Ambient CO2 Levels Research Articles

Whole-plant Net CO2 Exchange of Raspberry as Influenced by Air and Root-zone Temperature, CO2 Concentration, Irradiation, and Humidity

The influence of irradiance, CO2, and temperature on whole-plant net CO2 exchange rate (NCER) of Rubus idaeus L. `Heritage' micropropagated raspberries was examined. Within the set of environmental conditions examined, irradiation was the most important factor, accounting for 58% of the whole-plant irradiance/CO2 concentration/temperature NCER model variation, followed by CO2 concentration (28%) and temperature (2.5%). Net photosynthesis (Pn) required irradiance levels >600 μmol·m-2·s-1 PPF for saturation, greatly increased under CO2 enrichment (up to 1500 μL·L-1), and was optimum at a whole-plant temperature of 20 °C. Temperature effects were partitioned in an experiment using varying air and root-zone temperatures (15, 20, 25, 30, and 35 °C) under saturated light and ambient CO2 levels (350 μL·L-1). Air and root-zone temperature influenced Pn, with maximum rates occurring at an air × root-zone temperature of 17/25 °C. The contribution of air and root-zone temperature to the NCER model varied, with air and root-zone temperature contributing 75% and 24%, respectively, to the total model variation (R2 = 0.96). Shoot dark respiration increased with air and root-zone temperature, and root respiration rates depended on air and root-zone temperature and shoot assimilation rate. Humidity also influenced Pn with a saturated vapor pressure deficit threshold >0.25 kPa resulting in a Pn decrease. Quantifying the physiological response of raspberries to these environmental parameters provides further support to recent findings that cool shoot/warm root conditions are optimum for raspberry plant growth.

Biocontrol Performance of Two Isolates ofPseudomonas fluorescensin Modified Soil Atmospheres

The incidence of tomato wilt, caused by Pseudomonas solanacearum, and the biocontrol performance of two isolates of Pseudomonas fluorescens (M29 and M40) against P. solanacearum were measured under four soil atmospheres containing O 2 /CO 2 concentrations of 210:0.3 (210 and 0.3 ml of O 2 and CO 2 per liter, respectively, ambient concentrations), 180:30, 150:60, or 120:90. Altering the O 2 and CO 2 concentrations of the soil atmosphere did not cause a statistically significant (P ≤ 0.05) change in disease incidence. However, suppression of wilt by M29 and M40 was significantly (P ≤ 0.05) decreased when roots were exposed to atmospheres containing lower than ambient levels of O 2 and higher than ambient levels of CO 2 . Isolate M29 significantly (P ≤ 0.05) reduced incidence of tomato wilt only under the ambient atmosphere and not under any of the three modified atmospheres tested. Isolate M40 reduced disease incidence significantly (P ≤ 0.05) only under the ambient atmosphere and one of the modified atmospheres containing O 2 /CO 2 concentrations of 180:30 ml/liter.

Elevated CO 2 and Leaf Shape: Are Dandelions Getting Toothier?

Heteroblastic leaf development in Taraxacum officinale is compared between plants grown under ambient (350 ppm) vs. elevated (700 ppm) CO2 levels. Leaves of elevated CO2 plants exhibited more deeply incised leaf margins and relatively more slender leaf laminae than leaves of ambient CO2 plants. These differences were found to be significant in allometric analyses that controlled for differences in leaf size, as well as analyses that controlled for leaf developmental order. The effects of elevated CO2 on leaf shape were most pronounced when plants were grown individually, but detectable differences were also found in plants grown at high density. Although less dramatic than in Taraxacum, significant effects of elevated CO2 on leaf shape were also found in two other weedy rosette species, Plantago major and Rumex crispus. These observations support the long-standing hypothesis that leaf carbohydrate level plays an important role in regulating heteroblastic leaf development, though elevated C02 may also affect leaf development through direct hormonal interactions or increased leaf water potential. In Taraxacum, pronounced modifications of leaf shape were found at CO2 levels predicted to occur within the next century.

Elevated CO2 and leaf shape: Are dandelions getting toothier?

