Effects Of CO2 Enrichment Research Articles

Response of water balance and nitrogen assimilation in cucumber seedlings to CO2 enrichment and salt stress

The effects of CO2 enrichment on water balance and nitrogen (N) assimilation in cucumber (Cucumis sativus L. cv. Jinyou No.35) seedlings under salt stress were investigated. Two-way randomized block design was used: the main treatment consisted of two [CO2] levels, ambient and enriched (400 and 800 ± 40 μmol mol−1, respectively), and the minor treatment consisted on two salinity treatment levels, 0 and 80 mmol L−1 NaCl. The results showed that, under the experimental conditions, enriched [CO2] and salt stress significantly inhibited the N assimilation process in cucumber leaves; however, enriched [CO2] had no effect on the nitrate (NO3−) reduction or ammonium (NH4+) assimilation of leaves under salt stress, inhibiting only the transamination. Moreover, enriched [CO2] increased the plasma membrane H+-ATPase activity, vacuolar membrane H+-ATPase activity and root hydraulic conductivity under salt stress, thereby increasing the ion selective absorption and water absorption capacity. To a certain extent, enriched [CO2] promoted the accumulation of K+ in plants, which significantly reduced the Na+/K+ ratio; moreover, the enrichment ultimately improved the water state conditions and helped to maintain the ion balance in plants under stress, ensuring normal enzymatic activity.

Positive effects of free air CO2 enrichment on N remobilization and post-anthesis N uptake in winter wheat

Elevated atmospheric CO2 concentration (e[CO2]) often increases cereal yield, but can also decrease vegetative and grain tissue nitrogen (N) concentration that might affect future food and feed quality. However, data about CO2 x N interactions on key processes determining grain N yield and concentration, which are remobilization of vegetative N taken up before anthesis (Nrem) and post-anthesis N uptake (Nabs), are scarce. Therefore, a two-year Free Air CO2 Enrichment (FACE) experiment was conducted with winter wheat grown under two CO2 (˜393 and 600 ppm) and three N levels (severe deficiency with N nutrition index (NNI) of 0.4, adequate with NNI of 0.8 and excess with NNI of 1.1).e[CO2] did not influence the allometric relation between aboveground N concentration and biomass up to anthesis. At anthesis, e[CO2] increased N acquisition of stem and ear, but not of leaf. Correspondingly, e[CO2] increased Nrem of stem and chaff. Moreover, e[CO2] enhanced the efficiency of Nrem of stem and aboveground plant in the first year, indicating increased N mobilization from vegetative tissue. Nabs tended to be increased by e[CO2], especially in the second year. Finally, e[CO2] increased grain N yield (8 to 12%), N use efficiency (13 to 18%) and N uptake efficiency (10 to 12%). Grain N concentration was slightly decreased by e[CO2] in both years (-1 to -6%), while grain N concentration was considerably larger (9 to 19%) in the second year compared to the first year. There was a strong linear relation between grain N yield and grain number (r2 = 0.98) that was not influenced by e[CO2], suggesting grain number as important factor determining the grain N yield increase under e[CO2]. Grain N concentration was more strongly affected by e[CO2] than mean N content per grain.

