Modelling the effects of elevated atmospheric CO2 on crown development, light interception and photosynthesis of poplar in open top chambers

An open-top chamber experiment was carried out to examine the likely effects of elevated atmospheric [CO₂] on architectural as well as on physiological characteristics of two poplar clones ( Populus trichocarpa × P. deltoides clone Beaupré and P. deltoides × P. nigra clone Robusta). Crown architectural parameters required as input parameters for a three-dimensional (3D) model of poplar structure, such as branching frequency and position, branch angle, internode length and its distribution pattern, leaf size and orientation, were measured following growth in ambient and elevated [CO₂ ] (ambient + 350 μmol mol^–1) treated open-top chambers. Based on this information, the light interception and photosynthesis of poplar canopies in different [CO₂] treatments were simulated using the 3D poplar tree model and a 3D radiative transfer model at various stages of the growing season. The first year experiments and modelling results showed that the [CO₂] enrichment had effects on light intercepting canopy structure as well as on leaf photosynthesis properties. The elevated [CO₂] treatment resulted in an increase of leaf area, canopy photosynthetic rate and above-ground biomass production of the two poplar clones studied. However, the structural components responded less than the process components to the [CO₂] enrichment. Among the structural components, the increase of LAI contributed the most to the canopy light interception and canopy photosynthesis; the change of other structural aspects as a whole caused by the [CO₂] enrichment had little effect on daily canopy light interception and photosynthesis.     

Growth in elevated CO2 enhances temperature response of photosynthesis in wheat

The temperature dependence of C₃ photosynthesis may be altered by the growth environment. The effects of long-term growth in elevated CO₂ on photosynthesis temperature response have been investigated in wheat ( Triticum aestivum L.) grown in controlled chambers with 370 or 700 μmol mol⁻¹ CO₂ from sowing through to anthesis. Gas exchange was measured in flag leaves at ear emergence, and the parameters of a biochemical photosynthesis model were determined along with their temperature responses. Elevated CO₂ slightly decreased the CO₂ compensation point and increased the rate of respiration in the light and ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) V_cmax, although the latter effect was reversed at 15°C. With elevated CO₂, J_max decreased in the 15–25°C temperature range and increased at 30 and 35°C. The temperature response (activation energy) of V_cmax and J_max increased with growth in elevated CO₂. CO₂ enrichment decreased the ribulose 1,5-bisphosphate (RuBP)-limited photosynthesis rates at lower temperatures and increased Rubisco- and RuBP-limited rates at higher temperatures. The results show that the photosynthesis temperature response is enhanced by growth in elevated CO₂. We conclude that if temperature acclimation and factors such as nutrients or water availability do not modify or negate this enhancement, the effects of future increases in air CO₂ on photosynthetic electron transport and Rubisco kinetics may improve the photosynthetic response of wheat to global warming.     

Increasing growth temperature reduces the stimulatory effect of elevated CO2 on photosynthesis or biomass in two perennial species

We examined how anticipated changes in CO₂ concentration and temperature interacted to alter plant growth, harvest characteristics and photosynthesis in two cold-adapted herbaceous perennials, alfalfa ( Medicago sativa L. cv. Arc) and orchard grass ( Dactylis glomerata L. cv. Potomac). Plants were grown at two CO₂ concentrations (362 [ambient] and 717 [elevated] μmol mol⁻¹ CO₂) and four constant day/night temperatures of 15, 20, 25 and 30°C in controlled environmental chambers. Elevated CO₂ significantly increased total plant biomass and protein over a wide range of temperatures in both species. Stimulation of photosynthetic rate, however, was eliminated at the highest growth temperature in M. sativa and relative stimulation of plant biomass and protein at high CO₂ declined as temperature increased in both species. Lack of a synergistic effect between temperature and CO₂ was unexpected since elevated CO₂ reduces the amount of carbon lost via photorespiration and photorespiration increases with temperature. Differences between anticipated stimulatory effects of CO₂ and temperature and whole plant single and leaf measurements are discussed. Data from this study suggest that stimulatory effects of atmospheric CO₂ on growth and photosynthesis may decline with anticipated increases in global temperature, limiting the degree of carbon storage in these two perennial species.     

