Effects Of Elevated CO2 Research Articles

Growth responses of light demanding and shade tolerant peat swamp forest saplings to elevated CO2

Aim: To determine the growth responses of two peat swamp forest species, Shorea platycarpa, a shade-tolerant slow-growing species and Macaranga pruinosa, a light-demanding fast-growing species under elevated atmospheric CO2 concentration. Methodology: The saplings of both species were grown in a shade house at ambient (400±50 µmol mol-1) and in an open roof ventilation greenhouse at elevated atmospheric CO2 concentration 800±50 µmol mol-1 for seven months. The temperature in both environments ranged between 25-33°C with 55–60% sunlight transmittance and the saplings were thoroughly watered twice a day. Plants growth measurements were estimated at frequent intervals. Saplings biomass characteristics were examined using destructive methods after seven months of treatment and non-destructive method was used for determination of leaf area. Results: Elevated CO2 enhanced all the growth characteristics in M. pruinosa with a significant increase was observed particularly on both height and diameter relative growth rate and biomass characteristics. The height relative growth rate and leaf area were significantly reduced under elevated CO2 in S. platycarpa but did not affect the shoot or root diameter and biomass significantly. A positive correlation (r =0.77, p>0.05) between stem biomass and basal diameter for plants under elevated CO2 was recorded for M. pruinosa, but not in S. platycarpa. Both species showed negative correlation (S. platycarpa; r = -0.53, M. pruinosa; r = -0.46, p>0.05) between stem growth and stem biomass at elevated CO2. Interpretation: These results unveiled profound effects of elevated CO2 on the growth of light-demanding species M. pruinosa, while shade-tolerant species S. platycarpa was not relatively affected by elevated CO2. This underscored the necessity to analyse different species performance to elevated CO2, thereby improving the ability to predict tropical swamp forest ecosystem responses to rising CO2.

Combined effect of partial root drying and elevated atmospheric CO2 on the physiology and fruit quality of two genotypes of tomato plants with contrasting endogenous ABA levels

Elevated CO2 concentration (e[CO2]) could induce the decline of nutrient concentration in tomato fruit, although it enhances the yield. Alternate partial root drying (PRD) irrigation is a water-saving irrigation strategy, which may enhance tomato fruit quality including both organic and inorganic attributes. Yet, it remains unknown whether PRD could alleviate the negative impact of e[CO2] on the quality attributes of tomato fruit. To investigate that, two genotypes of tomato plants differing in their endogenous abscisic acid level, i.e. Ailsa Craig (wild type, WT) and its correspondent ABA-deficient mutant (flacca), were grown in ambient CO2 (a[CO2], 400 ppm) and e[CO2] (800 ppm) environment, respectively. And three irrigation regimes including full irrigation (FI), deficit irrigation (DI) and PRD were applied during anthesis to fruit ripping stages. The results showed that e[CO2] increased net photosynthetic rate, decreased stomatal conductance and transpiration rate. Tomato yield was more sensitive to irrigation regimes than [CO2], and the reduction of fruit yield caused by PRD was attenuated under e[CO2], especially in flacca. Both e[CO2] and PRD enhanced water use efficiency. The concentration of total soluble solid, total sugar and total acid, as well as fruit firmness were improved in PRD. A negative effect of e[CO2] on fruit mineral nutrition was seen only in flacca, and as expected, such impact was attenuated by the reduced irrigation regimes (DI and PRD). Collectively, it is suggested that the responses of tomato fruit quality to e[CO2] and reduced irrigation regimes are genotypic-dependent, where the endogenous ABA level of the plants plays an important role, and this must be considered in climate management in greenhouse tomato cultivation.