Heteroblastic leaf development in Taraxacum officinale is compared between plants grown under ambient (350 ppm) vs. elevated (700 ppm) CO2 levels. Leaves of elevated CO2 plants exhibited more deeply incised leaf margins and relatively more slender leaf laminae than leaves of ambient CO2 plants. These differences were found to be significant in allometric analyses that controlled for differences in leaf size, as well as analyses that controlled for leaf developmental order. The effects of elevated CO2 on leaf shape were most pronounced when plants were grown individually, but detectable differences were also found in plants grown at high density. Although less dramatic than in Taraxacum, significant effects of elevated CO2 on leaf shape were also found in two other weedy rosette species, Plantago major and Rumex crispus. These observations support the long‐standing hypothesis that leaf carbohydrate level plays an important role in regulating heteroblastic leaf development, though elevated C02 may also affect leaf development through direct hormonal interactions or increased leaf water potential. In Taraxacum, pronounced modifications of leaf shape were found at CO2 levels predicted to occur within the next century.

Net Carbon Dioxide Exchange Rates of Raspberries at Varying Irradiances, Carbon Dioxide Concentrations, and Air and Soil Temperatures

The influence of irradiance, CO2, and temperature on whole-plant net C exchange rate (NCER) of micropropagated raspberries (Rubus idaeus L. cv. `Heritage') was examined in 1994. Irradiances >1000 μmol–m–2–s–1 PAR were required for light saturation, and net photosynthesis (Pn) greatly increased under CO2 enrichment (up to 2000 μl–liter–1) and was optimum at 17C. Temperature effects were separated in another experiment using varying air and soil temperatures (15, 20, 25, 30, and 35C) under saturated light and ambient CO2 levels (350 μl–liter–1). Both air and soil temperature influenced net Pn, with maximum rates occurring at an air/soil temperature of 17/25C and each contributing 71.2% and 26.7%, respectively, to the total variation explained by a polynomial model (R2 = 0.96). Dark respiration and root respiration rates also increased significantly with elevated air and soil temperatures. Therefore, results from this study indicate that maximum net Pn occurred at an air/soil temperature of 17/25C and that irradiance, CO2 levels, and shoot and root temperatures are all important factors in examining NCER in raspberries.

Rhizodeposition under ambient and elevated CO2 levels

As global CO2 levels rise, can soils store more carbon and so buffer atmospheric CO2 levels? Answering this question requires a knowledge of the rates of C inputs to soil and of CO2 outputs via decomposition. Below-ground inputs from roots are a major component of the C flow into soils but are still poorly understood. In this article, new techniques for measuring rhizodeposition are reviewed and discussed and the need for cross-comparisons between methods is identified. One component of rhizodeposition, root exudation, is examined in more detail and evidence is presented which suggests that current estimates of exudate flow into soils are incorrect. A mechanistic mathematical model is used to explore how exudate flows might change under elevated CO2.

Gas Exchange of Citrus Seedlings at Different Temperatures, Vapor-pressure Deficits, and Soil Water Contents

Midday reductions of stomatal conductance and carbon dioxide assimilation rates (Aco2) in Citrus are typically attributed to large leaf-to-air vapor-pressure differences or high atmospheric vapor-pressure deficits (VPD). This study investigated air temperature (Ta) and available soil water (ASW) level as corollary factors of atmospheric VPD that influence midday reduction of net gas exchange in citrus leaves. The influence of elevated atmospheric CO2 under conditions that inhibit net canopy Aco2 was also investigated. Net canopy Aco2 and evapotranspiration rates of Carrizo citrange [Poncirus trifoliata Raf × Citrus sinensis (L.) Osbeck] and Swingle citrumelo (P. trifoliata Raf × C. paradisii Macf.) seedlings grown in outdoor controlled-environment growth chambers were measured under two levels of Ta with concomitant changes in VPD and two levels of atmospheric CO2 concentration, which were changed in steps over time. Cyclical depletion of ASW was allowed to occur at each set of Ta/VPD and CO2 combinations. Highest net canopy Ace, rates at ambient CO2 concentration (330 μmol·mol-1) were obtained at the low Ta/VPD level (29C/2.4 kPa) and ASW >50%. Diurnal canopy CO2 uptake rates decreased at the high Ta/VPD level (37C/3.6 kPa), and midday depression of canopy Aco2 was observed at ASW levels <50%. Net canopy Aco2 decreased at higher levels of ASW under the high Ta/VPD treatment than at the low Ta/VPD treatment. At the elevated CO2 concentration (840 μmol·mol-1) net canopy CO2 uptake rates were double those that occurred at ambient CO2 levels and they did not exhibit midday reduction. Our data indicate that, when soil water is not readily available, citrus seedlings are more sensitive to high levels of Ta and VPD which results in reduction of CO2 uptake. The inhibitory effects of elevated VPD and reduced ASW on citrus net Aco2 were lessened at the elevated atmospheric CO2 level.

