Q10 Factor Research Articles

Linking Biogeochemical and Hydrodynamic Processes to Model Methane Fluxes in Shallow, Tropical Floodplain Lakes

AbstractFloodplains lakes are abundant in the Amazon basin and are important methane sources to the atmosphere. Existing biogeochemical models require modifications and inclusion of hydrodynamic processes operative in shallow, warm waters to be applied to these aquatic ecosystems. We modified a 1‐dimensional process‐based, lake biogeochemical model and combined a 3‐dimensional hydrodynamic model to suit Amazon floodplains. We evaluated the combined model's performance simulating methane concentrations and fluxes and several related processes in the open lake and an embayment of a well‐studied Amazon lake. Parameters for calibration were selected through sensitivity tests using a machine learning‐based algorithm, classification, and regression trees. Comparison between simulated and measured fluxes indicate generally good agreement in seasonal patterns and magnitudes. Comparisons of near‐surface concentrations varied with no clear patterns. Simulations of methane concentrations at near‐surface and near‐bottom, and diffusive emissions are most sensitive to carbon mineralization rate, Q10 factors for methanogenesis and oxidation, and methane oxidation potential. Modeled rates of planktonic photosynthesis were generally lower than measurements, though simulated planktonic respiration was often similar to measurements. Simulated rates of methane oxidation were considerably lower, with a few exceptions, than measurements of methane oxidation in oxic water of the lake. Improvements of results of the linked hydrodynamic‐biogeochemical model will result from inclusion of advective transport, use of parameter values appropriate for tropical waters, especially for methane oxidation and photosynthesis, and addition of changes in hydrostatic pressure to model of ebullition.

The Stability of Phenolic Compounds in Fruit, Berry, and Vegetable Purees Based on Accelerated Shelf-Life Testing Methodology.

Evaluating the stability of polyphenols in fruit, berry, and vegetable purees helps to assess the quality of these products during storage. This study aimed to (1) monitor the stability of total phenolic content (TPC) in four-grain puree with banana and blueberry (FGBB), mango-carrot-sea buckthorn puree (MCB), and fruit and yogurt puree with biscuit (FYB); (2) study the effect of aluminum-layered vs. aluminum-free packaging on the changes in TPC; and (3) assess the suitability of accelerated shelf-life testing (ASLT) methodology to evaluate the stability of polyphenols. The samples were stored at 23 °C for 182, 274, 365, and 427 days. The corresponding time points during ASLT at 40 °C were 28, 42, 56, and 66 days, calculated using Q10 = 3. The TPC was determined with Folin-Ciocalteu method. The results revealed that the biggest decrease in TPC took place with high-pH FGBB, which contained fewer ingredients with bioactive compounds. Minor changes were seen in FYB and MCB, which had lower pH values, and contained a larger amount of ingredients that include polyphenols. In addition, the choice of packaging material did not affect the TPC decrease in each puree. Finally, it was concluded that the ASLT methodology is suitable for studying the TPC changes in such purees, but the corresponding Q10 factors may vary and should be determined based on the chemical profile and ingredient list of the product.

Investigating the effect of replacing the antioxidants Ascorbyl palmitate and tocopherol instead of TBHQ on the shelf life of sunflower oil using temperature accelerated method

In this study, D-alpha-tocopherol and Ascorbyl palmitate antioxidants were used in sunflower oil instead of TBHQ, and the effect of these antioxidants on the shelf-life factor was determined. The Rancimat stability of sunflower oil samples with different concentrations of D-alpha-tocopherol and Ascorbyl palmitate was evaluated. The results showed that the samples containing 200 ppm of Ascorbyl palmitate along with 100 ppm of D-alpha-tocopherol have the highest Rancimat resistance. This indicates the synergistic effect of the combination of D-alpha-tocopherol with Ascorbyl palmitate, which has better stability than the individual effect of each of them. To quantitatively and accurately the shelf life of the product, the accelerated temperature method (ASLT) was chosen and the progress of the oxidation reaction was determined by peroxide value (PV), anisidine index, and the amount of free fatty acids (FFA) at temperatures of 40, 80, and 110 °C for samples A, B, and C. By obtaining the retention time through the Arrhenius equation and determining the Q10 factor, the shelf life of the product was limited to 628.48 h when the peroxide reached the set limit. The results showed the presence of antioxidants Ascorbyl palmitate and tocopherol was comparable to TBHQ and had a similar increasing trend.

