Short-term effects of aphid feeding on photosynthetic CO2 exchange and dark respiration in legume leaves

Net CO₂ exchange rates and dark respiration rates were determined for single attached legume leaves (leaflets) after 6 to 9 days of aphid infestation. Plant-aphid combinations used were broad bean ( Vicia faba L. cv. Aquadulce) and cowpea [ Vigna unguiculata (L.) Walp. cv. Caloona)] infested with cowpea aphids ( Aphis craccivora Koch) and broad bean and garden pea ( Pisum sativum L. cv. Victory Freezer) infested with pea aphids [ Acyrthosiphon pisum (Harris)]. Leaves from all aphid-infested plants had significantly greater net CO₂ exchange rates in the light than their respective controls and rates of dark respiration of leaves from infested cowpea and garden pea were also significantly greater than those of controls. Dark respiration, as a percentage of net CO₂ exchange rates in the light, was greater in aphid-infested than in control plants. When the mean net daily carbon gain was calculated for the leaves of each plant-aphid combination, leaves from aphid-infested plants had the greatest gain. It is proposed that net CO₂, exchange rates increased due to increased sink demand and dark respiration rates increased to meet the increased energy requirements of phloem loading and cellular maintenance associated with aphid feeding. The apparent compensatory carbon gain of infested leaves was consumed by the aphids.     

In situ studies of water relations and CO2 exchange of the tropical macrolichen, Sticta tomentosa

Diel (24-h) time courses of CO₂ exchange, water relations, and microclimate of the foliose lichen, Sticta tomentosa (Swartz) Ach., and responses to experimentally manipulated conditions were measured at a forest edge in a lower montane rainforest in Panama.
Similar to earlier observations on two other rain forest lichens, daily desiccation suppressed net photosynthesis (NP) during the period when irradiation was highest. Not surprisingly, the light response curves of NP showed saturation at rather low light levels. Rehydration was associated with an initial resaturation burst of short duration, which could be demonstrated both under natural conditions and experimentally. This additional loss of CO₂ seems too low to be ecologically relevant. Moreover, high thallus hydration was also detrimental to NP: at maximum water content net CO₂ uptake was depressed by >50%. Although NP was well adapted to the prevailing high temperatures, the latter also stimulated dark respiration. On average, almost 60% of the diurnal carbon gain was lost during the night.
In spite of these limitations, the integrated 24-h C gain was quite high, on average 0·5% of the thallus C content. Whilst these figures were determined for horizontally exposed samples, we also assessed the role of different exposures on photosynthetic performance. Diel C gain was highest under conditions of semi-shade (westerly exposure), which allowed long periods of activity, whilst much higher irradiance at other exposures could not be utilized for photosynthetic production: easterly exposed thalli dried out even faster than horizontally exposed samples.     

The glands of Tamarix aphylla: a system for salt recretion or for carbon concentration?

During periods of high atmospheric humidity, twigs of Tamarix aphylla (L.) Karst. become covered by an alkaline solution. The pH of that solution fluctuates between 8.0 – 8.5 in the dark and 10.5 during the light hours. Such a solution, produced by the glands, constitutes an efficient trap for atmospheric CO₂. Upon the periodic drop in pH, much of the preabsorbed carbon may gradually be released from the solution. This enriches the immediate surroundings of the twigs with CO₂ for prolonged periods of time. The expected concentrations of CO₂, at the boundary layer between the atmosphere and the surfaces of the twigs, are over 1 000 ppm. As net photosynthesis of T. aphylla reaches maximal rates only at CO₂ concentrations of above 500 ppm, the plants may benefit from this extra source of carbon and may exploit it for maximal assimilation during the early morning hours. Thus, the "salt glands'of Tamarix , which are liable for the production of the alkaline recretum, may serve a triple purpose: (a) removal of excess salts out of the twigs, (b) provision of a cover of hygroscopic solutes that moistens the twigs and shortens the duration of transpiration, and (c) providing the plants with an environment enriched in CO₂.     

