Ambient CO2 Concentration Research Articles

Is the Seasonal Variation in Frost Resistance and Plant Performance in Four Oak Species Affected by Changing Temperatures?

Research Highlights: We found seasonal variation in frost resistance (FR) and plant performance which were affected by growth temperature. This helps to better understand ecophysiological processes in the light of climate change. Background and Objectives: FR and photosynthesis are important plant characteristics that vary with the season. The aim of this study was to find out whether there is a seasonal variation in FR, photosynthetic CO2 assimilation rates and leaf functional traits associated with performance such as specific leaf area (SLA), leaf dry matter content (LDMC), chlorophyll content, stomatal characteristics and leaf thickness in two evergreen and two deciduous species, and whether this is influenced by different temperature treatments. Additionally, the trade-off between FR and photosynthetic performance, and the influence of leaf functional traits was analyzed. By understanding these processes better, predicting species behavior concerning plant performance and its changes under varying climate regimes can be improved. Materials and Methods: 40 individuals of four oak species were measured weekly over the course of ten months with one half of the trees exposed to frost in winter and the other half protected in the green house. Two of these species were evergreen (Quercus ilex L., Quercus rhysophylla Weath.), and two were deciduous (Quercus palustris L., Quercus rubra L.). We measured FR, the maximum assimilation rate at light saturation under ambient CO2 concentrations (Amax), chlorophyll fluorescence and the leaf functional traits SLA, LDMC, stomatal pore area index (SPI), chlorophyll content (Chl) and leaf thickness. Results: All parameters showed a significant species-specific seasonal variation. There was a difference in all traits investigated between evergreen and deciduous species and between the two temperature treatments. Individuals that were protected from frost in winter showed higher photosynthesis values as well as SLA and Chl, whereas individuals exposed to frost had overall higher FR, LDMC, SPI and leaf thickness. A trade-off between FR and SLA, rather than FR and photosynthetic performance was found.

The potential implications of a plasma membrane aquaporin in improving CO2 transport capacity, photosynthetic potential and water use efficiency under contrasting CO2 source in Solanum lycopersicum (tomato)

Mesophyll conductance has been increasingly recognized as a limiting-factor for carbon transport and fixation during photosynthetic process. Despite mesophyll conductance performs a significant role in determining photosynthetic and yield potential, its molecular mechanisms are uncertain and controversy. In the present study, the function of a plasma membrane aquaporin SlPIP1;2 in facilitating CO2 transport across the plasma membrane under contrasting CO2 concentrations was evaluated, according to the photosynthetic performance of transgenic lines of overexpression and knock-out. The relative importance of PIP-channel in determining membrane permeability and mesophyll conductance is largely depend on the ambient and intercellular CO2 concentration. Under the current ambient CO2 concentration, SlPIP1;2 had minor effect on photosynthetic performance. Overexpression of the target gene substantially enhanced CO2 membrane permeability under CO2 enrichment, according to the photosynthetic performance: overexpression SlPIP1;2 significantly improved mesophyll conductance and photosynthesis rate, which translated into improvement in crop productivity and water use efficiency. The present results suggested that SlPIP1;2 is potentially involved in facilitating CO2 transport across the plasma membrane under CO2 enrichment, which subsequently affect crop productivity and water use efficiency.

Elevated Atmospheric CO2 Concentration Improved C4 Xero-Halophyte Kochia prostrata Physiological Performance under Saline Conditions.

A significant increase in atmospheric CO2 concentration and associated climate aridization and soil salinity are factors affecting the growth, development, productivity, and stress responses of plants. In this study, the effect of ambient (400 ppm) and elevated (800 ppm) CO2 concentrations were evaluated on the C4 xero-halophyte Kochia prostrata treated with moderate salinity (200 mM NaCl) and polyethylene glycol (PEG)-induced osmotic stress. Our results indicated that plants grown at elevated CO2 concentration had different responses to osmotic stress and salinity. The synergistic effect of elevated CO2 and osmotic stress increased proline accumulation, but elevated CO2 did not mitigate the negative effects of osmotic stress on dark respiration intensity and photosystem II (PSII) efficiency. This indicates a stressful state, which is accompanied by a decrease in the efficiency of light reactions of photosynthesis and significant dissipative respiratory losses, thereby resulting in growth inhibition. Plants grown at elevated CO2 concentration and salinity showed high Na+ and proline contents, high water-use efficiency and time required to reach the maximum P700 oxidation level (PSI), and low dark respiration. Maintaining stable water balance, the efficient functioning of cyclic transport of PSI, and the reduction of dissipation costs contributed to an increase in dry shoot biomass (2-fold, compared with salinity at 400 ppm CO2). The obtained experimental data and PCA showed that elevated CO2 concentration improved the physiological parameters of K. prostrata under salinity.

