Low CO2 Treatment Research Articles

Effect of CO<sub>2</sub> on the properties and sinking velocity of aggregates of the coccolithophore <I>Emiliania huxleyi</I>

Abstract. Coccolithophores play an important role in organic matter export due to their production of the mineral calcite that can act as ballast. Recent studies indicated that calcification in coccolithophores may be affected by changes in seawater carbonate chemistry. We investigated the influence of CO2 on the aggregation and sinking behaviour of the coccolithophore Emiliania huxleyi (PML B92/11) during a laboratory experiment. The coccolithophores were grown under low (~180 μatm), medium (~380 μatm), and high (~750 μatm) CO2 conditions. Aggregation of the cells was promoted using roller tables. Size and settling velocity of aggregates were determined during the incubation using video image analysis. Our results indicate that aggregate properties are sensitive to changes in the degree of ballasting, as evoked by ocean acidification. Average sinking velocity was highest for low CO2 aggregates (~1292 m d−1) that also had the highest particulate inorganic to particulate organic carbon (PIC/POC) ratio. Lowest PIC/POC ratios and lowest sinking velocity (~366 m d−1) at comparable sizes were observed for aggregates of the high CO2 treatment. Aggregates of the high CO2 treatment showed a 4-fold lower excess density (~4.2×10−4 g cm−3) when compared to aggregates from the medium and low CO2 treatments (~1.7 g×10−3 cm−3). We also observed that more aggregates formed in the high CO2 treatment, and that those aggregates contained more bacteria than aggregates in the medium and low CO2 treatment. If applicable to the future ocean, our findings suggest that a CO2 induced reduction of the calcite content of aggregates could weaken the deep export of organic matter in the ocean, particularly in areas dominated by coccolithophores.

The effects of carbon dioxide on performance and histopathology of rainbow trout Oncorhynchus mykiss in water recirculation aquaculture systems

Chronic exposure to elevated levels of dissolved carbon dioxide (CO2) has been linked to reduced growth, physiological disturbances and negative health outcomes in intensively reared fish. Although pumping to a degassing tower can lower concentrations of dissolved CO2 in water recirculation aquaculture systems (WRAS), pumping can be a significant cost for operators. A 6-month trial was conducted to compare the effects of high (24±1mg/L; partial pressure=8.79mmHg) and low (8±1mg/L; partial pressure=2.91mmHg) dissolved CO2 concentrations on rainbow trout Oncorhynchus mykiss performance and health in replicated WRAS operated at low-exchange rates (0.26% of the total recirculating flow). Rainbow trout (62±1g) were randomly stocked into six replicated WRAS and into three small tanks within a flow-through system to provide a physiological comparison. All study fish were maintained at densities between 25 and 80kg/m3, at water temperatures of approximately 13–14°C, and at dissolved oxygen concentrations of approximately saturation. A 24-h photoperiod was provided and all fish groups were fed equal portions every 2h during the study period. Fish health and performance were assessed with daily mortality and monthly length and weight data collection, as well as multiple tissue samplings for histopathological assessment. At the study's end, percentage survival for both groups was high (>97%). No significant (p<0.05) differences in growth or survival were observed between CO2 treatments. No nephrocalcinosis or related pathologies were noted. Skin and gill pathologies were common in both treatment groups; however, there were few statistically significant differences between groups for any of the tissue types evaluated: high CO2 fish were more likely to exhibit lymphocytic portal hepatitis, while the low CO2 treatment group exhibited greater gill epithelial hyperplasia. None of the pathologies observed were substantive or likely to cause mortality. The results of this study indicate that raising rainbow trout to market size in WRAS with CO2 concentrations of 24mg/L does not significantly affect their overall health and performance.

