ABSTRACT
*The delay in autumnal senescence that has occurred in recent decades has been linked to rising temperatures. Here, we suggest that increasing atmospheric CO2 may partly account for delayed autumnal senescence and for the first time, through transcriptome analysis, identify gene expression changes associated with this delay. *Using a plantation of Populus x euramericana grown in elevated [CO2] (e[CO2]) with free-air CO2 enrichment (FACE) technology, we investigated the molecular and biochemical basis of this response. A Populus cDNA microarray was used to identify genes representing multiple biochemical pathways influenced by e[CO2] during senescence. Gene expression changes were confirmed through real-time quantitative PCR, and leaf biochemical assays. *Pathways for secondary metabolism and glycolysis were significantly up-regulated by e[CO2] during senescence, in particular, those related to anthocyanin biosynthesis. Expressed sequence tags (ESTs) representing the two most significantly up-regulated transcripts in e[CO2], LDOX (leucoanthocyanidin dioxgenase) and DFR (dihydroflavonol reductase), gave (e[CO2]/ambient CO(2) (a[CO2])) expression ratios of 39.6 and 19.3, respectively. *We showed that in e[CO2] there was increased autumnal leaf sugar accumulation and up-regulation of genes determining anthocyanin biosynthesis which, we propose, prolongs leaf longevity during natural autumnal senescence.
Subject(s)
Anthocyanins/biosynthesis , Carbon Monoxide/pharmacology , Gene Expression Profiling , Gene Expression Regulation, Plant/drug effects , Populus/genetics , Seasons , Carbohydrates/analysis , Chlorophyll/metabolism , Genes, Plant/genetics , Metabolic Networks and Pathways/drug effects , Metabolic Networks and Pathways/genetics , Oligonucleotide Array Sequence Analysis , Plant Leaves/drug effects , Plant Leaves/metabolism , RNA, Messenger/genetics , RNA, Messenger/metabolism , Reproducibility of Results , Reverse Transcriptase Polymerase Chain Reaction , Time FactorsABSTRACT
Recent evidence from novel phytotron and free-air ozone (O3) fumigation experiments in Europe and America on forest tree species is highlighted in relation to previous chamber studies. Differences in O3 sensitivity between pioneer and climax species are examined and viewed for trees growing at the harsh alpine timberline ecotone. As O3 apparently counteracts positive effects of elevated CO2 and mitigates productivity increases, response is governed by genotype, competitors, and ontogeny rather than species per se. Complexity in O3 responsiveness increased under the influence of pathogens and herbivores. The new evidence does not conflict in principle with previous findings that, however, pointed to a low ecological significance. This new knowledge on trees' O3 responsiveness beyond the juvenile stage in plantations and forests nevertheless implies limited predictability due to complexity in biotic and abiotic interactions. Unravelling underlying mechanisms is mandatory for assessing O3 risks as an important component of climate change scenarios.
Subject(s)
Air Pollutants/toxicity , Betula/drug effects , Climate Change , Forestry/methods , Populus/drug effects , Air Pollutants/analysis , Betula/growth & development , Populus/growth & developmentABSTRACT
The use of agroforestry crops is a promising tool for reducing atmospheric carbon dioxide concentration through fossil fuel substitution. In particular, plantations characterised by high yields such as short rotation forestry (SRF) are becoming popular worldwide for biomass production and their role acknowledged in the Kyoto Protocol. While their contribution to climate change mitigation is being investigated, the impact of climate change itself on growth and productivity of these plantations needs particular attention, since their management might need to be modified accordingly. Besides the benefits deriving from the establishment of millions of hectares of these plantations, there is a risk of increased release into the atmosphere of volatile organic compounds (VOC) emitted in large amounts by most of the species commonly used. These hydrocarbons are known to play a crucial role in tropospheric ozone formation. This might represent a negative feedback, especially in regions already characterized by elevated ozone level.