Growth and Photosynthetic Responses of Seedlings of Japanese White Birch, a Fast-Growing Pioneer Species, to Free-Air Elevated O3 and CO2

Plant growth is not solely determined by the net photosynthetic rate (A), but also influenced by the amount of leaves as a photosynthetic apparatus. To evaluate growth responses to CO2 and O3, we investigated the effects of elevated CO2 (550–560 µmol mol−1) and O3 (52 nmol mol−1; 1.7 × ambient O3) on photosynthesis and biomass allocation in seedlings of Japanese white birch (Betula platyphylla var. japonica) grown in a free-air CO2 and O3 exposure system without any limitation of root growth. Total biomass was enhanced by elevated CO2 but decreased by elevated O3. The ratio of root to shoot (R:S ratio) showed no difference among the treatment combinations, suggesting that neither elevated CO2 nor elevated O3 affected biomass allocation in the leaf. Accordingly, photosynthetic responses to CO2 and O3 might be more important for the growth response of Japanese white birch. Based on A measured under respective growth CO2 conditions, light-saturated A at a light intensity of 1500 µmol m−2 s−1 (A1500) in young leaves (ca. 30 days old) exhibited no enhancement by elevated CO2 in August, suggesting photosynthetic acclimation to elevated CO2. However, lower A1500 was observed in old leaves (ca. 60 days old) of plants grown under elevated O3 (regulated to be twice ambient O3). Conversely, light-limited A measured under a light intensity of 200 µmol m−2 s−1 (A200) was significantly enhanced by elevated CO2 in young leaves, but suppressed by elevated O3 in old leaves. Decreases in total biomass under elevated O3 might be attributed to accelerated leaf senescence by O3, indicated by the reduced A1500 and A200 in old leaves. Increases in total biomass under elevated CO2 might be attributed to enhanced A under high light intensities, which possibly occurred before the photosynthetic acclimation observed in August, and/or enhanced A under limiting light intensities.

Aggregate fractions shaped molecular composition change of soil organic matter in a rice paddy under elevated CO2 and air warming

To understand how climate change impacts soil fertility and ecosystem functioning, it is necessary to explore how different pools of soil organic matter (SOM) at aggregate scale are functionally affected in their molecular composition. Here, we collected rhizospheric soil at rice harvest from a paddy field in which a simulated climate change experiment was conducted for 6 years, including CO2 enrichment up to 500 μmol mol−1 (CE), air warming by 2 °C (WA), combination of CO2 enrichment and air warming (CW), and the ambient environment as control. The soil samples were separated in three aggregate fractions (macroaggregates, 2000-250 μm; microaggregates, 250-53 μm; clay & silt, <53 μm) by wet sieving procedure, their molecular composition was detected by off-line pyrolysis gas chromatography mass spectrometry (GC/MS), and the analysis of microbial communities was conducted by phospholipid fatty acids (PLFAs). The mass proportion of macroaggregates increased by 32%, 55%, and 109%, while that of microaggregates decreased by 30%, 14% and 54%, compared to control under CE, WA, and CW treatments, respectively. The mass proportion of macroaggregates was significantly positively correlated with root biomass, while it was significantly negatively correlated in microaggregates, which suggested that the formation of macroaggregates was derived from microaggregates due to root entanglement, and/or mucilage. The molecular composition of SOM depleted in phenolic compounds (phenols and phenolic compounds) while accumulated in lipids (alcohols, alkanes/alkenes/alkynes and fatty acids) with decreasing aggregate size. The increased yields of lipids and phenolic compounds in macro-and microaggregates under CE treatment were likely related to the enhanced root litter, whereas they were reduced under WA treatment due to increase of fungal dominance. A lesser increment of those compounds was noticed under CW treatment and it was attributed to the antagonistic effect, in which the increment effect of CO2 elevation can be counteracted by warming. The molecular composition hardly changed in clay & silt fraction under all climatic treatments, thus suggesting that the effect of elevated CO2 and/or warming on SOM molecular composition faded with decreasing aggregate size. Shared by control and a climatic treatment, changes of common molecules in the whole soils depended on their distribution among aggregates. Moreover, the differences in common molecules distribution induced by climatic treatments were significantly correlated to those in mass proportion of aggregates. Considering that common molecules dominated the molecular abundance across all aggregate fractions, our findings indicate that the alteration of SOM molecular composition in the whole soils under climatic treatments appears to be modified by the variation in mass proportion of aggregates.

