Respiratory Quotient Research Articles

How to interpret and apply the results of indirect calorimetry studies: A case-based tutorial

Evidence is growing that the individual adjustment of energy targets guided by indirect calorimetry (IC) can improve outcome. With the development of a new generation of devices that are easier to use and rapid, it appears important to share knowledge and expertise that may be used to individualize nutrition care. Despite the focus of this tutorial being on one contemporary device, the principles of IC apply across existing devices and can assist tailoring the nutrition prescription and in assessing response to nutrition therapy. The present tutorial addresses its clinical application in intubated mechanically ventilated and spontaneously breathing adult patients (canopy), i.e. it covers the range from critical illness to outpatients.The cases that are presented show how the measured energy expenditure (mEE), and the respiratory quotient (RQ), i.e. the ratio of expired CO2 to consumed O2, should be applied in different cases, to adapt and individualize nutrition prescription, as it is a good marker of over- or underfeeding at the different stages of disease. The RQ also informs about the patient's body’s capacity to use different substrates: the variations of RQ indicating the metabolic changes revealing insufficient or excessive feeding. The different cases reflect the use of a new generation device as a metabolic monitor that should be combined with other clinical observations and laboratory biomarkers. The tutorial also points to some shortcomings of the method, proposing alternatives.

Dietary macronutrient composition and its effect on 24-h substrate oxidation: A study of diurnal variations in carbohydrate and fat intake

IntroductionIn recent times, the complexity of food styles and meal content has increased, leading to significant variations in macronutrient composition between meals. This has coincided with a rise in obesity rates. ObjectiveTo determine if a larger variation in macronutrient composition between meals results in lower fat oxidation. MethodsA cross-over study was conducted on 13 healthy young male individuals using whole-body indirect calorimetry to test energy metabolic responses under three conditions: regular meals (R), high-carbohydrate breakfast (CB), or high-fat breakfast (FB), each with different macronutrient contents. R included three meals daily with the same macronutrient composition. CB included a high-carbohydrate meal at breakfast, a high-fat meal at lunch, and a high-carbohydrate meal at dinner. FB included a high-fat meal at breakfast, a high-carbohydrate meal at lunch, and a high-carbohydrate meal at dinner. The daily macronutrient compositions were similar across the three conditions, except CB and FB had larger variations in carbohydrate and fat balance between meals than R. The participants were tested in random order. ResultsThere were no significant differences in the measures of energy expenditure among the three conditions. However, after adjusting for the sleeping respiratory quotient (RQ) on the preceding day, the 24-hour RQ was lower under FB than under R (β=−0.0087, P=0.0077) or CB conditions (β=−0.0078, P=0.016). There was no difference in the magnitude of the 5-hour RQ change from lunch to dinner under the CB condition and in the magnitude of change from breakfast to lunch under the FB condition. ConclusionsA large variation in carbohydrate and fat balance between meals does not decrease daily fat oxidation. A FB may increase daily fat oxidation compared to a CB when the daily food quotient is equal, but this impact may not involve radical acceleration of fat oxidation.

Microbial metabolic traits drive the differential contribution of microbial necromass to soil organic carbon between the rhizosphere of absorptive roots and transport roots

The rhizosphere is a typical soil microbial hotspot, however, not a homogeneous entity. Due to root functional differentiation, different root functional modules (i.e., absorptive roots and transport roots) can play distinct roles in microbial necromass formation and subsequent soil organic carbon (SOC) sequestration by influencing microbial metabolic activity in the surrounding soil. Yet, how microbial metabolic traits mediated by different root functional modules regulate the accumulation of microbial necromass C (MNC) in the rhizosphere remains poorly understood. Herein, we quantified and compared the differences in the contribution of MNC to SOC between the rhizosphere of two root functional modules, and explored the role of microbial metabolic traits in influencing the contribution of MNC to rhizosphere SOC in different root functional modules in two spruce (Picea asperata Mast.) plantations. Our findings revealed that absorptive roots exhibited a significantly higher contribution of MNC to SOC (32.9–37.5%) compared to transport roots (27.7–30.5%) in the rhizosphere. This suggests that absorptive roots possess a greater ability to promote MNC accumulation in the rhizosphere than transport roots. This observation was mainly attributed to the difference in the trade-offs between microbial growth and investment traits between the two root functional modules. Specifically, the rhizosphere of absorptive roots had greater microbial C use efficiency (CUE), faster growth and turnover rates, lower respiratory quotients and biomass-specific enzyme activity than did those of transport roots, suggesting that absorptive roots support greater microbial growth yields and subsequently greater necromass production. Collectively, our findings demonstrate that the contribution of MNC to SOC in the rhizosphere largely depends on the trade-offs of microbial metabolic traits mediated by root functional differentiation. Our study also provides novel and direct empirical evidence supporting the need to integrate function-based fine root classifications with the different contributions of MNC to SOC sequestration in the rhizosphere into land surface models of C cycling.