Effects of free-air CO2 enrichment on flower opening time in rice

ABSTRACTFlower opening time (FOT) is important for reproductive success in higher plants. Rice plants exhibit phenotypic plasticity in FOT in response to environmental factors such as temperature. However, the effect of the concentration of atmospheric CO2 ([CO2]) on FOT has not yet been reported. Elevated [CO2] (E-[CO2]) increases the temperature of panicles, which may in turn advance FOT. We investigated the effect of E-[CO2] on FOT in rice using a free-air CO2 enrichment facility where we increased [CO2] by about 200 μmol mol−1 above the ambient level (A-[CO2]). By photographing panicles at 10-min intervals, we determined 10%FOT and 50%FOT (the time of the day in Japan Standard Time when 10% and 50% of the flowers had opened, respectively). E-[CO2] advanced 10%FOT and 50%FOT by 4 and 5 min at the 10% and 5% levels of significance, respectively. Daily mean air temperature (Ta), solar radiation, and vapor-pressure deficit were negatively correlated with 50%FOT. Regression line slopes for Ta versus 10%FOT and 50%FOT were slightly steeper for A-[CO2] than those for E-[CO2]. Our results suggest that the most probable reason why E-[CO2] advanced FOT is an increase in panicle temperature arising from a reduction in leaf stomatal conductance.Abbreviations: 10%FOT: the time of the day in Japan Standard Time when 10% of the flowers had opened; 50%FOT: the time of the day in Japan Standard Time when 50% of the flowers had opened; A-[CO2]: ambient CO2; [CO2]: the concentration of atmospheric carbon dioxide; E-[CO2]: elevated [CO2]; FACE: free-air CO2 enrichment; FOT: flower opening time; JST: Japan Standard Time; RH: relative humidity; Rs: solar radiation; Ta: air temperature; Tp: panicle temperature; VPD: vapor-pressure deficit

Interaction of Supplementary Light and CO2 Enrichment Improves Growth, Photosynthesis, Yield, and Quality of Tomato in Autumn through Spring Greenhouse Production

During the autumn/spring “off” season, yield and quality of tomatoes are often affected by insufficient CO2 and low light in greenhouse production. Although tomato is one of the most widely cultivated vegetables, few studies have investigated the interactive effects of supplementary light and CO2 enrichment on its growth, photosynthesis, yield, and fruit quality in greenhouse production. This study investigates the effects of supplementary light (200 ± 20 μmol·m–2·s–1) and CO2 enrichment (increases to about 800 μmol·mol–1), independently and in combination, on these parameters in autumn through spring tomato production. Compared with tomatoes grown under ambient CO2 concentrations and no supplementary light (CaLn), supplementary light (CaLs) and supplementary light and CO2 enrichment (CeLs) significantly promoted growth and dry weight accumulation. Meanwhile, CO2 enrichment (CeLn) and CaLs significantly improved photosynthetic pigment contents and net photosynthetic (Pn) rates, whereas CeLs further improved these and also increased water use efficiency (WUE). CeLn, CaLs, and CeLs significantly increased single fruit weight by 16.2%, 28.9%, and 36.6%, and yield per plant by 19.0%, 35.6%, and 60.8%, respectively. The effect of supplementary light on these parameters was superior to that of CO2 enrichment. In addition, CaLs and CeLs improved nutritional quality significantly. Taken together, CeLs promoted the greatest yield, WUE, and fruit quality, suggesting it may be a worthwhile practice for off-season tomato cultivation.

A triple trophic boost: How carbon emissions indirectly change a marine food chain.

The pervasive enrichment of CO2 in our oceans is a well-documented stressor to marine life. Yet, there is little understanding about how CO2 affects species indirectly in naturally complex communities. Using natural CO2 vents, we investigated the indirect effects of CO2 enrichment through a marine food chain. We show how CO2 boosted the biomass of three trophic levels: from the primary producers (algae), through to their grazers (gastropods), and finally through to their predators (fish). We also found that consumption by both grazers and predators intensified under CO2 enrichment, but, ultimately, this top-down control failed to compensate for the boosted biomass of both primary producers and herbivores (bottom-up control). Our study suggests that indirect effects can buffer the ubiquitous and direct, negative effects of CO2 enrichment by allowing the upward propagation of resources through the food chain. Maintaining the natural complexity of food webs in our ocean communities could, therefore, help minimize the future impacts of CO2 enrichment.

