Q10 Values Research Articles

Challenging Popular Belief, Mosquito Larvae Breathe Underwater.

Immature mosquitoes are thought to breathe only atmospheric air through their siphons despite reports of prolonged submerged survival. We studied the survival of last-instar larvae of Aedes aegypti fully submerged at different temperatures and measured the oxygen consumption from air and water-dissolved larvae and pupae of this species under different conditions. Larvae survived much longer than expected, reaching 50% mortality only after 58, 10, and 5 days at 15°, 25°, and 35 °C, respectively. Larval to pupa molt was only observed in larvae with access to air, whereas individuals kept submerged never molted. Although most of the oxygen was obtained from the air, larvae obtained 12.72% of their oxygen from the water, while pupae took only 5.32%. In both media, temperature affected the respiration rate of the larvae, with relatively close Q10 values (1.56 and 1.83 for water and air, respectively). A similar pattern of O2 consumption was observed in Ae. albopictus, whose larvae obtained 12.14% of their oxygen from the water. The detailed quantification of oxygen consumption by mosquito larvae showed that water-dissolved oxygen is not negligible and physiologically relevant, challenging the idea that mosquito larvae only breathe atmospheric oxygen.

Activation Energy, Temperature Coefficient and Q10 Value Estimations of the Growth of an SDS-degrading Bacterium

This research delves into how temperature affects the growth rates of bacteria in relation to the breakdown of sodium dodecyl sulfate (SDS) by types of microbes. A graph resembling a Chevron pattern, which plots the growth rate against temperature (1/T), revealed a change at 32.19 °C, indicating a crucial temperature for optimizing bacterial growth. Through regression analysis, activation energies were determined to be 65.10±10.83 kJ/mol for temperatures between 20 30°C and 36.31±0.97 kJ/mol for temperatures between 35 45°C showing that metabolic demands are higher at temperatures. The theta value was calculated to be 1.06, which closely aligns with known values for processes hinting at moderate temperature sensitivity. These results highlight the impact of temperature on microbial metabolic efficiency, requiring energy at lower temperatures due to increased enzyme activity demands while operating more efficiently at higher temperatures with lower energy needs. This study emphasizes incorporating temperature-related factors like Q10 and theta values into models that predict bioremediation strategies. Understanding these dynamics can improve the success of bioremediation efforts by ensuring breakdown in diverse environmental conditions. The insights gained from this research can inform management practices. Advance the development of biotechnological applications sensitive to temperature variations.

Disentangle the drivers of soil organic carbon mineralization and their temperature sensitivity in both topsoil and subsoil: Implication of thermal stability and chemical composition

Information about the temperature dependence of soil organic carbon (SOC) mineralization is important to predict the possible carbon (C) release from the terrestrial ecosystem facing global warming. However, the way in which SOC quality and mineral protection of SOC affects mineralization rates and their response to increasing temperature remains poorly understood. Here, we focused on investigating thermal stability and chemical composition of soils which differed greatly with the type and extent of organo-mineral associations, and revealing their implications for SOC mineralization. Chemical composition and thermal stability of SOC were analyzed with 13C nuclear magnetic resonance spectroscopy (13C NMR) and simultaneous thermogravimeteric analysis and differential scanning calorimetry (TG-DSC), respectively. Soil mineralization and its temperature sensitivity (Q10) were assessed by incubating soils at 15 and 25 °C for 90 days.Our results showed that SOC of subsoil was more biologically stable, but exhibited higher temperature sensitivity than those of topsoil. Significant differences in chemical composition and thermal stability of SOC were detected across soils developed from four parent materials but not between two soil layers, and indicators obtained from the two techniques showed apparent associations with depth-specific SOC mineralization rates. Increase in SOC mineralization rates at two incubation temperatures and two soil layers were observed when the soils were characterized by higher percentage of labile SOC fractions (i.e., O-alkyl C and organic carbon oxidized during exothermic reactions). The Q10 values of topsoil were positively and mostly related to the percentage of Alkyl C. In addition to notable relationships with chemical composition, the Q10 values of subsoil were positively correlated with Exo1/Exo2 ratios and Energy density values, and negatively correlated with TG-50. It was interesting to note that thermal stability was possibly as a function of soil texture and total oxides. Results from VPA analysis further revealed that SOC mineralization rates at two soil layers and Q10 of topsoil were mainly driven by SOC quality, while it was related to both SOC quality and chemical protection for subsoil, implying that factors controlling the temperature sensitivity of SOC mineralization were depth-specific. Altogether, substrate accessibility as a function of chemical composition and chemical protection would play vital role in determining the feedbacks of the subsoil SOC pool to the future climate warming.

