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• Concentrations of atmospheric CO2 and tropospheric ozone (O3) are rising concurrently in the atmosphere, with potentially antagonistic effects on forest net primary production (NPP) and implications for terrestrial carbon sequestration. • Using free-air CO2 enrichment (FACE) technology, we exposed north-temperate forest communities to concentrations of CO2 and O3 predicted for the year 2050 for the first 7 yr of stand development. Site-specific allometric equations were applied to annual nondestructive growth measurements to estimate above- and below-ground biomass and NPP for each year of the experiment. • Relative to the control, elevated CO2 increased total biomass 25, 45 and 60% in the aspen, aspen–birch and aspen–maple communities, respectively. Tropospheric O3 caused 23, 13 and 14% reductions in total biomass relative to the control in the respective communities. Combined fumigation resulted in total biomass response of −7.8, +8.4 and +24.3% relative to the control in the aspen, aspen–birch and aspen–sugar maple communities, respectively. • These results indicate that exposure to even moderate levels of O3 significantly reduce the capacity of NPP to respond to elevated CO2 in some forests. [ABSTRACT FROM AUTHOR]

• Concentrations of atmospheric CO2 and tropospheric ozone (O3) are rising concurrently in the atmosphere, with potentially antagonistic effects on forest net primary production (NPP) and implications for terrestrial carbon sequestration. • Using free-air CO2 enrichment (FACE) technology, we exposed north-temperate forest communities to concentrations of CO2 and O3 predicted for the year 2050 for the first 7 yr of stand development. Site-specific allometric equations were applied to annual nondestructive growth measurements to estimate above- and below-ground biomass and NPP for each year of the experiment. • Relative to the control, elevated CO2 increased total biomass 25, 45 and 60% in the aspen, aspen–birch and aspen–maple communities, respectively. Tropospheric O3 caused 23, 13 and 14% reductions in total biomass relative to the control in the respective communities. Combined fumigation resulted in total biomass response of −7.8, +8.4 and +24.3% relative to the control in the aspen, aspen–birch and aspen–sugar maple communities, respectively. • These results indicate that exposure to even moderate levels of O3 significantly reduce the capacity of NPP to respond to elevated CO2 in some forests. [ABSTRACT FROM AUTHOR]

Details a study which examined the accumulation of H2O2 within the leaf mesophyll of Populus tremuloides aspen genotypes and seedlings of paper birch Betula papyrifera. Gene expression of catalase; Effects of ozone and carbon dioxide on the structure of ozone-tolerant aspen; Correlation between aspen clones, elevated ozone, birch and peroxisomes levels.

Summary: Leaves with stomata on both upper and lower surfaces, termed amphistomatous, are relatively rare compared with hypostomatous leaves with stomata only on the lower surface. Amphistomaty occurs predominantly in fast‐growing herbaceous annuals and in slow‐growing perennial shrubs and trees. In this paper, we present the current understanding and hypotheses on the costs and benefits of amphistomaty related to water and CO2 transport in contrasting leaf morphologies. First, there is no evidence that amphistomatous species achieve higher stomatal densities on a projected leaf area basis than hypostomatous species, but two‐sided gas exchange is less limited by boundary layer effects. Second, amphistomaty may provide a specific advantage in thick leaves by shortening the pathway for CO2 transport between the atmosphere and the chloroplasts. In thin leaves of fast‐growing herbaceous annuals, in which both the adaxial and abaxial pathways are already short, amphistomaty enhances leaf–atmosphere gas‐exchange capacity. Third, amphistomaty may help to optimise the leaf‐interior water status for CO2 transport by reducing temperature gradients and so preventing the condensation of water that could limit CO2 diffusion. Fourth, a potential cost of amphistomaty is the need for additional investments in leaf water transport tissue to balance the water loss through the adaxial surface. [ABSTRACT FROM AUTHOR]

Ventilated Solardomes (hemispherical glasshouses) have been used for 20 yr for studying the effects of gaseous pollutants on plants. This paper describes a computer-operated facility for studying the effects of CO2 × temperature regimes on plants. The eight chambers were set up for factorial design experiments - with two levels of CO2 (ambient and ambient+ 340 ppmv), two levels of temperature (ambient and 3 °C tracked continuously above ambient) and two replicates of each CO2 × temperature treatment. Monitoring of environmental conditions within the chambers over a 2 yr period has shown highly effective control of CO2 and temperature regimes. Even with high-quality and u.v.-B transmitting glass, the irradiance in the PAR region was reduced by 18% within the domes. Variation in temperature across the radii of the domes increased with higher photosynthetic photon flux density (PPFD). Vapour pressure deficits (VPDs) in the ambient temperature domes compared well with outside conditions but were higher in the elevated temperature domes. The watering regime within the domes affected intermittently the relationship between 'dome' and 'outside' VPDs. The Solardome facility has been used extensively for studies of the impacts of climate change within the UK Programme on Terrestrial Initiative on Global Environmental Research (TIGER). [ABSTRACT FROM AUTHOR]

• A previously published model of crop nitrogen (N) status based on intercepted photosynthetically active radiation ( Ri, mol per plant) suggested that plant organic N accumulation is related to Ri by a constant ratio, defined hereafter as the radiation use efficiency for N (NRUE). The aim of this paper was to compare the effects of N nutrition and CO2 enrichment on NRUE and RUE (radiation use efficiency for biomass accumulation). • In three unrelated glasshouse experiments, tomato plants ( Solanum lycopersicum) grown in hydroponics were fed for 28 d (exponential growth) with full solutions containing constant concentrations ([ ]) ranging from 0.05 to 15 mol m−3, both under ambient or CO2-enriched (1000 µl l−1) air. • Each experiment comprised five harvests. Low [ ] (< 0.3 mol m−3) limited growth via leaf area (LA) restriction and decreased light interception. CO2 enrichment enhanced dry weight and LA. RUE was not affected by [ ], but increased under CO2-enriched air. By contrast, NRUE was not affected by [ ] or CO2 enrichment. • It is suggested that the radiation efficiency for organic N acquisition (NRUE) did not depend on C or N nutrition for young plants grown under unstressed conditions. [ABSTRACT FROM AUTHOR]

