Elevated CO2 Treatments Research Articles

Effect of elevated ozone, carbon dioxide and their interaction on growth, biomass and water use efficiency of chickpea (Cicer arietinum L.)

Global climate change has a major impact on growth and sustainability of agro-ecosystem. Keeping in view the importance of rising O3 and CO2 concentration in atmosphere, a field experiment was conducted on chickpea (variety: Pusa 5023) in the experimental farm in Free Air Ozone and Carbon dioxide Enrichment (FAOCE) facility at ICAR-Indian Agricultural Research Institute (IARI), New Delhi underfour ozone and carbon dioxide treatments (ECO: elevated CO 2 (550±10 ppm) +elevated O3 (70 ±10 ppb); EC: elevated CO 2 (550±10 ppm ppm) + ambient O3 (30±10 ppb); EO: elevated O3 (70±10 ppb)+ ambient CO 2 (400±10 ppm) and AMB; ambient CO 2 (400±10 ppm)+ ambient O3 (30± 10 ppb) during rabi season of 2016-17. The results revealed that the plant height, above ground biomass, CGR and RGR and seed yield of chickpea was significantly highest in elevated CO2 (EC) treatment followed by ECO treatment and lowest in elevated O3 (EO) treatment. Elevated ozone had negative impact whereas elevated carbon dioxide had positive impact on growth, biomass and WUE of chickpea and when both are combined the negative impact of elevated ozone were counteracted by elevated carbon dioxide.

Data‐Constrained Projections of Methane Fluxes in a Northern Minnesota Peatland in Response to Elevated CO2 and Warming

AbstractLarge uncertainties exist in predicting responses of wetland methane (CH4) fluxes to future climate change. However, sources of the uncertainty have not been clearly identified despite the fact that methane production and emission processes have been extensively explored. In this study, we took advantage of manual CH4 flux measurements under ambient environment from 2011 to 2014 at the Spruce and Peatland Responses Under Changing Environments (SPRUCE) experimental site and developed a data‐informed process‐based methane module. The module was incorporated into the Terrestrial ECOsystem (TECO) model before its parameters were constrained with multiple years of methane flux data for forecasting CH4 emission under five warming and two elevated CO2 treatments at SPRUCE. We found that 9°C warming treatments significantly increased methane emission by approximately 400%, and elevated CO2 treatments stimulated methane emission by 10.4%–23.6% in comparison with ambient conditions. The relative contribution of plant‐mediated transport to methane emission decreased from 96% at the control to 92% at the 9°C warming, largely to compensate for an increase in ebullition. The uncertainty in plant‐mediated transportation and ebullition increased with warming and contributed to the overall changes of emissions uncertainties. At the same time, our modeling results indicated a significant increase in the emitted CH4:CO2 ratio. This result, together with the larger warming potential of CH4, will lead to a strong positive feedback from terrestrial ecosystems to climate warming. The model‐data fusion approach used in this study enabled parameter estimation and uncertainty quantification for forecasting methane fluxes.

Temporal and Spatial Variation in Peatland Carbon Cycling and Implications for Interpreting Responses of an Ecosystem‐Scale Warming Experiment