Legacy effects of long-term CO2 enrichment on plant biomass recovery from fire seven years after return to ambient CO2 levels1

We sought to determine if elevated CO2 resulted in long-lasting changes to plant structure and function, particularly disturbance response patterns. Minimal legacy effects were observed 1 yr after the termination of a previous long-term experiment; however, those observations were based on 1 yr of data and only focused on fine root growth, herbivory, and arthropod diversity. We examined above- and belowground biomass inside the footprints of chambers from a former long-term elevated CO2 experiment in a scrub-oak community 7 yr after CO2 enrichment ceased and 2 yr after fire. Aboveground biomass was 40.6% higher in the previously elevated plots compared with ambient plots, suggesting that there are legacy effects in the form of more rapid aboveground recovery from fire on previously elevated CO2 plots. Belowground biomass exhibited minimal change since the historic CO2 enrichment, suggesting that differences were a result of the original treatment. After disturbance, regrowth occurs via sprouting from large belowground structures; thus changes in aboveground recovery are likely due to changes to belowground biomass caused by altered atmospheric CO2. Elevated CO2 has significantly affected disturbance recovery patterns in this community. These changes have the potential to alter plant carbon allocation patterns in frequently disturbed systems.

Effects of free-air CO2 enrichment on heat-induced sterility and pollination in rice

ABSTRACTGlobal climate changes may cause heat-induced sterility in rice, threatening the global production of this important crop. Although little is currently known about the combined effects of the concentration of atmospheric CO2 ([CO2]) and temperature on heat-induced sterility, elevated [CO2] (E-[CO2]) will likely increase the panicle temperature and thereby exacerbate heat-induced sterility, but this was not tested in open fields. Therefore, we investigated the effect of E-[CO2] on heat-induced sterility and sterility-related traits in rice by increasing E-[CO2] by approximately 200 μmol mol−1 above ambient levels using a free-air CO2 enrichment (FACE) facility for six growing seasons with variable growing season temperatures. The percentage fertility was not significantly correlated with the air temperature (Ta) between 09:00 and 12:00 on each flowering day, but it did significantly vary among the years, with 2011 experiencing cool temperatures resulting in chilling-induced mild sterility. When data from 2011 were removed, there was a significant negative correlation between fertility and Ta between 09:00 and 12:00 on each flowering day under E-[CO2], whereas no such effect was seen under ambient [CO2]. E-[CO2] also significantly reduced the number of pollen grains deposited on the stigma by 10%, but it slightly increased the anther length by 1.3%, indicating that it had both negative and positive effects on heat-induced sterility. These findings suggest that E-[CO2] affects many traits related to heat-induced sterility and may sometimes exacerbate sterility by reducing pollen grain deposition.Abbreviations: A-[CO2]: ambient CO2; [CO2]: the concentration of carbon dioxide; E-[CO2]: elevated [CO2]; FACE: free-air CO2 enrichment; Ta: air temperature

Combined effects of drought and CO2 enrichment on foliar metabolites of potato (Solanum tuberosum L.) cultivars

ABSTRACT Drought invokes a variety of metabolic alterations in plant leaves to cope with stress situations. To understand the effects of CO2 and drought stress for leaf metabolic changes in potato [Solanum tuberosum (L)], two contrasting potato cultivars Harley Blackwell (HB, an early maturing, newer cultivar) and Snowden (SD, an established, full-season cultivar) were tested under water-limited conditions and CO2 enrichment. The results revealed that most of the drought-triggered metabolites were lower in HB compared to SD. However, HB showed quicker adjustments in the metabolic processes such as conversion of starch into soluble sugars and biosynthesis of phenylalanine and other compatible solutes at the early stages of the drought progression. Moreover, the existence of genotypic differences for leaf water potential (LWP) in response to CO2 enrichment was evident. Our study provides insights into the possible metabolic strategies of drought tolerance in potato cultivars under ambient and elevated CO2.

