Latitudinal gradient in the respiration quotient and the implications for ocean oxygen availability

Climate-driven depletion of ocean oxygen strongly impacts the global cycles of carbon and nutrients as well as the survival of many animal species. One of the main uncertainties in predicting changes to marine oxygen levels is the regulation of the biological respiration demand associated with the biological pump. Derived from the Redfield ratio, the molar ratio of oxygen to organic carbon consumed during respiration (i.e., the respiration quotient, r−O2:C) is consistently assumed constant but rarely, if ever, measured. Using a prognostic Earth system model, we show that a 0.1 increase in the respiration quotient from 1.0 leads to a 2.3% decline in global oxygen, a large expansion of low-oxygen zones, additional water column denitrification of 38 Tg N/y, and the loss of fixed nitrogen and carbon production in the ocean. We then present direct chemical measurements of r−O2:C using a Pacific Ocean meridional transect crossing all major surface biome types. The observed r−O2:C has a positive correlation with temperature, and regional mean values differ significantly from Redfield proportions. Finally, an independent global inverse model analysis constrained with nutrients, oxygen, and carbon concentrations supports a positive temperature dependence of r−O2:C in exported organic matter. We provide evidence against the common assumption of a static biological link between the respiration of organic carbon and the consumption of oxygen. Furthermore, the model simulations suggest that a changing respiration quotient will impact multiple biogeochemical cycles and that future warming can lead to more intense deoxygenation than previously anticipated.

Using respiration quotients to track changing sources of soil respiration seasonally and with experimental warming

Developing a more mechanistic understanding of soil respiration is hampered by the difficulty in determining the contribution of different organic substrates to respiration and in disentangling autotrophic-versus-heterotrophic and aerobic-versus-anaerobic processes. Here, we use a relatively novel tool for better understanding soil respiration: the apparent respiration quotient (ARQ). The ARQ is the amount of CO2 produced in the soil divided by the amount of O2 consumed, and it changes according to which organic substrates are being consumed and whether oxygen is being used as an electron acceptor. We investigated how the ARQ of soil gas varied seasonally, by soil depth, and by in situ experimental warming (+4 ∘C) in a coniferous-forest whole-soil-profile warming experiment over 2 years. We then compared the patterns in ARQ to those of soil δ13CO2. Our measurements showed strong seasonal variations in ARQ, from ≈0.9 during the late spring and summer to ≈0.7 during the winter. This pattern likely reflected a shift from respiration being fueled by oxidized substrates like sugars and organic acids derived from root and root respiration during the growing season to more reduced substrates such as lipids and proteins derived from microbial necromass during the winter. This interpretation was supported by δ13CO2 values, which were lower, like lipids, in the winter and higher, like sugars, in the summer. Furthermore, experimental warming significantly changed how both ARQ and δ13CO2 responded to soil temperature. Wintertime ARQ and δ13CO2 values were higher in heated than in control plots, probably due to the warming-driven increase in microbial activity that may have utilized oxidized carbon substrates, while growing-season values were lower in heated plots. Experimental warming and phenology change the sources of soil respiration throughout the soil profile. The sensitivity of ARQ to these changes demonstrates its potential as a tool for disentangling the biological sources contributing to soil respiration.

The Resting-State Pulse-Respiration Quotient of Humans: Lognormally Distributed and Centered Around a Value of Four

The pulse-respiration quotient (heart rate divided by the respiration rate, PRQ = HR/RR) is a parameter capturing the complex state of cardiorespiratory interactions. We analysed 482 single PRQ values obtained from measurement on 134 healthy adult subjects (49 men, 85 women, age: 24.7 ± 3.4, range: 20–46 years) during rest. We found that the distribution of PRQ values (i) has a global maximum at around a value of 4 (median: 4.19) and (ii) follows a lognormal distribution function. A multimodality of the distribution, associated with several PRQ attractor states was not detected by our group-level based analysis. In summary, our analysis shows that in healthy humans the resting-state PRQ is around 4 and lognormally distributed. This finding supports claims about the special role of the 4 to 1 cardiorespiratory coupling in particular and the PRQ in general for physiological and medical views and applications. To the best of our knowledge, our study is the largest conducted so far in healthy adult humans about reference values of the PRQ during a resting-state at day.

Using Respiration Quotients to Track Changing Sources of Soil Respiration Seasonally and with Experimental Warming

Developing a more mechanistic understanding of soil respiration is hampered by the difficulty in determining the contribution of different organic substrates to respiration and in disentangling autotrophic versus heterotrophic and aerobic versus anaerobic processes. Here, we present a relatively novel tool for better understanding soil respiration: the apparent respiration quotient (ARQ). ARQ is the amount of CO2 produced in the soil divided by the amount of O2 consumed and it changes according to which organic substrates are being consumed and whether oxygen is being used as an electron acceptor. We investigated how the ARQ of soil gas varied seasonally, by soil depth, and by experimental warming in situ in a coniferous forest whole-soil-profile warming experiment over two years. We then compared the patterns in ARQ to those of soil δ13CO2. Our measurements showed strong seasonal variations in ARQ from ≈ 0.9 during the late spring and summer to ≈ 0.7 during the winter. This pattern likely reflected a shift from respiration being fueled by oxidized substrates like sugars and organic acids derived from root and root respiration during the growing season to more reduced substrates such as lipids and proteins derived from microbial necromass during the winter. This interpretation was supported by δ13CO2 values, which were relatively depleted, like lipids, in the winter and more enriched, like sugars, in the summer. Furthermore, wintertime ARQ was higher in warmed (+4 °C) than in control plots, probably due to an increase in the use of more oxidized carbon substrates with warming. Our results demonstrate that soil ARQ shows strong seasonal patterns in line the phenology of carbon inputs and patterns in soil δ13CO2, verifying ARQ as a tool for disentangling the biological sources contributing to soil respiration.

Study and Analysis of Human Survival Parameters in Mine Refuge Station

In order to study life support key techniques in mine refuge station, test the clinical emergency response of participants and human survival parameters in rescue state. A manned test with 50 miners for 48h in a real underground refuge station was conducted in Guilaizhuang gold mine. The experiment simulated rescue living environment of human and consisted of three stages (the passive stage, the compressed air supplying stage, and the compressed O supplying stage). By monitoring environmental concentrations of O2, CO2, temperature, relative humidity, and human activity states during the test, the O2 consumption, CO2 production and respiration quotient was obtained and analysed in different activities, time quantum and O2 concentration. On the basis, the minimum air supply volumes for the survival of test personnel were determined. That is 0.067m/min per person and is far lower than the national standard 0.3m/min per person. During the test, no people experienced discomfort by health check and questionnaire. It is expected that the conclusions provide an important reference for the design of underground refuge stations and mine emergency rescue.