Effects of increased CO2 levels on growth, photosynthesis, ammonium uptake and cell composition in the macroalga Hypnea spinella (Gigartinales, Rhodophyta)

The red seaweed Hypnea spinella (Gigartinales, Rhodophyta), was cultured at laboratory scale under three different CO₂ conditions, non-enriched air (360?ppm CO₂) and CO₂-enriched air at two final concentrations (750 and 1,600?ppm CO₂), in order to evaluate the influence of increased CO₂ concentrations on growth, photosynthetic capacity, nitrogen removal efficiency, and chemical cellular composition. Average specific growth rates of H. spinella treated with 750 and 1,600?ppm CO₂-enriched air increased by 85.6% and 63.2% compared with non-enriched air cultures. CO₂ reduction percentages close to 12% were measured at 750?ppm CO₂ with respect to 5% and 7% for cultures treated with air and 1,600?ppm CO₂, respectively. Maximum photosynthetic rates were enhanced significantly for high CO₂ treatments, showing P _max values 1.5-fold higher than that for air-treated cultures. N–NH ₄ ⁺ consumption rates were also faster for algae growing at 750 and 1,600?ppm CO₂ than that for non-enriched air cultures. As a consequence of these experimental conditions, soluble carbohydrates increased and soluble protein contents decreased in algae treated with CO₂-enriched air. However, internal C and N contents remained constant at the different CO₂ concentrations. No significant differences in data obtained with both elevated CO₂ treatments, under the assayed conditions, indicate that H. spinella is saturated at dissolved inorganic carbon concentrations close by twice the actual atmospheric levels. The results show that increased CO₂ concentrations might be considered a key factor in order to improve intensively cultured H. spinella production yields and carbon and nitrogen bioremediation efficiencies.     

Life Cycle Assessment of Diesel and Electric Public Transportation Buses

The Clean Air Act in the United States identifies diesel‐powered motor vehicles, including transit buses, as significant sources of several criteria pollutants that contribute to ground‐level ozone formation or smog. The effects of air pollution in urban areas are often more significant due to congestion and can lead to respiratory and cardiovascular health impacts. Life cycle assessment (LCA) has been utilized in the literature to compare conventional gasoline‐powered passenger cars with various types of electric and hybrid‐powered alternatives, however, no similarly detailed studies exist for mass transit buses. LCA results from this study indicate that the use phase, consisting of diesel production/combustion for the conventional bus and electricity generation for the electric bus, dominates most impact categories; however, the effects of battery production are significant for global warming, carcinogens, ozone depletion, and eco‐toxicity. There is a clear connection between the mix of power‐generation technologies and the preference for the diesel or electric bus. With the existing U.S. average grid, there is a strong preference for the conventional diesel bus over the electric bus when considering global warming impacts alone. Policy makers must consider regional variations in the electricity grid prior to recommending the use of battery electric buses to reduce carbon dioxide (CO₂) emissions. This study found that the electric bus was preferable in only eight states, including Washington and Oregon. Improvements in battery technology reduce the life cycle impacts from the electric bus, but the electricity grid makeup is the dominant variable.     

Elevated co2 has Differential Effects on Five Species of Microalgae from a Subtropical Freshwater Lake: Possible Implications for Phytoplankton Species Composition

Rising atmospheric CO₂ concentrations are predicted to have a significant impact on global phytoplankton populations. Of particular interest in freshwater systems are those species that produce toxins or impact water quality, though evidence for how these species, and many others, will respond is limited. This study investigated the effects of elevated CO₂ (1,000 ppm) relative to current atmospheric CO₂ partial pressures (400 ppm), on growth, cell size, carbon acquisition, and photophysiology of five freshwater phytoplankton species including a toxic cyanophyte, Raphidiopsis raciborskii, from Lake Wivenhoe, Australia. Effects of elevated CO₂ on growth rate varied between species; notably growth rate was considerably higher for Staurastrum sp. and significantly lower for Stichococcus sp. with a trend to lower growth rate for R. raciborskii. Surface area to volume ratio was significantly lower with elevated CO₂, for all species except Cyclotella sp. Timing of maximum cell concentrations of those genera studied in monoculture occurred in the lake in order of CO₂ affinity when free CO₂ concentrations dropped below air equilibrium. The results presented here suggest that as atmospheric levels of CO₂ rise, R. raciborskii may become less of a problem to water quality, while some species of chlorophytes may become more dominant. This has implications for stakeholders of many freshwater systems.     

