Relationships Between Microbial Community Structure and Soil Processes Under Elevated Atmospheric Carbon Dioxide

There is little current understanding of the relationship between soil microbial community composition and soil processes rates, nor of the effect climate change and elevated CO₂ will have on microbial communities and their functioning. Using the eastern cottonwood (Populus deltoides) plantation at the Biosphere 2 Laboratory, we studied the relationships between microbial community structure and process rates, and the effects of elevated atmospheric CO₂ on microbial biomass, activity, and community structure. Soils were sampled from three treatments (400, 800, and 1200 ppm CO₂), a variety of microbial biomass and activity parameters were measured, and the bacterial community was described by 16S rRNA libraries. Glucose substrate-induced respiration (SIR) was significantly higher in the 1200 ppm CO₂ treatment. There were also a variety of complex, nonlinear responses to elevated CO₂. There was no consistent effect of elevated CO₂ on bacterial diversity; however, there was extensive variation in microbial community structure within the plantation. The southern ends of the 800 and 1200 ppm CO₂ bays were dominated by β-Proteobacteria, and had higher fungal biomass, whereas the other areas contained more α-Proteobacteria and Acidobacteria. A number of soil process rates, including salicylate, glutamate, and glycine substrate-induced respiration and proteolysis, were significantly related to the relative abundance of the three most frequent bacterial taxa, and to fungal biomass. Overall, variation in microbial activity was better explained by microbial community composition than by CO₂ treatment. However, the altered diversity and activity in the southern bays of the two high CO₂ treatments could indicate an interaction between CO₂ and light.     

Carbon Dioxide Exchange Between an Old-growth Forest and the Atmosphere

Eddy-covariance and biometeorological methods show significant net annual carbon uptake in an old-growth Douglas-fir forest in southwestern Washington, USA. These results contrast with previous assumptions that old-growth forest ecosystems are in carbon equilibrium. The basis for differences between conventional biomass-based carbon sequestration estimates and the biometeorologic estimates are discussed. Annual net ecosystem exchange was comparable to younger ecosystems at the same latitude, as quantified in the AmeriFlux program. Net ecosystem carbon uptake was significantly correlated with photosynthetically active radiation and air temperature, as well as soil moisture and precipitation. Optimum ecosystem photosynthesis occurred at relatively cool temperatures (5°–10°C). Understory and soil carbon exchange always represented a source of carbon to the atmosphere, with a strong seasonal cycle in source strength. Understory and soil carbon exchange showed a Q₁₀ temperature dependence and represented a substantial portion of the ecosystem carbon budget. The period of main carbon uptake and the period of soil and ecosystem respiration are out of phase, however, and driven by different climatic boundary conditions. The period of strongest ecosystem carbon uptake coincides with the lowest observed values of soil and ecosystem respiration. Despite the substantial contribution of soil, the overall strength of the photosynthetic sink resulted in the net annual uptake. The net uptake estimates here included two correction methods, one for advection and the other for low levels of turbulence.     

Internal Mass Transfer Limitation During Enzymatic Esterification in Supercritical Carbon Dioxide and Hexane

A kinetic study of ethyl myristate formation by esterification of myristic acid with ethanol catalysed by a lipase from Mucor miehei immobilized on Duolite A 568, has been carried out.

The reaction was done in a two liquid phase system in which the non-aqueous solvent was supercritical carbon dioxide (P= 12.5 MPa, T = 323 K) or n-hexane (P = 0.1 MPa, T = 323K). In heteregenous catalysis, it is important to study the internal mass transfer limitation. For this, the support was sieved into different size series (from 300 to 600 mm) and the reaction was carried out for each size series. The samples were analyzed by gas chromatography and the esterification was shown to follow Ping Pong Bi Bi kinetics with competitive substrate inhibition. The Thiele modulus values show that there is, in the hexane case, a diffusional control while in SCCO₂ media, we obtained an intermediate rate between reactional and diffusional rates.     

Studies of the Processes of the Trypsin Interactions with Ion Exchange Fibers and Chitosan

Russian Journal of Bioorganic Chemistry - A localization of charged and hydrophobic amino acid residues in the trypsin molecule was studied, and a percentage of the amino acids of different types...     

The Effects of pH and Carbon Dioxide on Ion Uptake by Excised Barley Roots

The effects of carbon dioxide concentrations up to 8 per centin air on uptake of potassium and chloride at two pH levels,nominally pH 6 and 8, werestudied. In all experiments, enhanced uptake of potassium occurred atthe higher pH level with carbon dioxidefree air, but chlorideuptake was generally unaffected. At nominal pH 6, 1 per cent carbon dioxide reduced and 6 percent increased potassium uptake. There was no effect on chlorideuptake except with 1 per cent carbon dioxide where a markedenhancement was recorded. At nominal pH 8, l and 2 per cent carbon dioxide increased potassiumuptake whereas 6 and 8 per cent were inhibitory. Chloride uptakewas favoured by 1 and 8 per cent concentrations of the gas.     