Carbon and water fluxes in a calcareous grassland under elevated CO2

1. As part of a long-term study of the effects of elevated CO₂ on biodiversity and ecosystem function in a calcareous grassland, we measured ecosystem carbon dioxide and water-vapour fluxes over 24-h periods during the 1994 and 1995 growing seasons. Data were used to derive CO₂ and H₂O gas-exchange response functions to quantum flux density (QFD).
2. The relative increase in net ecosystem CO₂ flux (NEC) owing to CO₂ enrichment increased as QFD rose. Daytime NEC at high QFD under elevated CO₂ increased by 25% to 60%, with the greatest increases in the spring and after mowing in June when above-ground biomass was lowest. There was much less stimulation of NEC in early June and again in October when the canopy was fully developed. Night-time NEC was not significantly altered under elevated CO₂.
3. Short-term reversal of CO₂ concentrations between treatments after two seasons of CO₂ exposure provided evidence for a 50% downward adjustment of NEC expressed per unit above-ground plant dry weight. However, when expressed on a land area basis, this difference disappeared because of a c. 20% increase in above-ground biomass under elevated CO₂.
4. Ecosystem evapotranspiration (ET) was not significantly altered by elevated CO₂ when averaged over all measurement dates and positions. However, ET was reduced 3–18% at high QFD in plots at the top of the slope at our study site. In summary, CO₂ enrichment resulted in a large stimulation of ecosystem CO₂ capture, especially during periods of a large demand of carbon in relationship to its supply, and resulted in a relatively small and variable effect on ecosystem water consumption.     

Effects of intermittent exposure to high atmospheric CO2 on vegetative growth in soybean

Short-term exposure to high CO₂ increases rates of photosynthesis and growth in soybeans, but with prolonged high CO₂ exposure, these high rates are sometimes not maintained. Growth of soybean (Glycine max (L.) Merrill cv. Fiskeby V) seedlings kept for 25 days at atmospheres of 350 or 1000 μ/l CO₂ was compared with growth of plants given 2, 4 or 6 day alternating exposure to high and low CO₂ levels (13 days of total exposure to each level). Final dry weight of plants increased with number of days in high CO₂ but leaf areas were not greatly affected. Thus dry weight gains per unit leaf area (net assimilation rates) were higher in high CO₂ than in low CO₂ throughout the entire period of the experiment and the pattern of exposure to high CO₂ did not affect the rate of dry weight gain in high CO₂.     

The active uptake of carbon dioxide by the unicellular green algae Chlorella saccharophila and C. ellipsoidea

Abstract. Mass spectrometry has been used to measure the rates of CO₂ uptake of acid- and alkali-grown cells of the green algae Chlorella ellipsoidea (UTEX 20) and C. saccharophila (UTEX 27). The time course of CO₂ formation on addition of 100mmol m⁻³ K₂CO₃ to cells in the dark was used as an assay for external carbonic anhydrase (CA). No external CA was detected in acid-grown cells of either species or in alkali-grown cells of C. ellipsoidea but was present in alkali-grown C. saccharophila . In the absence of external CA, or when it was inhibited by 5mmol m⁻³ acetazolamide, cells of both species, on illumination, rapidly depleted the free CO₂ in the medium at pH 7.5 to near zero concentrations before maximum photosynthetic O₂ evolution rates were established. Addition of bovine CA rapidly restored the equilibrium CO₂ concentration in the medium, indicating that the cells were selectively taking up CO₂. Transfer of cells to the dark caused a rapid increase in the CO₂ concentration in the medium largely due to the efflux of inorganic carbon from the cells as CO₂. This rapid light-dependent CO₂ uptake takes place against pH and concentration gradients and, thus, has the characteristics of active transport.     

Effect of elevated CO2 on carbon partitioning and exudate release from Plantago lanceolata seedlings

Plantago lanceolata L. seedlings were grown in sand microcosm units over a 43‐day experimental period under two CO₂ regimes (800 or 400 µmol mol⁻¹) to investigate the effect of elevated atmospheric CO₂ concentration on carbon partitioning and exudate release. Total organic carbon (TOC) content of the collected exudate material was measured throughout the experimental period. After 42 days growth the seedlings were labelled with [¹⁴C]‐CO₂ and the fate of the label within the plant and its release by the roots monitored. Elevated CO₂ significantly (P ≤ 0.001) enhanced shoot, root and total dry matter production although the R:S ratio was unaltered, suggesting no alteration in gross carbon partitioning. The cumulative release of TOC (in mg C) over 0‐42 days was unaltered by CO₂ treatment however, when expressed as a percentage of net assimilated C, ambient‐grown plants released a significantly (P≤ 0.001) higher percentage from their roots compared to elevated CO₂‐grown plants (i.e. 8 vs 3%). The distribution of ¹⁴C‐label was markedly altered by CO₂ treatment with significantly (P≤ 0.001) greater per cent label partitioned to the roots under elevated CO₂. This indicates increased partitioning of recent assimilate below‐ground under elevated CO₂ treatment although there was no significant difference in the percentage of ¹⁴C‐label released by the roots. Comparison of plant C budgets based on ¹⁴C‐pulse‐chase methodology and TOC measurements is discussed.     

