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1.
Sap-feeding insects such as aphids are the only insect herbivores that show positive responses to elevated CO2. Recent models predict that increased nitrogen will increase aphid population size under elevated CO2, but few experiments have tested this idea empirically. To determine whether soil nitrogen (N) availability modifies aphid responses to elevated CO2, we tested the performance of Macrosiphum euphorbiae feeding on two host plants; a C3 plant (Solanum dulcamara), and a C4 plant (Amaranthus viridis). We expected aphid population size to increase on plants in elevated CO2, with the degree of increase depending on the N availability. We found a significant CO2× N interaction for the response of population size for M. euphorbiae feeding on S. dulcamara: aphids feeding on plants grown in ambient CO2, low N conditions increased in response to either high N availability or elevated CO2. No population size responses were observed for aphids infesting A. viridis. Elevated CO2 increased plant biomass, specific leaf weight, and C : N ratios of the C3 plant, S. dulcamara but did not affect the C4 plant, A. viridis. Increased N fertilization significantly increased plant biomass, leaf area, and the weight : height ratio in both experiments. Elevated CO2 decreased leaf N in S. dulcamara and had no effect on A. viridis, while higher N availability increased leaf N in A. viridis and had no effect in S. dulcamara. Aphid infestation only affected the weight : height ratio of S. dulcamara. We only observed an increase in aphid population size in response to elevated CO2 or increased N availability for aphids feeding on S. dulcamara grown under low N conditions. There appears to be a maximum population growth rate that M. euphorbiae aphids can attain, and we suggest that this response is because of intrinsic limits on development time and fecundity.  相似文献   

2.
1 Broad beans (Vicia faba L.) were grown at either ambient (350 μL/L) or elevated (700 μL/L) CO2. Elevated CO2 increased shoot weight by 14% and root weight by 24% compared to ambient, but did not affect flowering. 2 A single pea aphid (Acyrthosiphon pisum (Harris)) and its progeny decreased shoot and root weights by 20 and 24%, respectively, at ambient CO2 after 20 days, but did not affect flower number. At elevated CO2A. pisum decreased shoot and root weights by 27 and 34% and flower number decreased by 73%. 3 A single glasshouse and potato aphid (Aulacorthum solani (Kaltenbach)) and its progeny had no effect on the growth of bean plants after 20 days at ambient CO2. At elevated CO2, A. solani decreased shoot and root weights by 20 and 18%, and flower number by 60%. 4 The large reduction in flowering caused by aphids at elevated CO2 suggests a change in resource allocation within the plants to compensate for aphid infestation. 5 Aphid density was unaffected by elevated CO2, although there were significant effects of CO2 on the resulting population structure of both A. pisum and A solani. We suggest that at elevated CO2, aphids appear not to achieve their maximum reproductive potential and their populations are limited by the lower carrying capacity of their host plants.  相似文献   

3.
4.
Environmental change is anticipated to negatively affect both plant and animal populations. As abiotic factors rapidly change habitat suitability, projections range from altered genetic diversity to wide-spread species loss. Here, we assess the degree to which changes in atmospheric composition associated with environmental change will influence not only the abundance, but also the genotypic/phenotypic diversity, of herbivore populations. Using free-air CO2 and O3 enrichment (FACE) technology, we assess numerical responses of pea aphids (Acyrthosiphon pisum) exhibiting a pink–green genetic polymorphism and an environmentally determined wing polyphenism on broad bean plants (Vicia faba) under enriched CO2 and/or O3 atmospheres, over multiple generations. We show that these two greenhouse gases alter not only aphid population sizes, but also genotypic and phenotypic frequencies. As the green genotype was positively influenced by elevated CO2 levels, but the pink genotype was not, genotypic frequencies (pink morph : green morph) ranged from 1 : 1 to 9 : 1. These two genotypes also displayed marked differences in phenotypic frequencies. The pink genotype exhibited higher levels of wing induction under all atmospheric treatments, however, this polyphenism was negatively influenced by elevated O3 levels. Resultantly, frequencies of winged phenotypes (pink morph : green morph) varied from 10 : 1 to 332 : 1. Thus, atmospheric conditions associated with environmental change may alter not just overall population sizes, but also genotypic and phenotypic frequencies of herbivore populations, thereby influencing community and ecosystem functioning.  相似文献   

