Respiratory Coefficient Research Articles

A time-of-flight mass spectrometer for monitoring the inhalational anesthesia concentration in the real-time mode

The use of a medical mass spectrometer for measuring the concentration of the gas mixture components in the breathing circuit of an inhalational anesthesia machine in the real-time mode is described. The resolution of the mass spectrometer is M/ΔM = 200, and the detection threshold in terms of the partial pressure of the analyzed gases is 2 × 10−12 mbar. The mass spectrometer is capable of measuring the volumetric content of CO2, O2, and inhalational anesthetic sevoflurane. The respiratory coefficient (CO2/O2) was measured during anesthesia to estimate the patient’s stress reaction to a surgical injury.

Hypolipemic Effect of Garcinia cambogia in Obese Women

Garcinia cambogia seems to promote weight reduction and improvement on lipid profile by its major compound, hydroxycitric acid (HCA), blocking ATP-citratelyase, potentially inhibiting lipogenesis. Furthermore, it is suggested that its extract is able to change the adipokine levels. Thus, the aim of this study was to analyse the effect of G. cambogia on the lipid profile, endocrine, calorimetric and anthropometric parameters of obese women. The women (BMI > 25 kg/m(2) ; age 25-60 years), divided in treated (n = 30) and control (n = 13) groups, received 2.4 g (800 mg 3×/day) of garcinia extract (50% of HCA) or placebo during 60 days, respectively, as well as dietary control. Weight, BMI, waist-hip ratio and percentage of fat mass, resting metabolic rate, respiratory coefficient, triglycerides (TG), total cholesterol, HDL and LDL, leptin and insulin serum levels were evaluated. TG was significantly reduced in the treated group (p = 0.0002) and the post-treatment variation was different compared to the placebo group (p = 0.04). No significant response was observed on other variables of the lipid profile, or on the anthropometric and calorimetric parameters. Leptin and insulin levels did not change significantly after the treatment. The short-term treatment with G. cambogia demonstrated a hypotriglyceridemic effect, which does not appear to be related to changes in leptinemia.

Mass-spectrometric monitoring of the stress reaction during anesthesia

Clinical testing data for a mass-spectrometric method of estimating the patient’s stress reaction to an injury done during anesthesia are presented. The essence of the method is monitoring the respiratory coefficient, which is defined as ratio N of the expiratory mass concentration of CO2 to the inspiratory mass concentration of O2 at each breathing cycle. For on-line monitoring of N, an electron ionization mass spectrometer connected to the breathing circuit of an inhalational anesthesia machine is used. Estimates of the anesthesia adequacy obtained with this method are compared with those obtained with the method that analyzes induced acoustic encephalographic potentials. It is shown that the method suggested is more sensitive to the level of the patient’s stress reaction during anesthesia than the induced potential method.

Role of Polyphosphate in Mitochondria: From Modification of Energy Metabolism to Induction of the Cell Death

Inorganic polyphosphate (polyP) is found in all living organisms ranging from bacteria to mammals. PolyP plays multiple physiological functions, which are distinct and dependent on the type of organism and the subcellular localization of the polymer. Recently we demonstrated that polyP levels are dependent on the cell metabolism and can be changed by mitochondrial substrates and inhibitors. We propose the existence of a feedback mechanism where polyP production and cell energy metabolism regulate each other. In order to investigate this we study the effect of polyP on mitochondrial oxygen consumption. We have found that application of short polyP (14 phosphate residues) or medium polyP (70 ortophosphates) significantly increase the level of respiratory coefficient by activation of state V3 and inhibition of V4 compare to control. Importantly, both short and medium polyP significantly reduced efficiency of oxidative phosphorylation (ADP/O ratio). It has previously been reported that polyP can modify membrane permeability for ions that can be a trigger for changes in mitochondrial metabolism. Furthermore polyP has been linked to activation of the mitochondrial permeability transition pore (mPTP) in different cells that also can be activated by calcium. Long, medium, and in lower degree, short polyP increase permeability of de-energised mitochondria for Ca2+. This effect was dependent on inhibitor of mPTP - cyclosporine A. We also found that long polyP (130 orthophosphates) caused cell death in primary neurons and astrocytes, while medium (70) polyP had a much smaller effect and short (14) did not cause any. Thus, polyP has a multiple action on mitochondrial function from modification of mitochondrial energy metabolism to stimulation of calcium permeability and cell death.