End-Tidal Carbon Monoxide in Newborn Infants: Observations during the 1st Week of Life

Serial end-tidal carbon monoxide corrected for ambient CO (ETCOc) levels were measured in an ethnically diverse population of 87 normal newborn infants during the first 5 days of life. The results demonstrate a progressive reduction in ETCOc from 1.6 +/- 0.4 to 0.8 +/- 0.2 ppm. These levels were unrelated to ethnicity, but were inversely related to serum bilirubin levels. We conclude that ETCOc is not a useful indicator for predicting the course of transitional hyperbilirubinemia in the normal newborn infant.

Photoautotrophic growth of soybean cells in suspension culture III. Characterization of carbon fixation products under high and low CO2 levels

A photoautotrophic soybean suspension culture (SB-P) was used to study CO2 assimilation while exposed to elevated or ambient CO2 levels. These studies showed that under elevated CO2 (5% v/v) malate is the dominant fixation product, strongly suggesting that phosphoenolpyruvate carboxylase (PEPCase) is the primary enzyme involved in carbon fixation in these cells under their normal growth conditions. Citrate and [aspartate + glutamate] were also significant fixation products during fifteen minutes of exposure to 14CO2. During the ten minute unlabeled CO2 chase however, 14C-malate continued to increase while citrate and [aspartate + glutamate] declined. Fixation of 14CO2 under ambient CO2 levels (0.037%) showed a very different product pattern as 3-phosphoglycerate was very high in the first one to two minutes followed by increases in [serine + glycine] and [aspartate + glutamate]. Hexose phosphates were also quite high initially but then declined relatively rapidly. Thus, the carbon fixation pattern at ambient CO2 levels resembles somewhat that seen in C3 leaf cells while that seen at elevated CO2 levels more closely resembles that of a C4 plant. The initial fixation product of C3 plants, 3-PGA, was never detectable under high CO2 conditions. These data suggest that an in vitro photoautotrophic system would be suitable for studying carbon fixation physiology during photosynthetic and non-photosynthetic growth.

Interactive effects of mycorrhization and elevated carbon dioxide on growth of young pedunculate oak (Quercus robur L.) trees

Pedunculate oak (Quercus robur L.) was germinated and grown at ambient CO2 level and 650 ppmv CO2 in the presence and absence of the ectomycorrhizal fungus Laccaria laccata for a total of 6 month under nutrient non-limiting conditions. Mycorrhization and elevated atmospheric CO2 each supported the growth of the trees. Stem height, stem diameter, and dry matter accumulation of pedunculate oak were increased by mycorrhization. Elevated atmospheric CO2 enhanced stem height, stem diameter, fresh weight and dry weight, as well as lateral root formation of the trees. In combination, mycorrhization and elevated atmospheric CO2 had a more than additive, positive effect on tree height and biomass accumulation, and further improved lateral root formation of the trees. From these findings it is suggested that the efficiency of the roots in supporting the growth of the shoot is increased in mycorrhized oak trees at elevated atmospheric CO2.

Energy content, construction cost and phytomass accumulation of Glycine max (L.) Merr. and Sorghum bicolor (L.) Moench grown in elevated CO2 in the field.

Grain sorghum [Sorghum bicolor (L.) Moench, a C4 crop] and soybean [Glycine max (L.) Merr. cv. Stonewall, a C3 crop] plants were grown in ambient (c. 360μl 1-1 ) and twice-ambient (c. 720 μl 1-1 ) CO2 levels in open-top chambers in soil without root constriction. Plant dry mass, energy content, composition and construction cost (i.e. amount of carbohydrate required to synthesize a unit of plant dry mass) were assessed at the end of the growing season. Elevated CO2 (a) increased phytomass accumulation (kg per plant) in both species, (b) had little affect on energy concentration (MJ kg-1 plant) but caused large increases in the amount of plant energy per ground area (MJ m-2 ground), and (c) did not alter specific growth cost (kg carbohydrate kg-1 plant growth) but greatly increased growth cost per ground area (kg carbohydrate m-2 ground) because growth was enhanced. For soybean, twice-ambient CO2 resulted in a 50 % increase in the amount of nitrogen and energy in grain (seed plus pod) per ground area. This response to elevated CO2 has important implications for agricultural productivity during the next century because the rate of human population growth is exceeding the rate of increase of land used for agriculture so that future food demands can only be met by greater production per ground area.