5.
Numerous reports indicate that pollution stress caused by sulphur dioxide (SO2), oxies of nitrogen or fluorides promote aphid growth on herbaceous and woody plants. At SO2 exposures, the response curve of aphids is bell-shaped having the peak at 100 ppb. This curvilinear response is related to physiological stress responses of host plants exposed to pollutants. On the other hand, observations of aphid performance on ozone-exposed (O3) or elevated carbon dioxide-exposed (CO2) plants have given very variable results. Depending on the duration and concentration of O3 or elevated CO2 exposure or the age of the exposed plants, aphid growth on the same plants either decreased or increased in comparison to growth on control plants grown in filtered air. The results of these studies suggest that there is no general air pollution-induced plant stress that triggers aphid outbreaks on plants. Plants grown in elevated CO2 usually have higher C/N ratios than plants grown in current ambient CO2 atmosphere. A reduced proportion of nitrogen in the plant foliage decreases growth of chewing herbivorous insects, but the few studies of elevated CO2 effects on sucking insects such as aphids have not yielded similar consistent effects. The present paper reviews recent studies of elevated CO2 effects on aphids and discusses the effects of combined elevated O3 and CO2 exposures on aphid performance on woody plants using pine and birch aphids as examples.  相似文献   

6.
1 This research was conducted at the Aspen FACE (Free Air CO2 Enrichment) site located in northern Wisconsin, U.S.A. where trembling aspen (Populus tremuloides Michaux) trees were exposed to one of four atmospheric treatments: elevated carbon dioxide (CO2; 560 µL/L), elevated ozone (O3; ambient × 1.5), elevated CO2 and O3, or ambient air. We evaluated the effects of these fumigants on aspen foliar quality and the performance of aspen blotch leafminer (Phyllonorycter tremuloidiella Braun). 2 CO2 and O3 each affected foliar quality, with the major changes consisting of an 11% reduction in nitrogen under elevated CO2 and a 20% reduction in tremulacin under elevated O3. In the CO2 + O3 treatment, nitrogen levels were reduced by 15% and CO2 ameliorated the O3‐mediated reduction in tremulacin levels. 3 Phyllonorycter tremuloidiella were allowed to colonize trees naturally. Elevated CO2 and O3 reduced colonization rates by 42 and 49% relative to ambient CO2 and O3, respectively. The only effect of fumigation treatments on larval performance occurred under elevated O3, where male development time and larval consumption increased by 8 and 28%, respectively, over insects reared under ambient O3. 4 These data demonstrate that the individual and combined effects of CO2 and O3 can alter aspen foliar chemistry and that these alterations in foliar chemistry produce little to no change in larval performance. However, both CO2 and O3 greatly reduced oviposition. In order to ascertain the full effects of CO2 and O3 on insect performance, future studies should address both population‐ and individual‐level characteristics.  相似文献   

7.
We analyzed growth data from model aspen (Populus tremuloides Michx.) forest ecosystems grown in elevated atmospheric carbon dioxide ([CO2]; 518 μL L?1) and ozone concentrations ([O3]; 1.5 × background of 30–40 nL L?1 during daylight hours) for 7 years using free‐air CO2 enrichment technology to determine how interannual variability in present‐day climate might affect growth responses to either gas. We also tested whether growth effects of those gasses were sustained over time. Elevated [CO2] increased tree heights, diameters, and main stem volumes by 11%, 16%, and 20%, respectively, whereas elevated ozone [O3] decreased them by 11%, 8%, and 29%, respectively. Responses similar to these were found for stand volume and basal area. There were no growth responses to the combination of elevated [CO2+O3]. The elevated [CO2] growth stimulation was found to be decreasing, but relative growth rates varied considerably from year to year. Neither the variation in annual relative growth rates nor the apparent decline in CO2 growth response could be explained in terms of nitrogen or water limitations. Instead, growth responses to elevated [CO2] and [O3] interacted strongly with present‐day interannual variability in climatic conditions. The amount of photosynthetically active radiation and temperature during specific times of the year coinciding with growth phenology explained 20–63% of the annual variation in growth response to elevated [CO2] and [O3]. Years with higher photosynthetic photon flux (PPF) during the month of July resulted in more positive growth responses to elevated [CO2] and more negative growth responses to elevated [O3]. Mean daily temperatures during the month of October affected growth in a similar fashion the following year. These results indicate that a several‐year trend of increasingly cloudy summers and cool autumns were responsible for the decrease in CO2 growth response.  相似文献   

