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International audience; Plant responses to rising atmospheric carbon dioxide (CO2) concentrations, together with projected variations in temperature and precipitation will determine future agricultural production. Estimates of the impacts of climate change on agriculture provide essential information to design effective adaptation strategies, and develop sustainable food systems. Here, we review the current experimental evidence and crop models on the effects of elevated CO2 concentrations. Recent concerted efforts have narrowed the uncertainties in CO2-induced crop responses so that climate change impact simulations omitting CO2 can now be eliminated. To address remaining knowledge gaps and uncertainties in estimating the effects of elevated CO2 and climate change on crops, future research should expand experiments on more crop species under a wider range of growing conditions, improve the representation of responses to climate extremes in crop models, and simulate additional crop physiological processes related to nutritional quality.Understanding of the effects of elevated CO2 on crops has improved sufficiently that modelling future climatic effects on agriculture should eliminate 'no CO2' simulations. Further advancement in the estimation of the effects can be realized by studying a wider variety of crop species under a wider range of growing conditions, improving the representation of responses to climate extremes in crop models and simulating additional crop physiological processes related to nutritional quality.

As a consequence of global change processes, plants will increasingly be challenged by extreme climatic events, against a background of elevated atmospheric CO2. We analysed responses of Arabidopsis thaliana to periods of a combination of elevated heat and water deficit at ambient and elevated CO2 in order to gain mechanistic insights regarding changes in primary metabolism. Metabolic changes induced by extremes of climate are dynamic and specific to different classes of molecules. Concentrations of soluble sugars and amino acids increased transiently after short (4-d) exposure to heat and drought, and readjusted to control levels under prolonged (8-d) stress. In contrast, fatty acids showed persistent changes during the stress period. Elevated CO2 reduced the impact of stress on sugar and amino acid metabolism, but not on fatty acids. Integrating metabolite data with transcriptome results revealed that some of the metabolic changes were regulated at the transcriptional level. Multivariate analyses grouped metabolites on the basis of stress exposure time, indicating specificity in metabolic responses to short and prolonged stress. Taken together, the results indicate that dynamic metabolic reprograming plays an important role in plant acclimation to climatic extremes. The extent of such metabolic adjustments is less under high CO2, further pointing towards the role of high CO2 in stress mitigation. ispartof: Journal of Experimental Botany vol:69 issue:8 pages:2159-2170 ispartof: location:England status: published

Free atmospheric CO 2 enrichment (FACE) studies conducted at the whole-tree and ecosystem scale indicate that there is a marked increase in primary production, mainly allocated into below-ground biomass. The enhanced carbon transfer to the root system may result in enhanced rhizodeposition and subsequent transfer to soil C pools. However, the impact of elevated CO 2 on soil C contents has yielded variable results. The fate and function of this extra C into the soil in response to elevated CO 2 are not clear. The POPFACE experiment was initiated early 1999 with the objective to determine the functional responses of a short-rotation poplar plantation to actual and future atmospheric CO 2 concentrations. During the first 2 years of the second rotation (2002–2003), the increase of total soil C% was larger under FACE than under ambient CO 2 . Chemical fractionation revealed the presence of more labile soil C under FACE, which is in agreement with the larger input of plant litter and root exudates under FACE. In order to gain insight into the fate and function of this extra C into the soil and the dynamics of soil C, we incubated soil samples, measured respiration rates and used a simple soil C model to interpret the results. FACE increased the accumulated 28-day CO 2 production and the initial C slow pool content (metabolizable plant remains and partly decomposed SOM). FACE also increased the decomposition rates of the metabolizable C pools (C fast + C slow ) in the top soil, while for the subsoil the opposite effect was observed. The modeled formation of humified SOM was also enhanced by FACE. Our results support the terrestrial feedback hypothesis, i.e. an increase of the long-term terrestrial C sink in response to increasing atmospheric CO 2 concentrations.

The influence of assimilate availability on the number of flowers per plant, individual flower size and plant height of chrysanthemum was investigated in different seasons, integrating the results from eight greenhouse experiments. Increased assimilate availability was obtained by higher light intensity, higher CO2 concentration, lower plant density or longer duration of the long-day (LD) period. Within each experiment, conditions that were expected to increase assimilate availability indeed resulted in higher total dry mass of the plant, excluding roots (TDMp). In contrast, flower mass ratio was hardly affected, except for the increased duration of the LD period that significantly reduced the partitioning towards the flowers. Consequently, an increase in total flower dry mass with assimilate availability was observed and this was mainly a result of higher numbers of flowers per plant, including flower buds (NoF). Individual flower size was only influenced by assimilate availability when average daily incident PAR during short-day period was lower than 7.5 mol m(-2) d(-1), resulting in lighter and smaller flowers. Excluding the positive linear effect of the duration of the LD period, assimilate availability hardly influenced plant height (