Heat Production of Iberian Pig Exposed to High Temperature and Effect of Dietary Supplementation with Betaine or Zinc.

The effect of heat, and dietary betaine or zinc on the heat production (HP) of Iberian pigs was studied. Thirty barrows (44 kg) were individually housed for 28 days and assigned to one of five treatments: (1) thermoneutrality (20 °C) and fed a control diet (TN-CON) ad libitum; (2) hot (30 °C) and fed a control diet (HT-CON) ad libitum; (3) thermoneutrality and pair fed a control diet (TN-CON-PF) to HT-CON; (4) hot and fed a betaine-supplemented (0.5%) diet (HT-BET) ad libitum; and (5) hot and fed a zinc-supplemented (0.012%) diet (HT-ZN) ad libitum. On the 18th day, pigs were moved to a respirometry chamber (two chambers) under their respective treatment. The metabolizable energy (ME) intake, HP and respiratory quotient (RQ) were measured over 24 h. No differences (p > 0.05) were found in HP and RE between treatments. For RQ, TN-CON was greater (p < 0.01) than HT treatments, except for HT-BET. All RQs indicated an overall lipogenesis where betaine supplementation showed an intermediate value, indicating that it may have a positive effect on lipogenesis and overall growth. At 30 °C, betaine or zinc had no effect on HP and RE; ME intake was not reduced, indicating a genetic adaptation of Iberian pigs to heat.

Effects of Short-Term Nighttime Carbohydrate Restriction Method on Exercise Performance and Fat Metabolism.

The sleep-low method has been proposed as a way to sleep in a low-glycogen state, increase the duration of low glycogen availability and sleep and temporarily restrict carbohydrates to improve exercise performance. However, long-term dietary restriction may induce mental stress in athletes. Therefore, if it can be shown that the effects of the sleep-low method can be achieved by restricting the carbohydrate intake at night (the nighttime carbohydrate restriction method), innovative methods could be developed to reduce weight in individuals with obesity and enhance athletes' performance with reduced stress and in a shorter duration when compared with those of previous studies. With this background, we conducted a study with the purpose of examining the intervention effects of a short-term intensive nighttime carbohydrate restriction method. A total of 22 participants were recruited among university students participating in sports club activities. The participants were assigned at random to groups, including a nighttime carbohydrate restriction group of 11 participants (6 males, 5 females; age 22.3 ± 1.23) who started a carbohydrate-restricted diet and a group of 11 participants (5 males, 6 females; age 21.9 ± 7.9) who continued with their usual diet. The present study had a two-group parallel design. In the first week, no dietary restrictions were imposed on either group, and the participants consumed their own habitual diets. In the second week, the total amount of calories and carbohydrate intake measured in the first week were divided by seven days, and the average values were calculated. These were used as the daily calorie and carbohydrate intakes in the second week. Only the nighttime carbohydrate restriction group was prohibited from consuming carbohydrates after 4:00 p.m. During the two-week study period, all participants ran for one hour each day before breakfast at a heart rate of 65% of their maximum heart rate. The results obtained from young adults participating in sports showed significant differences in peak oxygen consumption (V·O2peak), work rate max, respiratory quotient (RQ), body weight and lean body mass after the intervention when compared with before the intervention in the nighttime carbohydrate restriction group (p < 0.05). Our findings suggest that the nighttime carbohydrate restriction method markedly improves fat metabolism even when performed for a short period. This method can be used to reduce body weight in individuals with obesity and enhance athletes' performance. However, it is important to consider the intake of nutrition other than carbohydrates.

