Μmol Mol Research Articles

High throughput procedure utilising chlorophyll fluorescence imaging to phenotype dynamic photosynthesis and photoprotection in leaves under controlled gaseous conditions

BackgroundAs yields of major crops such as wheat (T. aestivum) have begun to plateau in recent years, there is growing pressure to efficiently phenotype large populations for traits associated with genetic advancement in yield. Photosynthesis encompasses a range of steady state and dynamic traits that are key targets for raising Radiation Use Efficiency (RUE), biomass production and grain yield in crops. Traditional methodologies to assess the full range of responses of photosynthesis, such a leaf gas exchange, are slow and limited to one leaf (or part of a leaf) per instrument. Due to constraints imposed by time, equipment and plant size, photosynthetic data is often collected at one or two phenological stages and in response to limited environmental conditions.ResultsHere we describe a high throughput procedure utilising chlorophyll fluorescence imaging to phenotype dynamic photosynthesis and photoprotection in excised leaves under controlled gaseous conditions. When measured throughout the day, no significant differences (P > 0.081) were observed between the responses of excised and intact leaves. Using excised leaves, the response of three cultivars of T. aestivum to a user—defined dynamic lighting regime was examined. Cultivar specific differences were observed for maximum PSII efficiency (Fv′/Fm′—P < 0.01) and PSII operating efficiency (Fq′/Fm′—P = 0.04) under both low and high light. In addition, the rate of induction and relaxation of non-photochemical quenching (NPQ) was also cultivar specific. A specialised imaging chamber was designed and built in-house to maintain gaseous conditions around excised leaf sections. The purpose of this is to manipulate electron sinks such as photorespiration. The stability of carbon dioxide (CO2) and oxygen (O2) was monitored inside the chambers and found to be within ± 4.5% and ± 1% of the mean respectively. To test the chamber, T. aestivum ‘Pavon76’ leaf sections were measured under at 20 and 200 mmol mol−1 O2 and ambient [CO2] during a light response curve. The Fv′/Fm′was significantly higher (P < 0.05) under low [O2] for the majority of light intensities while values of NPQ and the proportion of open PSII reaction centers (qP) were significantly lower under > 130 μmol m−2 s−1 photosynthetic photon flux density (PPFD).ConclusionsHere we demonstrate the development of a high-throughput (> 500 samples day−1) method for phenotyping photosynthetic and photo-protective parameters in a dynamic light environment. The technique exploits chlorophyll fluorescence imaging in a specifically designed chamber, enabling controlled gaseous environment around leaf sections. In addition, we have demonstrated that leaf sections do not different from intact plant material even > 3 h after sampling, thus enabling transportation of material of interest from the field to this laboratory based platform. The methodologies described here allow rapid, custom screening of field material for variation in photosynthetic processes.

Transcriptome Reveals the Rice Response to Elevated Free Air CO2 Concentration and TiO2 Nanoparticles.

Increasing CO2 levels are speculated to change the effects of engineered nanomaterials in soil and on plant growth. How plants will respond to a combination of elevated CO2 and nanomaterials stress has rarely been investigated, and the underlying mechanism remains largely unknown. Here, we conducted a field experiment to investigate the rice (Oryza sativa L. cv. IIyou) response to TiO2 nanoparticles (nano-TiO2, 0 and 200 mg kg-1) using a free-air CO2 enrichment system with different CO2 levels (ambient ∼370 μmol mol-1 and elevated ∼570 μmol mol-1). The results showed that elevated CO2 or nano-TiO2 alone did not significantly affect rice chlorophyll content and antioxidant enzyme activities. However, in the presence of nano-TiO2, elevated CO2 significantly enhanced the rice height, shoot biomass, and panicle biomass (by 9.4%, 12.8%, and 15.8%, respectively). Furthermore, the Kyoto Encyclopedia of Genes and Genomes pathway enrichment analysis revealed that genes involved in photosynthesis were up-regulated while most genes associated with secondary metabolite biosynthesis were down-regulated in combination-treated rice. This indicated that elevated CO2 and nano-TiO2 might stimulate rice growth by adjusting resource allocation between photosynthesis and metabolism. This study provides novel insights into rice responses to increasing contamination under climate change.

