Genotypic variation in the response of two perennial grass species to elevated carbon dioxide

Shoot and reproductive biomass of genotypes of Bromus erectus and Dactylis glomerata grown in competition at ambient and elevated CO₂ were examined for 2 consecutive years in order to test whether genetic variation in those traits exists and whether it is maintained over time. At the species level, a positive CO₂ response of shoot biomass of both species was only found in the first year of treatment. At the genotype level, no significant CO₂2genotype interaction was found at any single harvest either for vegetative or reproductive biomass of either species. Analysis over time, however, indicated that there is a potential for evolutionary adaptation only for D. glomerata: (1) repeated measures ANOVA detected a marginally significant CO₂2genotype2time interaction for shoot biomass, because the range of the genotypes CO₂ response increased over time; (2) genotypes that displayed the highest response during the first year under elevated CO₂ also showed the highest response the second year. Null (B. erectus) or weak (D. glomerata) selective potentials of elevated CO₂ were detected in this experiment, but short time series could underestimate this potential with perennial species.     

Plant-insect herbivore interactions in elevated CO(2) environments

The increasing concentration of CO(2) in the atmosphere is expected to lead to global changes in the physical environment of terrestrial organisms. We are beginning to understand how these changes are transmitted into pervasive effects on the interactions between plants and their leaf-feeding insect herbivores. An elevated CO(2) atmosphere often stimulates plant carbon assimilation and growth and alters carbon allocation patterns. This, in turn, determines the quality of plants as resources for herbivorous insects. These 'quality' factors include: the concentrations of water, nitrogen and allelochemicals in host-plant leaves, and the toughness and starch and fiber content of leaf tissue. Because these parameters change in plants grown in enriched CO(2) environments, the doubled CO(2) levels anticipated for the next century will alter the dynamics of plant-insect herbivore interactions because herbivore consumption, growth and fitness are affected by the typically lower quality of plants grown under these conditions.     

Nitrogen deposition limits photosynthetic response to elevated CO2 differentially in a dioecious species

Sexual dimorphisms of dioecious plants are important in controlling and maintaining sex ratios under changing climate environments. Yet, little is known about sex-specific responses to elevated CO₂ with soil nitrogen (N) deposition. To investigate sex-related physiological and biochemical responses to elevated CO₂ with N deposition, Populus cathayana Rehd. was employed as a model species. The cuttings were subjected to two CO₂ regimes (350 and 700???mol?mol^?1) with two N levels (0 and 5?g?N?m^?2?year^?1). Our results showed that elevated CO₂ and N deposition separately increased the total number of leaves, leaf area (LA), leaf mass, net photosynthetic rate (P _n), light saturated photosynthetic rate (P _max), chlorophyll a (Chl a), and chlorophyll a to chlorophyll b ratio (Chl a/b) in both males and females of P. cathayana. However, the effects on LA, leaf mass, P _n, P _max, Chl a and Chl a/b were weakened under the combined treatment of elevated CO₂ and N deposition. Males had higher leaf mass, P _n, P _max, apparent quantum yield (??), carboxylation efficiency (CE), Chl a, Chl a/b, leaf N, and root carbon to N ratio (C/N) than did females under elevated CO₂ with N deposition. In contrast to males, females had significantly higher levels of soluble sugars in leaves and greater starch accumulation in roots and stems under the same condition. The results of the present work imply that P. cathayana females are more responsive and suffer from greater negative effects on growth and photosynthetic capacity than do males when grown under elevated CO₂ with soil N deposition.     

Fermentation and malate metabolism in response to elevated CO2 concentrations in two strawberry cultivars

Concentrations of acetaldehyde, ethanol, ethyl acetate (EA), organic acids and activities and gene expression of alcohol dehydrogenase (ADH; EC 1.1.1.1), pyruvate decarboxylase (PDC; EC 4.1.1.1), alcohol acyltransferase (AAT; EC 1.4.1.14), malate dehydrogenase (MDH; EC 1.1.1.37), malic enzyme (ME; EC 1.1.1.40) and glutamate dehydrogenase (EC 1.4.1.14) were investigated in two strawberry ( Fragaria × ananassa Duch) cultivars with different responses to CO₂ during storage. 'Jewel' fruit treated with CO₂ accumulated acetaldehyde and ethanol but little EA, while 'Cavendish' accumulated little acetaldehyde or ethanol but accumulated EA. In CO₂-treated fruit, PDC activity was positively correlated with EA accumulation in 'Jewel' but not in 'Cavendish', while no differential effect of atmosphere was observed on its gene expression. ADH activity and gene expression show a correlation with ethanol accumulation in 'Cavendish'. In 'Jewel', there was a positive correlation between ADH gene expression and enzyme activity; however, this correlation does not explain ethanol accumulation in this cultivar. EA accumulation did not show any correlation with AAT activity and gene expression in any of the cultivars. Succinate concentrations were highest and those of malate lowest in CO₂-treated fruit of both cultivars, but MDH and ME activities were not affected by CO₂. Gene expression of MDH and ME were not affected by atmosphere in 'Cavendish', although in 'Jewel' the MDH expression was slightly lower in CO₂- than air-treated fruit. The results of this study show that differences in fermentation products and malate accumulation in CO₂-treated strawberry fruit are not consistently correlated with enzyme activities and gene expression.     