Growth and photosynthetic response of three soybean cultivars to simultaneous increases in growth temperature and CO2

Three soybean ( Glycine max L. Merr.) cultivars (Maple Glen, Clark and CNS) were exposed to three CO₂ concentrations (370, 555 and 740 μmol mol⁻¹) and three growth temperatures (20/15°, 25/20° and 31/26°C, day/night) to determine intraspecific differences in single leaf/whole plant photosynthesis, growth and partitioning, phenology and final biomass. Based on known carboxylation kinetics, a synergistic effect between temperature and CO₂ on growth and photosynthesis was predicted since elevated CO₂ increases photosynthesis by reducing photorespiration and photorespiration increases with temperature. Increasing CO₂ concentrations resulted in a stimulation of single leaf photosynthesis for 40–60 days after emergence (DAE) at 20/15°C in all cultivars and for Maple Glen and CNS at all temperatures. For Clark, however, the onset of flowering at warmer temperatures coincided with the loss of stimulation in single leaf photosynthesis at elevated CO₂ concentrations. Despite the season-long stimulation of single leaf photosynthesis, elevated CO₂ concentrations did not increase whole plant photosynthesis except at the highest growth temperature in Maple Glen and CNS, and there was no synergistic effect on final biomass. Instead, the stimulatory effect of CO₂ on growth was delayed by higher temperatures. Data from this experiment suggest that: (1) intraspecific variation could be used to select for optimum soybean cultivars with future climate change; and (2) the relationship between temperature and CO₂ concentration may be expressed differently at the leaf and whole plant levels and may not solely reflect known changes in carboxylation kinetics.     

Coppicing shifts CO2 stimulation of poplar productivity to above-ground pools: a synthesis of leaf to stand level results from the POP/EUROFACE experiment

A poplar short rotation coppice (SRC) grown for the production of bioenergy can combine carbon (C) storage with fossil fuel substitution. Here, we summarize the responses of a poplar ( Populus ) plantation to 6 yr of free air CO₂ enrichment (POP/EUROFACE consisting of two rotation cycles). We show that a poplar plantation growing in nonlimiting light, nutrient and water conditions will significantly increase its productivity in elevated CO₂ concentrations ([CO₂]). Increased biomass yield resulted from an early growth enhancement and photosynthesis did not acclimate to elevated [CO₂]. Sufficient nutrient availability, increased nitrogen use efficiency (NUE) and the large sink capacity of poplars contributed to the sustained increase in C uptake over 6 yr. Additional C taken up in high [CO₂] was mainly invested into woody biomass pools. Coppicing increased yield by 66% and partly shifted the extra C uptake in elevated [CO₂] to above-ground pools, as fine root biomass declined and its [CO₂] stimulation disappeared. Mineral soil C increased equally in ambient and elevated [CO₂] during the 6 yr experiment. However, elevated [CO₂] increased the stabilization of C in the mineral soil. Increased productivity of a poplar SRC in elevated [CO₂] may allow shorter rotation cycles, enhancing the viability of SRC for biofuel production.     

The role of temperature in determining the stimulation of CO2 assimilation at elevated carbon dioxide concentration in soybean seedlings

Soybean ( Glycine max cv. Clark) was grown at both ambient (ca 350 μmol mol⁻¹) and elevated (ca 700 μmol mol⁻¹) CO₂ concentration at 5 growth temperatures (constant day/night temperatures of 20, 25, 30, 35 and 40°C) for 17–22 days after sowing to determine the interaction between temperature and CO₂ concentration on photosynthesis (measured as A, the rate of CO₂ assimilation per unit leaf area) at both the single leaf and whole plant level. Single leaves of soybean demonstrated increasingly greater stimulation of A at elevated CO₂ as temperature increased from 25 to 35°C (i.e. optimal growth rates). At 40°C, primary leaves failed to develop and plants eventually died. In contrast, for both whole plant A and total biomass production, increasing temperature resulted in less stimulation by elevated CO₂ concentration. For whole plants, increased CO₂ stimulated leaf area more as growth temperature increased. Differences between the response of A to elevated CO₂ for single leaves and whole plants may be related to increased self-shading experienced by whole plants at elevated CO₂ as temperature increased. Results from the present study suggest that self-shading could limit the response of CO₂ assimilation rate and the growth response of soybean plants if temperature and CO₂ increase concurrently, and illustrate that light may be an important consideration in predicting the relative stimulation of photosynthesis by elevated CO₂ at the whole plant level.     