8.
Elevated levels of CO2 and O3 affect plant growth and phytochemistry, which in turn can alter physiological performance of associated herbivores. Little is known, however, about how generalist insect herbivores respond behaviorally to CO2‐ and O3‐mediated changes in their host plants. This research examined the effects of elevated CO2 and O3 levels on host plant preferences and consumption of forest tent caterpillar (FTC, Malacosoma disstria Hbn.) larvae. Dual choice feeding assays were performed with foliage from birch (Betula papyrifera Marsh.) and aspen (Populus tremuloides Michx., genotypes 216 and 259). Trees were grown at the Aspen Free Air CO2 Enrichment (FACE) facility near Rhinelander, WI, USA, and had been exposed to ambient or elevated concentrations of CO2 and/or O3. Levels of nutritional and secondary compounds were quantified through phytochemical analyses. The results showed that elevated O3 levels increased FTC larval preferences for birch compared with aspen, whereas elevated CO2 levels had the opposite effect. In assays with the two aspen genotypes, addition of both CO2 and O3 caused a shift in feeding preferences from genotype 259 to genotype 216. Consumption was unaffected by experimental treatments in assays comparing aspen and birch, but were increased for larvae given high O3 foliage in the aspen genotype assays. Elevated levels of CO2 and O3 altered tree phytochemistry, but did not explain shifts in feeding preferences. The results demonstrate that increased levels of CO2 and O3 can alter insect host plant preferences both between and within tree species. Also, consequences of altered host quality (e.g., compensatory consumption) may be buffered by partial host shifts in situations when alternative plant species are available. Environmentally induced changes in host plant preferences may have the potential to alter the distribution of herbivory across plant genotypes and species, as well as competitive interactions among them.  相似文献   

9.
Decomposition of soybean grown under elevated concentrations of CO2 and O3   总被引:1,自引:0,他引:1  
A critical global climate change issue is how increasing concentrations of atmospheric CO2 and ground‐level O3 will affect agricultural productivity. This includes effects on decomposition of residues left in the field and availability of mineral nutrients to subsequent crops. To address questions about decomposition processes, a 2‐year experiment was conducted to determine the chemistry and decomposition rate of aboveground residues of soybean (Glycine max (L.) Merr.) grown under reciprocal combinations of low and high concentrations of CO2 and O3 in open‐top field chambers. The CO2 treatments were ambient (370 μmol mol?1) and elevated (714 μmol mol?1) levels (daytime 12 h averages). Ozone treatments were charcoal‐filtered air (21 nmol mol?1) and nonfiltered air plus 1.5 times ambient O3 (74 nmol mol?1) 12 h day?1. Elevated CO2 increased aboveground postharvest residue production by 28–56% while elevated O3 suppressed it by 15–46%. In combination, inhibitory effects of added O3 on biomass production were largely negated by elevated CO2. Plant residue chemistry was generally unaffected by elevated CO2, except for an increase in leaf residue lignin concentration. Leaf residues from the elevated O3 treatments had lower concentrations of nonstructural carbohydrates, but higher N, fiber, and lignin levels. Chemical composition of petiole, stem, and pod husk residues was only marginally affected by the elevated gas treatments. Treatment effects on plant biomass production, however, influenced the content of chemical constituents on an areal basis. Elevated CO2 increased the mass per square meter of nonstructural carbohydrates, phenolics, N, cellulose, and lignin by 24–46%. Elevated O3 decreased the mass per square meter of these constituents by 30–48%, while elevated CO2 largely ameliorated the added O3 effect. Carbon mineralization rates of component residues from the elevated gas treatments were not significantly different from the control. However, N immobilization increased in soils containing petiole and stem residues from the elevated CO2, O3, and combined gas treatments. Mass loss of decomposing leaf residue from the added O3 and combined gas treatments was 48% less than the control treatment after 20 weeks, while differences in decomposition of petiole, stem, and husk residues among treatments were minor. Decreased decomposition of leaf residues was correlated with lower starch and higher lignin levels. However, leaf residues only comprised about 20% of the total residue biomass assayed so treatment effects on mass loss of total aboveground residues were relatively small. The primary influence of elevated atmospheric CO2 and O3 concentrations on decomposition processes is apt to arise from effects on residue mass input, which is increased by elevated CO2 and suppressed by O3.  相似文献   

