Ambient CO2 Treatments Research Articles

Effects of CO2 Treatments on Functional Carbon Efficiencies and Growth of Forest Tree Seedlings: A Study of Four Early-Successional Deciduous Species

Atmospheric CO2 levels have been increasing, and these changes may result in differential adaptive responses in both genera and species and highlight the need to increase carbon sequestration. Ecophysiological and morphological responses of four early-successional deciduous species were examined under ambient CO2 (aCO2, 400 ppm) and elevated CO2 (eCO2, 800 ppm) treatments. The four species, all of which are used in restoration, were Alnus viridis subsp. crispa (Ait.) Turrill (green alder), A. incana subsp. rugosa (Du Roi) R.T. Clausen (speckled alder), Betula populifolia (Marshall) (gray birch), and B. papyrifera (Marshall) (white birch); all are from the same phylogenetic family, Betulaceae. We examined biochemical efficiencies, gas exchange, chlorophyll fluorescence, chlorophyll concentrations, foliar nitrogen (N), and growth traits. A general linear model, analysis of variance, was used to analyze the functional carbon efficiency and growth differences, if any, among genera, species, and provenances (only for growth traits). The alders had greater biochemical efficiency traits than birches, and alders upregulated these traits, whereas birches mostly downregulated these traits in response to eCO2. In response to eCO2, assimilation either remained the same or was upregulated for alders but downregulated for birches. Stomatal conductance was downregulated for all four species in response to eCO2. Intrinsic water use efficiency was greater for alders than for birches. Alders exhibited a consistent upregulation of stem dry mass and height growth, whereas birches were somewhat lower in height and stem dry mass in response to eCO2. Foliar N played an important role in relation to ecophysiological traits and had significant effects relative to genus (alders > birches) and CO2 (aCO2 > eCO2), and a significant genus × CO2 interaction, with alders downregulating foliar N less than did birches. Covariate analysis examining carbon efficiency traits in relation to foliar N showed clear functional responses. Both species in both genera were consistent in their ecophysiological and morphological responses to CO2 treatments. There was supporting evidence that assimilation was sink-driven, which is related to a plant organ’s ability to continue to grow and incorporate assimilates. The alders used in this study are actinorhizal, and the additional available foliar N, paired with increased stem dry mass sink activity, appeared to be driving upregulation of the carbon efficiencies and growth in response to eCO2. Alders’ greater carbon efficiencies and carbon sequestration in impoverished soils demonstrate that alders, as opposed to birches, should be used to accelerate ecological restoration in a world of increasing atmospheric CO2.

Photosynthetic Physiological Response of Porphyra yezoensis to Light Change at Different CO2 Concentrations

The effect of different CO2 concentrations and their subsequent light changes on the photosynthetic characteristics of Porphyra yezoensis are not well understood. The relationship between the availability of CO2 and light to physiological traits of the thalli could help understand the response and adaptation mechanisms of P. yezoensis to extreme weather changes. In this study, the photosynthetic response of P. yezoensis to light changes at different CO2 concentrations was determined. Under low light intensity, the high CO2 concentration promoted the relative growth rate (RGR) of P. yezoensis by 22.79% compared to that of ambient CO2 treatment. The net photosynthetic rate and phycoerythrin (PE) content under high CO2 were also significantly greater than those under ambient CO2 treatment at low light therapy. Under high light intensity, high CO2 exacerbated the inhibitory effect of light on the RGR of thalli. The net photosynthetic rate and PE content were significantly reduced by 12.53% and 14.06% at elevated CO2 concentration under a high light intensity, respectively. Furthermore, the net photosynthetic rate was significantly decreased when the light intensity was rapidly reduced, especially under simultaneously elevated CO2 concentrations. These findings indicate that elevated CO2 concentration increased the RGR and PE content at low light intensity of P. yezoensis. In addition, this study provides a theoretical basis for the response and adaptation mechanism of P. yezoensis to extreme weather changes.

Effects of Elevated CO2 on the Fitness Parameters of Individually- and Group-Reared Agasicles hygrophila (Coleoptera: Chrysomelidae).