Anthropogenic nitrate attenuation versus nitrous oxide release from a woodchip bioreactor

Nitrogen loss via overland flow from agricultural land use is a global threat to waterways. On-farm denitrifying woodchip bioreactors can mitigate NO3− exports by increasing denitrification capacity. However, denitrification in sub-optimal conditions releases the greenhouse gas nitrous oxide (N2O), swapping the pollution from aquatic to atmospheric reservoirs. Here, we assess NO3−-N removal and N2O emissions from a new edge-of-field surface-flow bioreactor during ten rain events on intensive farming land. Nitrate removal rates (NRR) varied between 5.4 and 76.2 g NO3−-N m−3 wetted woodchip d−1 with a mean of 30.3 ± 7.3 g NO3−-N m−3. The nitrate removal efficiency (NRE) was ∼73% in ideal hydrological conditions and ∼18% in non-ideal conditions. The fraction of NO3−-N converted to N2O (rN2O) in the bioreactor was ∼3.3 fold lower than the expected 0.75% IPCC emission factor. We update the global bioreactor estimated Q10 (NRR increase every 10 °C) from a recent meta-analysis with previously unavailable data to >20 °C, yielding a new global Q10 factor of 3.1. Mean N2O CO2-eq emissions (431.9 ± 125.4 g CO2-eq emissions day−1) indicate that the bioreactor was not significantly swapping aquatic NO3− for N2O pollution. Our estimated NO3−-N removal from the bioreactor (9.9 kg NO3−-N ha−1 yr−1) costs US$13.14 per kg NO3−-N removed and represents ∼30% NO3−-N removal when incorporating all flow and overflow events. Overall, edge-of-field surface-flow bioreactors seem to be a cost-effective solution to reduce NO3−-N runoff with minor pollution swapping to N2O.

Sensory Shelf Life Estimation of Novel Fortified Blended Foods Under Accelerated and Real-Time Storage Conditions.

Fortified blended foods (FBFs), a staple of food aid around the world, must maintain desirable characteristics for long periods of storage. This study estimated the shelf life of FBFs, including a traditional FBF (nonextruded corn soy blend plus [CSB+]) and 13 novel extrusion cooked FBFs. All products were stored under accelerated and real-time environments (real time = 30 °C and 65% relative humidity [RH], accelerated = 50 °C and 70% RH based on a Q10 factor of 2). Products were made into porridges and evaluated by a descriptive sensory panel for five times in each shelf life condition. Rancid and painty sensory characteristics were key determining factors for shelf life. Real-time (RT) and accelerated shelf life (ASL) testing agreed that most novel extrusion cooked FBFs had shelf lives of at least 2 years, which is comparable to current CSB+. However, ASL testing failed to predict RT shelf life of two novel FBFs, which were estimated by RT testing to have a 2+ year shelf life. The results indicated that novel extrusion cooked FBFs have high potential for use as alternative complementary food and maintain quality for long storage periods. It is essential to conduct RT testing parallel with ASLT testing, especially for new products, to obtain a more precise estimation of products' shelf life. PRACTICAL APPLICATION: These findings show that extrusion cooked novel fortified blended foods made with extrusion generally can last up to or exceeding 24 months at ambient conditions as measured either real-time or under accelerated conditions. This is plenty of time for storage, shipping, distribution, and home storage of such products by recipients. Thus, there should be no concerns about shelf life of these products for international distribution.