The Association of White Blood Cells and Air Pollutants-A Population-Based Study.

The links of air pollutants to health hazards have been revealed in literature and inflammation responses might play key roles in the processes of diseases. WBC count is one of the indexes of inflammation, however the l iterature reveals inconsistent opinions on the relationship between WBC counts and exposure to air pollutants. The goal of this population-based observational study was to examine the associations between multiple air pollutants and WBC counts. This study recruited community subjects from Kaohsiung city. WBC count, demographic and health hazard habit data were collected. Meanwhile, air pollutants data (SO2, NO2, CO, PM10, and O3) were also obtained. Both datasets were merged for statistical analysis. Single- and multiple-pollutants models were adopted for the analysis. A total of 10,140 adults (43.2% males; age range, 33~86 years old) were recruited. Effects of short-term ambient concentrations (within one week) of CO could increase counts of WBC, neutrophils, monocytes, and lymphocytes. However, SO2 could decrease counts of WBC, neutrophils, and monocytes. Gender, BMI, and smoking could also contribute to WBC count increases, though their effects are minor when compared to CO. Air pollutants, particularly SO2, NO2 and CO, may thus be related to alterations of WBC counts, and this would imply air pollution has an impact on human systematic inflammation.

Effects of head-down tilt bed rest plus elevated CO2 on cognitive performance.

Microgravity and elevated CO2 levels are two important environmental spaceflight stressors that can adversely affect astronaut cognitive performance and jeopardize mission success. This study investigated the effects of 6° head-down tilt bed rest (HDBR) with (n = 11 participants, 30-day HDBR) and without (n = 8 participants, 60-day HDBR) elevated ambient (3.73 mmHg) CO2 concentrations on cognitive performance. Participants of both groups performed all 10 tests of NASA's Cognition battery and a brief alertness and mood survey repeatedly before, during, and after the HDBR period. Test scores were adjusted for practice and stimulus set effects. Concentrating on the first 30 days of HDBR, a modest but statistically significant slowing across a range of cognitive domains was found in both groups (controls: -0.37 SD; 95% CI -0.48, -0.27; adjusted P < 0.0001; CO2: -0.25 SD; 95% CI -0.34, -0.16; adjusted P < 0.001), most prominently for sensorimotor speed. These changes were observed early during HDBR and did not further deteriorate or improve with increasing time in HDBR. The study found similar cognitive effects of HDBR irrespective of CO2 levels, suggesting that elevated CO2 neither ameliorated nor worsened the HDBR effects. In both groups, cognitive performance after 15 days of recovery was statistically indistinguishable from pre-HDBR performance. However, subjects undergoing 60 days of HDBR rated themselves as feeling more sleepy, tired, physically exhausted, stressed, and unhealthy during recovery compared to their 30-day counterparts.NEW AND NOTEWORTHY This study investigated the effects of prolonged head-down tilt bed rest with and without elevated (3.73 mmHg) levels of ambient CO2 on cognitive performance across a range of cognitive domains and is one of the few studies investigating combined effects of environmental stressors prevalent in spaceflight. The study showed moderate declines in cognitive speed induced by head-down tilt bed rest and suggests that exposure to elevated levels of ambient CO2 did not modify this effect.

Interactive Effects of Elevated CO2 Concentration and Light on the Picophytoplankton Synechococcus