Valores de referência e fatores relacionados à mobilidade torácica em crianças brasileiras

OBJETIVO: Fornecer valores de referência e avaliar os fatores que influenciam a mobilidade torácica de crianças entre sete e 11 anos. MÉTODOS: Foram avaliadas 166 crianças de escolas públicas e privadas (90 meninas e 76 meninos) da cidade de Natal, no estado do Rio Grande do Norte. Foram coletados dados pessoais, antropométricos e perímetros torácicos por cirtometria. O teste t de Student não pareado e a análise de variância compararam o coeficiente respiratório xifoidiano entre os sexos e as idades, respectivamente. Diferenças no coeficiente respiratório axilar entre os sexos e as idades foram verificadas com os testes de Mann-Whitney e Kruskal-Wallis, respectivamente, com diferenças localizadas pelo teste post-hoc de Duncan. Coeficientes de correlação de Spearman e Pearson relacionaram variáveis independentes com os coeficientes avaliados. RESULTADOS: As médias das perimetrias axilar e xifoidiana foram 5,00±1,59 e 4,75±1,56cm, respectivamente. Observou-se baixa correlação, sem significância estatística, entre o coeficiente respiratório xifoidiano e as variáveis idade, sexo, peso, altura e índice de massa corpórea. O coeficiente respiratório axilar correlacionou-se com peso e altura. Foram encontradas diferenças no coeficiente respiratório axilar nas faixas etárias entre oito e dez anos (p=0,03) e 10 e 11 anos (p=0,02). CONCLUSÕES: Foram disponibilizados valores de referência de cirtometria torácica para crianças entre sete e 11 anos. Sexo, idade, peso, altura e índice de massa corpórea não influenciaram o coeficiente respiratório xifoidiano. O coeficiente respiratório axilar diferiu-se entre idades, a partir dos oito anos, sendo influenciado pelo peso e pela altura, independentemente do sexo.

Effects of Activation of TRPM8 Ion Channels on Thermoregulatory Reactions in Cooling

Animal experiments were performed to study the effects of activation of cold- and menthol-sensitive TRPM8 receptors by menthol on thermoregulatory parameters in thermoneutral conditions and on cooling. Total oxygen consumption was measured, along with expiration of carbon dioxide, the respiratory coefficient, the skin vessel constriction reaction, and contractile muscle activity. Application of menthol in thermoneutral conditions led to increased oxygen consumption and a decrease in the respiratory coefficient which, in the absence of shivering, provides evidence of increased non-contractile thermogenesis and lipolysis. Cooling on the background of activation of the TRPM8 receptor was characterized by decreases in the thresholds of all thermoregulatory reactions with no change in their initiation sequence, along with increases in the metabolic components of emergency thermogenesis, leading to improved maintenance of deep body temperature when environmental cold acts on the body. These results provide evidence for a contribution of TRPM8 ion channels to increased activation of thermoreceptor structures generating afferent signals involved in maintaining metabolism in thermoneutral conditions and forming the structure of the efferent response of the body to cold.

Effects of Wheelchair Sports on Respiratory Muscle Strength and Thoracic Mobility of Individuals with Spinal Cord Injury

The aim of this study was to evaluate the effects of wheelchair sports on respiratory muscle strength and the thoracic mobility of individuals with spinal cord injury. Thirty male subjects with chronic spinal cord injury (American Spinal Injury Association Impairment Scale grade A) took part in the study and were divided into four groups: sedentary subjects with quadriplegia (S-QUAD, n = 7), wheelchair rugby athletes with quadriplegia (A-QUAD, n = 8), sedentary subjects with paraplegia (S-PARA, n = 6), and wheelchair basketball athletes with paraplegia (A-PARA, n = 9). The main outcome measures were maximal inspiratory and expiratory pressure and the respiratory coefficients at the axillary and xiphoid levels. A-QUAD group presented values significantly higher for all respiratory variables studied compared with the S-QUAD group. No significant differences in any of the respiratory variables were observed between S-PARA and A-PARA groups. There was a negative correlation between spinal cord injury level and respiratory variables for the S-QUAD and S-PARA groups. There were positive correlations in the A-QUAD group between time of training and maximal inspiratory pressure (adjusted R = 0.84; P = 0.001) and respiratory coefficients at the axillary level (adjusted R = 0.80; P = 0.002). Physical training seems to have a positive influence on respiratory muscle strength and thoracic mobility, especially in subjects with quadriplegia.