Free-air CO2 enrichment (FACE) experiments provide a remarkable wealth of data which can be used to evaluate and improve terrestrial ecosystem models (TEMs). In the FACE model-data synthesis project, 11 TEMs were applied to two decadelong FACE experiments in temperate forests of the southeastern U.S.—the evergreen Duke Forest and the deciduous Oak Ridge Forest. In this baseline paper, we demonstrate our approach to model-data synthesis by evaluating the models' ability to reproduce observed net primary productivity (NPP), transpiration, and leaf area index (LAI) in ambient CO2 treatments. Model outputs were compared against observations using a range of goodness-of-fit statistics. Many models simulated annual NPP and transpiration within observed uncertainty. We demonstrate, however, that high goodness-of-fit values do not necessarily indicate a successful model, because simulation accuracy may be achieved through compensating biases in component variables. For example, transpiration accuracy was sometimes achieved with compensating biases in leaf area index and transpiration per unit leaf area. Our approach to model-data synthesis therefore goes beyond goodness-of-fit to investigate the success of alternative representations of component processes. Here we demonstrate this approach by comparing competing model hypotheses determining peak LAI. Of three alternative hypotheses—(1) optimization to maximize carbon export, (2) increasing specific leaf area with canopy depth, and (3) the pipe model—the pipe model produced peak LAI closest to the observations. This example illustrates how data sets from intensive field experiments such as FACE can be used to reduce model uncertainty despite compensating biases by evaluating individual model assumptions.

We determined the proximate chemical composition as well as the construction costs of leaves of 27 species, grown at ambient and at a twice-ambient partial pressure of atmospheric CO2, These species comprised wild and agricultural herbaceous plants as well as tree seedlings, Both average responses across species and the range in response were considered, Expressed on a total dry weight basis, the main change in chemical composition due to CO2 was the accumulation of total non-structural carbohydrates (TNC), To a lesser extent, decreases were found for organic N compounds and minerals, Hardly any change was observed for total structural carbohydrates (cellulose plus hemicellulose), lignin and lipids, When expressed on a TNC-free basis, decreases in organic N compounds and minerals were still present. On this basis, there was also an increase in the concentration of soluble phenolics, In terms of glucose required for biosynthesis, the increase in costs for one chemical compound - TNC - was balanced by a decrease in the costs for organic N compounds, Therefore, the construction costs, the total amount of glucose required to produce 1 g of leaf, were rather similar for the two CO2 treatments; on average a small decrease of 3% was found, This decrease was attributable to a decrease of up to 30% in the growth respiration coefficient, the total CO2 respired [mainly for NAD(P)H and ATP] in the process of constructing 1 g of biomass, The main reasons for this reduction were the decrease in organic N compounds and the increase in TNC.

We determined the proximate chemical composition as well as the construction costs of leaves of 27 species, grown at ambient and at a twice-ambient partial pressure of atmospheric CO2, These species comprised wild and agricultural herbaceous plants as well as tree seedlings, Both average responses across species and the range in response were considered, Expressed on a total dry weight basis, the main change in chemical composition due to CO2 was the accumulation of total non-structural carbohydrates (TNC), To a lesser extent, decreases were found for organic N compounds and minerals, Hardly any change was observed for total structural carbohydrates (cellulose plus hemicellulose), lignin and lipids, When expressed on a TNC-free basis, decreases in organic N compounds and minerals were still present. On this basis, there was also an increase in the concentration of soluble phenolics,In terms of glucose required for biosynthesis, the increase in costs for one chemical compound - TNC - was balanced by a decrease in the costs for organic N compounds, Therefore, the construction costs, the total amount of glucose required to produce 1 g of leaf, were rather similar for the two CO2 treatments; on average a small decrease of 3% was found, This decrease was attributable to a decrease of up to 30% in the growth respiration coefficient, the total CO2 respired [mainly for NAD(P)H and ATP] in the process of constructing 1 g of biomass, The main reasons for this reduction were the decrease in organic N compounds and the increase in TNC.

Background - Process-based ecophysiological crop models are pivotal in assessing responses of crop productivity and designing strategies of adaptation to climate change. Most existing crop models generally over-estimate the effect of elevated atmospheric [CO2], despite decades of experimental research on crop growth response to [CO2]. Analysis - A review of the literature indicates that the quantitative relationships for a number of traits, once expressed as a function of internal plant nitrogen status, are altered little by the elevated [CO2]. A model incorporating these nitrogen-based functional relationships and mechanisms simulated photosynthetic acclimation to elevated [CO2], thereby reducing the chance of over-estimating crop response to [CO2]. Robust crop models to have small parameterization requirements and yet generate phenotypic plasticity under changing environmental conditions need to capture the carbon–nitrogen interactions during crop growth. Conclusions - The performance of the improved models depends little on the type of the experimental facilities used to obtain data for parameterization, and allows accurate projections of the impact of elevated [CO2] and other climatic variables on crop productivity.