Laboratory Assessment of Altered Atmospheric Carbon Dioxide on Filamentous Green Algae Phenolic Content and Caddisfly Growth and Survival

ABSTRACT To test global change effects on lentic ecosystems, we examined I) if algae phenolic content was influenced by CO2 treatments, and 2) if algivores fed CO2-treated algae were impacted. Four common Chlorophytes (Cladophora glomerata, Spirogyra grevilleana, Ulothrix, fimbriata, and Zygnema sp.) were grown under three atmospheric carbon dioxide environments (200, 360, and 3000 mg/L). Algivore (the microcaddisfly Hydroptila waubesiana [Trichoptera: Hydroptilidae]) feeding assays, using identically treated algae (C. glomarata and U. fimbriata) as a food source, were run in parallel. Generally, Folin-Denis reactive phenolics were highest among algae grown under high CO2 treatments, intermediate at ambient CO2, and lowest under low CO2 treatment. Differential species responses in reactive phenolics were observed, with U. fimbriata being most responsive (∼6 %) to CO2 enrichment, and C. glomarata being unresponsive (<1%). Regardless of algal species or CO2 treatment, developmental rates of H. wauhesiana larvae to mid and late instars were statistically identical. Percent survival for larvae given U. fimbriata and C. glomerata were similar; however, survival rates were higher when larvae were fed low CO2 treated U. fimbriata. For larvae fed C. glomerata, the general trend was that larvae fed algae grown at high CO2 levels had the greatest head capsule width; those fed algae at low CO2 levels had the greatest head capsule length and pronotal length. In contrast, larvae fed U. fimbriata had the largest head capsule widths under ambient CO2 levels, the largest head capsule widths under high levels, and had equal pronotal lengths at all CO2 levels. Larvae fed C. glomerata grown under ambient conditions produced portable cases of the greatest length at the experiment's conclusion, but no distinct trend was seen for larvae fed U. fimbriata. Overall, CO2 induced production of reactive phenolics in chlorophytes did not appreciably influence herbivorous microcaddisfly development or survival.

Effects of arbuscular mycorrhizae on biomass and nutrients in the aquatic plant Littorella uniflora

Summary1. It has been hypothesised that the symbiosis with arbuscular mycorrhizal fungi (AMF) leads to a higher uptake of phosphorus (P) and nitrogen (N) in aquatic plants, but it has never been shown experimentally without the use of fungicides. In particular, the symbiosis may be important for nutrient uptake by isoetids in oligotrophic lakes, where low concentrations of inorganic N and P both in the water and in the sediment limit the growth of plants and where symbiosis facilitates the uptake of nutrients from the sediment.2. Plants of the isoetid Littorella uniflora were propagated under the sterile conditions without an AMF infection. The plants were then grown for 60 days with and without re‐infection by AMF, and with either high (150 μm) or low (ambient concentration approximately 15 μm) CO2 concentration.3. The study proved that the symbiosis between AMF and L. uniflora had a positive impact on the retention of N and P in the plants at very low nutrient concentrations in the water and on biomass development. Shoot biomass and standing stocks of both P and N were significantly higher in re‐infected plants.4. Raised CO2 concentration resulted in a fivefold increase in hyphal infection, but had no impact on the number of arbuscules and vesicles in the cross sections. There were significantly higher biomass and lower tissue P and N concentrations in the plants from high CO2 treatments. This resulted in similar standing stocks of P and N in plants from low and high CO2 treatments.5. The results from this study showed that the symbiosis between AMF and L. uniflora is an important adaptation enabling isoetids to grow on nutrient‐poor sediments in oligotrophic lakes.

CO2 effects on taxonomic composition and nutrient utilization in an Equatorial Pacific phytoplankton assemblage

We report the results of a field incubation experiment demonstrating a substantial shift in the taxonomic composition of Equatorial Pacific phytoplankton assemblages exposed to CO2 levels of 150 and 750 ppm (dissolved CO2 ~3 to 25 µM). By the end of the experiment, the phytoplankton community in all samples was dominated by diatoms and Phaeocystis sp. However, the relative abun- dance of these phytoplankton taxa differed significantly between CO2 treatments. Taxonomic pig- ment analysis and direct microscopic examination of samples revealed that the abundance of diatoms decreased by ~50% at low CO2 relative to high CO2, while the abundance of Phaeocystis increased by ~60% at low CO2. This CO2-dependent shift was associated with a significant change in nutrient utilization, with higher ratios of nitrate:silicate (N:Si) and nitrate:phosphate (N:P) consumption by phytoplankton in the low CO2 treatment. Despite the significant changes in taxonomic composition and nutrient consumption ratios, total biomass and primary productivity did not differ significantly between the CO2 treatments. Our results suggest that CO2 concentrations could potentially influence competition among marine phytoplankton taxa and affect oceanic nutrient cycling.