Effects of Elevated CO2 and Heat on Wheat Grain Quality.

Wheat is one of the most important staple foods in temperate regions and is in increasing demand in urbanizing and industrializing countries such as China. Enhancing yield potential to meet the population explosion around the world and maintaining grain quality in wheat plants under climate change are crucial for food security and human nutrition. Global warming resulting from greenhouse effect has led to more frequent occurrence of extreme climatic events. Elevated atmospheric CO2 concentration (eCO2) along with rising temperature has a huge impact on ecosystems, agriculture and human health. There are numerous studies investigating the eCO2 and heatwaves effects on wheat growth and productivity, and the mechanisms behind. This review outlines the state-of-the-art knowledge regarding the effects of eCO2 and heat stress, individually and combined, on grain yield and grain quality in wheat crop. Strategies to enhance the resilience of wheat to future warmer and CO2-enriched environment are discussed.

Divergent terrestrial responses of soil N2O emissions to different levels of elevated CO2and temperature

Understanding the responses of soil nitrous oxide (N2O) emissions from terrestrial ecosystems to future CO2enrichment and warming is critical for the development of mitigation and adaptation policies. The effects of continuous increase in elevated CO2(EC) and elevated temperature (ET) on N2O emissions are not fully known. We synthesized 209 measurements from 70 published studies and carried out a meta‐analysis to examine individual and interactive effects of EC and ET on N2O emissions from grasslands, croplands and forests. On average, a significant increase of 23% in N2O emissions was observed under EC across all case studies. EC did not affect N2O emissions from grasslands or forests, but significantly increased N2O emissions in croplands by 38%. The extent of ET effects on N2O emissions was nonsignificant and there was no significant difference in N2O emission responses among these three terrestrial systems. ET only promoted N2O emissions in forest by about 32% when ET was less than 2°C. The interactive effect of EC and ET on N2O emissions was significantly synergistic, showing a greater increase than the sum of the effects caused by EC and ET alone. Our findings indicated that the combination of EC and ET substantially promoted soil N2O and highlighted the urgent need to explore its mechanisms to better understand N2O responses under future climate change.

Interactive Effect of Elevated CO2 and Moisture Stress on Anatomical Configuration in Brassica Species

Free-Air CO2 Enrichment (FACE) was developed as a means to study the crops response to elevated level of CO2 under the fully open-air field conditions. In this study, results of FACE experiments are summarized by disusing the root and shoot anatomy. Result indicated that elevated Co2 significantly altered the root and shoot xylem and phloem characters such as both proto and meta xylem and phloem; vessels, character of root and shoots which are vital for the transpiration regulation, along with leaves photosynthesis as a whole. The coexistence of two ontogenetically different phloem sieve element in Brassica plant under elevated CO2 might have possibility of two different transport functions at the same time. One may be involved in supplying for the structural development (leaf size, stem girth and root volume) and other may cater the need of increased new sinks. Though these parameters were found to decrease under moisture stress condition but these impacts of stress were reduced at higher level of atmospheric CO2.