Interactions of Carbon Dioxide and Food Odours in Drosophila: Olfactory Hedonics and Sensory Neuron Properties

Behavioural responses of animals to volatiles in their environment are generally dependent on context. Most natural odours are mixtures of components that can each induce different behaviours when presented on their own. We have investigated how a complex of two olfactory stimuli is evaluated by Drosophila flies in a free-flying two-trap choice assay and how these stimuli are encoded in olfactory receptor neurons. We first observed that volatiles from apple cider vinegar attracted flies while carbon dioxide (CO₂) was avoided, confirming their inherent positive and negative values. In contradiction with previous results obtained from walking flies in a four-field olfactometer, in the present assay the addition of CO₂ to vinegar increased rather than decreased the attractiveness of vinegar. This effect was female-specific even though males and females responded similarly to CO₂ and vinegar on their own. To test whether the female-specific behavioural response to the mixture correlated with a sexual dimorphism at the peripheral level we recorded from olfactory receptor neurons stimulated with vinegar, CO₂ and their combination. Responses to vinegar were obtained from three neuron classes, two of them housed with the CO₂-responsive neuron in ab1 sensilla. Sensitivity of these neurons to both CO₂ and vinegar per se did not differ between males and females and responses from female neurons did not change when CO₂ and vinegar were presented simultaneously. We also found that CO₂-sensitive neurons are particularly well adapted to respond rapidly to small concentration changes irrespective of background CO₂ levels. The ability to encode temporal properties of stimulations differs considerably between CO₂- and vinegar-sensitive neurons. These properties may have important implications for in-flight navigation when rapid responses to fragmented odour plumes are crucial to locate odour sources. However, the flies’ sex-specific response to the CO₂-vinegar combination and the context-dependent hedonics most likely originate from central rather than peripheral processing.     

Transcutaneous Carbon Dioxide Induces Mitochondrial Apoptosis and Suppresses Metastasis of Oral Squamous Cell Carcinoma In Vivo

Squamous cell carcinoma (SCC) is the main histological type of oral cancer. Its growth rate and incidence of metastasis to regional lymph nodes is influenced by various factors, including hypoxic conditions. We have previously reported that transcutaneous CO₂ induces mitochondrial apoptosis and decreases lung metastasis by reoxygenating sarcoma cells. However, previous studies have not determined the sequential mechanism by which transcutaneous CO₂ suppresses growth of epithelial tumors, including SCCs. Moreover, there is no report that transcutaneous CO₂ suppresses lymphogenous metastasis using human cell lines xenografts. In this study, we examined the effects of transcutaneous CO₂ on cancer apoptosis and lymphogenous metastasis using human SCC xenografts. Our results showed that transcutaneous CO₂ affects expressions of PGC-1α and TFAM and protein levels of cleavage products of caspase-3, caspase-9 and PARP, which relatives mitochondrial apoptosis. They also showed that transcutaneous CO₂ significantly inhibits SCC tumor growth and affects expressions of HIF-1α, VEGF, MMP-2 and MMP-9, which play essential roles in tumor angiogenesis, invasion and metastasis. In conclusion, transcutaneous CO₂ suppressed tumor growth, increased mitochondrial apoptosis and decreased the number of lymph node metastasis in human SCC by decreasing intra-tumoral hypoxia and suppressing metastatic potential with no observable effect in vivo. Our findings indicate that transcutaneous CO₂ could be a novel therapeutic tool for treating human SCC.     

Carbon Dioxide and Fruiting in Sphaerobolus

In cultures bathed in air deprived of its CO² fruiting in Sphaerobolusis greatly reduced or fails completely. However, increasingthe concentration of CO² in the air to 1or 5 per cent tendsto reduce fruiting as compared with normal air. The stimulatoryeffect of CO² in normal air appears to be exerted at the stageof development when sporophore primordia are being produced.The CO² does not seem to require the immediate presence of lightto exert its effect. It has not been found possible to replacethe effect of CO² by substituting Krebs-cycle organic acids.Using ¹⁴CO² it is shown that ¹⁴C is incorporated in the myceliumboth in light and in darkness.     

Short- and Long-Term Inhibition of Respiratory Carbon Dioxide Efflux by Elevated Carbon Dioxide

Dark carbon dioxide efflux rates of recently fully expandedleaves and whole plants of Amaranthus hypochondriacus L., Glycinemax (L.) Merr., and Lycopersicon esculentum Mill. grown in controlledenvironments at 35 and 70 Pa carbon dioxide pressure were measuredat 35 and 70 Pa carbon dioxide pressure. Harvest data and whole-plant24-h carbon dioxide exchange were used to determine relativegrowth rates, net assimilation rates, leaf area ratios, andthe ratio of respiration to photosynthesis under the growthconditions. Biomass at a given time after planting was greaterat the higher carbon dioxide pressure in G. max and L. esculentum,but not the C₄ species, A. hypochondriacus. Relative growthrates for the same range of masses were not different betweencarbon dioxide treatments in the two C₃ species, because highernet assimilation rates at the higher carbon dioxide pressurewere offset by lower leaf area ratios. Whole plant carbon dioxideefflux rates per unit of mass were lower in plants grown andmeasured at the higher carbon dioxide pressure in both G. maxand L. esculentum, and were also smaller in relation to daytimenet carbon dioxide influx. Short-term responses of respirationrate to carbon dioxide pressure were found in all species, withcarbon dioxide efflux rates of leaves and whole plants lowerwhen measured at higher carbon dioxide pressure in almost allcases. Amaranthus hypochondriacus L., Glycine max L. Merr., Lycopersicon esculentum Mill., soybean, tomato, carbon dioxide, respiration, growth