Synechococcus is a major contributor to the primary production in tropic and subtropical oceans worldwide. Responses of this picophytoplankton to changing light and CO2 levels is of general concern to understand its ecophysiology in the context of ocean global changes. We grew Synechococcus sp. (WH7803), originally isolated from subtropic North Atlantic Ocean, under different PAR levels for about 15 generations and examined its growth, photochemical performance and the response of these parameters to elevated CO2 (1,000 μatm). The specific growth rate increased from 6 μmol m–2 s–1 to reach a maximum (0.547 ± 0.026) at 25 μmol m–2 s–1, and then became inhibited at PAR levels over 50 μmol m–2 s–1, with light use efficiency (α) and photoinhibition coefficient (β) being 0.093 and 0.002, respectively. When the cells were grown at ambient and elevated CO2 concentration (400 vs. 1,000 μatm), the high-CO2 grown cells showed significantly enhanced rates of electron transport and quantum yield as well as significant increase in specific growth rate at the limiting and inhibiting PAR levels. While the electron transport rate significantly increased at the elevated CO2 concentration under all tested light levels, the specific growth did not exhibit significant changes under the optimal growth light condition. Our results indicate that Synechococcus WH7803 grew faster under the ocean acidification (OA) treatment induced by CO2 enrichment only under limiting and inhibiting light levels, indicating the interactive effects and implying that the picophytoplankton respond differentially at different depths while exposing changing light conditions.

Relationship between endophytic microbial diversity and grain quality in wheat exposed to multi-generational CO2 elevation.

To explore the potential association between the diversity of endophytic microorganisms and modifications of grain quality in wheat exposed to multi-generational elevated CO2 concentration, the grain quality attributes and microbial diversity were tested after five generations successively grown in ambient CO2 concentration (F5_A, 400μmolL-1) and elevated CO2 concentration (F5_E, 800μmolL-1). Elevated CO2 concentration significantly increased the grain number and starch concentration, while decreased the grain protein concentration. Multi-generational exposure to elevated CO2 concentration also led to significant changes in grain amino acid concentration. In response to the elevated CO2 concentration, Pseudomonas, Rhodococcus, Ralstonia, and Klebsiella were the dominant bacterial genera, while Penicillium, Cutaneotrichosporon, Fusarium, Sarocladium, Acremonium and Aspergillus were the dominant fungal genera in wheat grain. A significantly positive correlation was found between Pseudomonas, Penicillium and ratio of starch to protein concentration, implying that the multi-generational CO2 elevation induced modifications in grain quality might be associated with the changes in grain microbial diversity. The results of this study suggest that the endophytic microbes may play an important role in modulating the grain nutritional quality in wheat under multi-generational e[CO2] exposure, through regulating starch and N metabolism and production of secondary metabolites.

The effect of individual and combined drought and heat stress under elevated CO2 on physiological responses in spring wheat genotypes

Abiotic stress due to climate change with continuous rise of atmospheric CO2 concentration is predicted to cause severe changes to crop productivity. Thus, research into wheat cultivars, capable of maintaining yield under limiting conditions is necessary. The aim of this study was to investigate the physiological responses of spring wheat to individual and combined drought- and heat events and their interaction with CO2 concentration. Two heat sensitive (LM19, KU10) and two heat tolerant (LM62, GN5) genotypes were selected and grown under ambient (400 ppm, aCO2) and elevated (800 ppm, eCO2) CO2 concentrations. At the tillering stage, the wheat plants were subjected to different treatments: control, progressive drought, heat and combined drought and heat stress. Our results showed that eCO2 mitigated the negative impact of the moderate stress in all genotypes. However, no distinctive responses were observed in some of the measured parameters between heat sensitive and tolerant genotypes. All genotypes grown at eCO2 had significantly higher net photosynthetic rates and maintained maximum quantum efficiency of PSII photochemistry under heat and combined stress compared to aCO2. Under heat and combined stress, the chlorophyll a:b ratios decreased only in heat tolerant genotypes at eCO2 compared to the control. Furthermore, the heat tolerant genotypes grown at eCO2 showed an increased glucose and fructose contents and a decreased sucrose content under combined stress compared to aCO2. These findings provide new insights into the underlying mechanisms of different genotypic responses to combined abiotic stresses at eCO2 that differ from the response to individual stresses.