Kinetic parameters of lipid oxidation in third generation (3G) snacks and its influence on shelf-life

Abstract In food systems, lipid oxidation is one of the most important factors affecting food quality, nutrition, safety, color and consumer acceptance. The objective of this study was to determine the kinetic parameters of lipid oxidation and its influence in the shelf life of third generation (3G) snacks stored in three types of packaging (polyethylene, polypropylene + Kraft paper, and polyethylene + polypropylene) at 25 °C and 40 °C. The peroxide value was the quality parameter selected and monitored for a 60 day period using a spectrophotometric technique. Based on the Arrhenius equation and activated complex theory, reaction rate constants (k), activation energies (Ea), Q10 factors, activation enthalpies (∆H‡), and activation entropies (∆S‡ ) for oxidative stability in 3G snacks were calculated. Results showed that oxidation phenomena can occur in the 3G snacks and affect its shelf-life. Packaging C (polyethylene + polypropylene) was the most appropriate for the storage of this kind of product. Finally, the shelf life of the analyzed pellets was longer than one year at 25 °C and it may be extended with the appropriate mix of packaging materials.

Previous degradation study of two herbicides to simulate their fate in a sandy loam soil: Effect of the temperature and the organic amendments

A laboratory study was designed to assess the following: i) the degradation kinetics of chlorotoluron and flufenacet at two different temperatures, 6 °C and 16 °C, in an unamended agricultural soil and one amended with spent mushroom substrate (SMS) and green compost (GC), and ii) the formation of the main metabolites of both herbicides with potential risk for water pollution over degradation time. The aim was to determine the dependence of these herbicide degradations on temperature (Q10 factor) using kinetic parameters, which is essential information for the later simulation of herbicide environmental fate with FOCUS models. SMS and GC were applied in situ to the natural soil as organic amendments at rates of 140 or 85 t residue ha−1, respectively. Unamended and amended soils were taken from the 0–10 cm topsoil of experimental plots (three replicates/treatment) located on an agricultural farm. Samples of soil + herbicides were incubated at 6 °C or 16 °C under laboratory conditions. The degradation curves of chlorotoluron and flufenacet were fitted to single first-order and first-order multicompartment kinetic models, respectively. The flufenacet degradation, the more hydrophobic herbicide, was slower than that of chlorotoluron in all the treatments. The application of the organic amendments to soil increased the half-lives (DT50) for both herbicides incubated at 6 °C (1.3–1.9 times) and 16 °C (1.4–1.9 times) due to their higher sorption and lower bioavailability for degradation in amended soils. The herbicides recorded a faster degradation at 16 °C than at 6 °C (Q10 = 1.9–2.8) due to the increased microbial biomass and/or activity with temperature. The metabolites desmethyl chlorotoluron, flufenacet ESA and flufenacet OA were detected in all the soil treatments at both incubation temperatures. The determination of Q10 factors in amended soils is very valuable for generating accurate input data for pesticide fate models such as FOCUS in order to improve the evaluation of the leaching of herbicides and their transformation products, which is a relevant goal to maintain the sustainability of agricultural systems.

Nonlinear diffusion and thermo-electric coupling in a two-variable model of cardiac action potential

This work reports the results of the theoretical investigation of nonlinear dynamics and spiral wave breakup in a generalized two-variable model of cardiac action potential accounting for thermo-electric coupling and diffusion nonlinearities. As customary in excitable media, the common Q10 and Moore factors are used to describe thermo-electric feedback in a 10° range. Motivated by the porous nature of the cardiac tissue, in this study we also propose a nonlinear Fickian flux formulated by Taylor expanding the voltage dependent diffusion coefficient up to quadratic terms. A fine tuning of the diffusive parameters is performed a priori to match the conduction velocity of the equivalent cable model. The resulting combined effects are then studied by numerically simulating different stimulation protocols on a one-dimensional cable. Model features are compared in terms of action potential morphology, restitution curves, frequency spectra, and spatio-temporal phase differences. Two-dimensional long-run simulations are finally performed to characterize spiral breakup during sustained fibrillation at different thermal states. Temperature and nonlinear diffusion effects are found to impact the repolarization phase of the action potential wave with non-monotone patterns and to increase the propensity of arrhythmogenesis.