Influence of elevated CO2 on arbuscular mycorrhizal fungal community elucidated using Illumina MiSeq platform in sub-humid tropical paddy soil

Arbuscular mycorrhizal fungi (AMF) are one of the beneficial soil microbial communities, playing an important role in abiotic and biotic stress management in agricultural crops, including rice. Climate change, particularly elevated CO2 (eCO2) alters the soil microbial community, but the alteration of AMF community has received little attention, partly because of inadequacy in understanding of AMF taxonomy. Therefore, an attempt was made to understand AMF community in paddy soil under long-term exposure (8 years) to eCO2 through sequencing 18S rRNA small subunit SSU based Illumina Miseq technique using the primer pair AML1/AML2. Changes in OTUs belonging to 23 AMF species were identified in the ambient (400 ± 10 μmol mol−1) and eCO2 (550 ± 20 μmol mol−1) conditions, respectively based on reads alignment using MaarjAM VT database. Moreover, principal coordinate (PCO) analysis clustered the related OTUs and suggested that long-term exposure of eCO2 suppressed the OTUs of Glomerales and encouraged the OTUs of Diversisporales. Overall, the present study indicates that long-term exposure of paddy soil to eCO2 (550 ppm) drastically reduced the commonly occuring AMF such as Claroideoglomus and Glomus species in sub-humid tropical condition.

Impacts of elevated CO2 on nitrogen uptake of cucumber plants and nitrogen cycling in a greenhouse soil

It remains unclear whether elevated CO2 would increase N uptake of vegetable and alleviate soil degradation via reducing N residual in greenhouse soils. This study investigated the effect of three CO2 concentrations 400 (ambient CO2), 800 (elevated CO2) and 1200 μmol mol−1 (super-elevated CO2) and two N application rates 0.06 (low N) and 0.24 g N kg−1 (high N) on N uptake of cucumber plants and N cycling in a greenhouse soil in open top chambers. Elevated CO2 increased the biomass and N concentration of fine roots in high N by 24% and 4%, respectively, indicating a greater improvement in N uptake efficiency. The improvement was greater under low N but to a lesser extent under super-elevated CO2. Elevated CO2 altered microbial community as indicated by decreased Shannon diversity, substrate richness and Shannon evenness when averaged N treatments possibly associated with the increased plant N uptake efficiency. Elevated CO2 and super-elevated CO2 tended to decrease gene abundances of soil bacterial amoA, nirS and nosZ in high N with increased plant N uptake and decreased concentrations of NH4+, NO2− and NO3− in soils resulting in less soil N loss. To conclude, moderate CO2 enrichment enhances N uptake efficiency in fine roots of cucumber plants and decreases soil N loss associated with decreased nitrification and denitrification under high N application in a greenhouse soil.

White birch has limited phenotypic plasticity to take advantage of increased photoperiods at higher latitudes north of the seed origin

