Differences In CO2 Production Research Articles

Impacts of Nutrients on Alkene Biodegradation Rates and Microbial Community Composition in Enriched Consortia from Natural Inocula.

There is a growing need for biological and chemical methods for upcycling plastic waste streams. Pyrolysis processes can accelerate plastic depolymerization by breaking polyethylene into smaller alkene components which may be more biodegradable than the initial polymer. While the biodegradation of alkanes has been extensively studied, the role microorganisms play in alkene breakdown is not well understood. Alkene biodegradation holds the potential to contribute to the coupling of chemical and biological processing of polyethylene plastics. In addition, nutrient levels are known to impact rates of hydrocarbon degradation. Model alkenes were used (C6, C10, C16, and C20) to follow the breakdown capability of microbial communities from three environmental inocula in three nutrient levels over the course of 5 days. Higher-nutrient cultures were anticipated to exhibit enhanced biodegradation capabilities. Alkene mineralization was assessed by measuring CO2 production in the culture headspace using GC-FID (gas chromatography-flame ionization detection), and alkene breakdown was directly quantified by measuring extracted residual hydrocarbons using gas chromatography-mass spectrometry (GC/MS). Here, the efficacy of enriched consortia derived from the microbial communities of three inoculum sources (farm compost, Caspian Sea sediment, and an iron-rich sediment) at alkene breakdown was investigated over the course of 5 days across three nutrient treatments. No significant differences in CO2 production across nutrient levels or inoculum types were found. A high extent of biodegradation was observed in all sample types, with most samples achieving 60% to 95% biodegradation of all quantified compounds. Here, our findings indicate that alkene biodegradation is a common metabolic process in diverse environments and that nutrient levels common to culture media can support the growth of alkene-biodegrading consortia, primarily from the families Xanthamonadaceae, Nocardiaceae, and Beijerinkiaceae. IMPORTANCE Excess plastic waste poses a major environmental problem. Microorganisms can metabolize many of the breakdown products (alkenes) of plastics. While microbial degradation of plastics is typically slow, coupling chemical and biological processing of plastics has the potential to lead to novel methods for the upcycling of plastic wastes. Here, we explored how microbial consortia derived from diverse environments metabolize alkenes, which are produced by the pyrolysis of polyolefin plastics such as HDPE, and PP. We found that microbial consortia from diverse environments can rapidly metabolize alkenes of different chain lengths. We also explored how nutrients affect the rates of alkene breakdown and the microbial diversity of the consortia. Here, the findings indicate that alkene biodegradation is a common metabolism in diverse environments (farm compost, Caspian sediment, and iron-rich sediment) and that nutrient levels common to culture medium can support growth of alkene-biodegrading consortia, primarily from families Xanthamonadaceae, Nocardiaceae, and Beijerinkiaceae.

Effects of food and feeding regime on CO2 fluxes from mangrove consumers – Do marine benthos breathe what they eat?

Intertidal benthos link tertiary predators and primary producers in marine food webs as well as directly contribute to sediment CO2 emission. However, current methods for studying food sources of marine benthos are time-consuming and does not allow direct estimates on feeding regime-related (including different diets, active versus dormant) CO2 production. We examined the food sources of mangrove crabs and gastropods as well as their corresponding CO2 production using cavity-ring down spectroscopy to measure the δ13C–CO2 respiration for consumers, considering the effects of feeding regime, benthos taxa, and dominant feeding habit. Benthos taxa and feeding habit have significant impact on δ13C–CO2 respiration. Particularly, the δ13C–CO2 respiration for crabs (−23.9 ± 0.4‰) was significantly lower than that for gastropods (−17.5 ± 1.3‰). The δ13C–CO2 respiration for deposit-feeders was significantly higher than that for detritivores. There are significant differences in the amount of CO2 emitted and δ13C–CO2 respiration for crabs under different feeding regimes. The differences reflect diet-switching and fuel-switching by the crabs, i.e. ‘you breathe what you eat’. Significant differences in CO2 production of crabs also exist between those feeding on microphytobenthos in the laboratory (0.13 ± 0.02 mmol g−1 day−1) and on field collection (i.e. just collected from the field) (0.31 ± 0.03 mmol g−1 day−1). CO2 production of crabs is strongly related to carapace width and length. The δ13C–CO2 respiration for mangrove crabs reflects their diet while crab-respired CO2 flux is related to crab size. These relationships enable partitioning the feeding habit and food sources of key benthos, and help incorporate their contribution into the overall sediment-atmosphere CO2 fluxes in mangrove forests.