Malate‐sensitive anion channels enable guard cells to sense changes in the ambient CO2 concentration

SummaryMalate is a characteristic metabolite in the photosynthesis of C4 and CAM plants. Furthermore, changes in the intracellular concentration of this organic acid provide part of the osmotic motor for guard cells. Since alterations in the malate concentration influence the photosynthetic capacity on one side and stomatal action on the other, it was studied whether the extracellular malate level represents an indicator of changes in the ambient CO2 concentration and a key regulator of ion transport in guard cells.Here it is demonstrated that alterations in the ambient CO2 level modify the extracellular malate concentration of Vicia faba leaves. Elevated external malate caused stomatal closure in a concentration‐dependent manner (Kmmal = 0.3 mM). Slight variations in the external malate concentration strongly regulate the voltage‐dependent properties of GCAC1, an anion‐release channel in the plasma membrane of guard cells. Superfusion of guard cell protoplasts with malate levels in the physiological range (Kmmal = 0.4 mM) caused the voltage gate to shift towards the resting potential of the cell‐activating GCAC1. Single‐channel conductance was dependent on the extracellular chloride concentration (KmCl = 3 mM). In the absence of extracellular chloride the plasma membrane lacked anion conductance until the addition of malate induced channel opening. Isophthalate was a powerful agonist in both malate‐induced processes, channel regulation and stomatal closure, indicating that modulation of GCAC1 is a key step in stomatal action. It was thus concluded that feedback regulation of volume and turgor with respect to the ambient CO2 concentration via malate‐sensitive anion channels may provide a CO2 sensor to guard cells.

Routine, Continuous Measurement of Carbon Monoxide with Parts per Billion Precision

A system including a commerical instrument (Thermo Electron Corp., Model 48) operating on the principle of gas filter correlation, nondispersive infrared absorption is utilized to approach 1 ppbv precision with a 1-h averaging period in the measurement of slowly varying ambient CO levels in rural and remote regions. The instrument modifications, setup, and signal averaging processes include gold-plated mirrors, selected detector, 1-s signal resonse time (all available as options from the manufacturer), installation of a lens to more fully focus the infrared beam on the detector, standard addition calibration, catalytic zeroing, rapid switching between equal time periods in the measurement and zero modes, and longterm averaging

Effects of free-air CO2 enrichment on microbial populations in the rhizosphere and phyllosphere of cotton

Cotton (Gossypium hirsutum L.) plants were exposed to free-air CO2 enriched (FACE = 550 μmol mol−1) or ambient (CONTROL = 370 μmol mol−1) levels of atmospheric CO2 and to wet (100% of evapotranspiration replaced) or dry (67% of ET replaced) soil water content treatments. Foliar, soil and root samples were collected in June and August 1991 to determine the effects of elevated CO2 on selected groups of phyllosphere and rhizosphere microorganisms. Foliage and rhizosphere soil were analyzed for bacteria and/or fungi using dilution plating. Mycorrhizal colonization of cotton roots was assessed. Root-zone soil was analyzed for populations of nematodes, microarthropods and Rhizoctonia using various extraction methods. A dehydrogenase assay for total microbial respiration and a bioassay for cotton root infecting organisms were also conducted using root-zone soil. Populations of fungi on cotton leaves varied, by genera, in response to CO2 enrichment, but none was affected by soil water content treatments; populations of foliar bacteria were not affected by either CO2 or soil water content treatments. In August, higher total numbers of rhizosphere fungi were found under the wet compared with the dry soil water treatment, but differences related to CO2 were not detected. There was a trend for infestation by Rhizoctonia solani to be higher under FACE in the August sample, but the soil bioassay demonstrated no increase in damping-off potential. There was a significant interaction between CO2 concentration and soil water content for populations of saprophagous nematodes; populations were different between the CO2 levels in the dry soil treatment only, with higher numbers under FACE. Microarthropod numbers were low; however, there was a trend for Collembola populations to be higher under FACE in the August sample and more fungi were isolated from Collembola in June. Total microbial activity was higher under FACE at both sample dates. Effects of elevated atmospheric CO2 on plant microbe interactions could have profound influence on the productivity of agro-ecosystems, and deserve further research.

