Effects of Elevated Carbon Dioxide on the Growth and Foliar Chemistry of Transgenic Bt Cotton

A field study was carried out to quantify plant growth and the foliar chemistry of transgenic Bacillus thuringiensis （Bt） cotton （cv. GK-12） exposed to ambient CO2 and elevated （double-ambient） CO2 for different lengths of time （1, 2 and 3 months） in 2004 and 2005. The results indicated that CO2 levels significantly affected plant height, leaf area per plant and leaf chemistry of transgenic Bt cotton. Significantly, higher plant height and leaf area per plant were observed after cotton plants that were grown in elevated CO2 were compared with plants grown in ambient CO2 for 1, 2 and 3 months in the investigation. Simultaneously, significant interaction between CO2 level x investigating year was observed in leaf area per plant. Moreover, foliar total amino acids were increased by 14%, 13%, 11% and 12%, 14%, 10% in transgenic Bt cotton after exposed to elevated CO2 for 1, 2 or 3 months compared with ambient CO2 in 2004 and 2005, respectively. Condensed tannin occurrence increased by 17%, 11%, 9% in 2004 and 12%, 11%, 9% in 2005 in transgenic Bt cotton after being exposed to elevated CO2 for 1, 2 or 3 months compared with ambient CO2 for the same time. However, Bt toxin decreased by 3.0%, 2.9%, 3.1% and 2.4%, 2.5%, 2.9% in transgenic Bt cotton after exposed to elevated CO2 for 1, 2 or 3months compared with ambient CO2 for same time in 2004 and 2005, respectively. Furthermore, there was prominent interaction on the foliar total amino acids between the CO2 level and the time of cotton plant being exposed to elevated CO2. It is presumed that elevated CO2 can alter the plant growth and hence ultimately the phenotype allocation to foliar chemistical components of transgenic Bt cotton, which may in turn, affect the plant-herbivore interactions.     

Increase of photosynthesis and starch in potato under elevated CO2 is dependent on leaf age

Potato plants (Solanum tuberosum cv. Bintje) were grown in open top chambers under ambient (400 microL L(-1)) and elevated CO2 (720 microL L(-1)). After 50 days one half of each group was transferred to the other CO2 concentration and the effects were studied in relation to leaf age (old, middle-aged and young leaves) in each of the four groups. Under long-term exposure to elevated CO2, photosynthesis increased between 10% and 40% compared to ambient CO2. A subsequent shift of the same plants to ambient CO2 caused a 20-40% decline in photosynthetic rate, which was most pronounced in young leaves. After shifting from long-term ambient to elevated CO2, photosynthesis also increased most strongly in young leaves (90%); these experiments show that photosynthesis was downregulated in the upper young fully expanded leaves of potato growing long-term under elevated CO2. Soluble sugar content in all leaf classes under long-term exposure was stable irrespective of the CO2 treatment, however under elevated CO2 young leaves showed a strongly increased starch accumulation (up to 400%). In all leaf classes starch levels dropped in response to the shift from 720 to 400 microL L(-1) approaching ambient CO2 levels. After the shift to 720 microL L(-1), sucrose and starch levels increased, principally in young Leaves. There is clear evidence that leaves of different age vary in their responses to changes in atmospheric CO2 concentration.     

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.     

Determination of the site of CO₂ sensing in poplar: is the area-based N content and anatomy of new leaves determined by their immediate CO₂ environment or by the CO₂ environment of mature leaves?

Exposure to an elevated CO(2) concentration ([CO(2)]) generally decreases leaf N content per unit area (N(area)) and stomatal density, and increases leaf thickness. Mature leaves can 'sense' elevated [CO(2)] and this regulates stomatal development of expanding leaves (systemic regulation). It is unclear if systemic regulation is involved in determination of leaf thickness and N(area)-traits that are significantly correlated with photosynthetic capacity. A cuvette system was used whereby [CO(2)] around mature leaves was controlled separately from that around expanding leaves. Expanding leaves of poplar (Populus trichocarpa×P. deltoides) seedlings were exposed to elevated [CO(2)] (720 μmol mol(-1)) while the remaining mature leaves inside the cuvette were under ambient [CO(2)] of 360 μmol mol(-1). Reverse treatments were performed. Exposure of newly developing leaves to elevated [CO(2)] increased their thickness, but when mature leaves were exposed to elevated [CO(2)] the increase in thickness of new leaves was less pronounced. The largest response to [CO(2)] was reflected in the palisade tissue thickness (as opposed to the spongy tissue) of new leaves. The N(area) of new leaves was unaffected by the local [CO(2)] where the new leaves developed, but decreased following the exposure of mature leaves to elevated [CO(2)]. The volume fraction of mesophyll cells compared with total leaf and the mesophyll cell density changed in a manner similar to the response of N(area). These results suggest that N(area) is controlled independently of the leaf thickness, and suggest that N(area) is under systemic regulation by [CO(2)] signals from mature leaves that control mesophyll cell division.     

