Effects of increased soil water availability on grassland ecosystem carbon dioxide fluxes

There is considerable interest in how ecosystems will respond to changes in precipitation. Alterations in rain and snowfall are expected to influence the spatio-temporal patterns of plant and soil processes that are controlled by soil moisture, and potentially, the amount of carbon (C) exchanged between the atmosphere and ecosystems. Because grasslands cover over one third of the terrestrial landscape, understanding controls on grassland C processes will be important to forecast how changes in precipitation regimes will influence the global C cycle. In this study we examined how irrigation affects carbon dioxide (CO₂) fluxes in five widely variable grasslands of Yellowstone National Park during a year of approximately average growing season precipitation. We irrigated plots every 2 weeks with 25% of the monthly 30-year average of precipitation resulting in plots receiving approximately 150% of the usual growing season water in the form of rain and supplemented irrigation. Ecosystem CO₂ fluxes were measured with a closed chamber-system once a month from May-September on irrigated and unirrigated plots in each grassland. Soil moisture was closely associated with CO₂ fluxes and shoot biomass, and was between 1.6% and 11.5% higher at the irrigated plots (values from wettest to driest grassland) during times of measurements. When examining the effect of irrigation throughout the growing season (May–September) across sites, we found that water additions increased ecosystem CO₂ fluxes at the two driest and the wettest sites, suggesting that these sites were water-limited during the climatically average precipitation conditions of the 2005 growing season. In contrast, no consistent responses to irrigation were detected at the two sites with intermediate soil moisture. Thus, the ecosystem CO₂ fluxes at those sites were not water-limited, when considering their responses to supplemental water throughout the whole season. In contrast, when we explored how the effect of irrigation varied temporally, we found that irrigation increased ecosystem CO₂ fluxes at all the sites late in the growing season (September). The spatial differences in the response of ecosystem CO₂ fluxes to irrigation likely can be explained by site specific differences in soil and vegetation properties. The temporal effects likely were due to delayed plant senescence that promoted plant and soil activity later into the year. Our results suggest that in Yellowstone National Park, above-normal amounts of soil moisture will only stimulate CO₂ fluxes across a portion of the ecosystem. Thus, depending on the topographic location, grassland CO₂ fluxes can be water-limited or not. Such information is important to accurately predict how changes in precipitation/soil moisture will affect CO₂ dynamics and how they may feed back to the global C cycle.     

Effects of elevated carbon dioxide, ozone and water availability on spring wheat growth and yield

Spring wheat (Triticum aestivum L. cv. Dragon) was exposed to elevated carbon dioxide (CO₂), alone (1995) or in combination with two levels of increased ozone (O₃) (1994) or increased irrigation (1996) during three successive growing seasons as part of the EU ESPACE‐wheat programme and conducted in open‐top chambers (OTCs) and ambient air (AA) plots at Östad, 50 km north‐east of Göteborg, Sweden. Doubling the CO₂ concentration had a positive effect on grain yield in all 3 years (+21, +7 and +11%, respectively), although only statistically significant in 1994. That year was characterised by a warm and dry summer in comparison with 1995 and 1996, in which the summers were more humid and typical for south‐west Sweden. In 1994, the CO₂‐induced increase in grain yield was associated with an increase in the duration of the green leaf area, a positive effect on straw yield and on the number of ears per square metre and a negative effect (?13%) on grain protein concentration. Harvest index was unaffected by the elevated CO₂ concentration. The only statistically significant effect of elevated CO₂ in 1995 was a decrease in the grain protein concentration (?11% in both CO₂ concentrations), and in 1996 an increase (+21%) in the straw yield. In 1996 the soil water potential was less negative in elevated CO₂, which is likely to reflect a lower water consumption of these plants. Addition of extra O₃ significantly affected the grain yield (?6 and ?10%, respectively) and the 1 000‐grain weight negatively (?3 and ?6%). Statistically significant interactions between CO₂ and O₃ were obtained for the number of ears per unit area and for the 1 000‐grain weight. The 1 000‐grain weight was negatively affected by O₃ in low CO₂, but remained unaffected in the high CO₂ treatment. There was a significant decrease (?6%) in the grain protein concentration induced by elevated irrigation. The chambers, compared with AA plots, had a positive effect on plant development and on grain yield in all 3 years.     