Core Ideas We compared spatial vs. temporal variation in C cycle processes and drivers in a bog. The bog was indistinguishable as a C source or sink because of high spatial variation. Sensitive C cycle parameters in the model differed under ambient vs. warming scenarios. Characterizing pretreatment variability is necessary when interpreting warming effects. We are conducting a large‐scale, long‐term climate change response experiment in an ombrotrophic peat bog in Minnesota to evaluate the effects of warming and elevated CO2 on ecosystem processes using empirical and modeling approaches. To better frame future assessments of peatland responses to climate change, we characterized and compared spatial vs. temporal variation in measured C cycle processes and their environmental drivers. We also conducted a sensitivity analysis of a peatland C model to identify how variation in ecosystem parameters contributes to model prediction uncertainty. High spatial variability in C cycle processes resulted in the inability to determine if the bog was a C source or sink, as the 95% confidence interval ranged from a source of 50 g C m–2 yr–1 to a sink of 67 g C m–2 yr–1. Model sensitivity analysis also identified that spatial variation in tree and shrub photosynthesis, allocation characteristics, and maintenance respiration all contributed to large variations in the pretreatment estimates of net C balance. Variation in ecosystem processes can be more thoroughly characterized if more measurements are collected for parameters that are highly variable over space and time, and especially if those measurements encompass environmental gradients that may be driving the spatial and temporal variation (e.g., hummock vs. hollow microtopographies, and wet vs. dry years). Together, the coupled modeling and empirical approaches indicate that variability in C cycle processes and their drivers must be taken into account when interpreting the significance of experimental warming and elevated CO2 treatments.

Genetic variation among pines and spruces in assimilation efficiencies and photosynthetic regulation under elevated CO2

Key message After 3 years of elevated CO2 treatments, spruce P n regulation from aCO2 to eCO2 was strongly related to total dry mass change (%), whereas pines displayed the same trend, but the relationship was not statistically significant.

Environmental Impact and Nutritional Improvement of Elevated CO2 Treatment: A Case Study of Spinach Production

The agriculture sector is known to be the one of the major contributors to global greenhouse gas (GHG) emissions. At the same time, global climate changes have affected the agriculture sector. In order to strengthen the sustainable development of agriculture, it is important to promote environmentally friendly farming and simultaneously increase the economic value. To improve the productivity of agriculture, technical advancements have occurred. Among those, we have focused on CO2 treatment in cultivation. We aimed to clarify the effectiveness of the elevated CO2 treatment of spinach based on GHG emission and the economic value using the eco-efficiency score. We assumed that nutrition could represent the value of the vegetable. We measured weights, vitamin C, and CO2 emissions of elevated CO2 treatment and conventional production. We used life cycle assessment (LCA) to estimate CO2 emissions. CO2 emissions of a 100-g bouquet of spinach were estimated from agricultural inputs, farming, transport, and distribution center processes at a model spinach farm in Japan. CO2 emission of elevated CO2 treatment was 29.0 g-CO2, and was 49.0 g-CO2 for conventional production. The net weight of a bouquet of elevated CO2-treated spinach was 1.69-fold greater than that of conventional production. Vitamin C per 100 g spinach produced via elevated CO2 treatment was 15.1 mg, and that of conventional production was 13.5 mg on average. Finally, based on the above results, we assessed the eco-efficiency scores of the elevated CO2 treatment and conventional production of spinach, enabling integration of the nutritional value and the environmental impact. The score showed that elevated CO2 treatment (0.76) was 2.9-fold more efficient than conventional production (0.26). This study suggested that elevated CO2 treatment could enhance growth and nutritional value of spinach, and further contribute to CO2 reduction.

Effects of Elevated Atmospheric CO2 on Photosynthesis, Growth and Biomass in Shorea platycarpa F. Heim (Meranti Paya)

Elevated atmospheric CO2 is widely reported to stimulate the plant growth and affect plant physiological processes. However, studies on the respond of tropical plant species to elevated CO2 are quite limited and remain largely unknown. The objective of this study was to investigate the effects of elevated atmospheric CO2 treatments on the photosynthetic characteristics, growth and biomass in Shorea platycarpa. Saplings of S. platycarpa were grown for seven months in the open roof gas chamber supplied with elevated CO2 (800±50 μmol mol-1) and in the shade house with ambient CO2 (400±50 μmol mol-1). Measurements of S. platycarpa growth and photosynthetic characteristics were made at frequent intervals. Biomass characteristics were determined using destructive methods after seven months of treatment and nondestructive method was used for leaf area index (LAI) determination. Photosynthetic rate (A) of S. platycarpa was not significantly affected by elevated CO2. Increased water use efficiency (WUE) of S. platycarpa grown in elevated CO2 was due to the reduced stomatal conductance (gs) and transpiration rate (E). The CO2 elevation had no significant effect on the S. platycarpa relative growth rates (RGR) and biomass but significantly reduced the leaf area. A weak correlation was found between photosynthetic rate (A) and relative growth rate (RGR). The results clearly showed that photosynthesis, growth rate and biomass of S. platycarpa were not significantly enhanced by elevated CO2. The findings indicated that elevated CO2 did not affect a relatively slow growing and a late successional peat swamp tree species.