Maximum impacts of future reforestation or deforestation on atmospheric CO2

There is scope for land‐use changes to increase or decrease CO₂ concentrations in the atmosphere over the next century. Here we make simple but robust calculations of the maximum impact of such changes. Historical land‐use changes (mostly deforestation) and fossil fuel emissions have caused an increase in atmospheric concentration of CO₂ of 90 ppm between the pre‐industrial era and year 2000. The projected range of CO₂ concentrations in 2100, under a range of emissions scenarios developed for the IPCC, is 170–600 ppm above 2000 levels. This range is mostly due to different assumptions regarding fossil fuel emissions. If all of the carbon so far released by land‐use changes could be restored to the terrestrial biosphere, atmospheric CO₂ concentration at the end of the century would be about 40–70 ppm less than it would be if no such intervention had occurred. Conversely, complete global deforestation over the same time frame would increase atmospheric concentrations by about 130–290 ppm. These are extreme assumptions; the maximum feasible reforestation and afforestation activities over the next 50 years would result in a reduction in CO₂ concentration of about 15–30 ppm by the end of the century. Thus the time course of fossil fuel emissions will be the major factor in determining atmospheric CO₂ concentrations for the foreseeable future.     

Variability in soil respiration across riparian-hillslope transitions

The spatial and temporal controls on soil CO₂ production and surface CO₂ efflux have been identified as outstanding gaps in our understanding of carbon cycling. We investigated both across two riparian-hillslope transitions in a subalpine catchment, northern Rocky Mountains, Montana. Riparian-hillslope transitions provide ideal locations for investigating the controls on soil CO₂ dynamics due to strong, natural gradients in the factors driving respiration, including soil water content (SWC) and soil temperature. We measured soil air CO₂ concentrations (20 and 50 cm), surface CO₂ efflux, soil temperature, and SWC at eight locations. We investigated (1) how soil CO₂ concentrations differed within and between landscape positions; (2) how the timing of peak soil CO₂ concentrations varied across riparian and hillslope zones; and (3) whether higher soil CO₂ concentrations necessarily resulted in higher efflux (i.e. did surface CO₂ efflux follow patterns of subsurface CO₂)? Soil CO₂ concentrations were significantly higher in the riparian zones, likely due to higher SWC. The timing of peak soil CO₂ concentrations also differed between riparian and hillslope zones, with highest hillslope concentrations near peak snowmelt and highest riparian concentrations during the late summer and early fall. Surface CO₂ efflux was relatively homogeneous at monthly timescales as a result of different combinations of soil CO₂ production and transport, which led to equifinality in efflux across the transects. However, efflux was 57% higher in the riparian zones when integrated to cumulative growing season efflux, and suggests higher riparian soil CO₂ production.     

The role of carbon dioxide in light-activated hydrogen production by Chlamydomonas reinhardtii

Light-activated hydrogen and oxygen evolution as a function of CO₂ concentration in helium were measured for the unicellular green alga Chlamydomonas reinhardtii. The concentrations were 58, 30, 0.8 and 0 ppm CO₂. The objective of these experiments was to study the differential affinity of CO₂/HCO ₃ ^- for their respective Photosystem II and Calvin cycle binding sites vis-à-vis photoevolution of molecular oxygen and the competitive pathways of hydrogen photoevolution and CO₂ photoassimilation. The maximum rate of hydrogen evolution occurred at 0.8 ppm CO₂, whereas the maximum rate of oxygen evolution occurred at 58 ppm CO₂. The key result of this work is that the rate of photosynthetic hydrogen evolution can be increased by, at least partially, satisfying the Photosystem II CO₂/HCO ₃ ^- binding site requirement without fully activating the Calvin-Benson CO₂ reduction pathway. Data are presented which plot the rates of hydrogen and oxygen evolution as functions of atmospheric CO₂ concentration in helium and light intensity. The stoichiometric ratio of hydrogen to oxygen changed from 0.1 at 58 ppm to approximately 2.5 at 0.8 ppm. A discussion of partitioning of photosynthetic reductant between the hydrogen/hydrogenase and Calvin-Benson cycle pathways is presented.Abbreviations PET photosynthetic electron transport - PS Photosystem     

