil water content of 2 stands in a secondary forest, with differing canopy openness, and 2 tea plantations, one actively cropped and the other abandoned for 2 yr, in Taiwan were measured monthly from June 2004 to July 2005. The first objective of this study was to quantify and compare soil CO2 efflux of the 4 stands. The second objective was to examine the relationship of environmental conditions, specially soil temperature and soil water contents, with soil CO2 efflux of the forest and tea plantations. Seasonal patterns were found in soil CO2 efflux and soil temperature but not in soil water content. The magnitude of the soil CO2 efflux varied from 1 to 3.5 μmol m^(-2)s^(-1) and from 0.5 to 5.0 μmol m^(-2)s^(-1) in the secondary forest and tea plantations, respectively. Within stands, seasonal changes in soil respiration were most highly correlated with soil temperature. The highest Q10 value, the factor by which the respiration rate differs for a temperature interval of 10℃, of 2.92 occurred in the actively cropped tea stand, the lowest of 1.83 was calculated for the open forest stand, and intermediate values of 1.94 and 1.98 were found in the dense forest stand and abandoned tea stand, respectively. The results indicate that among the 4 stands, the soil CO2 efflux of the actively cropped tea stand was most sensitive to changes in soil temperature.

Exponential growth of “snow molds” at sub-zero temperatures: an explanation for high beneath-snow respiration rates and Q 10 values

Numerous studies have demonstrated exceptionally high temperature sensitivity of the beneath-snow respiratory flux in cold-winter ecosystems. The most common, but still untested, explanation for this high sensitivity is a physical one based on the observation that water availability in soils increases exponentially as soils warm from −3 to 0°C. Here, we present evidence for a biological hypothesis to explain exponential kinetics and high Q10 values as beneath-snow soils warm from −3 to 0°C during the early spring in a high-elevation subalpine forest. First, we show that some of the dominant organisms of the beneath-snow microbial community, “snow molds”, exhibit robust exponential growth at temperatures from −3 to −0.3°C. Second, Q10 values based on growth rates across the temperature range of −2 to −0.3°C for these snow molds vary from 22 to 330. Third, we derive an analytical equation that combines the relative contributions of microbial growth and microbial metabolism to the temperature sensitivity of respiration. Finally, we use this equation to show that with only moderate snow mold growth (several generations), the combined sensitivities of growth and metabolism to small changes in beneath-snow soil temperature, create a double exponential in the Q10 function that may explain the extremely high (~1 × 106) Q10 values observed in past studies. Our biological explanation for high Q10 levels is supported by several independent studies that have demonstrated build up of microbial biomass under the snow as temperatures warm from −2 to 0°C.

Stem CO<sub>2</sub> efflux of a Populus nigra stand: effects of elevated CO<sub>2</sub>, fertilization, and shoot size

To determine whether long-term growth in elevated atmospheric CO2 concentration [CO2] and nitrogen fertilization affects woody tissue CO2 efflux, we measured stem CO2 efflux as a function of temperature in three different size classes of shoots of Populus nigra L. (clone Jean Pourtet) on two occasions in 2004. Trees were growing in a short rotation coppice in ambient (370 µmol mol−1) and elevated (550 µmol mol−1, realised by a Free Air Carbon dioxide Enrichment system) [CO2], and measurements were performed during the third growing season of the second rotation. Elevated CO2 did not affect Q10 or specific stem CO2 efflux (E10) of overall poplar shoots. The lack of any effect of N on stem CO2 efflux indicated that nutrients were sufficient. Specific stem CO2 efflux differed significantly between shoot sizes, emphasizing the importance of tree size when scaling-up respiration measurements to the stand level. Variation in stem CO2 efflux could not be satisfactorily explained by temperature as the only driving variable. We hypothesize that transport of CO2 with the sapflow might have confounded our results and could explain the high Q10 values reported here. Predicting the respiratory carbon loss in a future elevated [CO2] world must therefore move beyond the single-factor temperature dependent respiration model and involve multiple factors affecting stem CO2 efflux rate.

