Search

Summary: The oxygen isotope composition of cellulose (δ18O values) has been suggested to contain information on stomatal conductance (gs) responses to rising pCO2. The extent by which pCO2 affects leaf water and cellulose δ18O values (δ18OLW and δ18OC) and the isotope processes that determine pCO2 effects on δ18OLW and δ18OC are, however, unknown.We tested the effects of pCO2 on gs, δ18OLW and δ18OC in a glasshouse experiment, where six plant species were grown under pCO2 ranging from 200 to 500 ppm.Increasing pCO2 caused a decline in gs and an increase in δ18OLW, as expected. Importantly, the effects of pCO2 on gs and δ18OLW were small and pCO2 effects on δ18OLW were not directly transferred to δ18OC but were attenuated in grasses and amplified in dicotyledonous herbs and legumes. This is likely because of functional group‐specific pCO2 effects on the model parameter pxpex.Our study highlights important uncertainties when using δ18OC as a proxy for gs. Specifically, pCO2‐triggered gs effects on δ18OLW and δ18OC are possibly too small to be detected in natural settings and a pCO2 effect on pxpex may render the commonly assumed negative linkage between δ18OC and gs to be incorrect, potentially confounding δ18OC based gs reconstructions. [ABSTRACT FROM AUTHOR]

The article discusses a study that examines the factors contributing to tree mortality in tropical forests. The research finds that the traits of trees in current forests are more important for predicting changes in forest health than climate projections or rising CO2 levels. The study emphasizes the importance of understanding the trait composition of forests, particularly in tropical regions. The findings suggest that future forest health may depend more on existing traits than on climate change. The study also highlights the need for collaboration between field ecology and vegetation model development. [Extracted from the article]

Summary: Mosses hold a unique position in plant evolution and are crucial for protecting natural, long‐term carbon storage systems such as permafrost and bogs. Due to small stature, mosses grow close to the soil surface and are exposed to high levels of CO2, produced by soil respiration. However, the impact of elevated CO2 (eCO2) levels on mosses remains underexplored.We determined the growth responses of the moss Physcomitrium patens to eCO2 in combination with different nitrogen levels and characterized the underlying physiological and metabolic changes.Three distinct growth characteristics, an early transition to caulonema, the development of longer, highly pigmented rhizoids, and increased biomass, define the phenotypic responses of P. patens to eCO2. Elevated CO2 impacts growth by enhancing the level of a sugar signaling metabolite, T6P. The quantity and form of nitrogen source influences these metabolic and phenotypic changes. Under eCO2, P. patens exhibits a diffused growth pattern in the presence of nitrate, but ammonium supplementation results in dense growth with tall gametophores, demonstrating high phenotypic plasticity under different environments.These results provide a framework for comparing the eCO2 responses of P. patens with other plant groups and provide crucial insights into moss growth that may benefit climate change models. [ABSTRACT FROM AUTHOR]

Summary: The elevation of CO2 in the atmosphere increases plant biomass but decreases their mineral content. The genetic and molecular bases of these effects remain mostly unknown, in particular in the root system, which is responsible for plant nutrient uptake.To gain knowledge about the effect of elevated CO2 on plant growth and physiology, and to identify its regulatory in the roots, we analyzed genome expression in Arabidopsis roots through a combinatorial design with contrasted levels of CO2, nitrate, and iron.We demonstrated that elevated CO2 has a modest effect on root genome expression under nutrient sufficiency, but by contrast leads to massive expression changes under nitrate or iron deficiencies. We demonstrated that elevated CO2 negatively targets nitrate and iron starvation modules at the transcriptional level, associated with a reduction in high‐affinity nitrate uptake. Finally, we inferred a gene regulatory network governing the root response to elevated CO2. This network allowed us to identify candidate transcription factors including MYB15, WOX11, and EDF3 which we experimentally validated for their role in the stimulation of growth by elevated CO2.Our approach identified key features and regulators of the plant response to elevated CO2, with the objective of developing crops resilient to climate change. See also the Commentary on this article by Kaiser, 239: 818–820. [ABSTRACT FROM AUTHOR]

Summary: The elevation of CO2 in the atmosphere increases plant biomass but decreases their mineral content. The genetic and molecular bases of these effects remain mostly unknown, in particular in the root system, which is responsible for plant nutrient uptake.To gain knowledge about the effect of elevated CO2 on plant growth and physiology, and to identify its regulatory in the roots, we analyzed genome expression in Arabidopsis roots through a combinatorial design with contrasted levels of CO2, nitrate, and iron.We demonstrated that elevated CO2 has a modest effect on root genome expression under nutrient sufficiency, but by contrast leads to massive expression changes under nitrate or iron deficiencies. We demonstrated that elevated CO2 negatively targets nitrate and iron starvation modules at the transcriptional level, associated with a reduction in high‐affinity nitrate uptake. Finally, we inferred a gene regulatory network governing the root response to elevated CO2. This network allowed us to identify candidate transcription factors including MYB15, WOX11, and EDF3 which we experimentally validated for their role in the stimulation of growth by elevated CO2.Our approach identified key features and regulators of the plant response to elevated CO2, with the objective of developing crops resilient to climate change. See also the Commentary on this article by Kaiser, 239: 818–820. [ABSTRACT FROM AUTHOR]

Summary: Plant responses to abiotic environmental challenges are known to have lasting effects on the plant beyond the initial stress exposure. Some of these lasting effects are transgenerational, affecting the next generation. The plant response to elevated carbon dioxide (CO2) levels has been well studied. However, these investigations are typically limited to plants grown for a single generation in a high CO2 environment while transgenerational studies are rare.We aimed to determine transgenerational growth responses in plants after exposure to high CO2 by investigating the direct progeny when returned to baseline CO2 levels.We found that both the flowering plant Arabidopsis thaliana and seedless nonvascular plant Physcomitrium patens continue to display accelerated growth rates in the progeny of plants exposed to high CO2. We used the model species Arabidopsis to dissect the molecular mechanism and found that DNA methylation pathways are necessary for heritability of this growth response.More specifically, the pathway of RNA‐directed DNA methylation is required to initiate methylation and the proteins CMT2 and CMT3 are needed for the transgenerational propagation of this DNA methylation to the progeny plants. Together, these two DNA methylation pathways establish and then maintain a cellular memory to high CO2 exposure. [ABSTRACT FROM AUTHOR]