Seasonal Dynamics of Soil Respiration and Its Autotrophic and Heterotrophic Components in Subtropical Camphor Forests

On a global scale, soil respiration (Rs), representing the CO2 flux between the soil surface and the atmosphere, ranks as the second-largest terrestrial carbon (C) flux. Understanding the dynamics between Rs and its autotrophic (Ra) and heterotrophic (Rh) components is necessary for accurately evaluating and predicting global C balance and net ecosystem production under environmental change. In this study, we conducted a two-year root exclusion experiment in subtropical China’s Camphor (Cinnamomum camphora (L.) Presl.) forests to assess seasonal changes in Ra and Rh and their relative contributions to Rs. Additionally, we examined the influence of environmental factors on the dynamics of Ra, Rh, and Rs. Our results showed that seasonal mean Rs values were 2.88 µmol m−2 s−1, with mean Ra and Rh of 1.21 and 1.67 µmol m−2 s−1, respectively, in the studied forests. On an annual basis, the annual values of mean Rs in the studied forests were 405 ± 219 g C m−2 year−1, with Rh and Ra accounting for 240 ± 120 and 164 ± 102 g C m−2 year−1, respectively. The seasonal mean ratio of Rh to Rs (Rh/Rs) was 58%, varying from 45 to 81%. Seasonal changes in Rs and Rh were strongly correlated with soil temperature but not soil water content. Both Rh and Rs increased exponentially with the average soil temperature measured in the topsoil layer (about 5 cm), with Q10 values of 2.02 and 1.73 for Rh and Rs, respectively. Our results suggest that the composition and activity of soil microbes and fauna play a primary role in releasing carbon flux from soil to the atmosphere in the studied forest ecosystems.

A kinetic study on carrot juice treated by dielectric barrier discharge (DBD) cold plasma during storage

This study aimed to investigate the efficacy of DBD cold plasma (CP) on carrot juice quality maintenance and develop suitable shelf life models based on carotenoid degradation and total mesophilic bacteria (TMB) growth. The physicochemical, microbial, and sensory properties of carrot juice treated with CP (8, 10, and 12 kV for 3 min) and heat (80 °C for 7 min) were evaluated during storage at 4 °C for 21 days. Results showed carrot juice treatment with the lowest voltage (8 kV) better preserved the physicochemical properties (ascorbic acid and total phenol), color changes, microbial growth, and sensory deterioration. The temperature effect on TMB growth was modeled using the Baranyi and Roberts model, followed by the Arrhenius and square root models. The Q10 and activation energy (Ea) values of TMB growth were higher than those for carotenoid degradation, proposing that bacterial growth could be a more reliable marker in the self life prediction of carrot juice treated by DBD cold plasma.