Effects of long-term CO2 enrichment on forage quality of extensively managed temperate grassland

Different studies revealed an increased biomass production in grasslands due to elevated CO2 (eCO2). Thus, the question arises whether forage quality of grassland biomass is also influenced.In the present study, we assessed the long-term effects of eCO2 in context of the accompanied site conditions soil moisture, air temperature and precipitation on different forage quality and energy parameters of grassland biomass in an extensively managed temperate grassland. The study took place at the Free-Air Carbon dioxide Enrichment site near Giessen [GiFACE], which was set up in 1998. Our main objective was to assess the differences in the quality and energy content of grassland forage, exposed to elevated CO2 [+ 20%; eCO2] and ambient CO2 (aCO2) concentrations. Crude protein, C/N-ratio, crude fat, total non-structural carbohydrates, ash, crude fibre, metabolisable energy [ME] and net energy for lactation [NEL] were determined to assess the forage quality and energy content of grassland biomass separated in grasses and forbs, which was harvested twice per year (end of May, beginning of September), over the period of 2006–2015.Forbs showed a significant decrease for most tested parameters under eCO2 at both harvests, except for crude fibre, which showed a significant increase at the second harvest of the year under eCO2. Grasses showed a significant negative CO2 effect for ash content at the first harvest of the year. In addition to eCO2, site and climatic conditions, e.g. soil moisture, affected the investigated parameters.Based on the last 10 observation years (2006–2015) within the 18 year long experiment, eCO2 is likely to cause a decline in forage quality, especially of forbs caused by reduced crude protein and fat contents and increased crude fibre content, in extensively managed grassland ecosystems. However, site and climatic conditions should also be considered showing the importance of long-term observations that contain the full range of climatic conditions. Periods of heat, drought and precipitation, which are expected to increase in the future, lead to a decrease of the CO2 fertilization effect on grassland biomass and also to a negative impact on forage quality.

The climatology of ambient CO2 concentrations from long-term observation in the Pearl River Delta region of China: Roles of anthropogenic and biogenic processes

The global/regional background CO2 has been investigated extensively. However, the monitoring of CO2 concentration remains sparse in the megacities of China. Understanding the ambient CO2 in urban areas and how it is influenced by meteorological conditions, anthropogenic emissions, and biogenic processes may shed light on improving the carbon evaluation. The climatology of ambient CO2 is reported for the period 2014–2017 at the Guangzhou Panyu Atmospheric Composition Site (GPACS), a suburban site in the Pearl River Delta (PRD) region of China. The ambient CO2 ranged from 420.50 ± 14.87 × 10−6 mol mol−1 (ppm) in the summer to 431.94 ± 15.13 ppm in the winter and had an annual mean of 428.16 ± 16.26 ppm. The high CO2 concentrations during the winter were a consequence of anthropogenic emissions and low solar radiation against mixing layer height (MLH). The diurnal variability of CO2 exhibited two peaks: one peak occurring at 0500–0700 and another at 2100–2200 LST (Local Standard Time), which roughly corresponds to local rush hour. CO2 decreased with near-surface wind speed (WS), most of which was constrained to WS less than 2.0 ms−1. Carbon monoxide (CO) concentrations were simultaneously measured to distinguish between biogenic and anthropogenic sources of CO2. △CO2 and △CO showed significant, positive correlations (r = 0.77–0.78, p < 0.001) in winter and autumn, reflecting common sources under synoptic air transport from the northwest and northeast directions. The correlation was lower in spring (r = 0.62, p < 0.001), possibly because the vegetation photosynthesis was stronger. A regression analysis of △CO2 against △CO showed that the intercepts varied between 4.3 and 10.3 ppm, indicating that respiration released more CO2 relative to photosynthesis. The mean diurnal slope (△CO2/△CO) ranged from 54.27 ± 5.36 to 71.07 ± 10.30 ppm ppm−1, indicating that the anthropogenic sources were the largest contributor to CO2 compared to biogenic processes. The fossil fuels from power and industries are responsible for the level of anthropogenic CO2, while vehicles are the main source of diurnal variations. The ratio of △CO2 to △CO was lower in winter, which indicates the contribution of CO emissions from traffic sources were associated with the lower ambient temperature. More fossil fuel combustion to heat buildings together with reduced biospheric respiration can also explain the lower △CO2/△CO ratios during the winter.

The Physiological Response of Lettuce to Red and Blue Light Dynamics Over Different Photoperiods.