Interspecific variation in the growth response of plants to an elevated ambient CO2 concentration

The effect of a doubling in the atmospheric CO₂ concentration on the growth of vegetative whole plants was investigated. In a compilation of literature sources, the growth stimulation of 156 plant species was found to be on average 37%. This enhancement is small compared to what could be expected on the basis of CO₂-response curves of photosynthesis. The causes for this stimulation being so modest were investigated, partly on the basis of an experiment with 10 wild plant species. Both the source-sink relationship and size constraints on growth can cause the growth-stimulating effect to be transient.Data on the 156 plant species were used to explore interspecific variation in the response of plants to high CO₂. The growth stimulation was larger for C₃ species than for C₄ plants. However the difference in growth stimulation is not as large as expected as C₄ plants also significantly increased in weight (41% for C₃ vs. 22% for C₄). The few investigated CAM species were stimulated less in growth (15%) than the average C₄ species. Within the group of C₃ species, herbaceous crop plants responded more strongly than herbaceous wild species (58%vs. 35%) and potentially fast-growing wild species increased more in weight than slow-growing species (54%vs. 23%). C₃ species capable of symbiosis with N₂-fixing organisms had higher growth stimulations compared to other C₃ species. A common denominator in these 3 groups of more responsive C₃ plants might be their large sink strength. Finally, there was some tendency for herbaceous dicots to show a larger response than monocots. Thus, on the basis of this literature compilation, it is concluded that also within the group of C₃ species differences exist in the growth response to high CO₂.Abbreviations LAR leaf area ratio - LWR leaf weight ratio - NAR net assimilation rate - PS_a rate of photosynthesis per unit leaf area - RGR relative growth rate - RWR root weight ratio - SLA specific leaf area     

Progressive N limitation of plant response to elevated CO2: a microbiological perspective

A major uncertainty in predicting long-term ecosystem C balance is whether stimulation of net primary production will be sustained in future atmospheric CO₂ scenarios. Immobilization of nutrients (N in particular) in plant biomass and soil organic matter (SOM) provides negative feedbacks to plant growth and may lead to progressive N limitation (PNL) of plant response to CO₂ enrichment. Soil microbes mediate N availability to plants by controlling litter decomposition and N transformations as well as dominating biological N fixation. CO₂-induced changes in C inputs, plant nutrient demand and water use efficiency often have interactive and contrasting effects on microbes and microbially mediated N processes. One critical question is whether CO₂-induced N accumulation in plant biomass and SOM will result in N limitation of microbes and subsequently cause them to obtain N from alternative sources or to alter the ecosystem N balance. We reviewed the experimental results that examined elevated CO₂ effects on microbial parameters, focusing on those published since 2000. These results in general show that increased C inputs dominate the CO₂ impact on microbes, microbial activities and their subsequent controls over ecosystem N dynamics, potentially enhancing microbial N acquisition and ecosystem N retention. We reason that microbial mediation of N availability for plants under future CO₂ scenarios will strongly depend on the initial ecosystem N status, and the nature and magnitude of external N inputs. Consequently, microbial processes that exert critical controls over long-term N availability for plants would be ecosystem-specific. The challenge remains to quantify CO₂-induced changes in these processes, and to extrapolate the results from short-term studies with step-up CO₂ increases to native ecosystems that are already experiencing gradual changes in the CO₂ concentration.     