Effects of carbon dioxide concentration on the interactive effects of temperature and water vapour on stomatal conductance in soybean

Soybeans were grown at three CO₂ concentrations in outdoor growth chambers and at two concentrations in controlled-environment growth chambers to investigate the interactive effects of CO₂, temperature and leaf-to-air vapour pressure difference (LAVPD) on stomatal conductance. The decline in stomatal conductance with CO₂ was a function of both leaf temperature and LAVPD. In the field measurements, stomatal conductance was more sensitive to LAVPD at low CO₂ at 30 °C but not at 35 °C. There was also a direct increase in conductance with temperature, which was greater at the two elevated carbon dioxide concentrations. Environmental growth chamber results showed that the relative stomatal sensitivity to LAVPD decreased with both leaf temperature and CO₂. Measurements in the environmental growth chamber were also performed at the opposing CO₂, and these experiments indicate that the stomatal sensitivity to LAVPD was determined more by growth CO₂ than by measurement CO₂. Two models that describe stomatal responses to LAVPD were compared with the outdoor data to evaluate whether these models described adequately the interactive effects of CO₂, LAVPD and temperature.     

Effects of sodium chloride and carbon dioxide on oxygen binding byArtemia hemoglobin

Summary The effects of both sodium chloride and CO₂ on oxygen binding by component II of the hemoglobin fromArtemia franciscana have been determined. Sodium chloride decreases both the oxygen affinity and cooperativity: the Hill coefficient decreases from 2.4 to 1.7 in the presence of 0.5 M NaCl at pH 7.5, 20°C. In contrast, CO₂ increases both the oxygen affinity and cooperativity. The effects of both agents are small and increase with the degree of oxygenation.     

Effects of carbon dioxide and oxygen on sapwood respiration in five temperate tree species

The gaseous environment surrounding parenchyma in woody tissue is low in O2 and high in CO2, but it is not known to what extent this affects respiration or might play a role in cell death during heartwood formation. Sapwood respiration was measured in two conifers and three angiosperms following equilibration to levels of O2 and CO2 common within stems, using both inner and outer sapwood to test for an effect of age. Across all species and tissue ages, lowering the O2 level from 10% to 5% (v/v) resulted in about a 25% decrease in respiration in the absence of CO2, but a non-significant decrease at 10% CO2. The inhibitory effect of 10% CO2 was smaller and only significant at 10% O2, where it reduced respiration by about 14%. Equilibration to a wider range of gas combinations in Pinus strobus L. showed the same effect: 10% CO2 inhibited respiration by about 15% at both 20% and 10% O2, but had no net effect at 5% O2. In an extreme treatment, 1% O2+20% CO2 increased respiration by over 30% relative to 1% O2 alone, suggesting a shift in metabolic response to high CO2 as O2 decreases. Although an increase in respiration would be detrimental under limiting O2, this extreme gas combination is unlikely to exist within most stems. Instead, moderate reductions in respiration under realistic O2 and CO2 levels suggest that within-stem gas composition does not severely limit respiration and is unlikely to cause the death of xylem parenchyma during heartwood formation.     

Effects of water stress on oxygen, hydrogen and carbon isotope ratios in two species of cotton plants

Abstract. Two cotton species ( Gossypium hirsutum L. cv. SJ-2 and Gossypium barbadence cv. S-5) were grown under irrigated (wet) and non-irrigated (dry) conditions in the same field. Leaf water was enriched in ¹⁸O and deuterium in the dry treatment relative to the wet treatment for both species. Only in plants of S-5 was a similar enrichment observed in leaf cellulose. In both species, the isotopic composition of leaf cellulose must reflect the isotopic composition of the actual water pool involved in cellulose synthesis. Therefore, our observations indicate that one species (SJ-2) can maintain a relative isolation of this water pool from direct evapotranspirational effects. Such plant species will more faithfully record, in the isotopic composition of organic matter, the isotopic composition of ground water. In contrast, the isotopic composition of organic matter in plants such as S-5 could be used as an integrated signal reflecting humidity conditions during growth. Water use efficiency, based on seed-cotton yield and total water applied, correlated linearly with differences in carbon isotopic ratios between species in both the wet and dry treatments and between treatments in each species.     

Effects of temperature and oxygen availability on circulating catecholamines in the toad Bufo marinus.