Contrasting impacts of plastic film mulching and nitrogen fertilization on soil organic matter turnover

Plastic film mulching and nitrogen (N) fertilization are two important field management practices used to increase crop yields in rain-fed agriculture in arid and semi-arid areas. These two practices, however, can have opposing effects on soil organic carbon (SOC) stock and turnover. To clarify and analyze the combined effects of these practices, we conducted a 7-year continuous maize cultivation experiment with four treatments: (1) no plastic film mulching without N fertilization (Control), (2) plastic film mulching without N fertilization (PFM), (3) N fertilization without plastic film mulching (N), and (4) plastic film mulching with N fertilization (PFM + N). The 13C natural abundance of in the light and heavy fractions of organic carbon (LFOC and HFOC) was used to differentiate “old” (>7 years) and “new” (<7 years) C in the soil after C3 to C4 vegetation change. PFM increased soil temperature and moisture content over 7 years and led to a 150 % and 108 % increase in the above-ground and root biomass of maize, respectively. Hot and wet conditions under PFM accelerated the decomposition of both labile C (i.e., LFOC) and persistent C (i.e., HFOC), as measured by CO2 efflux from the soil. PFM decreased the LFOC and HFOC pools due to the fast decomposition of “old” C and inadequate stabilization of “new” C. Furthermore, PFM accelerated HFOC decomposition to a greater extent than that of LFOC. The Q10 values of SOC decomposition remained similar both in the presence and absence of PFM. Nitrogen fertilization increased the aboveground and root biomass of maize by 54 % and 40 %, respectively. In the control soil, microorganisms decomposed organic N owing to limited availability of mineral N and in the absence of any from replenishment by fertilizer N. Thus, the increase in LFOC content under N fertilization, was primarily attributed to the reduced decomposition of “old” C. The use of N fertilization produced a similar HFOC content as that of the control soil, while also accelerating the decomposition of “old” C and promoting the stabilization of “new” C, resulting in a faster turnover rate. Consequently, the impact of N fertilization on SOC turnover was negligible owing to the contrasting effects on LFOC and HFOC. The application of N fertilization resulted in a reduction of the Q10 value as compared to control. The combination of PFM and N fertilization accelerated the decomposition of HFOC and SOC, while having absent effect on SOC, labile C and persistent C contents. This indicates that 7 years weren’t long enough to trigger a response to the combination of PFM and N fertilization from SOC and HFOC contents. In summary, PFM led to a decline in the SOC content by accelerating the decomposition of both LFOC and HFOC. Conversely, N fertilization maintained SOC content by inhibiting LFOC decomposition and enhancing HFOC decomposition.

Temperature sensitivity of methanogenesis and anaerobic methane oxidation in thermokarst lakes modulated by surrounding vegetation on the Qinghai-Tibet Plateau

Understanding the balance between methane (CH4) production (methanogenesis) and its oxidation is important for predicting carbon emissions from thermokarst lakes under global warming. However, the response of thermokarst lake methanogenesis and the anaerobic oxidation of methane (AOM) to warming, especially from Qinghai-Tibetan Plateau (QTP), is still not quantified. In this study, sediments were collected from 11 thermokarst lakes on the QTP. These lakes are surrounded with different vegetation types, including alpine desert (AD), alpine steppe (AS), alpine meadow (AM) and alpine swamp meadow (ASM). The results showed that methanogenesis and AOM rates exponentially increased with temperature, while the temperature sensitivity (Q10, average Q10 values of methanogenesis and AOM were 0.69–30 and 0.54–16.9 respectively) of methanogenesis were larger than AOM, but not significant, showing a similar temperature dependence of methanogenesis and AOM in thermokarst lake sediments. Thermokarst lake sediments in the ASM had higher methanogenesis and anaerobic oxidation potential, matching its higher NDVI and relative abundances of methanogens and SBM (syntrophic bacteria with methanogens). Although the thermokarst lake sediments AOM depleted 15 %–27.8 % of the total CH4 production, the AOM rate was lower than methanogenesis in thermokarst lake sediments, it did not offset increased CH4 production under anaerobic conditions. The increase in CH4 production in thermokarst lake sediments will likely lead to higher emissions within a warming world. These findings indicate that methanogenesis and AOM in thermokarst lake sediments are sensitive to climate change. Models should consider the Q10 values of methanogenesis and AOM and vegetation types when predicting carbon cycle in thermokarst lakes under global warming.