Agasicles hygrophila Selman and Vogt (Coleoptera: Chrysomelidae) is a natural enemy of Alternanthera philoxeroides (Mart.) Griseb (Amaranthaceae: Alternanthera), a worldwide invasive weed. Elevated atmospheric CO2 concentrations may have significant impacts plants, herbivorous insects, and natural enemies. To assess the concurrent effect of elevated CO2 on the development time, fecundity, and population parameters of A. hygrophila, the age-stage, two-sex life table was used to understand the fitness and population parameters of individually-reared and group-reared A. hygrophila under elevated CO2 concentration. In individually-reared population, the development time of preadults, adult pre-oviposition period, and total pre-oviposition period of A. hygrophila in the elevated CO2 (eCO2, 750 ppm) treatment were shorter than those in the ambient CO2 (aCO2, 420 ppm) treatment. In group-reared population, the developmental time of preadults, female adult longevity, female proportion, adult pre-oviposition period, and total pre-oviposition period of A. hygrophila in eCO2 were longer than those in aCO2. Additionally, in both individually-reared and group-reared population, fecundity and oviposition days of A. hygrophila in eCO2 were higher than those in aCO2, and a higher intrinsic rate of increase, finite rate of increase, and the net reproductive rate of A. hygrophila were observed at eCO2. Moreover, shorter preadult development time, adult pre-oviposition period, total pre-oviposition period, male adult longevity, and higher fecundity were found in group-reared cohort at both aCO2 and eCO2. The results indicates that elevated CO2 has effects on the growth and reproduction of A. hygrophila, and the population growth rate of group-reared was faster and produced more offspring.

Effect of gradual increase of atmospheric CO2 concentration on nitrate-dependent anaerobic methane oxidation in paddy soils

Nitrate-dependent anaerobic oxidation of methane (AOM) is a new pathway to reduce methane emissions from paddy ecosystems. The elevated atmospheric CO2 concentration can affect methane emissions from paddy ecosystems, but its impact on the process of nitrate-dependent AOM is poorly known. Based on the automatic CO2 control platform with open top chambers and the 13CH4 stable isotope experiments, the responses of the activity of nitrate-dependent AOM, abundance and community composition of Candidatus Methanoperedens nitroreducens (M. nitroreducens)-like archaea to the gradual increase of CO2 concentration were investigated in paddy fields. We set up two CO2 concentration treatments, including an ambient CO2 and a gradual increase of CO2(increase of 40 μL·L-1 per year above ambient CO2 concentration until 160 μL·L-1). The results showed the nitrate-dependent AOM rate of 0.7-11.3 nmol CO2·g-1·d-1 in the studied paddy fields, and quantitative PCR showed the abundance of M. nitroreducens-like archaeal mcrA genes of 2.2×106-8.5×106 copies·g-1. Compared to the ambient CO2 treatment, the slow elevated CO2 treatment enhanced the nitrate-dependent AOM rate and stimulated the abundance of M. nitroreducens-like archaea, particularly in 5-10 cm soil layer. The gradual increased CO2 concentration treatment did not change the community composition of M. nitroreducens-like archaea, but significantly decreased their diversity. The soil organic carbon content was an important factor influencing the nitrate-dependent AOM process. Overall, our results showed that the gradual increase of CO2 concentration could promote the nitrate-dependent AOM, suggesting its positive role in mitigating methane emissions from paddy ecosystems under future climate change.

Effects of Elevated CO2 on the Fitness of Three Successive Generations of Lipaphis erysimi.