Carbon dioxide enrichment alters predator avoidance and sex determination but only sex is mediated by GABAA receptors

We hypothesized that near-future elevated CO2 would affect the antipredatory behavior of two freshwater organisms; a pulmonate gastropod (Physella columbiana) and a cladoceran crustacean (Daphnia magna). Studies have found that pCO2 and increased acidification due to CO2 impedes fright responses to predators by activating GABAA receptors. After administration of predator-derived kairomones and conspecific alarm cues, we also briefly exposed some of the animals to gabazine which is a GABAA receptor antagonist to restore a fright response. We found that added carbon dioxide negatively affected the antipredatory behavior of both species but gabazine did not reverse this effect. To further examine the effect of CO2 and gabazine, we also tested the effect of stressful crowding, cold, and acidic conditions on the production of male daphnid offspring. An increase in ratio of male to female offspring is a common and expected response to stress by daphnids. We found that stress increased the production of males and gabazine reversed this at a pH of 5.5 but not at pH 6.2 or 6.5. Our study suggest that while the main negative effects of anthropogenic CO2 enrichment can be robust, the myriad indirect effects of CO2 make predictions about future predator prey systems less clear.

Bacterial community response to a preindustrial-to-future CO2 gradient is limited and soil specific in Texas Prairie grassland.

Rising atmospheric CO2 concentration directly stimulates plant productivity and affects nutrient dynamics in the soil. However, the influence of CO2 enrichment on soil bacterial communities remains elusive, likely due to their complex interactions with a wide range of plant and soil properties. Here, we investigated the bacterial community response to a decade long preindustrial-to-future CO2 gradient (250-500ppm) among three contrasting soil types using 16S rRNA gene amplicon sequencing. In addition, we examined the effect of seasonal variation and plant species composition on bacterial communities. We found that Shannon index (H') and Faith's phylogenetic diversity (PD) did not change in response to the CO2 gradient (R2 =0.01, p>0.05). CO2 gradient and season also had a negligible effect on overall community structure, although silty clay soil communities were better structured on a CO2 gradient (p<0.001) among three soils. Similarly, CO2 gradient had no significant effect on the relative abundance of different phyla. However, we observed soil-specific variation of CO2 effects in a few individual families. For example, the abundance of Pirellulaceae family decreased linearly with CO2 gradient, but only in sandy loam soils. Conversely, the abundance of Micromonosporaceae and Gaillaceae families increased with CO2 gradient in clay soils. Soil water content (SWC) and nutrient properties were the key environmental constraints shaping bacterial community structure, one manifestation of which was a decline in bacterial diversity with increasing SWC. Furthermore, the impact of plant species composition on community structure was secondary to the strong influence of soil properties. Taken together, our findings indicate that bacterial communities may be largely unresponsive to indirect effects of CO2 enrichment through plants. Instead, bacterial communities are strongly regulated by edaphic conditions, presumably because soil differences create distinct environmental niches for bacteria.

Effects of CO2 enrichment on two microalgae species: A toxicity approach using consecutive generations

As a result of the increasing pressure provoked by anthropogenic activities, the world climate is changing and oceans health is in danger. One of the most important factors affecting the marine environment is the well-known process called ocean acidification. Also, there are other natural or anthropogenic processes that produce an enrichment of CO2 in the marine environment (CO2 leakages from Carbon Capture and Storage technologies (CCS), organic matter diagenesis, volcanic vents, etc). Most of the studies related to acidification of the marine environment by enrichment of CO2 have been focused on short-term experiments. To evaluate the effects related to CO2 enrichment, laboratory-scale experiments were performed using the marine microalgae Tetraselmis chuii and Phaeodactylum tricornutum. Three different pH values (two treatments - pH 7.4 and 6.0 - and a control - pH 8.0) were tested on the selected species across four consecutive generations. Seawater was collected and exposed to different scenarios of CO2 enrichment by means of CO2 injection. The results showed different effects depending on the species and the generation used. Effects on T. chuii were shown on cell density, chlorophyll-a and metabolic activity, however, a slight adaptation across generations was found in this last parameter. P. tricornutum was more sensitive to acidification conditions through generations, with practically total growth inhibition in the fourth one. The conclusions obtained in this work are useful to address the potential ecological risk related to acidification by enrichment of CO2 on the marine ecosystem by using consecutive generations of microalgae.