The effect of temperature on the energy budget of the Manila clam, Ruditapes philippinarum

In this study, the energy budget of the Manila clam, Ruditapes philippinarum, was evaluated after one-week acclimation periods at 5, 10, 15, 20, and 25°C. Small clams (151 ± 12 mg DW) and large clams (353 ± 16 mg DW) were fed with the microalgae, Isochrysis galbana. Filtration rate, ingestion rate, assimilation efficiency, oxygen-consumption rate, and ammonia excretion rate were measured. Both filtration rate and ingestion rate of small and large clams were found to be related to temperature. The highest Q10 values were measured in the range 15–20°C for both small and large clams. Assimilation efficiency of both small and large clams was not significantly influenced by temperature, although the maximum mean values were detected at 20°C. Oxygen consumption rate and ammonia excretion rate of small and large clams were found to be related directly to temperature over the entire range, with a maximum being detected at 25°C. The highest Q10 value was estimated in the range 10–15°C with regard to oxygen consumption rate, and in the range of 15–20°C with regard to ammonia excretion rate. Scope for growth (SFG) was positive at all temperatures, achieving a maximum value at 20°C in both small and large clams, primarily as a consequence of the enhanced ingestion rate which offset the concomitant elevation in the metabolic rate. In this study we have estimated the thermal optimum for this species at 20°C.

Delayed arm regeneration in the Antarctic brittle star Ophionotus victoriae

We describe the levels of natural arm damage in the Antarctic brittle star Ophionotus victoriae and the rate of arm regeneration over the period of 1 yr, as measured in our aquarium facil- ities at Rothera Point, West Antarctic Peninsula. The natural incidence of arm damage in O. victoriae is high (97% of individuals examined). The rate of regeneration was 0.44 mm wk -1 , which is slow, but within the range of data from temperate brittle stars and also in line with data from the literature showing a general trend of decreasing arm regeneration rate with temperature. The Q10 for arm regeneration rate of 2.6 across brittle stars is within the expected biological range. However, O. victo- riae arm regeneration experiences a lag phase of up to 5 mo before reproducible amounts of new tissue are produced. Such a long lag phase has not been documented for any other brittle star species and produces a range of Q10 values from 3.6 (when compared to the slowest documented lag phase for a temperate brittle star) to exceptionally high Q10 values of 14.9 and 15.4 (when either fastest or average regeneration times are considered for temperate brittle stars and this Antarctic species). This indicates that the initial process of arm regeneration in O. victoriae is either different to that of other brittle stars or it is dependent on factors other than the effects of temperature on enzyme-mediated biochemical reactions, such as gonadal cycles and seasonality.

Temperature acclimation of growth, photosynthesis and respiration in two mesophilic phytoplankton species

P.A. Staehr and M.J. Birkeland. 2006. Temperature acclimation of growth, photosynthesis and respiration in two mesophilic phytoplankton species. Phycologia 45: 648–656. DOI: 10.2216/06-04.1Temperature acclimation in two mesophilic microalgae, Microcystis aeruginosa (Cyanobacteriales) and Scenedesmus acutus (Chlorococcales), was studied by measuring growth rate, photosynthesis, respiration, cell size, cellular pigment content and Chl a-specific light absorption. Phytoplankton were grown as nutrient-replete semicontinuous cultures for 2 weeks at 5, 15 and 25°C, during which growth rate was determined from changes in Chl a. Gross photosynthesis (GP) was measured as 14C assimilation at saturating light and respiration (R) was measured as O2 uptake along a temperature gradient from 0 to 40°C. Net photosynthesis (NP) was determined as the difference between GP and R. For both species, acclimation to increasing growth temperatures resulted in increasing growth rate, cellular pigment content and decreasing cell size and Chl a-specific light absorption. Scenedesmus acutus and M. aeruginosa showed the same overall pattern of metabolic acclimation to increasing temperatures: (1) overall higher GP and NP but lower R; (2) increasing optimum temperatures for GP, NP and R and (3) higher metabolic rates at supraoptimal temperatures. Microcystis aeruginosa showed several warm-loving traits. It was more sensitive to increasing temperatures (higher Q10 values), had higher metabolic rates and optimum temperatures and performed better at high incubation temperatures than S. acutus did. This study shows that phytoplankton have a considerable and rapid ability to adjust cellular physiology, metabolism and growth to relatively large changes in growth temperature. This suggests a significant ability to acclimate to increasing temperatures associated with forthcoming climate changes.