Water vapour fluxes and their impact under elevated CO2 in a C4-tallgrass prairie

We measured leaf-level stomatal conductance, xylem pressure potential, and stomate number and size as well as whole plant sap flow and canopy-level water vapour fluxes in a C4-tallgrass prairie in Kansas exposed to ambient and elevated CO₂. Stomatal conductance was reduced by as much as 50% under elevated CO₂ compared to ambient. In addition, there was a reduction in stomate number of the C4 grass, Andropogon gerardii Vitman, and the C3 dicot herb, Salvia pitcheri Torr., under elevated CO₂ compared to ambient. The result was an improved water status for plants exposed to elevated CO₂ which was reflected by a less negative xylem pressure potential compared to plants exposed to ambient CO₂. Sap flow rates were 20 to 30% lower for plants exposed to elevated CO₂ than for those exposed to ambient CO₂. At the canopy level, evapotranspiration was reduced by 22% under elevated CO₂. The reduced water use by the plant canopy under elevated CO₂ extended the photosynthetically-active period when water became limiting in the ecosystem. The result was an increased above- and belowground biomass production in years when water stress was frequent.     

Gas exchange measurements required to predict the newly fixed carbon pool size in a source leaf of corn (Zea mays L.)

Abstract. Steady-state photosynthesis (P_n), post-illumination CO₂ release rates (R), sucrose-phosphate synthase (SPS) activities, and levels of starch, sucrose and hexoses were measured in the source leaf of corn ( Zea mays L.) during a 16-h photoperiod at 800 μmol m ² s ¹. P_n and SPS activity remained constant. Carbohydrate pools increased at a linear rate, except the first and last hour of the photoperiod. Both the CO₂ evolution rate at the moment of light removal (R_max) and SPS activity decreased by one half after the onset of darkness (0 60 min). Sucrose diminished during this period by 40%, whereas the starch remained constant. Thereafter, starch mobilization began, followed by a gradual decline in leaf respiration. The average dark export rate was calculated to be 60% less than that during the day. Maintenance respiration (R_m) of an attached leaf after 48 h darkness was determined. Plants were illuminated for different intervals (e.g. 5, 10 or 20 min), each followed by dark periods sufficient for respiration to decline to R_m. The ratio of C assimilated in light to that released in dark was 6:1. After the 48-h dark period, the minimal period of illumination (T_min) required to restore P_n and R_max to the original level was determined. A mathematical analysis of the kinetics involved in the recovery of P_n and R_max provided an estimate of turnover time (0.22h) and pool size 9.15 mmol m ²) for the newly fixed carbon.     

Direct and indirect effects of Cd2+ on photosynthesis in sugar beet (Beta vulgaris)

Sugar-beet plants ( Beta vulgaris L. cv. Monohill) were cultivated for 4 weeks in a complete nutrient solution. Indirect effects of cadmium were studied by adding 5, 10 or 20 μ M CdCl₂ to the culture medium while direct effects were determined by adding 1, 5, 20, 50 or 2 000 μ M CdCl₂ to the assay media. The photosynthetic properties were characterized by measurement of CO₂ fixation in intact plants, fluorescence emission by intact leaves and isolated chloroplasts, photosystem (PS) I and PSII mediated electron transport of isolated chloroplasts, and CO₂-dependent O₂ evolution by protoplasts. When directly applied to isolated leaves, protoplasts and chloroplasts. Cd²⁺ impeded CO₂ fixation without affecting the rates of electron transport of PSI or PSII or the rate of dark respiration. When Cd²⁺ was applied through the culture medium the capacity for, and the maximal quantum yield of CO₂ assimilation by intact plants both decreased. This was associated with: (1) decreased total as well as effective chlorophyll content (PSII antennae size), (2) decreased coupling of electron transport in isolated chloroplasts, (3) perturbed carbon reduction cycle as indicated by fluorescence measurements. Also, protoplasts isolated from leaves of Cd²⁺-cultivated plants showed an increased rate of dark respiration.     