119 PHOTOSYNTHESIS AND RESPIRATION OF APPLE PLANTS AT DIFFERENT CARBON DIOXIDE CONCENTRATIONS

Low CO2 concentrations ([CO2]) frequently occur in dense crop canopy. To determine plant performance under sub-atmospheric [CO2], young `Gala' apple plants were phytotron-grown at 928 mmole m-2s-1 light intensity. Whole-plant photosynthesis and respiration under [CO2] between 0 and the ambient level (382 to 460 ml 1-1) were measured by monitoring [CO2] of the air entering and coming out of a 38-1 clear plexiglass gas exchange chamber at either 3.4 or 6.2 1 min-1. The chamber seals two plants of up to 77 cm height for long-term experiments. There was a linear relationship between [CO2] and net photosynthesis (Pn), with the R2 being as high as 0.99. The increase of Pn with increased [CO2] was 51% greater for the high air flow than for the low air flow. At the ambient CO2 level Pn at the high flow rate was 49% higher than that at the low flow rate. CO2 compensation points were 57.6 and 58.5 ml 1-1 at the high and low flow rates, respectively. The relationship between [CO2] and dark respiration was linear. Dark respiration decreased by 20% on average as the [CO2] increased from 0 to the ambient level, and it was 11% higher at the high flow rate than at the low flow rate. These results suggest that wind may act to reduce Pn depression in dense crop canopy by both reducing leaf resistance and atmospheric [CO2] gradient outside the boundary layer.

Biomass production in a nitrogen-fertilized, tallgrass prairie ecosystem exposed to ambient and elevated levels of CO2

Biomass production in a nitrogen-fertilized, tallgrass prairie ecosystem exposed to ambient and elevated levels of CO2

Elevated atmospheric CO2 alters stomatal responses to variable sunlight in a C4 grass

Native tallgrass prairie in NE Kansas was exposed to elevated (twice ambient) or ambient atmospheric CO2 levels in open-top chambers. Within chambers or in adjacent unchambered plots, the dominant C4 grass, Andropogon gerardii, was subjected to fluctuations in sunlight similar to that produced by clouds or within canopy shading (full sun > 1500 μmol m−2 s−1 versus 350 μmol m−2 s−1 shade) and responses in gas exchange were measured. These field experiments demonstrated that stomatal conductance in A. gerardii achieved new steady state levels more rapidly after abrupt changes in sunlight at elevated CO2 when compared to plants at ambient CO2. This was due primarily to the 50% reduction in stomatal conductance at elevated CO2, but was also a result of more rapid stomatal responses. Time constants describing stomatal responses were significantly reduced (29–33%) at elevated CO2. As a result, water loss was decreased by as much as 57% (6.5% due to more rapid stomatal responses). Concurrent increases in leaf xylem pressure potential during periods of sunlight variability provided additional evidence that more rapid stomatal responses at elevated CO2 enhanced plant water status. CO2-induced alterations in the kinetics of stomatal responses to variable sunlight will likely enhance direct effects of elevated CO2 on plant water relations in all ecosystems.

Photosynthetic and Growth Responses of Variegated Ornamental Species to Elevated CO2