Elevated CO2 reduces leaf damage by insect herbivores in a forest community

By altering foliage quality, exposure to elevated levels of atmospheric CO(2) potentially affects the amount of herbivore damage experienced by plants. Here, we quantified foliar carbon (C) and nitrogen (N) content, C : N ratio, phenolic levels, specific leaf area (SLA) and the amount of leaf tissue damaged by chewing insects for 12 hardwood tree species grown in plots exposed to elevated CO(2) (ambient plus 200 microl l(-1)) using free-air CO(2) enrichment (FACE) over 3 yr. The effects of elevated CO(2) varied considerably by year and across species. Elevated CO(2) decreased herbivore damage across 12 species in 1 yr but had no detectable effect in others. Decreased damage may have been related to lower average foliar N concentration and SLA and increased C : N ratio and phenolic content for some species under elevated compared with ambient CO(2). It remains unclear how these changes in leaf properties affect herbivory. Damage to the leaves of hardwood trees by herbivorous insects may be reduced in the future as the concentration of CO(2) continues to increase, perhaps altering the trophic structure of forest ecosystems.     

Leaf photosynthesis and simulated carbon budget of Gentiana straminea from a decade-long warming experiment

Aims Alpine ecosystems may experience larger temperature increases due to global warming as compared with lowland ecosystems. Information on physiological adjustment of alpine plants to temperature changes can provide insights into our understanding how these plants are responding to current and future warming. We tested the hypothesis that alpine plants would exhibit acclimation in photosynthesis and respiration under long-term elevated temperature, and the acclimation may relatively increase leaf carbon gain under warming conditions.Methods Open-top chambers (OTCs) were set up for a period of 11 years to artificially increase the temperature in an alpine meadow ecosystem. We measured leaf photosynthesis and dark respiration under different light, temperature and ambient CO₂ concentrations for Gentiana straminea, a species widely distributed on the Tibetan Plateau. Maximum rates of the photosynthetic electron transport (J max), RuBP carboxylation (V c max) and temperature sensitivity of respiration Q 10 were obtained from the measurements. We further estimated the leaf carbon budget of G. straminea using the physiological parameters and environmental variables obtained in the study.Important findings1)?The OTCs consistently elevated the daily mean air temperature by ~1.6°C and soil temperature by ~0.5°C during the growing season. 2)?Despite the small difference in the temperature environment, there was strong tendency in the temperature acclimation of photosynthesis. The estimated temperature optimum of light-saturated photosynthetic CO₂ uptake (A max) shifted ~1°C higher from the plants under the ambient regime to those under the OTCs warming regime, and the A max was significantly lower in the warming-acclimated leaves than the leaves outside the OTCs. 3)?Temperature acclimation of respiration was large and significant: the dark respiration rates of leaves developed in the warming regime were significantly lower than leaves from the ambient environments. 4)?The simulated net leaf carbon gain was significantly lower in the in situ leaves under the OTCs warming regime than under the ambient open regime. However, in comparison with the assumed non-acclimation leaves, the in situ warming-acclimated leaves exhibited significantly higher net leaf carbon gain. 5)?The results suggest that there was a strong and significant temperature acclimation in physiology of G. straminea in response to long-term warming, and the physiological acclimation can reduce the decrease of leaf carbon gain, i.e. increase relatively leaf carbon gain under the warming condition in the alpine species.     