Carbon dioxide-independent and -dependent components of light inhibition of the conversion of 1-aminocyclopropane-1-carboxylic acid to ethylene in oat leaves

Light inhibits while carbon dioxide enhances the conversion of 1-aminocyclopropane-1-carboxylic acid (ACC) to ethylene in oat ( Avena sativa L. cv. Victory) leaf segments. The possibility that the light inhibition is mediated through changes of carbon dioxide has been investigated. The level of CO₂ increases or decreases in the sealed incubation vial in darkness or in light, respectively, which can apparently account for the differences in ACC-dependent ethylene production between the dark and light treatments. However, although the evolution of ethylene from ACC in the dark is reduced upon depletion of CO₂, the difference between light and dark is still very noticeable. Moreover, the production of the ethylene in CO₂-free air in the dark was still higher than in the light, where the concentration of CO₂ was 0.01%. It is proposed that the light effect on the conversion of ACC to ethylene is composed of two distinguishable components: one CO₂-mediated and the other CO₂-independent.     

Effect of darkness and CO2 starvation on NH4+ and NO3− assimilation in the unicellular alga Cyanidium caldarium

Cyanidium caldarium (Tilden) Geitler, a non-vacuolate unicellular alga, resuspended in medium flushed with air enriched with 5% CO₂, assimilated NH₄⁺ at high rates both in the light and in the dark. The assimilation of NO₃⁻, by contrast, was inhibited by 63% in the dark. In cell suspensions flushed with CO₂-free air, NH₄⁺ assimilation decreased with time both in the light and in the dark and ceased almost completely after 90 min. The addition of CO₂ completely restored the capacity of the alga to assimilate NH₄⁺. NO₃⁻ assimilation, by contrast, was 33% higher in the absence of CO₂ and was linear with time. It is suggested that NO₃⁻ and NH₄⁺ metabolism in C. caldarium are differently controlled in response to the light and carbon conditions of the cell.     

Soil drying and nitrogen availability modulate carbon and water exchange over a range of annual precipitation totals and grassland vegetation types

Increased intensity in precipitation events and longer periods of water deficit are predicted as a general trend under future climate scenarios with potentially large effects on terrestrial ecosystem function. The primary objective of this study was to understand how variation in the intensity of precipitation inputs followed by intermittent soil drying events influence leaf and ecosystem carbon dioxide (CO₂) and water exchange in a California annual grassland mesocosm experiment. We further examined how nitrogen (N) availability, and differences in plant community composition (grass-forb combinations) affected gas exchange responses to the precipitation treatments. Net ecosystem CO₂ exchange (NEE) and evapotranspiration (ET) increased significantly with greater precipitation and were positively correlated with soil moisture. A repeated 10-day soil drying period, following 11 days of watering, strongly depressed NEE over a range of annual precipitation totals (297, 657 and 987 mm), and plant community types. Ecosystem dark respiration ( R _e) and leaf level photosynthesis ( A _max) showed greater sensitivity to periods of soil drying in the low precipitation plots (297 mm). N additions significantly increased NEE and R _e, particularly as water availability was increased. Across the range of precipitation totals and plant community types, intermittent periods of soil moisture deficit and native soil N availability constrained leaf and ecosystem level CO₂ exchange, while the influence on water vapor exchange was less pronounced.     

