Saving Energy versus Saving Materials

To reduce energy consumption and carbon dioxide (CO₂) emissions in housing construction, the energy-intensive processes and life-cycle stages should be identified and integrated. The environmental impact of vertically integrated factory-built homes (VIHs) constructed with increased material inputs in Japan's northern island of Hokkaido was assessed using life-cycle inventory (LCI) analysis methods. Manufacturing process energy and CO₂ intensities of the homes were evaluated based on the material inputs. They were compared with those of a counterpart home hypothetically built using the vertically integrated construction methods, but in accordance with the specifications of a less material-intensive conventional home (CH) in Hokkaido today. Cumulative household energy consumption and CO₂ emissions were evaluated and compared with those of the production stages. The annual household energy consumption was compared among a VIH, a CH, and an average home in Hokkaido. The energy intensity of the VIH was 3.9 GJ production energy per m² of floor area, 59% higher than that of the CH. Net CO₂ emissions during VIH manufacturing processes were 293 kg/m², after discounting the carbon fixation during tree growth. The cumulative use-phase household energy consumption and CO₂ emissions of a VIH will exceed energy consumption and CO₂ emissions during the initial production stage in less than six years. Although VIHs housed 21% more residents on average, the energy consumption per m2 was 17% lower than that of a CH. This may indicate that using more materials initially can lead to better energy efficiency.     

Leaf isoprene emission rate as a function of atmospheric CO2 concentration

There is considerable interest in modeling isoprene emissions from terrestrial vegetation, because these emissions exert a principal control over the oxidative capacity of the troposphere. We used a unique field experiment that employs a continuous gradient in CO₂ concentration from 240 to 520 ppmv to demonstrate that isoprene emissions in Eucalyptus globulus were enhanced at the lowest CO₂ concentration, which was similar to the estimated CO₂ concentrations during the last Glacial Maximum, compared with 380 ppmv, the current CO₂ concentration. Leaves of Liquidambar styraciflua did not show an increase in isoprene emission at the lowest CO₂ concentration. However, isoprene emission rates from both species were lower for trees grown at 520 ppmv CO₂ compared with trees grown at 380 ppmv CO₂. When grown in environmentally controlled chambers, trees of Populus deltoides and Populus tremuloides exhibited a 30–40% reduction in isoprene emission rate when grown at 800 ppmv CO₂, compared with 400 ppmv CO₂. P. tremuloides exhibited a 33% reduction when grown at 1200 ppmv CO₂, compared with 600 ppmv CO₂. We used current models of leaf isoprene emission to demonstrate that significant errors occur if the CO₂ inhibition of isoprene is not taken into account. In order to alleviate these errors, we present a new model of isoprene emission that describes its response to changes in atmospheric CO₂ concentration. The model logic is based on assumed competition between cytosolic and chloroplastic processes for pyruvate, one of the principal substrates of isoprene biosynthesis.     

A review of nitrogen enrichment effects on three biogenic GHGs: the CO2 sink may be largely offset by stimulated N2O and CH4 emission

Anthropogenic nitrogen (N) enrichment of ecosystems, mainly from fuel combustion and fertilizer application, alters biogeochemical cycling of ecosystems in a way that leads to altered flux of biogenic greenhouse gases (GHGs). Our meta-analysis of 313 observations across 109 studies evaluated the effect of N addition on the flux of three major GHGs: CO₂, CH₄ and N₂O. The objective was to quantitatively synthesize data from agricultural and non-agricultural terrestrial ecosystems across the globe and examine whether factors, such as ecosystem type, N addition level and chemical form of N addition influence the direction and magnitude of GHG fluxes. Results indicate that N addition increased ecosystem carbon content of forests by 6%, marginally increased soil organic carbon of agricultural systems by 2%, but had no significant effect on net ecosystem CO₂ exchange for non-forest natural ecosystems. Across all ecosystems, N addition increased CH₄ emission by 97%, reduced CH₄ uptake by 38% and increased N₂O emission by 216%. The net effect of N on the global GHG budget is calculated and this topic is reviewed. Most often N addition is considered to increase forest C sequestration without consideration of N stimulation of GHG production in other ecosystems. However, our study indicated that although N addition increased the global terrestrial C sink, the CO₂ reduction could be largely offset (53–76%) by N stimulation of global CH₄ and N₂O emission from multiple ecosystems.     