Carbon isotope discrimination and bundle sheath leakiness in three C(4) subtypes grown under variable nitrogen,water and atmospheric CO(2) supply

The changes in composition and productivity of semi-arid C(4) grassland, anticipated with rising atmospheric CO(2), will depend on soil water and nutrient availability. The interactive effects of soil resource limitation and elevated CO(2 )on these grasses, furthermore, may vary among C(4) biochemical subtypes (NADP-ME, NAD-ME, PCK) that differ in bundle sheath leakiness (Phi) responses to drought and nitrogen supply. To address C(4) subtype responses to soil resource gradients, the carbon isotope discrimination (Delta), bundle sheath leakiness (Phi), leaf gas exchange (A, g(s), c(i)/c(a)) and above-ground biomass accumulation were measured on three dominant grasses of semi-desert grassland in south-eastern Arizona. Bouteloua curtipendula (PCK), Aristida glabrata (NADP-ME) and the non-native Eragrostis lehmanniana (NAD-ME) were grown in controlled-environment chambers from seed under a complete, multi-factorial combination of present ambient (370 ppm) and elevated (690 ppm) CO(2) concentration and under high and low water and nitrogen supply. E. lehmanniana (NAD-ME) had the highest photosynthetic rate (A) and lowest Phi compared to the other two grasses when grown under low nitrogen and water availability. However, favourable water and nitrogen supply and elevated atmospheric CO(2) enhanced photosynthetic performance and above-ground biomass production of B. curtipendula (PCK) to a greater extent than in A. glabrata and E. lehmanniana. Contrary to pre vious studies, Phi and Delta in the NADP-ME subtype (A. glabrata) were most affected by changing environmental conditions compared to the other subtypes; deviations from the classic NADP-ME anatomy in Aristida could have accounted for this result. Overall, response of semi-arid grasslands to rising atmospheric CO(2) may depend more on species-specific responses to drought and nitrogen limitation than on general C(4) subtype responses.     

Elevated CO(2) induces biochemical and ultrastructural changes in leaves of the C(4) cereal sorghum

We analyzed the impact of growth at either 350 (ambient) or 700 (elevated) microL L(-1) CO(2) on key elements of the C(4) pathway (photosynthesis, carbon isotope discrimination, and leaf anatomy) using the C(4) cereal sorghum (Sorghum bicolor L. Moench.). Gas-exchange analysis of the CO(2) response of photosynthesis indicated that both carboxylation efficiency and the CO(2) saturated rate of photosynthesis were lower in plants grown at elevated relative to ambient CO(2). This was accompanied by a 49% reduction in the phosphoenolpyruvate carboxylase content of leaves (area basis) in the elevated CO(2)-grown plants, but no change in Rubisco content. Despite the lower phosphoenolpyruvate carboxylase content, there was a 3-fold increase in C isotope discrimination in leaves of plants grown at elevated CO(2) and bundle sheath leakiness was estimated to be 24% and 33%, respectively, for the ambient and elevated CO(2)-grown plants. However, we could detect no difference in quantum yield. The ratio of quantum yield of CO(2) fixation to PSII efficiency was lower in plants grown at elevated CO(2), but only when leaf internal was below 50 microL L(-1). This suggests a reduction in the efficiency of the C(4) cycle when [CO(2)] is low, and also implies increased electron transport to acceptors other than CO(2). Analysis of leaf sections using a transmission electron microscope indicated a 2-fold decrease in the thickness of the bundle sheath cell walls in plants grown at elevated relative to ambient CO(2). These results suggest that significant acclimation to increased CO(2) concentrations occurs in sorghum.     

Photosynthetic acclimation to elevated CO2 in a sunflower canopy

Sunflower canopies were grown in mesocosom gas exchange chambers at ambient and elevated CO2 concentrations (360 and 700 ppm) and leaf photosynthetic capacities measured at several depths within each canopy. Elevated [CO2] had little effect on whole-canopy photosynthetic capacity and total leaf area, but had marked effects on the distribution of photosynthetic capacity and leaf area within the canopy. Elevated [CO2] did not significantly reduce the photosynthetic capacities per unit leaf area of young leaves at the top of the canopy, but it did reduce the photosynthetic capacities of older leaves by as much as 40%. This effect was not dependent on the canopy light environment since elevated [CO2] also reduced the photosynthetic capacities of older leaves exposed to full sun on the south edge of the canopy. In addition to the effects on leaf photosynthetic capacity, elevated [CO2] shifted the distribution of leaf area within the canopy so that more leaf area was concentrated near the top of the canopy. This change resulted in as much as a 50% reduction in photon flux density in the upper portions of the elevated [CO2] canopy relative to the ambient [CO2] canopy, even though there was no significant difference in the total canopy leaf area. This reduction in PFD appeared to account for leaf carbohydrate contents that were actually lower for many of the shaded leaves in the elevated as opposed to the ambient [CO2] canopy. Photosynthetic capacities were not significantly correlated with any of the individual leaf carbohydrate contents. However, there was a strong negative correlation between photosynthetic capacity and the ratio of hexose sugars to sucrose, consistent with the hypothesis that sucrose cycling is a component of the biochemical signalling pathway controlling photosynthetic acclimation to elevated [CO2].     

