Long-term growth of soybean at elevated [CO2] does not cause acclimation of stomatal conductance under fully open-air conditions

Accurately predicting plant function and global biogeochemical cycles later in this century will be complicated if stomatal conductance (g(s)) acclimates to growth at elevated [CO(2)], in the sense of a long-term alteration of the response of g(s) to [CO(2)], humidity (h) and/or photosynthetic rate (A). If so, photosynthetic and stomatal models will require parameterization at each growth [CO(2)] of interest. Photosynthetic acclimation to long-term growth at elevated [CO(2)] occurs frequently. Acclimation of g(s) has rarely been examined, even though stomatal density commonly changes with growth [CO(2)]. Soybean was grown under field conditions at ambient [CO(2)] (378 micromol mol(-1)) and elevated [CO(2)] (552 micromol mol(-1)) using free-air [CO(2)] enrichment (FACE). This study tested for stomatal acclimation by parameterizing and validating the widely used Ball et al. model (1987, Progress in Photosynthesis Research, vol IV, 221-224) with measurements of leaf gas exchange. The dependence of g(s) on A, h and [CO(2)] at the leaf surface was unaltered by long-term growth at elevated [CO(2)]. This suggests that the commonly observed decrease in g(s) under elevated [CO(2)] is due entirely to the direct instantaneous effect of [CO(2)] on g(s) and that there is no longer-term acclimation of g(s) independent of photosynthetic acclimation. The model accurately predicted g(s) for soybean growing under ambient and elevated [CO(2)] in the field. Model parameters under ambient and elevated [CO(2)] were indistinguishable, demonstrating that stomatal function under ambient and elevated [CO(2)] could be modelled without the need for parameterization at each growth [CO(2)].     

Increased temperatures may safeguard the nutritional quality of crops under future elevated CO2 concentrations

Iron (Fe) and zinc (Zn) deficiencies are a global human health problem that may worsen by the growth of crops at elevated atmospheric CO₂ concentration (eCO₂). However, climate change will also involve higher temperature, but it is unclear how the combined effect of eCO₂ and higher temperature will affect the nutritional quality of food crops. To begin to address this question, we grew soybean (Glycine max) in a Temperature by Free‐Air CO₂ Enrichment (T‐FACE) experiment in 2014 and 2015 under ambient (400 μmol mol^?1) and elevated (600 μmol mol^?1) CO₂ concentrations, and under ambient and elevated temperatures (+2.7°C day and +3.4°C at night). In our study, eCO₂ significantly decreased Fe concentration in soybean seeds in both seasons (?8.7 and ?7.7%) and Zn concentration in one season (?8.9%), while higher temperature (at ambient CO₂ concentration) had the opposite effect. The combination of eCO₂ with elevated temperature generally restored seed Fe and Zn concentrations to levels obtained under ambient CO₂ and temperature conditions, suggesting that the potential threat to human nutrition by increasing CO₂ concentration may not be realized. In general, seed Fe concentration was negatively correlated with yield, suggesting inherent limitations to increasing seed Fe. In addition, we confirm our previous report that the concentration of seed storage products and several minerals varies with node position at which the seeds developed. Overall, these results demonstrate the complexity of predicting climate change effects on food and nutritional security when various environmental parameters change in an interactive manner.     

Evolutionary context for understanding and manipulating plant responses to past, present and future atmospheric [CO2

Variation in atmospheric [CO(2)] is a prominent feature of the environmental history over which vascular plants have evolved. Periods of falling and low [CO(2)] in the palaeo-record appear to have created selective pressure for important adaptations in modern plants. Today, rising [CO(2)] is a key component of anthropogenic global environmental change that will impact plants and the ecosystem goods and services they deliver. Currently, there is limited evidence that natural plant populations have evolved in response to contemporary increases in [CO(2)] in ways that increase plant productivity or fitness, and no evidence for incidental breeding of crop varieties to achieve greater yield enhancement from rising [CO(2)]. Evolutionary responses to elevated [CO(2)] have been studied by applying selection in controlled environments, quantitative genetics and trait-based approaches. Findings to date suggest that adaptive changes in plant traits in response to future [CO(2)] will not be consistently observed across species or environments and will not be large in magnitude compared with physiological and ecological responses to future [CO(2)]. This lack of evidence for strong evolutionary effects of elevated [CO(2)] is surprising, given the large effects of elevated [CO(2)] on plant phenotypes. New studies under more stressful, complex environmental conditions associated with climate change may revise this view. Efforts are underway to engineer plants to: (i) overcome the limitations to photosynthesis from today's [CO(2)] and (ii) benefit maximally from future, greater [CO(2)]. Targets range in scale from manipulating the function of a single enzyme (e.g. Rubisco) to adding metabolic pathways from bacteria as well as engineering the structural and functional components necessary for C(4) photosynthesis into C(3) leaves. Successfully improving plant performance will depend on combining the knowledge of the evolutionary context, cellular basis and physiological integration of plant responses to varying [CO(2)].     