Global warming induced northward migration will expose trees to longer photoperiod regimes during the growing season. The phenotypic ability of trees to take advantage of the longer photoperiods and elevated atmospheric CO2 concentration ([CO2]) will likely be a critical factor for determining their success and performance at the new locations. We investigated how growth, biomass, and biomass allocations respond to the interactive effects of photoperiod regimes and [CO2] in white birch (Betula papyrifera Marsh.). Seedlings were exposed to ambient (400 μmol mol−1) or elevated concentration (1000 μmol mol−1) [CO2], and four photoperiod regimes corresponding to 48 (seed origin), 52, 55, and 58°N latitude for two growing seasons. Our results show that growth, biomass, and biomass allocation were affected by photoperiod regime but not by [CO2]. Seedling growth and biomass were stimulated by the three photoperiod regimes north of the seed origin. Plants under the photoperiod regime of 52°N were 15% higher in growth and 18% higher in biomass than under the photoperiod regime of the seed origin (48°N). However, increases in photoperiod regimes beyond that of 4° north of the seed origin did not lead to an additional increase in growth and biomass. The differences in biomass components among the three longer photoperiods were statistically insignificant, but the leaf biomass and stem biomass were higher under the longer photoperiods relative to the seed origin. While the differences between two adjacent photoperiods were not always statistically significant during the two growing seasons, biomass allocated to roots showed a general decreasing trend with increases in photoperiod from the seed origin to 58°N latitude. Our results suggest that despite the limited plasticity in growth and biomass displayed in much higher latitudes, white birch will likely benefit from the longer photoperiod regimes during the growing season associated with migration or seed transfer to higher latitudes.

UK greenhouse gas measurements at two new tall towers for aiding emissions verification

Abstract. Under the UK-focused Greenhouse gAs and Uk and Global Emissions (GAUGE) project, two new tall tower greenhouse gas (GHG) observation sites were established in the 2013/2014 Northern Hemispheric winter. These sites, located at existing telecommunications towers, utilized a combination of cavity ring-down spectroscopy (CRDS) and gas chromatography (GC) to measure key GHGs (CO2, CH4, CO, N2O and SF6). Measurements were made at multiple intake heights on each tower. CO2 and CH4 dry mole fractions were calculated from either CRDS measurements of wet air, which were post-corrected with an instrument-specific empirical correction, or samples dried to between 0.05 % H2O and 0.3 % H2O using a Nafion® dryer, with a smaller correction applied for the residual H2O. The impact of these two drying strategies was examined. Drying with a Nafion® dryer was not found to have a significant effect on the observed CH4 mole fraction; however, Nafion® drying did cause a 0.02 µmol mol−1 CO2 bias. This bias was stable for sample CO2 mole fractions between 373 and 514 µmol mol−1 and for sample H2O up to 3.5 %. As the calibration and standard gases are treated in the same manner, the 0.02 µmol mol−1 CO2 bias is mostly calibrated out with the residual error (≪0.01 µmol mol−1 CO2) well below the World Meteorological Organization (WMO) reproducibility requirements. Of more concern was the error associated with the empirical instrument-specific water correction algorithms. These corrections are relatively stable and reproducible for samples with H2O between 0.2 % and 2.5 %, CO2 between 345 and 449 µmol mol−1, and CH4 between 1743 and 2145 nmol mol−1. However, the residual errors in these corrections increase to &gt; 0.05 µmol mol−1 for CO2 and &gt; 1 nmol mol−1 for CH4 (greater than the WMO internal reproducibility guidelines) at higher humidities and for samples with very low (&lt; 0.5 %) water content. These errors also scale with the absolute magnitude of the CO2 and CH4 mole fractions. As such, water corrections calculated in this manner are not suitable for samples with low (&lt; 0.5 %) or high (&gt; 2.5 %) water contents and either alternative correction methods should be used or partial drying or humidification considered prior to sample analysis.

Yield, dry matter distribution and photosynthetic characteristics of rice under elevated CO2 and increased temperature conditions

