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Background: Rising CO2 is expected to result in changes in plant traits that will increase plant productivity for some functional groups. Differential plant responses to elevated CO2 are likely to drive changes in competitive outcomes, with consequences for community structure and plant diversity. Many of the traits that are enhanced under elevated CO2 also confer competitive success to invasive species, and it is widely believed that invasive species will be more successful in high CO2. However, this is likely to depend on plant functional group, and evidence suggests that C3 plants tend to respond more strongly to CO2. Results: We tested the hypothesis that invasive species would be more productive than noninvasive species under elevated CO2 and that stronger responses would be seen in C3 than C4 plants. We examined responses of 15 grass species (eight C3, seven C4), classified as noninvasive or invasive, to three levels of CO2 (390, 700 and 1000 ppm) in a closed chamber experiment. Elevated CO2 decreased conductance and %N and increased shoot biomass and C/N ratio across all species. Differences between invasive and noninvasive species depended on photosynthetic mechanism, with more differences for traits of C3 than C4 plants. Differences in trait means between invasive and noninvasive species tended to be similar across CO2 levels for many of the measured responses. However, noninvasive C3 grasses were more responsive than invasive C3 grasses in increasing tiller number and root biomass with elevated CO2, whereas noninvasive C4 grasses were more responsive than invasive C4 grasses in increasing shoot and root biomass with elevated CO2. For C3 grasses, these differences could be disadvantageous for noninvasive species under light competition, whereas for C4 grasses, noninvasive species may become better competitors with invasive species under increasing CO2. Conclusions: The ecophysiological mechanisms underlying invasion success of C3 and C4 grasses may differ. However, given that the direction of trait differences between invasive and noninvasive grasses remained consistent under ambient and elevated CO2, our results provide evidence that increases in CO2 are unlikely to change dramatically the competitive hierarchy of grasses in these functional groups. [ABSTRACT FROM AUTHOR]

The spotted-wing drosophila (Drosophila suzukii Matsumura) is an invasive species of Asian origin that is now widely distributed in North America and Europe. Because of the female's serrated ovipositor, eggs are laid in preharvest fruit, causing large economic losses in cultivated berries and stone fruit. Modeling D. suzukii population dynamics and potential distribution will require information on its thermal tolerance. Large summer populations have been found in regions with severe winter conditions, though little is known about responses to prolonged low-temperature exposure. We used controlled chambers to examine D. suzukii fecundity, development rate, and mortality across a range of temperatures encompassing the upper and lower thresholds (5–35°C). Optimal temperatures (Topt) were found to be 28.2°C for the development of the egg-to-adult stage, and 22.9°C for reproductive output. No adult eclosion occurred below 8.1°C (Tlower) or above 30.9°C (Tupper). We also investigated survival outcomes following prolonged (42-d) low-temperature exposure to a simulated cold winter (–5, –3, –1, 1, 3, and 5°C). Adult survival was dependent on temperature, with a mean LT50 of 4.9°C. There were no effects of sex, mating status, geographic strain, and photoperiod preexposure on overwintering survival. Thirty-eight percent of females that were mated prior, but not after, prolonged low-temperature exposure produced viable offspring, suggesting that this species may undergo sperm storage. This study provides data on the thermal tolerances of D. suzukii, which can be used for models of D. suzukii population dynamics, degree-day, and distribution models. [ABSTRACT FROM AUTHOR]

1. The performance of foliage feeders tends to decrease under elevated CO2, but the responses of phloem-feeding insects have been much more equivocal. As phloem tissues are less accessible than whole-plant tissues, much less is known about how phloem composition is altered under elevated CO2 and the mechanisms driving changes in aphid performance. 2. In this study, the plant mechanisms underlying the performance of Rhopalosiphum padi aphids on Hordeum vulgare (barley) grown under ambient (390 ppm) and elevated (700 ppm) CO2 were examined. We used aphid stylectomy to sample pure phloem from plants in CO2-controlled conditions and high-performance liquid chromatography to analyse phloem samples for amino acid concentrations. 3. Aphid abundance significantly increased by 127% under elevated CO2. Consequently, plant biomass decreased under elevated CO2 in trials with herbivores present, possibly due to the increased herbivore load, but increased when aphids were absent. The intrinsic rate of population increase ( rm) was significantly higher under elevated CO2; however, there were no statistically significant effects on aphid fecundity or development time. The concentration of individual amino acids tended to increase, although these increases were statistically significant in only a few cases. A principal components analysis revealed that the relative abundance (mol %) of those amino acids considered essential for aphids tended to increase under elevated CO2. 4. These results indicate that CO2 may affect nutrient translocation in plants in ways that are contrary to predictions about nitrogen metabolite responses to CO2. Such plant biochemical responses may underlie observations of improved phloem feeder performance under elevated CO2. [ABSTRACT FROM AUTHOR]