Open top chambers for exposing plant canopies to elevated CO2 concentration and for measuring net gas exchange

Open top chamber design and function are reviewed. All of the chambers described maintain CO₂ concentrations measured at a central location within ±30 ppm of a desired target when averaged over the growing season, but the spatial and temporal range within any chamber may be closer to 100 ppm. Compared with unchambered companion plots, open top chambers modify the microenvironment in the following ways: temperatures are increased up to 3°C depending on the chamber design and location of the measurement; light intensity is typically diminished by as much as 20%; wind velocity is lower and constant; and relative humidity is higher. The chamber environment may significantly alter plant growth when compared with unchambered controls, but the chamber effect on growth has not been clearly attributed to a single or even a few environmental factors.A method for modifying an open top chamber for tracking gas exchange between natural vegetation and the ambient air is described. This modification consists of the addition of a top with exit chimney to reduce dilution of chamber CO₂ by external ambient air, is quickly made and permits estimation of the effects of elevated CO₂ and water vapor exchange.The relatively simple design and construction of open top chambers make them the most likely method to be used in the near future for long-term elevated CO₂ exposure of small trees, crops and grassland ecosystems. Improvements in the basic geometry to improve control of temperature, reduce the variation of CO₂ concentrations, and increase the turbulence and wind speed in the canopy boundary layer are desirable objectives. Similarly, modifications for measuring water vapor and carbon dioxide gas exchange will extend the usefulness of open top chambers to include non-destructive monitoring of the responses of ecosystems to rising atmospheric CO₂.     

Endogenous levels of oxygen,carbon dioxide and ethylene in stems of Norway spruce trees during one growing season

Summary The trees sampled in this study came from two stands of Norway spruce, Picea abies (L.) Karst., near Stockholm, Sweden, differing in mean age and height. Holes were bored perpendicular to the stem surface, and gas samples were taken from the outer part of the sapwood throughout one growing season. Endogenous levels of molecular oxygen (O₂), carbon dioxide (CO₂) and ethylene in the outer sapwood were determined by combined gas chromatography — mass spectrometry (GC-MS) and GC. O₂ concentrations began to decrease as growth started in spring. The lowest levels (<5%) were recorded around mid-summer. In the younger stand concentrations remained below 5% until September. In October, O₂ concentrations in the sapwood were similar to those of air. Concentrations of CO₂ were below 1% in spring, but began to rise in May, peaking a month later at approximately 10%. Thereafter a slow decrease occurred until October, by which time levels had returned to those recorded in spring. Ethylene concentrations in the older stand reached 75 ppm early in May, while levels in the younger stand peaked at around 30 ppm later in May. Thereafter ethylene levels in both stands started to decrease down to ppb levels. The correlation between determined gas levels and physiological events associated with the seasonal growth cycle in temperate zones is discussed.     

Photosynthetic and growth response to fumigation with SO2 at elevated CO2 for C3 and C4 plants

Summary Six early successional plant species with differing photosynthetic pathways (3 C₃ species and 3 C₄ species) were grown at either 300, 600, or 1,200 ppm CO₂ and at either 0.0 or 0.25 ppm SO₂. Total plant growth increased with CO₂ concentration for the C₃ species and varied only slightly with CO₂ for the C₄ species. Fumigation with SO₂ caused reduced growth of the C₃ species at 300 ppm CO₂ but not at the higher concentrations of CO₂. Fumigation with SO₂ reduced growth of the C₄ species at high CO₂ and increased growth at 300 ppm CO₂. Leaf area increased with increasing CO₂ for all plant species. Fumigation with SO₂ reduced leaf area of C₃ plants more at low CO₂ than at high CO₂ while leaf area of C₄ plants was reduced more at high CO₂ than at low CO₂. These results support the notion that C₃ species are more sensitive to SO₂ fumigation than are C₄ species at concentrations of CO₂ equal to that found in normal ambient air. However, the difference in sensitivity to SO₂ between C₃ and C₄ species was found to be reversed at higher concentrations of CO₂. A possible explanation for this reversal based upon differences in stomatal response to elevated CO₂ between C₃ and C₄ species is discussed.     