This study aimed to evaluate the effect of dynamic red and blue light parameters on the physiological responses and key metabolites in lettuce and also the subsequent impact of varying light spectra on nutritive value. We explored the metabolic changes in carotenes, xanthophylls, soluble sugars, organic acids, and antioxidants; the response of photosynthetic indices [photosynthetic (Pr) and transpiration (Tr) rates]; and the intracellular to ambient CO2 concentration ratios (Ci/Ca) in lettuce (Lactuca sativa L. “Lobjoits Green Cos”). They were cultivated under constant (con) or parabolic (dyn) blue (B, 452 nm) and/or red (R, 662 nm) light-emitting diode (LED) photosynthetic photon flux densities (PPFDs) at 12, 16, and 20 h photoperiods, maintaining consistent daily light integrals (DLIs) for each light component in all treatments, at 2.3 and 9.2 mol m–2 per day for blue and red light, respectively. The obtained results and principal component analysis (PCA) confirmed a significant impact of the light spectrum, photoperiod, and parabolic profiles of PPFD on the physiological response of lettuce. The 16 h photoperiod resulted in significantly higher content of xanthophylls (neoxanthin, violaxanthin, lutein, and zeaxanthin) in lettuce leaves under both constant and parabolic blue light treatments (BconRdyn 16 h and BdynRdyn 16 h, respectively). Lower PPFD levels under a 20 h photoperiod (BdynRdyn 20 h) as well as higher PPFD levels under a 12 h photoperiod (BdynRdyn 12 h) had a pronounced impact on leaf gas exchange indices (Pr, Tr, Ci/Ca), xanthophylls, soluble sugar contents, and antioxidant properties of lettuce leaves. The parabolic PPFD lighting profile over a 16 h photoperiod (BdynRdyn 16 h) led to a significant decrease in Ci/Ca, which resulted in decreased Pr and Tr, compared with constant blue or red light treatments with the same photoperiod (BconRdyn and BdynRcon 16 h). Additionally, constant blue lighting produced higher α + β-carotene and anthocyanin (ARI) content and increased carotenoid to chlorophyll ratio (CRI) but decreased biomass accumulation and antioxidant activity.

Combined and single effects of elevated CO2 and temperatures on rice bakanae disease under controlled conditions in phytotrons

AbstractBakanae disease, caused by Fusarium fujikuroi, was investigated under different CO2 and temperature environments in order to simulate climate changes in the F. fujikuroi–rice pathosystem. F. fujikuroi‐infected plants were grown under six phytotron conditions: low (18/22 °C night/day), medium (22/26 °C), and high (26/30 °C) temperature, at either ambient (450 ppm) or elevated (850 ppm) CO2 concentrations. Bakanae disease index (DI), seedling death incidence, fungal DNA quantity, and chlorophyll and carbohydrate contents varied significantly in infected plants as a consequence of changes in both CO2 and temperature. Plant height and dry weight were only influenced by single factors (temperature for height, and temperature or CO2 for dry weight), and not by the CO2 × temperature interaction. Medium and high temperatures (irrespective of the CO2 level) increased the DI significantly (range from 67.5% to 95.8%) compared to low temperatures (range from 45.8% to 47.5%). Under elevated CO2 levels, noticeable differences in the expression of four rice defence‐related genes and fungal DNA quantity were observed between those plants grown at higher temperatures and those at lower temperatures. Overall, combined and single effects of elevated CO2 and high temperatures seem to be favourable for bakanae disease development in the Mediterranean basin.

The process of methanogenesis in paddy fields under different elevated CO2 concentrations

Understanding the process of methanogenesis in paddy fields under the scenarios of future climate change is of great significance for reducing greenhouse gas emissions and regulating the soil carbon cycle. Methyl Coenzyme M Reductase subunit A (mcrA) of methanogens is a rate-limiting enzyme that catalyzes the final step of CH4 production. However, the mechanism of methanogenesis change in the paddy fields under different elevated CO2 concentrations (e[CO2]) is rarely explored in earlier studies. In this research, we explored how the methanogens affect CH4 flux in paddy fields under various (e[CO2]). CH4 flux and CH4 production potential (MPP), and mcrA gene abundance were quantitatively analyzed under C (ambient CO2 concentration), C1 (C + 160 ppm CO2), and C2 (C + 200 ppm CO2) treatments. Additionally, the community composition and structure of methanogens were also compared with Illumina MiSeq sequencing. The results showed that C2 treatment significantly increased CH4 flux and MPP at the tillering stage. E[CO2] had a positive effect on the abundance of methanogens, but the effect was insignificant. We detected four known dominant orders of methanogenesis in this study, such as Methanosarcinales, Methanobacteriales, Methanocellales, and Methanomicrobiales. Although e[CO2] did not significantly change the overall community structure and diversity of methanogens, C2 treatment significantly reduced the relative abundance of two uncultured genera compared to C treatment. A linear regression model of DOC, methanogenic abundance, and MPP can explain 67.2% of the variation of CH4 flux under e[CO2]. Overall, our results demonstrated that CH4 flux in paddy fields under e[CO2] was mainly controlled by soil unstable C substrate and the abundance and activity of methanogens in rhizosphere soil.