The response of plants to elevated CO2

Summary Communities, consisting of six co-occurring, disturbed site annuals, were subjected to CO₂ unenriched (300 ppm) and to CO₂ enriched (450 and 600 ppm) atmospheres at different levels of light and nutrient availability. In general, total community production increased with CO₂ enrichment to 450 ppm, but a further increase in CO₂ to 600 ppm had little or no effect. The response of community production to CO₂ level was not affected by nutrient availability but was affected by light level.Of the six species, four display C₃ metabolism. The proportion of total community production contributed by these species increased as a result of CO₂ enrichment, and was dependent upon both light and nutrient availability. The relative success of some species, particularly in terms of reproduction (total seed biomass), was significantly altered by CO₂ concentration depending on the level of nutrients. There were not only changes in reproductive success (seed biomass) and shoot biomass but also changes in the proportion of biomass allocated to seed.These experiments demonstrate that CO₂ enrichment does affect annual plant communities both in terms of productivity and species composition and that the affect of CO₂ on such system may depend upon other resources such as light and nutrients.     

The response of plants to elevated CO2

Tree saplings, two groups of three species from each of two deciduous tree communities, were grown in competition at three CO₂ concentrations and two light levels. After one growing season, biomass was measured to assess the effect of CO₂ on community structure, and nitrogen and phosphorus concentrations were measured for leaves, stems, and roots of all trees. Gas-exchange measurements were made on the same species grown under the same CO₂ concentrations.Photosynthetic capacity (rate of photosynthesis at saturating CO₂ and light) tended to decline as CO₂ concentration increased, but differences were not statistically significant. Stomatal conductance declined significantly as CO₂ increased. Nitrogen and phosphorus concentrations generally declined as CO₂ increased, but there were some unexpected patterns in roots and stems. CO₂ concentration did not significantly affect the overall growth of either community after one season, but the relative biomass of each species changed in a complex way, depending on CO₂ light level, and community.     

The response of plants to elevated CO2

Summary Four coexisting annual plant species were grown in competition at three levels of CO₂ (300, 600, and 1,200 ppm) and two levels of soil moisture (moist and dry). Plant height was higher at high CO₂ concentrations for the three C₃ species but not for the C₄ species (Amaranthus retroflexus). Total community biomass increased with increasing CO₂ at both soil moisture levels. The contribution of each species to total community biomass was influenced by CO₂ concentration. The effects were especially pronounced for Polygonum pensylvanicum which contributed more to community production as CO₂ and soil moisture increased. Amaranthus behaved in exactly the reverse way; it did best under ambient CO₂ and dry soil moisture conditions. The results suggest that changes in competitive interactions and community structure will occur with the anticipated rise in global CO₂ concentration.     

Long-term effects of elevated atmospheric CO2 on below-ground biomass and transformations to soil organic matter in grassland

We determined the effects of elevated [CO₂] on the quantity and quality of below-ground biomass and several soil organic matter pools at the conclusion of an eight-year CO₂ enrichment experiment on native tallgrass prairie. Plots in open-top chambers were exposed continuously to ambient and twice-ambient [CO₂] from early April through late October of each year. Soil was sampled to a depth of 30 cm beneath and next to the crowns of C4 grasses in these plots and in unchambered plots. Elevated [CO₂] increased the standing crops of rhizomes (87%), coarse roots (46%), and fibrous roots (40%) but had no effect on root litter (mostly fine root fragments and sloughed cortex material >500 μm). Soil C and N stocks also increased under elevated [CO₂], with accumulations in the silt/clay fraction over twice that of particulate organic matter (POM; >53 μm). The mostly root-like, light POM (density ≤1.8 Mg m^-3) appeared to turn over more rapidly, while the more amorphous and rendered heavy POM (density >1.8 Mg m^-3) accumulated under elevated [CO₂]. Overall, rhizome and root C:N ratios were not greatly affected by CO₂ enrichment. However, elevated [CO₂] increased the C:N ratios of root litter and POM in the surface 5 cm and induced a small but significant increase in the C:N ratio of the silt/clay fraction to a depth of 15 cm. Our data suggest that 8 years of CO₂ enrichment may have affected elements of the N cycle (including mineralization, immobilization, and asymbiotic fixation) but that any changes in N dynamics were insufficient to prevent significant plant growth responses. This revised version was published online in June 2006 with corrections to the Cover Date.     

Tree species diversity interacts with elevated CO2 to induce a greater root system response

As a consequence of land‐use change and the burning of fossil fuels, atmospheric concentrations of CO₂ are increasing and altering the dynamics of the carbon cycle in forest ecosystems. In a number of studies using single tree species, fine root biomass has been shown to be strongly increased by elevated CO₂. However, natural forests are often intimate mixtures of a number of co‐occurring species. To investigate the interaction between tree mixture and elevated CO₂, Alnus glutinosa, Betula pendula and Fagus sylvatica were planted in areas of single species and a three species polyculture in a free‐air CO₂ enrichment study (BangorFACE). The trees were exposed to ambient or elevated CO₂ (580 μmol mol^?1) for 4 years. Fine and coarse root biomass, together with fine root turnover and fine root morphological characteristics were measured. Fine root biomass and morphology responded differentially to the elevated CO₂ at different soil depths in the three species when grown in monocultures. In polyculture, a greater response to elevated CO₂ was observed in coarse roots to a depth of 20 cm, and fine root area index to a depth of 30 cm. Total fine root biomass was positively affected by elevated CO₂ at the end of the experiment, but not by species diversity. Our data suggest that existing biogeochemical cycling models parameterized with data from species grown in monoculture may be underestimating the belowground response to global change.     