Substrate‐derived CO2 is important in the development of Sphagnum spp.

Summary The effects of different CO2 concentrations in the acrotelm pore water on the development of Sphagnum magellanicum monoliths grown in wet conditions in the laboratory are reported here. Decomposition processes result in much higher CO2 concentrations in bog acrotelms than atmospheric concentrations. We therefore hypothesized that this substrate‐derived carbon provides an important carbon source for Sphagnum. S. magellanicum hummocks developed only when CO2 concentrations in the acrotelm water were high. Plants in the low CO2 treatment appeared to be carbon‐limited; they had increased nutrient concentrations and decreased ratios of carbon to other nutrients. Chlorophyll concentrations were much higher in these plants, probably allowing them to harvest more CO2, but the allocation of carbon to structural tissues was lower, resulting in weak stems that were unable to remain upright. As a result of carbon‐limitation, net biomass and height increases of the monoliths were much lower in the low CO2 treatment. Results indicate that, at least in wet conditions, atmospheric CO2 alone is not sufficient to enable S. magellanicum to develop its normal vertical growth pattern. We conclude that the role of substrate‐derived CO2 as a carbon source for Sphagna is underestimated and requires reconsideration.

Photosynthetic enhancement and conductance to water vapor of field-grown Solanum tuberosum (L.) in response to CO2 enrichment

The photosynthetic responses of potato [Solanum tuberosum(L.)] to CO2 enrichment were studied in open-topped field chambers. Plants were raised in 2.4 m 2 plastic enclosures over three growing seasons from 1996 to 1998. Plots were continuously fertilized with 1, 1.5 and 2 times ambient daytime CO2. These were the low (L), medium (M) and high (H) CO2 treatments, respectively. Tuber dry matter yields were increased 9 and 40%, respectively, in the M and H treatments compared to the L CO2 treatment. Net photosynthesis (Pn) and conductance to water vapor (gs) of upper canopy leaves were measured at 1 or 2-week intervals at the growth CO2 partial pressure and then Pn of plants in the L treatment was determined at 70 Pa CO2 (L70). Leaflet P n rates averaged over all measurement dates were 28, 49 and 84% greater, respectively, in the M, H and L70 CO2 treatments, compared to plants in the L treatment. Changes of Pn in response to the L, M and H CO2 treatments were proportional to increases of internal CO2 (Ci) and at low leaf-to-air vapor pressure deficits mid-day gs was inversely related to growth CO2. The ratio of Pn at H compared to L70 was 0.81 when averaged over all measurement dates. Leaf soluble protein, Rubisco protein and chlorophyll ( a+b ) levels were unaffected by CO2 treatment. Total Rubisco activity was decreased by CO2 enrichment in 1998, but percent activation was similar in the L, M and H plots. Leaf starch was increased but sucrose, glucose and fructose were unaffected by CO2 treatment. The above findings indicated that a down regulation of Pn in response to elevated CO2 was consistently observed in field-grown potato. This was attributed to a decrease of total Rubisco activity that was potentially due to the presence of inhibitory compounds bound to the active site of the enzyme. The amount of photosynthetic acclimation observed here did not preclude a persistent enhancement of Pn under the elevated CO2 growth conditions.

The significance of differences in the mechanisms of photosynthetic acclimation to light, nitrogen and CO2 for return on investment in leaves

1. We report changes in photosynthetic capacity of leaves developed in varying photon flux density (PFD), nitrogen supply and CO2 concentration. We determined the relative effect of these environmental factors on photosynthetic capacity per unit leaf volume as well as the volume of tissue per unit leaf area. We calculated resource‐use efficiencies from the photosynthetic capacities and measurements of leaf dry mass, carbohydrates and nitrogen content. 2. There were clear differences between the mechanisms of photosynthetic acclimation to PFD, nitrogen supply and CO2. PFD primarily affected volume of tissue per unit area whereas nitrogen supply primarily affected photosynthetic capacity per unit volume. CO2 concentration affected both of these parameters and interacted strongly with the PFD and nitrogen treatments. 3. Photosynthetic capacity per unit carbon invested in leaves increased in the low PFD, high nitrogen and low CO2 treatments. Photosynthetic capacity per unit nitrogen was significantly affected only by nitrogen supply. 4. The responses to low PFD and low nitrogen appear to function to increase the efficiency of utilization of the limiting resource. However, the responses to elevated CO2 in the high PFD and high nitrogen treatments suggest that high CO2 can result in a situation where growth is not limited by either carbon or nitrogen supply. Limitation of growth at elevated CO2 appears to result from internal plant factors that limit utilization of carbohydrates at sinks and/or transport of carbohydrates to sinks.