The oxygen isotope composition of cellulose (δ 18 O values) has been suggested to contain information on stomatal conductance (g s ) responses to rising pCO 2 . The extent by which pCO 2 affects leaf water and cellulose δ 18 O values (δ 18 O LW and δ 18 O C ) and the isotope processes that determine pCO 2 effects on δ 18 O LW and δ 18 O C are, however, unknown. We tested the effects of pCO 2 on g s , δ 18 O LW and δ 18 O C in a glasshouse experiment, where six plant species were grown under pCO 2 ranging from 200 to 500 ppm. Increasing pCO 2 caused a decline in g s and an increase in δ 18 O LW , as expected. Importantly, the effects of pCO 2 on g s and δ 18 O LW were small and pCO 2 effects on δ 18 O LW were not directly transferred to δ 18 O C but were attenuated in grasses and amplified in dicotyledonous herbs and legumes. This is likely because of functional group-specific pCO 2 effects on the model parameter p x p ex . Our study highlights important uncertainties when using δ 18 O C as a proxy for g s . Specifically, pCO 2 -triggered g s effects on δ 18 O LW and δ 18 O C are possibly too small to be detected in natural settings and a pCO 2 effect on p x p ex may render the commonly assumed negative linkage between δ 18 O C and g s to be incorrect, potentially confounding δ 18 O C based g s reconstructions., (© 2024 The Authors. New Phytologist © 2024 New Phytologist Foundation.)

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]

Summary: Plant responses to elevated atmospheric carbon dioxide (eCO2) have been hypothesized as a key mechanism that may ameliorate the impact of future drought. Yet, despite decades of experiments, the question of whether eCO2 reduces plant water use, yielding 'water savings' that can be used to maintain plant function during periods of water stress, remains unresolved. In this Viewpoint, we identify the experimental challenges and limitations to our understanding of plant responses to drought under eCO2. In particular, we argue that future studies need to move beyond exploring whether eCO2 played 'a role' or 'no role' in responses to drought, but instead more carefully consider the timescales and conditions that would induce an influence. We also argue that considering emergent differences in soil water content may be an insufficient means of assessing the impact of eCO2. We identify eCO2 impact during severe drought (e.g. to the point of mortality), interactions with future changes in vapour pressure deficit and uncertainty about changes in leaf area as key gaps in our current understanding. New insights into CO2 × drought interactions are essential to better constrain model theory that governs future climate model projections of land–atmosphere interactions during periods of water stress. [ABSTRACT FROM AUTHOR]

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.

Summary: Trees are increasingly exposed to hot droughts due to CO2‐induced climate change. However, the direct role of [CO2] in altering tree physiological responses to drought and heat stress remains ambiguous.Pinus halepensis (Aleppo pine) trees were grown from seed under ambient (421 ppm) or elevated (867 ppm) [CO2]. The 1.5‐yr‐old trees, either well watered or drought treated for 1 month, were transferred to separate gas‐exchange chambers and the temperature gradually increased from 25°C to 40°C over a 10 d period. Continuous whole‐tree shoot and root gas‐exchange measurements were supplemented by primary metabolite analysis.Elevated [CO2] reduced tree water loss, reflected in lower stomatal conductance, resulting in a higher water‐use efficiency throughout amplifying heat stress. Net carbon uptake declined strongly, driven by increases in respiration peaking earlier in the well‐watered (31–32°C) than drought (33–34°C) treatments unaffected by growth [CO2]. Further, drought altered the primary metabolome, whereas the metabolic response to [CO2] was subtle and mainly reflected in enhanced root protein stability.The impact of elevated [CO2] on tree stress responses was modest and largely vanished with progressing heat and drought. We therefore conclude that increases in atmospheric [CO2] cannot counterbalance the impacts of hot drought extremes in Aleppo pine. [ABSTRACT FROM AUTHOR]

Summary: Vegetation nutrient limitation is essential for understanding ecosystem responses to global change. In particular, leaf nitrogen (N) is known to be plastic under changed nutrient limitation. However, models can often not capture these observed changes, leading to erroneous predictions of whole‐ecosystem stocks and fluxes.We hypothesise that an optimality approach can improve representation of leaf N content compared to existing empirical approaches. Unlike previous optimality‐based approaches, which adjust foliar N concentrations based on canopy carbon export, we use a maximisation criterion based on whole‐plant growth, and allow for a lagged response of foliar N to this maximisation criterion to account for the limited plasticity of this plant trait. We test these model variants at a range of Free‐Air CO2 Enrichment and N fertilisation experimental sites.We show that a model based solely on canopy carbon export fails to reproduce observed patterns and predicts decreasing leaf N content with increased N availability. However, an optimal model which maximises total plant growth can correctly reproduce the observed patterns.The optimality model we present here is a whole‐plant approach which reproduces biologically realistic changes in leaf N and can thereby improve ecosystem‐level predictions under transient conditions. [ABSTRACT FROM AUTHOR]

Mosses hold a unique position in plant evolution and are crucial for protecting natural, long-term carbon storage systems such as permafrost and bogs. Due to small stature, mosses grow close to the soil surface and are exposed to high levels of CO 2 , produced by soil respiration. However, the impact of elevated CO 2 (eCO 2 ) levels on mosses remains underexplored. We determined the growth responses of the moss Physcomitrium patens to eCO 2 in combination with different nitrogen levels and characterized the underlying physiological and metabolic changes. Three distinct growth characteristics, an early transition to caulonema, the development of longer, highly pigmented rhizoids, and increased biomass, define the phenotypic responses of P. patens to eCO 2 . Elevated CO 2 impacts growth by enhancing the level of a sugar signaling metabolite, T6P. The quantity and form of nitrogen source influences these metabolic and phenotypic changes. Under eCO 2 , P. patens exhibits a diffused growth pattern in the presence of nitrate, but ammonium supplementation results in dense growth with tall gametophores, demonstrating high phenotypic plasticity under different environments. These results provide a framework for comparing the eCO 2 responses of P. patens with other plant groups and provide crucial insights into moss growth that may benefit climate change models., (© 2023 The Authors. New Phytologist © 2023 New Phytologist Foundation This article has been contributed to by U.S. Government employees and their work is in the public domain in the USA.)