Strawberry-Based Cosmetic Formulations Protect Human Dermal Fibroblasts against UVA-Induced Damage.

Extreme exposure of skin to Ultraviolet A (UVA)-radiation may induce a dysregulated production of reactive oxygen species (ROS) which can interact with cellular biomolecules leading to oxidative stress, inflammation, DNA damage, and alteration of cellular molecular pathways, responsible for skin photoaging, hyperplasia, erythema, and cancer. For these reasons, the use of dietary natural bioactive compounds with remarkable antioxidant activity could be a strategic tool to counteract these UVA-radiation-caused deleterious effects. Thus, the purpose of the present work was to test the efficacy of strawberry (50 μg/mL)-based formulations supplemented with Coenzyme Q10 (100 μg/mL) and sun protection factor 10 in human dermal fibroblasts irradiated with UVA-radiation. The apoptosis rate, the amount of intracellular reactive oxygen species (ROS) production, the expression of proteins involved in antioxidant and inflammatory response, and mitochondrial functionality were evaluated. The results showed that the synergic topical use of strawberry and Coenzyme Q10 provided a significant (p < 0.05) photoprotective effect, reducing cell death and ROS, increasing antioxidant defense, lowering inflammatory markers, and improving mitochondrial functionality. The obtained results suggest the use of strawberry-based formulations as an innovative, natural, and useful tool for the prevention of UVA exposure-induced skin diseases in order to decrease or substitute the amount of synthetic sunscreen agents.

Effects of Temperature on Heteromeric Kv11.1a/1b and Kv11.3 Channels

Kv11.1 channels are crucial in cardiac physiology, and there is increasing evidence of physiological roles of different Kv11 channels outside the heart. The HERG (human Kv11.1a) channel has previously been shown to carry substantially more current at elevated temperatures, and we have now comparably investigated the temperature dependence of neuronal Kv11.3 channels and the more ubiquitous heteromeric Kv11.1a/1b channels. Transiently expressed rat Kv11 channels were studied at 21°C, 30°C, and 35°C. At near-physiological temperature, the maximal sustained outward current density was almost three times the mean value obtained at room temperature for Kv11.1a/1b, and increased by ∼150% for Kv11.3. For both channels, reduced inactivation contributed to the current increase at higher temperature. Elevated temperature moved Kv11.1a/1b isochronal activation curves to more negative potentials, but shifted the potential of half-maximal Kv11.3 channel activation to more depolarized values and reduced its voltage sensitivity. Thus, increased temperature stabilized the open state over the closed state of Kv11.1a/1b channels and exerted the opposite effect on Kv11.3 channel activation. Both Kv11 channels exhibited an overall high temperature sensitivity of most gating parameters, with remarkably high Q10 factors of ∼5 for the rate of Kv11.1a/1b activation. The Q10 factors for Kv11.3 gating were more uniform, but still higher for activation than for inactivation kinetics. The results demonstrate that characteristic differences between Kv11.1a/1b and Kv11.3 determined at room temperature do not necessarily apply to physiological conditions. The data provided here can aid in the design of models that will enhance our understanding of the role of Kv11 currents in excitable cells.

Can the Thermodynamic Hodgkin-Huxley Model of Voltage-Dependent Conductance Extrapolate for Temperature?

Hodgkin and Huxley (H-H) fitted their model of voltage-dependent conductances to experimental data using empirical functions of voltage. The thermodynamic H-H model of voltage dependent conductances is more physically plausible, as it constrains and parameterises its empirical fit by assuming that ion channel transition rates depend exponentially on a free energy barrier that in turn, linearly or non-linearly, depends on voltage. The original H-H model contains no explicit temperature terms and requires Q10 factors to describe data at different temperatures. The thermodynamic H-H model does have explicit terms for temperature. Do these endow the model with extrapolation for temperature? We utilised voltage clamp data for a voltage-gated K+ current, recorded at three different temperatures. The thermodynamic H-H model’s free parameters were fitted (Marquardt-Levenberg algorithm) to a data set recorded at one (or more) temperature(s). Then we assessed whether it could describe another data set, recorded at a different temperature, with these same free parameter values and its temperature terms set to the new temperature. We found that it could not.