ABA and BAP improve the accumulation of carbohydrates and alter carbon allocation in potato plants at elevated CO2.

Elevated CO2 interactions with other factors affects the plant performance. Regarding the differences between cultivars in response to CO2 concentrations, identifying the cultivars that better respond to such conditions would maximize their potential benefits. Increasing the ability of plants to benefit more from elevated CO2 levels alleviates the adverse effects of photoassimilate accumulation on photosynthesis and increases the productivity of plants. Despite its agronomic importance, there is no information about the interactive effects of elevated CO2 concentration and plant growth regulators (PGRs) on potato (Solanum tuberosum L.) plants. Hence, the physiological response and source-sink relationship of potato plants (cvs. Agria and Fontane) to combined application of CO2 levels (400 vs. 800µmolmol-1) and plant growth regulators (PGR) [6-benzylaminopurine (BAP) + Abscisic acid (ABA)] were evaluated under a controlled environment. The results revealed a variation between the potato cultivars in response to a combination of PGRs and CO2 levels. Cultivars were different in leaf chlorophyll content; Agria had higher chlorophyll a, b, and total chlorophyll content by 23, 43, and 23%, respectively, compared with Fontane. The net photosynthetic rate was doubled at the elevated compared with the ambient CO2. In Agria, the ratio of leaf intercellular to ambient air CO2 concentrations [Ci:Ca] was declined in elevated-CO2-grown plants, which indicated the stomata would become more conservative at higher CO2 levels. On the other hand, the increased Ci:Ca in Fontane showed a stomatal acclimation to higher CO2 concentration. The higher leaf dark respiration of the elevated CO2-grown and BAP + ABA-treated plants was associated with a higher leaf soluble carbohydrates and starch content. Elevated CO2 and BAP + ABA shifted the dry matter partitioning to the belowground more than the above-media organs. The lower leaf soluble carbohydrate content and greater tuber yield in Fontane might indicate a more efficient photoassimilate translocation than Agria. The results highlighted positive synergic effects of the combined BAP + ABA and elevated CO2 on tuber yield and productivity of the potato plants.

Extending a land-surface model with &amp;lt;i&amp;gt;Sphagnum&amp;lt;/i&amp;gt; moss to simulate responses of a northern temperate bog to whole ecosystem warming and elevated CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;

Abstract. Mosses need to be incorporated into Earth system models to better simulate peatland functional dynamics under the changing environment. Sphagnum mosses are strong determinants of nutrient, carbon, and water cycling in peatland ecosystems. However, most land-surface models do not include Sphagnum or other mosses as represented plant functional types (PFTs), thereby limiting predictive assessment of peatland responses to environmental change. In this study, we introduce a moss PFT into the land model component (ELM) of the Energy Exascale Earth System Model (E3SM) by developing water content dynamics and nonvascular photosynthetic processes for moss. The model was parameterized and independently evaluated against observations from an ombrotrophic forested bog as part of the Spruce and Peatland Responses Under Changing Environments (SPRUCE) project. The inclusion of a Sphagnum PFT with some Sphagnum-specific processes in ELM allows it to capture the observed seasonal dynamics of Sphagnum gross primary production (GPP) albeit with an underestimate of peak GPP. The model simulated a reasonable annual net primary production (NPP) for moss but with less interannual variation than observed, and it reproduced aboveground biomass for tree PFTs and stem biomass for shrubs. Different species showed highly variable warming responses under both ambient and elevated atmospheric CO2 concentrations, and elevated CO2 altered the warming response direction for the peatland ecosystem. Microtopography is critical: Sphagnum mosses on hummocks and hollows were simulated to show opposite warming responses (NPP decreasing with warming on hummocks but increasing in hollows), and hummock Sphagnum was modeled to have a strong dependence on water table height. The inclusion of this new moss PFT in global ELM simulations may provide a useful foundation for the investigation of northern peatland carbon exchange, enhancing the predictive capacity of carbon dynamics across the regional and global scales.