Combined effect of elevated CO2 concentration and drought on the photosynthetic apparatus and leaf morphology traits in seedlings of yellow poplar

AbstractTo counter the threat of drought, which is expected to increase in the future, we analyzed the combined effects of elevated carbon dioxide (CO2) concentration and drought on the photosynthetic apparatus and morphological traits in seedlings of yellow poplar (Liriodendron tulipifera). The plants were grown for four months in a phytotron under different CO2 concentrations [ambient CO2, 430 ppm, AC) and elevated CO2, 640 ppm, EC] and water treatment [field capacity, FC and 50% of field capacity, FC50]. FC50 was sufficient for inducing a reduction in the photosynthetic rate of L. tulipifera. However, under FC50 combined with EC, we observed an increase in photosynthetic rate with increased photopigment content, photochemistry efficiency, and light harvesting ability. Further, decreased specific leaf area and increased wax coverage in EC suggested that EC contributed to protect chloroplasts and reduce water loss. In conclusion, functional improvements of the photosynthetic apparatus with changes in morphological traits were observed under FC50 combined with EC and EC ameliorated the adverse effect of FC50 on the seedlings of L. tulipifera.

The impact of elevated CO2 and water deficit stress on growth and photosynthesis of juvenile cacao (Theobroma cacao L.).

Atmospheric CO2 concentration continues to rise and is predicted to reach approximately 700 ppm by 2100. Some predictions suggest that the dry season in West Africa could be extended with climate change. This study examined the effects of elevated CO2 concentration and water deficit on growth and photosynthesis of juvenile cacao. Light-saturated photosynthesis (Pmax), quantum efficiency, and intrinsic water-use efficiency increased significantly in response to elevated CO2, as did a range of growth and development responses (e.g. leaf area and leaf number), but the magnitude of the increase was dependent on the water treatment. Stomatal index was significantly greater in the elevated CO2 treatment; an atypical response which may be a reflection of the environment in which cacao evolved. This study shows a positive effect of elevated CO2 on juvenile cacao which may help to alleviate some of the negative impacts of water deficit stress.

The effect of elevated carbon dioxide on the sinking and swimming of the shelled pteropod Limacina retroversa

Abstract Shelled pteropods are planktonic molluscs that may be affected by ocean acidification. Limacina retroversa from the Gulf of Maine were used to investigate the impact of elevated carbon dioxide (CO2) on shell condition as well as swimming and sinking behaviours. Limacina retroversa were maintained at either ambient (ca. 400 µatm) or two levels of elevated CO2 (800 and 1200 µatm) for up to 4 weeks, and then examined for changes in shell transparency, sinking speed, and swimming behaviour assessed through a variety of metrics (e.g. speed, path tortuosity, and wing beat frequency). After exposures to elevated CO2 for as little as 4 d, the pteropod shells were significantly darker and more opaque in the elevated CO2 treatments. Sinking speeds were significantly slower for pteropods exposed to medium and high CO2 in comparison to the ambient treatment. Swimming behaviour showed less clear patterns of response to treatment and duration of exposure, but overall, swimming did not appear to be hindered under elevated CO2. Sinking is used by L. retroversa for predator evasion, and altered speeds and increased visibility could increase the susceptibility of pteropods to predation.