Soil microbial response in tallgrass prairie to elevated CO2

Terrestrial responses to increasing atmospheric CO₂ are important to the global carbon budget. Increased plant production under elevated CO₂ is expected to increase soil C which may induce N limitations. The objectives of this study were to determine the effects of increased CO₂ on 1) the amount of carbon and nitrogen stored in soil organic matter and microbial biomass and 2) soil microbial activity. A tallgrass prairie ecosystem was exposed to ambient and twice-ambient CO₂ concentrations in open-top chambers in the field from 1989 to 1992 and compared to unchambered ambient CO₂ during the entire growing season. During 1990 and 1991, N fertilizer was included as a treatment. The soil microbial response to CO₂ was measured during 1991 and 1992. Soil organic C and N were not significantly affected by enriched atmospheric CO₂. The response of microbial biomass to CO₂ enrichment was dependent upon soil water conditions. In 1991, a dry year, CO₂ enrichment significantly increased microbial biomass C and N. In 1992, a wet year, microbial biomass C and N were unaffected by the CO₂ treatments. Added N increased microbial C and N under CO₂ enrichment. Microbial activity was consistently greater under CO₂ enrichment because of better soil water conditions. Added N stimulated microbial activity under CO₂ enrichment. Increased microbial N with CO₂ enrichment may indicate plant production could be limited by N availability. The soil system also could compensate for the limited N by increasing the labile pool to support increased plant production with elevated atmospheric CO₂. Longer-term studies are needed to determine how tallgrass prairie will respond to increased C input.     

Intra- specific variation in response of Jatropha (Jatropha curcas L.) to elevated CO2 conditions

Twenty genotypes of Jatropha collected from diverse eco-geographic regions from the states of Chhattisgarh (3), Andhra Pradesh (12), Rajasthan (4) and Uttarakhand (1) of India were subjected to elevated CO₂ conditions. All the genotypes showed significant difference (p < 0.05 and 0.01) in the phenotypic traits in both the environments (elevated and ambient) and genotype x environment interaction. Among the physiological traits recorded, maximum photosynthetic rate was observed in IC565048 (48.8 μmol m⁻² s⁻¹) under ambient controlled conditions while under elevated conditions maximum photosynthetic rate was observed in IC544678 (41.3 μmol m⁻² s⁻¹), and there was no significant difference in the genotype x environment interaction. Stomatal conductance (Gs) emerged as the key factor as it recorded significant difference among the genotypes, between the environments and also genotype x environment interaction. The Gs and transpiration (E) recorded a significant decline in the genotypes under the elevated CO₂ condition over the ambient control. Under elevated CO₂ conditions, the minimum values recorded for Gs and E were 0.03 mmol m⁻² s⁻¹ and 0.59 mmol m⁻² s⁻¹ respectively in accession IC565039, while the maximum values for Gs and E were 1.8 mmol m⁻² s⁻¹ and 11.5 mmol m⁻² s⁻¹ as recorded in accession IC544678. The study resulted in the identification of potential climate ready genotypes viz. IC471314, IC544654, IC541634, IC544313, and IC471333 for future use.     

Genetic variation in expression of defense phenotype may mediate evolutionary adaptation of Asclepias syriaca to elevated CO2

How species interactions may modify the effects of environmental change on evolutionary adaptation is poorly understood. Elevated CO₂ is known to alter plant–herbivore interactions, but the evolutionary consequences for plant populations have received little attention. We conducted an experiment to determine the effects of elevated CO₂ and herbivory by a specialist insect herbivore (Danaus plexippus) on the expression of constitutive and induced plant defense traits in five genotypes of Asclepias syriaca, and assessed the heritability of these traits. We also examined changes in relative fitness among plant genotypes in response to altered CO₂ and herbivory. The expression of plant defense traits varied significantly among genotypes. Elevated CO₂ increased plant growth and physical defenses (toughness and latex), but decreased investment in chemical defenses (cardenolides). We found no effect of elevated CO₂ on plant induction of cardenolides in response to caterpillar herbivory. Elevated CO₂ decreased the expression of chemical defenses (cardenolides) to a different extent depending on plant genotype. Differential effects of CO₂ on plant defense expression, rather than direct effects on relative fitness, may alter A. syriaca adaptation to changing climate.     