Impact of Immune Function on Aerobic Capacity in Rats

BackgroundThe use of immunocompromised animals has been indispensable in cancer and immunology research. The use of exercise with these models in these areas of research has increased dramatically over the past decade, with little to no evidence of how immune modification of strains of animals is impacting exercise capacity and/or responses to training. This data is critical for extrapolation to exercise recommendations in humans as the majority of cancer patients do not present with primary immunodeficiency diseases. Recently, observations of lower skeletal muscle oxidative capacity between RNU (NIH Nude, immunocompromised) and Copenhagen rats (immunocompetent) have been speculated to result from possible differences between immune function in animals. The purpose of this study was to determine if there are differences in maximal aerobic capacity, through assessment of V̇o2max, between immune‐competent and ‐compromised animals of the same strain. We tested the hypothesis that immunocompromised animals would have a lower aerobic capacity than their immunocompetent counterparts.MethodsRNU 316 (NU−/−, T‐cell deficient; n=10) and RNU 118 (NU+/−, no deficiency; n=10) male rats (~4 months old) were obtained from Charles River. Both groups were acclimated to motorized treadmill running at varying speeds (20–40 m/min) for 3–5 sessions before beginning V̇o2max assessment. V̇o2max graded treadmill testing consisted of a 2‐minute warm‐up at 25 m/min at a 5% incline followed by 2 minutes at 35 m/min, and subsequent increases in speed of 5 m/min every minute after until a plateau was seen in oxygen consumption with increased speed, or test termination was required for safety of the animal. Tests were repeated a minimum of two times (3 maximally) per animal to verify maximum values were achieved.ResultsThere were no significant differences in body mass (NU−, 347±12 g, NU+, 321±8 g; p=0.17). V̇o2max was lower in NU− vs NU+ animals (80.0±1.5 vs. 88.4±1.9 ml·min−1·kg−1; p<0.01). There was a significant difference in respiratory exchange ratio (RER) at V̇o2max (NU−, 1.05±0.01 vs. NU+, 0.98±0.01; p<0.05), but no difference in CO2 production (NU−, 83.7±1.3 vs. NU+, 86.7±1.5 ml·min−1·kg−1; p>0.05).ConclusionThis study suggests that immunocompromised animals have a decreased aerobic capacity compared to immunocompetent counterparts. This should be considered when both designing exercise interventions in immunedeficient/compromised animals as well as interpretations derived from such studies.Support or Funding InformationNIH HL137156‐01A1ACS RSG‐14‐150‐01‐CCE

Real-time multi-level CO2 concentration monitoring in vadose zone wells and the implication for detecting leakage events