Efeito da fisioterapia sobre os parâmetros ventilatórios e a dinâmica tóraco-abdominal de crianças respiradoras bucais

Este estudo objetivou avaliar o efeito da fisioterapia nos parâmetros ventilatórios e na dinâmica tóraco-abdominal de crianças respiradoras bucais. Dez crianças respiradoras bucais foram submetidas a um programa de reeducação respiratória e correção postural durante 20 sessões de exercícios de alongamento e fortalecimento muscular sobre a bola suíça, estimulação diafragmática e alongamento dos músculos acessórios da inspiração. Os dados coletados foram as medidas de pressões inspiratórias e expiratórias máximas (PIM e PEM), capacidade inspiratória (CI), pico de fluxo expiratório (PFE), mobilidade torácica por meio do coeficiente respiratório (Cr) nos níveis axilar (CrA), xifoide (CrX) e umbilical (CrU) e análise biofotogramétrica do ângulo de Charpy. Estes foram verificados antes e após 10 e 20 atendimentos. Os dados foram submetidos a uma análise de variância (ANOVA) e, nas diferenças encontradas entre as médias, aplicou-se o Teste de Tukey com nível de significância de 5% (p<0,05). Houve melhora para as medidas referentes ao ângulo de Charpy (p=0,048), CI (p=0,037), PFE (0,002), PIM (0,007), CrA (p=0,008) e CrX (p=0,041). A PEM e o CrU, apesar da melhora nos valores absolutos, não apresentaram resultados estatisticamente significativos. O programa de fisioterapia respiratória e postural produziu efeitos positivos sobre a função ventilatória de crianças respiradoras bucais.

Effect of transfer of the chromosome 13 fragment containing gene il6st on parameters of temperature homeostasis in mice

Mechanisms of maintenance of temperature homeostasis in warm and under effect of cold were studied in mice of AKR line and of its coherent line AKR.CBA-D13Mit76 with the changed gene i16 encoding the gp130 receptor via which IL-6 performs its action. Under thermoneutral conditions and under action of cold, there were recorded temperature parameters, total oxygen consumption, carbon dioxide release, respiratory coefficient, and electrical muscle activity. Animals of the studied lines demonstrated different reactions to equal cold effect. At cooling, all mice of the AKR line entered the state of hypothermia by decreasing metabolism. Mice of the AKR.CBAD13Mit76 line showed 2 different types of reaction: 39% of animals of this line reacted like mice of the AKR line, but the majority (61%) resisted actively to the cold action, which was manifested as a marked increase of metabolism. Taking into account the gene penetrance, this can indicate effect of the gene i16 on choice of the active (“regulated”) or passive (“dependent”) way of the organism reacting to temperature actions.

Seasonal fluctuations inVitis viniferaroot respiration in the field

We studied the seasonal fluctuation of soil respiration (R(S)), and its root-dependent (R(R)) and basal (R(B)) components, in a Vitis vinifera (Chardonnay) vineyard. The R(S) components were estimated through independent field methods (y-intercept and trenching) and modeled on the basis of a Q(10) response to soil temperature, and fine and coarse root respiration coefficients. The effect of assimilate availability on R(R) was assessed through a trunk girdling treatment. The apparent Q(10) for R(R) was twice that of R(B) (3.5 vs 1.6) and increased linearly with increasing vine root biomass. The fastest R(R) of fine roots was during rapid fruit growth and the fastest R(R) of coarse roots was immediately following fruit development. R(S) was estimated at 32.6 kg ha(-1) d(-1) (69% as a result of R(R) ) for the hottest month and at 7.6 kg ha(-1) d(-1) (18% as a result of R(R)) during winter dormancy. Annual R(S) was low compared with other natural and cultivated ecosystems: 5.4 Mg ha(-1) (46% as a result of R(R)). Our estimates of annual vineyard R(S) are the first for any horticultural crop and suggest that the assumption that they are similar to those of annual crops or forest trees might lead to an overestimation.