Modeling Corn Ethanol and Climate

New fuel regulations based on life cycle greenhouse gas (GHG) emissions have focused renewed attention on life cycle models of biofuels. The BESS model estimates 25% lower life cycle GHG emissions for corn ethanol than does the well-known GREET model, which raises questions about which model is more accurate. I develop a life cycle metamodel to compare the GREET and BESS models in detail and to explain why the results from these models diverge. I find two main reasons for the divergence: (1) BESS models a more efficient biorefinery than is modeled in the cases to which its results have been compared, and (2) in several instances BESS fails to properly count upstream emissions. Adjustments to BESS to account for these differences raise the estimated global warming intensity (not including land use change) of the corn ethanol pathway considered in that model from 45 to 61 g CO₂e MJ⁻¹. Adjusting GREET to use BESS's biorefinery performance and coproduct credit assumptions reduces the GREET estimate from 64 to 61 g CO₂e MJ⁻¹. Although this analysis explains the gap between the two models, both models would be improved with better data on corn production practices and by better treatment of agricultural inputs.     

Assessment of CO 2 Emission Reduction Strategies for the Japanese Petrochemical Industry

Abstract: This article analyzes the possibilities for reducing carbon dioxide (CO₂) emissions in the life cycle of Japanese petrochemicals, focusing primarily on the nonenergy use of fossil fuels. For this purpose a linear programming model called CHEAP (CHemical industry Environmental strategy Analysis Program) has been developed. The results show a moderate autonomous growth of emissions by 5% in the period 2000 to 2020, if it is assumed that no new technology is introduced and demand (measured in physical units) increases 1% per year, on average. However, if it is assumed that ongoing technology development succeeds, emissions in 2020 may decrease by 5% from 2000 levels (a decrease of 10% compared to the case that assumes no new technology). This is a significant contribution to emission reduction. According to this model, a further emission reduction by 10% in 2020 is possible but costly as it requires emission reduction incentives of up to 10,000 yen per ton CO₂ (approximately 100 US/ton). The use of biomass feed-stocks, waste recycling, energy recovery from waste and gas-based co-generation are the main strategies for achieving this emission reduction.     

The Impact of Social Factors and Consumer Behavior on Carbon Dioxide Emissions in the United Kingdom

In this article we apply geodemographic consumer segmentation data in an input−output framework to understand the direct and indirect carbon dioxide (CO₂) emissions associated with consumer behavior of different lifestyles in the United Kingdom. In a subsequent regression analysis, we utilize the lifestyle segments contained in the dataset to control for aspects of behavioral differences related to lifestyles in an analysis of the impact of various socioeconomic variables on CO₂ emissions, such as individual aspirations and people's attitudes toward the environment, as well as the physical context in which people act.
This approach enables us to (1) test for the significance of lifestyles in determining CO₂ emissions, (2) quantify the importance of a variety of individual socioeconomic determinants, and (3) provide a visual representation of "where" the various factors exert the greatest impact, by exploiting the spatial information contained in the lifestyle data.
Our results indicate the importance of consumer behavior and lifestyles in understanding CO₂ emissions in the United Kingdom. Across lifestyle groups, CO₂ emissions can vary by a factor of between 2 and 3. Our regression results provide support for the idea that sociodemographic variables are important in explaining emissions. For instance, controlling for lifestyles and other determinants, we find that emissions are increasing with income and decreasing with education. Using the spatial information, we illustrate how the lifestyle mix of households in the United Kingdom affects the geographic distribution of environmental impacts.     