Divergent seasonal patterns and drivers of soil respiration in alpine forests of northwestern China

Uncertainty about winter carbon (C) fluxes and their drivers hinders the accurate estimation of C budgets in high-latitude and high-altitude ecosystems. We conducted 3-year-long field observations of soil respiration (Rs) in an alpine forest in northwestern China. The results showed that the mean winter Rs ranged from 193.79 to 233.03 g C m−2 year−1 and significantly increased with elevation, while the mean growing season Rs ranged from 467.29 to 711.25 g C m−2 year−1 and significantly decreased with elevation. The ratio of winter to annual soil CO2 emissions ranged from 21.96 to 34.24 %. The Q10 value (temperature sensitivity of Rs) also varied seasonally, with significantly higher values in winter (3.00–3.85) than in the growing season (2.08–2.22). During the growing season, the Rs was directly regulated by soil temperature (ST), fine root biomass, and microbial activity and indirectly regulated by nitrate nitrogen via an increase in fine root biomass and microbial activity. In addition to the direct effects of soil moisture (SM), ST, and the ratio of fungi to bacteria (F/B) on winter Rs, we revealed another effect: the indirect effect on Rs of the interaction of ST with SM (decreasing ST and increasing SM) with elevation by reducing the soil aggregate stability, probably improving the organic substrate availability, and decreasing the F/B. The ST was the most important factor affecting the growing season Rs, and SM had the greatest effect on the winter Rs. Overall, our findings indicated that the patterns and underlying mechanisms of Rs dynamics in alpine forests in winter are different from those in the growing season and that research on winter Rs dynamics in alpine forests under future climate conditions is needed due to the greater temperature response of Rs in winter than in the growing season.

The long-term effects of thinning on soil respiration vary with season in subalpine spruce plantations

Thinning is a principal silvicultural practice in temperate plantations with potential impacts on soil respiration (Rs). However, most of the existing measurements of Rs dynamics after thinning have been performed during the growing season, while those in the nongrowing season have been seldom determined, even though recent evidence demonstrates that the nongrowing season Rs occupied a considerable proportion of the annual carbon (C) budgets in temperate forests. Here, we investigated the long-term (17 years) impacts of thinning on Rs in middle-aged subalpine spruce plantations in northwestern China. We found that thinning significantly (p < 0.001) increased Rs from 3.00 to 4.18 μmol m−2 s−1 in the growing season while significantly (p < 0.001) decreasing Rs from 1.05 to 0.90 μmol m−2 s−1 in the nongrowing season; additionally, thinning had no significant (p = 0.0989) effect on the Q10 value (temperature sensitivity of Rs) in the growing season, with values ranging from 2.10 to 2.44, while it significantly (p < 0.01) increased the Q10 value from 2.91 to 3.48 in the nongrowing season. In the growing season, increased nitrate nitrogen due to elevated soil moisture (SM) played a fundamental role in stimulating Rs by improving microbial biomass (MB) and fine root biomass, and increased soil temperature (ST) also contributed to the increases in MB and Rs. However, these variables and pathways were not applicable in the nongrowing season, when decreased dissolved organic C induced by decreased ST explained most of the decline in MB and Rs. Our results revealed that the long-term effects of thinning on the nongrowing season Rs were completely different from those in the growing seasons in subalpine spruce plantations. Furthermore, the greatly increased Q10 value in the nongrowing season indicated that a substantial increase in Rs can be expected in subalpine forests after thinning due to nongrowing season warming at high altitudes.