Simple SummaryGlobal warming caused by the increase in atmospheric CO2 concentration is becoming a major environmental issue. Lipaphis erysimi is one of the most damaging pests of cruciferous crops worldwide, and L. erysimi has strong adaptability to the environment and reproductive capacity. The age-stage, two-sex life table is currently used by many researchers in place of the traditional age-specific life table, providing many details such as fitness and potential damage. In this study, the individual fitness and population dynamics parameters of three successive generations of L. erysimi were analyzed using the age-stage, two-sex life table. The results show that a high CO2 concentration had a cumulative effect on the survival rate and fecundity of L. erysimi, and elevated CO2 had a negative effect on the individual fitness parameters of L. erysimi. The life expectancy (exj) is significantly lower in elevated CO2 than that in ambient CO2 treatment in the three successive generations, indicating that L. erysimi was more sensitive to CO2 concentration and the life of L. erysimi was shortened under elevated CO2. Additionally, we can find that elevated CO2 has a short-term effect on the population parameters, including the intrinsic rate of increase (r) and finite rate of increase (λ) in L. erysimi. Through the data from this experiment, we believe that the individual and population fitness of L. erysimi will be decreased under elevated CO2, which indicates that the damage caused by L. erysimi may be reduced in the future with increasing CO2 levels.To assess the effect of elevated CO2 on the development, fecundity, and population dynamic parameters of L. erysimi, the age-stage, two-sex life table was used to predict the individual fitness and population parameters of three successive generations of L. erysimi in this study. The results show that a significantly longer total pre-adult stage before oviposition (TPOP) was observed in the third generation compared with the first generation of L. erysimi under the 800 μL/L CO2 treatment. The fecundity is significantly lower in the 800 μL/L CO2 treatment than that in the 400 μL/L CO2 treatment in the third generation of L. erysimi, which indicates that elevated CO2 had a negative effect on the individual fitness parameters of L. erysimi. Additionally, the life expectancy (exj) is significantly lower under the 800 μL/L CO2 treatment than that under the 400 μL/L CO2 treatment in the three successive generations. A significantly higher intrinsic rate of increase (r) and finite rate of increase (λ) were found in the second generation compared with those in the first and third generations of L. erysimi under the 800 μL/L CO2 treatment. Moreover, significantly lower r and λ were observed under the 800 μL/L CO2 treatment compared with those under the 400 μL/L and 600 μL/L CO2 treatments in the first generation of L. erysimi, which indicates that elevated CO2 has a short-term effect on the population parameters (r and λ) of L. erysimi. Our experiment can provide the data for the comprehensive prevention and control of L. erysimi in the future with increasing CO2 levels.

Fungi Dominated the Incorporation of 13C-CO2 into Microbial Biomass in Tomato Rhizosphere Soil under Different CO2 Concentrations.

An elevated CO2 (eCO2) fumigation experiment was carried out to study the influence of various CO2 concentrations on microorganisms involved in the incorporation of root-derived C in greenhouse soil systems. In this study, 400 and 800 µmol·mol−1 CO2 fumigation treatments were conducted during tomato planting. Phospholipid fatty acid (PLFA) profiling based on the stable isotope probing (SIP) technique was applied to trace active microorganisms. The absolute total abundance of 13C-PLFAs was much higher under eCO2 treatment. Most of the 13C-CO2 was incorporated into the 13C-PLFAs 18:2ω6,9 (fungi), 16:0 (general PLFA), 18:1ω9c (Gram-negative bacteria, G−) and i17:0 (Gram-positive bacteria, G+) via rhizodeposition from tomato under ambient CO2 (aCO2) and eCO2 treatments, suggesting similar responses of active microorganisms to different CO2 treatments. However, the fungi (characterized by the 13C-PLFA 18:2ω6,9) played a much more dominant role in the incorporation of root-derived C under eCO2. Actinomycetes, marked by the 13C-PLFA 10-Me-18:0, occurred only on labeling day 15 under the eCO2 treatment, indicating that the actinomycetes fed on both soil organic carbon and fresh rhizodeposition. It was indicated that eCO2 significantly affected microbial biomass and microbial community structures involved in the incorporation of 13C-CO2 via tomato root secretions, as supported by Adonis analysis and the Mantel test.

Effect of enriched CO2 atmosphere on morphological and chemical characteristics of Alternanthera philoxeroides