Climate Change Impacts on the Future of Forests in Great Britain

Forests provide important ecosystem services but are being affected by climate change, not only changes in temperature and precipitation but potentially also directly through the plant-physiological effects of increases in atmospheric CO2. We applied a tree-species-based dynamic model (LPJ-GUESS) at a high 5-km spatial resolution to project climate and CO2 impacts on tree species and thus forests in Great Britain. Climatic inputs consisted of a novel large climate scenario ensemble derived from a regional climate model (RCM) under an RCP 8.5 emission scenario. The climate change impacts were assessed using leaf area index (LAI) and net primary productivity (NPP) for the 2030s and the 2080s compared to baseline (1975–2004). The potential CO2 effects, which are highly uncertain, were examined using a constant CO2 level scenario for comparison. Also, a climate vulnerability index was developed to assess the potential drought impact on modeled tree species. In spite of substantial future reductions in rainfall, the mean projected LAI and NPP generally showed an increase over Britain, with a larger increment in Scotland, northwest England, and west Wales. The CO2 increase led to higher projected LAI and NPP, especially in northern Britain, but with little effect on overall geographical patterns. However, without accounting for plant-physiological effects of elevated CO2, NPP in Southern and Central Britain and easternmost parts of Wales showed a decrease relative to 2011, implying less ecosystem service provisioning, e.g., in terms of timber yields and carbon storage. The projected change of LAI and NPP varied from 5 to 100% of the mean change, due to the uncertainty arising from natural weather-induced variability, with Southeast England being most sensitive to this. It was also the most susceptible to climate change and drought, with reduced suitability for broad-leaved trees such as beech, small-leaved lime, and hornbeam. These could lead to important changes in woodland composition across Great Britain.

NODULE CHARACTERISTICS OF THREE-YEAR-OLD CARAGANA MICROPHYLLA AND THEIR RESPONSES TO ENVIRONMENTAL CHANGES IN AN INNER MONGOLIA GRASSLAND

Aims Caragana microphylla widely spreads in Inner Mongolia grasslands as a dominant shrubby legume. Its nodule growth has been poorly addressed. Our objective is to examine nodule characteristics and their responses to different environmental factors to provide insights into their nitro-gen fixing and nitrogen cycling processes under future changing environments. Methods We conducted a field experiment in 2008 using open-top chambers at the Inner Mongolia Grassland Ecosystem Research Station of Chinese Academy of Sciences. We examined the number,weight and length of nodules of three-year-old C. microphylla individuals and their responses to nitro-gen addition,drought,water addition and elevated atmospheric CO2 concentration. Important findings Nodules were mainly distributed in lateral roots,and most had buff or brown color. Nodule shapes were diverse,being pyriform,globular,claviform,fusiform,and Y shaped. Root growth and nodule growth were significantly inhibited under the nitrogen addition treatment,resulting in roots being whitened and most nodules dead and black-brown. Drought depressed root nodulation,with mean length of nodules decreased significantly by 50.4% compared with that under normal water supply. Water addition stimulated root growth and nodule growth. Roots nodulated best under the com-bined treatment of water addition,elevated CO2 and non-nitrogen addition,with maximum mean length and weight of individual nodules and the maximum nodule weight per plant. Nodules in fibers relatively increased with increasing water supply. Nodule growth did not significantly respond to elevated CO2. Nodule number is more sensitive to environmental changes than nodule size,there are significant nitro-gen × water interactions on nodule number and weight per plant and the effects of three environmental factors on nodule growth are different. The negative effect of nitrogen is larger than the positive effects of water and elevated CO2. It is inferred that water is the major factor affecting the infection of rhizobia and the generation of nodules in this semiarid grassland ecosystem.

Interactive Effect of Elevated CO2 and Drought Stress on Leaf Anatomy in Brassica Species

The aim of present study was to understand how the ultrastructure of the leaf mesophyll cells in Brassica leaf can be altered under elevated CO2 by interactive effect of elevated CO2 on leaf anatomy and ultra structure of Brassica species under moisture stress conditions. Results of the experiment revealed that the crop genotypes differ greatly in response to elevated CO2 and moisture stress conditions. Elevated CO2 brought about an increase in cell and chloroplast expansion in Brassica genotypes. Elevated CO2 also increased the thickness of epidermis, size ofmesophyll cells, accumulation of starch and size and number of starch granules per chloroplast in Brassica juncea and Brassica juncea cultivars. These alterations in the ultra structure of cells in plants might help to plant adjustment to changing climate in the future.