Root competition and elevated CO2: effects on seedling growth in Linum usitatissimum populations and Linum–Silene cretica mixtures

1. Root competition can be an important determinant of the performance of neighbours within plant populations and communities. Because plants often maintain larger root systems and allocate more of their carbon to root systems under elevated atmospheric CO2 than they do at lower CO2 concentrations, root–root interactions could play an increasingly important role in determining competitive outcomes among individuals and plant species as global CO2 concentration continues to rise. 2. We established 12 pure stands of Linum usitatissimum (flax) and 12 mixed stands of Linum and its naturally co‐occurring weed species Silene cretica in opaque plastic trays each filled with the same amount of nutrient‐rich soil mix. In half of the trays from each of these stand types, vertical waterproof partitions separated the root systems of individual plants from each other to prevent root competition, while in the other half no partitions were present. Half of the trays from all treatments were allowed to grow under low atmospheric CO2 concentration (320μll–1) and the other half under elevated CO2 (600μll–1), in daylight growth chambers for 30 days from seedling emergence until harvest in mid‐June. All trays received equal amounts of water so that soils in the low CO2 treatment were maintained at field capacity. 3. Our results indicate that under high soil fertilities: (1) intra‐specific root–root interactions alone play a relatively insignificant role in determining plant biomass production within pure Linum populations and (2) the impact of an aggressive species (Silene) on co‐occurring less aggressive species (Linum) becomes more severe under elevated CO2 as a result of amplified interspecific root competition.

Low Activation State of Ribulose-1,5-Bisphosphate Carboxylase/Oxygenase in Carboxysome-Defective Synechococcus Mutants.

The high-CO2-requiring mutant of Synechococcus sp. PCC 7942, EK6, was obtained after extension of the C terminus of the small subunit of ribulose-1,5-bisphosphate (RuBP) carboxylase/oxygenase (Rubisco). The carboxysomes in EK6 were much larger than in the wild type, but the cellular distribution of the large and small sub-units of Rubisco was not affected. The kinetic parameters of in vitro-activated Rubisco were similar in EK6 and in the wild type. On the other hand, Rubisco appeared to be in a low state of activation in situ in EK6 cells pretreated with an air level of CO2. This was deduced from the appearance of a lag phase when carboxylation was followed with time in cells permeabilized by detergent and subsequently supplied with saturating CO2 and RuBP. Pretreatment of the cells with high CO2 virtually abolished the lag. After low-CO2 treatment, the internal RuBP pool was much higher in mutant cells than in the wild-type cells; pretreatment with high CO2 reduced the pool in mutant cells. We suggest that the high-CO2-requiring phenotype in mutants that possess aberrant carboxysomes arises from the inactivated state of Rubisco when the cells are exposed to low CO2.

Water stress, carbon dioxide, and light effects on sucrose-phosphate synthase activity in Phaseolus vulgaris

The characteristics of sucrose-phosphate synthase (SPS; EC 2.4.1.14) activity in leaves of Phaseolus vulgaris L. cv. Linden was studied in plants subjected to water stress and various CO2 and light treatments. When water was withheld for 3 days causing mild water stress (–0.9 MPa), the activity of SPS measured in crude extracts was reduced ca 50%. The effect of water stress was most evident when the enzyme was assayed with saturating amounts of its substrates fructose 6-phosphate and UDP glucose. Placing a water-stressed plant in an atmosphere containing 1% CO2 reversed the effect of water stress on SPS activity over 5 h even though the water stress was not relieved. Holding unstressed leaves in low CO2 partial pressure reduced the extractable activity of SPS. After 1 h of low CO2 treatment the effect of low CO2 could be reversed by 20 min of 5% CO2. However, after 24 h of low CO2 treatment, less SPS activity was recovered by the 20 min treatment. The cytosolic protein synthesis inhibitor cycloheximide prevented the slow recovery of SPS activity, but did not affect the rapid recovery of SPS. We conclude that the effect of water stress on SPS activity was a consequence of the inhibition of photosynthesis caused by stomatal closure. Responses of Phaseolus vulgaris SPS to light were similar to the response to low CO2 in that the effects were most pronounced under Vmax assay conditions. This is the first report of this type of light response of SPS in a dicotyledonous species.