In this review, we discuss the potential for mycorrhizal fungi to act as a source or sink for carbon (C) under elevated CO2 and nitrogen deposition. Mycorrhizal tissue has been estimated to comprise a significant fraction of soil organic matter and below-ground biomass in a range of systems. The current body of literature indicates that in many systems exposed to elevated CO2, mycorrhizal fungi might sequester increased amounts of C in living, dead and residual hyphal biomass in the soil. Through this process, the fungi might serve as a negative feedback on the rise in atmospheric CO2 levels caused by fossil fuel burning and deforestation. By contrast, a few preliminary studies suggest that N deposition might increase turnover rates of fungal tissue and negate CO2 effects on hyphal biomass. If these latter responses are consistent among ecosystems, C storage in hyphae might decline in habitats surrounding agricultural and urban areas. When N additions occur without CO2 enrichment, effects on mycorrhizal growth are inconsistent. We note that analyses of hyphal decomposition under elevated CO2 and N additions are extremely sparse but are critical in our understanding of the impact of global change on the cycling of mycorrhizal C. Finally, shifts in the community composition of arbuscular and ectomycorrhizal fungi with increasing CO2 or N availability are frequently documented. Since mycorrhizal groups vary in growth rate and tissue quality, these changes in species assemblages could produce unforeseeable impacts on the productivity, survivorship, or decomposition of mycorrhizal biomass.

Summary: Elevated atmospheric carbon dioxide (eCO2) concentrations promote symbiosis between roots and arbuscular mycorrhizal fungi (AMF), modifying plant nutrient acquisition and cycling of carbon, nitrogen and phosphate. However, the biological mechanisms by which plants transmit aerial eCO2 cues to roots, to alter the symbiotic associations remain unknown.We used a range of interdisciplinary approaches, including gene silencing, grafting, transmission electron microscopy, liquid chromatography tandem mass spectrometry (LC–MS/MS), biochemical methodologies and gene transcript analysis to explore the complexities of environmental signal transmission from the point of perception in the leaves at the apex to the roots.Here we show that eCO2 triggers apoplastic hydrogen peroxide (H2O2)‐dependent auxin production in tomato shoots followed by systemic signaling that results in strigolactone biosynthesis in the roots. This redox‐auxin‐strigolactone systemic signaling cascade facilitates eCO2‐induced AMF symbiosis and phosphate utilization.Our results challenge the current paradigm of eCO2 effects on AMF and provide new insights into potential targets for manipulation of AMF symbiosis for high nutrient utilization under future climate change scenarios. See also the Commentary on this article by Hause, 224: 5–7. [ABSTRACT FROM AUTHOR]

Summary: It has been suggested that plant carbon (C) use by symbiotic arbuscular mycorrhizal fungi (AMF) may be compensated by higher photosynthetic rates because fungal metabolism creates a strong C sink that prevents photosynthate accumulation and downregulation of photosynthesis. This mechanism remains largely unexplored and lacks experimental evidence.We report here two experiments showing that the experimental manipulation of the mycorrhizal C sink significantly affected the photosynthetic rates of cucumber host plants. We expected that a sudden reduction in sink strength would cause a significant reduction in photosynthetic rates, at least temporarily.Excision of part of the extraradical mycorrhizal mycelium from roots, and causing no disturbance to the plant, induced a sustained (10–40%) decline in photosynthetic rates that lasted from 30 min to several hours in plants that were well‐nourished and hydrated, and in the absence of growth or photosynthesis promotion by mycorrhizal inoculation. This effect was though minor in plants growing at high (700 ppm) atmospheric CO2.This is the first direct experimental evidence for the C sink strength effects exerted by arbuscular mycorrhizal symbionts on plant photosynthesis. It encourages further experimentation on mycorrhizal source–sink relations, and may have strong implications in large‐scale assessments and modelling of plant photosynthesis. [ABSTRACT FROM AUTHOR]

Summary: Resistance against pathogens and herbivorous insects in many plant results from the expression of resistance (R) genes. Few reports, however, have considered the effects of elevated CO2 on R gene‐based resistance in plants. The current study determined the responses of two near isogenic Medicago truncatula genotypes (Jester has an R gene and A17 does not) to the pea aphid and elevated CO2 in open‐top chambers in the field. Aphid abundance, mean relative growth rate and feeding efficiency were increased by elevated CO2 on A17 plants but were reduced on Jester plants. According to proteomic and gene expression data, elevated CO2 enhanced pathogen‐associated molecular pattern (PAMP)‐triggered immunity (PTI) but decreased the effector‐triggered immunity (ETI) in aphid‐infested A17 plants. For aphid‐infested Jester plants, by contrast, elevated CO2 enhanced the ETI‐related heat shock protein (HSP) 90 and its co‐chaperones, the jasmonic acid (JA) signaling pathway, and ubiquitin‐mediated proteolysis. In a loss‐of‐function experiment, silencing of the HSP90 gene in Jester plants impaired the JA signaling pathway and ubiquitin‐mediated proteolysis against the aphid under ambient CO2, and negated the increased resistance against the aphid under elevated CO2. Our results suggest that increases in expression of HSP90 are responsible for the enhanced resistance against the aphid under elevated CO2. [ABSTRACT FROM AUTHOR]

The elevation of CO 2 in the atmosphere increases plant biomass but decreases their mineral content. The genetic and molecular bases of these effects remain mostly unknown, in particular in the root system, which is responsible for plant nutrient uptake. To gain knowledge about the effect of elevated CO 2 on plant growth and physiology, and to identify its regulatory in the roots, we analyzed genome expression in Arabidopsis roots through a combinatorial design with contrasted levels of CO 2 , nitrate, and iron. We demonstrated that elevated CO 2 has a modest effect on root genome expression under nutrient sufficiency, but by contrast leads to massive expression changes under nitrate or iron deficiencies. We demonstrated that elevated CO 2 negatively targets nitrate and iron starvation modules at the transcriptional level, associated with a reduction in high-affinity nitrate uptake. Finally, we inferred a gene regulatory network governing the root response to elevated CO 2 . This network allowed us to identify candidate transcription factors including MYB15, WOX11, and EDF3 which we experimentally validated for their role in the stimulation of growth by elevated CO 2 . Our approach identified key features and regulators of the plant response to elevated CO 2 , with the objective of developing crops resilient to climate change., (© 2023 The Authors. New Phytologist © 2023 New Phytologist Foundation.)