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.

Effect of Geometry and Blood Flow in Cooling of Upper Leg

Systemic hypothermia has been shown to reduce neurological damage in postcardiac arrest patients. Most doctors conductively cool patients with liquid-circulating devices or ice. However, there is a lack of knowledge about the thermal response of tissue to localized cooling. Current thermal models are designed for determining human comfort and have not been evaluated for the targeted low temperatures required for inducing hypothermia. Metabolic heat generation and tissue perfusion rate can significantly change under low temperature, which in turn affects the overall heat flux and cooling rates.This study evaluates the effects of geometry and blood flow in the upper leg by comparing numerical simulation results with previous experimental data.A geometrically accurate 3D model of the Visible Human Male upper leg was simulated using COMSOL Multiphysics. The segmented tissue included skin, fat, muscle, and bone. Large blood vessels, femoral vein and artery, great saphenous vein, and anterior femoral vein, are modeled, as they can be significant heat sources.Penne's bioheat equation was used to solve the temperature field. Variation of metabolic heat generation with temperature is modeled using the Q10 factor of 2, as widely used in literature [1]. Cutaneous vasoconstriction, tissue blood flow, and shivering are modeled using correlations provided by Fiala [1]. The numerical model results were compared with cold immersion studies [2–4].As seen in Fig. 1, the simulation results agree well with experimental data during whole-body cooling at 18 °C, but there is significant discrepancy with experimental data in localized cooling at 4 °C. The most likely reason for this discrepancy is hypothesized to be incorrect modeling of cutaneous blood flow at low temperatures. Data from immersion at 8 °C shows that low temperatures result is cold-induced vasodilation [4], which is not accounted for in the current model. When cutaneous blood flow is set constant at initial value, the error is significantly reduced. With vasodilation, local heat flux increases by 40% at 40 minutes, showing that proper modeling of vasoconstriction can significantly improve the model.Analysis of muscle temperature profile during cooling at 8 °C shows disagreement between experimental data and the current model. Fig. 2 shows the temperature profiles at 70 min of cooling. The most likely cause of this discrepancy was hypothesized to be inaccurate modeling of the muscle blood flow.Gergson et al. observed that femoral artery blood flow dropped to nearly half the initial value during immersion at 8 °C [4]. Combined with the fact that skin blood flow did not decrease (due to cold-induced vasodilation), they were able to conclude that the muscle blood flow must drop. In the current model, when the muscle perfusion is held constant at half the initial value, the results are significantly closer to experimental data.Results from the current simulations show that cutaneous and muscle perfusion both significantly influence the response of the model. Current perfusion models are not accurate at low temperature cooling.

Kinetic modeling of ascorbic acid loss in baobab drink at pasteurization and storage temperatures.

The degradation kinetics of ascorbic acid was determined in baobab drink during pasteurization and storage temperatures at 60-90°C for 3 hours and 0 - 40 o C for 5 weeks respectively. The loss of ascorbic acid at all temperatures followed the first order kinetic model as the coefficient of determination (i.e. R 2 -value) ≥ 0.953. Rate constants of ascorbic acid degradation ranged from 9.72 - 26.31 x10 -3 /minute and 5.266 - 29.95x10 -3 /day during pasteurization and storage respectively. Decimal reduction time (D-value) and half-life ranged between 87.52 - 236.87 and 26.35 - 71.30 minutes and 76.89 - 437.78 and 23.15 - 131.78 days for pasteurization and storage temperatures respectively The temperature dependence of degradation reaction was well described by the Arrhenius relationship. The activation energy, Q10 factor, and Z-value obtained ranged from 24.24 - 58.66 kJ/mol, 1.06 - 1.58 and 4.74 - 7.96 o C for the temperature range within which experiments were carried out.