Influence of L-Carnitine intake for maximal exercise performance and fatigue recovery exercise athletes: based on elite soccer players

This study was performed to determine the most suitable L-Carnitine intake amount for prevention of L-Carnitine intake abuse and enhancement of physical performance and body composition in elite athletes. The participants were all elite university soccer players. A total of 36 participants were separated into five L-Carnitine intake groups (CT) (2g, 3g, 4g, 5g, and 6g) (n = 30) and one control group (CON) (n = 6). The experiments were conducted over 4 weeks. The VO2max level was increased in every group. The VO2max levels in the 4g and 5g CT intake groups were higher than other groups, whereas the 4g CT group was significantly higher than the 2g CT group. HRmax was slightly increased in the 3g, 4g, 5g, and 6g CT groups; the 4g and 5g CT groups showed significantly higher HRmax compared to the 2g CT group. Respiratory coefficient was increased in every group; it was highly increased in the 5g, 4g, and 6g CT groups. Ventilation was increased significantly in the 5g, 4g, 6g, and 2g CT groups, and main and interaction effects were also verified. Lactate concentration associated with recovery from fatigue showed significant differences in main effect verification according to treatment duration and treatment time; the 4g and 6g CT groups showed the highest reduction rates immediately after exercise and after 15 minutes of recovery. We demonstrated that L-Carnitine has the potential to enhance endurance and recovery from fatigue in elite athletes.

Agonist of TRPM8 channel, menthol, facilitates the initiation of thermoregulatory responses to external cooling

The effects of activation of the cold and menthol sensitive TRPM8 ion channel on different thermoregulatory parameters (total oxygen consumption, carbon dioxide release, respiratory coefficient, vasoconstriction response of skin blood vessels and shivering) were studied in anaesthetized rats subjected to two types of external cooling—rapid and slow. Activation of TRPM8 by menthol even in thermoneutral conditions produced an increase in oxygen consumption and decrease in respiratory coefficient, which may be evidence of enhanced fat oxidation. Menthol, an agonist of the cold sensitive TRPM8 ion channel, decreased the temperature thresholds of all thermoregulatory responses induced by rapid and slow cooling without affecting the sequence of their initiation. Under menthol stimulation, there was enhancement of the first (urgent) phase of metabolic response at rapid cooling, and an increase in the skin blood vessel constrictor response at slow cooling. These changes lead to improved maintenance of core temperature when the organism is subjected to rapid or slow cooling. These data are compelling evidence for the contribution of TRPM8 ion channels to the formation of the thermal afferent signals in the initiation of cold defense responses. The effects of TRPM8 activation by menthol on metabolic parameters in thermoneutral conditions and under cooling suggest the continuous involvement of TRPM8 channel in regulation of total metabolism.

A new CALMAR benthic chamber operating by submersible: First application in the cold‐seep environment of Napoli mud volcano (Mediterranean Sea)

A new submersible‐operated benthic chamber has been developed to measure benthic organism metabolism and chemical exchange rates at the sediment‐water interface up to 6000 m depth. This equipment can be used everywhere on soft sediment, but particularly to deploy it on small area reached only by submersible‐like cold seep. The chamber, 41 cm diameter cylinder, includes six 100 mL‐sampling cells to isolate aliquots, which are sampled at predetermined intervals and an oxygen‐optode probe. This chamber named CALMAR (Chambre Autonome Légère MAnipulable par ROV) was used for the first time during the Medeco cruise (2007) in Eastern Mediterranean Sea. It allowed measurement of fluxes of oxygen, dissolved inorganic carbon, and methane on the Napoli mud volcano site. Two benthic chambers were deployed with the ROV Victor, respectively, on small, active, cold seep colonized by Siboglinidae worms and mussels (Station A), and at about 3 m from the first where no visible animals were observed (Station B). The oxygen flux was 35 mmol O2 m−2 d−1 in sediment colonized by large organisms (Station A) and 13.5 mmol O2 m−2 d−1 on the inactive area (CALMAR B). In terms of inorganic carbon, the fluxes were 34 and 10.5 mmol m−2 d−1, respectively, at A and B, and the calculated respiratory coefficient was 0.97 at A and 0.78 at B. The methane flux was only observed on the Siboglinidae colony (3 mmol m−2 d−1) and not on Station B.