Glutamatergic signaling from melanin-concentrating hormone-producing neurons: A requirement for memory regulation, but not for metabolism control.

Melanin-concentrating hormone-producing neurons (MCH neurons), found mainly in the lateral hypothalamus and surrounding areas, play essential roles in various brain functions, including sleep and wakefulness, reward, metabolism, learning, and memory. These neurons coexpress several neurotransmitters and act as glutamatergic neurons. The contribution of glutamate from MCH neurons to memory- and metabolism-related functions has not been fully investigated. In a mouse model, we conditionally knocked out Slc17a6 gene, which encodes for vesicular glutamate transporter 2 (vGlut2), in the MCH neurons exclusively by using two different methods: the Cre recombinase/loxP system and in vivo genome editing using CRISPR/Cas9. Then, we evaluated several aspects of memory and measured metabolic rates using indirect calorimetry. We found that mice with MCH neuron-exclusive vGlut2 ablation had higher discrimination ratios between novel and familiar stimuli for novel object recognition, object location, and three-chamber tests. In contrast, there was no significant change in body weight, food intake, oxygen consumption, respiratory quotient, or locomotor activity. These findings suggest that glutamatergic signaling from MCH neurons is required to regulate memory, but its role in regulating metabolic rate is negligible.

Effect of carnitine supplementation on energy utilization in patients with type 2 diabetes and long-term tube feeding: A CARE-compliant case report

Introduction: Carnitine is essential for the energy utilization of long-chain fatty acids. However, the effects of carnitine supplementation on patients undergoing tube feeding remain unclear, and some enteral formula products do not contain carnitine. In order to gain insights into the role of carnitine supplementation on energy utilization in patients with long-term tube feeding, we observed the changes in respiratory quotient (RQ) of patients before and after the addition of carnitine due to the renewal of an enteral formula product. Case presentation: We observed 6 patients who continued tube feeding with the same enteral formula product scheduled for renewal. All 6 participants had diabetes, and indirect calorimetry data were available for 4 patients. Participants were observed for 3 months after switching to the new formulation. After the switching, a carnitine supplementation of 120 to 180 mg/day was provided, depending on the intake amount. One month after switching, blood free carnitine and total carnitine levels in all 6 patients increased from below the lower limit to within the range of the Japanese reference standard. In 3 of the 4 patients for whom indirect calorimetry was possible, the fasting RQ at baseline was &gt;0.90, suggesting impaired lipid utilization. The mean fasting RQ significantly decreased 2 months after the switch. The 1- and 2-hour postprandial RQ also showed a significant decrease after switching. Conclusion: Carnitine supplementation of enteral formulas may be important for normal energy utilization of lipids in patients receiving long-term tube feeding. An evaluation using randomized controlled trials with a larger number of patients is required.

Enhancing biodegradation of aged hydrocarbon-contaminated soils through toluene addition: assessing effects on solid and slurry phase treatments.

The main challenge in treating aged soils highly contaminated with total petroleum hydrocarbons (TPH) is to enhance their bioavailability for microbial degradation. Hydrocarbons in soils undergo chemical changes that make them more resistant to biodegradation. This study investigates toluene's efficacy in enhancing the biodegradation of aged hydrocarbon-contaminated soil containing 292,000mg TPH kg-1 dry soil. Toluene's effect was compared between solid phase (SOP) and slurry phase (SLP) treatments using a microbial consortium isolated from Cyperus laxus rhizosphere. TPH biodegradation and microbial respiration were measured, the latter to estimate the respiratory quotient (RQ, the ratio between moles of carbon dioxide released and moles of oxygen absorbed during respiration). Toluene significantly accelerated TPH biodegradation in both treatments, achieving ~ 30% higher removal than in a non-solvent control, possibly through improved bioavailability of aromatic compounds and other low molecular weight compounds. According to the RQ analysis, toluene enhanced microbial respiratory processes and hydrocarbon catabolism with higher hydrocarbon mineralization (RQ = ~ 0.5) in both SOP and SLP assays. Our results reveal toluene's potential to increase hydrocarbon availability and microbial degradation efficiency in aged contaminated soils; its use in various bioremediation techniques could be of broad applicability across diverse soil types and pollutants.