Influence of enhanced CO2 on growth and photosynthesis of the red algaeGracilaria sp. andG. chilensis

The influence of elevated CO₂ concentrations on growth and photosynthesis ofGracilaria sp. andG. chilensis was investigated in order to procure information on the effective utilization of CO₂. Growth of both was enhanced by CO₂ enrichment (air + 650 ppm CO₂, air + 1250 ppm CO₂, the enhancement being greater inGracilaria sp. Both species increased uptake of NO₃ ^– with CO₂ enrichment. Photosynthetic inorganic carbon uptake was depressed inG. chilensis by pre-culture (15 days) with CO₂ enrichment, but little affected inGracilaria sp. Mass spectrometric analysis showed that O₂ uptake was higher in the light than in the dark for both species and in both cases was higher inGracilaria sp. The higher growth enhancement inGracilaria sp. was attributed to greater depression of photorespiration by the enrichment of CO₂ in culture.     

Effect of CO2 on the germination of conidiospores of Aspergillus niger

Summary The effect of different concentrations of CO₂ on the germination of conidiospores of Aspergillus niger A 5 has been studied using Pardee's buffer mixtures which maintain constant CO₂ tensions. The beneficial effect of CO₂ on germination is maximum at 0.5% CO₂ concentration, when 70–90% of the spores germinate within 6 hours, whereas in controls with air containing 0.03% CO₂ there is only 15–20% germination at 6 hours. At higher CO₂ concentrations this beneficial effect of CO₂ on germination diminishes and at 3% there is a complete inhibition of spore germination.The spore density and the ph of the medium have a noticeable effect on germination rates in presence of 0.5% CO₂. The germination rates decrease at spore densities higher than 5 · 10⁵/ml and at a ph of 6.8.Communication No. 431.     

Changes in specific radioactivity of sunflower leaf metabolites during photosynthesis in 14CO2 and 12CO2 at three concentrations of CO2

Summary Sunflower (Helianthus annuus L.) leaf discs were exposed to ¹⁴CO₂ or ¹⁴CO₂ followed by ¹²CO₂ at 21% O₂ and three different CO₂ concentrations. After intervals of up to 15 min, the specific activity of some photosynthetic intermediates was determined. At all CO₂ concentrations, the specific activity of 3-phosphoglyceric acid (3-PGA) increased most rapidly and after 15 min of ¹⁴CO₂ feeding was 92% (967 ppm CO₂), 87% (400 ppm CO₂) and 53% (115 ppm CO₂) of CO₂ supplied to the assimilation chamber. The specific activity of glycine, serine and the photorespiratory CO₂ was similar at all CO₂ concentrations, in aggreement with their proposed close metabolic relationship in the glycolate pathway. However, the kinetics of serine and glycine labelling suggested that serine was not totally derived from glycine. Because the specific activity of these glycolate-pathway intermediates was very differnet from that of 3-PGA at all CO₂ concentrations, not all of the carbon traversing this pathway came directly from the Calvin cycle. The non-equilibration of the 3-PGA with the feeding gas reflects the recycling of C from the glycolate pathway into the photosynthetic reduction cycle. Measurements of the rates of CO₂ evolution in the light and estimates of the C flux through the glycolate pathway suggest that the photorespiratory activity was high and similar at 115 ppm CO₂ and 400 ppm CO₂ but inhibited at 967 ppm CO₂.     