Plant responses to abiotic environmental challenges are known to have lasting effects on the plant beyond the initial stress exposure. Some of these lasting effects are transgenerational, affecting the next generation. The plant response to elevated carbon dioxide (CO 2 ) levels has been well studied. However, these investigations are typically limited to plants grown for a single generation in a high CO 2 environment while transgenerational studies are rare. We aimed to determine transgenerational growth responses in plants after exposure to high CO 2 by investigating the direct progeny when returned to baseline CO 2 levels. We found that both the flowering plant Arabidopsis thaliana and seedless nonvascular plant Physcomitrium patens continue to display accelerated growth rates in the progeny of plants exposed to high CO 2 . We used the model species Arabidopsis to dissect the molecular mechanism and found that DNA methylation pathways are necessary for heritability of this growth response. More specifically, the pathway of RNA-directed DNA methylation is required to initiate methylation and the proteins CMT2 and CMT3 are needed for the transgenerational propagation of this DNA methylation to the progeny plants. Together, these two DNA methylation pathways establish and then maintain a cellular memory to high CO 2 exposure., (© 2023 The Authors New Phytologist © 2023 New Phytologist Foundation.)

Extramatrical mycelia ( EMM) of ectomycorrhizal fungi are important in carbon (C) and nitrogen (N) cycling in forests, but poor knowledge about EMM biomass and necromass turnovers makes the quantification of their role problematic., We studied the impacts of elevated CO2 and N fertilization on EMM production and turnover in a Pinus taeda forest. EMM C was determined by the analysis of ergosterol (biomass), chitin (total bio- and necromass) and total organic C ( TOC) of sand-filled mycelium in-growth bags. The production and turnover of EMM bio- and necromass and total C were estimated by modelling., N fertilization reduced the standing EMM biomass C to 57% and its production to 51% of the control (from 238 to 122 kg C ha−1 yr−1), whereas elevated CO2 had no detectable effects. Biomass turnover was high (˜13 yr−1) and unchanged by the treatments. Necromass turnover was slow and was reduced from 1.5 yr−1 in the control to 0.65 yr−1 in the N-fertilized treatment. However, TOC data did not support an N effect on necromass turnover., An estimated EMM production ranging from 2.5 to 6% of net primary production stresses the importance of its inclusion in C models. A slow EMM necromass turnover indicates an importance in building up forest humus. [ABSTRACT FROM AUTHOR]

The first generation of forest free-air CO2 enrichment (FACE) experiments has successfully provided deeper understanding about how forests respond to an increasing CO2 concentration in the atmosphere. Located in aggrading stands in the temperate zone, they have provided a strong foundation for testing critical assumptions in terrestrial biosphere models that are being used to project future interactions between forest productivity and the atmosphere, despite the limited inference space of these experiments with regards to the range of global ecosystems. Now, a new generation ofFACEexperiments in mature forests in different biomes and over a wide range of climate space and biodiversity will significantly expand the inference space. These new experiments are: EucFACE in a mature Eucalyptus stand on highly weathered soil in subtropical Australia; AmazonFACE in a highly diverse, primary rainforest in Brazil; BIFoR-FACE in a 150-yr-old deciduous woodland stand in central England; and SwedFACE proposed in a hemiboreal, Pinus sylvestris stand in Sweden. We now have a unique opportunity to initiate a model-data interaction as an integral part of experimental design and to address a set of cross-site science questions on topics including responses of mature forests; interactions with temperature, water stress, and phosphorus limitation; and the influence of biodiversity. [ABSTRACT FROM AUTHOR]

Proline (Pro) is a versatile metabolite playing a role in the protection of plants against environmental stresses. To gain a deeper understanding of the regulation of Pro metabolism under predicted future climate conditions, including drought stress, elevated temperature and CO2, we combined measurements in contrasting grassland species (two grasses and two legumes) at multiple organisational levels, that is, metabolite concentrations, enzyme activities and gene expression., Drought stress (D) activates Pro biosynthesis and represses its catabolism, and elevated temperature ( DT) further elevated its content. Elevated CO2 attenuated the DT effect on Pro accumulation., Computational pathway control analysis allowed a mechanistic understanding of the regulatory changes in Pro metabolism. This analysis indicates that the experimentally observed coregulation of multiple enzymes is more effective in modulating Pro concentrations than regulation of a single step. Pyrroline-5-carboxylate synthetase (P5 CS) and pyrroline-5-carboxylate reductase (P5 CR) play a central role in grasses ( Lolium perenne, Poa pratensis), and arginase ( ARG), ornithine aminotransferase ( OAT) and P5 CR play a central role in legumes ( Medicago lupulina, Lotus corniculatus)., Different strategies in the regulation of Pro concentrations under stress conditions were observed. In grasses the glutamate pathway is activated predominantly, and in the legumes the ornithine pathway, possibly related to differences in N-nutritional status. [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]