Alteration of forest succession and carbon cycling under elevated CO2

Regenerating forests influence the global carbon (C) cycle, and understanding how climate change will affect patterns of regeneration and C storage is necessary to predict the rate of atmospheric carbon dioxide (CO₂) increase in future decades. While experimental elevation of CO₂ has revealed that young forests respond with increased productivity, there remains considerable uncertainty as to how the long‐term dynamics of forest regrowth are shaped by elevated CO₂ (eCO₂). Here, we use the mechanistic size‐ and age‐ structured Ecosystem Demography model to investigate the effects of CO₂ enrichment on forest regeneration, using data from the Duke Forest Free‐Air Carbon dioxide Enrichment (FACE) experiment, a forest chronosequence, and an eddy‐covariance tower for model parameterization and evaluation. We find that the dynamics of forest regeneration are accelerated, and stands consistently hit a variety of developmental benchmarks earlier under eCO₂. Because responses to eCO₂ varied by plant functional type, successional pathways, and mature forest composition differed under eCO₂, with mid‐ and late‐successional hardwood functional types experiencing greater increases in biomass compared to early‐successional functional types and the pine canopy. Over the simulation period, eCO₂ led to an increase in total ecosystem C storage of 9.7 Mg C ha^‐1. Model predictions of mature forest biomass and ecosystem–atmosphere exchange of CO₂ and H₂O were sensitive to assumptions about nitrogen limitation; both the magnitude and persistence of the ecosystem response to eCO₂ were reduced under N limitation. In summary, our simulations demonstrate that eCO₂ can result in a general acceleration of forest regeneration while altering the course of successional change and having a lasting impact on forest ecosystems.     

Evidence that elevated CO2 reduces resistance to the European large raspberry aphid in some raspberry cultivars

Global climate change, such as elevated atmospheric carbon dioxide (eCO₂), may accelerate the breakdown of crop resistance to insect pests by compromising expression of resistance genes. This study investigated how eCO₂ (700 μmol/mol) affected the susceptibility of red raspberry (Rubus idaeus) to the European large raspberry aphid (Amphorophora idaei) Börner (Homoptera: Aphididae), using a susceptible cultivar (Malling Jewel) and cultivars containing either the A₁ (Glen Lyon) or A₁₀ (Glen Rosa) resistance genes. Compared to plants grown at ambient CO₂ (aCO₂) (375 μmol/mol), growth rates were significantly increased (ranging from 42–300%) in all cultivars at eCO₂. There was some evidence that plants containing the A₁ gene were more susceptible to aphids at eCO₂, with aphid populations doubling in size compared to the same plants grown at aCO₂. Moreover, aphids grew 38% larger (1.36 mg compared with 0.98 mg) on plants with the A₁ resistance gene at eCO₂ compared with those at aCO₂. Aphid performance on plants containing the A₁ gene grown at eCO₂ was therefore similar to that of aphids reared on entirely susceptible plants under either CO₂ treatment. In contrast, aphids did not respond to eCO₂ when reared on plants with the A₁₀ resistance gene, suggesting that plants with this resistance gene remained resistant to aphids at eCO₂.     

Second generation bioenergy crops and climate change: a review of the effects of elevated atmospheric CO2 and drought on water use and the implications for yield

Second-generation, dedicated lignocellulosic crops for bioenergy are being hailed as the sustainable alternative to food crops for the generation of liquid transport fuels, contributing to climate change mitigation and increased energy security. Across temperate regions they include tree species grown as short rotation coppice and intensive forestry (e.g. Populus and Salix species) and C₄ grasses such as miscanthus and switchgrass. For bioenergy crops it is paramount that high energy yields are maintained in order to drive the industry to an economic threshold where it has competitive advantage over conventional fossil fuel alternatives. Therefore, in the face of increased planting of these species, globally, there is a pressing need for insight into their responses to predicted changes in climate to ensure these crops are 'climate proofed' in breeding and improvement programmes. In this review, we investigate the physiological responses of bioenergy crops to rising atmospheric CO₂ ([Ca]) and drought, with particular emphasis on the C₃ Salicaceae trees and C₄ grasses. We show that while crop yield is predicted to rise by up to 40% in elevated [Ca], this is tempered by the effects of water deficit. In response to elevated [Ca] stomatal conductance and evapotranspiration decline and higher leaf–water potentials are observed. However, whole-plant responses to [Ca] are often of lower magnitude and may even be positive (increased water use in elevated [Ca]). We conclude that rising [Ca] is likely to improve drought tolerance of bioenergy crop species due to improved plant water use, consequently yields in temperate environments may remain high in future climate scenarios.     