Why the free floating macrophyte Stratiotes aloides mainly grows in highly CO2-supersaturated waters

We examined how the freely floating macrophyte, Stratiotes aloides L., sampled from a CO₂-supersaturated pond, changes leaf morphology, photosynthesis and inorganic carbon acquisition during its different submerged and emerged life stages in order to evaluate whether S. aloides requires consistently supersaturated CO₂ conditions to grow and complete its life cycle. Submerged rosettes formed from over-wintering turions had typical traits of submerged plants with high specific leaf area and low chlorophyll a concentrations. Emergent leaf parts of mature, floating specimens had typical terrestrial traits with stomata, low specific leaf area and high chlorophyll a content, while offsets formed vegetatively and basal, submerged parts of mature plants showed traits in between. All submerged leaf types exhibited some ability to use HCO₃⁻ but only rosettes formed from turions had efficient HCO₃⁻ use. Rosettes also had the highest CO₂ affinity and maximum CO₂-saturated photosynthesis in water. Half-saturation constants for CO₂ (21–74 μM CO₂) were for all submerged leaf parts 5–140 times lower than the concentrations of free CO₂ in the pond (350–2800 μM CO₂). Emergent leaves were less efficient in water but had significantly higher photosynthesis than submerged, mature leaf parts in air, and rates of photosynthesis of emergent leaves in air were three to five times higher than rates of CO₂-saturated photosynthesis of the three submerged leaf types in water. Underwater photosynthetic rates estimated at CO₂ concentrations corresponding to air equilibrium were not sufficiently high to support any noticeable growth except for rosettes, in which bicarbonate utilization combined with high CO₂ affinity resulted in photosynthetic rates corresponding to almost 34% of maximum rates at high free CO₂. We conclude that S. aloides requires consistently high CO₂-supersaturation to support high growth and to complete its life cycle, and we infer that this requirement explains why S. aloides mainly grows in ponds, ditches and reed zones that are characterized by strong CO₂-supersaturation.     

Rising CO2 from historical concentrations enhances the physiological performance of Brassica napus seedlings under optimal water supply but not under reduced water availability

The productivity of many important crops is significantly threatened by water shortage, and the elevated atmospheric CO₂ can significantly interact with physiological processes and crop responses to drought. We examined the effects of three different CO₂ concentrations (historical ~300 ppm, ambient ~400 ppm and elevated ~700 ppm) on physiological traits of oilseed rape (Brassica napus L.) seedlings subjected to well‐watered and reduced water availability. Our data show (1) that, as expected, increasing CO₂ level positively modulates leaf photosynthetic traits, leaf water‐use efficiency and growth under non‐stressed conditions, although a pronounced acclimation of photosynthesis to elevated CO₂ occurred; (2) that the predicted elevated CO₂ concentration does not reduce total evapotranspiration under drought when compared with present (400 ppm) and historical (300 ppm) concentrations because of a larger leaf area that does not buffer transpiration; and (3) that accordingly, the physiological traits analysed decreased similarly under stress for all CO₂ concentrations. Our data support the hypothesis that increasing CO₂ concentrations may not significantly counteract the negative effect of increasing drought intensity on Brassica napus performance.     

Water availability moderates N2 fixation benefit from elevated [CO2]: A 2‐year free‐air CO2 enrichment study on lentil (Lens culinaris MEDIK.) in a water limited agroecosystem

Increased biomass and yield of plants grown under elevated [CO₂] often corresponds to decreased grain N concentration ([N]), diminishing nutritional quality of crops. Legumes through their symbiotic N₂ fixation may be better able to maintain biomass [N] and grain [N] under elevated [CO₂], provided N₂ fixation is stimulated by elevated [CO₂] in line with growth and yield. In Mediterranean‐type agroecosystems, N₂ fixation may be impaired by drought, and it is unclear whether elevated [CO₂] stimulation of N₂ fixation can overcome this impact in dry years. To address this question, we grew lentil under two [CO₂] (ambient ~400 ppm and elevated ~550 ppm) levels in a free‐air CO₂ enrichment facility over two growing seasons sharply contrasting in rainfall. Elevated [CO₂] stimulated N₂ fixation through greater nodule number (+27%), mass (+18%), and specific fixation activity (+17%), and this stimulation was greater in the high than in the low rainfall/dry season. Elevated [CO₂] depressed grain [N] (?4%) in the dry season. In contrast, grain [N] increased (+3%) in the high rainfall season under elevated [CO₂], as a consequence of greater post‐flowering N₂ fixation. Our results suggest that the benefit for N₂ fixation from elevated [CO₂] is high as long as there is enough soil water to continue N₂ fixation during grain filling.     