Effects of CO2 enrichment, LED inter-lighting, and high plant density on growth of Nicotiana benthamiana used as a host to express influenza virus hemagglutinin H1

Plants are being recognized as promising hosts for molecular farming and several molecular tools have been developed over the last two decades to optimize recombinant protein yields. However, the effects of basic growth factors on protein yield have been much less studied. Here, we investigated the effects of supplemental light emitting diode (LED) inter-lighting, CO2 enrichment, and plant density on growth and recombinant protein yield of Nicotiana benthamiana used as a host to express the vaccine antigen influenza virus hemagglutinin H1. LED inter-lighting improved plant growth and recombinant protein yield on a per-plant basis. CO2 enrichment also enhanced plant growth, but its effect on recombinant protein yield was not significant. By comparison, high plant density decreased recombinant protein production per plant, mainly because of its negative impact on protein accumulation on a per-plant basis. On a whole-crop area basis, supplemental lighting, CO2 enrichment, and high plant density improved plant growth, while only LED inter-lighting and high plant density positively impacted recombinant protein yield. We suggest that LED inter-lighting and an elevated plant density should be used to maximize H1 antigen yield in large-scale protein production systems using N. benthamiana.

High CO2 effects on growth and biometal contents in the pioneer species Senna reticulata: climate change predictions

The aim of the present study consisted in evaluating the effects of CO2 enrichment on the growth and biometal/nutrient content and accumulation in Senna reticulata germinated under two different carbon dioxide concentrations: atmospheric (360 mg L−1) and elevated (720 mg L−1). Biometal/nutrient determinations were performed on three different plant portions (leaflets, stem and root) using flame atomic absorption spectrometry. In general, the biometal and nutrient stoichiometries in roots were increased, probably due to reduced transpiration, and consequent biometal accumulation. An Artifical Neural Network analysis suggests that Mg, Na and Fe display the most different behavior when comparing plants germinated at atmospheric and elevated CO2 conditions. Biomass and growth increases and certain elemental levels indicate that S. reticulata benefits from increased CO2 levels, however some results indicate the contrary, making further studies in this context necessary, as these changes may lead to direct effects on food safety, crop yields, and phytoremediation efficiency.

Regional Simulations of Loblolly Pine Productivity with CO2 Enrichment and Changing Climate Scenarios

The relationship between forests and changing global climate is of major importance to forest landowners and policymakers. In this study, we apply an empirical growth and yield model for loblolly pine (Pinus taeda) to the southeastern United States in an effort to predict the impacts of changing climate and ambient CO2 concentrations on loblolly pine productivity across its natural range. Regional model runs were made, assuming planting on all available land area for each year from 1980 to 2035 and harvesting in 25 years, under multiple future climate scenarios and ambient CO2 concentration inputs. While there are many caveats and assumptions underpinning the results, they suggest that while changes in climate have a moderately beneficial effect on productivity, increased atmospheric CO2 concentration has a much greater beneficial effect, with the mean predicted increase across the loblolly pine growing region in the 2040–2059 time period being 30.4% by 2060 under effects of both climate and CO2 enrichment in Representative Concentration Pathway (RCP) 8.5, the high greenhouse gas future scenario.

Autumnal leaf abscission of sugar maple is not delayed by atmospheric CO&lt;sub&gt;2&lt;/sub&gt; enrichment