大气CO2浓度和气温升高对麦田节肢动物群落的影响

为了预测气候变化对麦田节肢动物群落多样性的影响, 本研究在麦田开放环境中设置4种处理, 分别是高温(高于当时气温2℃和当前CO₂浓度)、高CO₂浓度(500 μL/L和当时气温)、高温+高CO₂浓度和对照(当前CO₂浓度和气温)等, 采用定期随机抽样方法调查节肢动物群落的多样性, 用经典的多样性指数对整体节肢动物群落以及不同食性节肢动物群落多样性进行分析。共采到节肢动物3纲10目42科52种。仅“高温”和“高温+高CO₂”处理显著增大节肢动物群落的均匀度, 其余处理均无显著影响。“高温+高CO₂”处理的影响随小麦生长发育期不同而略有差异, 在苗期可增大Shannon-Wiener多样性指数, 而在后期使该指数减小; “高温+高CO₂”与“高温”处理的群落多样性较为相似。对不同食性节肢动物群落的分析表明, 与对照相比, 植食性昆虫群落在“高CO₂”下丰富度显著增大; 寄生性昆虫群落的多度在“高温”下显著增大; 腐食性等节肢动物群落的多度在“高CO₂+高温”和“高温”处理下有所增大、均匀度在“高温”下略降低, 但均未达统计上的显著水平; 捕食性节肢动物群落不受影响。本研究说明, CO₂浓度和气温升高不同程度地影响麦田节肢动物群落的物种多样性, 两类因素同时升高与各自单独升高的影响不完全一致。     

Accumulation of soil carbon under elevated CO2 unaffected by warming and drought

Elevated atmospheric CO₂ concentration and climate change may substantially alter soil carbon (C) dynamics, which in turn may impact future climate through feedback cycles. However, only very few field experiments worldwide have combined elevated CO₂ (eCO₂) with both warming and changes in precipitation in order to study the potential combined effects of changes in these fundamental drivers of C cycling in ecosystems. We exposed a temperate heath/grassland to eCO₂, warming, and drought, in all combinations for 8 years. At the end of the study, soil C stocks were on average 0.927 kg C/m² higher across all treatment combinations with eCO₂ compared to ambient CO₂ treatments (equal to an increase of 0.120 ± 0.043 kg C m^?2 year^?1), and showed no sign of slowed accumulation over time. However, if observed pretreatment differences in soil C are taken into account, the annual rate of increase caused by eCO₂ may be as high as 0.177 ± 0.070 kg C m^?2 year^?1. Furthermore, the response to eCO₂ was not affected by simultaneous exposure to warming and drought. The robust increase in soil C under eCO₂ observed here, even when combined with other climate change factors, suggests that there is continued and strong potential for enhanced soil carbon sequestration in some ecosystems to mitigate increasing atmospheric CO₂ concentrations under future climate conditions. The feedback between land C and climate remains one of the largest sources of uncertainty in future climate projections, yet experimental data under simulated future climate, and especially including combined changes, are still scarce. Globally coordinated and distributed experiments with long‐term measurements of changes in soil C in response to the three major climate change‐related global changes, eCO₂, warming, and changes in precipitation patterns, are, therefore, urgently needed.     

Transgenerational effects of global environmental change: long-term CO2 and nitrogen treatments influence offspring growth response to elevated CO2