• This paper presents the results of 2 yr of CO2 flux measurements on grassland communities of varying species richness, exposed to either the current or a warmer climate. • We grew experimental plant communities containing one, three or nine grassland species in 12 sunlit, climate-controlled chambers. Half of these chambers were exposed to ambient air temperatures, while the other half were warmed by 3°C. Equal amounts of water were added to heated and unheated communities, implying drier soils if warming increased evapotranspiration. Three main CO2 fluxes (gross photosynthesis, above-ground and below-ground respiration) were measured multiple times per year and reconstructed hourly or half-hourly by relating them to their most important environmental driver. • While CO2 outputs through respiration were largely unchanged under warming, CO2 inputs through photosynthesis were lowered, especially in summer, when heat and drought stress were higher. Above-ground CO2 fluxes were significantly increased in multispecies communities, as more complementary resource use stimulated productivity. Finally, effects of warming appeared to be smallest in monocultures. • This study shows that in a future warmer climate the CO2 sink capacity of temperate grasslands could decline, and that such adverse effects are not likely to be mitigated by efforts to maintain or increase species richness. [ABSTRACT FROM AUTHOR]

Summary • Reproductive traits are key characteristics for predicting the response of communities and ecosystems to global change. • We used meta-analysis to integrate data on eight reproductive traits from 159 CO 2 enrichment papers that provided information on 79 species. • Across all species, CO 2 enrichment (500–800 µl l -1 ) resulted in more flowers (+19%), more fruits (+18%), more seeds (+16%), greater individual seed mass (+4%), greater total seed mass (+25%), and lower seed nitrogen concentration, (N) (-14%). Crops and undomesticated (wild) species did not differ in total mass response to elevated CO 2 (+31%), but crops allocated more mass to reproduction and produced more fruits (+28% vs +4%) and seeds (+21% vs +4%) than did wild species when grown at high CO 2 . Seed [N] was not affected by high CO 2 concentrations in legumes, but declined significantly in most nonlegumes. • Our results provide robust estimates of average plant reproductive responses to CO 2 enrichment and demonstrate important differences among individual taxa and among functional groups. In particular, crops were more responsive to elevated CO 2 than were wild species. These differences and the substantial decline in seed [N] in many species have broad implications for the functioning of future natural and agro-ecosystems. [ABSTRACT FROM AUTHOR]

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 sonic down- regulation, 1-yr-old E shoots also had higher rates of photosynthesis than their A counterpart. 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 tot the modelling of growth and allocation and the potential utility of the branch bag technique are discussed. [ABSTRACT FROM AUTHOR]

This paper reports general patterns of relative growth rate and related traits in response to elevated atmospheric CO2 in eight woody species ranging widely in life form, leaf habit, taxonomy and ecology. Young plants of these species, all of comparable ontogenetic phases, were grown simultaneously in large containers with favourable nutrient and water availability in transparent outdoor chambers at 350 and 700 μl l-1 CO2 for one growing season. We found the following consistent responses. (1) All species grew faster at elevated CO2, whereas the following leaf and allocation traits were consistently lower in CO2-enriched environments: specific leaf area (quotient of leaf area and leaf weight), leaf area ratio (quotient of total leaf area and plant weight), weight-based foliar N concentration and, to a smaller extent, leaf weight fraction (quotient of leaf weight and plant weight). (2) There was important interspecific variation in the magnitude of the response of relative growth rate to CO2. Specific leaf area at ambient CO2 explained 88% of the variation in relative growth rate to CO2 among the eight species. At ambient CO2, relative growth rate itself, was significantly correlated with the relative growth rate response to CO2 only if the leafless species Ulex gallii was excluded from analysis. (3) The four deciduous species had a significantly stronger relative growth rate response to CO2 than the four evergreens. This corresponded with their generally higher specific leaf area. (4) Specific leaf area and leaf habit might be useful for scaling up exercises, as easy-to-measure substitutes for growth responses of (woody) vegetation to elevated CO2. However, the usefulness of such traits in this context needs to be tested in realistic, longer-term manipulative experiments in real ecosystems. [ABSTRACT FROM AUTHOR]

Theoretical developments in our understanding of leaf gas exchange processes and carbon isotope composition (δ13C) mean that it should now be possible to model their responses to global environmental change. Such a model would be of use for process-based interpretations of historical changes in leaf δ13C and for understanding the global stable carbon isotope balance. This paper describes the development and validation of a model towards this aim. The resulting model is used to simulate changes in leaf photosynthesis, stomatal conductance and δ13C of limber pine (Pinus flexilis) in response to the past 30000 y of global environmental change. The predictions of needle δ13C are in line with reported measurements of δ13C from fossilized Pinus flexilis needles preserved in packrat middens in western USA. Leaf gas exchange predictions show that the increased water use efficiency (WUE) of these trees growing in present-day environments, relative to the past, was brought about through an increase in photosynthetic rates and a decrease in stomatal conductance. This contrasts with the explanation of the recent (past 200 y) increase in the WUE of temperate and Mediterranean ecosystems inferred from δ13C measurements which are predicted by the model to have arisen largely by a decrease in stomatal conductance in response to increases in the concentration of atmospheric CO2 since the pre-industrial era. The model as described offers the potential to contribute to our understanding of vegetation effects on the global carbon isotope balance during the glacial periods, and therefore to provide a further constraint on the carbon cycle models used to explain the low concentrations of atmospheric CO2 at these times. [ABSTRACT FROM AUTHOR]

Because of their prominent role in the global carbon balance and their possible carbon sequestration, trees are very important organisms in relation to global climatic changes. Knowledge of these processes is the key to understanding the functioning of the whole forest ecosystem which can be modelled and predicted based on the physiological process information. This paper reviews the major methods and techniques used to examine the likely effects of elevated CO2 on woody plants, as well as the major physiological responses of trees to elevated CO2. The available exposure techniques and approaches are described. An overview table with all relevant literature data over the period 1989-93 summarizes the percent changes in biomass. root/shoot ratio, photosynthesis, leaf area and water use efficiency under elevated CO2. Interaction between growth, photosynthesis and nutrition is discussed with a special emphasis on downward regulation of photosynthesis. The stimulation or reduction found in the respiratory processes of woody plants are reviewed, as well as the effect of elevated CO2 on stomatal density, conductance and water use efficiency. Changes in plant quality and their consequences are examined. Changes in underground processes under elevated CO2 are especially emphasized and related to the functioning of the ecosystem. Some directions for future research arc put forward. [ABSTRACT FROM AUTHOR]