Multi-level wells screened at different depths in the vadose zone were installed and used for CO2 and carbon isotope monitoring. Well CO2 time series data were collected along with subsurface and atmospheric parameters such as air pressure, temperature, wind speed, and moisture content. Our aim was to determine the natural factors affecting the variation of CO2 concentration and how the influence of these factors varies with time of day and seasons of the year. We were motivated to understand the cause and extent of CO2 natural fluctuations in vadose zone wells in order to separate natural variation from signals due to anthropogenic CO2 leaks anticipating future monitoring using these wells. Variations of seasonal mean and variance of CO2 concentrations at different depths seem to follow the diurnal trend of subsurface temperature changes that reflect the atmospheric temperature but with time delay and amplitude damping due to heat transport considerations. The temperature in the ground lags behind the change in the atmospheric temperature, thus, the deeper the depth, the longer the time delay and the smaller the amplitude of the change. Monitored seasonal variation as shown in Appendix A shows the temperature-dependent depth-dependent CO2 production in the soil zone indicating higher CO2 concentrations in the summer and fall seasons with high concentrations ranging between 10,990 and 51,600 ppm from spring to summer, and 40,100 and 17,760 ppm from fall to winter. As the temperature in the organic-rich topsoil layer changes from daytime to nighttime, the concentration of CO2 in the soils also changes dynamically in response to chemical and biological reactions. When a screened well is installed in the vadose zone the dynamic temporal and depth difference in CO2 production is further complicated by upward (out of the subsurface) or downward (into the subsurface) gas flow, which will amplify or attenuate the temporal and vertical biochemically produced differences. Nested wells screened at different depths in the vadose zone and wells fully screened through the vadose zone were used for comparison. In addition, experiments changing the well from open to surface air to sealed at the top were conducted. The flow rates of inhaled (downward) and exhaled (upward) gas were estimated based on multi-level monitoring data. Based on time-series monitoring data, we proposed a time-dependent conceptual model to explain the changes of CO2 concentration in wells. The conceptual model was tested through analytical model computations. This conceptual model of natural variation of CO2 will be helpful in utilizing the vadose zone well as a method for monitoring CO2 leakage from subsurface storage or anthropogenic CO2 -producing activities.

Understanding the fate of soil organic matter in submerging coastal wetland soils: A microcosm approach

Coastal wetland submergence can occur when rates of relative sea-level rise exceed that of soil elevation gain or landward transgression. In highly organic soils, the collapse of the wetland platform into open water can cause disarticulation of the soil structure, exposing previously protected anaerobic microzones to oxygenated seawater, which may accelerate mineralization rates. Nine soil cores (1 m deep) were collected from three sites within Barataria Bay, LA (USA), a region known for high rates of wetland submergence. Both the biogeochemical properties of the soils with depth were determined, as well as the impacts of the introduction of oxygenated seawater on carbon mineralization rates. Both field enzyme activity (β‑glucosidase, N‑acetyl‑beta‑d‑glucosaminidase, alkaline phosphatase, β‑xylosidase, and β‑cellobiosidase) and microbial biomass carbon (MBC) did not significantly change with depth until 50 cm, where activity increased dramatically, then gradually decreased. Total carbon (C), total nitrogen, and percent organic matter were highest between 50 and 100 cm. Following initial biogeochemical characterization, soil microcosms were created for 11 depth segments under anaerobic conditions (mimicking an intact wetland) and aerobic conditions (mimicking a submerging wetland mixing with oxygenated water); carbon dioxide (CO2) production was measured within the bottles over 14 days. Carbon dioxide production averaged 66% greater in the aerobic treatment than the anaerobic treatment. Both treatments exhibited a general trend of increasing CO2 production with depth (particularly from 40 to 100 cm), with the difference in CO2 production between aerobic and anaerobic treatments being 4× greater at 90–100 cm than at the soil surface (0–5 cm). The increase in C mineralization rates observed at depth was positively correlated with indicators of greater microbial activity (i.e., higher enzyme activity and MBC) and greater nutrient availability. Study results indicate coastal wetland submergence into open water could significantly enhance CO2 emissions, even in deep (40+ cm) soils, contrary to the typically observed pattern of soil microbial activity and soil quality decreasing with depth. These findings underline the need to analyze deeper soil samples (1+ m) in order to fully understand the implications of sea level rise on C loss from submerging coastal wetland soils.