Carbon dioxide (CO2) is one of the vital resources for plants and its concentrations in the atmosphere have been on the increase globally from the 18th century, and continue to rise at approximately 0.4% per year. Atmospheric CO2 enrichment could possibly modify growth and chemical profiles of plants, as well as plant–insect interactions. The present study investigated the effects of elevated atmospheric CO2 on stem diameters, above-ground biomass and secondary metabolite components of both terrestrial and aquatic forms of Alternanthera philoxeroides. Stem fragments of the weed were grown in six Open Top Chambers (OTCs): three chambers of ambient (~400 ppm) and three chambers of elevated (~1000 ppm) CO2 levels to simulate the current and future CO2 levels, respectively, based on prediction by IPCC (2013). Total dry weights of leaves and stems, as well as stem diameters were measured to evaluate growth and biomass accumulation in A. philoxeroides. Furthermore, chemical analyses were performed on leaf tissues of plants grown under both elevated and ambient atmospheric CO2 treatments to determine the concentration of secondary metabolites (phenolic acids and flavonoids). Results of the analyses revealed that CO2 enrichment significantly increased stem diameters and enhanced above-ground biomass accumulation in both aquatic and terrestrial environments. Enriched CO2 atmosphere treatments increased concentration of secondary metabolites in leaf tissues, with leaves of plants grown under elevated CO2 exhibiting remarkably higher concentrations of phenolic acids and flavonoids. Total flavonoid content increased by 51.02% in aquatic plants and by 99.03% in terrestrial plants. Total phenolic content increased by 29.57% in aquatic plant leaves while in terrestrial plant leaves the increase was by 61.11%. Above-ground biomass accumulation and increase in stem diameters could enhance competitive ability of the species and its ability to invade and colonize new habitats in response to a future CO2-enriched atmosphere.

The effect of long-term CO2 enrichment on carbon and nitrogen content of roots and soil of natural pastureland

Abstract Increasing levels of atmospheric CO2 may change C and N dynamics in pasture ecosystems. The present study was conducted to examine the impact of four years of CO2 enrichment on soil and root composition and soil N transformation in natural pastureland. Plots of open-top growth chambers were continuously injected with ambient CO2 (350 µL L–1) and elevated CO2 (625 µL L–1). Soil cores exposed to ambient and elevated CO2 treatment were incubated and collected each year. Net N-mineralization rates in soil (NH4 +-N plus NO3ˉ–-N), in addition to total C and N content (%) of soil and root tissues were measured. Results revealed that elevated CO2 caused a significant reduction in soil NO3 (P < 0.05), however, no significant CO2 effect was found on total soil C and N content (%). Roots of plants grown under elevated CO2 treatment had higher C/N ratios. Changes in root C/N ratios were driven by changes in root N concentrations as total root N content (%) was significantly reduced by 30% (P < 0.05). Overall, findings suggest that the effects of CO2 enrichment was more noticeable on N content (%) than C content (%) of soil and roots; elevated CO2 significantly affected soil N-mineralization and total N content (%) in roots, however, no substantial change was found in C inputs in CO2-enriched soil.

Warming and elevated CO2 alter tamarack C fluxes, growth and mortality: evidence for heat stress-related C starvation in the absence of water stress.

Climate warming is increasing the frequency of climate-induced tree mortality events. While drought combined with heat is considered the primary cause of this mortality, little is known about whether moderately high temperatures alone can induce mortality, or whether rising CO2 would prevent mortality at high growth temperatures. We grew tamarack (Larix laricina) under ambient (400p.p.m.) and elevated (750p.p.m.) CO2 concentrations combined with ambient, ambient +4 °C and ambient +8 °C growth temperatures to investigate whether high growth temperatures lead to carbon (C) limitations and mortality. Growth at +8 °C led to 40% mortality in the ambient CO2 (8TAC) treatment, but no mortality in the elevated CO2 treatment. Thermal acclimation of respiration led to similar leaf C balances across the warming treatments, despite a lack of photosynthetic acclimation. Photosynthesis was stimulated under elevated CO2, increasing seedling growth, but not leaf C concentrations. However, growth and foliar C concentrations were lowest in the +8 °C treatments, even with elevated CO2. Dying 8TAC seedlings had lower needle C concentrations and lower ratios of photosynthesis to respiration than healthy 8TAC seedlings, indicating that C limitations were likely the cause of seedling mortality under high growth temperatures.

Elevated Atmospheric CO2 and Nitrogen Fertilization Affect the Abundance and Community Structure of Rice Root-Associated Nitrogen-Fixing Bacteria.