Ecophysiological responses to elevated CO2 and temperature in Cystoseira tamariscifolia (Phaeophyceae)

Ocean acidification increases the amount of dissolved inorganic carbon (DIC) available in seawater which can benefit photosynthesis in those algae that are currently carbon limited, leading to shifts in the structure and function of seaweed communities. Recent studies have shown that ocean acidification-driven shifts in seaweed community dominance will depend on interactions with other factors such as light and nutrients. The study of interactive effects of ocean acidification and warming can help elucidate the likely effects of climate change on marine primary producers. In this study, we investigated the ecophysiological responses of Cystoseira tamariscifolia (Hudson) Papenfuss. This large brown macroalga plays an important structural role in coastal Mediterranean communities. Algae were collected from both oligotrophic and ultraoligotrophic waters in southern Spain. They were then incubated in tanks at ambient (ca. 400–500 ppm) and high CO2 (ca. 1200–1300 ppm), and at 20 °C (ambient temperature) and 24 °C (ambient temperature +4 °C). Increased CO2 levels benefited the algae from both origins. Biomass increased in elevated CO2 treatments and was similar in algae from both origins. The maximal electron transport rate (ETRmax), used to estimate photosynthetic capacity, increased in ambient temperature/high CO2 treatments. The highest polyphenol content and antioxidant activity were observed in ambient temperature/high CO2 conditions in algae from both origins; phenol content was higher in algae from ultraoligotrophic waters (1.5–3.0%) than that from oligotrophic waters (1.0–2.2%). Our study shows that ongoing ocean acidification can be expected to increase algal productivity (ETRmax), boost antioxidant activity (EC 50 ), and increase production of photoprotective phenols. Cystoseira tamariscifolia collected from oligotrophic and ultraoligotrophic waters were able to benefit from increases in DIC at ambient temperatures. Warming, not acidification, may be the key stressor for this habitat as CO2 levels continue to rise.

Attaining whole-ecosystem warming using air and deep-soil heating methods with an elevated CO<sub>2</sub> atmosphere

Abstract. This paper describes the operational methods to achieve and measure both deep-soil heating (0–3 m) and whole-ecosystem warming (WEW) appropriate to the scale of tall-stature, high-carbon, boreal forest peatlands. The methods were developed to allow scientists to provide a plausible set of ecosystem-warming scenarios within which immediate and longer-term (1 decade) responses of organisms (microbes to trees) and ecosystem functions (carbon, water and nutrient cycles) could be measured. Elevated CO2 was also incorporated to test how temperature responses may be modified by atmospheric CO2 effects on carbon cycle processes. The WEW approach was successful in sustaining a wide range of aboveground and belowground temperature treatments (+0, +2.25, +4.5, +6.75 and +9 °C) in large 115 m2 open-topped enclosures with elevated CO2 treatments (+0 to +500 ppm). Air warming across the entire 10 enclosure study required ∼ 90 % of the total energy for WEW ranging from 64 283 mega Joules (MJ) d−1 during the warm season to 80 102 MJ d−1 during cold months. Soil warming across the study required only 1.3 to 1.9 % of the energy used ranging from 954 to 1782 MJ d−1 of energy in the warm and cold seasons, respectively. The residual energy was consumed by measurement and communication systems. Sustained temperature and elevated CO2 treatments were only constrained by occasional high external winds. This paper contrasts the in situ WEW method with closely related field-warming approaches using both aboveground (air or infrared heating) and belowground-warming methods. It also includes a full discussion of confounding factors that need to be considered carefully in the interpretation of experimental results. The WEW method combining aboveground and deep-soil heating approaches enables observations of future temperature conditions not available in the current observational record, and therefore provides a plausible glimpse of future environmental conditions.