Rising atmospheric CO2 has been shown to alter plant nitrogen metabolism, growth and secondary chemistry. We hypothesized that altered aphid performance under elevated CO2 is linked to phloem nitrogen chemistry., Rhopalosiphum padi performance on endophyte-infected or uninfected tall fescue was examined under three levels of CO2 (ambient, 800 and 1000 p.p.m.) and high and low nitrogen fertilization. Ethylenediaminetetracetic acid-facilitated exudation was used to sample phloem sap, followed by quantification of relative amino acid concentrations using reverse-phase high-performance liquid chromatography., Aphid abundance was reduced at 800 p.p.m. relative to ambient CO2 but returned to baseline at 1000 p.p.m. The density of aphids was reduced in both the elevated CO2 treatments. Aphids were unsuccessful at colonizing endophyte-infected plants, possibly as a result of the presence of loline alkaloids., Multivariate analysis showed that certain groups of phloem amino acids were altered by nitrogen fertilization and CO2. We found that four amino acids (valine, arginine, glutamine and aspartate) were correlated with aphid performance. These findings partially explained the effect of plant nitrogen fertilization and elevated CO2 on aphids., The present study represents a first step toward providing a mechanistic explanation of the aphid performance changes that may result from rising atmospheric CO2. [ABSTRACT FROM AUTHOR]

1. Elevated CO2 can alter plant physiology and morphology, and these changes are expected to impact diet quality for insect herbivores. While the plastic responses of insect herbivores have been well studied, less is known about the propensity of insects to adapt to such changes. Genetic variation in insect responses to elevated CO2 and genetic interactions between insects and their host plants may exist and provide the necessary raw material for adaptation. 2. We used clonal lines of Rhopalosiphum padi (L.) aphids to examine genotype-specific responses to elevated CO2. We used the host plant Schedonorus arundinaceus (tall fescue; Schreb), which is capable of asexual reproduction, to investigate host plant genotype-specific effects and possible host plant-by-insect genotype interactions. The abundance and density of three R. padi genotypes on three tall fescue genotypes under three concentrations of CO2 (ambient, 700, and 1000 ppm) in a controlled greenhouse environment were examined. 3. Aphid abundance decreased in the 700 ppm CO2 concentration, but increased in the 1000 ppm concentration relative to ambient. The effect of CO2 on aphid density was dependent on host plant genotype; the density of aphids in high CO2 decreased for two plant genotypes but was unchanged in one. No interaction between aphid genotype and elevated CO2 was found, nor did we find significant genotype-by-genotype interactions. 4. This study suggests that the density of R. padi aphids feeding on tall fescue may decrease under elevated CO2 for some plant genotypes. The likely impact of genotype-specific responses on future changes in the genetic structure of plant and insect populations is discussed. [ABSTRACT FROM AUTHOR]

1. Elevated CO2 can alter plant physiology and morphology, and these changes are expected to impact diet quality for insect herbivores. While the plastic responses of insect herbivores have been well studied, less is known about the propensity of insects to adapt to such changes. Genetic variation in insect responses to elevated CO2 and genetic interactions between insects and their host plants may exist and provide the necessary raw material for adaptation. 2. We used clonal lines of Rhopalosiphum padi (L.) aphids to examine genotype-specific responses to elevated CO2. We used the host plant Schedonorus arundinaceus (tall fescue; Schreb), which is capable of asexual reproduction, to investigate host plant genotype-specific effects and possible host plant-by-insect genotype interactions. The abundance and density of three R. padi genotypes on three tall fescue genotypes under three concentrations of CO2 (ambient, 700, and 1000 ppm) in a controlled greenhouse environment were examined. 3. Aphid abundance decreased in the 700 ppm CO2 concentration, but increased in the 1000 ppm concentration relative to ambient. The effect of CO2 on aphid density was dependent on host plant genotype; the density of aphids in high CO2 decreased for two plant genotypes but was unchanged in one. No interaction between aphid genotype and elevated CO2 was found, nor did we find significant genotype-by-genotype interactions. 4. This study suggests that the density of R. padi aphids feeding on tall fescue may decrease under elevated CO2 for some plant genotypes. The likely impact of genotype-specific responses on future changes in the genetic structure of plant and insect populations is discussed. [ABSTRACT FROM AUTHOR]