Elevated atmospheric CO2 (eCO2) results in plant growth and N limitation, yet how root-associated nitrogen-fixing bacterial communities respond to increasing atmospheric CO2 and nitrogen fertilization (eN) during the growth stages of rice is unclear. Using the nifH gene as a molecular marker, we studied the combined effect of eCO2 and eN on the diazotrophic community and abundance at two growth stages in rice (tillering, TI and heading, HI). Quantitative polymerase chain reaction (qPCR) showed that eN had no obvious effect on nifH abundance in rice roots under either ambient CO2 (aCO2) or eCO2 treatment at the TI stage; in contrast, at the HI, nifH copy numbers were increased under eCO2 and decreased under aCO2. For rhizosphere soils, eN significantly reduced the abundance of nifH under both aCO2 and eCO2 treatment at the HI stage. Elevated CO2 significantly increased the nifH abundance in rice roots and rhizosphere soils with nitrogen fertilization, but had no obvious effect without N addition at the HI stage. There was a significant interaction [CO2 × N fertilization] effect on nifH abundance in root zone at the HI stage. In addition, the nifH copy numbers in rice roots were significantly higher at the HI stage than at the TI stage. Sequencing analysis indicated that the root-associated diazotrophic community structure tended to cluster according to the nitrogen fertilization treatment and that Rhizobiales were the dominant diazotrophs in all root samples at the HI stage. Additionally, nitrogen fertilization significantly increased the relative abundance of Methylosinus (Methylocystaceae) under eCO2 treatment, but significantly decreased the relative abundance of Rhizobium (Rhizobiaceae) under aCO2 treatment. Overall, the combined effect of eN and eCO2 stimulates root-associated diazotrophic methane-oxidizing bacteria while inhibits heterotrophic diazotrophs.

Impacts of elevated atmospheric CO2 on arbuscular mycorrhizal fungi and their role in moderating plant allometric partitioning.

Elevated atmospheric CO2 concentration (eCO2) effects on plants depend on several factors including plant photosynthetic physiology (e.g. C3, C4), soil nutrient availability and plants' co-evolved soil-dwelling fungal symbionts, namely arbuscular mycorrhizal (AM) fungi. Complicated interactions among these components will determine the outcomes for plants. Therefore, clearer understanding is needed of how plant growth and nutrient uptake, along with root-colonising AM fungal communities, are simultaneously impacted by eCO2. We conducted a factorial growth chamber experiment with a C3 and a C4 grass species (± AM fungi and ± eCO2). We found that eCO2 increased plant biomass allocation towards the roots, but only in plants without AM fungi, potentially associated with an eCO2-driven increase in plant nutrient requirements. Furthermore, our data suggest a difference in the identities of root-colonising fungal taxa between ambient CO2 and eCO2 treatments, particularly in the C4 grass species, although this was not statistically significant. As AM fungi are ubiquitous partners of grasses, their response to increasing atmospheric CO2 is likely to have important consequences for how grassland ecosystems respond to global change.

Effect of elevated carbon-dioxide on plant growth, physiology, yield and seed quality of chickpea (Cicer arietinum L.) in Indo-Gangetic plains.

In the present scenario of climate change with constantly increasing CO2 concentration, there is a risk of altered crop performance in terms of growth, yield, grain nutritional value and seed quality. Therefore, an experiment was conducted in open top chamber (OTCs) during 2017-18 and 2018-19 to assess the effect of elevated atmospheric carbondioxide (e[CO2]) (600ppm) on chickpea (cv. JG 14) crop growth, biomass accumulation, physiological function, seed yield and its quality in terms of germination and vigour. The e[CO2] treatment increased the plant height, leaf and stem biomass over ambient CO2 (a[CO2]) treatment. The e[CO2] increased seed yield by 11-18% which was attributed to an increase in the number of pods (6-10%) and seeds plant-1 (8-9%) over a[CO2]. However, e[CO2] reduced the seed protein (7%), total phenol (13%) and thiobarbituric acid reactive substances (12%) and increased the starch (21%) and water uptake rate as compared to seeds harvested from a[CO2] environment. Exposing chickpea plant to e[CO2] treatment had no impact on germination and vigour of the harvested seeds. Also, the physical attributes, total soluble sugar and antioxidant enzymes activities of harvested seeds were comparable in a[CO2] and e[CO2] treatment. Hence, the experimental findings depict that e[CO2] upto 600ppm could add to the growth and productivity of chickpea in a sub-tropical climate with an implication on its nutritional quality of the produce.