Subject(s)
Forestry/methods , Air Pollution/analysis , Air Pollution/prevention & control , Atmosphere/chemistry , Carbon Dioxide/analysis , Conservation of Natural Resources , Global Warming/prevention & control , Ozone/analysis , Soil/analysis , Trees/growth & development , Trees/metabolismABSTRACT
Natural areas are important interfaces between air quality, the public, science and regulation. In the United States and Canada, national parks received over 315million visits during 2004. Many natural areas have been experiencing decreased visibility, increased ozone (O(3)) levels and elevated nitrogen deposition. Ozone is the most pervasive air pollutant in North American natural areas. There is an extensive scientific literature on O(3) exposure-tree response in chambered environments and, lately, free-air exposure systems. Yet, less is known about O(3) impacts on natural terrestrial ecosystems. To advance scientifically defensible O(3) risk assessment for natural forest areas, species-level measurement endpoints must be socially, economically and ecologically relevant. Exposure-based indices, based on appropriate final endpoints, present an underused opportunity to meet this need. Exposure-plant indices should have a high degree of statistical significance, have high goodness of fit, be biologically plausible and include confidence intervals to define uncertainty. They must be supported by exposure-response functions and be easy to use within an air quality regulation context. Ozone exposure-response indices developed within an ambient air context have great potential for improving risk assessment in natural forest areas and enhancing scientific literacy.
Subject(s)
Air Pollution/adverse effects , Conservation of Natural Resources/methods , Ecosystem , Air Pollutants/adverse effects , Air Pollutants/analysis , Air Pollution/analysis , Canada , Climate , Conservation of Natural Resources/legislation & jurisprudence , Environmental Monitoring/methods , Humans , Ozone/adverse effects , Ozone/analysis , Recreation , Trees/growth & development , United States , United States Environmental Protection AgencyABSTRACT
Micropropagation offers opportunities to propagate, preserve and ship tree germplasm. It also reduces the risk of moving pathogens and insects with the germplasm due to built-in pathogen detection capabilities of aseptic cultures. For the past few decades, our laboratory has been involved in a project to preserve and restore a large, cold hardy, and historically important Chinese elm (Ulmus parvifolia Jacq. 'A/Ross Central Park') tree. Here we present three simple and efficient systems for its micropropagation, germplasm conservation and distribution: (1) in vitro plant formation from meristematic nodules (MNs), (2) plantlet generation from axillary buds, and (3) in vitro rooting of micro-cuttings from 20-years-old hedged stock plants. Newly flushed nodal segments were used as explants. WPM with 0.5 mg/l BA was found to be the best medium for meristematic shoot development and WPM supplemented with 2.0 mg/l 4-CPPU and 0.5 mg/l TDZ was best for meristematic nodule formation. Rhizogenesis of regenerants and micro-cuttings was best achieved on WPM with 1.0 mg/l NAA and 2% sucrose. Rooted plants were readily acclimatized to the greenhouse ambient environment and continued to grow well under greenhouse conditions. The survival rate of acclimatized plantlets under ex vitro conditions was 100% after 4 weeks. Plants looked healthy with no visually detectable phenotypic variation based on observation of about 1,000 plants. Cycling of shoot explants and MNs through repetitive cultures was effective in scaling-up propagules.
Subject(s)
Conservation of Natural Resources/methods , Tissue Culture Techniques/methods , Ulmus/genetics , Ulmus/physiology , Culture Media , Forestry/methods , Plant Roots/growth & development , Plant Shoots/growth & developmentABSTRACT
Because seedlings and mature trees do not necessarily respond similarly to O(3) stress, it is critically important that exposure systems be developed that allow exposure of seedlings through to mature trees. Here we describe three different O(3) Free-Air Exposure Systems that have been used successfully for exposure at all growth stages. These systems of spatially uniform O(3) release have been shown to provide reliable O(3) exposure with minimal, if any, impact on the microclimate. This methodology offers a welcome alternative to chamber studies which had severe space constraints precluding stand or community-level studies and substantial chamber effects on the microclimate and, hence physiological tree performance.