Characterization of Indoor Environmental Quality in Primary Schools in Maia: A Portuguese Case Study

Scientific evidence associates indoor environment pollutants with respiratory effects (asthma and allergies), and children constitute one of most sensitive groups. Indoor air quality (IAQ) in schools may indeed be a significant health factor for children, with effects on school attendance and performance. Our aim was to characterize IAQ of classrooms in Maia County (north of Portugal) for which there was no information available. The study was conducted in 21 of the 40 primary schools, selected by stratified random sampling. Depending on the dimension, one or two classrooms were tested at each school. Walkthrough surveys of school grounds, buildings, and individual classrooms were done. Continuous measurements were taken of temperature, relative humidity, airborne respirable particles, total volatile organic compounds, and carbon dioxide, whereas bioaerosols were counted on Plate Count Agar during regular school activities. The indoor arithmetic mean for PM₁₀, CO₂, TCOV, and bioaerosol concentrations were 0.14 mg/m³, 999 ppm, 0.41 mg/m³, and 4140 UCF/m³, respectively. The values of PM₁₀ and CO₂ were close to their acceptable maximum values, but bioaerosols were much higher. This study supports previous studies conducted in school environments and emphasizes the need for proactive indoor air quality audits in school buildings.     

Estimating respiration of roots in soil: Interactions with soil CO2, soil temperature and soil water content

Little information is available on the variability of the dynamics of the actual and observed root respiration rate in relation to abiotic factors. In this study, we describe I) interactions between soil CO₂ concentration, temperature, soil water content and root respiration, and II) the effect of short-term fluctuations of these three environmental factors on the relation between actual and observed root respiration rates. We designed an automated, open, gas-exchange system that allows continuous measurements on 12 chambers with intact roots in soil. By using three distinct chamber designs with each a different path for the air flow, we were able to measure root respiration over a 50-fold range of soil CO₂ concentrations (400 to 25000 ppm) and to separate the effect of irrigation on observed vs. actual root respiration rate. All respiration measurements were made on one-year-old citrus seedlings in sterilized sandy soil with minimal organic material.Root respiration was strongly affected by diurnal fluctuations in temperature (Q₁₀ = 2), which agrees well with the literature. In contrast to earlier findings for Douglas-fir (Qi et al., 1994), root respiration rates of citrus were not affected by soil CO₂ concentrations (400 to 25000 ppm CO₂; pH around 6). Soil CO₂ was strongly affected by soil water content but not by respiration measurements, unless the air flow for root respiration measurements was directed through the soil. The latter method of measuring root respiration reduced soil CO₂ concentration to that of incoming air. Irrigation caused a temporary reduction in CO₂ diffusion, decreasing the observed respiration rates obtained by techniques that depended on diffusion. This apparent drop in respiration rate did not occur if the air flow was directed through the soil. Our dynamic data are used to indicate the optimal method of measuring root respiration in soil, in relation to the objectives and limitations of the experimental conditions.     

Photosynthesis and transpiration of tomato and CO2 fluxes in a greenhouse under changing environmental conditions in winter