10.
The fitness of natural enemies should be altered in response to changes in herbivore quality induced by the impact of increased atmospheric CO2 levels on plants. We studied the effect of different CO2 levels on the aphid predator Episyrphus balteatus DeGeer fed either specialist or generalist aphids reared on either of two host plants under laboratory conditions. In the host plant that contains sinigrin (black mustard), elevated CO2 increased the sinigrin content of both host plant and the specialist aphid, but reduced the already very low levels in the generalist aphid. Predator development time increased with elevated CO2, while fecundity decreased. Consequently, individual fitness decreased slightly with increasing atmospheric CO2. Sinigrin significantly decreased fecundity and increased development time of the predator. As a result, fitness was significantly lower too. The consumption rate was influenced significantly by plant and prey solely and the interactions of host plant × prey type and CO2 level × prey type. Further research on the effects of climate change parameters (e.g. greenhouse gases such as CO2, ozone (O3) and nitrogen dioxide (NO2), etc.) separately and jointly under controlled environmental conditions will help to understand the nature and direction of their effects on natural enemies as part of the tritrophic system.  相似文献   

11.
Leaf gas exchange parameters and the content of ribulose‐1,5‐bisphosphate carboxylase/oxygenase (Rubisco) in the leaves of two 2‐year‐old aspen (Populus tremuloides Michx.) clones (no. 216, ozone tolerant and no. 259, ozone sensitive) were determined to estimate the relative stomatal and mesophyll limitations to photosynthesis and to determine how these limitations were altered by exposure to elevated CO2 and/or O3. The plants were exposed either to ambient air (control), elevated CO2 (560 p.p.m.) elevated O3 (55 p.p.b.) or a mixture of elevated CO2 and O3 in a free air CO2 enrichment (FACE) facility located near Rhinelander, Wisconsin, USA. Light‐saturated photosynthesis and stomatal conductance were measured in all leaves of the current terminal and of two lateral branches (one from the upper and one from the lower canopy) to detect possible age‐related variation in relative stomatal limitation (leaf age is described as a function of leaf plastochron index). Photosynthesis was increased by elevated CO2 and decreased by O3 at both control and elevated CO2. The relative stomatal limitation to photosynthesis (ls) was in both clones about 10% under control and elevated O3. Exposure to elevated CO2 + O3 in both clones and to elevated CO2 in clone 259, decreased ls even further – to about 5%. The corresponding changes in Rubisco content and the stability of Ci/Ca ratio suggest that the changes in photosynthesis in response to elevated CO2 and O3 were primarily triggered by altered mesophyll processes in the two aspen clones of contrasting O3 tolerance. The changes in stomatal conductance seem to be a secondary response, maintaining stable Ci under the given treatment, that indicates close coupling between stomatal and mesophyll processes.  相似文献   

12.
We reviewed the effects of elevated ozone (O3), alone and in combination with elevated carbon dioxide (CO2) on primary and secondary metabolites of trees and performance of insect herbivores by means of meta‐analysis. Our database consisted of 63 studies conducted on 22 species of trees and published between 1990 and 2005. Ozone alone had no overall effect on concentrations of carbohydrates or nutrients, whereas in combination with CO2, elevated O3 reduced nutrient concentrations and increased carbohydrate concentrations. In contrast to primary metabolites, concentrations of phenolics and terpenes were significantly increased by 16% and 8%, respectively, in response to elevated O3. Effects of ozone in combination with elevated CO2 were weaker than those of ozone alone on phenolics, but stronger than those of ozone alone on terpenes. The magnitude of secondary metabolite responses depended on the type of ozone exposure facility and increased in the following order: indoor growth chamber 3 than gymnosperms, as shifts in concentrations of carbohydrate and phenolics were observed in the former, but not in the latter. Elevated O3 had positive effects on some indices of insect performance: pupal mass increased and larval development time shortened, but these effects were counteracted by elevated CO2. Therefore, despite the observed increase in secondary metabolites, elevated O3 tends to increase tree foliage quality for herbivores, but elevated CO2 may alleviate these effects. Our meta‐analysis clearly demonstrated that effects of elevated O3 alone on leaf chemistry and some indices of insect performance differed from those of O3+CO2, and therefore, it is important to study effects of several factors of global climate change simultaneously.  相似文献   