Subject(s)
Air , Ozone/pharmacology , Research Design , Trees/drug effects , Finland , FumigationABSTRACT
Three model communities of trembling aspen (monoculture, and mixed with either paper birch or sugar maple) were grown for seven years in elevated atmospheric CO(2) and O(3) using Free Air CO(2) Enrichment (FACE) technology. We utilized trends in species' importance, calculated as an index of volume growth and survival, as indications of shifting community composition. For the pure aspen communities, different clones emerged as having the highest change in relative importance values depending on the pollutant exposure. In the control and elevated CO(2) treatments, clone 42E was rapidly becoming the most successful clone while under elevated O(3), clone 8 L emerged as the dominant clone. In fact, growth of clone 8 L was greater in the elevated O(3) treatment compared to controls. For the mixed aspen-birch community, importance of aspen and birch changed by - 16 % and + 62 %, respectively, in the controls. In the treatments, however, importance of aspen and birch changed by - 27 % and + 87 %, respectively, in elevated O(3), and by - 10 % and + 45 %, respectively, in elevated CO(2). Thus, the presence of elevated O(3) hastened conversion of stands to paper birch, whereas the presence of elevated CO(2) delayed it. Relative importance of aspen and maple changed by - 2 % and + 3 %, respectively, after seven years in the control treatments. But in elevated O(3), relative importance of aspen and maple changed by - 2 % and + 5 %, respectively, and in elevated CO(2) by + 9 and - 20 %, respectively. Thus, elevated O(3) slightly increases the rate of conversion of aspen stands to sugar maple, but maple is placed at a competitive disadvantage to aspen under elevated CO(2).
Subject(s)
Acer/drug effects , Atmosphere , Betula/drug effects , Carbon Dioxide/pharmacology , Ozone/pharmacology , Species SpecificityABSTRACT
The United States and Canada currently use exposure-based metrics to protect vegetation from O(3). Using 5 years (1999-2003) of co-measured O(3), meteorology and growth response, we have developed exposure-based regression models that predict Populus tremuloides growth change within the North American ambient air quality context. The models comprised growing season fourth-highest daily maximum 8-h average O(3) concentration, growing degree days, and wind speed. They had high statistical significance, high goodness of fit, include 95% confidence intervals for tree growth change, and are simple to use. Averaged across a wide range of clonal sensitivity, historical 2001-2003 growth change over most of the 26 Mha P. tremuloides distribution was estimated to have ranged from no impact (0%) to strong negative impacts (-31%). With four aspen clones responding negatively (one responded positively) to O(3), the growing season fourth-highest daily maximum 8-h average O(3) concentration performed much better than growing season SUM06, AOT40 or maximum 1h average O(3) concentration metrics as a single indicator of aspen stem cross-sectional area growth.
Subject(s)
Oxidants, Photochemical/toxicity , Ozone/toxicity , Populus/growth & development , Air Pollution/adverse effects , Environmental Exposure/adverse effects , Environmental Monitoring/methods , Models, Statistical , North America , Populus/drug effects , Regression Analysis , Risk Assessment/methods , Seasons , UncertaintyABSTRACT
Epicuticular waxes of three trembling aspen (Populus tremuloides Michx.) clones differing in O3 tolerance were examined over six growing seasons (1998-2003) at three bioindicator sites in the Lake States region of the USA and at FACTS II (Aspen FACE) site in Rhinelander, WI. Differences in epicuticular wax structure were determined by scanning electron microscopy and quantified by a coefficient of occlusion. Statistically significant increases in stomatal occlusion occurred for the three O3 bioindicator sites, with the higher O3 sites having the most affected stomata for all three clones as well as for all treatments including elevated CO2, elevated O3, and elevated CO2 + O3. We recorded statistically significant differences between aspen clones and between sampling period (spring, summer, fall). We found no statistically significant differences between treatments or aspen clones in stomatal frequency.