Lipid oxidation during physical exercises of different intensity in patients with abdominal obesity

The objective of this work was to study the character of lipid oxidation during physical exercises of different intensity and identify factors influencing this process in patients with abdominal obesity. The study included 90 patients aged from 30 to 55 years with abdominal obesity (AO). Lipid oxidation (LO) during physical exercises (PE) was measured by the indirect colorimetric technique with the assessment of oxygen consumption (VO2peak), anaerobic threshold (AT), and respiratory coefficient (RQ). The level of physical activity (PA) and body composition were determined. Patients with abdominal obesity exhibited maximum lipid oxidation at low-intensity physical exercise; it decreased with increasing PE intensity. Lipid oxidation was related to AT (r=0,6; p=0,0001), heart rate at maximum PE (r=0,8; p<0,001), energy expenditure during physical exercices (r=0,98; p=0,016), total energy consumption for the maintenance of physical activity (r=0,3; p<0,035), lean body mass (r=0,3; p=0,04), and duration of obesity (r=0,6; p=0,04).

Wood CO2 efflux and foliar respiration for Eucalyptus in Hawaii and Brazil

We measured CO(2) efflux from wood for Eucalyptus in Hawaii for 7 years and compared these measurements with those on three- and four-and-a-half-year-old Eucalyptus in Brazil. In Hawaii, CO(2) efflux from wood per unit biomass declined approximately 10x from age two to age five, twice as much as the decline in tree growth. The CO(2) efflux from wood in Brazil was 8-10x lower than that for comparable Hawaii trees with similar growth rates. Growth and maintenance respiration coefficients calculated from Hawaii wood CO(2) efflux declined with tree age and size (the growth coefficient declined from 0.4 mol C efflux mol C(-1) wood growth at age one to 0.1 mol C efflux mol C(-1) wood growth at age six; the maintenance coefficient from 0.006 to 0.001 micromol C (mol C biomass)(-1) s(-1) at 20 degrees C over the same time period). These results suggest interference with CO(2) efflux through bark that decouples CO(2) efflux from respiration. We also compared the biomass fractions and wood CO(2) efflux for the aboveground woody parts for 3- and 7-year-old trees in Hawaii to estimate how focusing measurements near the ground might bias the stand-level estimates of wood CO(2) efflux. Three-year-old Eucalyptus in Hawaii had a higher proportion of branches < 0.5 cm in diameter and a lower proportion of stem biomass than did 7-year-old trees. Biomass-specific CO(2) efflux measured at 1.4 m extrapolated to the tree could bias tree level estimates by approximately 50%, assuming no refixation from bark photosynthesis. However, the bias did not differ for the two tree sizes. Foliar respiration was identical per unit nitrogen for comparable treatments in Brazil and Hawaii (4.2 micromol C mol N(-1) s(-1) at 20 degrees C).

On‐line adaptive metabolic flux analysis: Application to PHB production by mixed microbial cultures

In this work, an algorithm for on-line adaptive metabolic flux analysis (MFA) is proposed and applied to polyhydroxybutyrate (PHB) production by mixed microbial cultures (MMC). In this process, population dynamics constitutes an important source of perturbation to MFA calculations because some stoichiometric and energetic parameters of the underlying metabolic network are continuously changing over time. The proposed algorithm is based on the application of the observer-based estimator (OBE) to the central MFA equation, whereby the role of the OBE is to force the accumulation of intracellular metabolites to converge to zero by adjusting the values of unknown network parameters. The algorithm was implemented in a reactor equipped with on-line analyses of dissolved oxygen and carbon dioxide through respirometric and titrimetric measurements. The oxygen and carbon dioxide fluxes were measured directly, whereas acetate, PHB, and sludge production fluxes were estimated indirectly using a projection of latent structures model calibrated a priori with off-line measurements. The algorithm was implemented in a way that the network parameters associated with biosynthesis were adjusted on-line. The algorithm proofed to converge exponentially with the steady state error always below 1 mmol/L. The estimated fluxes passed the consistency index test for experimental error variances as low as 1%. The comparison of measured and estimated respiratory coefficient and of the theoretical and estimated yield of sludge on acetate further confirmed the metabolic consistency of the parameters that were estimated on-line.