Global environmental changes can have immediate impacts on plant growth, physiology, and phenology. Long-term effects that are only observable after one or more generations are also likely to occur. These transgenerational effects can result either from maternal environmental effects or from evolutionary responses to novel selection pressures and are important because they may alter the ultimate ecological impact of the environmental change. Here, we show that transgenerational effects of atmospheric carbon dioxide (CO₂) and soil nitrogen (N) treatments influence the magnitude of plant growth responses to elevated CO₂ (eCO₂). We collected seeds from Lupinus perennis, Poa pratensis, and Schizachyrium scoparium populations that had experienced five growing seasons of ambient CO₂ (aCO₂) or eCO₂ treatments and ambient or increased N deposition and planted these seeds into aCO₂ or eCO₂ environments. We found that the offspring eCO₂ treatments stimulated immediate increases in L. perennis and P. pratensis growth and that the maternal CO₂ environment influenced the magnitude of this growth response for L. perennis: biomass responses of offspring from the eCO₂ maternal treatments were only 54% that of the offspring from the aCO₂ maternal treatments. Similar trends were observed for P. pratensis and S. scoparium. We detected some evidence that long-term N treatments also altered growth responses to eCO₂; offspring reared from seed from maternal N-addition treatments tended to show greater positive growth responses to eCO₂ than offspring from ambient N maternal treatments. However, the effects of long-term N treatments on offspring survival showed the opposite pattern. Combined, our results suggest that transgenerational effects of eCO₂ and N-addition may influence the growth stimulation effects of eCO₂, potentially altering the long-term impacts of eCO₂ on plant populations.     

The future of the northeast Atlantic benthic flora in a high CO2 world

Seaweed and seagrass communities in the northeast Atlantic have been profoundly impacted by humans, and the rate of change is accelerating rapidly due to runaway CO₂ emissions and mounting pressures on coastlines associated with human population growth and increased consumption of finite resources. Here, we predict how rapid warming and acidification are likely to affect benthic flora and coastal ecosystems of the northeast Atlantic in this century, based on global evidence from the literature as interpreted by the collective knowledge of the authorship. We predict that warming will kill off kelp forests in the south and that ocean acidification will remove maerl habitat in the north. Seagrasses will proliferate, and associated epiphytes switch from calcified algae to diatoms and filamentous species. Invasive species will thrive in niches liberated by loss of native species and spread via exponential development of artificial marine structures. Combined impacts of seawater warming, ocean acidification, and increased storminess may replace structurally diverse seaweed canopies, with associated calcified and noncalcified flora, with simple habitats dominated by noncalcified, turf‐forming seaweeds.     

Interactive direct and plant‐mediated effects of elevated atmospheric [CO2] and temperature on a eucalypt‐feeding insect herbivore

Understanding the direct and indirect effects of elevated [CO₂] and temperature on insect herbivores and how these factors interact are essential to predict ecosystem‐level responses to climate change scenarios. In three concurrent glasshouse experiments, we measured both the individual and interactive effects of elevated [CO₂] and temperature on foliar quality. We also assessed the interactions between their direct and plant‐mediated effects on the development of an insect herbivore of eucalypts. Eucalyptus tereticornis saplings were grown at ambient or elevated [CO₂] (400 and 650 μmol mol^?1 respectively) and ambient or elevated ( + 4 °C) temperature for 10 months. Doratifera quadriguttata (Lepidoptera: Limacodidae) larvae were feeding directly on these trees, on their excised leaves in a separate glasshouse, or on excised field‐grown leaves within the temperature and [CO₂] controlled glasshouse. To allow insect gender to be determined and to ensure that any sex‐specific developmental differences could be distinguished from treatment effects, insect development time and consumption were measured from egg hatch to pupation. No direct [CO₂] effects on insects were observed. Elevated temperature accelerated larval development, but did not affect leaf consumption. Elevated [CO₂] and temperature independently reduced foliar quality, slowing larval development and increasing consumption. Simultaneously increasing both [CO₂] and temperature reduced these shifts in foliar quality, and negative effects on larval performance were subsequently ameliorated. Negative nutritional effects of elevated [CO₂] and temperature were also independently outweighed by the direct positive effect of elevated temperature on larvae. Rising [CO₂] and temperature are thus predicted to have interactive effects on foliar quality that affect eucalypt‐feeding insects. However, the ecological consequences of these interactions will depend on the magnitude of concurrent temperature rise and its direct effects on insect physiology and feeding behaviour.     

Strong ecological but weak evolutionary effects of elevated CO2 on a recombinant inbred population of Arabidopsis thaliana

Increases in atmospheric CO2 concentration have an impact on plant communities by influencing plant growth and morphology, species interactions, and ecosystem processes. These ecological effects may be accompanied by evolutionary change if elevated CO2 (eCO2) alters patterns of natural selection or expression of genetic variation. Here, a statistically powerful quantitative genetic experiment and manipulations of CO2 concentrations in a field setting were used to investigate how eCO2 impacts patterns of selection on ecologically important traits in Arabidopsis thaliana; heritabilities, which influence the rate of response to selection; and genetic covariances between traits, which may constrain responses to selection. CO2 had strong phenotypic effects; plants grown in eCO2 were taller and produced more biomass and fruits. Also, significant directional selection was observed on many traits and significant genetic variation was observed for all traits. However, no evolutionary effect of eCO2 was detected; patterns of selection, heritabilities and genetic correlations corresponded closely in ambient and elevated CO2 environments. The data suggest that patterns of natural selection and the quantitative genetic parameters of this A. thaliana population are robust to increases in CO2 concentration and that responses to eCO2 will be primarily ecological.     