Atmospheric CO2 is expected to increase to between 550 ppm and 1000 ppm in the next century. CO2-induced changes in plant physiology can have ecosystem-wide implications and may alter plant-plant, plant-herbivore and plant-symbiont interactions. We examined the effects of three concentrations of CO2 (390, 800 and 1000 ppm) and two concentrations of nitrogen fertilizer (0.004 g N/week versus 0.2 g N/week) on the physiological response of Neotyphodium fungal endophyte-infected and uninfected tall fescue plants. We used quantitative PCR to estimate the concentration of endophyte under altered CO2 and N conditions. We found that elevated CO2 increased the concentration of water-soluble carbohydrates and decreased the concentration of plant total amino acids in plants. Fungal-derived alkaloids decreased in response to elevated CO2 and increased in response to nitrogen fertilization. Endophyte concentration (expressed as the number of copies of an endophyte-specific gene per total genomic DNA) increased under elevated CO2 and nitrogen fertilization. The correlation between endophyte concentration and alkaloid production observed at ambient conditions was not observed under elevated CO2. These results suggest that nutrient exchange dynamics important for maintaining the symbiotic relationship between fungal endophytes and their grass hosts may be altered by changes in environmental variables such as CO2 and nitrogen fertilization. [ABSTRACT FROM AUTHOR]

Contents [ABSTRACT FROM AUTHOR]

Elevated atmospheric CO 2 concentration increases the performance of invasive plants relative to natives when grown in monoculture, but it is unclear how that will affect the relative competitive abilities per se of invasive and native grasses grown together. We tested competitive outcomes for four native and four invasive perennial C3 and C4 grasses under ambient (390 ppm) and elevated (700 or 1000 ppm) CO 2 concentrations in the greenhouse with non-limiting water and nutrients. We predicted that elevated CO 2 would increase the competitive suppression of native grasses by invasive grasses. To test this, we determined the relative interaction intensity of biomass allocation for natives grown alone vs. those grown in native-invasive species pairs. We also measured photosynthetic traits that contribute to plant invasiveness and may be affected by elevated CO 2 concentrations for species pairs in mixture to determine native-invasive relative performance. We found no effect of CO 2 for the aboveground biomass and tiller production measures of interaction intensity or for relative performance for most of the measured photosynthetic traits. In competition, the invaders nearly always outperform natives in biomass and tiller production, regardless of CO 2 level. The results suggest that increasing CO 2 concentration alone has little effect on grass competitive outcomes under controlled conditions.

Atmospheric CO2 is expected to increase to between 550 ppm and 1000 ppm in the next century. CO2-induced changes in plant physiology can have ecosystem-wide implications and may alter plant-plant, plant-herbivore and plant-symbiont interactions. We examined the effects of three concentrations of CO2 (390, 800 and 1000 ppm) and two concentrations of nitrogen fertilizer (0.004 g N/week versus 0.2 g N/week) on the physiological response of Neotyphodium fungal endophyte-infected and uninfected tall fescue plants. We used quantitative PCR to estimate the concentration of endophyte under altered CO2 and N conditions. We found that elevated CO2 increased the concentration of water-soluble carbohydrates and decreased the concentration of plant total amino acids in plants. Fungal-derived alkaloids decreased in response to elevated CO2 and increased in response to nitrogen fertilization. Endophyte concentration (expressed as the number of copies of an endophyte-specific gene per total genomic DNA) increased under elevated CO2 and nitrogen fertilization. The correlation between endophyte concentration and alkaloid production observed at ambient conditions was not observed under elevated CO2. These results suggest that nutrient exchange dynamics important for maintaining the symbiotic relationship between fungal endophytes and their grass hosts may be altered by changes in environmental variables such as CO2 and nitrogen fertilization., (© 2013 John Wiley & Sons Ltd.)

We conducted the most extensive meta-analysis of plant and animal responses to elevated CO(2) to date. We analysed > 5000 data points extracted from 270 papers published between 1979 and 2009. We examined the changes in 19 animal response variables to the main effect of elevated CO(2). We found strong evidence for significant variation among arthropod orders and feeding guilds, including interactions in the direction of response. We also examined the main effects of elevated CO(2) on: six plant growth and allocation responses, seven primary metabolite responses, eight secondary metabolite responses, and four physical defence responses. We examined these response variable changes under two-way and three-way interactions between CO(2) and: soil nitrogen, ambient temperature, drought, light availability, photosynthetic pathway, reproductive system, plant growth rate, plant growth form, tissue type, and nitrogen fixation. In general we found smaller effect sizes for many response variables than have been previously reported. We also found that many of the oft-reported main effects of CO(2) obscure the presence of significant two- and three-way interactions, which may help better explain the relationships between the response variables and elevated CO(2)., (© 2012 The Authors. New Phytologist © 2012 New Phytologist Trust.)