Impacts of Elevated Atmospheric CO2 and Plant Species Composition on Methane Emissions from Subarctic Wetlands

Elevated atmospheric CO2 may create greater methane (CH4) emissions from subarctic wetlands. To date such ecosystem feedbacks remain poorly understood, particularly in relation to how different wetland plant species will control such feedbacks. In this study we exposed plant-peat mesocosms planted with four Cyperaceae species to 400 and 800 ppm atmospheric CO2 concentrations and measured plant and peat properties as well as CH4 fluxes. Above ground biomass for plants grown at 800 ppm CO2 increased for E. angustifolium, Eriophorum vaginatum and Carex brunnescens, but the total biomass of C. acuta decreased relative to the ambient CO2 treatment. The plant species and elevated CO2 treatment affected both peat redox potential and pore water chemistry. There was no overall effect of the elevated CO2 on CH4 emissions, however, CH4 emissions were related to above ground biomass and redox potential, both of which were significantly altered by elevated CO2. Our study shows that species composition poses an important control on how wetland communities will respond to elevated CO2 and that plant mediated changes of peat biogeochemical processes, in response to elevated CO2 levels, may affect CH4 emissions from sub-arctic wetlands, but any such responses will differ among species.

Changes of Soil Microbes Related with Carbon and Nitrogen Cycling after Long-Term CO2 Enrichment in a Typical Chinese Maize Field

Elevated atmospheric CO2 concentration (eCO2) has been the most important driving factor and characteristic of climate change. To clarify the effects of eCO2 on the soil microbes and on the concurrent status of soil carbon and nitrogen, an experiment was conducted in a typical summer maize field based on a 10-year mini FACE (Free Air Carbon Dioxide Enrichment) system in North China. Both rhizospheric and bulk soils were collected for measurement. The soil microbial carbon (MBC), nitrogen (MBN), and soil mineral N were measured at two stages. Characteristics of microbes were assayed for both rhizospheric soil and bulk soils at the key stage. We examined the plasmid copy numbers, diversities, and community structures of bacteria (in terms of 16s rRNA), fungi (in terms of ITS-internal transcribed spacer), ammonia oxidizing bacteria (AOB) and denitrifiers including nirK, nirS, and nosZ using the Miseq sequencing technique. Results showed that under eCO2 conditions, both MBC and MBN in rhizospheric soil were increased significantly. The quantity of ITS was increased in the eCO2 treatment compared with that in the ambient CO2 (aCO2) treatment, while the quantity of 16s rRNA in rhizospheric soil showed decrease in the rhizospheric soil in the eCO2 treatment. ECO2 changed the relative abundance of microbes in terms of compositional proportion of some orders or genera particularly in the rhizospheric soil-n particular, Chaetomium increased for ITS, Subgroups 4 and 6 increased for 16s rRNA, Nitrosospira decreased for AOB, and some genera showed increase for nirS, nirK, and nosZ. Nitrate N was the main inorganic nitrogen form at the tasseling stage and both quantities of AOB and denitrifiers, as well as the nosZ/(nirS+nirK) showed an increase under eCO2 conditions particularly in the rhizospheric soil. The Nitrosospira decreased in abundance under eCO2 conditions in the rhizospheric soil and some genera of denitrifiers also showed differences in abundance. ECO2 did not change the diversities of microbes significantly. In general, results suggested that 10 years of eCO2 did affect the active component of C and N pools (such as MBC and MBN) and both the quantities and relative abundance of microbes which are involved in carbon and nitrogen cycling, possibly due to the differences in both the quantities and component of substrate for relevant microbes in the rhizospheric soils.