Biocontainment of Engineered Synechococcus elongatus PCC 7942 for Photosynthetic Production of α-Farnesene from CO2.

Biocontainment systems have been developed to mitigate the concerns regarding biosafety and environmental risk because of the possible escape of genetically modified organisms into the environment following large-scale outdoor cultivation. Here, we present a biocontainment system entailing genetically modified Synechococcus elongatus PCC 7942, also engineered for α-farnesene production using a de-evolutionary strategy. In this approach, the gene cluster encoding the β-carboxysome and the associated carbon concentrating mechanism (CCM) were deleted in the α-farnesene-producing cyanobacteria, resulting in no cell growth and no α-farnesene production at ambient CO2 concentrations (100% air bubbling). However, cell growth and α-farnesene production were detected in the CCM-deficient strains at high CO2 concentrations (5% CO2 [v/v], 10% CO2 [v/v]), albeit at levels lower than those of the parental control. To overcome this limitation, the overexpression of carbonic anhydrase and bicarbonate transporter genes in the CCM-deficient strains restored cell growth and the production level of α-farnesene (5.0 ± 0.6 mg/L) to that of the parental control. The production of α-farnesene in the later strains strictly depended on CO2 concentration in the photobioreactor and did not rely on a chemical induction process. Thus, next generation bio-solar cell factories could be promoted with the suggested biocontainment system.

Interactive Effect of Elevated CO2 and Reduced Summer Precipitation on Photosynthesis is Species-Specific: The Case Study with Soil-Planted Norway Spruce and Sessile Oak in a Mountainous Forest Plot

We investigated how reduced summer precipitation modifies photosynthetic responses of two model tree species—coniferous Norway spruce and broadleaved sessile oak—to changes in atmospheric CO2 concentration. Saplings were grown under mountainous conditions for two growing seasons at ambient (400 μmol CO2 mol–1) and elevated (700 μmol CO2 mol–1) CO2 concentration. Half were not exposed to precipitation during the summer (June–August). After two seasons of cultivation under modified conditions, basic photosynthetic characteristics including light-saturated rate of CO2 assimilation (Amax), stomatal conductance (GSmax), and water use efficiency (WUE) were measured under their growth CO2 concentrations together with in vivo carboxylation rate (VC) and electron transport rate (J) derived from CO2-response curves at saturating light. An increase in Amax under elevated CO2 was observed in oak saplings, whereas it remained unchanged or slightly declined in Norway spruce, indicating a down-regulation of photosynthesis. Such acclimation was associated with an acclimation of both J and VC. Both species had increased WUE under elevated CO2 although, in well-watered oaks, WUE remained unchanged. Significant interactive effects of tree species, CO2 concentration, and water availability on gas-exchange parameters (Amax, GSmax, WUE) were observed, while there was no effect on biochemical (VC, J) and chlorophyll fluorescence parameters. The assimilation capacity (Asat; CO2 assimilation rate at saturating light intensity and CO2 concentration) was substantially reduced in spruce under the combined conditions of water deficiency and elevated CO2, but not in oak. In addition, the stimulatory effect of elevated CO2 on Amax persisted in oak, but completely diminished in water-limited spruce saplings. Our results suggest a strong species-specific response of trees to reduced summer precipitation under future conditions of elevated CO2 and a limited compensatory effect of elevated CO2 on CO2 uptake under water-limited conditions in coniferous spruce.

Plant productivity is a key driver of soil respiration response to climate change in a nutrient-limited soil.

Despite knowledge of the interaction between climate change factors significant uncertainty exists concerning the individual and interactive effects of elevated carbon dioxide (eCO2) and elevated temperature (eT) on the soil microbiome and function. Here we examine the individual and interactive effects of eCO2 and eT on tree growth, soil respiration (Rsoil), biomass, structural and functional composition of microbial community, nitrogen (N) mineralisation and N availability in a whole tree chamber experiment. Eucalyptus globulus plants were grown from seedling to ca. 10 m tall for 15 months in a nutrient-poor sandy soil under ambient and elevated (+ 240 ppm) atmospheric CO2 concentrations combined with ambient or elevated temperatures (+ 3 °C) in a full factorial design. Plant growth was strongly stimulated under eCO2, but eT had little impact on any measured plant property. In contrast, Rsoil was not consistently affected by eCO2 or eT, but correlated strongly with root and leaf biomass. The response of N-mineralisation and nutrient availability to eCO2 and eT varied across time, and available N correlated strongly with plant height. Further, the C:N ratio of the microbial biomass and leaves were both higher under eCeT treatment. However, these functional measures were not significantly linked to either structural or functional diversity of the soil microbiome. Taken together, these results suggest that in this low-nutrient soil, belowground processes are principally driven by aboveground productivity. Our work provides novel insight into mechanisms underlying above- and belowground response to climate change, and the potential to sequester C in a low-nutrient status soil under future climatic conditions may be limited .