Active and passive components in the length-dependent stiffness of tracheal smooth muscle during isotonic shortening.

Contraction of smooth muscle tissue involves interactions between active and passive structures within the cells and in the extracellular matrix. This study focused on a defined mechanical behavior (shortening-dependent stiffness) of canine tracheal smooth muscle tissues to evaluate active and passive contributions to tissue behavior. Two approaches were used. In one, mechanical measurements were made over a range of temperatures to identify those functions whose temperature sensitivity (Q(10)) identified them as either active or passive. Isotonic shortening velocity and rate of isometric force development had high Q(10) values (2.54 and 2.13, respectively); isometric stiffness showed Q(10) values near unity. The shape of the curve relating stiffness to isotonic shortening lengths was unchanged by temperature. In the other approach, muscle contractility was reduced by applying a sudden shortening step during the rise of isometric tension. Control contractions began with the muscle at the stepped length so that properties were measured over comparable length ranges. Under isometric conditions, redeveloped isometric force was reduced, but the ratio between force and stiffness did not change. Under isotonic conditions beginning during force redevelopment at the stepped length, initial shortening velocity and the extent of shortening were reduced, whereas the rate of relaxation was increased. The shape of the curve relating stiffness to isotonic shortening lengths was unchanged, despite the step-induced changes in muscle contractility. Both sets of findings were analyzed in the context of a quasi-structural model describing the shortening-dependent stiffness of lightly loaded tracheal muscle strips.

The Response of Soil Processes to Climate Change: Results from Manipulation Studies of Shrublands Across an Environmental Gradient

Predicted changes in climate may affect key soil processes such as respiration and net nitrogen (N) mineralization and thus key ecosystem functions such as carbon (C) storage and nutrient availability. To identify the sensitivity of shrubland soils to predicted climate changes, we have carried out experimental manipulations involving ecosystem warming and prolonged summer drought in ericaceous shrublands across a European climate gradient. We used retractable covers to create artificial nighttime warming and prolonged summer drought to 20-m2 experimental plots. Combining the data from across the environmental gradient with the results from the manipulation experiments provides evidence for strong climate controls on soil respiration, net N mineralization and nitrification, and litter decomposition. Trends of 0%–19% increases of soil respiration in response to warming and decreases of 3%–29% in response to drought were observed. Across the environmental gradient and below soil temperatures of 20°C at a depth of 5–10 cm, a mean Q10 of 4.1 in respiration rates was observed although this varied from 2.4 to 7.0 between sites. Highest Q10 values were observed in Spain and the UK and were therefore not correlated with soil temperature. A trend of increased accumulated surface litter mass loss was observed with experimental warming (2%– 22%) but there was no consistent response to experimental drought. In contrast to soil respiration and decomposition, variability in net N mineralization was best explained by soil moisture rather than temperature. When water was neither limiting or in excess, a Q10 of 1.5 was observed for net N mineralization rates. These data suggest that key soil processes will be differentially affected by predicted changes in rainfall pattern and temperature and the net effect on ecosystem functioning will be difficult to predict without a greater understanding of the controls underlying the sensitivity of soils to climate variables.

Environmental factors influencing attenuation of methane and hydrochlorofluorocarbons in landfill cover soils.