El efecto de los polímeros absorbentes en la actividad microbiologica del suelo bajo condiciones mediterráneas

Objetivo. El objetivo de este estudio pasa por evaluar el efecto del-Terracottem- en la actividad microbiana del suelo mediante la medida de la respiración edáfica y la pérdida de nitrógeno mineral por lixiviación. El ensayo se ha realizado en condiciones de laboratorio controladas y con suelos naturales. Materiales y metodos. Para el experimento, se han diseñado varios tratamientos: i) suelos naturales a los que se les ha adicionado compuestos nitrogenados de libre disponibilidad (Kg N ha-1); ii) suelos naturales a los que se les ha adicionado carbohidratos de libre disponibilidad (1% de solución de glucosa); iii) suelos naturales a los que se les ha adicionado una mezcla de compuestos nitrogenados de libre disponibilidad (Kg N ha-1) con carbohidratos (1% de solución de glucosa). En cada variante se han testeado diferentes dosis del polímero. Resultados. Los resultados han demostrado que la actividad respiratoria del suelo es independiente de la disponibilidad de compuestos como el nitrógeno o carbono. Tampoco se han observado diferencias significativas entre las diferentes dosis del polímero. Por el contrario, si se observaron diferencias en la producción de CO2. Conclusiones. La lixiviación únicamente se producía cuando los suelos era enmendado con compuestos únicamente nitrogenados o únicamente sólo carbonosos.

Seasonal dynamics of soil CO2 production in the arboretum of the Moscow State University Botanical Garden

This paper tracks the annual dynamics of carbon dioxide production (emission and profile concentration) by soils of the arboretum in the Moscow State University Botanical Garden that are planted with Siberian spruce and common pine. The high biological activity of the studied soils is caused by the high content of organic matter, slightly alkaline reaction, and good structure and texture. Differences in CO2 production by the soils of a spruce and pine forest (1.5–2 times higher in the latter) can be explained by different structures of soil profiles rather than a temperature regime. The seasonal dynamics of CO2 production are the same for both soils and associated with seasonal changes in climatic parameters. In the cold season, there is noticeable production of carbon dioxide by soils.

Validation of the doubly labeled water method using integrated cavity output spectroscopy against isotope ratio mass spectrometry and whole‐room indirect calorimetry

BackgroundThe doubly‐labeled water (DLW) method is the gold standard methodology for determination of free‐living energy expenditure. Isotope enrichments have traditionally been determined by isotope ratio mass spectrometry (IRMS), but new technologies are emerging, such as off‐axis integrated cavity output spectroscopy (OA‐ICOS). We have previously shown that compared to IRMS, OA‐ICOS provides comparable isotope enrichments of standard waters and of human urine samples, and to carbon dioxide (CO2) production measured using whole‐room indirect calorimetry (IC). In this study, we compared CO2 production in humans measured using OA‐ICOS and IRMS to simultaneous whole‐room indirect calorimetry (IC) measurements over a period of 7 days.Methods12 subjects (5 male, 7 female; age=24 to 63 yrs.; body mass index=19.4 to 46.4 kg/m2) were studied for 7 consecutive days in the IC. Prior to entry on the first day, subjects consumed an oral dose of 0.25 g H218O (95% APE) and 0.14 g 2H2O (99.8% APE) per kg of total body water (estimated as 73% of fat free mass, measured using Dual X‐ray Absorptiometry). Urine samples were obtained daily, and the samples on day 1 and 8 were used to measure average CO2 production over the 7 days using both OA‐ICOS and IRMS.ResultsAverage estimated CO2 production by IC, TIWA, and IRMS was 413.6±69.4, 400.6±74.5, and 385.5±71.1 L/day (P=0.03), respectively (mean±SD). Post‐hoc comparisons indicated significant differences in CO2 production between IRMS and IC (95% confidence interval of difference = +3.7 to +52.5 L/min), but not between TIWA and IC (−11.4 to 37.5 L/min) or TIWA and IRMS (−9.3 to 39.5 L/min). CO2 production measured with the different instruments were significantly correlated: TIWA vs. IC (r=0.89), IRMS vs. IC (r=0.93), IRMS vs. TIWA (r=0.86).ConclusionsOA‐ICOS produces valid measurements of CO2 production compared to IC, and comparable results to IRMS. OA‐ICOS provides a valid and viable alternative to IRMS for DLW studies in humans.Support or Funding InformationThis work was supported by NIH SBIR 1R43DK093362‐01, The Colorado Nutrition and Obesity Research Center (P30 DK048520) and Colorado Clinical and Translational Science Institute (UL1 TR000154).