Predicting the response of fine roots to increased atmospheric CO2 concentration has important implications for carbon (C) and nutrient cycling in forest ecosystems. Root architecture is known to play an important role in how trees acquire soil resources in changing environments. However, the effects of elevated CO2 on the fine-root architecture of trees remain unclear., We investigated the architectural response of fine roots exposed to 14 yr of CO2 enrichment and 6 yr of nitrogen (N) fertilization in a Pinus taeda (loblolly pine) forest. Root traits reflecting geometry, topology and uptake function were measured on intact fine-root branches removed from soil monoliths and the litter layer., CO2 enrichment resulted in the development of a fine-root pool that was less dichotomous and more exploratory under N-limited conditions. The per cent mycorrhizal colonization did not differ among treatments, suggesting that root growth and acclimation to elevated CO2 were quantitatively more important than increased mycorrhizal associations., Our findings emphasize the importance of architectural plasticity in response to environmental change and suggest that changes in root architecture may allow trees to effectively exploit larger volumes of soil, thereby pre-empting progressive nutrient limitations. [ABSTRACT FROM AUTHOR]

Models of forest energy, water and carbon cycles assume decreased stomatal conductance with elevated atmospheric CO2 concentration ([CO2]) based on leaf-scale measurements, a response not directly translatable to canopies. Where canopy-atmosphere are well-coupled, [CO2]-induced structural changes, such as increasing leaf-area index ( LD), may cause, or compensate for, reduced mean canopy stomatal conductance ( GS), keeping transpiration ( EC) and, hence, runoff unaltered., We investigated GS responses to increasing [CO2] of conifer and broadleaved trees in a temperate forest subjected to 17-yr free-air CO2 enrichment (FACE; + 200 μmol mol−1). During the final phase of the experiment, we employed step changes of [CO2] in four elevated-[CO2] plots, separating direct response to changing [CO2] in the leaf-internal air-space from indirect effects of slow changes via leaf hydraulic adjustments and canopy development., Short-term manipulations caused no direct response up to 1.8 × ambient [CO2], suggesting that the observed long-term 21% reduction of GS was an indirect effect of decreased leaf hydraulic conductance and increased leaf shading. Thus, E C was unaffected by [CO2] because 19% higher canopy LD nullified the effect of leaf hydraulic acclimation on GS., We advocate long-term experiments of duration sufficient for slow responses to manifest, and modifying models predicting forest water, energy and carbon cycles accordingly. [ABSTRACT FROM AUTHOR]

• Elevated atmospheric CO2 concentration (eCO2) has the potential to increase vegetation carbon storage if increased net primary production causes increased long-lived biomass. Model predictions of eCO2 effects on vegetation carbon storage depend on how allocation and turnover processes are represented. • We used data from two temperate forest free-air CO2 enrichment (FACE) experiments to evaluate representations of allocation and turnover in 11 ecosystem models. • Observed eCO2 effects on allocation were dynamic. Allocation schemes based on functional relationships among biomass fractions that vary with resource availability were best able to capture the general features of the observations. Allocation schemes based on constant fractions or resource limitations performed less well, with some models having unintended outcomes. Few models represent turnover processes mechanistically and there was wide variation in predictions of tissue lifespan. Consequently, models did not perform well at predicting eCO2 effects on vegetation carbon storage. • Our recommendations to reduce uncertainty include: use of allocation schemes constrained by biomass fractions; careful testing of allocation schemes; and synthesis of allocation and turnover data in terms of model parameters. Data from intensively studied ecosystem manipulation experiments are invaluable for constraining models and we recommend that such experiments should attempt to fully quantify carbon, water and nutrient budgets. [ABSTRACT FROM AUTHOR]

We analysed the responses of 11 ecosystem models to elevated atmospheric [ CO2] (e CO2) at two temperate forest ecosystems ( Duke and Oak Ridge National Laboratory ( ORNL) Free- Air CO2 Enrichment ( FACE) experiments) to test alternative representations of carbon ( C)-nitrogen ( N) cycle processes., We decomposed the model responses into component processes affecting the response to e CO2 and confronted these with observations from the FACE experiments., Most of the models reproduced the observed initial enhancement of net primary production ( NPP) at both sites, but none was able to simulate both the sustained 10-yr enhancement at Duke and the declining response at ORNL: models generally showed signs of progressive N limitation as a result of lower than observed plant N uptake. Nonetheless, many models showed qualitative agreement with observed component processes. The results suggest that improved representation of above-ground-below-ground interactions and better constraints on plant stoichiometry are important for a predictive understanding of e CO2 effects. Improved accuracy of soil organic matter inventories is pivotal to reduce uncertainty in the observed C- N budgets., The two FACE experiments are insufficient to fully constrain terrestrial responses to eCO2, given the complexity of factors leading to the observed diverging trends, and the consequential inability of the models to explain these trends. Nevertheless, the ecosystem models were able to capture important features of the experiments, lending some support to their projections. [ABSTRACT FROM AUTHOR]

Plant regeneration from seed is largely governed by germinability and speed of germination. These fitness components have received considerably less attention in CO2 research relative to studies of vegetative or reproductive output responses. Moreover, the limited literature has not been rigorously examined for generalizable patterns of responses and/or potential mechanisms. We used a meta-analytic approach to summarize literature results of seed germination characteristics in response to parental CO2 enrichment ( e CO2). The direct effects of e CO2 on germination components were also analyzed. The data set came from 29 original research papers encompassing 64 species and 116 observations. Across all studies, parental e CO2 increased subsequent germination by 9%, but the responses varied among species by as much as 300%. The response was significantly higher in trees than in other life forms. With the exception of crops, parental e CO2 also increased germination rate in most life forms and functional groups. Despite a considerable interspecific variability, we found a positive correlation between germination success and seed mass responses to parental e CO2. Therefore, the observed diversity of regeneration success responses to parental e CO2 is partly controlled by the direction and magnitude of changes in seed mass. [ABSTRACT FROM AUTHOR]