The release of catecholamines during hypoxia has received limited attention in amphibians and the adrenergic regulation of cardio-pulmonary functions is, therefore, not well understood at the organismic level. To describe the changes in plasma catecholamine concentrations, we exposed toads (Bufo marinus) to different levels of hypoxia at two temperatures (15 and 25 degrees C). In addition, blood oxygen binding properties were determined in vitro at 15 and 25 degrees C at two different pH values. Hypoxia elicited a significant increase in plasma catecholamines (adrenaline and noradrenaline) at both temperatures, in spite of a respiratory alkalosis. At 15 degrees C, the increase was from 2.6+/-1.0 in normoxia to 4.8+/-1.4 ng ml(-1) at an inspired oxygen fraction of 0.05. At 25 degrees C, the hypoxic release of catecholamines was significantly higher (maximum levels of 44.8+/-11.6 ng ml(-1)). Plasma noradrenaline concentration was elevated at the most severe hypoxic levels, suggestive of an adrenal release. The arterial oxygen threshold for catecholamine release were approximately 1.0 mmol O(2) l(-1) blood or a PaO(2) of 30 mmHg. The P(50) values at 15 degrees C were 23.5+/-0.7 and 28.9+/-1.0 mmHg at pH 7.98+/-0.01 and 7.62+/-0.02, respectively, and increased to 36.5+/-0.6 and 43.0+/-1.1 mmHg at pH 8.04+/-0.04 and 7.67+/-0.05, respectively, at 25 degrees C. The oxygen equilibrium curves were linear when transformed to Hill-plots and Hills n (the haemoglobin subunit co-operativity) ranged between 2.24 and 2.75. The in vitro blood O(2) binding properties corresponded well with in vivo data.     

Simultaneous measurements on the effect of oxygen concentration on water vapor and carbon dioxide exchange in leaves

Summary Transpiration rate was unaffected by O₂ concentration in the range 1–80% when illuminated leaves ofAtriplex patula andA. rosea were kept at low CO₂ concentrations. Moreover, the marked increase in the rate of light-saturated photosynthesis that takes place in many plant species when O₂ concentration is reduced from 21% to a few percent was not accompanied by any change in transpiration rate inA. patula andSolanum dulcamara. The results indicate that higher plant photosynthesis in normal air and saturating light is not determined by physical barriers to gas diffusion alone but that it is markedly limited by biochemical processes.C.I.W.-D.P.B.Publ. No. 454.     

Effects of carbon dioxide and oxygen on the regulation of photosynthetic carbon metabolism by ammonia in spinach mesophyll cells

Photosynthetic carbon metabolism of isolated spinach mesophyll cells was characterized under conditions favoring photorespiratory (PR; 0.04% CO₂ and 20% O₂) and nonphotorespiratory (NPR; 0.2% CO₂ and 2% O₂) metabolism, as well as intermediate conditions. Comparisons were made between the metabolic effects of extracellularly supplied NH₄⁺ and intracellular NH₄⁺, produced primarily via PR metabolism. The metabolic effects of ¹⁴CO₂ fixation under PR conditions were similar to perturbations of photosynthetic metabolism brought about by externally supplied NH₄⁺; both increased labeling and intracellular concentrations of glutamine at the expense of glutamate and increased anaplerotic synthesis through α-ketoglutarate. The metabolic effects of added NH₄⁺ during NPR fixation were greater than those during PR fixation, presumably due to lower initial NH₄⁺ levels during NPR fixation. During PR fixation, addition of ammonia caused decreased pools and labeling of glutamate and serine and increased glycolate, glyoxylate, and glycine labeling. The glycolate pathway was thus affected by increased rates of carbon flow and decreased glutamate availability for glyoxylate transamination, resulting in increased usage of serine for transamination. Sucrose labeling decreased with NH₄⁺ addition only during PR fixation, suggesting that higher photosynthetic rates under NPR conditions can accommodate the increased drain of carbon toward amino acid synthesis while maintaining sucrose synthesis.     