A comparative investigation of metal-support interactions on the catalytic activity of Pt nanoparticles for ethanol oxidation in alkaline medium

The effects of interactions of Pt nanoparticles with hybrid supports on reactivity towards ethanol oxidation in alkaline solution are investigated. Studies involve catalysts with identical Pt nanoparticles on six hybrid supports containing carbon powder and transition metal oxides (TiO2, ZrO2, SnO2, CeO2, MoO3 and WO3). In situ X-ray absorption spectroscopy (XAS) results evidence that metal-support interactions produce changes in the Pt 5d band vacancy, which appears to determine the catalytic activity. The highest and lowest activities are observed for Pt nanoparticles on hybrid supports containing TiO2 and CeO2, respectively. Further studies are presented for these two catalysts. In situ FTIR reflection spectroscopy measurements, taken using both multi-stepped FTIR spectroscopy (MS-FTIR) and single potential alteration FTIR spectroscopy (SPA-FTIR), evidence that the main product of ethanol oxidation is acetate, although signals attributed to carbonate and CO2 indicate some differences in CO2 production. Fuel cell performances of these catalysts, tested in a 4.5 cm2 single cell at different temperatures (40–90 °C) show good agreement with data obtained by electrochemical techniques. Results of this comprehensive study point out the possibility of compensating a reduction of noble metal load with an increase in activity promoted by interactions between metallic nanoparticles and a support.

Use of glucose and carbon isotope fractionation by microbial cells immobilized on solid-phase surface

By the example of glucose uptake by the soil bacteria Pseudomonas aureofaciens BS1393(pBS216) and Rhodococcus sp. 3–30 immobilized on a solid-phase surface (quartz sand), their growth parameters were determined: growth rate (doubling time), total CO2 production, CO2 production per cell, lag period with respect to substrate uptake, respiratory quotient. The growth of P. aureofaciens and Rhodococcus sp. on glucose revealed (1) differences of the lag period with respect to substrate (lag time of ∼4 h for P. aureofaciens and ∼26 h for Rhodococcus sp.); (2) differences between the maximal rates of CO2 production (∼50 μg C-CO2 g−1 sand h−1 for P. aureofaciens and ∼8.5 μg C-CO2 g−1 sand h−1 for Rhodococcus sp.); (3) differences in CO2 production per cell (∼1.94 × 10−9 μM CO2/CFU for P. aureofaciens and more than ∼3.4 × 10−9 μM CO2/CFU for Rhodococcus sp.). The kinetics of the metabolic CO2 isotopic composition was shown to be determined by the difference in the carbon isotopic characteristics of products in the cell. Upon introduction of glucose into the medium (the preparatory stage of the metabolism), the uptake of intracellular 13C-depleted products (lipids) is noted; at the stage of the maximal cell growth rate, introduced glucose is mainly metabolized; and at the final stage, upon exhaustion of substrate, the “stored” products—the lipid fraction—get involved in the metabolism. At the maximal rate of glucose uptake, the CO2 carbon isotopic fractionation coefficient relative to organic products of microbial biosynthesis was determined to be α = 1.009 ± 0.002.