Stem wood properties of mature Norway spruce after 3 years of continuous exposure to elevated [CO2] and temperature

The objective of the study was to investigate the interactive effects of elevated atmospheric carbon dioxide concentration, [CO₂], and temperature on the wood properties of mature field-grown Norway spruce ( Picea abies (L.) Karst.) trees. Material for the study was obtained from an experiment in Flakaliden, northern Sweden, where trees were grown for 3 years in whole-tree chambers at ambient (365 μmol mol⁻¹) or elevated [CO₂] (700 μmol mol⁻¹) and ambient or elevated air temperature (ambient +5.6 °C in winter and ambient +2.8 °C in summer). Elevated temperature affected both wood chemical composition and structure, but had no effect on stem radial growth. Elevated temperature decreased the concentrations of acetone-soluble extractives and soluble sugars, while mean and earlywood (EW) cell wall thickness and wood density were increased. Elevated [CO₂] had no effect on stem wood chemistry or radial growth. In wood structure, elevated [CO₂] decreased EW cell wall thickness and increased tracheid radial diameter in latewood (LW). Some significant interactions between elevated [CO₂] and temperature were found in the anatomical and physical properties of stem wood (e.g. microfibril angle, and LW cell wall thickness and density). Our results show that the wood material properties of mature Norway spruce were altered under exposure to elevated [CO₂] and temperature, although stem radial growth was not affected by the treatments.     

Elevated atmospheric [CO2] promotes frost damage in evergreen tree seedlings

Growth under elevated [CO₂] promoted spring frost damage in field grown seedlings of snow gum ( Eucalyptus pauciflora Sieb. ex Spreng.), one of the most frost tolerant of eucalypts. Freezing began in the leaf midvein, consistent with it being a major site of frost damage under field conditions. The average ice nucleation temperature was higher in leaves grown under elevated [CO₂] (– 5·7 °C versus – 4·3 °C), consistent with the greater incidence of frost damage in these leaves (34% versus 68% of leaves damaged). These results have major implications for agriculture, forestry and vegetation dynamics, as an increase in frost susceptibility may reduce potential gains in productivity from CO₂ fertilization and may affect predictions of vegetation change based on increasing temperature.     

Respiration in a future, higher-CO2 world

Abstract. Apart from its impact on global warming, the annually increasing atmospheric [CO₂] is of interest to plant scientists primarily because of its direct influence on photosynthesis and photorespiration in C₃ species. But in addition, 'dark' respiration, another major component of the carbon budget of higher plants, may be affected by a change in [CO₂] independent of an increase in temperature. Literature pertaining to an impact of [CO₂] on respiration rate is reviewed. With an increase in [CO₂], respiration rate is increased in some cases, but decreased in others. The effects of [CO₂] on respiration rate may be direct or indirect. Mechanisms responsible for various observations are proposed. These proposed mechanisms relate to changes in: (1) levels of nonstructural carbohydrates, (2) growth rate and structural phytomass accumulation, (3) composition of phytomass, (4) direct chemical interactions between CO₂ and respiratory enzymes, (5) direct chemical interactions between CO₂ and other cellular components, (6) dark CO₂ fixation rate, and (7) ethylene biosynthesis rate. Because a range-of (possibly interactive) effects exist, and present knowledge is limited, the impact of future [CO₂] on respiration rate cannot be predicted. Theoretical considerations and types of experiments that can lead to an increase in the understanding of this issue are outlined.     

Growth response of branches of Picea sitchensis to four years exposure to elevated atmospheric carbon dioxide concentration

Branch bags were used to expose branches on mature Sitka spruce trees to either ambient [CO₂] (A) or elevated [CO₂] (E) for 4 yr. This paper reports the effects of this treatment on the growth, development and phenology of the branches, including shoot expansion, shoot numbers, needle dimensions, needle numbers and stomatal density. The effect of elevated [CO₂] on the relationship between leaf area and sapwood area was investigated. Exposure to elevated [CO₂] doubled photosynthetic rates in current-year shoots and, despite some down-regulation, 1-yr-old E shoots also had higher rates of photosynthesis than their A counterparts. Thus, the amount of assimilate fixed by E branches was substantially more than that fixed by A branches; however, this increase in the local production of assimilate did not lead to an increase in non-structural carbohydrate or stimulate growth or meristematic activity within the E branches. There was a very consistent relationship between leaf area and stem cross-sectional area that was not influenced by [CO₂]. However, unbagged branches had thicker stems than bagged branches, resulting in a slightly lower ratio of leaf area to cross-sectional area. The implications of the results for the modelling of growth and allocation and the potential utility of the branch bag technique are discussed.     