Leaf age and eCO2 both influence photosynthesis by increasing light harvesting in mature Eucalyptus tereticornis at EucFACE

Only a few previous studies have examined how photosynthetically active radiation absorptance, pigments and electron flow change in mature trees exposed to long-term increase in CO2 concentration. We investigated pigment concentrations, leaf optical properties and quantum yield of old and new leaves exposed to ambient (aCO2) and elevated (eCO2) CO2 treatments. Leaf absorptance was around 90% in E. tereticornis trees across both foliage age classes and CO2 treatments. New leaves had 15% higher quantum yield with increased absorptance within the blue spectrum than old leaves; while they reflected and transmitted more photons. In addition, young foliage had increased mass-based concentrations of chlorophyll and carotenoids; however, pigment concentrations were reduced when expressed on area-basis. Quantum yield was 9% higher in eCO2 than aCO2 across both foliage age classes. The CO2 effect was stronger in new leaves where the quantum yield was 17% higher in eCO2 than aCO2, but not different in old leaves between CO2 treatments. New leaves had higher transmittance of photons in eCO2 than aCO2, while there was no change in old leaves. Mass-based concentrations of chlorophyll and carotenoids were reduced in eCO2 compared to aCO2 while concentrations of anthocyanins were higher in response to CO2 treatment. There was a significant effect of Age x CO2 interaction on ratio a/b with larger eCO2-related reductions in old leaves (–5%) but no change in new leaves. Generally, new leaves were more efficient in utilizing the absorbed photons than old leaves, especially under eCO2 which resulted in more carbon fixation. This implies that leaves can adjust their light harvesting capacity to eCO2, particularly in younger leaves which have higher photosynthetic activity.

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 8years. At the end of the study, soil C stocks were on average 0.927kgC/m2 higher across all treatment combinations with eCO2 compared to ambient CO2 treatments (equal to an increase of 0.120±0.043kgCm-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±0.070kgCm-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.

Increase in Growth and Alteration of C:N Ratios of Avicennia marina and Rhizophora stylosa Subject to Elevated CO2 Concentrations and Longer Tidal Flooding Duration

We investigated the effects of elevated CO2 concentrations and longer tidal flooding duration on two-year-old Avicennia marina and Rhizophora stylosa seedlings for a full year. The seedlings were grown in greenhouses for ambient CO2 (400 ppm) and in enclosed CO2-controlled chambers, which were installed inside the greenhouses for elevated CO2 (800 ppm). The tidal flooding duration was set-up according to the species distribution in the intertidal zone in New Caledonia for the controlled treatment and was increased by 1 h 45 min for the experimental treatment. A total of 400 A. marina and 720 R. stylosa were monitored during this experiment. We measured heights and basal diameters of all seedlings every 90 days, and we determined the above and below ground biomass at the end of the experiment. Our results showed that elevated CO2 increased the growth rates of both A. marina and R. stylosa, for which the final biomass was, respectively, 46 and 32% higher than in the ambient CO2 treatment. We suggest that this increase was driven by a stimulation of photosynthesis under elevated CO2, as demonstrated in a previous study. Considering the tidal flooding duration treatment, we observed a contrasted effect between the species. Longer tidal flooding increased the growth of A. marina, whereas it reduced the growth of R. stylosa in comparison to the controlled treatment. This result may be related to the specific ecosystem zonation in this semi-arid climate, which limits water inputs into the Avicennia zone that increases the salt concentration in the soil, whereas Rhizophora is regularly submerged by tides due to its lower position in the intertidal zone. As a result, the combination of both treatments had a positive cumulative effect on the growth of A. marina. Although it was not the case for R. stylosa, the negative effect of longer tidal flooding on this species did not suppress the enhancement of growth resulting from elevated CO2 concentrations. At the end of the experiment, elevated CO2 increased the C:N ratios of the seedlings, thereby producing a more refractory organic matter, which will potentially result in lower decomposition rates and thus may increase carbon accumulation in mangrove soils. These results suggest that future climate changes may enhance the productivity of mangrove seedlings by increasing their growth, which may in turn increase the carbon storage potential of mangroves in their biomass.