Evidence that carbon dioxide enrichment alleviates ureide-induced decline of nodule nitrogenase activity

The hypothesis that elevated [CO(2)] alleviates ureide inhibition of N(2)-fixation was tested. Short-term responses of the acetylene reduction assay (ARA), ureide accumulation and total non-structural carbohydrate (TNC) levels were measured following addition of ureide to the nutrient solution of hydroponically grown soybean. The plants were exposed to ambient (360 micromol mol(-1)) or elevated (700 micromol mol(-1)) [CO(2)]. Addition of 5 and 10 mM ureide to the nutrient solution inhibited N(2)-fixation activity under both ambient and elevated [CO(2)] conditions. However, the percentage inhibition following ureide treatment was significantly greater under ambient [CO(2)] as compared with that under elevated [CO(2)]. Under ambient [CO(2)] conditions, ARA was less than that under elevated [CO(2)] 1 d after ureide treatment. Under ambient [CO(2)], the application of ureide resulted in a significant accumulation of ureide in all plant tissues, with the highest concentration increases in the leaves. However, application of exogenous ureide to plants subjected to elevated [CO(2)] did not result in increased ureide concentration in any tissues. TNC concentrations were consistently higher under elevated [CO(2)] compared with those under ambient [CO(2)]. For both [CO(2)] treatments, the application of ureide induced a significant decrease of TNC concentrations in the leaves and nodules. For both leaves and nodules, a negative correlation was observed between TNC and ureide levels. Results indicate that product(s) of ureide catabolism rather than tissue ureide concentration itself are critical in the regulation of N(2)-fixation.     

CO2浓度升高对沉水植物菹草叶表型及生理生化特征的影响

 对菹草 (Potamogeton crispus) 叶在高CO2 (1 000±50 μmol·mol-1)和对照浓度(约380 μmol·mol-1)下的表型及一些生理生化指标进行了比较研究。结果表明：CO2浓度升高明显地改变了菹草叶的表型特征,外形更为粗短,叶宽、单叶面积、单株总叶面积、叶面积率、叶重比明显增加,但特殊叶面积和叶长增加不明显。线性回归分析表明单株总叶面积和植株大小密切相关。异速生长分析表明叶面积的变化不是可塑性反应,而是受植株大小所制约。此外,CO2浓度升高后植物的色素含量和一些化学物质含量明显改变。叶绿素a、叶绿素b、总叶绿素及类胡萝卜素含量减少,且叶绿素a/b也降低;可溶性糖含量增加,而蛋白质、N和P浓度降低。     

Foliage of oaks grown under elevated CO2 reduces performance of Antheraea polyphemus (Lepidoptera: Saturniidae)

To understand how the increase in atmospheric CO2 from human activity may affect leaf damage by forest insects, we examined host plant preference and larval performance of a generalist herbivore, Antheraea polyphemus Cram., that consumed foliage developed under ambient or elevated CO2. Larvae were fed leaves from Quercus alba L. and Quercus velutina Lam. grown under ambient or plus 200 microl/liter CO2 using free air carbon dioxide enrichment (FACE). Lower digestibility of foliage, greater protein precipitation capacity in frass, and lower nitrogen concentration of larvae indicate that growth under elevated CO2 reduced the food quality of oak leaves for caterpillars. Consuming leaves of either oak species grown under elevated CO2 slowed the rate of development of A. polyphemus larvae. When given a choice, A. polyphemus larvae preferred Q. velutina leaves grown under ambient CO2; feeding on foliage of this species grown under elevated CO2 led to reduced consumption, slower growth, and greater mortality. Larvae compensated for the lower digestibility of Q. alba leaves grown under elevated CO2 by increasing the efficiency of conversion of ingested food into larval mass. Despite equivalent consumption rates, larvae grew larger when they consumed Q. alba leaves grown under elevated compared with ambient CO2. Reduced consumption, slower growth rates, and increased mortality of insect larvae may explain lower total leaf damage observed previously in plots in this forest exposed to elevated CO2. By subtly altering aspects of leaf chemistry, the ever-increasing concentration of CO2 in the atmosphere will change the trophic dynamics in forest ecosystems.     