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.     

Intraspecific variation in the response of rice (Oryza sativa) to increased CO2– photosynthetic, biomass and reproductive characteristics

Two rice ( Oryza sativa L.) cultivars of contrasting morphologies, IR-36 and Fujiyama-5, were exposed to ambient (360 μl l⁻¹) and ambient plus 300 μl l⁻¹ CO₂ from time of emergence until ca 50% grain fill at the Duke University Phytotron, Durham, North Carolina. Exposure to increased CO₂ resulted in about a 50% increase in the photosynthetic rate for both cultivars and photosynthetic enhancement was still evident after 3 months of exposure to a high CO₂ environment. The photosynthetic response at 5% CO₂ and the response of CO₂ assimilation (A) to internal CO₂ (C_i) suggest a reallocation of biochemical resources from RuBP carboxylation to RuBP regeneration. Increases in total plant biomass at elevated CO₂ were approximately the same in both cultivars, although differences in allocation patterns were noted in root/shoot ratio. Differences in reproductive characteristics were also observed between cultivars at an elevated CO₂ environment with a significant increase in harvest index for IR-36 but not for Fujiyama-5. Changes in carbon allocation in reproduction between these two cultivars suggest that lines of rice could be identified that would maximize reproductive output in a future high CO₂ environment.     

Western European Materials as Sources and Sinks of CO2

Materials use is an important factor influencing carbon dioxide (CO₂) emissions because significant amounts of carbon dioxide are released during the production of materials from natural resources, and because products and wastes can function as important sinks for CO₂. This article analyzes the impact of Western European materials use on CO₂ emissions. The material flows for steel, cement, petrochemicals, and wood products are analyzed in more detail. The analysis shows that particular characteristics of the materials system must be considered in the development of emission reduction strategies. It is important to select a relatively closed system for policymaking, as in Western Europe, in order to prevent unwanted transboundary effects. The materials stored in the form of products, and the net exports of materials, products, and waste limit the potential of a recycling strategy. Carbon storage in products and waste disposal sites is significant both for synthetic and natural organic materials, but is not accounted for in natural organic materials in current emissions statistics. Accordingly the emissions accounting practices should be modified to reflect the storage of such materials.     

Future energy potential of Miscanthus in Europe

European field experiments have demonstrated Miscanthus can produce some of the highest energy yields per hectare of all potential energy crops. Previous modelling studies using MISCANMOD have calculated the potential energy yield for the EU27 from mean historical climate data (1960–1990). In this paper, we have built on the previous studies by further developing a new Miscanthus crop growth model MISCANFOR in order to analyse (i) interannual variation in yields for past and future climates, (ii) genotype-specific parameters on yield in Europe. Under recent climatic conditions (1960–1990) we show that 10% of arable land could produce 1709 PJ and mitigate 30 Tg of carbon dioxide-carbon (CO₂-C) equivalent greenhouse gasses (GHGs) compared with EU27 primary energy consumption of 65 598 PJ, emitting 1048 Tg of CO₂-C equivalent GHGs in 2005. If we continue to use the clone Miscanthus × giganteus , MISCANFOR shows that, as climate change reduces in-season water availability, energy production and carbon mitigation could fall 80% by 2080 for the Intergovernmental Panel on Climate Change A2 scenario. However, because Miscanthus is found in a huge range of climates in Asia, we propose that new hybrids will incorporate genes conferring superior drought and frost tolerance. Using parameters from characterized germplasm, we calculate energy production could increase from present levels by 88% (to 2360 PJ) and mitigate 42 Tg of CO₂-C equivalent using 10% arable land for the 2080 mid-range A2 scenario. This is equivalent to 3.6% of 2005 EU27 primary energy consumption and 4.0% of total CO₂ equivalent C GHG emissions.     