Subject(s)
Air Pollutants/toxicity , Ecology/methods , Environment , Greenhouse Effect , Ozone/toxicity , Plant Leaves/physiology , Populus , Germany , Plant Leaves/drug effects , Plant Transpiration/drug effects , Populus/drug effects , United StatesABSTRACT
Expression of 4600 poplar expressed sequence tags (ESTs) was studied over the 2001-2002 growing seasons using trees of the moderately ozone (O(3))-tolerant trembling aspen (Populus tremuloides) clone 216 exposed to elevated CO(2) and/or O(3) for their entire 5-yr life history. Based on replication of the experiment in years 2001 and 2002, 238 genes showed qualitatively similar expression in at least one treatment and were retained for analysis. Of these 238 genes, 185 were significantly regulated (1.5-fold) from one year to the other in at least one treatment studied. Less than 1% of the genes were regulated 2-fold or more. In the elevated CO(2) treatment, relatively small numbers of genes were up-regulated, whereas in the O(3) treatment, higher expression of many signaling and defense-related genes and lower expression of several photosynthesis and energy-related genes were observed. Senescence-associated genes (SAGs) and genes involved in the flavonoid pathway were also up-regulated under O(3), with or without CO(2) treatment. Interestingly, the combined treatment of CO(2) plus O(3) resulted in the differential expression of genes that were not up-regulated with individual gas treatments. This study represents the first investigation into gene expression following long-term exposure of trees to the interacting effects of elevated CO(2) and O(3) under field conditions. Patterns of gene-specific regulation described in this study correlated with previously published physiological responses of aspen clone 216.
Subject(s)
Carbon Dioxide/physiology , Gene Expression Profiling , Gene Expression Regulation, Plant/drug effects , Ozone/toxicity , Populus/drug effects , Adaptation, Physiological , Atmosphere , Carbon Dioxide/pharmacology , Cluster Analysis , Ecosystem , Expressed Sequence Tags , Oxidants, Photochemical/toxicity , Populus/metabolism , Time FactorsABSTRACT
⢠Saplings of three aspen (Populus tremuloides) genotypes and seedlings of paper birch (Betula papyrifera) were exposed to elevated ozone (1.5× ambient) and 560 p.p.m. CO2 , singly and in combination, from 1998 at the Aspen-FACE (free-air CO2 enrichment) site (Rhinelander, USA). ⢠The plants were studied for H2 O2 accumulation within the leaf mesophyll, number of peroxisomes, level of gene expression for catalase (Cat), and changes in ultrastructure. ⢠In tolerant clones, ozone-elicited excess H2 O2 production was restricted to the apoplast, without any ultrastructural injuries. This was associated with ozone-induced proliferation of peroxisomes and increased transcript levels of Cat. In sensitive plants, ozone-induced H2 O2 accumulation continued from the cell wall to the plasma membrane, cytosol and chloroplasts, particularly in older leaves. However, chloroplastic precipitation was absent in the presence of elevated CO2 . In the most sensitive aspen clone, H2 O2 accumulation was found in conjunction with chloroplast injuries, low number of peroxisomes and low cell wall volume, whereas in birch a simultaneous increase in cell wall thickness indicated defence activation. ⢠Our results indicate that oxidative stress manifests as H2 O2 effects on leaf ultrastructure in sensitive trees exposed to elevated ozone. However, CO2 enrichment appears to alleviate chloroplastic oxidative stress.
ABSTRACT
To study the impact of ozone (O3) and O3 plus CO2 on aspen growth, we planted two trembling aspen clones, differing in sensitivity to O3 in the ground in open-top chambers and exposed them to different concentrations of O3 and O3 plus CO, for 98 days. Ozone exposure (58 to 97 microl l(-1)-h. total exposure) decreased growth and modified crown architecture of both aspen clones. Ozone exposure decreased leaf, stem, branch, and root dry weight particularly in the O3 sensitive clone (clone 259). The addition of CO2 (150 microl l(-1) over ambient) to the O3 exposure counteracted the negative impact of O3 only in the O3 tolerant clone (clone 216). Ozone had relatively little effect on allometric ratios such as, shoot/root ratio, leaf weight ratio, or root weight ratio. In both clones, however, O3 decreased the shoot dry weight, shoot length ratio and shoot diameter. This decrease in wood strength caused both current terminals and long shoots to droop and increased the branch angle of termination. These results show that aspen growth is highly sensitive to O3 and that O3 can also significantly affect crown architecture. Aspen plants with drooping terminals and lateral branches would be at a competitive disadvantage in dense stands with limited light.