Rice production in a changing climate: a meta-analysis of responses to elevated carbon dioxide and elevated ozone concentration

Rice is arguably the most important food source on the planet and is consumed by over half of the world's population. Considerable increases in yield are required over this century to continue feeding the world's growing population. This meta-analysis synthesizes the research to date on rice responses to two elements of global change, rising atmospheric carbon dioxide concentration ([CO₂]) and rising tropospheric ozone concentration ([O₃]). On an average, elevated [CO₂] (627 ppm) increased rice yields by 23%. Modest increases in grain mass and larger increases in panicle and grain number contributed to this response. The response of rice to elevated [CO₂] varied with fumigation technique. The more closely the fumigation conditions mimicked field conditions, the smaller was the stimulation of yield by elevated [CO₂]. Free air concentration enrichment (FACE) experiments showed only a 12% increase in rice yield. The rise in atmospheric [CO₂] will be accompanied by increases in tropospheric O₃ and temperature. When compared with rice grown in charcoal-filtered air, rice exposed to 62 ppb O₃ showed a 14% decrease in yield. Many determinants of yield, including photosynthesis, biomass, leaf area index, grain number and grain mass, were reduced by elevated [O₃]. While there have been too few studies of the interaction of CO₂ and O₃ for meta-analysis, the interaction of temperature and CO₂ has been studied more widely. Elevated temperature treatments negated any enhancement in rice yield at elevated [CO₂], which suggests that identifying high temperature tolerant germplasm will be key to realizing yield benefits in the future.     

Elevated concentrations of atmospheric CO2 protect against and compensate for O3 damage to photosynthetic tissues of field-grown wheat

The effects of elevated concentrations of atmospheric carbon dioxide and ozone on diurnal patterns of photosynthesis have been investigated in field-grown spring wheat ( Triticum aestivum ). Plants cultivated under realistic agronomic conditions, in open-top chambers, were exposed from emergence to harvest to reciprocal combinations of two carbon dioxide and two ozone treatments: [CO₂] at ambient (380 μmol mol⁻¹, seasonal mean) or elevated (692 μmol mol⁻¹) levels, [O₃] at ambient (27 nmol mol⁻¹, 7 hr seasonal mean) or elevated (61 nmol mol⁻¹) levels. After anthesis, diurnal measurements were made of flag-leaf gas-exchange and in vitro Rubisco activity and content. Elevated [CO₂] resulted in an increase in photoassimilation rate and a loss of excess Rubisco activity. Elevated [O₃] caused a loss of Rubisco and a decline in photoassimilation rate late in flag-leaf development. Elevated [CO₂] ameliorated O₃ damage. The mechanisms of amelioration included a protective stomatal restriction of O₃ flux to the mesophyll, and a compensatory effect of increased substrate on photoassimilation and photosynthetic control. However, the degree of protection and compensation appeared to be affected by the natural seasonal and diurnal variations in light, temperature and water status.     

Effects of long-term elevated [CO2] from natural CO2 springs on Nardus stricta: photosynthesis, biochemistry, growth and phenology

Plants of Nardus stricta growing near a cold, naturally emitting CO₂ spring in Iceland were used to investigate the long-term (> 100 years) effects of elevated [CO₂] on photosynthesis, biochemistry, growth and phenology in a northern grassland ecosystem. Comparisons were made between plants growing in an atmosphere naturally enriched with CO₂ (≈ 790 μ mol mol^–1) near the CO₂ spring and plants of the same species growing in adjacent areas exposed to ambient CO₂ concentrations (≈360 μ mol mol^–1). Nardus stricta growing near the spring exhibited earlier senescence and reductions in photosynthetic capacity (≈25%), Rubisco content (≈26%), Rubisco activity (≈40%), Rubisco activation state (≈23%), chlorophyll content (≈33%) and leaf area index (≈22%) compared with plants growing away from the spring. The potential positive effects of elevated [CO₂] on grassland ecosystems in Iceland are likely to be reduced by strong down-regulation in the photosynthetic apparatus of the abundant N. stricta species.     