Gas exchange studies in two Portuguese grapevine cultivars

Gas exchange characteristics of leaves of Vitis vinifera L. cvs Tinta Amarela and Periquita, two grapevine cultivars grown in distinct climatic regions of Portugal, were studied under natural and controlled conditions. Daily time courses of gas exchange were measured on both a hot, sunny day and a cooler, partly cloudy day. Responses of net photosynthesis to irradiance and internal partial pressure of CO₂, were also obtained. A strong correlation between net photosynthesis (P_N) and leaf conductance (g_s) was found during the diurnal time courses of gas exchange, as well as a relatively constant internal partial pressure of CO₂ (P_i), even under non-steady-state conditions. On the cloudless day, both P_N and g_s were lower in the afternoon than in the morning, despite similar conditions of leaf temperature, air to leaf water vapor deficit and irradiance. The response curves of net photosynthesis to internal CO₂ showed linearity up to p_i values of 50 Pa, possibly indicating a substantial excess of photosynthetic capacity. When measured at low partial pressures of O₂ (1 kPa), P_N became inhibited at high CO₂ levels. Inhibition of P_N at high CO₂ was absent under normal levels of O₂ (21 kPa). Significant differences in gas exchange characteristics were found between the two cultivars, with T. Amarela having higher rates under similar measurement conditions. In particular, the superior performance of T. Amarela at high temperatures may represent adaptation to the warmer conditions at its place of origin.     

Mycorrhiza formation and elevated CO2 both increase the capacity for sucrose synthesis in source leaves of spruce and aspen

The effects of mycorrhiza formation in combination with elevated CO₂ concentrations on carbon metabolism of Norway spruce ( Picea abies ) seedlings and aspen ( Populus tremula × Populus tremuloides ) plantlets were analysed. Plants were inoculated for 6 wk with the ectomycorrhizal fungi Amanita muscaria and Paxillus involutus (aspen only) in an axenic Petri-dish culture at 350 and 700 μl l⁻¹ CO₂ partial pressure. After mycorrhiza formation, a stimulation of net assimilation rate was accompanied by decreased activities of sucrose synthase, an increased activation state of sucrose-phosphate synthase, decreased fructose-2,6-bisphosphate and starch, and slightly elevated glucose-6-phosphate contents in source leaves of both host species, independent of CO₂ concentration. Exposure to elevated CO₂ generally resulted in higher net assimilation rates, increased starch as well as decreased fructose-2,6-bisphosphate (aspen only) content in source leaves of both mycorrhizal and nonmycorrhizal plants. Our data indicate only slightly improved carbon utilization by mycorrhizal plants at elevated CO₂. They demonstrate however, that both factors which modulate the sink-source properties of plants increase the capacity for sucrose synthesis in source leaves mainly by allosteric enzyme regulation.     

Elevated CO2 and ozone reduce nitrogen acquisition by Pinus halepensis from its mycorrhizal symbiont

The effects of 700 μmol mol⁻¹ CO₂ and 200 nmol mol⁻¹ ozone on photosynthesis in Pinus halepensis seedlings and on N translocation from its mycorrhizal symbiont, Paxillus involutus, were studied under nutrient-poor conditions. After 79 days of exposure, ozone reduced and elevated CO₂ increased net assimilation rate. However, the effect was dependent on daily accumulated exposure. No statistically significant differences in total plant mass accumulation were observed, although ozone-treated plants tended to be smaller. Changes in atmospheric gas concentrations induced changes in allocation of resources: under elevated ozone, shoots showed high priority over roots and had significantly elevated N concentrations. As a result of different shoot N concentration and net carbon assimilation rates, photosynthetic N use efficiency was significantly increased under elevated CO₂ and decreased under ozone. The differences in photosynthesis were mirrored in the growth of the fungus in symbiosis with the pine seedlings. However, exposure to CO₂ and ozone both reduced the symbiosis-mediated N uptake. The results suggest an increased carbon cost of symbiosis-mediated N uptake under elevated CO₂, while under ozone, plant N acquisition is preferentially shifted towards increased root uptake.     

Partitioning of dry mass and leaf area within plants of three species grown at elevated CO2

1. We tested the hypothesis that the net partitioning of dry mass and dry mass:area relationships is unaltered when plants are grown at elevated atmospheric CO₂ concentrations.
2. The total dry mass of Dactylis glomerata, Bellis perennis and Trifolium repens was higher for plants in 700 compared to 350 μmol CO₂ mol^–1 when grown hydroponically in controlled-environment cabinets.
3. Shoot:root ratios were higher and leaf area ratios and specific leaf areas lower in all species grown at elevated CO₂. Leaf mass ratio was higher in plants of B. perennis and D. glomerata grown at elevated CO₂.
4. Whilst these data suggest that CO₂ alters the net partitioning of dry mass and dry mass:leaf area relationships, allometric comparisons of the components of dry mass and leaf area suggest at most a small effect of CO₂. CO₂ changed only two of a total of 12 allometric coefficients we calculated for the three species: ν relating shoot to root dry mass was higher in D. glomerata , whilst ν relating leaf area to total dry mass was lower in T. repens .
5. CO₂ alone has very little effect on partitioning when the size of the plant is taken into account.     