Exchanges of oxygen, carbon dioxide, nitrogen and water in the caecilian Dermophis mexicanus

Oxygen consumption was measured in five Dermophis mexicanus and averaged (±SEM) 0.047 ± 0.004 ml O₂ g⁻¹ h⁻¹. Carbon dioxide production averaged 0.053 ± 0.005 ml CO₂ g⁻¹ h⁻¹ in the same five animals 1 week later. This metabolic rate is similar to metabolic rates of other Gymnophionans but lower than metabolic rates reported for Anurans and Urodeles. Total nitrogen excretion averaged 1.37 μmol N g⁻¹ h⁻¹ which is higher than that found for other amphibians. Of this, 82.5% (1.13 μmol N g⁻¹ h⁻¹) was in the form of urea while 17.5% (0.24 μmol N g⁻¹ h⁻¹) was in the form of NH₃ + NH⁺ ₄. Such ureotelism is typical of terrestrial amphibians like D. mexicanus. Osmotic water flux averaged 0.0193 ml g⁻¹ h⁻¹ in control (sham injected) animals and was not significantly altered by injection of either arginine vasotocin or mesotocin. This osmotic flux is similar to osmotic fluxes found for other terrestrial amphibians. The combined data suggest that metabolism in D. mexicanus is, like most other Gymnophionans, lower than other amphibians. The high rates of nitrogen (especially urea) excretion suggests that this fossorial animal accumulates urea like other burrowing amphibians. Accepted: 27 June 2000     

Effects of time delay and body temperature on measurements of central venous oxygen saturation,venous-arterial blood carbon dioxide partial pressures difference,venous-arterial blood carbon dioxide partial pressures difference/arterial-venous oxygen difference ratio and lactate

Background

Central venous oxygen saturation (ScvO₂), venous-arterial blood carbon dioxide partial pressures difference (Pv-aCO₂), venous-arterial blood carbon dioxide partial pressures difference/arterial-venous oxygen difference ratio (Pv-aCO₂/Ca-vO₂) and lactate are important parameters employed during shock resuscitation. We designed this study to confirm the effects of time delay and body temperature on measurements of these four parameters.

Methods

Arterial and central venous blood samples were simultaneously drawn by plastic syringes via indwelling intra-arterial and central venous catheters from critically ill patients. Blood gas analyses were performed on both samples and repeated after 10, 20, 30, 40, 50 and 60?min. Patients were divided into a control group and a high temperature group according to whether the body temperature was greater than 38?°C.

Results

A total of 30 critically ill patients were enrolled. There was a trend of increasing values for ScvO₂, Pv-aCO₂, Pv-aCO₂/Ca-vO₂ and lactate over time (P?<?0.001). The ScvO₂ differences were all lower in high temperature group after 10, 20, 30, 40, 50 and 60?min when compared to the corresponding differences in the control group (P?<?0.05). The differences in lactate values were slightly higher in the high temperature group, relative to the control group after 20, 30, 40, 50 and 60?min (P?<?0.05).

Conclusions

Measurements of ScvO₂, Pv-aCO₂, lactate and Pv-aCO₂/Ca-vO₂ were affected by time delay or body temperature. We recommend that arterial and central venous blood gas samples be analyzed quickly within 10?min, especially for patients with body temperature <38?°C.

Trial registration

ChiCTR, ChiCTR1800014484. Registered 16 January 2018.

     

Effects of glycine hydroxamate, carbon dioxide, and oxygen on photorespiratory carbon and nitrogen metabolism in spinach mesophyll cells

The effects of added glycine hydroxamate on the photosynthetic incorporation of ¹⁴CO₂ into metabolites by isolated mesophyll cells of spinach (Spinacia oleracea L.) was investigated under conditions favorable to photorespiratory (PR) metabolism (0.04% CO₂ and 20% O₂) and under conditions leading to nonphotorespiratory (NPR) metabolism (0.2% CO₂ and 2.7% O₂). Glycine hydroxamate (GH) is a competitive inhibitor of the photorespiratory conversion of glycine to serine, CO₂ and NH₄⁺. During PR fixation, addition of the inhibitor increased glycine and decreased glutamine labeling. In contrast, labeling of glycine decreased under NPR conditions. This suggests that when the rate of glycolate synthesis is slow, the primary route of glycine synthesis is through serine rather than from glycolate. GH addition increased serine labeling under PR conditions but not under NPR conditions. This increase in serine labeling at a time when glycine to serine conversion is partially blocked by the inhibitor may be due to serine accumulation via the “reverse” flow of photorespiration from 3-P-glycerate to hydroxypyruvate when glycine levels are high. GH increased glyoxylate and decreased glycolate labeling. These observations are discussed with respect to possible glyoxylate feedback inhibition of photorespiration.