13.
Increases in atmospheric CO2 and tropospheric O3 may affect forest N cycling by altering plant litter production and the availability of substrates for microbial metabolism. Three years following the establishment of our free‐air CO2–O3 enrichment experiment, plant growth has been stimulated by elevated CO2 resulting in greater substrate input to soil; elevated O3 has counteracted this effect. We hypothesized that rates of soil N cycling would be enhanced by greater plant productivity under elevated CO2, and that CO2 effects would be dampened by O3. We found that elevated CO2 did not alter gross N transformation rates. Elevated O3 significantly reduced gross N mineralization and microbial biomass N, and effects were consistent among species. We also observed significant interactions between CO2 and O3: (i) gross N mineralization was greater under elevated CO2 (1.0 mg N kg?1 day?1) than in the presence of both CO2 and O3 (0.5 mg N kg?1 day?1) and (ii) gross NH4+ immobilization was also greater under elevated CO2 (0.8 mg N kg?1 day?1) than under CO2 plus O3 (0.4 mg N kg?1 day?1). We used a laboratory 15N tracer method to quantify transfer of inorganic N to organic pools. Elevated CO2 led to greater recovery of NH4+15N in microbial biomass and corresponding lower recovery in the extractable NO3? pool. Elevated CO2 resulted in a substantial increase in NO3?15N recovery in soil organic matter. We observed no O3 main effect and no CO2 by O3 interaction effect on 15N recovery in any soil pool. All of the above responses were most pronounced beneath Betula papyrifera and Populus tremuloides, which have grown more rapidly than Acer saccharum. Although elevated CO2 has increased plant productivity, the resulting increase in plant litter production has yet to overcome the influence of the pre‐existing pool of soil organic matter on soil microbial activity and rates of N cycling. Ozone reduces plant litter inputs and also appears to affect the composition of plant litter in a way that reduces microbial biomass and activity.  相似文献   

14.
In the present open‐top chamber experiment, two silver birch clones (Betula pendula Roth, clone 4 and clone 80) were exposed to elevated levels of carbon dioxide (CO2) and ozone (O3), singly and in combination, and soil CO2 efflux was measured 14 times during three consecutive growing seasons (1999–2001). In the beginning of the experiment, all experimental trees were 7 years old and during the experiment the trees were growing in sandy field soil and fertilized regularly. In general, elevated O3 caused soil CO2 efflux stimulation during most measurement days and this stimulation enhanced towards the end of the experiment. The overall soil respiration response to CO2 was dependent on the genotype, as the soil CO2 efflux below clone 80 trees was enhanced and below clone 4 trees was decreased under elevated CO2 treatments. Like the O3 impact, this clonal difference in soil respiration response to CO2 increased as the experiment progressed. Although the O3 impact did not differ significantly between clones, a significant time × clone × CO2× O3 interaction revealed that the O3‐induced stimulation of soil respiration was counteracted by elevated CO2 in clone 4 on most measurement days, whereas in clone 80, the effect of elevated CO2 and O3 in combination was almost constantly additive during the 3‐year experiment. Altogether, the root or above‐ground biomass results were only partly parallel with the observed soil CO2 efflux responses. In conclusion, our data show that O3 impacts may appear first in the below‐ground processes and that relatively long‐term O3 exposure had a cumulative effect on soil CO2 efflux. Although the soil respiration response to elevated CO2 depended on the tree genotype as a result of which the O3 stress response might vary considerably within a single tree species under elevated CO2, the present experiment nonetheless indicates that O3 stress is a significant factor affecting the carbon cycling in northern forest ecosystems.  相似文献   