Region-specific assessment of greenhouse gas mitigation with different manure management strategies in four agroecological zones

Livestock farming systems are major sources of trace gases contributing to emissions of the greenhouse gases (GHG) nitrous oxide (N₂O) and methane (CH₄), i.e. N₂O accounts for 10% and CH₄ for 30% of the anthropogenic contributions to net global warming. This paper presents scenario assessments of whole-system effects of technologies for reducing GHG emissions from livestock model farms using slurry-based manure management. Changes in housing and storage practice, mechanical separation, and incineration of the solid fraction derived from separation were evaluated in scenarios for Sweden, Denmark, France, and Italy. The results demonstrated that changes in manure management can induce significant changes in CH₄ and N₂O emissions and carbon sequestration, and that the effect of introducing environmental technologies may vary significantly with livestock farming practice and interact with climatic conditions. Shortening the in-house manure storage time reduced GHG emissions by 0–40%. The largest GHG reductions of 49 to, in one case, 82% were obtained with a combination of slurry separation and incineration, the latter process contributing to a positive GHG balance of the system by substituting fossil fuels. The amount and composition of volatile solids (VS) and nitrogen pools were main drivers in the calculations performed, and requirements to improve the assessment of VS composition and turnover during storage and in the field were identified. Nevertheless, the results clearly showed that GHG emission estimates will be unrealistic, if the assumed manure management or climatic conditions do not properly represent a given country or region. The results also showed that the mitigation potential of specific manure management strategies and technologies varied depending on current management and climatic conditions.     

Elevated atmospheric CO2 influences the interaction between the parasitic angiosperm Orobanche minor and its host Trifolium repens

The influence of the root holoparasitic angiosperm Orobanche minor Sm. on the biomass, photosynthesis, carbohydrate and nitrogen content of Trifolium repens L. was determined for plants grown at two CO₂ concentrations (350 and 550 μmol mol⁻¹). Infected plants accumulated less biomass than their uninfected counterparts, although early in the association there was a transient stimulation of growth. Infection also influenced biomass allocation both between tissues (infected plants had lower root:shoot ratios) and within tissues:infected roots were considerably thicker before the point of parasite attachment and thinner below. Higher concentrations of starch were also found in roots above the point of attachment, particularly for plants grown in elevated CO₂. Elevated CO₂ stimulated the growth of T. repens only during the early stages of development. There was a significant interaction between infection and CO₂ on growth, with infected plants showing a greater response, such that elevated CO₂ partly alleviated the effects of the parasite on host growth. Elevated CO₂ did not affect total O. minor biomass per host, the number of individual parasites supported by each host, or their time of attachment to the host root system. Photosynthesis was stimulated by elevated CO₂ but was unaffected by O. minor . There was no evidence of down-regulation of photosynthesis in T. repens grown at elevated CO₂ in either infected or uninfected plants. The data are discussed with regard to the influence of elevated CO₂ on other parasitic angiosperm-host associations and factors which control plant responses to elevated CO₂.     

Nitrite accumulation by Synechococcus 6301 as a consequence of carbon- or sulfur-deficiency

Abstract Air grown cultures of the cyanobacterium Synechococcus 6301, when incubated under continuous illumination with nitrate as the sole nitrogen source, started to liberate nitrite from the second day of inoculation. Nitrite accumulation depended on culture density and was caused by CO₂ deficiency since it could be prevented by addition of 5% CO₂ to the gas stream. Nitrite excreted during growth with air (0.035% CO₂) was taken up after an increase in CO₂ concentration to 5%.
In sulfur depleted cultures, nitrite excretion took place also with saturating CO₂ concentration. In this case nitrite accumulation could be reversed by addition of a suitable sulfur source.
Under both conditions for nitrite accumulation, carbon and sulfur deficiency, a significant decrease in nitrite reductase activity was observed which might account for nitrite liberation.     