Effects of elevated CO2 on resistant and susceptible rice cultivar and its primary host, brown planthopper (BPH), Nilaparvata lugens (St\xe5l)

The elevated CO2 (eCO2) has positive response on plant growth and negative response on insect pests. As a contemplation, the feeding pattern of the brown plant hopper, Nilaparvata lugens Stål on susceptible and resistant rice cultivars and their growth rates exposed to eCO2 conditions were analyzed. The eCO2 treatment showed significant differences in percentage of emergence and rice biomass that were consistent across the rice cultivars, when compared to the ambient conditions. Similarly, increase in carbon and decrese in nitrogen ratio of leaves and alterations in defensive peroxidase enzyme levels were observed, but was non-linear among the cultivars tested. Lower survivorship and nutritional indices of N. lugens were observed in conditions of eCO2 levels over ambient conditions. Results were nonlinear in manner. We conclude that the plant carbon accumulation increased due to eCO2, causing physiological changes that decreased nitrogen content. Similarly, eCO2 increased insect feeding, and did alter other variables such as their biology or reproduction.

Elevated CO2‐mediated plant VOCs change aggravates invasive thrips occurrence by altering their host‐selection behaviour

AbstractGlobally rising atmosphere CO2 has been predicted to affect the emission of plant volatile organic compounds (VOCs) and the interaction with insect herbivores. CO2‐mediated plant VOCs change might contribute to develop effective management strategies for insect pests by using VOCs related biological control methods. In this study, we analysed the effect of elevated CO2 on the host‐selection behaviour of western flower thrips (Frankliniella occidentalis) and studied how they were affected by the release of VOCs from kidney bean plants (Phaseolus vulgaris). A four‐chamber olfactometer was used to quantify the host‐selection of F. occidentalis for P. vulgaris. Elevated CO2 increased F. occidentalis' selection for P. vulgaris wounded by mechanical damage (MD) and thrips infestation (TI) that might via regulating the gene expression of CSP1, CSP1‐q, OBP1 and OBP1‐q in F. occidentalis. Besides, we cultivated kidney beans at ambient CO2 (400 ppm) and elevated CO2 (800 ppm), and quantified the emission of plant VOCs by using GC‐MS. Thirty VOCs belonging to ten chemical groups were identified from P. vulgaris, including aromatic hydrocarbons, ethers, alkanes, cycloalkanes, alcohols, alkenes, aromatic derivatives, phenols, ketones and esters. Furthermore, six VOCs from P. vulgaris were significantly affected by CO2 level, wounding way and the interaction between them, including ethyl benzene, 1,3‐dimethyl benzene, 1,3‐dimethyl‐4‐ethyl benzene, (E,E,E,E)‐squalene, 2,6‐ditert‐butyl‐4‐methyl phenol and dioctyl phthalate. Our study indicates that elevated CO2 might increase the host‐selection of F. occidentalis for wounded P. vulgaris due to the changed plant VOCs.

Amaranthus retroflexus L. (Redroot Pigweed): Effects of Elevated CO2 and Soil Moisture on Growth and Biomass and the Effect of Radiant Heat on Seed Germination

Amaranthus retroflexus L. (Amaranthaceae), Redroot pigweed, is native to North America, but has become a weed of agriculture worldwide. Previous research into competition with food crops found it significantly reduces yields. Additionally, taxonomy, biomass allocation, physiological responses to light intensity, water stress, elevated CO2, and herbicide resistance have been investigated. To extend other research findings, we investigated growth and biomass yield in response to (i) soil moisture stress, and (ii) drought and elevated CO2. Additionally, we investigated seed germination rates following exposure to three elevated temperatures for two different time periods. Overall, moisture stress reduced plant height, stem diameter, and number of leaves. Elevated CO2 (700 ppm) appeared to reduce negative impacts of drought on biomass productivity. Heating seeds at 120 °C and above for either 180 or 300 s significantly reduced germination rate. These results inform an understanding of potential responses of A. retroflexus to future climate change and will be used to predict future occurrence of this weed. The finding that exposing seeds to high temperatures retards germination suggests fire could be used to prevent seed germination from soil seed banks, particularly in no-till situations, and therefore may be used to address infestations or prevent further spread of this weed.