Evaluation of a portable, lightweight modular system to deliver high inspired oxygen to trauma casualties without the use of pressurised cylinders

IntroductionAdministering supplemental oxygen is a standard of care for trauma casualties to minimise the deleterious effects of hypoxaemia. Forward deployment of oxygen using pressurised cylinders is challenging, for example, logistics...

Incremental supply of fat, lactose, or protein influences the diurnal pattern of heat production and substrate oxidation in preweaning calves

Increasing nutrient supply to dairy calves has well known benefits; however, the effects of milk replacer (MR) composition when supplied in higher amounts are not fully understood, particularly in the first weeks of life. To better understand the metabolism of macronutrient supply in young calves (21 d old), we investigated diurnal patterns of heat production and substrate oxidation in young calves fed MR with an incremental supply of fat, lactose, or protein. Thirty-two groups of 3 mixed-sex Holstein-Friesian newborn calves (3.4 ± 1.6 d of age), were randomly assigned to one of 4 dietary treatments and studied for 21 d. Diets consisted of a basal MR (23.3% CP, 21.2% EE, and 48.8% lactose of DM) fed at 550 kJ/kg BW0.85 per day (CON; n = 24), or the basal MR incrementally supplied with 126 kJ of digestible energy/BW0.85 per day as milk fat (+FAT; n = 23), lactose (+LAC; n = 24), or milk protein (+PRO; n = 23). Calves were fed MR in 2 daily meals and had ad libitum access to water, but were not supplied with any calf starter nor forage. After 2 weeks of adaptation to the diets, groups of 3 calves were placed for 1 wk in an open-circuit respiration chamber for nitrogen and energy balance measurements (lasting 7 d). On d 3, glucose oxidation kinetics was estimated by using [U-13C]glucose. Measurements included total heat production (total energy [HP], activity [Hact] expenditure, resting metabolic rate [RMR]), respiration quotient (RQ), carbohydrate (COX) and fat oxidation (FOX) in 10 min. intervals and averaging these values per hour over days. Incremental supply of lactose and fat increased body fat deposition, with observed patterns in RMR indicating that this increase occurred primarily after the meals. Specifically, the average daily RMR was highest in the +PRO group and lowest in the CON treatment. The HP was higher in the +PRO group and throughout the day, hourly means of HP were higher in this treatment mainly caused by an increase in Hact. The recovery of 13CO2 from oral pulse-dosed [U-13C]glucose was high (77%), and not significantly different between treatments, indicating that ingested lactose was oxidized to a similar extent across treatments. Increasing lactose supply in young calves increased fat retention by reduction in fatty oxidation. Calves fed a MR with additional protein or fat raised RMR persistently throughout the day, whereas the extra lactose supply only affects RMR after the meal. Dietary glucose was almost completely oxidized (77% based on (13C) glucose measurement) regardless of nutrient supplementation. Extra protein supply increased HP and FOX compared with similar intakes of fat and lactose. Fasting heat production (FHP) of young, group-housed calves is comparable to literature values and unaffected by energy intake. Overall, these findings deepen our understanding of how different nutrients affect metabolic processes, fat retention, and energy expenditure in young dairy calves.

The Role of Macronutrients in Chronic Obstructive Pulmonary Disease: A Review

The incidence of chronic obstructive pulmonary disease (COPD) is rising and is still regarded as one of the challenging medical issues. Regardless of the main relationship between tobacco smoking and toxic particle exposure with COPD, factors like nutritional status also play an important role in COPD progression and outcome, as the factor is an adaptable aspect. Malnutrition, sarcopenia, and obesity are nutritional problems that are often encountered in COPD patients. Macronutrients, namely carbohydrates, fat, and protein, support the adjunctive treatment options for COPD. The ideal dietary pattern includes low carbohydrates, medium fats preferably polyunsaturated fatty acids (PUFA), and high proteins to improve COPD symptoms, preserve muscle mass, and delay disease progression. High carbohydrate intake might also increase the respiratory quotient (RQ) which results in higher carbon dioxide (CO2) production and oxygen (O2) demand compared to fat and protein intake. Daily calorie intake should be adjusted to personal nutritional status. Higher calories in malnourished, sarcopenic patients and targeted weight loss in obese patients show improvements in lung function, frequency of exacerbations, and hospitalization rate. In obese individuals with COPD, however, maintaining a slightly higher body mass index (BMI) of 25-30 kg/m2 was associated with lower mortality. This literature review summarized the significant role of macronutrients in COPD patients and the practical approach to macronutrient intervention in individuals with different nutritional statuses.