The influence of different environmental factors on methane oxidation and degradation of hydrochlorofluorocarbons (HCFCs) was investigated in microcosms containing soil sampled at Skellingsted Landfill, Denmark. The soil showed a high capacity for methane oxidation resulting in a maximum oxidation rate of 104 microg CH4 g(-1) h(-1) and a low affinity of methane with a half-saturation constant of 2.0% v/v. The hydrochlorofluorocarbons HCFC-21 (dichlorofluoromethane) and HCFC-22 (chlorodifluoromethane) were rapidly oxidized and the oxidation occurred in parallel with the oxidation of methane. The maximal HCFC oxidation rates were 0.95 and 0.68 microg g(-1) h(-1) for HCFC-21 and HCFC-22, respectively. Increasing concentrations of HCFCs resulted in decreased methane oxidation rates. However, compared with typical concentrations in landfill gas, relatively high HCFC concentrations were needed to obtain a significant inhibition of methane oxidation. In general, the environmental factors studied influenced the degradation of HCFCs in almost the same way as they influenced methane oxidation. Temperature had a strong influence on the methanotrophic activity giving high Q10 values of 3.4 to 4.1 over the temperature range of 2 to 25 degrees C. Temperature optimum was around 30 degrees C; however, oxidation occurred at temperatures as low as 2 degrees C. A moisture content of 25% w/w yielded the maximum oxidation rate as it allowed good gas transport together with sufficient microbial activity. The optimum pH was around neutrality (pH = 6.5-7.5) showing that the methanotrophs were optimally adapted to the in situ pH, which was 6.9. Copper showed no inhibitory effect when added in relatively high concentrations (up to 60 mg kg(-1)), most likely due to sorption of copper ions to soil particles. At higher copper concentrations the oxidation rates decreased. The oxidation rates for methane, HCFC-21, and HCFC-22 were unaltered in ammonium-amended soil up to 14 mg kg(-1). Higher ammonium concentrations inhibited the oxidation process. The most important parameters controlling oxidation in landfill cover soil were found to be temperature, soil moisture, and methane and oxygen supply.

Environmental Factors Influencing Attenuation of Methane and Hydrochlorofluorocarbons in Landfill Cover Soils

The influence of different environmental factors on methane oxidation and degradation of hydrochlorofluorocarbons (HCFCs) was investigated in microcosms containing soil sampled at Skellingsted Landfill, Denmark. The soil showed a high capacity for methane oxidation resulting in a maximum oxidation rate of 104 μg CH4 g−1 h−1 and a low affinity of methane with a half-saturation constant of 2.0% v/v. The hydrochlorofluorocarbons HCFC-21 (dichlorofluoromethane) and HCFC-22 (chlorodifluoromethane) were rapidly oxidized and the oxidation occurred in parallel with the oxidation of methane. The maximal HCFC oxidation rates were 0.95 and 0.68 μg g−1 h−1 for HCFC-21 and HCFC-22, respectively. Increasing concentrations of HCFCs resulted in decreased methane oxidation rates. However, compared with typical concentrations in landfill gas, relatively high HCFC concentrations were needed to obtain a significant inhibition of methane oxidation. In general, the environmental factors studied influenced the degradation of HCFCs in almost the same way as they influenced methane oxidation. Temperature had a strong influence on the methanotrophic activity giving high Q10 values of 3.4 to 4.1 over the temperature range of 2 to 25°C. Temperature optimum was around 30°C; however, oxidation occurred at temperatures as low as 2°C. A moisture content of 25% w/w yielded the maximum oxidation rate as it allowed good gas transport together with sufficient microbial activity. The optimum pH was around neutrality (pH = 6.5–7.5) showing that the methanotrophs were optimally adapted to the in situ pH, which was 6.9. Copper showed no inhibitory effect when added in relatively high concentrations (up to 60 mg kg−1), most likely due to sorption of copper ions to soil particles. At higher copper concentrations the oxidation rates decreased. The oxidation rates for methane, HCFC-21, and HCFC-22 were unaltered in ammonium-amended soil up to 14 mg kg−1 Higher ammonium concentrations inhibited the oxidation process. The most important parameters controlling oxidation in landfill cover soil were found to be temperature, soil moisture, and methane and oxygen supply.

Metabolic cold adaptation in arthropods: a smaller‐scale perspective

Metabolic cold adaptation in arthropods: a smaller‐scale perspective