Impact of elevated CO2 and temperature on quality and biochemical parameters of bell pepper (Capsicum annuum) crop

Experiment was conducted during 2014 and 2015 to study effect of elevated CO2 and temperature on quality and biochemical parameters of bell pepper (Capsicum annuum L.) crop. To carry out experiment there were four conditions, i.e. in three Open Top Chambers, (T1: OTC with elevated CO2550±10 ppm; T2: OTC with elevated temperature 1◦C and elevated CO2550±10 ppm; T3: OTC with ambient temperature and CO2(reference) and T4: natural air and temperature). Pooled data for two years indicated that higher fruit size (40.19 cm2) and average fruit weight (63.06 g/ fruit) was obtained in plants grown under elevated CO2. Elevated CO2 and temperature treatment resulted lower leaf chlorophyll (1 708.71 mg/kg). Higher ascorbic acid content in fruits (159.12 mg/100g) was recorded under elevated CO2 and temperature. Lower total soluble solids were observed under elevated CO2 (4.02°B) while higher under elevated CO2 and temperature (5.39°B). Higher N content (5.73%) was recorded under natural condition and lower under elevated CO2 (4.08%). Higher P (0.39%), K (5.21%) and Mg (0.49%) content was recorded under natural condition and lower values were recorded under elevated CO2 and temperature. Significantly higher Ca content (0.46%) was recorded in elevated CO2 and lowest in natural condition (0.35%). Both elevated temperature and CO2 had significant effects on quality and biochemical parameters in vegetables. These parameters of bell pepper crop were affected negatively by changing climatic conditions, i.e. elevated CO2 and temperature where positive effect of CO2 offset by elevated temperature effect.

English

Nocturnal dark respiration (Rn) in wild type and transgenic soybean plants grown at SoyFACE research facility, Illinois, USA under ambient and elevated CO2 conditions was examined in this study. Transgenic plants were transformed to overexpress a key Calvin cycle enzyme sedoheptulose-1,7-bisphosphatase (SBP) which is thought to improve yield in the field by at least 11%. Heating was applied using infrared heaters mounted 1.2 m above the plants in the field during the growing season of 2015 summer and Rn measurements taken for wild type and SBP overexpressors at ambient and elevated CO2 plots from V4 to R6 developmental stages. The objective was to study the effects of elevated CO2 of approximately 585 μmol mol-1 and +3.5 increase in temperature on wildtype and transgenic SBP plants. Measurements were recorded at growth and constant temperature for both varieties. Experimental plants were transferred to a controlled growth chamber at V4 and R6 developmental stages and the temperature responses examined from 15 to 40°C. Specific leaf area (SLA) and its relations to Rn were also determined. Results indicate that SLA decreased significantly relative to control in the wild type and transgenic soybean plants by R6. Differential responses of Rn to ambient and elevated CO2 treatments were observed in both plants. In addition, results indicate that Rn declined generally in both varieties under elevated temperature. Lower Rn was attributed to temperature acclimation. Key words: Dark respiration, soybean, ambient CO2, elevated CO2, transgenic plant, sedoheptulose-1,7-bisphosphatase (SBP), heating, acclimation.

Effects of nitrogen addition and elevated CO2 concentration on soil dissolved organic carbon and nitrogen in rhizosphere and non-rhizosphere of Bothriochloa ischaemum

A pot experiment was conducted to study soil dissolved organic carbon (DOC) and dissolved organic nitrogen (DON) in the rhizosphere and non-rhizosphere of Bothriochloa ischaemum in loess hilly-gully region under the different treatments of CO2 concentrations (400 and 800 μmol·mol-1) and nitrogen addition (0, 2.5, 5.0 g N·m-2·a-1). The results showed that eleva-ted CO2 treatments had no significant effect on the contents of DOC, dissolved total nitrogen (DTN), DON, dissolved ammonium nitrogen (NH4+-N) and dissolved nitrate nitrogen (NO3--N) in the soil of rhizosphere and non-rhizosphere of B. ischaemum. The contents of DTN, DON, and NO3--N in the rhizosphere soil were significantly increased with the nitrogen application and the similar results of DTN and NO3--N also were observed in the non-rhizosphere of B. ischaemum. Nitrogen application significantly decreased DOC/DON in the rhizosphere of B. ischaemum. The contents of DTN, NO3--N and DON in the soil of rhizosphere were significantly lower than that in the non-rhizosphere soil, and DOC/DON was significantly higher in the rhizosphere soil than that in the non-rhizosphere soil. It indicated that short-term elevated CO2 concentration had no significant influence on the contents of soil dissolved organic carbon and nitrogen. Simulated nitrogen deposition, to some extent, increased the content of soil dissolved nitrogen, but it was still insufficient to meet the demand of dissolved nitrogen for plant growing.