Evaluation of metabolic changes in clinic attendees with therapeutic carbohydrate restriction

Background: Obesity and related metabolic health disorders are major clinical problems that have become increasingly prevalent worldwide.Aim: This before-after study examined the impact of therapeutic carbohydrate restriction (TCR) in managing metabolic health and promoting weight loss in a clinical setting using indirect calorimetry (IC).Setting: Data were collected from medical records obtained from a specialised allied health clinic focusing on metabolic health.Methods: The study analysed retrospective data from 202 overweight or obese participants (77% female, mean age 47.3) who received TCR as part of a behavioural modification programme involving multiple visits where their lifestyle, body composition and respiratory quotient (RQ), a key indicator of fat oxidation were recorded.Results: The study found that TCR improved fat oxidation in 84% of participants at short term visit (around 2 weeks), with an average weight loss of 1.8 kg. At medium term visit (around 12 weeks), 82% of participants maintained an increase in fat oxidation rate, with an average weight loss of 3.9 kg. In addition, among those with recorded body composition and waist circumference, 71% of weight lost was from fat, with an average reduction of 4.9 cm in waist measurements.Conclusion: This real-world study suggests that personalised TCR guided by IC can be an effective strategy for improving metabolic flexibility to help manage excess weight and related co-morbidities in a free-living population. Further research is needed to examine the long-term effects of TCR using this approach.Contribution: The utilisation of IC allows for the examination of individual shifts and improvements in metabolism among patients undergoing TCR.

New aspects on the determination of soil‐specific respiration quotients of arable soils for the application in the barometric process separation technique

AbstractBackgroundThe respiratory quotient, that is, the CO2–O2‐exchange ratio during aerobic heterotrophic soil respiration, (RQAHR) is one of the key variables of the barometric process separation (BaPS) technique. For reliable application, the BaPS method requires the adjustment of RQAHR to soil‐specific substrate conditions.AimThe objective of the present study was to determine RQAHR in five arable soils varying between pH 4 and 8 and carbon/nitrogen (C/N) ratios between 8.4 and 11.9 using the BaPS–15N method. Further, we aimed to elucidate whether RQAHR can be estimated from basic soil properties.ResultsDetermined RQAHRs were soil specific and ranged between 0.74 and 1.53. RQAHR particularly affected the calculation of gross nitrification rates but not soil respiration rates. Based on a multiple linear regression analysis, soil pH and the C/N ratio of the soil organic matter pool were identified to explain well (R2 = 0.984) the measured RQAHRs. Applying the thus derived RQMLR to the calculation procedure led to good agreement between gross nitrification rates derived by the 15N pool dilution technique.ConclusionsFuture studies are needed to test whether this empirical relationship between RQAHR, pH, and C/N ratio is generalizable. If this would be the case, the BaPS method could be applied without the use of a stable isotope and thus, being less resource demanding than the 15N pool dilution technique.