Photosynthesis, growth and structural characteristics of holm oak resprouts originated from plants grown under elevated CO2

The physiological characteristics of holm oak ( Quercus ilex L.) resprouts originated from plants grown under current CO₂ concentration (350 μl l⁻¹) (A-resprouts) were compared with those of resprouts originated from plants grown under elevated CO₂ (750 μl l⁻¹) (E-resprouts). At their respective CO₂ growth concentration, no differences were observed in photosynthesis and chlorophyll fluorescence parameters between the two kinds of resprout. E-resprouts appeared earlier and showed lower stomatal conductance, higher water-use efficiency and increased growth (higher leaf, stem and root biomass and increased height). Analyses of leaf chemical composition showed the effect of elevated [CO₂] on structural polysaccharide (higher cellulose content), but no accumulation of total non-structural carbohydrate on area or dry weight basis was seen. Four months after appearance, downregulation of photosynthesis and electron transport components was observed in E-resprouts: lower photosynthetic capacity, photosystem II quantum efficiency, photochemical quenching of fluorescence and relative electron transport rate. Reduction in ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCo) activity, deduced from the maximum carboxylation velocity of RuBisCo, accounts for the observed acclimation. Increased susceptibility of photosynthetic apparatus to increasing irradiance was detected in E-resprouts.     

Leaf structure and chemical composition as affected by elevated CO2: genotypic responses of two perennial grasses

Genotypic variability was studied in two Mediterranean grass species, Bromus erectus and Dactylis glomerata , with regard to the response to CO₂ of leaf total non-structural carbohydrate concentration ([TNC]_lf), specific leaf area (SLA), and leaf carbon and nitrogen concentrations ([C]_lf and [N]_lf, respectively). Fourteen genotypes of each species were grown together on intact soil monoliths at ambient and elevated CO₂ concentrations (350 and 700 μmol mol⁻¹, respectively). In both species, the most consistent effect of elevated CO₂ was an increase in [TNC]_lf and a decrease in leaf nitrogen concentration when expressed either as total dry mass [N_m]_lf, structural dry mass [N_mst]_lf or leaf area [N_a]_lf. The SLA decreased only in D. glomerata , due to an accumulation of total non-structural carbohydrates and to an increase in leaf density. No genotypic variability was found for any variable in B. erectus , suggesting that genotypes responded in a similar way to elevated CO₂. In D. glomerata , a genotypic variability was found only for [Cst], [N_m]_lf, [N_mst]_lf and [N_a]_lf. Since [N_m]_lf is related to plant growth and is a strong determinant of plant–herbivore interactions, our results suggest evolutionary consequences of elevated CO₂ through competitive interactions or herbivory.     

The response of nodulated alfalfa to water supply, temperature and elevated CO2: photosynthetic downregulation

Plants grown in an environment of elevated CO₂ and temperature often show reduced CO₂ assimilation capacity, providing evidence of photosynthetic downregulation. The aim of this study was to analyse the downregulation of photosynthesis in elevated CO₂ (700 µmol mol⁻¹) in nodulated alfalfa plants grown at different temperatures (ambient and ambient + 4°C) and water availability regimes in temperature gradient tunnels. When the measurements were taken in growth conditions, a combination of elevated CO₂ and temperature enhanced the photosynthetic rate; however, when they were carried out at the same CO₂ concentration (350 and 700 µmol mol⁻¹), elevated CO₂ induced photosynthetic downregulation, regardless of temperature and drought. Intercellular CO₂ concentration measurements revealed that photosynthetic acclimation could not be accounted for by stomatal limitations. Downregulation of plants grown in elevated CO₂ was a consequence of decreased carboxylation efficiency as a result of reduced rubisco activity and protein content; in plants grown at ambient temperature, downregulation was also induced by decreased quantum efficiency. The decrease in rubisco activity was associated with carbohydrate accumulation and depleted nitrogen availability. The root nodules were not sufficiently effective to balance the source–sink relation in elevated CO₂ treatments and to provide the required nitrogen to counteract photosynthetic acclimation.     

The Effect of Elevated [CO2] on Uptake and Allocation of 13C and 15N in Beech (Fagus sylvatica L.) during Leafing

Abstract: A continuous dual ¹³CO₂ and ¹⁵NH₄¹⁵NO₃ labelling experiment was undertaken to determine the effects of ambient (350μmol mol^-1) or elevated (700μmol mol^-1) atmospheric CO₂ concentrations on C and N uptake and allocation within 3-year-old beech ( Fagus sylvatica L.) during leafing. After six weeks of growth, total carbon uptake was increased by 63 % (calculated on total C content) under elevated CO₂ but the carbon partitioning was not altered. 56 % of the new carbon was found in the leaves. On a dry weight basis was the content of structural biomass in leaves 10 % lower and the lignin content remained unaffected under elevated as compared to ambient [CO₂]. Under ambient [CO₂] 37 %, and under elevated [CO₂] 51 %, of the lignin C of the leaves derived from new assimilates. For both treatments, internal N pools provided more than 90 % of the nitrogen used for leaf-growth and the partitioning of nitrogen was not altered under elevated [CO₂]. The C/N ratio was unaffected by elevated [CO₂] at the whole plant level, but the C/N ratio of the new C and N uptake was increased by 32 % under elevated [CO₂].     