A novel approach for ecosystem respiration simulation in drylands

Terrestrial ecosystem respiration (Reco) in drylands (arid and semi-arid areas) contributes to the largest uncertainty of the global carbon cycle. Here, using the Reco data from 24 sites (98 site-years) in drylands from Fluxnet and corresponding MODIS remote sensing products, we develop a novel semi-empirical, yet physiologically-based remote sensing model: the ILEP_Reco model (a Reco model derived from ILEP, the acronym for “integrated LE and EVI proxy”). This model can simulate Reco observations across most biomes in drylands with a small margin of error (R2 = 0.56, RMSE = 1.12 gCm−2d−1, EF = 0.46, MBE = −0.06 gCm−2d−1) and performs significantly better than the previous model: Ensemble_all. The seasonal variation of Reco in drylands can be well simulated by the ILEP_Reco model. When we relate ILEP to the Q10 model, the corresponding ILEP_Q10 values in all 98 site-years distribute quite convergently, which greatly facilitates fixing the ILEP_Q10 value as a constant in different site-years. The spatial variation of Reco in drylands is then defined as reference respiration at the annual mean ILEP, which can be easily and powerfully simulated by the ILEP_Reco model. These results help us understand the spatial-temporal variations of Reco in drylands and thus will shed light on the carbon budget on a regional scale, or even a global one.

Effect of temperature and Q10 values of acid phosphatase activity in alfisols and vertisols of Andhra Pradesh

The enzyme phosphatase plays an important role in the mineralization of organically bound P that leads to absorption of P by the plants. Phosphatases are inducible enzymes that are produced predominantly under conditions of low phosphorus availability. The abiotic enzymes present in the soil play an important role in catalyzing several important reactions necessary for the life processes of microorganisms in soils and thereby stabilizing the soil structure, the decomposition of organic wastes, organic matter formation, and nutrient cycling. When the temperatures are increased due to various changes caused by global warming it has a profound influence on soil enzymes. Every enzyme has its optimum temperature below which the enzyme activity is less due to inactivation. Further, with an increase in temperature the enzymes get denatured and result in a decrease in nutrient availability and indirectly affecting productivity. To study the effect of temperature on soil enzyme activity, four alfisols and four vertisols were collected and labortory incubation studies were carried out at different temperatures ranging from 20oC to 90oC. The acid phosphatase activity (µg of 4-nitrophenol g-1 soil h-1) ranged from 62.3 to 516.4 in alfisols while in vertisols the activity varied from 35.1 to 486.0. Temperature coefficient values (Q10) were calculated in the temperature range of 20 to 90oC. These values depending on the type of soil varied from 0.42 to 1.91 in alfisols and 0.36 to 1.95 in vertisols.

Temperature Sensitivity of Soil Respiration in Grasslands in Temperate Continental Climate Zone: Analysis of 25-Year-Long Monitoring Data

Field observations of soil respiration (SR) in different types of terrestrial ecosystems are very relevant because of high temporal and spatial variations of SR rate. The intra-annual dynamics of SR is mainly determined by the changes in hydrothermal conditions during the year and is often described with temperature sensitivity coefficient (Q10), which usually has a fixed value in many of the used models. This study is focused on the assessment of seasonal and interannual dynamics of SR temperature sensitivity in two grasslands in the southern Moscow oblast (temperate continental climate) based on continuous 25-year-long all-year-round measurements of CO2 emission from soils. The grasslands have been formed on two different soil types: sandy soddy-podbur (Entic Podzol (Arenic)) and gray loamy soil (Haplic Luvisol (Loamic)). The SR rate has been continuously measured from December 1997 to November 2022 with an interval of 7–10 days using the technique of closed static chambers. The temperature sensitivity of SR, estimated from the entire set of data, is higher in Haplic Luvisol as compared with Entic Podzol (3.47 vs. 2.59). The Q10 values for SR in both soils are 1.2–1.4-fold lower in dry years as compared with wet years. The interannual variation of Q10 values in grassland ecosystems amounts to 21–36% depending on the considered temperature range. A statistically significant positive correlation between the Q10 values in the temperature range ≥1°С and wetness indices is observable in both grasslands. A differentiated approach integrating different values of temperature coefficients for SR into the used models is necessary to improve the predictions of C budget in ecosystems.