Helium-oxygen reduces the production of carbon dioxide during weaning from mechanical ventilation

BackgroundProlonged weaning from mechanical ventilation has a major impact on ICU bed occupancy and patient outcome, and has significant cost implications.There is evidence in patients around the period of extubation that helium-oxygen leads to a reduction in the work of breathing. Therefore breathing helium-oxygen during weaning may be a useful adjunct to facilitate weaning. We hypothesised that breathing helium-oxygen would reduce carbon dioxide production during the weaning phase of mechanical ventilation.Materials/patients and methodsWe performed a prospective randomised controlled single blinded cross-over trial on 19 adult intensive care patients without significant airways disease who fulfilled criteria for weaning with CPAP. Patients were randomised to helium-oxygen and air-oxygen delivered during a 2 hour period of CPAP ventilation. Carbon dioxide production (VCO2) was measured using a near patient main stream infrared carbon dioxide sensor and fixed orifice pneumotachograph.ResultsCompared to air-oxygen, helium-oxygen significantly decreased VCO2 production at the end of the 2 hour period of CPAP ventilation; there was a mean difference in CO2 production of 48.9 ml/min (95% CI 18.7-79.2 p = 0.003) between the groups. There were no significant differences in other respiratory and haemodynamic parameters.ConclusionThis study shows that breathing a helium-oxygen mixture during weaning reduces carbon dioxide production. This physiological study supports the need for a clinical trial of helium-oxygen mixture during the weaning phase of mechanical ventilation with duration of weaning as the primary outcome.Trial registrationISRCTN56470948

Injection of pig slurry and its effects on dynamics of nitrogen and carbon in a loamy soil unter laboratory conditions

Dynamics of nitrogen (N) and carbon (C) were investigated in a loamy soil amended or injected with pig slurry. Treatments were with or without acetylene C2H2 (which is assumed to inhibit reduction of nitrous oxide (N2O) to dinitrogen (N2), and soil cores were conditioned for 15 days at 25°C while pH, production of CO2 and N2O, ammonia (NH3) emission and (nitrate) (NO3 –) and (ammonium) (NH4 +) concentrations were monitored. There was no significant difference in CO2 production between the injected and surface applied pig slurry treatments, and within 15 days ca. 5% of the C applied had been mineralized, if no priming effect was assumed. Neither the production of N2O nor the total gaseous production of the denitrification process (N2O plus N2) were affected by the way the pig slurry was added to the soil. NH3 volatilization, however, decreased by 90% when pig slurry was injected. The addition of C2H2 significantly increased the CO2 production and the concentration of NH4 +, but significantly decreased the concentration of NO3 –. It was concluded that the injection of pig slurry to a dry soil was an acceptable alternative to its application to the soil surface, as not only was NH3 volatilization reduced, but the production of N2O and N2 through denitrification was not stimulated. It is also suggested that the composition of the organic C fraction in the pig slurry, most likely the concentration of fatty acids, had an important effect on the dynamics of N and C in the soil.

Measuring energy costs of leisure activity in adolescents using a CO2 breath test.

To determine whether a 13C-bicarbonate, isotope dilution technique could be used to estimate relative changes in energy expenditure of leisure activities of short duration, we studied eight adolescents who performed the following activities: watching television (120 min); playing a stringed instrument (60 min plus 60 min of sitting); and walking plus rest during two approximately isocaloric sessions (slow walk at 40% of peak VO2 for 43 min plus 77 min of sitting; fast walk at 73% of peak VO2 for 22 min plus 98 min of sitting). The rate of appearance of CO2 (RaCO2) was determined from the ratio of the oral dose of 13C-bicarbonate and the isotopic enrichment of breath CO2. The net rates of excretion of CO2 (VCO2) and oxygen consumption were measured. VCO2 and RaCO2, were correlated (r = 0.93; P < 0.05). To adjust for the systematic difference in CO2 production between methods, determinations were expressed as a fraction of that during television viewing. For RaCO2, the ratios for instrument playing, walking at 40% peak VCO2, and walking at 73% peak VO2 were respectively 133 +/- 20%, 186 +/- 38%, and 206 +/- 34%; for VCO2, the respective ratios were 129 +/- 19, 210 +/- 50, and 232 +/- 39 (P > 0.05 for methods and interaction, two-way ANOVA). RaCO2 may be a useful method for detecting relative differences in energy expenditure associated with leisure activities of brief duration.