Species-specific and needle age-related responses of photosynthesis in two Pinus species to long-term exposure to elevated CO2 concentration

There is, so far, no common conclusion about photosynthetic responses of trees to long-term exposure to elevated CO₂. Photosynthesis and specific leaf area (SLA) of 1-year-old and current-year needles in Pinus koraiensis and P. sylvestriformis grown in open-top chambers were measured monthly for consecutive two growing seasons (2006, 2007) after 8–9 years of CO₂ enrichment in northeastern China, to better understand species-specific and needle age-related responses to elevated CO₂ (500 μmol mol⁻¹ CO₂). The light-saturated photosynthetic rates (P _Nsat) increased in both species at elevated CO₂, but the stimulation magnitude varied with species and needle age. Photosynthetic acclimation to elevated CO₂, in terms of reduced V _cmax (maximum carboxylation rate) and J _max (maximum electron transport rate), was found in P. koraiensis but not in P. sylvestriformis. The photosynthetic parameters (V _cmax, J _max, P _Nsat) measured in different-aged needles within each species responded to elevated CO₂ similarly, but elevated CO₂ resulted in much pronounced variations of those parameters in current-year needles than in 1-year-old needles within each species. This result indicated that needle age affects the magnitude but not the patterns of photosynthetic responses to long-term CO₂ enrichment. The present study indicated that different species associated with different physioecological properties responded to elevated CO₂ differently. As global change and CO₂ enrichment is more or less a gradual rather than an abrupt process, long-term global change experiments with different plant species are still needed to character and better predict the global change effects on terrestrial ecosystems.     

Genotypic variation in source and sink traits affects the response of photosynthesis and growth to elevated atmospheric CO2

This study aimed to understand the response of photosynthesis and growth to e-CO₂ conditions (800 vs. 400 μmol mol⁻¹) of rice genotypes differing in source–sink relationships. A proxy trait called local C source–sink ratio was defined as the ratio of flag leaf area to the number of spikelets on the corresponding panicle, and five genotypes differing in this ratio were grown in a controlled greenhouse. Differential CO₂ resources were applied either during the 2 weeks following heading (EXP1) or during the whole growth cycle (EXP2). Under e-CO₂, low source–sink ratio cultivars (LSS) had greater gains in photosynthesis, and they accumulated less nonstructural carbohydrate in the flag leaf than high source–sink ratio cultivars (HSS). In EXP2, grain yield and biomass gain was also greater in LSS probably caused by their strong sink. Photosynthetic capacity response to e-CO₂ was negatively correlated across genotypes with local C source–sink ratio, a trait highly conserved across environments. HSS were sink-limited under e-CO₂, probably associated with low triose phosphate utilization (TPU) capacity. We suggest that the local C source–sink ratio is a potential target for selecting more CO₂-responsive cultivars, pending validation for a broader genotypic spectrum and for field conditions.     

Interspecific variation and elevated CO2 influence the relationship between plant chemical resistance and regrowth tolerance

To understand how comprehensive plant defense phenotypes will respond to global change, we investigated the legacy effects of elevated CO₂ on the relationships between chemical resistance (constitutive and induced via mechanical damage) and regrowth tolerance in four milkweed species (Asclepias). We quantified potential resistance and tolerance trade‐offs at the physiological level following simulated mowing, which are relevant to milkweed ecology and conservation. We examined the legacy effects of elevated CO₂ on four hypothesized trade‐offs between the following: (a) plant growth rate and constitutive chemical resistance (foliar cardenolide concentrations), (b) plant growth rate and mechanically induced chemical resistance, (c) constitutive resistance and regrowth tolerance, and (d) regrowth tolerance and mechanically induced resistance. We observed support for one trade‐off between plant regrowth tolerance and mechanically induced resistance traits that was, surprisingly, independent of CO₂ exposure. Across milkweed species, mechanically induced resistance increased by 28% in those plants previously exposed to elevated CO_2. In contrast, constitutive resistance and the diversity of mechanically induced chemical resistance traits declined in response to elevated CO₂ in two out of four milkweed species. Finally, previous exposure to elevated CO₂ uncoupled the positive relationship between plant growth rate and regrowth tolerance following damage. Our data highlight the complex and dynamic nature of plant defense phenotypes under environmental change and question the generality of physiologically based defense trade‐offs.