Responses of tomato leaves in a greenhouse to light and CO₂ were examined at the transient stage at the end of winter, when both photoperiod and irradiance gradually increase. Additionally, CO₂ fluxes were calculated for a greenhouse without supplementary lighting and without CO₂ enrichment based on CO₂ sinks (plant photosynthesis) and CO₂ sources (plant and substrate respiration). In January, tomato leaves in the greenhouse showed low photosynthesis with a maximum assimilation of 6–8 μmol CO₂ m⁻² s⁻¹, a quantum yield of 0.06 μmol CO₂ μmol⁻¹ photosynthetic active radiation (PAR) and a low light compensation point of 26 μmol PAR m⁻² s⁻¹, a combination which classifies them as shade leaves. In February, tomato leaves increased their light compensation point to 39 μmol PAR m⁻² s⁻¹ and quantum yield to 0.08, the former indicating the adaptation to increased irradiance and photoperiod. These tomato leaves increased their transpiration from 0.4 to 0.9 in January to ∼2 mmol H₂O m⁻² s⁻¹ in February. Both photosynthesis and transpiration were primarily limited by light but neither by stomatal conductivity nor by CO₂. In January, light response of photosynthesis, dark respiration and transpiration were negligibly affected by increasing CO₂ concentrations from 600 to 900 ppm CO₂ under low light conditions, indicating no benefit of CO₂ enrichment unless light intensity increased. In February, tomato leaves were photoinhibited at inherent greenhouse CO₂ concentrations on the first sunny day; this photoinhibition was further enhanced by an increased CO₂ concentration of 1000 ppm. CO₂ fluxes in the greenhouse appeared strongly dependent on solar radiation. After exceeding the light compensation point in the morning, greenhouse CO₂ concentrations decreased by 58 or by 110 ppm CO₂ h⁻¹ on a sunny day in January or February and by 23 ppm on overcast days in both months. Calculated per overall tomato canopy, plant photosynthesis contributed 42–50% to the morning CO₂ depletion in the greenhouse. Dark respiration of tomato leaves was ∼2 μmol CO₂ m⁻² s⁻¹ in January and ∼3 μmol CO₂ m⁻² s⁻¹ in February. This dark respiration resulted in rises of 15 and 17 ppm CO₂ h⁻¹ at night in the greenhouse compartment and was identified as primary source of CO₂. Respiration of the substrate used to grow the plants, which produced 7.3 ppm CO₂ h⁻¹, was identified as secondary source of CO₂. The combined plant and substrate respiration resulted in peaks of up to 900 ppm CO₂ in the greenhouse before dawn.     

Responses of multiple generations of Gastrophysa viridula, feeding on Rumex obtusifolius, to elevated CO2

Rumex obtusifolius plants and three generations of the tri-voltine leaf beetle Gastrophysa viridula were simultaneously exposed to elevated CO₂ (600 ppm) to determine its effect on plant quality and insect performance. This exposure resulted in a reduction in leaf nitrogen, an increase in the C/N ratio and lower concentrations of oxalate in the leaves than in ambient air (350 ppm). Despite these changes in food quality, the effect of elevated CO₂ on larvae of Gastrophysa viridula over three generations was minimal. However, the effect of CO₂ did differ slightly between the generations of the insect. For the first generation, the results obtained were different from many of the published results in that elevated CO₂ had no measurable effects on performance, except that third instar larvae showed compensatory feeding. Food quality, including leaf nitrogen content, declined over time in material grown in both ambient and elevated CO₂. The results obtained for the second generation were similar to the first except that first instar larvae showed reduced relative growth rate in elevated CO₂. Development time from hatching to pupation decreased over each generation, probably as a result of increasing temperatures. Measurements of adult performance showed that fecundity at the end of the second generation was reduced relative to the first, in line with the reduction in food quality. In addition at the end of the second generation, but not at the end of the first generation, adult females in elevated CO₂ laid 30% fewer eggs per day and the eggs laid were 15% lighter than those in ambient conditions. These lighter eggs, coupled with no effect of elevated CO₂ on growth during the third generation, meant that the larvae were consistently smaller in elevated CO₂ during this generation. These results offer further insights into the effect that elevated CO₂ will have on insect herbivores and provide a more detailed basis for population predictions.     

Combined effects of CO2 concentration and nutrient status on the biomass production and nutrient uptake of birch seedlings (Betula pendula)

Birch seedlings (Betula pendula) were grown for four months in a greenhouse at three nutrient levels (fertilization of 0, 100 and 500 kg ha^-1 monthy) and at four CO₂ concentrations (350, 700, 1050 and 1400 ppm). The effect of CO₂ concentration on the biomass production depended on the nutrient status. When mineralization of the soil material was the only source of nutrients (0 kg ha^-1), CO₂ enhancement reduced the biomass production slightly, whereas the highest production increase occurred at a fertilization of 100 kg ha^-1, being over 100% between 350 and 700 ppm CO₂. At 500 kg ha^-1 the production increase was smaller, and the production decreased beyond a CO₂ concentration of 700 ppm. The CO₂ concentration had a slight effect on the biomass distribution, the leaves accounting for the highest proportion at the lowest CO₂ concentration (350 ppm). An increase in nutrient status led to a longer growth period and increased the nutrient concentrations in the plants, but the CO₂ concentration had no effect on the growth rhythm and higher CO₂ reduced the nutrient concentrations.