Temperature Sensitivity of Soil Respiration in Grasslands under the Temperate Continental Climate Zone: Analysis of 25-Year Monitoring Data

Field observations of soil respiration (SR) in different types of terrestrial ecosystems seem to be very relevant, since the SR rate is characterized by high temporal and spatial variability. The intra-annual dynamics of SR is determined mainly by the change in hydrothermal conditions during the year and is often described using a temperature sensitivity coefficient (Q10), which usually has a fixed value in many of the models used. The aim of this study was to assess the seasonal and interannual dynamics of SR temperature sensitivity in two grasslands in the southern part of Moscow region (temperate continental climate) based on continuous 25-year year-round measurements of CO2 emissions from soils. Grasslands were formed on two different types of soils: soddy-podbur sandy soil (Entic Podzol (Arenic)) and gray loamy soil (Haplic Luvisol (Loamic)). The SR rate was measured continuously from December 1997 to November 2022 with an interval of 7–10 days using the closed static chamber method. The temperature sensitivity of SR, estimated from the entire set of data, had higher values on Haplic Luvisol compared to Entic Podzol (3.47 vs 2.59). The values of Q10 for SR in both types of soils in dry years were 1.2–1.4 times lower than in years with a normal moisture level. The interannual variability of Q10 values in grassland ecosystems was 21–36%, depending on the temperature range that was taken into account. A significant positive correlation between Q10 values in the temperature range ≥1°С and humidity indices was found in both grasslands. To obtain more accurate forecasts of the C balance in ecosystems, a differentiated approach should be applied by integrating different values of temperature coefficients for SR into the models.

A geostatistical approach to estimate flow duration curve parameters in ungauged basins

Flow duration curve represents the percentage of time that a river flow is equal to or greater. As these curves provide a direct response to the behavior of water resources in a basin, which is used widely in hydropower projects, it is important to predict flow duration curves in no metering basins, named “ungagged basins.” The geostatistical approach to predict the values of these curves in non-measured stations shows the expansion of the range of studies in this topic. The aim of this study is to predict the flow duration curve over long periods of time in a basin with ungauged regions using probability kriging, inverse distance weighting (IDW) and maximum likelihood (ML) methods. Flow data from 38 flow measuring stations in the Dez Basin were used to map different discharges of the flow duration curve, and as a result, in order to complete their values, zone and quantify them, three different values of Q10, Q50 and Q90 of the flow duration curve acquired. The results show that as the flow rate increases (or the time percentage decreases), the amount of computational error increases and in all cases, the probability kriging method has a smaller error (0.96) than the IDW (1.65) and ML (1.15) methods.

Impact of temperature on the performance of compost-based landfill biocovers

Methane (CH4) emissions from landfills are a major contributor to global greenhouse gas emissions. Compost-based biocovers offer a viable approach to reduce CH4 emissions from landfills; however, the effectiveness in climates with varying temperatures is not well understood. The methane removal performances of two compost-based biocover materials (food and yard waste compost) were examined under different temperature conditions using laboratory column experiments. A reactive transport model was used to simulate the experimental results to develop a better quantitative understanding of the effect of temperature on overall methane removal efficiency. As expected, experimental results indicated that the oxidation rate was influenced by temperature, as it was reduced when the temperature decreased from 22 °C to 8 °C. However, some oxidation was observed at a lower temperature, which was confirmed by CO2 concentrations above the initial level and the observed temperatures above the exposure temperature along the height of biocover column. Furthermore, results showed that when the compost-based materials were subjected to 8 °C and then increased to 22 °C, methane oxidation within the material recovered quickly and returned to similar oxidation rates as observed before the temperature was reduced, suggesting that compost-based biocovers may not be affected by cyclic temperature variations when used in colder climates. Methane oxidation capacity was limited by the maximum oxidation rate, the biocover porosity, and the gas saturation profile that affects residence time and overall methane oxidation in the columns. The model results show that the CH4 oxidation rate was reduced by one order of magnitude when the temperature decreased from 22 °C to 8 °C. Therefore, the calculated Q10 values were 4.19 and 5.18 for the food and yard waste compost, respectively. Overall, compost-based landfill biocovers, such as food and yard waste compost, are capable of mitigate CH4 emissions from old and small landfills under different temperature conditions.