Elevated atmospheric CO2 might increase the health risk of long-term ingestion of leafy vegetables cultivated in residual DDT polluted soil

Residual dichlorodiphenyltrichloroethane (DDT) in the environment and a continuously increasing atmospheric carbon dioxide (CO2) concentration are two issues that have received a lot of attention. This study was conducted using a pot experiment to investigate the interactive effects of elevated CO2 and DDT on the uptake of DDT, the physiological responses and the resulting health risks in three vegetables. These vegetables included Brassica juncea var. foliosa Bailey (B. Bailey), Brassica campestris L. var. communis Tsen et Lee Suzhou Qing (B. Lee) and Brassica campestris L. ssp. pekinensis (Lour.) Olsson Chun Dawang (B. Olsson). Two levels of CO2 and four DDT treatment levels were set up. Results showed 5 mg kg−1 DDT significantly reduced the shoot biomass of B. Bailey when compared to 0 mg kg−1 DDT treatment under ambient CO2 condition. Elevated CO2 concentration stimulated the growth of B. Bailey and B. Lee, increased the DDT uptake in the shoots of both vegetables and the values of some photosynthesis indices, and triggered the activity of peroxidase and catalase in the shoots when compared to the related ambient CO2 treatment. Elevated CO2 concentration increased the values of hazard indexes for non-carcinogenic and cancer risks of all vegetables when compared to the individual ambient CO2 treatment (each of vegetable has an ambient CO2 treatment), especially for B. Bailey (increase amplitude of 123.81%–127.78% at 5 mg kg−1 DDT). Long-term ingestion with these DDT-polluted vegetables might result in an elevated carcinogenic risk and elevated atmospheric CO2 may enhance the non-carcinogenic and carcinogenic risks.

Divergent responses of Atlantic cod to ocean acidification and food limitation.

In order to understand the effect of global change on marine fishes, it is imperative to quantify the effects on fundamental parameters such as survival and growth. Larval survival and recruitment of the Atlantic cod (Gadus morhua) were found to be heavily impaired by end-of-century levels of ocean acidification. Here, we analysed larval growth among 35-36days old surviving larvae, along with organ development and ossification of the skeleton. We combined CO2 treatments (ambient: 503µatm, elevated: 1,179µatm) with food availability in order to evaluate the effect of energy limitation in addition to the ocean acidification stressor. As expected, larval size (as a proxy for growth) and skeletogenesis were positively affected by high food availability. We found significant interactions between acidification and food availability. Larvae fed ad libitum showed little difference in growth and skeletogenesis due to the CO2 treatment. Larvae under energy limitation were significantly larger and had further developed skeletal structures in the elevated CO2 treatment compared to the ambient CO2 treatment. However, the elevated CO2 group revealed impairments in critically important organs, such as the liver, and had comparatively smaller functional gills indicating a mismatch between size and function. It is therefore likely that individual larvae that had survived acidification treatments will suffer from impairments later during ontogeny. Our study highlights important allocation trade-off between growth and organ development, which is critically important to interpret acidification effects on early life stages of fish.

Starvation rates in larval and juvenile Atlantic silversides (Menidia menidia) are unaffected by high CO2 conditions

Over the past decade, laboratory experiments on fish early life stages have found many traits that are evidently sensitive to elevated CO2 levels. With respect to larval growth, high CO2 environments are commonly assumed to increase acid–base regulation and other plastic responses, thus incurring additional metabolic costs that reduce the scope for growth. This assumption is not well supported by empirical evidence. One reason might be that experiments often provide unrestricted feeding conditions, which could allow larvae to compensate for higher costs by increased food intake. To remove potentially confounding effects of larval feeding, we conducted a series of starvation trials on offspring of the Atlantic silverside (Menidia menidia), predicting faster starvation at high compared to ambient CO2 treatments. We compiled observations from five separate experiments spanning different years, laboratories, temperatures (17–26 °C), life stages (newly hatched larvae, previously fed larvae, early juveniles), and CO2 levels (300–6500 µatm). Contrary to expectation, we found that starvation rates were largely independent of the CO2 environment in this fish species. The one exception occurred at the lowest temperature and most extreme CO2 treatment, which resulted in slower not faster starvation in newly hatched larvae at high compared to ambient CO2 treatments. The apparent failure of starvation rate as a proxy for CO2 effects on larval fish metabolism may have several reasons, including potential CO2 tolerance of offspring, observed large stochasticity in early life survival masking small metabolic costs of high CO2, and the general depression and reconfiguration of fish metabolism in response to food deprivation.