When 8-day seedlings were exposed to 14CO2 in light, approximately 2 hours were required for 14C to reach the apices of the roots. One method used to detect the progress of 14C down the root was to scan the root with a radiochromatogram strip scanner. At this stage most in aqueous ethanol extracts of roots was present as sucrose, equally labelled in glucose and fructose. This was converted only slowly to other components of the soluble fraction so that after 12 hours almost 50% of 14C was still retained in sucrose. 14C exuded from intact roots into surrounding solutions was present in both volatile and non-volatile compounds. In the non-volatile fraction glutamine, glutamic and aspartic acids were the main 14C-amino acids. Exudation of 14C was not affected by changing the inorganic composition of the collecting solution. A change in pH of collecting solution from 6.4 to 5.9 increased exudation. Exudation also increased markedly when 2,4-dinitrophenol or potassium cyanide was present in the collecting solution. [ABSTRACT FROM AUTHOR]

Summary: We present a robust estimation of the CO2 concentration at the surface of photosynthetic mesophyll cells (cw), applicable under reasonable assumptions of assimilation distribution within the leaf. We used Capsicum annuum, Helianthus annuus and Gossypium hirsutumas model plants for our experiments.We introduce calculations to estimate cw using independent adaxial and abaxial gas exchange measurements, and accounting for the mesophyll airspace resistances.The cw was lower than adaxial and abaxial estimated intercellular CO2 concentrations (ci). Differences between cw and the ci of each surface were usually larger than 10 μmol mol−1. Differences between adaxial and abaxial ci ranged from a few μmol mol−1 to almost 50 μmol mol−1, where the largest differences were found at high air saturation deficits (ASD). Differences between adaxial and abaxial ci and the ci estimated by mixing both fluxes ranged from −30 to +20 μmol mol−1, where the largest differences were found under high ASD or high ambient CO2 concentrations.Accounting for cw improves the information that can be extracted from gas exchange experiments, allowing a more detailed description of the CO2 and water vapor gradients within the leaf. [ABSTRACT FROM AUTHOR]

Summary: Generalised dose–response curves are essential to understand how plants acclimate to atmospheric CO2. We carried out a meta‐analysis of 630 experiments in which C3 plants were experimentally grown at different [CO2] under relatively benign conditions, and derived dose–response curves for 85 phenotypic traits. These curves were characterised by form, plasticity, consistency and reliability. Considered over a range of 200–1200 µmol mol−1 CO2, some traits more than doubled (e.g. area‐based photosynthesis; intrinsic water‐use efficiency), whereas others more than halved (area‐based transpiration). At current atmospheric [CO2], 64% of the total stimulation in biomass over the 200–1200 µmol mol−1 range has already been realised. We also mapped the trait responses of plants to [CO2] against those we have quantified before for light intensity. For most traits, CO2 and light responses were of similar direction. However, some traits (such as reproductive effort) only responded to light, others (such as plant height) only to [CO2], and some traits (such as area‐based transpiration) responded in opposite directions. This synthesis provides a comprehensive picture of plant responses to [CO2] at different integration levels and offers the quantitative dose–response curves that can be used to improve global change simulation models. [ABSTRACT FROM AUTHOR]

Summary: Meta‐analyses enable synthesis of results from globally distributed experiments to draw general conclusions about the impacts of global change factors on ecosystem function. Traditional meta‐analyses, however, are challenged by the complexity and diversity of experimental results. We illustrate how several key issues can be addressed by a multivariate, hierarchical Bayesian meta‐analysis (MHBM) approach applied to information extracted from published studies.We applied an MHBM to log‐response ratios for aboveground biomass (AB, n = 300), belowground biomass (BB, n = 205) and soil CO2 exchange (SCE, n = 544), representing 100 studies. The MHBM accounted for study duration, climate effects and covariation among the AB, BB and SCE responses to elevated CO2 (eCO2) and/or warming.The MHBM revealed significant among‐study covariation in the AB and BB responses to experimental treatments. The MHBM imputed missing duration (4.2%) and climate (6%) data, and revealed that climate context governs how eCO2 and warming impact ecosystem function. Predictions identified biomes that may be particularly sensitive to eCO2 or warming, but that are under‐represented in global change experiments.The MHBM approach offers a flexible and powerful tool for synthesising disparate experimental results reported across multiple studies, sites and response variables. [ABSTRACT FROM AUTHOR]

Focuses on paleoatmospheric reconstructions of carbon dioxide concentration that have utilized the observed physiological relationship between atmospheric carbon dioxide and stomatal frequency. Details of the physically based model developed for the study; Nonlinear response of gaseous diffusion through stomatal pores; Fundamental laws governing diffusion.

Summary: Atmospheric carbon dioxide concentration ([CO2]) is increasing, which increases leaf‐scale photosynthesis and intrinsic water‐use efficiency. These direct responses have the potential to increase plant growth, vegetation biomass, and soil organic matter; transferring carbon from the atmosphere into terrestrial ecosystems (a carbon sink). A substantial global terrestrial carbon sink would slow the rate of [CO2] increase and thus climate change. However, ecosystem CO2 responses are complex or confounded by concurrent changes in multiple agents of global change and evidence for a [CO2]‐driven terrestrial carbon sink can appear contradictory. Here we synthesize theory and broad, multidisciplinary evidence for the effects of increasing [CO2] (iCO2) on the global terrestrial carbon sink. Evidence suggests a substantial increase in global photosynthesis since pre‐industrial times. Established theory, supported by experiments, indicates that iCO2 is likely responsible for about half of the increase. Global carbon budgeting, atmospheric data, and forest inventories indicate a historical carbon sink, and these apparent iCO2 responses are high in comparison to experiments and predictions from theory. Plant mortality and soil carbon iCO2 responses are highly uncertain. In conclusion, a range of evidence supports a positive terrestrial carbon sink in response to iCO2, albeit with uncertain magnitude and strong suggestion of a role for additional agents of global change. See also the Commentary on this article by Way et al., 229: 2383–2385. [ABSTRACT FROM AUTHOR]