298 Impact of ruminal acidosis on cattle energy metabolism

Abstract The objective of this study was to determine the impact of a bout of ruminal acidosis on energy metabolism of cattle unadapted to a high concentrate diet. Eleven ruminally cannulated steers [body weight (BW) = 352 kg ± 27] were blocked into 3 groups based on initial BW. Before the start of the experiment, animals were consuming a forage-based diet as well as adapted to the headbox style respiration chambers. Additionally, before the experiment, gas emission data were collected over a 24-h period when cattle received an ad libitum forage-based diet for use as a covariate in the statistical analysis. For the experiment, steers were moved into headboxes at the conclusion of a 24-h fast and subsequently received 1 of 2 treatment diets: control (CON), forage-based diet or acidosis (AC), concentrate-based diet. Steers remained in the headboxes for 48 h. Gas concentrations from each headbox were collected hourly and analyzed with an infrared photoacoustic gas analyzer. Ruminal pH, fecal pH, volatile fatty acids, and lactate were also measured during the acidosis challenge. Data were analyzed with the MIXED procedure of SAS 9.4. A treatment × day effect (P = 0.03) was observed for dry matter intake with intake being similar for both CON and AC steers on d 1 but AC steers consuming 2.02 kg less on d 2. Treatment affected ruminal pH (P &amp;lt; 0.01) as CON steers had a greater ruminal pH than AC steers. Greater total volatile fatty acids (P &amp;lt; 0.01) were observed for steers on AC treatment compared with CON. A treatment × time interaction (P &amp;lt; 0.01) was observed for ruminal lactate concentration with AC steers having greater concentrations from h 16 to 36. Fecal pH was affected by a treatment × time interaction (P = 0.05) as AC steers had lower fecal pH from h 24 to h 32. Over the 48-h observation period, there was a treatment × time interaction (P = 0.04) for carbon dioxide production as AC steers produced less CO2 after h 24. No treatment × time interaction was detected for oxygen consumption. However, there was a time effect (P &amp;lt; 0.01). Respiratory quotient was not affected by treatment, day, or their interaction (P ≥ 0.19). Heat production tended (P = 0.06) to be different between treatments, with AC having less heat production than CON. Thus, the effects of ruminal acidosis on gas emissions and energetics may be more transient during the time course of an acidotic bout or have a longer duration even after ruminal pH has recovered.

Decoding Stress: The Universal Language of Entropy Production

The accurate quantification of stress remains a formidable challenge in the realm of physiological research, largely owing to the intricate nature of the stress response and its potential overlap with other physiological processes. In this vein, our research introduces a novel metric: the stress entropic load (SEL), grounded in thermodynamic principles. SEL is mathematically construed as a time-dependent function, articulated through various heat and temperature alterations, as well as changes in respiratory gas exchanges. This measure is posited as a predictive tool for stress and metabolic alterations in homeothermic organisms, including humans. Our empirical exploration involved 12 healthy male volunteers, structured in a dual-phase experimental design. The initial phase focused on achieving a resting metabolic rate (RMR), guided by specific criteria encompassing oxygen uptake, carbon dioxide release, and respiratory quotient. In instances where RMR benchmarks were not met within a 40-minute window, the study progressed, presuming RMR attainment. The collected data from this segment were pivotal in calculating the body's entropy production at rest. The subsequent phase entailed participants engaging in tasks via the WinSCAT software, signifying the onset of the stress phase. Here, entropy production was scrutinized to gauge stress levels. Crucially, SEL was ascertained by contrasting entropy production during the RMR phase (serving as a baseline) against that recorded throughout the experiment's entirety. Our findings indicate that SEL, as an indicator of specific entropy production, emerges as a viable marker of stress induced by prolonged mental effort. Notably, extended interaction with WinSCAT software markedly augmented SEL rates. The progression of SEL over time offered insights into when participants commenced stress-inducing tasks, underscoring its viability as a biological marker for mental exertion. Intriguingly, such stress did not manifest in conventional stress indicators like blood pressure or heart rate, though it did affect oxygen and carbon dioxide production. While these results lend credence to the utility of SEL as a stress marker, they are preliminary in nature, illuminating the prospective significance of SEL in the realms of stress measurement and physiological research. The project was funded by MUNI/G/1249/2021 grant by the Masaryk University. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Unequal impacts of unidirectional freeze-thaw on different soil layers and aggregate sizes: Evidenced by microbial communities and CO2 emissions