Temperature Sensitivity of Methane Production in the Permafrost Active Layer at Stordalen, Sweden: A Comparison with Non-permafrost Northern Wetlands

Relationships were determined between methane (CH4) production and in situ conditions within the permafrost active layer during a single melt season at Stordalen, Sweden, with a specific emphasis on temperature sensitivity of methanogenesis. In situ temperature, moisture, pH, dissolved organic carbon, and CH4 concentration data were measured at three contrasting active layer sites (sedge mire, Sphagnum mire, and ombrotrophic bog), and laboratory incubations of active layer material were subsequently employed to determine the sensitivity of CH4 production to temperature. Q10 values, describing the CH4 production response of peat to a temperature change of 10 °C, ranged from 1.9 to 3.5 and 2.4 to 5.8 for the sedge and Sphagnum mire sites, respectively. A wider review of the literature on Q10 responses of methanogenesis in northern peatlands shows similar features to the temperature response of CH4 production in the active layer at Stordalen. In general, Q10 values are not significantly different in Arctic permafrost wetlands than non-Arctic northern wetlands; however, Sphagnum sites display Q10 responses (mean Q10 = 8) that are notably greater than that of wetter minerotrophic-sedge environments (mean Q10 = 4.3). This finding has implications for the parameterization of Q10 factors in numerical carbon cycling models, and suggests that the use of spatially variable Q10 values could be a useful approach for more accurate modeling of CH4 fluxes from northern wetlands under different climatic change scenarios.

Inactivating ion channels augment robustness of subthreshold intrinsic response dynamics to parametric variability in hippocampal model neurons

Voltage-gated ion channels play a critical role in regulating neuronal intrinsic response dynamics (IRD). Here, we computationally analysed the roles of the two inactivating subthreshold conductances (A and T), individually and in various combinations with the non-inactivating h conductance, in regulating several physiological IRD measurements in the theta frequency range. We found that the independent presence of a T conductance, unlike that of an h conductance, was unable to sustain an inductive phase lead in the theta frequency range, despite its ability to mediate theta frequency resonance. The A conductance, on the other hand, when expressed independently, acted in a manner similar to a leak conductance with reference to most IRD measurements. Next, analysing the impact of pair-wise coexpression of these channels, we found that the coexpression of the h and T conductances augmented the range of parameters over which they sustained resonance and inductive phase lead. Additionally, coexpression of the A conductance with the h or the T conductance elicited changes in IRD measurements that were similar to those obtained with the expression of a leak conductance with a resonating conductance. Finally, to understand the global sensitivity of IRD measurements to all parameters associated with models expressing all three channels, we generated 100,000 neuronal models, each built with a unique set of parametric values. We categorized valid models among these by matching their IRD measurements with experimental counterparts, and found that functionally similar models could be achieved even when underlying parameters displayed tremendous variability and exhibited weak pair-wise correlations. Our results suggest that the three prominent subthreshold conductances contribute differently to intrinsic excitability and to phase coding. We postulate that the differential expression and activity-dependent plasticity of these conductances contribute to robustness of subthreshold IRD, whereby response homeostasis is achieved by recruiting several non-unique combinations of these channel parameters.

Temperature effect on apple biospeckle activity evaluated with different indices

The physical explanation of the biospeckle phenomenon is well known; however, there is lack of biologically related interpretation, which limits a possible application of the method as a new, nondestructive technique for evaluation of fruit quality. Physically, biospeckles are the result of scattering of coherent light on moving particles inside living tissue. Almost all biological processes are temperature-dependent; therefore, the aim of this study was to investigate a temperature effect on biospeckle activity in apples and determine the extent to which this activity results from biological processes in the tissues of the fruit. Apples of ‘Idared’ cultivar were cooled in a storage room from high room temperature 29°C down to 2°C, which resulted in apple surface temperatures in the range 29–4°C. To evaluate the biospeckle activity, three methods of image analysis were used: correlation coefficient, speckle contrast, and the moment of inertia. The results showed that biospeckle activity measured by each method decreases with temperature decreases. However, the correlation coefficient was found as the most robust indicator of biospeckle activity and Q10 factor indicates a mostly biological basis for this phenomenon.