Infestation with the bird cherry-oat aphid considerably reduced the dry weight yield, the leaf area, the number of tillers and the number of leaves of barley plants. Growth analysis revealed that the major effect of infestation was to reduce unit leaf rate. However, infested plants compensated partially for this by allocating a greater proportion of their dry weight to the production of leaf laminae than did the control plants. Rates of net photosynthesis in individual, attached leaves were measured using the carbon dioxide exchange method; infested and control plants were found to have very similar rates of photosynthesis. Thus the reduction of unit leaf rate did not result from an effect of photosynthesis. It is suggested that the decreased growth of the barley plants is explicable in terms of cumulative assimilate loss due to aphid feeding. [ABSTRACT FROM AUTHOR]

Young plants of the wilty tomato mutant, flacea, in which the stomata resist closure, were sprayed with abscisic acid eight times over a period of 24 hours in light and darkness. The hormone induced closure of stomata similarly in leaves treated either in light or in darkness. Abscisic add does not appear to induce stomatal closure in darkness by increasing the internal CO2 concentration in the leaf, since this concentration should already be very high in darkness. A considerable and rapid decrease of CO2 assimilation and increase of CO2 evolution were demonstrated in mutant as well as in normal plants transferred from light to darkness. [ABSTRACT FROM AUTHOR]

The state of knowledge of the transition of sapwood into heartwood in trees is reviewed, and attention is drawn to the composition of the gas mixture available to such cells as remain alive in wood. The probable effect of such a mixture is postulated and experiments indicate that the high concentrations of carbon dioxide known to exist inside wood are conducive to formation of compounds known to be typical of the heartwood of Acacia mearnsii. [ABSTRACT FROM AUTHOR]

Summary: Rising atmospheric CO2 (ca) is expected to promote tree growth and lower water loss via changes in leaf gas exchange. However, uncertainties remain if gas‐exchange regulation strategies are homeostatic or dynamical in response to increasing ca, as well as evolving climate and pollution inputs.Using a suite of tree ring‐based δ13C‐derived physiological parameters (Δ13C, ci, iWUE) and tree growth from a mesic, low elevation stand of canopy‐dominant Tsuga canadensis in north‐eastern USA, we investigated the influence of rising ca, climate and pollution on, and characterised the dynamical regulation strategy of, leaf gas exchange at multidecadal scales.Isotopic and growth time series revealed an evolving physiological response in which the species shifted its leaf gas‐exchange strategy dynamically (constant ci; constant ci/ca; constant ca − ci) in response to rising ca, moisture availability and site conditions over 111 yr. Tree iWUE plateaued after 1975, driven by greater moisture availability and a changing soil biogeochemistry that may have impaired a stomatal response.Results suggested that trees may exhibit more complex physiological responses to the changing environmental conditions over multidecadal periods, and complicating the parameterisation of Earth system models and the estimation of future carbon sink capacity and water balance in midlatitude forests and elsewhere. [ABSTRACT FROM AUTHOR]

Summary: C2 photosynthesis is a carbon concentrating mechanism that can increase net CO2 assimilation by capturing, concentrating and re‐assimilating CO2 released by photorespiration. Empirical and modelling studies indicate that C2 plants assimilate more carbon than C3 plants under high temperature, bright light, and low CO2 conditions. I argue that engineering C2 photosynthesis into C3 crops is a promising approach to improve photosynthetic performance under these – and temporally heterogeneous – environments, and review the modifications that may re‐create a C2 phenotype in C3 plants. Although a C2 engineering program would encounter many of the same challenges faced by C4 engineering programmes, the simpler leaf anatomical requirements make C2 engineering a feasible approach to improve crops in the medium term. [ABSTRACT FROM AUTHOR]

The author discusses the role of coccolithophore Emiliania huxleyi (E. huxleyi) in ocean acidification. He says that E. huxleyi accounts on global ocean calcium carbonate production. Also investigated is the study conducted by L. T. Bach and colleagues which shows that E. huxleyi provides evidence on carbon concentrating mechanism (CCM) that is not driven by calcification and suggests that E. huxleyi growth in marine system is not stimulated by carbon dioxide as the climate change progresses.

The article comments on a study of lateral diffusion of carbon dioxide conducted by R. Pieruschka et al and published in a 2006 issue of "New Phytologist." It outlines the major arguments of the study and presents a discussion on leaf anatomy and patchy stomata behavior of leaves. It considers the importance of lateral carbon dioxide diffusion.

Summary: Plants grow and transpire during the night. The aim of the present work was to assess the relative flows of carbon, water and solutes, and the energy involved, in sustaining night‐time transpiration and leaf expansive growth under control and salt‐stress conditions.Published and unpublished data were used, for barley plants grown in presence of 0.5–1 mM NaCl (control) and 100 mM NaCl.Night‐time leaf growth presents a more efficient use of taken‐up water compared with day‐time growth. This efficiency increases several‐fold with salt stress. Night‐time transpiration cannot be supported entirely through osmotically driven uptake of water through roots under salt stress. Using a simple three‐ (root medium/cytosol/vacuole) compartment approach, the energy required to support cell expansion during the night is in the lower percentage region (0.03–5.5%) of the energy available through respiration, under both, control and salt‐stress conditions. Use of organic (e.g. hexose equivalents) rather than inorganic (e.g. Na+, Cl−, K+) solutes for generation of osmotic pressure in growing cells, increases the energy demand by orders of magnitude, yet requires only a small portion of carbon assimilated during the day.Night‐time transpiration and leaf expansive growth should be considered as a potential acclimation mechanism to salinity. See also the Commentary on this article by Sanders, 225: 1047–1048. [ABSTRACT FROM AUTHOR]