Variegated and completely green cultivars of oleander (Nerium oleander L.) and willow myrtle (Agonis flexuosa (Willd.) Sweet) were grown in controlled environment cabinets for 3 and 5 months, respectively, under either ambient levels of CO2 or with supplementary CO2 to a partial pressure of 800 μbar. Photosynthesis of entirely green leaves and the green portions of variegated leaves on both species was greatly stimulated by high CO2 and there was no evidence of downward adjustment (acclimation) of photosynthetic rates to high CO2 during the experiment. Dark respiration rates of these leaves were lowered by high CO2. The yellow portions of willow myrtle leaves showed a low level of photosynthetic activity which was stimulated by high CO2; however, dark respiration rates showed little response to elevated CO2. Green and yellow areas on variegated leaves of willow myrtle had much lower dark respiration rates than completely green leaves, but this difference was not evident for oleander. Yellow portions of oleander leaves showed little evidence of photosynthetic capacity. This was also confirmed by a low photochemical efficiency as determined by chlorophyll fluorescence. A major effect of variegation was to slow overall plant growth compared with completely green plants. The respective 3-fold and 6-7-fold differences in biomass between fully green and variegated cultivars of oleander and willow myrtle was closely related to estimated net carbon gain per day by the plant canopy. Variegation for both species averaged close to 50:50, green:yellow areas. Variegated plants developed about twice the leaf area ratio and specific leaf area compared with their completely green counterparts. The relative growth response to high CO2 was significantly greater for the variegated plants compared to the completely green plants.

Photosynthetic and Water Relations Responses to Elevated CO<sub>2</sub> in the C<sub>4</sub> Grass Andropogon gerardii

Undisturbed tallgrass prairie, dominated by the C₄ grass Andropogon gerardii, was exposed to ambient and elevated (double ambient) levels of atmospheric CO₂ in large open-top chambers throughout the 1991 and 1992 growing seasons. Responses in leaf xylem pressure potential (ψ), net photosynthesis (A), and stomatal conductance (g) were measured in both years for A. gerardii grown within chambers and from adjacent field plots. In 1992, maximum photosynthetic capacity (A_max), apparent quantum requirement (Q_r), the photosynthetic light compensation point (LCP), and dark respiration (<tex-math>$R_{d}$</tex-math>) were also measured. Midday ψ was significantly higher in plants grown at elevated CO₂ in both years, and seasonally averaged ψ was 0.48-0.70 MPa lower in 1991 (a dry year) than 1992 (a wet year). In 1991, A and g were significantly higher (regardless of measurement CO₂ level) in plants grown at elevated vs. ambient CO₂. These increases were measured in well-watered plants insuring that these plants differed only in CO₂ growth conditions and previous exposure to low ψ. Increased A at elevated CO₂ occurred (as much as <tex-math>$7.1\ \mu {\rm mol}\ {\rm m}^{-2}\ {\rm s}^{-1}$</tex-math>) over a broad range of temperatures (17-35 C), but the temperature optimum for A was similar at both 350 and <tex-math>$700\ \mu {\rm L}\ {\rm L}^{-1}\ {\rm CO}_{2}$</tex-math>. In 1992, no differences in A, A_max, Q_r, LCP, or <tex-math>$R_{d}$</tex-math> were detected when ambient and elevated CO₂ plants were compared. In plants collected from field plots, <tex-math>$R_{d}$</tex-math>, LCP, and leaf N were significantly higher than in plants within the chambers indicating that a chamber effect exists for these parameters. In both years, g was significantly reduced (21%-51%) when measured at 700 vs. <tex-math>$350\ \mu {\rm L}\ {\rm L}^{-1}\ {\rm CO}_{2}$</tex-math>. Peak aboveground biomass was increased at elevated CO₂ in 1991 but not in 1992. These data indicate that for C₄ grasses, effects of elevated CO₂ may only be detectable in years with significant water stress, a common occurrence in the central North American tallgrass prairies.

Effect of carbon dioxide on the reaction of YBa2Cu2O6.5+x with water vapour

The influence of carbon dioxide on the reaction between YBa2Cu3O6.5+x powder and air saturated with water vapour was studied. Superconductor powder samples were exposed to air that was saturated with water vapour which (a) was free of CO2, (b) was saturated with CO2, and (c) contained ambient levels of CO2. In another experiment, the effect of pure, dry CO2 (1 atmosphere partial pressure) was studied. The time variations of sample weight, oxygen content and X-ray diffraction (XRD) spectrum were determined. In water-saturated air, the rate of decrease of the oxygen content in YBa2Cu3O6.5+x decreased with increasing partial pressure of CO2. XRD was used to identify the reaction products. Higher partial pressures of CO2 favour the formation of a barrier layer (BaCO3) which inhibits the reaction of the underlying YBa2Cu3O6.5+x with water vapour. Very little decrease in oxygen content occurred on exposure of YBa2Cu3O6.5+x to pure, dry CO2.