Subject(s)
Carbon Dioxide/pharmacology , Ozone/pharmacology , Plant Structures/drug effects , Salicaceae/drug effects , Air Pollutants/adverse effects , Air Pollutants/pharmacology , Atmosphere Exposure Chambers , Carbon/metabolism , Cloning, Organism , Drug Interactions , Genotype , Ozone/adverse effects , Plant Structures/genetics , Plant Structures/growth & development , Salicaceae/genetics , Salicaceae/growth & development , Trees/drug effects , Trees/genetics , Trees/growth & developmentABSTRACT
The Intergovernmental Panel of Climate Change (IPCC) has concluded that the greenhouse gases carbon dioxide (CO2) and tropospheric ozone (O3) are increasing concomitantly globally. Little is known about the effect of these interacting gases on growth, survival, and productivity of forest ecosystems. In this study we assess the effects of three successive years of exposure to combinations of elevated CO2 and O3 on growth responses in a five trembling aspen (Populus tremuloides) clonal mixture in a regenerating stand. The experiment is located in Rhinelander, Wisconsin, USA (45 degrees N 89 degrees W) and employs free air carbon dioxide and ozone enrichment (FACE) technology. The aspen stand was exposed to a factorial combination of four treatments consisting of elevated CO2 (560 ppm), elevated O3 (episodic exposure-90 microl l(-1) hour(-1)), a combination of elevated CO2 and O3, and ambient control in 30 m treatment rings with three replications. Our overall results showed that our three growth parameters including height, diameter and volume were increased by elevated CO2, decreased by elevated O3, and were not significantly different from the ambient control under elevated CO2 + O3. However, there were significant clonal differences in the responses; all five clones exhibited increased growth with elevated CO2, one clone showed an increase with elevated O3, and two clones showed an increase over the control with elevated CO2 + O3, two clones showed a decrease, and one was not significantly different from the control. Notably. there was a significant increase in current terminal shoot dieback with elevated CO2 during the 1999-2000 dormant season. Dieback was especially prominent in two of the five clones, and was attributed to those clones growing longer into the autumnal season where they were subject to frost. Our results show that elevated O3 negates expected positive growth effects of elevated CO2 in Populus tremuloides in the field, and suggest that future climate model predictions should take into account the offsetting effects of elevated O3 on CO2 enrichment when estimating future growth of trembling aspen stands.
Subject(s)
Carbon Dioxide/pharmacology , Ozone/pharmacology , Plant Shoots/drug effects , Salicaceae/drug effects , Air Pollutants/pharmacology , Air Pollution/statistics & numerical data , Atmosphere , Atmosphere Exposure Chambers , Cloning, Organism , Drug Interactions , Ecosystem , Forestry , Greenhouse Effect , Plant Shoots/growth & development , Salicaceae/growth & development , Seasons , Trees/drug effects , Trees/growth & development , United StatesABSTRACT
Atmospheric chemical composition affects foliar chemical composition, which in turn influences the dynamics of both herbivory and decomposition in ecosystems. We assessed the independent and interactive effects of CO2 and O3 fumigation on foliar chemistry of quaking aspen (Populus tremuloides) and paper birch (Betula papyrifera) at a Free-Air CO2 Enrichment (FACE) facility in northern Wisconsin. Leaf samples were collected at five time periods during a single growing season, and analyzed for nitrogen. starch and condensed tannin concentrations, nitrogen resorption efficiencies (NREs), and C:N ratios. Enriched CO2 reduced foliar nitrogen concentrations in aspen and birch; O3 only marginally reduced nitrogen concentrations. NREs were unaffected by pollution treatment in aspen, declined with 03 exposure in birch, and this decline was ameliorated by enriched CO2. C:N ratios of abscised leaves increased in response to enriched CO2 in both tree species. O3 did not significantly alter C:N ratios in aspen, although values tended to be higher in + CO2 + O3 leaves. For birch, O3 decreased C:N ratios under ambient CO2 and increased C:N ratios under elevated CO2. Thus, under the combined pollutants, the C:N ratios of both aspen and birch leaves were elevated above the averaged responses to the individual and independent trace gas treatments. Starch concentrations were largely unresponsive to CO2 and O3 treatments in aspen. but increased in response to elevated CO2 in birch. Levels of condensed tannins were negligibly affected by CO2 and O3 treatments in aspen, but increased in response to enriched CO2 in birch. Results from this work suggest that changes in foliar chemical composition elicited by enriched CO2 are likely to impact herbivory and decomposition, whereas the effects of O3 are likely to be minor, except in cases where they influence plant response to CO2.