大气CO2浓度升高和N沉降对南亚热带主要乡土树种叶片元素含量的影响

大气CO₂浓度升高和N沉降以及二者之间的耦合作用对陆地森林生态系统的影响是当前国际生态学界关注的热点之一。该实验运用大型开顶箱(open-top chamber, OTC)研究: 1)高CO₂浓度(700 μmol×mol^-1) +高N沉降(100 kg N×hm^-2×a^-1) (CN); 2)高CO₂浓度(700 μmol×mol^-1)和背景N沉降(CC); 3)高N沉降(100 kg N×hm^-2×a^-1)和背景CO₂浓度(NN); 4)背景CO₂和背景N沉降(CK) 4种处理对南亚热带主要乡土树种木荷(Schima superba)、红锥(Castanopsis hystrix)、肖蒲桃(Acmena acuminatissima)、红鳞蒲桃(Syzygium hancei)、海南红豆(Ormosia pinnata)叶片元素含量的影响。研究结果表明, 大气CO₂浓度升高对5种乡土树种叶片元素含量有较大的影响, 除海南红豆叶片的Ca含量外, 其他树种的叶片元素含量在高CO₂浓度处理下都显著升高(p < 0.05); 而在N沉降处理下, 5个树种的叶片K和Ca含量都降低。大气CO₂浓度升高与N沉降处理对5种乡土树种植物叶片元素含量影响的交互作用不是很明显, 仅仅木荷和红鳞蒲桃的叶片Ca和Mn以及海南红豆的叶片Mn含量在大气CO₂浓度上升和N沉降交互处理下显著下降, 而肖蒲桃的叶片P含量在大气CO₂浓度上升和N沉降交互处理下显著上升。     

Higher daytime leaf temperatures contribute to lower freeze tolerance under elevated CO2

Elevated atmospheric CO2 adversely affects freezing tolerance in many evergreens, but the underlying mechanism(s) have been elusive. We compared effects of elevated CO2 with those of daytime warming on acclimation of snow gum (Eucalyptus pauciflora) to freezing temperatures under field conditions. Reduction in stomatal conductance g(c) under elevated CO2 was shown to cause leaf temperature to increase by up to 3 degrees C. In this study, this increase in leaf temperature was simulated under ambient CO2 conditions by using a free air temperature increase (FATI) system to warm snow gum leaves during daytime, thereby increasing the diurnal range in temperature without affecting temperature minima. Acclimation to freezing temperatures was assessed using measures of electrolyte leakage and photosynthetic efficiency of leaf discs exposed to different nadir temperatures. Here, we show that both elevated CO2 and daytime warming delayed acclimation to freezing temperatures for 2-3 weeks after which time freeze tolerance of the treated plants in both the FATI and open top chamber (OTC) experiments did not differ from control plants. Our results support the hypothesis that delayed development of freezing tolerance under elevated CO2 is because of higher daytime leaf temperatures under elevated CO2. Thus, potential gains in productivity in response to increasing atmospheric CO2 and prolonging the growing season may be reduced by an increase in freezing stress in frost-prone area.     

Increase in leaf mass per area benefits plant growth at elevated CO2 concentration