Summary: Photosynthesis in bryophytes and lycophytes has received less attention than terrestrial plant groups. In particular, few studies have addressed the nonstomatal diffusion conductance to CO2gnsd of these plant groups.Their lower photosynthetic rate per leaf mass area at any given nitrogen concentration compared with vascular plants suggested a stronger limitation by CO2 diffusion. We hypothesized that bryophyte and lycophyte photosynthesis is largely limited by low gnsd. Here, we studied CO2 diffusion inside the photosynthetic tissues and its relationships with photosynthesis and anatomical parameters in bryophyte and lycophyte species in Antarctica, Australia, Estonia, Hawaii and Spain.On average, lycophytes and, specially, bryophytes had the lowest photosynthetic rates and nonstomatal diffusion conductance reported for terrestrial plants. These low values are related to their very thick cell walls and their low exposure of chloroplasts to cell perimeter.We conclude that the reason why bryophytes lie at the lower end of the leaf economics spectrum is their strong nonstomatal diffusion conductance limitation to photosynthesis, which is driven by their specific anatomical characteristics. [ABSTRACT FROM AUTHOR]

Summary: Phosphenolpyruvate carboxylase (PEPC)‐catalysed fixation of bicarbonate to C4 acids is commonly believed to represent a rather small flux in illuminated leaves. In addition, its potential variation with O2 and CO2 is not documented and thus is usually neglected in gas‐exchange studies.Here, we used quantitative NMR analysis of sunflower leaves labelled with 13CO2 (99% 13C) under controlled conditions and measured the amount of 13C found in the four C‐atom positions in malate, the major product of PEPC activity.We found that amongst malate 13C‐isotopomers present after labelling, most molecules were labelled at both C‐1 and C‐4, showing the incorporation of 13C at C‐4 by PEPC fixation and subsequent redistribution to C‐1 by fumarase (malate–fumarate equilibrium). In addition, absolute quantification of 13C content showed that PEPC fixation increased at low CO2 or high O2, and represented up to 1.8 μmol m−2 s−1, that is, 40% of net assimilation measured by gas exchange under high O2/CO2 conditions.Our results show that PEPC fixation represents a quantitatively important CO2‐fixing activity that varies with O2 and/or CO2 mole fraction and this challenges the common interpretation of net assimilation in C3 plants, where PEPC activity is often disregarded or considered to be constant at a very low rate. [ABSTRACT FROM AUTHOR]

ContentsSummary652I.Introduction652II.Discrepancy in predicting the effects of rising [CO2] on the terrestrial C sink655III.Carbon and nutrient storage in plants and its modelling656IV.Modelling the source and the sink: a plant perspective657V.Plant‐scale water and Carbon flux models660VI.Challenges for the future662Acknowledgements663Authors contributions663References663 Summary: The increase in atmospheric CO2 in the future is one of the most certain projections in environmental sciences. Understanding whether vegetation carbon assimilation, growth, and changes in vegetation carbon stocks are affected by higher atmospheric CO2 and translating this understanding in mechanistic vegetation models is of utmost importance. This is highlighted by inconsistencies between global‐scale studies that attribute terrestrial carbon sinks to CO2 stimulation of gross and net primary production on the one hand, and forest inventories, tree‐scale studies, and plant physiological evidence showing a much less pronounced CO2 fertilization effect on the other hand. Here, we review how plant carbon sources and sinks are currently described in terrestrial biosphere models. We highlight an uneven representation of complexity between the modelling of photosynthesis and other processes, such as plant respiration, direct carbon sinks, and carbon allocation, largely driven by available observations. Despite a general lack of data on carbon sink dynamics to drive model improvements, ways forward toward a mechanistic representation of plant carbon sinks are discussed, leveraging on results obtained from plant‐scale models and on observations geared toward model developments. [ABSTRACT FROM AUTHOR]

• Reassimilation of internal CO2 via corticular photosynthesis (PScort) has an important effect on the carbon economy of trees. However, little is known about its role as a source of O2 supply to the stem parenchyma and its implications in consumption and movement of O2 within trees. • PScort of young Populus nigra (black poplar) trees was investigated by combining optical micro‐optode measurements with monitoring of stem chlorophyll fluorescence. • During times of zero sap flow in spring, stem oxygen concentrations (cO2) exhibited large temporal changes. In the sapwood, over 80% of diurnal changes in cO2 could be explained by respiration rates (Rd(mod)). In the cortex, photosynthetic oxygen release during the day altered this relationship. With daytime illumination, oxygen levels in the cortex steadily increased from subambient and even exhibited a diel period of superoxia of up to 110% (% air sat.). By contrast, in the sapwood, cO2 never reached ambient levels; the diurnal oxygen deficit was up to 25% of air saturation. • Our results confirm that PScort is not only a CO2‐recycling mechanism, it is also a mechanism to actively raise the cortical O2 concentration and counteract temporal/spatial hypoxia inside plant stems. [ABSTRACT FROM AUTHOR]

Contents986I.987II.987III.988IV.991V.992VI.995VII.997VIII.998References998 Summary: It has been 75 yr since leaf respiratory metabolism in the light (day respiration) was identified as a low‐flux metabolic pathway that accompanies photosynthesis. In principle, it provides carbon backbones for nitrogen assimilation and evolves CO2 and thus impacts on plant carbon and nitrogen balances. However, for a long time, uncertainties have remained as to whether techniques used to measure day respiratory efflux were valid and whether day respiration responded to environmental gaseous conditions. In the past few years, significant advances have been made using carbon isotopes, ‘omics’ analyses and surveys of respiration rates in mesocosms or ecosystems. There is substantial evidence that day respiration should be viewed as a highly dynamic metabolic pathway that interacts with photosynthesis and photorespiration and responds to atmospheric CO2 mole fraction. The view of leaf day respiration as a constant and/or negligible parameter of net carbon exchange is now outdated and it should now be regarded as a central actor of plant carbon‐use efficiency. [ABSTRACT FROM AUTHOR]