Subject(s)
Betula/drug effects , Carbon Dioxide/pharmacology , Ozone/pharmacology , Plant Leaves/drug effects , Salicaceae/drug effects , Betula/chemistry , Betula/physiology , Carbon/metabolism , Ecosystem , Forestry , Nitrogen/metabolism , Plant Leaves/chemistry , Plant Leaves/physiology , Salicaceae/chemistry , Salicaceae/physiology , Starch/metabolism , Tannins/metabolism , Trees/chemistry , Trees/drug effects , Trees/physiology , United StatesABSTRACT
The effects of industrial pollution on allelic and genotypic structures of Norway spruce. European silver fir and European beech were investigated by means of isozyme analysis. In a mixed Norway spruce-silver fir forest stand in an area heavily polluted by sulphur dioxide and heavy metals in the region of Spis (eastern Slovakia), pairs of neighbouring damaged and apparently healthy trees were selected in two replicates (44 and 69 pairs in a heavily and moderately damaged stand, respectively). Pairwise sampling of trees with contrasting vitality was applied to reduce potential effects of site heterogeneity on the vitality of sampled trees. No significant differences in allelic and genotypic frequencies were found between sets of healthy and declining trees. There were differences in the single-locus heterozygosities, but these were not consistent between the replicates. However, the set of damaged trees exhibited higher levels of genetic multiplicity and diversity, possibly due to the deleterious effect of rare alleles under the conditions of air pollution. Consequently. following the decline of pollutant-sensitive trees, the remaining stand will be depleted of a part of alleles with unknown adaptive value to future selection pressures.
Subject(s)
Air Pollutants/pharmacology , Plants/genetics , Selection, Genetic , Abies/genetics , Abies/metabolism , Air Pollutants/analysis , Data Collection , Ecosystem , Fagus/genetics , Fagus/metabolism , Forestry , Gene Frequency/drug effects , Genetic Variation/drug effects , Genotype , Heterozygote , Isoenzymes/analysis , Metals, Heavy/pharmacology , Picea/genetics , Picea/metabolism , Plants/metabolism , Slovakia , Sulfur Dioxide/pharmacologyABSTRACT
Impacts of elevated atmospheric O3 and/or CO2 on three clones of aspen (Populus tremuloides Michx.) and birch (Betula papyrifera Marsh.) were studied to determine, whether or not elevated CO2 ameliorates O3-induced damage to leaf cells. The plants were exposed for 3 years at the Aspen FACE exposure site in Wisconsin (USA) prior to sampling for ultrastructural investigations on 19 June 1999. In the aspen clones, elevated CO2 increased chloroplast cover index, leaf and spongy mesophyll layer thickness, intercellular air space volume in mesophyll, amount of starch in chloroplasts and cytoplasmic lipids but decreased the number of plastoglobuli in chloroplasts. In contrast, elevated O3 decreased chloroplast cover index, starch content, and the proportion of cytoplasm and intercellular space in mesophyll, and increased the proportion of vacuoles, the amount of condensed vacuolar tannins and the number of plastoglobuli. Ozone also caused structural thylakoid injuries (dilation, distortion) and stromal condensation in chloroplasts, which was ameliorated by elevated CO2 by 5-66% in aspen clones and by 2-10% in birch. Birch ultrastructure was less affected by elevated CO2 or O3 stress compared to aspen. In the most O3-sensitive aspen clone, thinner leaves and cell walls, lower proportion of cell wall volume, and higher volume for vacuoles was found compared to more-tolerant clones.