Linking soil dissolved organic matter characteristics and the temperature sensitivity of soil organic carbon decomposition in the riparian zone of the Three Gorges Reservoir

Soil dissolved organic matter (DOM) is highly sensitive to external interference. However, little attention has been paid on how soil DOM characteristics in the dry period affect the warming response of soil organic carbon (SOC) decomposition in riparian ecosystems under flooding conditions. The temperature sensitivity (Q10) of SOC decomposition was determined by incubating 99 riparian soils under flooding across 11 transects of the Three Gorges Reservoir. Soil DOM characteristics in the dry period were measured by ultraviolet–visible spectroscopy (i.e., a254, a350, SUVA254 and SR) and 3D-fluorescence spectroscopy (such as FI, β:α, BIX, and HIX). The fluorescence components of C1, C3, and C4 were determined by parallel factor analysis. SOC decomposition was sensitive to warming with a higher Q10 value for CH4 (2.34 ± 1.30) and lower for CO2 (1.37 ± 0.23) under flooding. The soil DOM in dry period was mainly autochthonous with FI > 1.9 and 90% of BIX > 0.7. The humification of soil DOM was relatively weak at ∼ 95% of HIX < 0.8. The Q10 value of CO2 was positively correlated with Ln (SUVA254) and Ln (HIX) whereas negatively correlated with Ln (DOC), Ln (a254), and Ln (a350). The Q10 of CH4 was positively related to Ln (HIX), while on the contrary, negatively related to Ln (C4). These variations in Q10 were mainly driven by the aromaticity and humification degree of DOM. Out of all DOM characteristics, the lignin component was the key predictor of the Q10 variation. Overall, findings of this study indicate that soil DOM characteristics in dry period are closely linked with the response of SOC decomposition to warming during the reservoir impoundment.

Osmo-respiratory compromise in the mosshead sculpin (Clinocottus globiceps): effects of temperature, hypoxia, and re-oxygenation on rates of diffusive water flux and oxygen uptake.

In nature, mosshead sculpins (Clinocottus globiceps) are challenged by fluctuations in temperature and oxygen levels in their environment. However, it is unclear how mosshead sculpins modulate the permeability of their branchial epithelia to water and O2 in response to temperature or hypoxia stress. Acute decrease in temperature from 13 to 6 oC reduced diffusive water flux rate by 22% and ṀO2 by 51%, whereas acute increase in temperature from 13 to 25 oC increased diffusive water flux rate by 217% and ṀO2 by 140%, yielding overall Q10 values of 2.08 and 2.47 respectively. Acute reductions in oxygen tension from >95% to 20% or 10% air saturation did not impact diffusive water flux rates, however, ṀO2 was reduced significantly by 36% and 65% respectively. During 1-h or 3-h recovery periods diffusive water flux rates were depressed while ṀO2 exhibited overshoots beyond the normoxic control level. Many responses differed from those seen in our parallel earlier study on the tidepool sculpin, a cottid with similar hypoxia tolerance but much smaller gill area that occupies a similar environment. Overall, our data suggest that during temperature stress, diffusive water flux rates and ṀO2 follow the traditional osmo-respiratory compromise pattern, but during hypoxia and re-oxygenation stress, diffusive water flux rates are decoupled from ṀO2.