15.
Abstract We report the results of a study investigating the influence of elevated CO2 on species interactions across three trophic levels: a plant (Brassica oleracea), two aphid herbivores (the generalist Myzus persicae and the specialist Brevicoryne brassicae), and two natural enemies (the coccinellid Hippodamia convergens (ladybird) and the parasitoid wasp Diaeretiella rapae). Brassica oleracea plants reared under elevated CO2 conditions (650 ppmv vs. 350 ppmv) were larger and had decreased water and nitrogen content. Brevicoryne brassicae reared on plants grown in elevated CO2 were larger and accumulated more fat, while there was no change in M. persicae traits. Fecundity of individual aphids appeared to be increased when reared on plants grown in elevated CO2. However, these differences were generally lost when aphids were reared in colonies, suggesting that such changes in plant quality will have subtle effects on aphid intraspecific interactions. Nevertheless, CO2 treatment did influence aphid distribution on plants, with significantly fewer M. persicae found on the shoots, and B. brassicae was only found on senescing leaves, when colonies were reared on plants grown in elevated CO2. We reared B. brassicae and M. persicae in competition on plants grown at both the CO2 concentration treatments. We found a significantly lower ratio of M. persicae: B. brassicae on plants grown under elevated CO2 conditions, strongly suggesting that increasing CO2 concentrations can alter the outcome of competition among insect herbivores. This was also reflected in the distribution of the aphids on the plants. While the CO2 treatment did not influence where B. brassicae were found, fewer M. persicae were present on senescing leaves under elevated CO2 conditions. Changes in plant quality resulting from the CO2 treatments did not appear to alter aphid quality as prey species, as the number consumed by the ladybird H. convergens, and the number parasitised by the parasitoid wasp D. rapae, did not change. To our knowledge, this study provides the first empirical evidence that changes in host plant quality mediated by increasing levels of CO2 can alter the outcome of interspecific competition among insect herbivores.  相似文献   

16.
Two cultivars of spring wheat (Triticum aestivum L. cvs. Alexandria and Hanno) and three cultivars of winter wheat (cvs. Riband, Mercia and Haven) were grown at two concentrations of CO2 [ambient (355 pmol mol?1) and elevated (708 μmol mol?1)] under two O3 regimes [clean air (< 5 nmol mol?1 O3) and polluted air (15 nmol mol?1 O3 at night rising to a midday maximum of 75 nmol mol?1)] in a phytotron at the University of Newcastle-upon-Tyne. Between the two-leaf stage and anthesis, measurements of leaf gas-exchange, non-structural carbohydrate content, visible O3 damage, growth, dry matter partitioning, yield components and root development were made in order to examine responses to elevated CO2 and/or O3. Growth at elevated CO2 resulted in a sustained increase in the rate of CO2 assimilation, but after roughly 6 weeks' exposure there was evidence of a slight decline in the photosynthetic rate (c.-15%) measured under growth conditions which was most pronounced in the winter cultivars. Enhanced rates of CO2 assimilation were accompanied by a decrease in stomatal conductance which improved the instantaneous water use efficiency of individual leaves. CO2 enrichment stimulated shoot and root growth to an equivalent extent, and increased tillering and yield components, however, non-structural carbohydrates still accumulated in source leaves. In contrast, long-term exposure to O3 resulted in a decreased CO2 assimilation rate (c. -13%), partial stomatal closure, and the accumulation of fructan and starch in leaves in the light. These effects were manifested in decreased rates of shoot and root growth, with root growth more severely affected than shoot growth. In the combined treatment growth of O3-treated plants was enhanced by elevated CO2, but there was little evidence that CO2 enrichment afforded additional protection against O3 damage. The reduction in growth induced by O3 at elevated CO2 was similar to that induced by O3 at ambient CO2 despite additive effects of the individual gases on stomatal conductance that would be expected to reduce the O3 flux by 20%, and also CO2-induced increases in the provision of substrates for detoxification and repair processes. These observations suggest that CO2 enrichment may render plants more susceptible to O3 damage at the cellular level. Possible mechanisms are discussed.  相似文献   

17.
Field‐growing silver birch (Betula pendula Roth) clones (clone 4 and 80) were exposed to elevated CO2 and O3 in open‐top chambers for three consecutive growing seasons (1999–2001). At the beginning of the OTC experiment, all trees were 7 years old. We studied the single and interaction effects of CO2 and O3 on silver birch below‐ground carbon pools (i.e. effects on fine roots and mycorrhizas, soil microbial communities and sporocarp production) and also assessed whether there are any clonal differences in these below‐ground CO2 and O3 responses. The total mycorrhizal infection level of both clones was stimulated by elevated CO2 alone and elevated O3 alone, but not when elevated CO2 was used in fumigation in combination with elevated O3. In both clones, elevated CO2 affected negatively light brown/orange mycorrhizas, while its effect on other mycorrhizal morphotypes was negligible. Elevated O3, instead, clearly decreased the proportions of black and liver‐brown mycorrhizas and increased that of light brown/orange mycorrhizas. Elevated O3 had a tendency to decrease standing fine root mass and sporocarp production as well, both of these O3 effects mainly manifesting in clone 4 trees. CO2 and O3 treatment effects on soil microbial community composition (PLFA, 2‐ and 3‐OH‐FA profiles) were negligible, but quantitative PLFA data showed that in 2001 the PLFA fungi : bacteria‐ratio of clone 80 trees was marginally increased because of elevated CO2 treatments. This study shows that O3 effects were most clearly visible at the mycorrhizal root level and that some clonal differences in CO2 and O3 responses were observable in the below‐ground carbon pools. In conclusion, the present data suggests that CO2 effects were minor, whereas increasing tropospheric O3 levels can be an important stress factor in northern birch forests, as they might alter mycorrhizal morphotype assemblages, mycorrhizal infection rates and sporocarp production.  相似文献   