Subject(s)
Air Pollutants/pharmacology , Betula/drug effects , Carbon Dioxide/pharmacology , Ozone/pharmacology , Plant Leaves/drug effects , Salicaceae/drug effects , Betula/metabolism , Betula/ultrastructure , Chloroplasts/drug effects , Chloroplasts/metabolism , Chloroplasts/ultrastructure , Databases as Topic , Drug Interactions , Ecosystem , Forestry , Microscopy, Electron , Plant Leaves/metabolism , Plant Leaves/ultrastructure , Salicaceae/metabolism , Salicaceae/ultrastructure , Vacuoles/drug effects , Vacuoles/metabolism , Vacuoles/ultrastructureABSTRACT
To determine whether elevated CO2 reduces or exacerbates the detrimental effects of O3 on aspen (Populus tremuloides Michx.). aspen clones 216 and 271 (O3 tolerant), and 259 (O3 sensitive) were exposed to ambient levels of CO2 and O3 or elevated levels of CO2, O3, or CO2 + O3 in the FACTS II (Aspen FACE) experiment, and physiological and molecular responses were measured and compared. Clone 259. the most O3-sensitive clone, showed the greatest amount of visible foliar symptoms as well as significant decreases in chlorophyll, carotenoid, starch, and ribulose-1, 5-bisphosphate carboxylase/oxygenase (Rubisco) concentrations and transcription levels for the Rubisco small subunit. Generally, the constitutive (basic) transcript levels for phenylalanine ammonialyase (PAL) and chalcone synthase (CHS) and the average antioxidant activities were lower for the ozone sensitive clone 259 as compared to the more tolerant 216 and 271 clones. A significant decrease in chlorophyll a, b and total (a + b) concentrations in CO2, O3, and CO2 + O3 plants was observed for all clones. Carotenoid concentrations were also significantly lower in all clones; however. CHS transcript levels were not significantly affected, suggesting a possible degradation of carotenoid pigments in O3-stressed plants. Antioxidant activities and PAL and 1-aminocyclopropane-l-carboxylic acid (ACC)-oxidase transcript levels showed a general increase in all O3 treated clones, while remaining low in CO2 and CO2 + O3 plants (although not all differences were significant). Our results suggest that the ascorbate-glutathione and phenylpropanoid pathways were activated under ozone stress and suppressed during exposure to elevated CO2. Although CO2 + O2 treatment resulted in a slight reduction of O3-induced leaf injury, it did not appear to ameliorate all of the harmful affects of O3 and, in fact. may have contributed to an increase in chloroplast damage in all three aspen clones.
Subject(s)
Air Pollutants/pharmacology , Carbon Dioxide/pharmacology , Ozone/pharmacology , Plant Leaves/drug effects , Salicaceae/drug effects , Antioxidants/metabolism , Ascorbic Acid/metabolism , Atmosphere Exposure Chambers , Carotenoids/metabolism , Chlorophyll/metabolism , Cloning, Organism , Drug Interactions , Gene Expression Profiling , Glutathione/metabolism , Phenylpropionates/metabolism , Photosynthesis/genetics , Photosynthesis/physiology , Plant Leaves/genetics , Plant Leaves/metabolism , Reactive Oxygen Species/metabolism , Ribulose-Bisphosphate Carboxylase/metabolism , Salicaceae/genetics , Salicaceae/metabolism , Sensitivity and SpecificityABSTRACT
Rising atmospheric CO2 may stimulate future forest productivity, possibly increasing carbon storage in terrestrial ecosystems, but how tropospheric ozone will modify this response is unknown. Because of the importance of fine roots to the belowground C cycle, we monitored fine-root biomass and associated C fluxes in regenerating stands of trembling aspen, and mixed stands of trembling aspen and paper birch at FACTS-II, the Aspen FACE project in Rhinelander, Wisconsin. Free-air CO2 enrichment (FACE) was used to elevate concentrations of CO2 (average enrichment concentration 535 µl l-1) and O3 (53 nl l-1) in developing forest stands in 1998 and 1999. Soil respiration, soil pCO2, and dissolved organic carbon in soil solution (DOC) were monitored biweekly. Soil respiration was measured with a portable infrared gas analyzer. Soil pCO2 and DOC samples were collected from soil gas wells and tension lysimeters, respectively, at depths of 15, 30, and 125 cm. Fine-root biomass averaged 263 g m-2 in control plots and increased 96% under elevated CO2. The increased root biomass was accompanied by a 39% increase in soil respiration and a 27% increase in soil pCO2. Both soil respiration and pCO2 exhibited a strong seasonal signal, which was positively correlated with soil temperature. DOC concentrations in soil solution averaged ~12 mg l-1 in surface horizons, declined with depth, and were little affected by the treatments. A simplified belowground C budget for the site indicated that native soil organic matter still dominated the system, and that soil respiration was by far the largest flux. Ozone decreased the above responses to elevated CO2, but effects were rarely statistically significant. We conclude that regenerating stands of northern hardwoods have the potential for substantially greater C input to soil due to greater fine-root production under elevated CO2. Greater fine-root biomass will be accompanied by greater soil C efflux as soil respiration, but leaching losses of C will probably be unaffected.