Enhancing the productivity of ryegrass at elevated CO2 is dependent on tillering and leaf area development rather than leaf-level photosynthesis.

Whilst a range of strategies have been proposed for enhancing crop productivity, many recent studies have focused primarily on enhancing leaf photosynthesis under current atmospheric CO2 concentrations. Given that the atmospheric CO2 concentration is likely to increase significantly in the foreseeable future, an alternative/complementary strategy might be to exploit any variability in the enhancement of growth/yield and photosynthesis at higher CO2 concentrations. To explore this, we investigated the responses of a diverse range of wild and cultivated ryegrass genotypes, with contrasting geographical origins, to ambient and elevated CO2 concentrations and examined what genetically tractable plant trait(s) might be targeted by plant breeders for future yield enhancements. We found substantial ~7-fold intraspecific variations in biomass productivity among the different genotypes at both CO2 levels, which were related primarily to differences in tillering/leaf area, with only small differences due to leaf photosynthesis. Interestingly, the ranking of genotypes in terms of their response to both CO2 concentrations was similar. However, as expected, estimates of whole-plant photosynthesis were strongly correlated with plant productivity. Our results suggest that greater yield gains under elevated CO2 are likely through the exploitation of genetic differences in tillering and leaf area rather than focusing solely on improving leaf photosynthesis.

Hyperspectral characteristics and inversion model estimation of winter wheat under different elevated CO2 concentrations

ABSTRACT As carbon dioxide (CO2) is required for plants photosynthesis, elevated CO2 (eCO2) concentrations have potential impacts on plant growth and development. The leaf area index (LAI) and soil and plant analysis development (SPAD), which are often used for characterize the chlorophyll content of plants, are important parameters for characterizing plant growth. The purpose of this study was to investigate the effects of different eCO2 concentrations on winter wheat growth and select sensitive spectral parameters to establish LAI and SPAD estimation models. A field experiment in which winter wheat was exposed to different eCO2 concentrations was performed using open-top chambers (OTCs) during the winter wheat growing season from 2017 to 2018. The experimental treatments consisted of exposure to the ambient CO2 concentration (CK), 80 μmol mol–1 CO2 above CK (T 1), and 200 μmol mol–1 CO2 above CK (T 2). The canopy spectral reflectance, LAI, and SPAD were measured during the main growth stages of the winter wheat. The results showed that no significant differences in LAI and SPAD were found under different treatments. Different eCO2 concentrations did not change the reflectance curves, solely affecting the reflectance. Elevated CO2 conditions induced the red edge parameters red shift first and then blue shift. The first derivative reflectance at 755 nm (R’ 755), red edge position (λ Red), ratio of the red edge area to the blue edge area (SDRed/SDBlue), and normalized value of the red edge area and blue edge area ((SDRed – SDBlue)/(SDRed + SDBlue)) were highly correlated with the LAI. The first derivative reflectance at 764 nm (R’ 764), SDRed/SDBlue, ratio of the red edge area to the yellow edge area (SDRed/SDYellow), (SDRed – SDBlue)/(SDRed + SDBlue), and normalized value of the red edge area and yellow edge area ((SDRed – SDYellow)/(SDRed + SDYellow)) were significantly correlated with the SPAD. The optimal regression model for the LAI was y = 0.49x 0.74, simulated by SDRed/SDBlue; that for the SPAD was y = – 0.035x 2–1.96x + 25.83, simulated by SDRed/SDYellow. The coefficient of determination (R 2) values were 0.49 and 0.61, respectively, and the root mean square error (RMSE) values were 0.38 and 1.51, respectively. Overall, our results indicate that inversion models based on SDRed/SDBlue and SDRed/SDYellow can be used to estimate the LAI and SPAD values under eCO2 concentration conditions during the winter wheat growth period.