The performance of herbivorous insects is greatly affected by plant nutritional quality and resistance, which are likely to be altered by rising concentrations of atmospheric CO2., We previously reported that elevated CO2 enhanced biological nitrogen (N) fixation of Medicago truncatula, which could result in an increased supply of amino acids to the pea aphid ( Acyrthosiphon pisum). The current study examined the N nutritional quality and aphid resistance of sickle, an ethylene-insensitive mutant of M. truncatula with supernodulation, and its wild-type control A17 under elevated CO2 in open-top field chambers., Regardless of CO2 concentration, growth and amino acid content were greater and aphid resistance was lower in sickle than in A17. Elevated CO2 up-regulated N assimilation and transamination-related enzymes activities and increased phloem amino acids in both genotypes. Furthermore, elevated CO2 down-regulated expression of 1-amino-cyclopropane-carboxylic acid ( ACC), sickle gene ( SKL) and ethylene response transcription factors ( ERF) genes in the ethylene signaling pathway of A17 when infested by aphids and decreased resistance against aphids in terms of lower activities of superoxide dismutase ( SOD), peroxidase ( POD), and polyphenol oxidase ( PPO)., Our results suggest that elevated CO2 suppresses the ethylene signaling pathway in M. truncatula, which results in an increase in plant nutritional quality for aphids and a decrease in plant resistance against aphids. [ABSTRACT FROM AUTHOR]

Rising atmospheric carbon dioxide ( CO2) could alter the carbon (C) and nitrogen (N) content of ecosystems, yet the magnitude of these effects are not well known. We examined C and N budgets of a subtropical woodland after 11 yr of exposure to elevated CO2., We used open-top chambers to manipulate CO2 during regrowth after fire, and measured C, N and tracer 15N in ecosystem components throughout the experiment., Elevated CO2 increased plant C and tended to increase plant N but did not significantly increase whole-system C or N. Elevated CO2 increased soil microbial activity and labile soil C, but more slowly cycling soil C pools tended to decline. Recovery of a long-term 15N tracer indicated that CO2 exposure increased N losses and altered N distribution, with no effect on N inputs., Increased plant C accrual was accompanied by higher soil microbial activity and increased C losses from soil, yielding no statistically detectable effect of elevated CO2 on net ecosystem C uptake. These findings challenge the treatment of terrestrial ecosystems responses to elevated CO2 in current biogeochemical models, where the effect of elevated CO2 on ecosystem C balance is described as enhanced photosynthesis and plant growth with decomposition as a first-order response. [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]

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]

Effects of elevated atmospheric [ CO2] on plant isoprene emissions are controversial. Relying on leaf-scale measurements, most models simulating isoprene emissions in future higher [ CO2] atmospheres suggest reduced emission fluxes. However, combined effects of elevated [ CO2] on leaf area growth, net assimilation and isoprene emission rates have rarely been studied on the canopy scale, but stimulation of leaf area growth may largely compensate for possible [ CO2] inhibition reported at the leaf scale. This study tests the hypothesis that stimulated leaf area growth leads to increased canopy isoprene emission rates., We studied the dynamics of canopy growth, and net assimilation and isoprene emission rates in hybrid aspen ( Populus tremula × Populus tremuloides) grown under 380 and 780 μmol mol−1 [ CO2]. A theoretical framework based on the Chapman- Richards function to model canopy growth and numerically compare the growth dynamics among ambient and elevated atmospheric [ CO2]-grown plants was developed., Plants grown under elevated [ CO2] had higher C : N ratio, and greater total leaf area, and canopy net assimilation and isoprene emission rates. During ontogeny, these key canopy characteristics developed faster and stabilized earlier under elevated [ CO2]. However, on a leaf area basis, foliage physiological traits remained in a transient state over the whole experiment., These results demonstrate that canopy-scale dynamics importantly complements the leaf-scale processes, and that isoprene emissions may actually increase under higher [ CO2] as a result of enhanced leaf area production. [ABSTRACT FROM AUTHOR]

Deserts are considered 'below-ground dominated', yet little is known about the impact of rising CO2 in combination with natural weather cycles on long-term dynamics of root biomass. This study quantifies the temporal dynamics of fine-root production, loss and standing crop in an intact desert ecosystem exposed to 10 yr of elevated CO2., We used monthly minirhizotron observations from 4 yr (2003-2007) for two dominant shrub species and along community transects at the Nevada Desert free-air CO2 enrichment Facility. Data were synthesized within a Bayesian framework that included effects of CO2 concentration, cover type, phenological period, antecedent soil water and biological inertia (i.e. the influence of prior root production and loss)., Elevated CO2 treatment interacted with antecedent soil moisture and had significantly greater effects on fine-root dynamics during certain phenological periods. With respect to biological inertia, plants under elevated CO2 tended to initiate fine-root growth sooner and sustain growth longer, with the net effect of increasing the magnitude of production and mortality cycles., Elevated CO2 interacts with past environmental (e.g. antecedent soil water) and biological (e.g. biological inertia) factors to affect fine-root dynamics, and such interactions are expected to be important for predicting future soil carbon pools. [ABSTRACT FROM AUTHOR]

The authors discuss the study by Bradford and colleagues on plant community and ecosystem responses to multiple levels of atmospheric [carbon dioxide (CO2)] and nitrogen (N) enrichment. They mention that the researchers used multi-level experiments which allow partitioning of change impacts into quadratic, linear and shaped responses. They note that their findings suggest that changes in abiotic soil properties related to change factor might influence plant productivity reactions.

Summary: •The response of nocturnal stomatal conductance (gs,n) to rising atmospheric CO2 concentration ([CO2]) is currently unknown, and may differ from responses of daytime stomatal conductance (gs,d). Because night‐time water fluxes can have a significant impact on landscape water budgets, an understanding of the effects of [CO2] and temperature on gs,n is crucial for predicting water fluxes under future climates.•Here, we examined the effects of [CO2] (280, 400 and 640 μmol mol−1), temperature (ambient and ambient + 4°C) and drought on gs,n, and gs,d in Eucalyptus sideroxylon saplings.•gs,n was substantially higher than zero, averaging 34% of gs,d. Before the onset of drought, gs,n increased by 85% when [CO2] increased from 280 to 640 μmol mol−1, averaged across both temperature treatments. gs,n declined with drought, but an increase in [CO2] slowed this decline. Consequently, the soil water potential at which gs,n was zero (Ψ0) was significantly more negative in elevated [CO2] and temperature treatments. gs,d showed inconsistent responses to [CO2] and temperature.•gs,n may be higher in future climates, potentially increasing nocturnal water loss and susceptibility to drought, but cannot be predicted easily from gs,d. Therefore, predictive models using stomatal conductance must account for both gs,n and gs,d when estimating ecosystem water fluxes. [ABSTRACT FROM AUTHOR]

Summary [ABSTRACT FROM AUTHOR]

The article discusses the impact of publication bias in ecological research. It says that meta-analysis, which is used to synthesize literature surveys, is influenced by publication bias or the publication of studies with significant outcome. It features the studies on the soil respiration response to elevated carbon dioxide (CO2) which the negative results were unpublished or unwritten. Furthermore, tests methods to detect publication bias on data sets are presented.