Interactive effects of carbon dioxide, low temperature, and ultraviolet-B radiation on cotton seedling root and shoot morphology and growth

Interactive effects of multiple environmental stresses are predicted to have a negative effect on cotton growth and development and these effects will be exacerbated in the future climate. The objectives of this study were to test the hypothesis that cotton cultivars differ in their responses to multiple environmental factors of (CO2) [400 and 750 µmol·mol–1 (+(CO2)], temperature [28/20 and 20/12°C (–T)], and UV–B radiation [0 and 10 kJ·m–2·d–1 (+ UV–B)]. A genetic and molecular standard (TM-1) and three modern cotton cultivars (DP1522B2XF, PHY496W3R, and ST4747GLB2) were grown in eight sunlit, controlled environment chambers with control treatment 400 µmol·mol–1 [CO2], 28/21°C temperature, and 0 kJ UV–B. The results showed significant differences among the cultivars for most of the shoot and root parameters. Plants grown under low temperature alone or as a combination with + UV–B treatment caused more detrimental effects on root and shoot vigor. Although the elevated CO2 treatments weakened the damaging effects of higher UV–B levels on cotton growth on all cultivars, increased CO2 could not mask the negative effects of low temperature. When comparing all cultivars, genetic standard TM-1 produced the smallest values for the majority of traits under CO2, UV–B, and low temperature either alone or in combination with other treatments. Based on principal component analysis, the four cultivars were classified as tolerant (DP1522B2XF), intermediate (PHY496W3R and ST4747GLB2) and sensitive (TM-1) to multiple environmental stresses.Low temperature was identified as the most damaging treatment to cotton early seedling vigor while elevated CO2 caused the least. Existing variability of cotton cultivars in response to multiple environmental stresses could allow for selection of cultivars with the best coping ability and higher lint yield for future climate change environments.

Effects of ocean acidification on pelagic carbon fluxes in a mesocosm experiment

Abstract. About a quarter of anthropogenic CO2 emissions are currently taken up by the oceans, decreasing seawater pH. We performed a mesocosm experiment in the Baltic Sea in order to investigate the consequences of increasing CO2 levels on pelagic carbon fluxes. A gradient of different CO2 scenarios, ranging from ambient ( ∼ 370 µatm) to high ( ∼ 1200 µatm), were set up in mesocosm bags ( ∼ 55 m3). We determined standing stocks and temporal changes of total particulate carbon (TPC), dissolved organic carbon (DOC), dissolved inorganic carbon (DIC), and particulate organic carbon (POC) of specific plankton groups. We also measured carbon flux via CO2 exchange with the atmosphere and sedimentation (export), and biological rate measurements of primary production, bacterial production, and total respiration. The experiment lasted for 44 days and was divided into three different phases (I: t0–t16; II: t17–t30; III: t31–t43). Pools of TPC, DOC, and DIC were approximately 420, 7200, and 25 200 mmol C m−2 at the start of the experiment, and the initial CO2 additions increased the DIC pool by ∼ 7 % in the highest CO2 treatment. Overall, there was a decrease in TPC and increase of DOC over the course of the experiment. The decrease in TPC was lower, and increase in DOC higher, in treatments with added CO2. During phase I the estimated gross primary production (GPP) was ∼ 100 mmol C m−2 day−1, from which 75–95 % was respired, ∼ 1 % ended up in the TPC (including export), and 5–25 % was added to the DOC pool. During phase II, the respiration loss increased to ∼ 100 % of GPP at the ambient CO2 concentration, whereas respiration was lower (85–95 % of GPP) in the highest CO2 treatment. Bacterial production was ∼ 30 % lower, on average, at the highest CO2 concentration than in the controls during phases II and III. This resulted in a higher accumulation of DOC and lower reduction in the TPC pool in the elevated CO2 treatments at the end of phase II extending throughout phase III. The “extra” organic carbon at high CO2 remained fixed in an increasing biomass of small-sized plankton and in the DOC pool, and did not transfer into large, sinking aggregates. Our results revealed a clear effect of increasing CO2 on the carbon budget and mineralization, in particular under nutrient limited conditions. Lower carbon loss processes (respiration and bacterial remineralization) at elevated CO2 levels resulted in higher TPC and DOC pools than ambient CO2 concentration. These results highlight the importance of addressing not only net changes in carbon standing stocks but also carbon fluxes and budgets to better disentangle the effects of ocean acidification.