ABSTRACT
We studied root growth and respiration of potted plants and field-grown aspen trees (Populus tremuloides Michx.) exposed to ambient or twice-ambient ozone. Root dry weight of potted plants decreased up to 45% after 12 weeks of ozone treatment, and root system respiration decreased by 27%. The ozone-induced decrease in root system respiration of potted plants was more closely correlated with decreased root dry weight than with specific root respiration, suggesting that aspen root metabolism was less affected by ozone than root growth. We used minirhizotrons to study the appearance and disappearance of roots in the field. Length of live roots of field-grown trees increased rapidly early in the season and peaked by midseason in association with a decrease in root production and an increase in root disappearance. In the twice-ambient ozone treatment, live root lengths were 17% less than those of controls, but the effect was not statistically significant. Seasonal soil CO(2) efflux of field-grown trees decreased significantly in the ozone treatments, but because differences in live root length were not significant and root dry weights were not available, the effect on CO(2) efflux could not be attributed directly to decreased root growth.
ABSTRACT
Rooted cuttings from three aspen (Populus tremuloides Michx.) clones (216, 271 and 259, classified as high, intermediate and low in O(3) tolerance, respectively) were exposed to either diurnal O(3) profiles simulating those of Michigan's Lower Peninsula (episodic treatments), or diurnal square-wave O(3) treatments in open-top chambers in northern Michigan, USA. Ozone was dispensed in chambers ventilated with charcoal-filtered (CF) air. In addition, seedlings were compared to rooted cuttings in their response to episodic O(3) treatments. Early in the season, O(3) caused decreased photosynthetic rates in mature leaves of all clones, whereas only the photosynthetic rates of recently mature leaves of the O(3)-sensitive Clone 259 decreased in response to O(3) exposure. During midseason, O(3) caused decreased photosynthetic rates of both recently mature and mature leaves of the O(3)-sensitive Clone 259, but it had no effect on the photosynthetic rate of recently mature leaves of the O(3)-tolerant Clone 216. Late in the season, however, photosynthetic rates of both recently mature and mature leaves of Clone 216 were lower than those of the control plants maintained in CF air. Ozone decreased the photosynthetic rate of mature leaves of Clone 271, but it increased or had no effect on the photosynthetic rate of recently mature leaves. Photosynthetic response patterns of seedlings to O(3) treatment were similar to those of the clones, but total magnitude of the response was less, perhaps reflecting the diverse genotypes of the seedling population. Early leaf abscission was observed in all clones exposed to O(3); however, Clones 216 and 259 lost more leaf area than Clone 271. By late August, leaf area in the highest O(3) treatment had decreased relative to the controls by 26, 24 and 9% for Clones 216, 259 and 271, respectively. Ozone decreased whole-tree photosynthesis in all clones, and the decrease was consistently less in Clone 271 (23%) than in Clones 216 (56%) and 259 (56%), and was accompanied by declines in total biomass of 19, 28 and 47%, respectively. The relationship between biomass and whole-tree photosynthesis indicates that the negative impact of O(3) on biomass in the clones was determined largely by lower photosynthetic productivity of the foliage, rather than by potential changes in the carbon relations of other plant organs.