Feasibility of Using Coal Ash Residues as CO-Composting Materials for Sewage Sludge

Alkaline coal ash residues produced from a coal-fired power plant were co-composted with sewage sludge to evaluate it's effect on heavy metal availability and the biological process of composting. Coal fly ash (FA) and lagoon ash (LA) were mixed with dewatered sludge at 0, 10 and 25% w/w, and the mixtures were composted for 100 days in laboratory batch reactors. The changes in pH, electrical conductivity (EC), CO2 production, microbial population, soluble and extractable heavy metal contents were measured during the composting period. Following an initial increase, pH started to decrease from day 7 onward till the end of the composting period for all treatments. Sludge with coal fly ash amendment had a higher pH and EC than those of the control and LA-sludge composts. Increasing fly ash amendment levels resulted in a significant reduction in DTPA-extractable Cd, Cu, Zn, Mn and Pb contents of the FA-sludge composts while the reduction was less obvious in the LA-sludge composts. No significant difference in CO2 production and the number of thermophilic bacteria were noted for all treatments except for 25% FA-sludge compost which had a reduced thermophilic bacterial growth and CO2 production. The inhibition which was possibly due to the high pH of coal fly ash, decreased with an increase in composting time. It can be concluded that the co-composting of coal ash residues with sewage sludge was able to reduce the availability of metals but did not exert a significant inhibition on the biological process of composting, except for 25% FA-sludge compost.

Relationships among panic-fear personality, aging, and ventilatory activity.

We have studied 204 healthy male subjects ranging in age from 20 to 59 years. They were divided into four 10-year age groups. Each age group was further divided into 2 subgroups with high and low Panic-Fear scores. The ventilatory activities of all the groups were compared. In the younger generation (20-39 years), the low PF group revealed a higher slope in CO2 response curve than the high PF group (p less than 0.05). This result was considered to be related to the difference in CO2 production between the two groups. In the older age groups, however, the high PF subjects exhibited a tendency to increase the CO2 response slope with increasing ages. This contradictory result was thought to be due to the age dependent change in biogenic amine activity.

Effect of Water‐Filled Pore Space on Carbon Dioxide and Nitrous Oxide Production in Tilled and Nontilled Soils

AbstractThe percentage of soil pore space filled with water (percent water‐filled pores, % WFP), as determined by water content and total porosity, appears to be closely related to soil microbial activity under different tillage regimes. Soil incubated in the laboratory at 60% WFP supported maximum aerobic microbial activity as determined by CO2 production and O2 uptake. In the field, % WFP of surface no‐tillage soils (0–75 mm) at four U.S. locations averaged 62% at time of sampling, whereas that for plowed soils was 44%. This difference in % WFP was reflected in 3.4 and 9.4 times greater CO2 and N2O production, respectively, from surface no‐tillage soils over a 24‐h period as compared to plowed soils. At a depth of 75 to 150 mm, % WFP values increased in both no‐tillage and plowed soils, averaging approximately 70% for no tillage compared with 50 to 60% for plowed soils. Production of CO2 in the plowed soils was enhanced by the increased % WFP, resulting in little or no difference in CO2 production between tillage treatments. Nitrous oxide production, however, remained greater under no‐tillage conditions. Substantially greater amounts of N2O were produced from the N‐fertilized soils, regardless of tillage practice. Production of CO2 and N2O was primarily related to the % WFP of tillage treatments although, in several instances, soil‐water‐soluble C and NO‐3 levels were important as well. Calculations of relative aerobic microbial activity between no‐tillage and plowed soils, based on differences in % WFP relative to maximum activity at 60%, indicated linear relationships for CO2 and N2O production between WFP values of 30 to 70%. Below 60% WFP, water limits microbial activity, but above 60%, aerobic microbial activity decreases—apparently the result of reduced aeration.