Document Type : Book Chapter; Lignins, major components of the vascular plant cell wall, provided the mechanical support that allowed the development of upright plants adapted to a terrestrial habitat. Their biosynthesis through the phenylpropanoid and monolignol pathways has been extensively studied and significant advances have recently been made in understanding the regulation of this process. Lignin deposition is also modified in response to both abiotic and biotic stresses. Here, we present an overview of lignin biosynthesis in response to various abiotic stresses: drought, salinity, heavy metals, wounding, low temperature, ozone, UV-B radiation, light, elevated CO2 and nitrogen stress. Although the stimulation of the phenylpropanoid pathway is a common feature of stress response, the subsequent synthesis of lignin is only demonstrated in some cases. The roles of lignins in different phases of abiotic stress response are discussed as well as the regulation of their synthesis under stress.

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.

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.

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 CO(2) 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 CO(2) concentrations ([CO(2)]). Increased biomass yield resulted from an early growth enhancement and photosynthesis did not acclimate to elevated [CO(2)]. 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 [CO(2)] was mainly invested into woody biomass pools. Coppicing increased yield by 66% and partly shifted the extra C uptake in elevated [CO(2)] to above-ground pools, as fine root biomass declined and its [CO(2)] stimulation disappeared. Mineral soil C increased equally in ambient and elevated [CO(2)] during the 6 yr experiment. However, elevated [CO(2)] increased the stabilization of C in the mineral soil. Increased productivity of a poplar SRC in elevated [CO(2)] may allow shorter rotation cycles, enhancing the viability of SRC for biofuel production.

This paper investigates the possible contribution of Short Rotation Cultures (SRC) to carbon sequestration in both current and elevated atmospheric CO2 concentrations ([CO2]). A dense poplar plantation (1 x 1 m) was exposed to a [CO2] of 550 ppm in Central Italy using the free-air CO2 enrichment (FACE) technique. Three species of Populus were examined, namely P. alba L., P. nigra L. and P. x euramericana Dode (Guinier). Aboveground woody biomass of trees exposed to elevated [CO2] for three growing seasons increased by 15 to 27%, depending on species. As a result, light-use efficiency increased. Aboveground biomass allocation was unaffected, and belowground biomass also increased under elevated [CO2] conditions, by 22 to 38%. Populus nigra, with total biomass equal to 62.02 and 72.03 Mg ha(-1) in ambient and elevated [CO2], respectively, was the most productive species, although its productivity was stimulated least by atmospheric CO2 enrichment. There was greater depletion of inorganic nitrogen from the soil after three growing seasons in elevated [CO2], but no effect of [CO2] on stem wood density, which differed significantly only among species.

We determined the proximate chemical composition as well as the construction costs of leaves of 27 species, grown at ambient and at a twice-ambient partial pressure of atmospheric CO2, These species comprised wild and agricultural herbaceous plants as well as tree seedlings, Both average responses across species and the range in response were considered, Expressed on a total dry weight basis, the main change in chemical composition due to CO2 was the accumulation of total non-structural carbohydrates (TNC), To a lesser extent, decreases were found for organic N compounds and minerals, Hardly any change was observed for total structural carbohydrates (cellulose plus hemicellulose), lignin and lipids, When expressed on a TNC-free basis, decreases in organic N compounds and minerals were still present. On this basis, there was also an increase in the concentration of soluble phenolics, In terms of glucose required for biosynthesis, the increase in costs for one chemical compound - TNC - was balanced by a decrease in the costs for organic N compounds, Therefore, the construction costs, the total amount of glucose required to produce 1 g of leaf, were rather similar for the two CO2 treatments; on average a small decrease of 3% was found, This decrease was attributable to a decrease of up to 30% in the growth respiration coefficient, the total CO2 respired [mainly for NAD(P)H and ATP] in the process of constructing 1 g of biomass, The main reasons for this reduction were the decrease in organic N compounds and the increase in TNC.

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.

This paper examines the extent to which atmospheric CO2 enrichment may influence growth of plant roots and function in terms of uptake of water and nutrients, and carbon allocation towards symbionts. It is concluded that changes in dry matter allocation greatly depend on the experimental conditions during the experiment, the growth phase of the plant, and its morphological characteristics. Under non-limiting conditions of water and nutrients for growth, dry matter partitioning to the root is not changed by CO2 enrichment. The increase in root/shoot ratio, frequently observed under limiting conditions of water and/or nutrients, enables the plant to explore a greater soil volume, and hence acquire more water and nutrients. However, more data on changes in dry matter allocation within the root due to atmospheric CO2 are needed. It is concluded that nitrogen fixation is favored by CO2 enrichment since nodule mass is increased, concomitant with an increase in root length. The papers available so far on the influence of CO2 enrichment on mycorrhizal functioning suggest that carbon allocation to the roots might be increased, but also here more experiments are needed.