Elevated CO2 modulates carbon assimilation and leaf water use efficiency of Nicotiana tabacum L. (tobacco) under patchy soil nutrient deficiency

Effect of elevated atmospheric CO2 (e[CO2]) on plant growth and physiology depends on soil nutrient availability. The objective of this study was to evaluate the effect of e[CO2] impact on tobacco (Nicotiana tabacum L.) growth and physiology, and to test if patchy root-zone nutrient supply could modulate the e[CO2] effects on tobacco crops. In this study, we investigated how partial root-zone nutrient deficiency (PRN) affect carbon assimilation, biomass accumulation and partitioning, and water use efficiency (WUE) of tobacco grown under e[CO2]. A split-pot experiment was conducted with tobacco plants grown in a sandy loam soil with two fertilizer levels [0 and 113-68-258 (N-P2O5-K2O) mg kg−1 soil] and three fertilization regimes (PRN, full root-zone fertilization – CRN, and no fertilization – CK) and two CO2 environments (400 μmol L−1 and 800 μmol L−1). Compared with ambient [CO2] (a[CO2]), e[CO2] increased the leaf photosynthetic rate (Pn) and reduced the transpiration rate (Tr) and stomatal conductance (gs), resulting in an increased WUE. Besides, e[CO2] enhanced tobacco leaf biomass and partitioning towards roots compared with a[CO2]. Improved growth under e[CO2] compared with a[CO2] was more pronounced under PRN than under CRN. Root hydraulic conductance was significantly greater under PRN as compared with other fertilization regimes particularly under e[CO2]. Root exudates of glucose and sucrose were significantly improved by the interaction of [CO2] and patchy fertilization regime, especially after 7 days exposure to different CO2 growth conditions. The soil pH was unaffected by CO2 growth environment but was significantly lowered in the fertilized side under PRN as compared to other fertilization regimes. Collectively, our results offer novel information about the modulation of e[CO2] on the physiology and growth of tobacco plants under patchy soil nutrient deficiency.

The effects of elevated-CO2 and UVR on photosynthetic performance and nitrate reductase activity of Ulva flexuosa Wulfen 1803

After the industrial revolution, increasing anthropogenic CO 2 emission causes a number of changes in seawater. These changes are known as ocean acidification and affect the seaweeds in various ways. Therefore, this study is aimed to determine the ecological succession of Ulva flexuosa Wulfen 1803 in future predicted CO 2 -induced low pH conditions alone and in combination with naturally relevant ultraviolet radiation (UVR). For this purpose, acidification experiments with and without UVR were conducted on U. flexuosa from the Mediterranean coast, and important physiological features of algae was investigated. In this study, the Fv/Fm ratios of U. flexuosa ranged from 0.718±0.01 to 0.754±0.009. While rETRmax values of samples exposed to elevated-CO 2 were measured between 112.13 – 151.93 µmol e - m -2 s -1 , it was determined between 111.7 – 158.4 µmol e - m -2 s -1 in samples exposed to ambient sea water. According to our results, increased CO 2 concentration in seawater did not improve the photosynthetic efficiency of U. flexuosa . However, when the specimens were exposed to elevated-CO 2 , nitrate reductase activity of U. flexuosa was declined drastically. According to the results, it is suggested that the elevated CO 2 may regulate the nitrogen preference of U. flexuosa . Besides, the data also show that U. flexuosa was not sensitive to UVR.

CO2 fertilization of Sphagnum peat mosses is modulated by water table level and other environmental factors.