C4 characteristics of photosynthesis in the C3 alga Hydrodictyon africanum

Abstract Results obtained with Hydrodictyon africanum, and data from the literature, show that most green algae of the chlorophyte type (e.g. Chlorella, Chlamydomonas, Hydrodictyon) differ in their photosynthetic C fixation characteristics from most green algae of the charophyte type (e.g. Spirogyra, Chara) and from C3 higher plants. The chlorophyte algae fix inorganic carbon by the photosynthetic carbon reduction cycle pathway, but have a low CO2 compensation point in 250 μM O2, a low inhibition of CO2 fixation from 10 μM CO2/250 μM O2 when compared with 10 μM CO2/zero O2, and a low half‐saturation constant for CO2. These three characteristics are different from those of charophytes and C3 higher plants, and resemble those of C4 higher plants. It is suggested that these characteristics of chlorophyte algae are the result of a ‘CO2 concentrating mechanism’ which increases the CO2/O2 ratio at the site of ribulose bisphosphate carboxylase‐oxygenase action in a similar way to that achieved by the C4?C3 acid cycle in C4 plants. In the chlorophyte algae, however, CO2 concentration probably involves active HCO3− transport at the inner membrane of the chloroplast envelope. Active HCO3− transport can occur at the plasmalemma of charophyte algae and submerged aquatic higher plants as well as chlorophyte algae, so it is unlikely to explain the differences between the two groups of aquatic green plants. Differences in the properties of ribulose bisphosphate carboxylase‐oxygenase, and differences in CO2 production in the light, also seem inadequate to account for the different photosynthetic characteristics. The chlorophyte type of ‘C02 concentrating mechanism’ appears to be common in other classes of eukaryotic algae, and in cyanophytes. Some of the ‘advanced’ members of these eukaryotic algal classes (including the chlorophytes) may lack the mechanism, while some ‘primitive’ charophytes may retain the mechanism which their ancestors presumably possessed.

Land Application of Sewage Sludge: V. Carbon Dioxide Production as Influenced by Sewage Sludge and Wood Waste Mixtures

AbstractCarbon dioxide production during a 367‐day period was used in assessing the rate of carbon oxidation when wood (W), bark (B), and wood‐bark (WB) mixture from Engelmann spruce (Picea Engelmannii Parry) were each mixed in different proportions with anaerobically digested sewage sludge and each mixture applied to a Nunn clay loam at rates of 22.4 to 224 metric tons/ha.Generally, as the application rate of organic material increased the CO2 production increased, but nonadditively for most time intervals. At the 22.4‐metric tons/ha rate, there were no consistent differences in CO2 production with variations in the proportion of wood materials to sludge. At the higher application rates, as the percentage of wood materials increased and sludge decreased, the CO2 accumulation increased up to 75% wood material — 25% sludge, then dropped with 100% wood material. The 22.4‐metric tons/ha application of 100% sludge also resulted in lower CO2 production rates than the mixtures of wood materials and sludge. The percentage decomposition of the added residues increased with decrease in application rate of the treatments, with values ranging from 11 to 55%.In concurrent studies, attempts were made to correlate CO2 production with N mineralized in laboratory incubation studies and with wheat growth in a greenhouse pot experiment. The appropriate regression equations were derived to describe the relationships obtained. It was concluded that microbial respiration was a good index of plant‐available N in soil, except where plant nutrients were deficient due to microbial immobilization, or where toxic factors were limiting to microbial activity.

Limiting factors involved in CO2 production by starved and x-irradiated starved yeast cells.

AbstractStudies of reduced CO2 production by starved yeast cells were carried out to localize the site limiting this process and responsible for a greater production by irradiated cells. Cell‐free extracts prepared before and after starvation of cells, and from irradiated and unirradiated cells, showed similar hexokinase activity and produced similar amounts of CO2. These results demonstrated that rate limiting glycolytic enzymes did not decay during starvation, were not induced during a lag period in CO2 production which could be overcome by glucose incubation, and were not responsible for differences in CO2 production between irradiated and unirradiated cells. Possible limiting factors involved in these differences include glucose transport as a consequence of differential decay during starvation, restricted cofactor synthesis and an enzymic binding or compartmentalization.