Long-term surface carbon dioxide flux monitoring at the Ketzin carbon dioxide storage test site

Subsurface geologic storage of carbon dioxide calls for sophisticated monitoring tools with respect to long-term safety and environmental impact issues. Despite extensive research, many factors governing the fate of injected carbon dioxide (CO2) remain unclear. To identify possible risks through leakage of the CO2 storage reservoir, a program for monitoring of the CO2 flux at the surface was started at the Ketzin test site, which allows to distinguish between natural temporal and spatial flux variations and a potential leakage. To gain adequate long-term baseline data on the local background CO2 flux variations, CO2 soil gas flux, soil moisture, and temperature measurements were conducted once a month during a 6-yr period. Furthermore, soil samples were analyzed for their organic carbon and total nitrogen contents. The mean flux of all sampling sites before the CO2 injection (2005–2007) was 2.8 mol m2 s1 (ranging from 2.4 to 3.5), with a Q10 factor of 2.4, and in the years after commencing injection (2009–2010), 2.4 mol m2 s1 (ranging from 2.2 to 2.5), with the same Q10 factor. The CO2 flux rate is mainly controlled by the soil temperature. A significant influence of diurnal temperature variation and soil moisture was not detected. The spatial variability of the CO2 flux among the 20 sampling locations ranges from 1.0 to 4.5 mol m2 s1, depending on the organic carbon and total nitrogen content of the soil. Through comparison with the long-term measurements, unusual high CO2 fluxes can theoretically be distinguished from natural variations.

Influence of storage temperature on Epidendrum ibaguense flowers

The present work was carried out to evaluate the influence of temperature and wet-versus-dry storage on longevity, respiration and ethylene production during storage of E. ibaguense flowers. The inflorescences were harvested and stored at 5, 10, 15, 20, 25, 30, 35, and 40&deg;C, in water or dry, until complete senescence. Respiration increased when inflorescences were treated with wet or dry storage. The Q10 factor for this flower, at temperatures ranging from 5 to 40&deg;C, was similar to most fresh horticultural products, varying between 1.2 and 3.31 depending on storage temperature. Production of ethylene by the inflorescence was maximal at 20&deg;C for flowers maintained in water, and at 35&deg;C for those flowers kept dry, followed by a sharp drop in both treatments. A maximal shelf life for cut flowers was obtained when the inflorescences were stored wet at 10&deg;C. Symptoms of chilling were observed in flowers stored in water after six to seven days at 5&deg;C, showing petal wilting and necrosis of the labellum. At 40&deg;C, flowers stored dry showed severe petal wilting and darkening of bud petals less than one day after harvest.

Estimation of daily soil CO2 flux using a single-time-point measurement

Information on soil CO2 emissions can be used in conjunction with data for C inputs from plants to estimate the soil C balance. Many studies assume a single-time-point measurement of soil CO2 flux taken in a day (Fh) is equal to its daily average value (Fd), which could result in over- or underestimation. A model using Fh, the temperature at the time the Fh is measured (Th), daily average temperature (Td) and Q10 factor to predict Fd was tested with extensive measurements of soil CO2 flux, temperature and moisture over 60 d from various treatments (no-till wheat, summer fallow and stubble, etc.) on a Swinton silt loam near Swift Current, Saskatchewan, Canada. A distinct hysteresis between flux and soil moisture was observed following rain events. Therefore, data for five rainy days were excluded from the analysis as the model does not consider the effect of hysteresis. Calculated Q10 factors were 1.86 and 1.54 for soil (Ts) and air (Ta) temperatures, respectively. The model using either Ts or Ta improved prediction of Fd in both calibration (49 d) and validation (6 d) datasets compared with Fh. Values of Fh measured in 6 yr were higher than modelled values of Fd in 96% of the 1602 treatment-days, hence if Fh is assumed to be equal to Fd, the averaged overestimation would be 17%.Key words: Soil CO2 flux, Q10 factor, temperature