•Simulation models indicate that the nitrogen (N) cycle plays a key role in how other ecosystem processes such as plant productivity and carbon (C) sequestration respond to elevated CO2 and warming. However, combined effects of elevated CO2 and warming on N cycling have rarely been tested in the field. •Here, we studied N cycling under ambient and elevated CO2 concentrations (600 μmol mol−1), and ambient and elevated temperature (1.5 : 3.0°C warmer day:night) in a full factorial semiarid grassland field experiment in Wyoming, USA. We measured soil inorganic N, plant and microbial N pool sizes and NO3− uptake (using a 15N tracer). •Soil inorganic N significantly decreased under elevated CO2, probably because of increased microbial N immobilization, while soil inorganic N and plant N pool sizes significantly increased with warming, probably because of increased N supply. We observed no CO2 × warming interaction effects on soil inorganic N, N pool sizes or NO3− uptake in plants and microbes. •Our results indicate a more closed N cycle under elevated CO2 and a more open N cycle with warming, which could affect long-term N retention, plant productivity, and C sequestration in this semiarid grassland. [ABSTRACT FROM AUTHOR]

•The delay in autumnal senescence that has occurred in recent decades has been linked to rising temperatures. Here, we suggest that increasing atmospheric CO2 may partly account for delayed autumnal senescence and for the first time, through transcriptome analysis, identify gene expression changes associated with this delay. •Using a plantation of Populus × euramericana grown in elevated [CO2] (e[CO2]) with free-air CO2 enrichment (FACE) technology, we investigated the molecular and biochemical basis of this response. A Populus cDNA microarray was used to identify genes representing multiple biochemical pathways influenced by e[CO2] during senescence. Gene expression changes were confirmed through real-time quantitative PCR, and leaf biochemical assays. •Pathways for secondary metabolism and glycolysis were significantly up-regulated by e[CO2] during senescence, in particular, those related to anthocyanin biosynthesis. Expressed sequence tags (ESTs) representing the two most significantly up-regulated transcripts in e[CO2], LDOX ( leucoanthocyanidin dioxgenase) and DFR ( dihydroflavonol reductase), gave (e[CO2]/ambient CO2 (a[CO2])) expression ratios of 39.6 and 19.3, respectively. •We showed that in e[CO2] there was increased autumnal leaf sugar accumulation and up-regulation of genes determining anthocyanin biosynthesis which, we propose, prolongs leaf longevity during natural autumnal senescence. [ABSTRACT FROM AUTHOR]

• Does transgenically incorporated insect resistance affect constitutive and herbivore-inducible terpenoid emissions and multitrophic communication under elevated atmospheric CO2 or ozone (O3)? This study aimed to clarify the possible interactions between allocation to direct defences ( Bacillus thuringiensis (Bt) toxin production) and that to endogenous indirect defences under future climatic conditions. • Terpenoid emissions were measured from vegetative-stage non-Bt and Bt Brassica napus grown in growth chambers under control or doubled CO2, and control (filtered air) or 100 ppb O3. The olfactometric orientation of Cotesia vestalis, an endoparasitoid of the herbivorous diamondback moth ( Plutella xylostella), was assessed under the corresponding CO2 and O3 concentrations. • The response of terpenoid emission to CO2 or O3 elevations was equivalent for Bt and non-Bt plants, but lower target herbivory reduced herbivore-inducible emissions from Bt plants. Elevated CO2 increased emissions of most terpenoids, whereas O3 reduced total terpenoid emissions. Cotesia vestalis orientated to host-damaged plants independent of plant type or CO2 concentration. Under elevated O3, host-damaged non-Bt plants attracted 75% of the parasitoids, but only 36.8% of parasitoids orientated to host-damaged Bt plants. • Elevated O3 has the potential to perturb specialized food-web communication in Bt crops. [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]

• In a water-limited system, the following hypotheses are proposed: warming will increase seedling mortality; elevated atmospheric CO2 will reduce seedling mortality by reducing transpiration, thereby increasing soil water availability; and longevity (i.e. whether a species is annual or perennial) will affect the response of a species to global changes. • Here, these three hypotheses are tested by assessing the impact of elevated CO2 (550 µmol mol−1) and warming (+2°C) on seedling emergence, survivorship and establishment in an Australian temperate grassland from autumn 2004 to autumn 2007. • Warming impacts on seedling survivorship were dependent upon species longevity. Warming reduced seedling survivorship of perennials through its effects on soil water potential but the seedling survivorship of annuals was reduced to a greater extent than could be accounted for by treatment effects on soil water potential. Elevated CO2 did not significantly affect seedling survivorship in annuals or perennials. • These results show that warming will alter recruitment of perennial species by changing soil water potential but will reduce recruitment of annual species independent of any effects on soil moisture. The results also show that exposure to elevated CO2 does not make seedlings more resistant to dry soils. [ABSTRACT FROM AUTHOR]

• Isoprene is the most important nonmethane hydrocarbon emitted by plants. The role of isoprene in the plant is not entirely understood but there is evidence that it might have a protective role against different oxidative stresses originating from heat shock and/or exposure to ozone (O3). Thus, plants under stress conditions might benefit by constitutively high or by higher stress-induced isoprene emission rates. • In this study, measurements are presented of isoprene emission from aspen ( Populus tremuloides) trees grown in the field for several years under elevated CO2 and O3. Two aspen clones were investigated: the O3-tolerant 271 and the O3-sensitive 42E. • Isoprene emission decreased significantly both under elevated CO2 and under elevated O3 in the O3-sensitive clone, but only slightly in the O3-tolerant clone. • This study demonstrates that long-term-adapted plants are not able to respond to O3 stress by increasing their isoprene emission rates. However, O3-tolerant clones have the capacity to maintain higher amounts of isoprene emission. It is suggested that tolerance to O3 is explained by a combination of different factors; while the reduction of O3 uptake is likely to be the most important, the capacity to maintain higher amounts of isoprene is an important factor in strengthening this character. [ABSTRACT FROM AUTHOR]