Sphagnum mosses account for most accumulated dead organic matter in peatlands. Therefore, understanding their responses to increasing atmospheric CO2 is needed for estimating peatland C balances under climate change. A key process is photorespiration: a major determinant of net photosynthetic C assimilation that depends on the CO2 to O2 ratio. We used climate chambers to investigate photorespiratory responses of Sphagnum fuscum hummocks to recent increases in atmospheric CO2 (from 280 to 400 ppm) under different water table, temperature, and light intensity levels. We tested the photorespiratory variability using a novel method based on deuterium isotopomers (D6S /D6R ratio) of photosynthetic glucose. The effect of elevated CO2 on photorespiration was highly dependent on water table. At low water table (-20 cm), elevated CO2 suppressed photorespiration relative to C assimilation, thus substantially increasing the net primary production potential. In contrast, a high water table (~0cm) favored photorespiration and abolished this CO2 effect. The response was further tested for Sphagnum majus lawns at typical water table levels (~0 and -7cm), revealing no effect of CO2 under those conditions. Our results indicate that hummocks, which typically experience low water table levels, benefit from the 20th century's increase in atmospheric CO2 .

Impacts of Surface Ozone Pollution on Global Crop Yields: Comparing Different Ozone Exposure Metrics and Incorporating Co-effects of CO2

Surface ozone (O3) pollution poses significant threats to crop production and food security worldwide, but an assessment of present-day and future crop yield losses due to exposure to O3 still abides with great uncertainties, mostly due: (1) to the large spatiotemporal variability and uncertain future projections of O3 concentration itself; (2) different methodological approaches to quantify O3 exposure and impacts; (3) difficulty in accounting for co-varying factors such as CO2 concentration and climatic conditions. In this paper, we explore these issues using a common framework: a consistent set of simulated present-day O3 fields from one chemical transport model, coupled with a terrestrial ecosystem-crop model to derive various O3 exposure metrics and impacts on relative crop yields worldwide, and examine the potential effects of elevated CO2 on O3-induced crop yield losses. Throughout, we review and explain the differences in formulation and parameterization in the various approaches, including the concentration-based metrics, flux-based metrics, and mechanistic biophysical crop modeling. We find that while the spatial pattern of yield losses for a given crop is generally consistent across metrics, the magnitudes can differ substantially. Pooling the concentration-based and flux-based metrics together, we estimate the present-day globally aggregated yield losses to be: 3.6 ± 1.1% for maize, 2.6 ± 0.8% for rice, 6.7 ± 4.1% for soybean, and 7.2 ± 7.3% for wheat; these estimates are generally consistent with previous studies but on the lower end of the uncertainty range covered. We attribute the large combined uncertainty mostly to the differences among methodological approaches, and secondarily to differences in O3 and meteorological inputs. Based on a biophysical crop model that mechanistically simulates photosynthetic and yield responses of crops to stomatal O3 uptake, we further estimate that increasing CO2 concentration from 390 to 600 ppm reduces the globally aggregated O3-induced yield loss by 21–52% for maize and by 27–38% for soybean, reflecting a CO2-induced reduction in stomatal conductance that in turn alleviates stomatal O3 uptake and thus crop damage. Rising CO2 may therefore render the currently used exposure-yield relationships less applicable in a future atmosphere, and we suggest approaches to address such issues.

Elevated CO2 shifts soil microbial communities from K‐ to r‐strategists

AbstractAimsSoil microbes are key to myriad processes in terrestrial ecosystems. Elevated CO2 represents a dominant driver of global climate change; however, it remains unclear to what extent elevated CO2 impacts soil microbial communities at ecosystem and global scales. Here, we sought to address the following questions: (a) Do the compositions of microbial communities shift from K‐ to r‐strategists under elevated CO2? (b) What is the extent of the compositional shifts of microbial communities affected by elevated CO2 concentrations, experimental duration, ecosystem types and/or background climates? (c) Are the responses of microbial communities to elevated CO2 associated with changes in soil pH and carbon and nitrogen availabilities?LocationGlobal.Time period1998–2020.Major taxa studiedSoil microbes.MethodsWe performed a global meta‐analysis of 965 observations from 122 studies, which tested the effects of elevated CO2 on microbial communities. The data covered broad variations in ecosystems, climate, CO2 concentrations, experimental duration, and soil factors.ResultsWe revealed that elevated CO2 decreased the K‐ to r‐strategist ratios with decreasing fungi : bacteria, Gram+ : Gram– bacteria, and Acidobacteria : Proteobacteria ratios, and increased bacterial biomass, microbial biomass carbon, Gram– bacteria, and Acidobacteria abundance. Moreover, the shifts from K‐ to r‐strategists were more pronounced under higher CO2 concentrations and longer experimental durations. The responses of microbial attributes to elevated CO2 did not differ significantly among croplands, forests and grasslands. Furthermore, the response of microbial biomass to elevated CO2 was negatively correlated with the response of soil pH, while those of bacterial biomass and fungi : bacteria ratios were positively correlated with those of soil organic carbon and soil carbon : nitrogen ratios, respectively.Main conclusionsOur results suggest that elevated CO2 shifts soil microbial communities from K‐ to r‐strategists, and provide supportive evidence for understanding responses of soil microbial processes to elevated CO2.