Mitochondrial respiration often appears to be inhibited in the light when compared with measurements in the dark. This inhibition is inferred from the response of the net CO2 assimilation rate ( A) to absorbed irradiance ( I), changing slope around the light compensation point ( Ic). We suggest a model that provides a plausible mechanistic explanation of this 'Kok effect'., The model uses the mathematical description of photosynthesis developed by Farquhar, von Caemmerer and Berry; it involves no inhibition of respiration rate in the light. We also describe a fitting technique for quantifying the Kok effect at low I., Changes in the chloroplastic CO2 partial pressure ( Cc) can explain curvature of A vs I, its diminution in C4 plants and at low oxygen concentrations or high carbon dioxide concentrations in C3 plants, and effects of dark respiration rate and of temperature. It also explains the apparent inhibition of respiration in the light as inferred by the Laisk approach., While there are probably other sources of curvature in A vs I, variation in Cc can largely explain the curvature at low irradiance, and suggests that interpretation of day respiration compared with dark respiration of leaves on the basis of the Kok effect needs reassessment. [ABSTRACT FROM AUTHOR]

We aimed to evaluate the importance of modulations of within-tree carbon (C) allocation by water and low-temperature stress for the prediction of annual forest growth with a process-based model., A new C allocation scheme was implemented in the CASTANEA model that accounts for lagged and direct environmental controls of C allocation. Different approaches (static vs dynamic) to modelling C allocation were then compared in a model-data fusion procedure, using satellite-derived leaf production estimates and biometric measurements at c. 104 sites., The modelling of the environmental control of C allocation significantly improved the ability of CASTANEA to predict the spatial and year-to-year variability of aboveground forest growth along regional gradients. A significant effect of the previous year's water stress on the C allocation to leaves and wood was reported. Our results also are consistent with a prominent role of the environmental modulation of sink demand in the wood growth of the studied species., Data available at large scales can inform forest models about the processes driving annual and seasonal C allocation. Our results call for a greater consideration of C allocation drivers, especially sink-demand fluctuations, for the simulations of current and future forest productivity with process-based models. [ABSTRACT FROM AUTHOR]

Effects of rhizosphere properties on the rhizosphere priming effect ( RPE) are unknown. This study aimed to link species variation in RPE with plant traits and rhizosphere properties., Four C3 species (chickpea, Cicer arietinum; field pea, Pisum sativum; wheat, Triticum aestivum; and white lupin, Lupinus albus) differing in soil acidification and root exudation, were grown in a C4 soil. The CO2 released from soil was trapped using a newly developed Na OH-trapping system., White lupin and wheat showed greater positive RPEs, in contrast to the negative RPE produced by chickpea. The greatest RPE of white lupin was in line with its capacity to release root exudates, whereas the negative RPE of chickpea was attributed to its great ability to acidify rhizosphere soil. The enhanced RPE of field pea at maturity might result from high nitrogen deposition and release of structural root carbon components following root senescence. Root biomass and length played a minor role in the species variation in RPE., Rhizosphere acidification was shown to be an important factor affecting the magnitude and direction of RPE. Future studies on RPE modelling and mechanistic understanding of the processes that regulate RPE should consider the effect of rhizosphere pH. [ABSTRACT FROM AUTHOR]

Diatoms are widespread in aquatic ecosystems where they may be limited by the supply of inorganic carbon. Their carbon dioxide-concentrating mechanisms ( CCMs) involving transporters and carbonic anhydrases ( CAs) are well known, but the contribution of a biochemical CCM involving C4 metabolism is contentious., The CCM(s) present in the marine-centric diatom, Thalassiosira pseudonana, were studied in cells exposed to high or low concentrations of CO2, using a range of approaches., At low CO2, cells possessed a CCM based on active uptake of CO2 (70% contribution) and bicarbonate, while at high CO2, cells were restricted to CO2. CA was highly and rapidly activated on transfer to low CO2 and played a key role because inhibition of external CA produced uptake kinetics similar to cells grown at high CO2. The activities of phosphoenolpyruvate ( PEP) carboxylase ( PEPC) and the PEP-regenerating enzyme, pyruvate phosphate dikinase ( PPDK), were lower in cells grown at low than at high CO2. The ratios of PEPC and PPDK to ribulose bisphosphate carboxylase were substantially lower than 1, even at low CO2., Our data suggest that the kinetic properties of this species results from a biophysical CCM and not from C4 type metabolism. [ABSTRACT FROM AUTHOR]

• The carbon sink intensity of the biosphere depends on the balance between gross primary productivity (GPP) of forest canopies and ecosystem respiration. GPP, however, cannot be directly measured and estimates are not well constrained. A new approach relying on canopy transpiration flux measured as sap flow, and water-use efficiency inferred from carbon isotope analysis (GPPSF) has been proposed, but not tested against eddy covariance-based estimates (GPPEC). • Here we take advantage of parallel measurements using the two approaches at a semi-arid pine forest site to compare the GPPSF and GPPEC estimates on diurnal to annual timescales. • GPPSF captured the seasonal dynamics of GPPEC (GPPSF = 0.99 × GPPEC, r² = 0.78, RMSE = 0.82, n = 457 d) with good agreement at the annual timescale (653 vs 670 g Cm-2 yr-1). Both methods showed that GPP ranged between 1 and 8 g Cm-2 d-1, and the GPPSF/GPPEC ratio was between 0.5 and 2.0 during 82% of the days. Carbon uptake dynamics at the individual tree scale conformed with leaf scale rates of net assimilation. • GPPSF can produce robust estimations of tree- and canopy-scale rates of CO2 uptake, providing constraints and greatly extending current GPPEC estimations. [ABSTRACT FROM AUTHOR]

Climate change as a consequence of increasing atmospheric CO2 influences plant photosynthesis and transpiration. Although the involvement of stomata in plant responses to elevated CO2 has been well established, the underlying mechanism of elevated CO2-induced stomatal movement remains largely unknown., We used diverse techniques, including laser scanning confocal microscopy, transmission electron microscopy, biochemical methodologies and gene silencing to investigate the signaling pathway for elevated CO2-induced stomatal movement in tomato ( Solanum lycopersicum)., Elevated CO2-induced stomatal closure was dependent on the production of RESPIRATORY BURST OXIDASE 1 ( RBOH1)-mediated hydrogen peroxide (H2O2) and NITRATE REDUCTASE ( NR)-mediated nitric oxide ( NO) in guard cells in an abscisic acid ( ABA)-independent manner. Silencing of OPEN STOMATA 1 ( OST1) compromised the elevated CO2-induced accumulation of H2O2 and NO, upregulation of SLOW ANION CHANNEL ASSOCIATED 1 ( SLAC1) gene expression and reduction of stomatal aperture, whereas silencing of RBOH1 or NR had no effects on the expression of OST1., Our results demonstrate that as critical signaling molecules, RBOH1-dependent H2O2 and NR-dependent NO act downstream of OST1 that regulate SLAC1 expression and elevated CO2-induced stomatal movement. This information is crucial to deepen the understanding of CO2 signaling pathway in guard cells. [ABSTRACT FROM AUTHOR]

Presents a study on the meta-analysis of carbon dioxide response based on plant's nutrient and sink activity. Importance of adequate moisture; Percentage of crop and wild species data; Emphasis of data treatment from technology-oriented or taxonomy-oriented data.