Jasmonate-mediated stomatal closure under elevated CO2 revealed by time-resolved metabolomics.

Foliar stomatal movements are critical for regulating plant water loss and gas exchange. Elevated carbon dioxide (CO2 ) levels are known to induce stomatal closure. However, the current knowledge on CO2 signal transduction in stomatal guard cells is limited. Here we report metabolomic responses of Brassica napus guard cells to elevated CO2 using three hyphenated metabolomics platforms: gas chromatography-mass spectrometry (MS); liquid chromatography (LC)-multiple reaction monitoring-MS; and ultra-high-performance LC-quadrupole time-of-flight-MS. A total of 358 metabolites from guard cells were quantified in a time-course response to elevated CO2 level. Most metabolites increased under elevated CO2 , showing the most significant differences at 10 min. In addition, reactive oxygen species production increased and stomatal aperture decreased with time. Major alterations in flavonoid, organic acid, sugar, fatty acid, phenylpropanoid and amino acid metabolic pathways indicated changes in both primary and specialized metabolic pathways in guard cells. Most interestingly, the jasmonic acid (JA) biosynthesis pathway was significantly altered in the course of elevated CO2 treatment. Together with results obtained from JA biosynthesis and signaling mutants as well as CO2 signaling mutants, we discovered that CO2 -induced stomatal closure is mediated by JA signaling.

Red alga Palmaria palmata—growth rate and photosynthetic performance under elevated CO2 treatment

Marine macroalgae offer a feasible solution for reducing CO2 emissions by fixing CO2 as algal biomass and thus providing a source of renewable energy. The perennial red alga Palmaria palmata was cultivated and supplied with increased CO2 concentrations starting with 22 μmol kg−1 (pH 8.53) to 9770 μmol kg−1 (pH 6.04). Experiments covered test periods of 28 days, 7 days, and 2 h to examine the possible influence of different treatment durations. Biomass productivity over 28 days showed an increased production rate, which continuously declined with increasing CO2 concentration. After 7 days, the productivity was below the controls, suggesting a lag phase or necessary adaptation period to elevated CO2 concentrations of more than 7 days. Concerning the effects on maximum electron transport rate (ETRmax), light-harvesting efficiency (alpha), and light saturation of the photosynthetic electron transport (E k ), a stimulating influence was identified with the effect becoming more significant the shorter the test period was. The treatment with elevated CO2 concentrations for 28 days led to a decrease in photochemical efficiency (Y(II)) and regulated nonphotochemical energy dissipation (Y(NPQ)). In contrast, the treatment duration of 7 days predominantly increased photochemical quenching whereas the 2-h treatment resulted in a significant increase in photochemical quenching and in a significant decrease in nonregulated nonphotochemical energy dissipation. Hence, elevated CO2 concentrations over a prolonged time period interfered more distinctively with the fluorescence quenching ability of P. palmata.