Currently available investigations often fail to adequately recognize that soil does not freeze or thaw instantly nor uniformly, but unidirectionally and progressively. Unidirectional freeze-thaw can re-organize soil physio-, chemical- and biological-properties across layers as well among aggregates, thus posing far-reaching yet undervalued impacts on soil carbon biogeochemical cycling, especially in eroding settings. In this study, a Mollisol was refilled into soil columns, and respectively experienced complete freeze-thaw (i.e., no layer distinguished), and progressive freeze-thaw (i.e., from outer layer T1, to inner core T3). After thawing, all soils were fractionated into six size classes, and each size class was then incubated at 10℃ over 7 days to measure daily CO2 emission rate. Our results show that: (1) The soil microbial biomass carbon (SMBC) was generally reduced by 25 % after freeze-thaw, but only the finest aggregates ≤ 32 μm maintained comparable CO2 emission rates. (2) The inner core T3 thawed last and survived with significantly more SMBC and CO2, but lower respiratory quotient (qCO2), than the outer layer T1 thawed first. (3) The fine aggregates survived with more SMBC and total CO2 emissions, but significantly lower qCO2 and smaller ratios of fungal to bacterial biomass carbon, than the coarse aggregates. The disproportionally less respiratory carbon losses (i.e., lower qCO2) in T3 was probably because the lagged freezing and thus weakened water-ice phase changes in the inner core helped to better preserve the soil microbes. The fungal-dominant coarse aggregates were very responsive to freezing and evidently more respiratory active, whereas the fine aggregates were more resilient as the enhanced freezing point depression and the thus prolonged unfrozen state, fostering a better microbial survival with bacteria-dominant communities and robust basal respiration. Although limited to controlled simulation, this study may help to disentangle the role of unidirectional freeze-thaw in perturbing slope-scale soil carbon biogeochemical cycling.

Effects of Land-Use Type and Salinity on Soil Carbon Mineralization in Coastal Areas of Northern Jiangsu Province

Sea level rise due to glacier melting caused by climate warming is a major global challenge, but the mechanism of the effect of salinity on soil carbon (C) mineralization in different land types is not clear. The pathways by which salinity indirectly affects soil carbon mineralization rates need to be investigated. Whether or not the response mode is consistent among different land-use types, as well as the intrinsic links and interactions between soil microbial resource limitation, environmental stress, microbial extracellular enzyme activity, and soil carbon mineralization, remain to be demonstrated. In this paper, three typical land-use types (wetland, forest, and agroforestry) were selected, and different salinity levels (0‰, 3‰, 6‰, and 32‰) were designed to conduct a 125-day laboratory incubation experiment to determine the soil CO2 release rate, soil physicochemical properties, and soil enzyme activities, and to correlate C mineralization with biotic and abiotic factors. A correlation analysis of soil physical and chemical properties, extracellular enzyme activities, and carbon mineralization rates was conducted to investigate their intrinsic linkages, and a multiple linear regression of C mineralization at different sites was performed to explore the variability of mineralization among different site types. Structural equation models were established in the pre- and post-incubation stages to study the pathways of soil C mineralization at different incubation times, and the mechanism of mineralization was further verified by enzyme stoichiometry. The results showed that, at the end of 125 days of incubation, the 32‰ salinity addition reduced the cumulative mineralization of forest and agroforestry types by 28.41% and 34.35%, respectively, compared to the 0‰ salinity addition. Soil C mineralization in the three different land-use types was highly correlated with the active C fractions of readily oxidizable C (ROC), dissolved organic C, and microbial biomass C (MBC) in the soil, with the standardized coefficients of multivariate linear regression reaching 0.67 for MBC in the wetland and −0.843 for ROC in the forest. Under long-term salinity additions, increased salinity would reduce the microbial respiratory quotient value by inhibiting β-glucosidase activity, thus indirectly affecting the rate of CO2 release. With added salinity, the mineralization of non-saline soil was more susceptible to the inhibitory effect of salinity, whereas the mineralization of salinized soil was more controlled by soil C pools.

Breathing Planet Earth: Analysis of Keeling’s Data on CO2 and O2 with Respiratory Quotient (RQ), Part II: Energy-Based Global RQ and CO2 Budget

For breathing humans, the respiratory quotient (RQ = CO2 moles released/O2 mols consumed) ranges from 0.7 to 1.0. In Part I, the literature on the RQ was reviewed and Keeling’s data on atmospheric CO2 and O2 concentrations (1991–2018) were used in the estimation of the global RQ as 0.47. A new interpretation of RQGlob is provided in Part II by treating the planet as a “Hypothetical Biological system (HBS)”. The CO2 and O2 balance equations are adopted for estimating (i) energy-based RQGlob(En) and (ii) the CO2 distribution in GT/year and % of CO2 captured by the atmosphere, land, and ocean. The key findings are as follows: (i) The RQGlob(En) is estimated as 0.35 and is relatively constant from 1991 to 2020. The use of RQGlob(En) enables the estimation of CO2 added to the atmosphere from the knowledge of annual fossil fuel (FF) energy data; (ii) The RQ method for the CO2 budget is validated by comparing the annual CO2 distribution results with results from more detailed models; (iii) Explicit relations are presented for CO2 sink in the atmosphere, land, and ocean biomasses, and storage in ocean water from the knowledge of curve fit constants of Keeling’s curves and the RQ of FF and biomasses; (iv) The rate of global average temperature rise (0.27 °C/decade) is predicted using RQGlob,(En) and the annual energy release rate and compared with the literature data; and (v) Earth’s mass loss in GT and O2 in the atmosphere are predicted by extrapolating the curve fit to the year 3700. The effect of RQGlob and RQFF on the econometry and policy issues is briefly discussed.