• Improvement in crop water-use efficiency (WUE) is a critical priority for regions facing increased drought or diminished groundwater resources. Despite new tools for the manipulation of stomatal development, the engineering of plants with high WUE remains a challenge. • We used Arabidopsis epidermal patterning factor (EPF) mutants exhibiting altered stomatal density to test whether WUE could be improved directly by manipulation of the genes controlling stomatal density. Specifically, we tested whether constitutive overexpression of EPF2 reduced stomatal density and maximum stomatal conductance (gw(max)) sufficiently to increase WUE. • We found that a reduction in gw(max) via reduced stomatal density in EPF2-overexpressing plants (EPF2OE) increased both instantaneous and long-term WUE without altering significantly the photosynthetic capacity. Conversely, plants lacking both EPF1 and EPF2 expression (epf1epf2) exhibited higher stomatal density, higher gw(max) and lower instantaneous WUE, as well as lower (but not significantly so) long-term WUE. • Targeted genetic modification of stomatal conductance, such as in EPF2OE, is a viable approach for the engineering of higher WUE in crops, particularly in future high-carbon-dioxide (CO2) atmospheres. [ABSTRACT FROM AUTHOR]

900I.900II.901III.901IV.902V.905VI.908909References909 Summary: Integrative concepts of the biosphere, ecosystem, biogeocenosis and, recently, Earth's critical zone embrace scientific disciplines that link matter, energy and organisms in a systems‐level understanding of our remarkable planet. Here, we assert the congruence of Tansley's (1935) venerable ecosystem concept of ‘one physical system’ with Earth science's critical zone. Ecosystems and critical zones are congruent across spatial–temporal scales from vegetation‐clad weathering profiles and hillslopes, small catchments, landscapes, river basins, continents, to Earth's whole terrestrial surface. What may be less obvious is congruence in the vertical dimension. We use ecosystem metabolism to argue that full accounting of photosynthetically fixed carbon includes respiratory CO2 and carbonic acid that propagate to the base of the critical zone itself. Although a small fraction of respiration, the downward diffusion of CO2 helps determine rates of soil formation and, ultimately, ecosystem evolution and resilience. Because life in the upper portions of terrestrial ecosystems significantly affects biogeochemistry throughout weathering profiles, the lower boundaries of most terrestrial ecosystems have been demarcated at depths too shallow to permit a complete understanding of ecosystem structure and function. Opportunities abound to explore connections between upper and lower components of critical‐zone ecosystems, between soils and streams in watersheds, and between plant‐derived CO2 and deep microbial communities and mineral weathering. See also the Commentary by Dan Binkley [ABSTRACT FROM AUTHOR]

Anthropogenic changes in atmospheric carbon dioxide ( CO2) and ozone (O3) are known to alter tree physiology and growth, but the cascading effects on herbivore communities and herbivore-mediated nutrient cycling are poorly understood., We sampled herbivore frass, herbivore-mediated greenfall, and leaf-litter deposition in temperate forest stands under elevated CO2 ( c. 560 ppm) and O3 ( c. 1.5× ambient), analyzed substrate chemical composition, and compared the quality and quantity of fluxes under multiple atmospheric treatments., Leaf-chewing herbivores fluxed 6.2 g m−2 yr−1 of frass and greenfall from the canopy to the forest floor, with a carbon : nitrogen (C : N) ratio 32% lower than that of leaf litter. Herbivore fluxes of dry matter, C, condensed tannins, and N increased under elevated CO2 (35, 32, 63 and 39%, respectively), while fluxes of N decreased (18%) under elevated O3. Herbivore-mediated dry matter inputs scaled across atmospheric treatments as a constant proportion of leaf-litter inputs., Increased fluxes under elevated CO2 were consistent with increased herbivore consumption and abundance, and with increased plant growth and soil respiration, previously reported for this experimental site. Results suggest that insect herbivory will reinforce other factors, such as photosynthetic rate and fine-root production, impacting C sequestration by forests in future environments. [ABSTRACT FROM AUTHOR]

Stomatal conductance ( gs) is constrained by the size and number of stomata on the plant epidermis, and the potential maximum rate of gs can be calculated based on these stomatal traits (Anatomical gsmax). However, the relationship between Anatomical gsmax and operational gs under atmospheric conditions remains undefined., Leaf-level gas-exchange measurements were performed for six Arabidopsis thaliana genotypes that have different Anatomical gsmax profiles resulting from mutations or transgene activity in stomatal development., We found that Anatomical gsmax was an accurate prediction of gs under gas-exchange conditions that maximized stomatal opening, namely high-intensity light, low [ CO2], and high relative humidity. Plants with different Anatomical gsmax had quantitatively similar responses to increasing [ CO2] when gs was scaled to Anatomical gsmax. This latter relationship allowed us to produce and test an empirical model derived from the Ball-Woodrow-Berry equation that estimates gs as a function of Anatomical gsmax, relative humidity, and [ CO2] at the leaf., The capacity to predict operational gs via Anatomical gsmax and the pore-specific short-term response to [ CO2] demonstrates a precise link between stomatal development and leaf physiology. This connection should be useful to quantify the gas flux of plants in past, present, and future CO2 regimes based upon the anatomical features of stomata. [ABSTRACT FROM AUTHOR]

A letter to the editor is presented in response to a study related to atmospheric CO2 and stomatal optimisation.