Interactions between increasing CO2 concentration and temperature on plant growth

The global environment is changing with increasing temperature and atmospheric carbon dioxide concentration, [CO₂]. Because these two factors are concomitant, and the global [CO₂] rise will affect all biomes across the full global range of temperatures, it is essential to review the theory and observations on effects of temperature and [CO₂] interactions on plant carbon balance, growth, development, biomass accumulation and yield. Although there are sound theoretical reasons for expecting a larger stimulation of net CO₂ assimilation rates by increased [CO₂] at higher temperatures, this does not necessarily mean that the pattern of biomass and yield responses to increasing [CO₂] and temperature is determined by this response. This paper reviews the interactions between the effects of [CO₂] and temperature on plants. There is little unequivocal evidence for large differences in response to [CO₂] at different temperatures, as studies are confounded by the different responses of species adapted and acclimated to different temperatures, and the interspecific differences in growth form and development pattern. We conclude by stressing the importance of initiation and expansion of meristems and organs and the balance between assimilate supply and sink activity in determining the growth response to increasing [CO₂] and temperature.     

Differential responses of Aedes and Culex mosquitoes to octenol or light in combination with carbon dioxide in Queensland, Australia

Abstract. Field studies were conducted with EVS (encephalitis vector surveillance) traps in south-eastern Queensland, Australia, to determine the relative response rates of mosquitoes to three levels (0.1, 4.5 and 30mg/h) of 1-octen-3-ol (octenol) in combination with a standard bait of 2200 g carbon dioxide (CO₂), compared with CO₂ alone or CO₂ with light from a 6V incandescent bulb. Compared to CO₂ alone, Aedes vigilax collections increased significantly when CO₂ was supplemented by all three octenol emission levels, but not by the addition of light. Furthermore, the 4.5 and 30 mg/h release rate of octenol gave a significant increase in numbers of Ae.vigilax relative to that from CO₂+ light. In contrast, collections of Culex annulirostris and Culex sitiens were not enhanced significantly by either the addition of light or octenol at all three levels. Fewer Cx sitiens were collected with octenol released at 4.5 mg/h in comparison to CO₂ alone. These differential sampling rates should be taken into account when using EVS traps.     

13C-isotope analyses reveal that chemolithoautotrophic Gamma- and Epsilonproteobacteria feed a microbial food web in a pelagic redoxcline of the central Baltic Sea

Marine pelagic redoxclines are zones of high dark CO₂ fixation rates, which can correspond up to 30% of the surface primary production. However, despite this significant contribution to the pelagic carbon cycle, the identity of most chemolithoautotrophic organisms is still unknown. Therefore, the aim of this study was to directly link the dark CO₂ fixation capacity of a pelagic redoxcline in the central Baltic Sea (Landsort Deep) with the identity of the main chemolithoautotrophs involved. Our approach was based on the analysis of natural carbon isotope signatures in fatty acid methyl esters (FAMEs) and on measurements of CO₂ incorporation in ¹³C-bicarbonate pulse experiments. The incorporation of ¹³C into chemolithoautotrophic cells was investigated by rRNA-based stable isotope probing (RNA-SIP) and FAME analysis after incubation for 24 and 72 h under in situ conditions. Our results demonstrated that fatty acids indicative of Proteobacteria were significantly enriched in ¹³C slightly below the chemocline. RNA-SIP analyses revealed that two different Gammaproteobacteria and three closely related Epsilonproteobacteria of the Sulfurimonas cluster were active dark CO₂-fixing microorganisms, with a time-dependent community shift between these groups. Labelling of Archaea was not detectable, but after 72 h of incubation the ¹³C-label had been transferred to a potentially bacterivorous ciliate related to Euplotes sp. Thus, RNA-SIP provided direct evidence for the contribution of chemolithoautotrophic production to the microbial food web in this marine pelagic redoxcline, emphasizing the importance of dark CO₂-fixing Proteobacteria within this habitat.