Effects of the Arrabidaea chica extract on energy metabolism in the rat liver

The bignoniaceous Arrabidaea chica (Bonpl.) B. Verl. (syn. Bignonia chica), Bignoniaceae, popularly known as carajuru, puca panga, chica or pariri is very common in the Amazon region. Leaves of this plant are widely used as anti-inflammatory and astringent agents as well as remedies for intestinal colic, sanguine diarrhea, leucorrhea, anemia and leukemia. The action of the extract from leaves and stems of Arrabidaea chica on hepatic energy metabolism was investigated in the perfused rat liver and isolated mitochondria. In isolated mitochondria the Arrabidaea chica extract (0.25-1.25 mg/ml) decreased the respiratory coefficient with the substrates β-hydroxybutyrate and succinate. The activities of succinate-oxidase and NADH-oxidase were inhibited and the ATPase of intact mitochondria was stimulated. The extract also inhibited the glucose 6-phosphatase of isolated microsomes. The cellular content of glucose 6-phosphate was increased, while the level of ATP was reduced. In perfused livers the extract (0.25-1.0 mg/ml) caused stimulation of oxygen consumption, inhibition of gluconeogenesis from lactate and pyruvate and reduction of glucose release from endogenous glycogen. The results of this investigation suggest that the inhibitory effect of the extract on hepatic glucose production is mainly related to its actions on the mitochondrial energy metabolism.

An improved state-parameter analysis of ecosystem models using data assimilation

Much of the effort spent in developing data assimilation methods for carbon dynamics analysis has focused on estimating optimal values for either model parameters or state variables. The main weakness of estimating parameter values alone (i.e., without considering state variables) is that all errors from input, output, and model structure are attributed to model parameter uncertainties. On the other hand, the accuracy of estimating state variables may be lowered if the temporal evolution of parameter values is not incorporated. This research develops a smoothed ensemble Kalman filter (SEnKF) by combining ensemble Kalman filter with kernel smoothing technique. SEnKF has following characteristics: (1) to estimate simultaneously the model states and parameters through concatenating unknown parameters and state variables into a joint state vector; (2) to mitigate dramatic, sudden changes of parameter values in parameter sampling and parameter evolution process, and control narrowing of parameter variance which results in filter divergence through adjusting smoothing factor in kernel smoothing algorithm; (3) to assimilate recursively data into the model and thus detect possible time variation of parameters; and (4) to address properly various sources of uncertainties stemming from input, output and parameter uncertainties. The SEnKF is tested by assimilating observed fluxes of carbon dioxide and environmental driving factor data from an AmeriFlux forest station located near Howland, Maine, USA, into a partition eddy flux model. Our analysis demonstrates that model parameters, such as light use efficiency, respiration coefficients, minimum and optimum temperatures for photosynthetic activity, and others, are highly constrained by eddy flux data at daily-to-seasonal time scales. The SEnKF stabilizes parameter values quickly regardless of the initial values of the parameters. Potential ecosystem light use efficiency demonstrates a strong seasonality. Results show that the simultaneous parameter estimation procedure significantly improves model predictions. Results also show that the SEnKF can dramatically reduce the variance in state variables stemming from the uncertainty of parameters and driving variables. The SEnKF is a robust and effective algorithm in evaluating and developing ecosystem models and in improving the understanding and quantification of carbon cycle parameters and processes.

Critical soil conditions for oxygen stress to plant roots: Substituting the Feddes-function by a process-based model