Seasonal Variation of Emission Fluxes of CO2, CH4, and N2O from Different Larch Forests in the Daxing’An Mountains of China

Using a static chamber-gas chromatography method, we investigate the characteristics of soil CO2, CH4, and N2O fluxes and their relationships with environmental factors during the growing season in four typical Larix gmelinii forests (moss–Larix gmelinii forest, Ledum palustre–Larix gmelinii forest, herbage–Larix gmelinii forest, and Rhododendron dauricum–Larix gmelinii forest) in the Greater Khingan Mountains. Our results show that all four forest types are sources of CO2 emissions, with similar average emission fluxes (146.71 mg·m−2 h−1–211.81 mg·m−2 h−1) and no significant differences. The soil in the moss–Larix gmelinii forest emitted CH4 (43.78 μg·m−2 h−1), while all other forest types acted as CH4 sinks (−56.02 μg·m−2 h−1–−28.07 μg·m−2 h−1). Although all forest types showed N2O uptake at the beginning of the growing season, the N2O fluxes (4.03 μg·m−2 h−1–5.74 μg·m−2 h−1) did not differ significantly among the four forest types for the entire growing season, and all acted as sources of N2O emissions. The fluxes of CO2, CH4, and N2O were significantly correlated with soil temperature and soil pH for all four forest types. Multiple regression analysis shows that considering the interactive effects of soil temperature and moisture could better explain the changes in greenhouse gas emissions among different forest types. The average Q10 value (8.81) of the moss–Larix gmelinii forest is significantly higher than that of the other three forest types (3.16–3.54) (p &lt; 0.05), indicating that the soil respiration in this forest type is more sensitive to temperature changes.

Temperature and soil moisture control CO2 flux and CH4 oxidation in urban ecosystems

Climate-driven shifts in soil temperature and soil moisture are crucial factors that control the ecosystem-atmosphere greenhouse gas (GHG) balance. In the present study, the relationship between CO2, CH4 fluxes and soil moisture content and temperature sensitivity was examined in three dominating types of urban ecosystems: grassland, city park and arable land. The analysis was based on the field measurements at biweekly intervals over a year using a static closed chamber method in Wroclaw urban area, Poland. The observed patterns of land-atmosphere CO2 and CH4 exchange varied across land cover types and were strongly influenced by seasonal variations in temperature and soil water content. Emission of CO2 from grassland and the city park was two times higher than from the arable land. The calculated CH4 oxidation rate was one and half times higher (p < 0.05) under grassland and the city park as compared to arable land.The estimated Q10 values ranged between 1.68 and 1.79 for CO2 and from 1.26 to 1.49 for CH4, depending on the ecosystem type. The temperature sensitivity of soil respiration decreased when the temperature was above 24.5 °C across the moisture gradient from 20 to 25 % m/v. Results suggest that despite the urban areas with agricultural land use revealed the lowest CO2 fluxes compared to grassland and city park, the former showed the lowest seasonal mean CH4 oxidation. This indicates that with ongoing warming, the higher Q10 of CO2 production vs. CH4 oxidation will further shift the carbon balance towards the source and this shift will be especially critical for arable lands in urban areas.

CO2 and CH4 fluxes from forest soil in the northern Da Xing’anling Mountains in Northeast China during the freezing and thawing periods of near-surface soil in 2018–2019

ABSTRACT Under a warming climate, the studies on effects of seasonal freeze–thaw cycles on soil respiration are key to understanding the soil carbon cycles and ecosystem responses and resilience at mid- and high latitudes. In this study, the effluxes of soil surface CO2 and absorption rates of CH4 were measured in the Xing'an larch (Larix gmelinii) forest in the northern Da Xing’anling Mountains, Northeast China using an automatic multichannel soil greenhouse gas measurement system (dynamic gas chamber method) during the periods of October–November 2018 and April–May 2019. The results showed that during the freezing period of near-surface soil, CO2 and CH4 fluxes significantly declined, approaching zero, at the end of November. During the thawing period of near-surface soil, CO2 and CH4 fluxes from surface soil fluctuated markedly at first and then rose rapidly. The respective Q10 values of 3.86 and 4.89 during the freezing and thawing periods of near-surface soil, respectively, indicate the important role of ground freeze–thaw cycles in the modifications of CO2 and CH4 fluxes. The results of this study could help assess the stability of the soil carbon pool and carbon flux strength in taiga-forested permafrost regions in the northern Da Xing’anling Mountains, Northeast China.