Field-based experimental acidification alters fouling community structure and reduces diversity.

Increasing levels of CO2 in the atmosphere are affecting ocean chemistry, leading to increased acidification (i.e. decreased pH) and reductions in calcium carbonate saturation state. Many species are likely to respond to acidification, but the direction and magnitude of these responses will be based on interspecific and ontogenetic variation in physiology and the relative importance of calcification. Differential responses to ocean acidification (OA) among species will likely result in important changes in community structure and diversity. To characterize the potential impacts of OA on community composition and structure, we examined the response of a marine fouling community to experimental CO2 enrichment in field-deployed flow-through mesocosm systems. Acidification significantly altered the community structure by altering the relative abundance of species and reduced community variability, resulting in more homogenous biofouling communities from one experimental tile to the next both among and within the acidified mesocosms. Mussel (Mytilus trossulus) recruitment was reduced by over 30% in the elevated CO2 treatment compared to the ambient treatment by the end of the experiment. Strong differences in mussel cover (up to 40% lower in acidified conditions) developed over the second half of the 10-week experiment. Acidification did not appear to affect the mussel growth, as average mussel sizes were similar between treatments at the end of the experiment. Hydroid (Obelia dichotoma) cover was significantly reduced in the elevated CO2 treatment after 8weeks. Conversely, the percentage cover of bryozoan colonies (Mebranipora membranacea) was higher under acidified conditions with differences becoming apparent after 6weeks. Neither recruitment nor final size of barnacles (Balanus crenatus) was affected by acidification. By the end of the experiment, diversity was 41% lower in the acidified treatment relative to ambient conditions. Overall, our findings support the general expectation that OA will simplify marine communities by acting on important ecological processes that ultimately determine the community structure and diversity.

Enhanced priming of old, not new soil carbon at elevated atmospheric CO2

Rising atmospheric CO2 concentrations accompanied by global warming and altered precipitation patterns calls for assessment of long-term effects of these global changes on carbon (C) dynamics in terrestrial ecosystems, as changes in net C exchange between soil and atmosphere will impact the atmospheric CO2 concentration profoundly. In many ecosystems, including the heath/grassland system studied here, increased plant production at elevated CO2 increase fresh C input from litter and root exudates to the soil and concurrently decrease soil N availability. Supply of labile C to the soil may accelerate the decomposition of soil organic C (SOC), a phenomenon termed ‘the priming effect’, and the priming effect is most pronounced at low soil N availability. Hence, we hypothesized that priming of SOC decomposition in response to labile C addition would increase in soil exposed to long-term elevated CO2 exposure. Further, we hypothesized that long-term warming would enhance SOC priming rates, whereas drought would decrease the priming response.We incubated soil from a long-term, full-factorial climate change field experiment, with the factors elevated atmospheric CO2 concentration, warming and prolonged summer drought with either labile C (sucrose) or water to assess the impact of labile C on SOC dynamics. We used sucrose with a 13C/12C signature that is distinct from that of the native SOC, which allowed us to assess the contribution of these two C sources to the CO2 evolved. Sucrose induced priming of SOC, and the priming response was higher in soil exposed to long-term elevated CO2 treatment. Drought tended to decrease the priming response, whereas long-term warming did not affect the level of priming significantly.We were also able to assess whether SOC-derived primed C in elevated CO2 soil was assimilated before or after the initiation of the CO2 treatment 8 years prior to sampling, because CO2 concentrations were raised by fumigating the experimental plots with pure CO2 that was 13C-depleted compared to ambient CO2. Surprisingly, we conclude that sucrose addition primed decomposition of relatively old SOC fractions, i.e. SOC assimilated more than 8 years before sampling.