Cumulative Energy and Global Warming Impact from the Production of Biomass for Biobased Products

The cumulative energy and global warming impacts associated with producing corn, soybeans, alfalfa, and switchgrass and transporting these crops to a central crop processing facility (called a "biorefinery") are estimated. The agricultural inputs for each crop are collected from seven states in the United States: Illinois, Indiana, Iowa, Michigan, Minnesota, Ohio, and Wisconsin. The cumulative energy requirement for producing and transporting these crops is 1.99 to 2.66 megajoules/kilo-gram (MJ/kg) for corn, 1.98 to 2.04 MJ/kg for soybeans, 1.24 MJ/kg for alfalfa, and 0.97 to 1.34 MJ/kg for switchgrass. The global warming impact associated with producing biomass is 246 to 286 grams (g) CO₂ equivalent/kg for corn, 159 to 163gCO₂ equivalent/kg for soybeans, 89 g CO₂ equivalent/ kg for alfalfa, and 124 to 147 g CO₂ equivalent/kg for switch-grass. The detailed agricultural data are used to assess previous controversies over the energy balance of bioethanol and, in light of the ongoing debates on this topic, provide a needed foundation for future life-cycle assessments.     

The regulation of photosynthetic rate and activation of extracellular carbonic anhydrase under CO2-limiting conditions in the marine diatom Skeletonema costatum

In the marine diatom Skeletonema costatum , carbonic anhydrase activity exterior to the plasma membrane (CA_ext) was detected only when the available CO₂ concentration was less than 5·0 mmol m^–3, this activity being unaffected by the total dissolved inorganic carbon concentration. The inhibition of CA_ext by dextran bound sulphonamide (DBS) demonstrated the key role of this enzyme in maintaining photosynthetic rate under CO₂-limited conditions. Treatment with trypsin followed by affinity chromatography on p-aminomethylbenzene-sulphamide agarose and subsequent SDS-PAGE analysis revealed a polypeptide from carbon-replete cells of identical molecular mass to the CA_ext released by trypsin from CO₂-limited cells. Redox activity in the plasma membrane of intact cells was measured by following the light-dependent reduction of ferricyanide or NADP, the greatest activity being shown by CO₂-limited cells. Overall the results suggest that high rates of redox activity under conditions of CO₂-limitation were required for the activation of CA_ext.     

Life-Cycle Energy, Costs, and Strategies for Improving a Single-Family House

The life-cycle energy, greenhouse gas emissions, and costs of a contemporary 2,450 sq ft (228 m³) U.S. residential home (the standard home, or SH) were evaluated to study opportunities for conserving energy throughout pre-use (materials production and construction), use (including maintenance and improvement), and demolition phases. Home construction and maintenance materials and appliances were inventoried totaling 306 metric tons. The use phase accounted for 91% of the total life-cycle energy consumption over a 50-year home life. A functionally equivalent energy-efficient house (EEH) was modeled that incorporated 11 energy efficiency strategies. These strategies led to a dramatic reduction in the EEH total life-cycle energy; 6,400 GJ for the EEH compared to 16,000 GJ for the SH. For energy-efficient homes, embodied energy of materials is important; pre-use energy accounted for 26% of life-cycle energy. The discounted (4%) life-cycle cost, consisting of mortgage, energy, maintenance, and improvement payments varied between 426,700 and 454,300 for a SH using four energy price forecast scenarios. In the case of the EEH, energy cost savings were offset by higher mortgage costs, resulting in total life-cycle cost between 434,100 and 443,200. Life-cycle greenhouse gas emissions were 1,010 metric tons CO₂ equivalent for an SH and 370 metric tons for an EEH.     