• Isoprene is the most important nonmethane hydrocarbon emitted by plants. The role of isoprene in the plant is not entirely understood but there is evidence that it might have a protective role against different oxidative stresses originating from heat shock and/or exposure to ozone (O3). Thus, plants under stress conditions might benefit by constitutively high or by higher stress-induced isoprene emission rates. • In this study, measurements are presented of isoprene emission from aspen ( Populus tremuloides) trees grown in the field for several years under elevated CO2 and O3. Two aspen clones were investigated: the O3-tolerant 271 and the O3-sensitive 42E. • Isoprene emission decreased significantly both under elevated CO2 and under elevated O3 in the O3-sensitive clone, but only slightly in the O3-tolerant clone. • This study demonstrates that long-term-adapted plants are not able to respond to O3 stress by increasing their isoprene emission rates. However, O3-tolerant clones have the capacity to maintain higher amounts of isoprene emission. It is suggested that tolerance to O3 is explained by a combination of different factors; while the reduction of O3 uptake is likely to be the most important, the capacity to maintain higher amounts of isoprene is an important factor in strengthening this character. [ABSTRACT FROM AUTHOR]

• Flowering is a critical stage in plant life cycles, and changes might alter processes at the species, community and ecosystem levels. Therefore, likely flowering-time responses to global change drivers are needed for predictions of global change impacts on natural and managed ecosystems. • Here, the impact of elevated atmospheric CO2 concentration ([CO2]) (550 µmol mol−1) and warming (+2ºC) is reported on flowering times in a native, species-rich, temperate grassland in Tasmania, Australia in both 2004 and 2005. • Elevated [CO2] did not affect average time of first flowering in either year, only affecting three out of 23 species. Warming reduced time to first flowering by an average of 19.1 d in 2004, acting on most species, but did not significantly alter flowering time in 2005, which might be related to the timing of rainfall. Elevated [CO2] and warming treatments did not interact on flowering time. • These results show elevated [CO2] did not alter average flowering time or duration in this grassland; neither did it alter the response to warming. Therefore, flowering phenology appears insensitive to increasing [CO2] in this ecosystem, although the response to warming varies between years but can be strong. [ABSTRACT FROM AUTHOR]

• Flowering is a critical stage in plant life cycles, and changes might alter processes at the species, community and ecosystem levels. Therefore, likely flowering-time responses to global change drivers are needed for predictions of global change impacts on natural and managed ecosystems. • Here, the impact of elevated atmospheric CO2 concentration ([CO2]) (550 µmol mol−1) and warming (+2ºC) is reported on flowering times in a native, species-rich, temperate grassland in Tasmania, Australia in both 2004 and 2005. • Elevated [CO2] did not affect average time of first flowering in either year, only affecting three out of 23 species. Warming reduced time to first flowering by an average of 19.1 d in 2004, acting on most species, but did not significantly alter flowering time in 2005, which might be related to the timing of rainfall. Elevated [CO2] and warming treatments did not interact on flowering time. • These results show elevated [CO2] did not alter average flowering time or duration in this grassland; neither did it alter the response to warming. Therefore, flowering phenology appears insensitive to increasing [CO2] in this ecosystem, although the response to warming varies between years but can be strong. [ABSTRACT FROM AUTHOR]

The article discusses the highlights of a session on meta-analysis held at the Ecological Society of America 92nd Annual Meeting in San Jose, California, in August 2007. Researchers discussed the use of meta-analysis in the field ecology during the session. They presented some techniques for ecological meta-analysis that have been borrowed from other disciplines.

• Species differ in their responses to global changes such as rising CO2 and temperature, meaning that global changes are likely to change the structure of plant communities. Such alterations in community composition must be underlain by changes in the population dynamics of component species. • Here, the impact of elevated CO2 (550 µmol mol−1) and warming (+2°C) on the population growth of four plant species important in Australian temperate grasslands is reported. Data collected from the Tasmanian free-air CO2 enrichment (TasFACE) experiment between 2003 and 2006 were analysed using population matrix models. • Population growth of Themeda triandra, a perennial C4 grass, was largely unaffected by either factor but population growth of Austrodanthonia caespitosa, a perennial C3 grass, was reduced substantially in elevated CO2 plots. Warming and elevated CO2 had antagonistic effects on population growth of two invasive weeds, Hypochaeris radicata and Leontodon taraxacoides, with warming causing population decline. Analysis of life cycle stages showed that seed production, seedling emergence and establishment were important factors in the responses of the species to global changes. • These results show that the demographic approach is very useful in understanding the variable responses of plants to global changes and in elucidating the life cycle stages that are most responsive. [ABSTRACT FROM AUTHOR]

• Information on the genetic variation of plant response to elevated CO2 (e[CO2]) is needed to understand plant adaptation and to pinpoint likely evolutionary response to future high atmospheric CO2 concentrations. • Here, quantitative trait loci (QTL) for above- and below-ground tree growth were determined in a pedigree – an F2 hybrid of poplar ( Populus trichocarpa and Populus deltoides), following season-long exposure to either current day ambient CO2 (a[CO2]) or e[CO2] at 600 µl l−1, and genotype by environment interactions investigated. • In the F2 generation, both above- and below-ground growth showed a significant increase in e[CO2]. Three areas of the genome on linkage groups I, IX and XII were identified as important in determining above-ground growth response to e[CO2], while an additional three areas of the genome on linkage groups IV, XVI and XIX appeared important in determining root growth response to e[CO2]. • These results quantify and identify genetic variation in response to e[CO2] and provide an insight into genomic response to the changing environment. [ABSTRACT FROM AUTHOR]