Effects of insufficient soil aeration on the functioning of plants form an important field of research. A well-known and frequently used utility to express oxygen stress experienced by plants is the Feddes-function. This function reduces root water uptake linearly between two constant pressure heads, representing threshold values for minimum and maximum oxygen deficiency. However, the correctness of this expression has never been evaluated and constant critical values for oxygen stress are likely to be inappropriate. In this paper, we propose a fundamentally different approach to assess oxygen stress: we built a plant physiological and soil physical process-based model to calculate the minimum gas filled porosity of the soil at which oxygen stress occurs. Effects of insufficient soil aeration on the functioning of plants form an important field of research. A well-known and frequently used utility to express oxygen stress experienced by plants is the Feddes-function. This function reduces root water uptake linearly between two constant pressure heads, representing threshold values for minimum and maximum oxygen deficiency. However, the correctness of this expression has never been evaluated and constant critical values for oxygen stress are likely to be inappropriate. On theoretical grounds it is expected that oxygen stress depends on various abiotic and biotic factors. In this paper, we propose a fundamentally different approach to assess oxygen stress: we built a plant physiological and soil physical process-based model to calculate the minimum gas filled porosity of the soil (phi gas_min) at which oxygen stress occurs. First, we calculated the minimum oxygen concentration in the gas phase of the soil needed to sustain the roots through (micro-scale) diffusion with just enough oxygen to respire. Subsequently, phi gas_min that corresponds to this minimum oxygen concentration was calculated from diffusion from the atmosphere through the soil (macro-scale). We analyzed the validity of constant critical values to represent oxygen stress in terms Of phi gas_min, based on model simulations in which we distinguished different soil types and in which we varied temperature, organic matter content, soil depth and plant characteristics. Furthermore, in order to compare our model results with the Feddes-function, we linked root oxygen stress to root water uptake (through the sink term variable F, which is the ratio of actual and potential uptake). The simulations showed that phi gas-min is especially sensitive to soil temperature, plant characteristics (root dry weight and maintenance respiration coefficient) and soil depth but hardly to soil organic matter content. Moreover, phi gas-min varied considerably between soil types and was larger in sandy soils than in clayey soils. We demonstrated that F of the Feddes-function indeed decreases approximately linearly, but that actual oxygen stress already starts at drier conditions than according to the Feddes-function. How much drier is depended on the factors indicated above. Thus, the Feddes-function might cause large errors in the prediction of transpiration reduction and growth reduction through oxygen stress. We made our method easily accessible to others by implementing it in SWAP, a user-friendly soil water model that is coupled to plant growth. Since constant values for phi gas_min in plant and hydrological modeling appeared to be inappropriate, an integrated approach, including both physiological and physical processes, should be used instead. Therefore, we advocate using our method in all situations where oxygen stress could occur. (C) 2008 Elsevier B.V. All rights reserved.

Optimization of ecosystem model parameters through assimilating eddy covariance flux data with an ensemble Kalman filter

Process-based terrestrial ecosystem models have been widely used to simulate carbon cycle, climate and ecosystem interactions. Some parameters used in biological functions often change seasonally and inter-annually. In this study, sequential data assimilation with an ensemble Kalman filter is designed to optimize the key parameters of the Boreal Ecosystem Producitivity Simulator (BEPS) model, taking into account the errors in the input, parameters and observation. The parameters adjusted through data assimilation include foliage clumping index ( C f), slope of stomatal conductance to the net photosynthetic rate ( m), maximum photosynthetic carboxylation rate ( V c max ) and electron transport rate ( J max) at reference temperature of 25 °C, multiplier to the soil organic matter decomposition rates ( K r). The fluxes of CO 2 (separated into gross primary production (GPP) and ecosystem respiration ( R E)) and water vapor measured using the eddy covariance technique at the BOREAS/BERMS Old Aspen site, Canada during 1997–2004 are used for the optimization. Parameters are optimized at a daily time step and presented as 10-day averages. The results show that the parameters varied significantly at seasonal and inter-annual scales. Photosynthetic capacity ( V c max , J max) usually increased rapidly at the leaf expansion stage and reached a plateau in the early summer, then followed an abrupt decrease when foliage senescence occurred. The multiplier K r to soil respiration coefficients were reduced to 0.5 in wintertime; however it increased rapidly in the spring and reached about 1.0 in summertime. The intensity of soil respiration may be related to the metabolic responses of the microbial communities and the availability of labile substances in summer and winter. From leaf expanding in the spring to senescing in the autumn, C f presented declining trend from 0.88 to 0.78 with slight variation; m increased from 5 and approached to an approximately stable value of 8 since early summer. With optimized parameters, the estimates of GPP, R E, net ecosystem production and water vapor fluxes were significantly improved compared with the measurements at daily and annual time steps. With eddy covariance fluxes, data assimilation with an ensemble Kalman filter can successfully retrieve the seasonal and inter-annual variations of parameters related to photosynthesis and respiration of this boreal ecosystem site.