How does the C4 grass Eragrostis pilosa respond to elevated carbon dioxide and infection with the parasitic angiosperm Striga hermonthica?

Eragrostis pilosa (Linn.) P Beauv., a C₄ grass native to east Africa, was grown at both ambient (350 μmol mol⁻¹ and elevated (700 μmol mol⁻¹) CO₂ in either the presence or absence of the obligate, root hemi-parasite Striga hermonthica (Del.) Benth. Biomass of infected grasses was only 50% that of uninfected grasses at both CO₂ concentrations, with stems and reproductive tissues of infected plants being most severely affected. By contrast, CO₂ concentration had no effect on growth of E. pilosa , although rates of photosynthesis were enhanced by 30–40% at elevated CO₂. Infection with S. hermonthica did not affect either rates of photosynthesis or leaf areas of E. pilosa , but did bring about an increase in root:shoot ratio, leaf nitrogen and phosphorus concentration and a decline in leaf starch concentration at both ambient and elevated CO₂. Striga hermonthica had higher rates of photosynthesis and shoot concentrations of soluble sugars at elevated CO₂, but there was no difference in biomass relative to ambient grown plants. Both infection and growth at elevated CO₂ resulted in an increase in the Δ¹³C value of leaf tissue of E. pilosa , with the CO₂ effect being greater. The proportion of host-derived carbon in parasite tissue, as determined from δ¹³C values, was 27% and 39% in ambient and elevated CO₂ grown plants, respectively. In conclusion, infection with S. hermonthica limited growth of E. pilosa , and this limitation was not removed or alleviated by growing the association at elevated CO₂.     

Elevated CO2 concentration, nitrogen use, and seed production in annual plants

Elevated atmospheric CO₂ concentration ([CO₂]) stimulates seed mass production in many species, but the extent of stimulation shows large variation among species. We examined (1) whether seed production is enhanced more in species with lower seed nitrogen concentrations, and (2) whether seed production is enhanced by elevated [CO₂] when the plant uses more N for seed production. We grew 11 annuals in open top chambers that have different [CO₂] conditions (ambient: 370 μmol mol⁻¹, elevated: 700 μmol mol⁻¹). Elevated [CO₂] significantly increased seed production in six out of 11 species with a large interspecific variation (0.84–2.12, elevated/ambient [CO₂]). Seed nitrogen concentration was not correlated with the enhancement of seed production by elevated [CO₂]. The enhancement of seed production was strongly correlated with the enhancement of seed nitrogen per plant caused by increased N acquisition during the reproductive period. In particular, legume species tended to acquire more N and produced more seeds at elevated [CO₂] than non-nitrogen fixing species. Elevated [CO₂] little affected seed [N] in all species. We conclude that seed production is limited primarily by nitrogen availability and will be enhanced by elevated [CO₂] only when the plant is able to increase nitrogen acquisition.     

Elevated CO2 increases photosynthesis, biomass and productivity, and modifies gene expression in sugarcane

Because of the economical relevance of sugarcane and its high potential as a source of biofuel, it is important to understand how this crop will respond to the foreseen increase in atmospheric [CO₂]. The effects of increased [CO₂] on photosynthesis, development and carbohydrate metabolism were studied in sugarcane ( Saccharum ssp.). Plants were grown at ambient (∼370 ppm) and elevated (∼720 ppm) [CO₂] during 50 weeks in open-top chambers. The plants grown under elevated CO₂ showed, at the end of such period, an increase of about 30% in photosynthesis and 17% in height, and accumulated 40% more biomass in comparison with the plants grown at ambient [CO₂]. These plants also had lower stomatal conductance and transpiration rates (−37 and −32%, respectively), and higher water-use efficiency (c.a. 62%). cDNA microarray analyses revealed a differential expression of 35 genes on the leaves (14 repressed and 22 induced) by elevated CO₂. The latter are mainly related to photosynthesis and development. Industrial productivity analysis showed an increase of about 29% in sucrose content. These data suggest that sugarcane crops increase productivity in higher [CO₂], and that this might be related, as previously observed for maize and sorghum, to transient drought stress.