Water stress, carbon dioxide, and light effects on sucrosephosphate synthase activity in Phaseolus vulgaris

The characteristics of sucrose‐phosphate synthase (SPS; EC 2.4.1.14) activity in leaves of Phaseolus vulgaris L. cv. Linden was studied in plants subjected to water stress and various CO2 and light treatments. When water was withheld for 3 days causing mild water stress (–0.9 MPa), the activity of SPS measured in crude extracts was reduced ca 50%. The effect of water stress was most evident when the enzyme was assayed with saturating amounts of its substrates fructose 6‐phosphate and UDP glucose. Placing a water‐stressed plant in an atmosphere containing 1% CO2 reversed the effect of water stress on SPS activity over 5 h even though the water stress was not relieved. Holding unstressed leaves in low CO2 partial pressure reduced the extractable activity of SPS. After 1 h of low CO2 treatment the effect of low CO2 could be reversed by 20 min of 5% CO2. However, after 24 h of low CO2 treatment, less SPS activity was recovered by the 20 min treatment. The cytosolic protein synthesis inhibitor cycloheximide prevented the slow recovery of SPS activity, but did not affect the rapid recovery of SPS. We conclude that the effect of water stress on SPS activity was a consequence of the inhibition of photosynthesis caused by stomatal closure. Responses of Phaseolus vulgaris SPS to light were similar to the response to low CO2 in that the effects were most pronounced under Vmax assay conditions. This is the first report of this type of light response of SPS in a dicotyledonous species.

Physiological and Quality Responses of `Bartlett' Pears to Reduced O2 and Enhanced CO2 Levels and Storage Temperature

`Bartlett' pears (Pyrus communis L.) tolerated up to 10 days of exposure to atmospheres containing 1.0%, 0.5%, or 0.25% O2 at 0, 5, or 10C without any detrimental effects on their quality attributes. The fruits also tolerated 4 to 6 days of exposure to air enriched with 20%, 50%, or 80% CO2 at the three temperatures. The beneficial effects of exposures to the O2-reduced or CO2-enriched atmospheres included reduction of respiration and ethylene production rates and retardation of skin yellowing and flesh softening. While 1.0% or 0.5% O2 and 20% CO2 did not increase ethanol and acetaldehyde contents, 0.25% O2 slightly increased and 50% or 80% CO2 dramatically increased the contents of these two volatiles in juice of the fruits. The effects of low O2 or high CO2 on the above attributes generally became more pronounced at the higher temperatures. The low O2 or high CO2 treatments did not significantly affect either soluble solids content or titratable acidity. Low O2 did not influence, but high CO2 slightly increased pH of the fruits.

The effects of oxides of nitrogen and carbon dioxide enrichment on photosynthesis and growth of lettuce (Lactuca sativa L.).

The response of glasshouse crops to the nitrogen oxide pollutants which may be generated during enrichment with O2 has been studied in controlled environments. Lettuce (Lactuca sativa L. cv. Ambassador) was grown in air containing either low CO2 , (380μmol mol-1 ), high CO2 , (1200 μmol mol -1 ), or high CO2 plus oxides of nitrogen? (NOx )- Carbondioxide enrichment increased the rate of emergence and expansion of leaves and the growth of Young plants. Addition of NOx (2μmol mol-1 NO and c. 0.5 μmol mol-1 NO2 ) to CO2 -enriched air significantly reduced the yield, compared with the 'clean, high CO2 treatment, without producing visible symptoms of toxicity. Fumigation of single plants in high CO2 , with NOx rapidly inhibited photosynthesis per unit leaf area. This did not appear to be due to a reduction in stomatal conductance. Removal of NOx from the atmosphere caused a rapid and complete recovery in the rate of photosynthesis. Studies were made of the effects of growing Plants for long periods in atmospheres containing high CO2 and NOx on the photosynthetic capacity of single leaves when measured in NOx -free air. The decrease in photosynthetic rate as the fourth leaf aged occurred earlier in plants grown in CO2 -enriched air than in those from the low CO2 treatment. Leaves which developed in the CO2 -enriched air containing NOx did not suffer any long-term damage to photosynthetic activity in comparison with those of the 'clean' high CO2 . In mature leaves the principal long-term effect of enrichment (with or without NOx was to reduce the rate of photosynthesis in saturating CO2 . In contrast, there was less effect on the rate of Photosynthesis in low CO2 . The absence of a long-term effect of NOx , on the photosynthetic capacity suggested that photosynthesis by the lettuce crop will be inhibited only during the transient periods of NOx accumulation in the glasshouse.