Effects of Elevated CO2 on Photosynthetic Accumulation, Sucrose Metabolism-Related Enzymes, and Genes Identification in Goji Berry (Lycium barbarum L.).

Goji berry (Lycium barbarum L.) exposure to elevated CO2 (eCO2) for long periods reduces their sugar and secondary metabolite contents. However, sugar accumulation in fruit depends on photosynthesis and photoassimilate partitioning. This study aimed to explore photosynthesis, sugar content, and sucrose metabolism-related enzyme activities in goji berry leaves and fruits under ambient and eCO2 levels, and identify the genes encoding L. barbarum acid invertase (LBAI), L. barbarum sucrose synthase (LBSS), L. barbarum sucrose phosphate synthase (LBSPS), and L. barbarum neutral invertase (LBNI), based on transcriptome profiling. Further, the characterization of four identified genes was analyzed including subcellular localization and expression patterns. In plants grown under eCO2 for 90 or 120 days, the expression of the above-mentioned genes changed significantly as the photosynthetic rate increased. In addition, leaf and fruit sugar contents decreased, and the activities of four sucrose metabolism-related enzymes increased in leaves, while acid and neutral invertase increased in fruits. Protein sequence analysis demonstrated that LBAI and LBNI contain a conservative structure domain belonging to the glycosyl hydrolases (Glyco_hydro) family, and both LBSS and LBSPS belonging to the sucrose synthase (Sucrose_synth) and glycosyltransferase (Glycos_transf) family. Subcellular localization analysis showed that LBAI, LBNI, and LBSS were all located in the nucleus, plasma membrane, and cytoplasm, while LBSPS was located in the plasma membrane. The expressions of LBAI, LBSPS, and LBNI were high in the stems, whereas LBSS was predominantly expressed in the fruits. Our findings provide fundamental data on photosynthesis and sugar accumulation trends in goji berries under eCO2 exposure.

Phytochelatins formation kinetics and Cd-induced growth inhibition in Lolium perenne L. at elevated CO2 level under Cd stress.

Elevated CO2 levels may alleviate toxicities induced by environmental stresses in plants, such as heavy metals. To assess this possibility, seedlings of Lolium perenne L. were exposed to different Cd stress and CO2 levels during hydroponic culture. The kinetics of growth, Cd accumulation, and thiol formation were investigated. Elevated CO2 levels increased the growth rate from 30 to 75%, and decreased the Cd accumulation rate from 36 to 42%, leading to a decrease of Cd content in root and shoot. However, an increase in Cd transport from root to shoot was observed at elevated CO2 under Cd stress. The production of phytochelatins (PCs) occurred earlier at elevated CO2 level than at ambient CO2 level after exposure to Cd stress. The mean SH/Cd ratio was relatively higher at elevated CO2 level, but elevated CO2 level significantly decreased thiol contents. The reduction of Cd contents, earlier production of PCs, and relatively higher SH/Cd ratio at the elevated CO2 level alleviated Cd toxicity in root and shoot to some extent, causing significant yield increase of L. perenne after exposure to Cd stress. This study could provide an important data support and theoretical basis in understanding the effects of elevated CO2 on plant growth, heavy metal accumulation, and thiol formation.