18.
Abstract Plants grown under elevated carbon dioxide (CO2) experience physiological changes that influence their suitability as food for insects. To determine the effects of living on soybean (Glycine max Linnaeus) grown under elevated CO2, population growth of the soybean aphid (Aphis glycines Matsumura) was determined at the SoyFACE research site at the University of Illinois, Urbana‐Champaign, Illinois, USA, grown under elevated (550 μL/L) and ambient (370 μL/L) levels of CO2. Growth of aphid populations under elevated CO2 was significantly greater after 1 week, with populations attaining twice the size of those on plants grown under ambient levels of CO2. Soybean leaves grown under elevated levels of CO2 were previously demonstrated at SoyFACE to have increased leaf temperature caused by reduced stomatal conductance. To separate the increased leaf temperature from other effects of elevated CO2, air temperature was lowered while the CO2 level was increased, which lowered overall leaf temperatures to those measured for leaves grown under ambient levels of CO2. Aphid population growth on plants grown under elevated CO2 and reduced air temperature was not significantly greater than on plants grown under ambient levels of CO2. By increasing Glycine max leaf temperature, elevated CO2 may increase populations of Aphis glycines and their impact on crop productivity.  相似文献   

19.
We investigated the interaction of elevated CO2 and/or (Ozone) O3 on the occurrence and severity of aspen leaf rust (Melampsora medusae Thuem. f. sp. tremuloidae) on trembling aspen (Populus tremuloides Michx.). Furthermore, we examined the role of changes in leaf surface properties induced by elevated CO2 and/or O3 in this host–pathogen interaction. Three‐ to five‐fold increases in levels of rust infection index were found in 2 consecutive years following growing‐season‐long exposures with either O3 alone or CO2 + O3 depending on aspen clone. Examination of leaf surface properties (wax appearance, wax amount, wax chemical composition, leaf surface and wettability) suggested significant effects by O3 and CO2 + O3. We conclude that elevated O3 is altering aspen leaf surfaces in such a way that it is likely predisposing the plants to increased infection by aspen leaf rust.  相似文献   

20.
As human activity continues to increase CO2 and O3, broad expanses of north temperate forests will be simultaneously exposed to elevated concentrations of these trace gases. Although both CO2 and O3 are potent modifiers of plant growth, we do not understand the extent to which they alter competition for limiting soil nutrients, like nitrogen (N). We quantified the acquisition of soil N in two 8‐year‐old communities composed of trembling aspen genotypes (n= 5) and trembling aspen–paper birch which were exposed to factorial combinations of CO2 (ambient and 560 μL L−1) and O3 (ambient = 30–40 vs. 50–60 nL L−1). Tracer amount of 15NH4+ were applied to soil to determine how these trace gases altered the competitive ability of genotypes and species to acquire soil N. One year after isotope addition, we assessed N acquisition by measuring the amount of 15N tracer contained in the plant canopy (i.e. recent N acquisition), as well as the total amount of canopy N (i.e. cumulative N acquisition). Exposure to elevated CO2 differentially altered recent and cumulative N acquisition among aspen genotypes, changing the rank order in which they obtained soil N. Elevated O3 also altered the rank order in which aspen genotypes obtained soil N by eliciting increases, decreases and no response among genotypes. If aspen genotypes respond similarly under field conditions, then rising concentrations of CO2 and O3 could alter the structure of aspen populations. In the aspen–birch community, elevated CO2 increased recent N (i.e. 15N) acquisition in birch (68%) to a greater extent than aspen (19%), suggesting that, over the course of this experiment, birch had gained a competitive advantage over aspen. The response of genotypes and species to rising CO2 and O3 concentrations, and how these responses are modified by competitive interactions, has the potential to change the future composition and productivity of northern temperate forests.  相似文献   

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