To investigate the effects of atmospheric CO2 enrichment on physiology and autumnal leaf phenology, we exposed 3-year-old sugar maple (Acer saccharum Marsh.) seedlings to 800 (A8), 600 (A6), and 400 μL(CO2) L–1 (AA) in nine continuous stirred tank reactor (CSTR) chambers during the growing season of 2014. Leaf abscission timing, abscised leaf area percentages, leaf number, light-saturated net photosynthetic rate (PNmax), leaf area, accumulative growth rates, and biomass were determined and assessed. The results suggested the following: (1) no significant differences were found in the timing of leaf abscission in the three CO2-concentration treatments; (2) PNmax was continuously stimulated to the greatest extent in A8 at 319% and 160% in A6 until the end of the growing season, respectively; and (3) leaf number, leaf area, and accumulative height growth all significantly increased by elevated CO2, which led to a 323% increase in A8 biomass and 235% in A6 biomass after 156-d fumigation. In summary, the results suggest, the timing of leaf abscission of sugar maple in fall was not modified by CO2 enrichment, the increased carbon gain by elevated CO2 was mainly due to increased leaf area, more leaves, and the continuously enhanced high photosynthesis throughout the growing season instead of the leaf life span.

Effects of increasing atmospheric CO2 on the marine phytoplankton and bacterial metabolism during a bloom: A coastal mesocosm study

Increases of atmospheric CO2 concentrations due to human activity and associated effects on aquatic ecosystems are recognized as an environmental issue at a global scale. Growing attention is being paid to CO2 enrichment effects under multiple stresses or fluctuating environmental conditions in order to extrapolate from laboratory-scale experiments to natural systems. We carried out a mesocosm experiment in coastal water with an assemblage of three model phytoplankton species and their associated bacteria under the influence of elevated CO2 concentrations. Net community production and the metabolic characteristics of the phytoplankton and bacteria were monitored to elucidate how these organisms responded to CO2 enrichment during the course of the algal bloom. We found that CO2 enrichment (1000μatm) significantly enhanced gross primary production and the ratio of photosynthesis to chlorophyll a by approximately 38% and 39%, respectively, during the early stationary phase of the algal bloom. Although there were few effects on bulk bacterial production, a significant decrease of bulk bacterial respiration (up to 31%) at elevated CO2 resulted in an increase of bacterial growth efficiency. The implication is that an elevation of CO2 concentrations leads to a reduction of bacterial carbon demand and enhances carbon transfer efficiency through the microbial loop, with a greater proportion of fixed carbon being allocated to bacterial biomass and less being lost as CO2. The contemporaneous responses of phytoplankton and bacterial metabolism to CO2 enrichment increased net community production by about 45%, an increase that would have profound implications for the carbon cycle in coastal marine ecosystems.

Elevated CO2 induces substantial and persistent declines in forage quality irrespective of warming in mixedgrass prairie.

Increasing atmospheric [CO2 ] and temperature are expected to affect the productivity, species composition, biogeochemistry, and therefore the quantity and quality of forage available to herbivores in rangeland ecosystems. Both elevated CO2 (eCO2 ) and warming affect plant tissue chemistry through multiple direct and indirect pathways, such that the cumulative outcomes of these effects are difficult to predict. Here, we report on a 7-yr study examining effects of CO2 enrichment (to 600ppm) and infrared warming (+1.5°C day/3°C night) under realistic field conditions on forage quality and quantity in a semiarid, mixedgrass prairie. For the three dominant forage grasses, warming effects on invitro dry matter digestibility (IVDMD) and tissue [N] were detected only in certain years, varied from negative to positive, and were relatively minor. In contrast, eCO2 substantially reduced IVDMD (two most abundant grasses) and [N] (all three dominant grass species) in most years, except the two wettest years. Furthermore, eCO2 reduced IVDMD and [N] independent of warming effects. Reduced IVDMD with eCO2 was related both to reduced [N] and increased acid detergent fiber (ADF) content of grass tissues. For the six most abundant forage species (representing 96% of total forage production), combined warming and eCO2 increased forage production by 38% and reduced forage [N] by 13% relative to ambient climate. Although the absolute magnitude of the decline in IVDMD and [N] due to combined warming and eCO2 may seem small (e.g., from 63.3 to 61.1% IVDMD and 1.25 to 1.04% [N] for Pascopyrum smithii), such shifts could have substantial consequences for the rate at which ruminants gain weight during the primary growing season in the largest remaining rangeland ecosystem in North America. With forage production increases, declining forage quality could potentially be mitigated by adaptively increasing stocking rates, and through management such as prescribed burning, fertilization at low rates, and legume interseeding to enhance forage quality.