Reduction of transpiration and altered nutrient allocation contribute to nutrient decline of crops grown in elevated CO2 concentrations

Plants grown in elevated [CO₂] have lower protein and mineral concentrations compared with plants grown in ambient [CO₂]. Dilution by enhanced production of carbohydrates is a likely cause, but it cannot explain all of the reductions. Two proposed, but untested, hypotheses are that (1) reduced canopy transpiration reduces mass flow of nutrients to the roots thus reducing nutrient uptake and (2) changes in metabolite or enzyme concentrations caused by physiological changes alter requirements for minerals as protein cofactors or in other organic complexes, shifting allocation between tissues and possibly altering uptake. Here, we use the meta‐analysis of previous studies in crops to test these hypotheses. Nutrients acquired mostly by mass flow were decreased significantly more by elevated [CO₂] than nutrients acquired by diffusion to the roots through the soil, supporting the first hypothesis. Similarly, Mg showed large concentration declines in leaves and wheat stems, but smaller decreases in other tissues. Because chlorophyll requires a large fraction of total plant Mg, and chlorophyll concentration is reduced by growth in elevated [CO₂], this supports the second hypothesis. Understanding these mechanisms may guide efforts to improve nutrient content, and allow modeling of nutrient changes and health impacts under future climate change scenarios.     

Epiphytic bromeliads in a changing world: the effect of elevated CO2 and varying water supply on growth and nutrient relations

• Global climate change is likely to impact all plant life. Vascular epiphytes represent a life form that may be affected more than any other by possible changes in precipitation leading to water shortage, but negative effects of drought may be mitigated through increasing levels of atmospheric CO₂.
• We studied the response of three epiphytic Aechmea species to different CO₂ and watering levels in a full‐factorial climate chamber study over 100 days. All species use crassulacean acid metabolism (CAM). Response variables were relative growth rate (RGR), nocturnal acidification and foliar nutrient levels (N, P, K, Mg).
• Both elevated CO₂ and increased water supply stimulated RGR, but the interaction of the two factors was not significant. Nocturnal acidification was not affected by these factors, indicating that the increase in growth in these CAM species was due to higher assimilation in the light. Mass‐based foliar nutrient contents were consistently lower under elevated CO₂, but most differences disappeared when expressed on an area basis.
• Compared to previous studies with epiphytes, in which doubling of CO₂ increased RGR, on average, by only 14%, these Aechmea species showed a relatively strong growth stimulation of up to +61%. Consistent with earlier findings with other bromeliads, elevated CO₂ did not mitigate the effect of water shortage.

     

大气CO2浓度升高对绿豆叶片光合作用及叶绿素荧光参数的影响

利用FACE系统在大田条件下通过盆栽试验研究了大气CO2浓度升高[CO2浓度平均为(550+60) μmol·mo1-1]对绿豆叶片光合生理和叶绿素荧光参数的影响.结果表明:与对照[ CO2浓度平均为(389+40) μmol·mol-1左右]相比,大气CO2浓度升高使花荚期绿豆叶片净光合速率(Pn)和胞间CO2浓度(Ci)分别升高11.7％和9.8％,气孔导度(Gs)和蒸腾速率(Tr)分别下降32.0％和24.6％,水分利用效率(WUE)提高83.5％;在蕾期,CO2浓度升高对绿豆叶片叶绿素初始荧光(Fo)、最大荧光(Fm)、可变荧光(Fv)、Fv/Fm和Fv/Fo没有显著影响;在鼓粒期,CO2浓度升高使绿豆叶片Fo增加19.1％,Fm和Fv分别下降9.0％和14.3％,Fv/Fo和Fv/Fm分别下降25.8％和6.2％.表明大气CO2浓度升高可能使绿豆生长后期光系统Ⅱ反应中心结构受到破坏,叶片的光合能力下降.     

Flowering phenology in a species-rich temperate grassland is sensitive to warming but not elevated CO2

* 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 micromol mol(-1)) and warming (+2 masculineC) 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.