Effect of CO2 enrichment and nitrogen availability on resource acquisition and resource allocation in a grass, Bromus mollis.

The effects of CO2 enrichment on the growth, biomass partitioning, photosynthetic rates, and leaf nitrogen concentration of a grass, Bromus mollis (C3), were investigated at a favorable and a low level of nitrogen availability. Despite increases in root: shoot ratios, leaf nitrogen concentrations were decreased under CO2 enrichment at both nitrogen levels. For the low-nitrogen treatment, this resulted in lower photosynthetic rates measured at 650 μl/l for the CO2-enriched plants, compared to photosynthetic rates measured at 350 μl/l for the non-enriched plants. At higher nitrogen availability, photosynthetic rates of plants grown and measured at 650 μl/l were greater than photosynthetic rates of the non-enriched plants measured at 350 μl/l. Water use efficiency, however, was increased in enriched plants at both nitrogen levels. CO2 enrichment stimulated vegetative growth at both high and low nitrogen during most of the vegetative growth phase but, at the end of the experiment, total biomass of the high and low CO2 treatments did not differ for plants grown at low nitrogen availability. While not statistically significant, CO2 tended to stimulate seed production at high nitrogen and to decrease it at low nitrogen.

Responses of Soybean Canopy Photosynthesis and Transpiration to Whole‐Day Temperature Changes in Different CO2 Environments1

AbstractResponse of plants to increased temperatures, as well as increased CO2, is one of the concerns about the global consequences of continued burning of fossil fuel. In this study, soybeans [Glycine max (L.) Merr. cv. Bragg] were grown in controlled‐environment chambers located outdoors and acclimated to two environmental CO2 levels, 330 and 800 µmol mol−1. Canopies were exposed to different day‐long dry bulb temperature treatments that were maintained for a few days. Comparisons of CER‐light response curves and daytime total CO2 exchange from both low and high CO2 treatments indicated that canopy CER was not significantly affected by dry bulb temperature in the range 28°C to 35°C (nighttime temperature was 23°C). Canopy water use increased significantly in both CO2 treatments as dry bulb temperature was increased and the dewpoint temperature was kept at 21°C. Calculated total canopy resistances were constant throughout the temperature treatments in each of the CO2 treatments. This indicated that between dry bulb treatments, changes in canopy water use resulted strictly from temperature‐driven changes in the vapor pressure gradients within the canopy. Characteristic ratios of internal to external canopy CO2 concentrations were calculated and found to be similar among all temperature treatments and in both CO2 treatments. Across all temperature treatments, cumulative daytime transpiration was nearly equal between the two CO2 treatments, however, water‐use efficiency (WUE) decreased in both CO2 treatments as dry bulb temperature increased. Since CER response in both CO2 treatments was unaffected by air temperature across the range of 28 to 35°C, the decrease in WUE with increasing temperature was due solely to increasing transpiration.

Modified Atmosphere Storage of Danish Cabbage

Abstract Danish cabbage was stored for several years from late November until April at 0°C and in various combinations CO2, O2 and N2. The best combinations of gas mixtures ranged between 21/2 to 5% of O2 and CO2 with N2 making up the remainder. These combinations reduced weight loss due to respiration and also trimming loss. In atmospheres of low O2 and CO2 tension, heads retained their green color, were succulent and firm, and remained dormant longer. Very low O2 and CO2 treatments had a sweeter taste than normal cabbage, while treatments with slightly higher CO2 had more pungent tastes characteristic of fresh cabbage. Treatments with 71/2% O2 and air checks were bland in taste. Color data were recorded by Hunterlab Color Difference Meter.