Ozone induced emissions of biogenic VOC from tobacco: relationships between ozone uptake and emission of LOX products

Volatile organic compound (VOC) emissions from tobacco ( Nicotiana tabacum L. var. Bel W3) plants exposed to ozone (O₃) were investigated using proton-transfer-reaction mass-spectrometry (PTR-MS) and gas chromatography mass-spectrometry (GC-MS) to find a quantitative reference for plants' responses to O₃ stress. O₃ exposures to illuminated plants induced post-exposure VOC emission bursts. The lag time for the onset of volatile C₆ emissions produced within the octadecanoid pathway was found to be inversely proportional to O₃ uptake, or more precisely, to the O₃ flux density into the plants. In cases of short O₃ pulses of identical duration the total amount of these emitted C₆ VOC was related to the O₃ flux density into the plants, and not to ozone concentrations or dose–response relationships such as AOT 40 values. Approximately one C₆ product was emitted per five O₃ molecules taken up by the plant. A threshold flux density of O₃ inducing emissions of C₆ products was found to be (1.6 ± 0.7) × 10⁻⁸ mol m⁻² s⁻¹.     

High carbon dioxide and sun/shade effects on isoprene emission from oak and aspen tree leaves

Abstract. Isoprene (2-methyl 1, 3-butadiene) is emitted from many plants, especially trees. We tested the effect of growth at high CO₂ partial pressure and sun versus shade conditions on the capacity of Quercus rubra L. (red oak) and Populus tremuloides Michx. (quaking aspen) leaves to make isoprene. Oak leaves grown at high CO₂ partial pressure (65 Pa) had twice the rate of isoprene emission as leaves grown at 40Pa CO₂. However, aspen leaves behaved oppositely, with high CO₂-grown leaves having just 60-70% the rate of isoprene emission as leaves grown in 40 Pa CO₂. Similar responses were observed from 25 to 35 °C leaf temperature during assay. The stimulation of isoprene emission by growth at high CO₂ and the stimulation in high temperature resulted in isoprene emission consuming over 15% of the carbon fixed during photosynthesis in high-CO₂ grown oak leaves assayed at 35 °C. Leaves from the south (sunny) sides of trees growing in natural conditions had rates of isoprene emission double those of leaves growing in shaded locations on the same trees. This effect was similar in both aspen and oak. The leaves used for these experiments had significantly different chlorophyll a/b ratios indicating they were functionally sun (from the sunny locations) or shade leaves (from the protected locations). Because the metabolic pathway of isoprene synthesis is unknown, we are unable to speculate about how or why these effects occur. However, these effects are more consistent with metabolic control of isoprene release rather than a metabolic leak of isoprene from metabolism. The results are also important for large scale modelling of isoprene emission and for predicting the effect of future increases in atmospheric CO₂ level on isoprene emission from vegetation.     

Soil CO2 efflux in a boreal pine forest under atmospheric CO2 enrichment and air warming

The response of forest soil CO₂ efflux to the elevation of two climatic factors, the atmospheric concentration of CO₂ (↑CO₂ of 700 μmol mol⁻¹) and air temperature (↑ T with average annual increase of 5°C), and their combination (↑CO₂+↑ T ) was investigated in a 4-year, full-factorial field experiment consisting of closed chambers built around 20-year-old Scots pines ( Pinus sylvestris L.) in the boreal zone of Finland. Mean soil CO₂ efflux in May–October increased with elevated CO₂ by 23–37%, with elevated temperature by 27–43%, and with the combined treatment by 35–59%. Temperature elevation was a significant factor in the combined 4-year efflux data, whereas the effect of elevated CO₂ was not as evident. Elevated temperature had the most pronounced impact early and late in the season, while the influence of elevated CO₂ alone was especially notable late in the season. Needle area was found to be a significant predictor of soil CO₂ efflux, particularly in August, a month of high root growth, thus supporting the assumption of a close link between whole-tree physiology and soil CO₂ emissions. The decrease in the temperature sensitivity of soil CO₂ efflux observed in the elevated temperature treatments in the second year nevertheless suggests the existence of soil response mechanisms that may be independent of the assimilating component of the forest ecosystem. In conclusion, elevated atmospheric CO₂ and air temperature consistently increased forest soil CO₂ efflux over the 4-year period, their combined effect being additive, with no apparent interaction.     

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].