CO2 enrichment affects eco-physiological growth of maize and alfalfa under different water stress regimes in the UAE.

Water stress has been reported to alter morphology and physiology of plants affecting chlorophyll content, stomatal size and density. In this study, drought stress mitigating effects of CO2 enrichment was assessed in greenhouse conditions in the hot climate of UAE. Commercially purchased maize (Zea mays L.) and alfalfa (Medicago sativa L.) were seeded in three different custom-built cage structures, inside a greenhouse. One cage was kept at 1000ppm CO2, the second at 700ppm CO2, and the third at ambient greenhouse CO2 environment (i.e. 435ppm). Three water stress treatments HWS (200ml per week), MWS (400ml per week), and CWS (600ml per week) were given to each cage so that five maize pots and five alfalfa pots in each cage received same water stress treatments. In maize, total chlorophyll content was similar or higher in water stress treatments compared to control for all CO2 concentrations. Stomatal lengths were higher in enriched CO2 environments under water stress. At 700ppm CO2, stomatal widths decreased as water stress increased from MWS to HWS. At both enriched CO2 environments, stomatal densities decreased compared to ambient CO2 environment. In alfalfa, there was no significant increase in total chlorophyll content under enriched CO2 environments, even though a slight increase was noticed.

What is the best endpoint for assessing environmental risk associated with acidification caused by CO2 enrichment using mussels?

Carbon capture and storage is a technology that has been widely determined to be one of the best choices for the short-term reduction of atmospheric CO2 emissions. The aim of this study was to analyze the effects of CO2 enrichment in the ocean on the mussel species Mytilus galloprovincialis using three different endpoints: mortality, embryo-larval development, and neutral red retention time assays (NRRT). Acute effects were found to be associated with a pH values of 6.0 while citotoxity effects and embryo-larval development were associated with a pH value of 7.0. The NRRT assay and embryo-larval development can be recommended as good endpoints for assessing the environmental risk associated with acidification by CO2 enrichment because they provide sensitive responses on the effects of changes in seawater pH on mussels in a short period of time. Moreover, this study may support policymakers in finding appropriate solutions for the conservation of marine ecosystems.

Flowering in grassland predicted by CO2 and resource effects on species aboveground biomass.

Continuing enrichment of atmospheric CO2 may change plant community composition, in part by altering the availability of other limiting resources including soil water, nutrients, or light. The combined effects of CO2 enrichment and altered resource availability on species flowering remain poorly understood. We quantified flowering culm and ramet production and biomass allocation to flowering culms/ramets for 10years in C4 -dominated grassland communities on contrasting soils along a CO2 concentration gradient spanning pre-industrial to expected mid-21st century levels (250-500μl/L). CO2 enrichment explained up to 77% of the variation in flowering culm count across soils for three of the five species, and was correlated with flowering culm count on at least one soil for four of five species. In contrast, allocation to flowering culms was only weakly correlated with CO2 enrichment for two species. Flowering culm counts were strongly correlated with species aboveground biomass (AGB; R2 =.34-.74), a measure of species abundance. CO2 enrichment also increased soil moisture and decreased light levels within the canopy but did not affect soil inorganic nitrogen availability. Structural equationmodels fit across the soils suggested species-specific controls on flowering in two general forms: (1) CO2 effects on flowering culm count mediated by canopy light level and relative species AGB (species AGB/total AGB) or by soil moisture effects on flowering culm count; (2) effects of canopy light level or soil inorganic nitrogen on flowering and/or relative species AGB, but with no significant CO2 effect. Understanding the heterogeneity in species responses to CO2 enrichment in plant communities across soils in edaphically variable landscapes is critical to predict CO2 effects on flowering and other plant fitness components, and species potential to adapt to future environmental changes.