An increase in leaf mass per area (MLA) of plants grown at elevated [CO2] is often accompanied by accumulation of non-structural carbohydrates, and has been considered to be a response resulting from source-sink imbalance. We hypothesized that the increase in MLA benefits plants by increasing the net assimilation rate through maintaining a high leaf nitrogen content per area (NLA). To test this hypothesis, Polygonum cuspidatum was grown at ambient (370 micro mol mol-1) and elevated (700 micro mol mol-1) [CO2] with three levels of N supply. Elevated [CO2] significantly increased MLA with smaller effects on NLA and leaf mass ratio (fLM). The effect of change in MLA on plant growth was investigated by the sensitivity analysis: MLA values observed at ambient and elevated [CO2] were substituted into a steady-state growth model to calculate the relative growth rate (R). At ambient [CO2], substitution of a high MLA (observed at elevated [CO2]) did not increase R, compared with R for a low MLA (observed at ambient [CO2]), whereas at elevated [CO2] the high MLA always increased R compared with R at the low MLA. These results suggest that the increase in MLA contributes to growth enhancement under elevated [CO2]. The optimal combination of fLM and MLA to maximize R was determined for different [CO2] and N availabilities. The optimal fLM was nearly constant, while the optimal MLA increased at elevated [CO2], and decreased at higher N availabilities. The changes in fLM of actual plants may compensate for the limited plasticity of MLA.     

Impact of elevated CO(2) and O(3) on gas exchange parameters and epidermal characteristics in potato (Solanum tuberosum L.)

Potato plants (Solanum tuberosum L. cv. Bintje) were grown in open-top chambers (OTCs) under three CO(2) levels (ambient and 24 h d(-1) seasonal mean concentrations of 550 and 680 micromol mol(-1)) and two O(3) levels (ambient and a seasonal mean 8 h d(-1) concentration of 50 nmol mol(-1)). The objectives were to determine the effects of season-long exposure to these key climate change gases on gas exchange, leaf thickness and epidermal characteristics. The experimental design also provided an ideal opportunity to examine within-leaf variation in epidermal characteristics at the whole-leaf level. Stomatal and epidermal cell density and stomatal index were measured at specific locations on the youngest fully expanded leaf (centre of lamina, mid-way between tip and base) and representative whole leaves from each treatment. Effects on leaf conductance, assimilation rate and instantaneous transpiration efficiency were determined by infrared gas analysis, while anatomical characteristics were examined using a combination of leaf impressions and thin sections. Exposure to elevated CO(2) or O(3) generally increased leaf thickness, leaf area, stomatal density, and assimilation rate, but reduced leaf conductance. The irregular stomatal distribution within leaves resulted from a combination of uneven differentiation and expansion of the epidermal cells. The results are discussed with reference to sampling protocols and the need to account for within-leaf variation when examining the impact of climate change or other environmental factors on epidermal characteristics.     

Olfactory preferences of Popillia japonica, Vanessa cardui, and Aphis glycines for Glycine max grown under elevated CO2

Levels of atmospheric CO(2) have been increasing steadily over the last century and are projected to increase even more dramatically in the future. Soybeans (Glycine max L.) grown under elevated levels of CO(2) have larger herbivore populations than soybeans grown under ambient levels of CO(2). Increased abundance could reflect the fact that these herbivores are drawn in by increased amounts of volatiles or changes in the composition of volatiles released by plants grown under elevated CO(2) conditions. To determine impacts of elevated CO(2) on olfactory preferences, Japanese beetles (Popillia japonica Newman) and soybean aphids (Aphis glycines Matsumura) were placed in Y-tube olfactometers with a choice between ambient levels of CO(2) gas versus elevated levels of CO(2) gas or damaged and undamaged leaves and plants grown under ambient levels of CO(2) versus damaged and undamaged plants grown under elevated levels of CO(2). All plants had been grown from seeds under ambient or elevated levels of CO(2). Painted lady butterflies (Vanessa cardui L.) were placed in an oviposition chamber with a choice between plants grown under ambient and elevated levels of CO(2). A. glycines and V. cardui showed no significant preference for plants in either treatment. P. japonica showed no significant preference between ambient levels and elevated levels of CO(2) gas. There was a significant P. japonica preference for damaged plants grown under ambient CO(2) versus undamaged plants but no preference for damaged plants grown under elevated CO(2) versus undamaged plants. P. japonica also preferred damaged plants grown under elevated levels of CO(2) versus damaged plants grown under ambient levels of CO(2). This lack of preference for damaged plants grown under elevated CO(2) versus undamaged plants could be the result of the identical elevated levels of a green leaf volatile (2-hexenal) present in all foliage grown under elevated CO(2) regardless of damage status. Green leaf volatiles are typically released from damaged leaves and are used as kairomones by many herbivorous insects for host plant location. An increase in production of volatiles in soybeans grown under elevated CO(2) conditions may lead to larger herbivore outbreaks in the future.