31I.31II.32III.34IV.35V.37VI.38VII.3941References41 Summary: The rhizosphere priming effect (RPE) is a mechanism by which plants interact with soil functions. The large impact of the RPE on soil organic matter decomposition rates (from 50% reduction to 380% increase) warrants similar attention to that being paid to climatic controls on ecosystem functions. Furthermore, global increases in atmospheric CO2 concentration and surface temperature can significantly alter the RPE. Our analysis using a game theoretic model suggests that the RPE may have resulted from an evolutionarily stable mutualistic association between plants and rhizosphere microbes. Through model simulations based on microbial physiology, we demonstrate that a shift in microbial metabolic response to different substrate inputs from plants is a plausible mechanism leading to positive or negative RPEs. In a case study of the Duke Free‐Air CO2 Enrichment experiment, performance of the PhotoCent model was significantly improved by including an RPE‐induced 40% increase in soil organic matter decomposition rate for the elevated CO2 treatment – demonstrating the value of incorporating the RPE into future ecosystem models. Overall, the RPE is emerging as a crucial mechanism in terrestrial ecosystems, which awaits substantial research and model development. [ABSTRACT FROM AUTHOR]

Disturbance affects most terrestrial ecosystems and has the potential to shape their responses to chronic environmental change., Scrub-oak vegetation regenerating from fire disturbance in subtropical Florida was exposed to experimentally elevated carbon dioxide ( CO2) concentration (+350 μl l−1) using open-top chambers for 11 yr, punctuated by hurricane disturbance in year 8. Here, we report the effects of elevated CO2 on aboveground and belowground net primary productivity ( NPP) and nitrogen ( N) cycling during this experiment., The stimulation of NPP and N uptake by elevated CO2 peaked within 2 yr after disturbance by fire and hurricane, when soil nutrient availability was high. The stimulation subsequently declined and disappeared, coincident with low soil nutrient availability and with a CO2-induced reduction in the N concentration of oak stems., These findings show that strong growth responses to elevated CO2 can be transient, are consistent with a progressively limited response to elevated CO2 interrupted by disturbance, and illustrate the importance of biogeochemical responses to extreme events in modulating ecosystem responses to global environmental change. [ABSTRACT FROM AUTHOR]

An introduction to the journal "New Phytologist," is presented in which the guest editor discuss the relationship of drought to forest mortality.

Changes in atmospheric carbon dioxide concentration ([ CO2]) affect plant carbon/water tradeoffs, with implications for drought tolerance. Leaf-level studies often indicate that drought tolerance may increase with rising [ CO2], but integrated leaf and xylem responses are not well understood in this respect. In addition, the influence of the low [ CO2] of the last glacial period on drought tolerance and xylem properties is not well understood., We investigated the interactive effects of a broad range of [ CO2] and plant water potentials on leaf function, xylem structure and function and the integration of leaf and xylem function in Phaseolus vulgaris., Elevated [ CO2] decreased vessel implosion strength, reduced conduit-specific hydraulic conductance, and compromised leaf-specific xylem hydraulic conductance under moderate drought. By contrast, at glacial [ CO2], transpiration was maintained under moderate drought via greater conduit-specific and leaf-specific hydraulic conductance in association with increased vessel implosion strength., Our study involving the integration of leaf and xylem responses suggests that increasing [ CO2] does not improve drought tolerance. We show that, under glacial conditions, changes in leaf and xylem properties could increase drought tolerance, while under future conditions, greater productivity may only occur when higher water use can be accommodated. [ABSTRACT FROM AUTHOR]

Plants form ubiquitous associations with diverse microbes. These interactions range from parasitism to mutualism, depending partly on resource supplies that are being altered by global change. While many studies have considered the separate effects of pathogens and mutualists on their hosts, few studies have investigated interactions among microbial mutualists and pathogens in the context of global change., Using two wild grass species as model hosts, we grew individual plants under ambient or elevated CO2, and ambient or increased soil phosphorus (P) supply. Additionally, individuals were grown with or without arbuscular mycorrhizal inoculum, and after 2 wk, plants were inoculated or mock-inoculated with a phloem-restricted virus., Under elevated CO2, mycorrhizal association increased the titer of virus infections, and virus infection reciprocally increased the colonization of roots by mycorrhizal fungi. Additionally, virus infection decreased plant allocation to root biomass, increased leaf P, and modulated effects of CO2 and P addition on mycorrhizal root colonization., These results indicate that plant mutualists and pathogens can alter each other's success, and predict that these interactions will respond to increased resource availability and elevated CO2. Together, our findings highlight the importance of interactions among multiple microorganisms for plant performance under global change. [ABSTRACT FROM AUTHOR]

The article offers the author's perspective on the credibility of the hypothesis made by Dirks and colleagues on glycine molecules. Dirks et al. believe that glycine molecules synthesized along the photorespiratory pathway have been simulated to feed peptide synthesis under certain circumstances rather than conversion to serine and carbon dioxide production. It concludes that both photorespiration and day respiration develop carbon dioxide.

The world's forests are currently exposed to increasing concentrations of carbon dioxide ( CO2) and ozone ( O3). Both pollutants can potentially exert a selective effect on plant populations. This, in turn, may lead to changes in ecosystem properties, such as carbon sequestration. Here, we report how elevated CO2 and O3 affect the genetic composition of a woody plant population via altered survival., Using data from the Aspen free-air CO2 enrichment ( FACE) experiment (in which aspen clones were grown in factorial combinations of CO2 and O3), we develop a hierarchical Bayesian model of survival. We also examine how survival differences between clones could affect pollutant responses in the next generation., Our model predicts that the relative abundance of the tested clones, given equal initial abundance, would shift under either elevated CO2 or O3 as a result of changing survival rates. Survival was strongly affected by between-clone differences in growth responses. Selection could noticeably decrease O3 sensitivity in the next generation, depending on the heritability of growth responses and the distribution of seed production. The response to selection by CO2, however, is likely to be small., Our results suggest that the changing atmospheric composition could shift the genotypic composition and average pollutant responses of tree populations over moderate timescales. [ABSTRACT FROM AUTHOR]