Structural complexity and benthic metabolism: resolving the links between carbon cycling and biodiversity in restored seagrass meadows

Abstract. Due to large losses of seagrass meadows worldwide, restoration is proposed as a key strategy for increasing coastal resilience and recovery. The emergence of a seagrass meadow is expected to substantially amplify biodiversity and enhance benthic metabolism by increasing primary productivity and respiration. Nevertheless, open questions remain regarding the metabolic balance of aging seagrass meadows and the roles benthic communities within the seagrass ecosystem play in overall metabolism. To address these questions, we investigated a chronosequence of bare sediments and adjacent Zostera marina meadows of 3 and 7 years since restoration alongside a natural meadow located within a high-temperate marine embayment in Gåsö, Sweden. We combined continuous measurements of O2 fluxes using underwater eddy covariance with dissolved inorganic carbon (DIC) and O2 fluxes from benthic chambers during the productive season (July). Based on the ratio between O2 and DIC, we derived site-specific photosynthetic and respiratory quotients, enabling the conversion of eddy covariance fluxes to DIC. We assessed benthic diversity parameters as potential drivers of metabolic flux variability. We observed high rates of gross primary productivity (GPP) spanning −18 to −82 mmolDICm-2d-1, which increased progressively with meadow age. Community respiration (CR) mirrored the GPP trend, and all meadows were net heterotrophic (GPP &lt; CR), with net community productivity (NCP) ranging from 16 to 28 mmolDICm-2d-1. While autotrophic biomass did not increase with meadow age, macrophyte diversity did, elucidating potential effects of niche complementarity among macrophytes on community metabolism. These findings provide valuable insights into how community composition and meadow development relate to ecosystem functioning, highlighting potential tradeoffs between carbon uptake and biodiversity.

Maximal cardiopulmonary exercise testing in glioblastoma patients undergoing chemotherapy: assessment of feasibility, safety, and physical fitness status.

Maximal cardiopulmonary exercise testing (max. CPET) provides the most accurate measurement of cardiorespiratory fitness. However, glioblastoma (GBM) patients often undergo less intensive tests, e.g., 6-min walk test or self-rating scales. This study aims to demonstrate feasibility and safety of max. CPET in GBM patients, concurrently evaluating their physical fitness status. Newly diagnosed GBM patients undergoing adjuvant chemotherapy were offered participation in an exercise program. At baseline, max. CPET assessed cardiorespiratory fitness including peak oxygen consumption (VO2peak), peak workload, and physical work capacity (PWC) at 75% of age-adjusted maximal heart rate (HR). Criteria for peak workload were predefined based on threshold values in HR, respiratory quotient, respiratory equivalent, lactate, and rate of perceived effort. Data were compared to normative values. Adverse events were categorized according to standardized international criteria. Further, self-reported exercise data pre- and post-diagnosis were gathered. All 36 patients (median-aged 60; 21 men) met the predefined criteria for peak workload. Mean absolute VO2peak was 1750 ± 529 ml/min, peak workload averaged 130 ± 43 W, and mean PWC was 0.99 ± 0.38 W/kg BW, all clinically meaningful lower than age- and sex-predicted normative values (87%, 79%, 90%, resp.). Only once (3%) a minor, transient side effect occurred (post-test dizziness, no intervention needed). Self-reported exercise decreased from 15.8 MET-h/week pre-diagnosis to 7.2 MET-h/week post-diagnosis. Max. CPET in this well-defined population proved feasible and safe. GBM patients exhibit reduced cardiorespiratory fitness, indicating the need for tailored exercise to enhance health and quality of life. CPET could be essential in establishing precise exercise guidelines.