Carbon dioxide (CO2)-induced stimulation of the leaf net photosynthetic rate (Amax) is projected to further increase with increasing temperature. Although the impact of rising temperature or CO2 on leaf photosynthesis parameters and dry matter (DM) accumulation and distribution has been widely investigated, less research has been conducted to evaluate the combined effects of these climate change factors on rice in field sites. In this study, the effects of the combination of two levels of CO2 (390 μmol mol−1 and 590 μmol mol-1) and two levels of temperature (no increase and increase of ˜1.5 °C) on the Amax, respiration rate (Rd), leaf biochemical parameters, DM accumulation and distribution and yield of rice were tested in a free air CO2-enrichment (FACE) system. Elevated CO2 dramatically increased DM accumulation before heading; however, rising temperature alone or in combination with CO2 concentration enrichment remarkably reduced DM at the heading stage compared to that under ambient conditions. Therefore, rising temperature leads to a decrease in rice yield, regardless of whether it occurs alone or in combination with high CO2 concentration. The negative effect of rising temperature alone or in combination with elevated CO2 was attributed to a reduced leaf area index, as both treatments had minor or positive effects on Amax and Rd. Increases in Amax and Rd under the combination of elevated CO2 and temperature were linked to improvements in the maximum carboxylation rate of Rubisco (Vc,max) and the maximum electron transport rate (Jmax). Furthermore, the increase in both CO2 and temperature significantly increased Amax compared to that under elevated CO2. Alleviation of the decrease in leaf nitrogen and Rubisco content by the increase in both CO2 and temperature compared to that observed with elevated CO2 alone accounted for the increase in Vc,max and Jmax. These results suggest that future climate conditions will be advantageous for leaf photosynthesis but not for the growth and yield of rice.

Biological control under a changing climate: The efficacy of the parthenium weed stem-galling moth under an atmosphere enriched with CO2

Parthenium hysterophorus (Parthenium weed) is a highly invasive species that has become a major weed in Australia and many other parts of the world. The present study reports on the effect of atmospheric CO2 enrichment upon the performance and effectiveness of one of its biological control agents, Epiblema strenuana (stem-galling moth). Parthenium weed plants, when grown under an elevated CO2 concentration (550 µmol mol−1), produced a significantly greater dry biomass (38%), produced more branches (35%) and seeds per plant (37%), than plants grown under an ambient CO2 concentration (380 µmol mol−1). Galls produced by E. strenuana significantly reduced the height (46%) and dry biomass (45%) of parthenium weed under the elevated CO2 concentration. In the presence of E. strenuana, the total number of cypselae produced by plants was 60 or 32% less at ambient or elevated CO2 concentrations, respectively. X-ray revealed that E. strenuana had a significant negative impact upon cypsela fill under elevated CO2 concentration with about 50% not being filled. Gall induction by E. strenuana stimulated lateral branching and this was observed in plants grown both under elevated and ambient CO2 concentrations. Under elevated CO2 and in the presence of E. strenuana, net photosynthesis and water use efficiency were decreased by 25 and 28%, respectively. Despite parthenium weed producing more biomass and seed, this study indicates that the efficacy of E. strenuana as a biological control agent of parthenium weed is likely to be retained in a future climate with an elevated CO2 concentration.

Free-Air CO2 Enrichment (FACE) and Free-Air Temperature Increase (FATI) Effects on Trifolium repens L. in Temperate Himalayas

Changes in phenology, growth, biomass production and photosynthetic parameters in Trifolium repens L. were studied under Free Air CO2 Enrichment (FACE; 550 ± 50 µmol mol−1 [CO2]) and Free Air Temperature Increment FATI for 2 years during 2010–11 and 2011–12 in temperate Himalaya. Plant height, root volume, leaf area and dry biomass of T. repens increased from 8.8 to 33.5% under elevated [CO2] but decreased from 4.6 to 58.1% under elevated temperature compared to ambient environment. Leaf area increased by 24.1 and 29.5% under elevated [CO2], however, elevated temperature reduced leaf area by 78.1 and 38.6% compared to ambient conditions during 2010–11 and 2011–12, respectively. Leaf net photosynthetic rates (PN) and stomatal conductance (gS) measured at 390 ± 10 µmol m−2 s−1 CO2, declined under FACE and FATI environment as compared to control conditions, with greater reduction during year 2011–12 than 2010–11. The values of PN in year 2011–2012 during spring and autumn were lower by 13% and 7% under FACE and 24% and 18% under FATI, respectively, compared to ambient (control) conditions, when measured at 400 µmol m−2 s−1. For year 2012, gS showed a decrease by 26% and 39% under FACE and by 21% under FATI during spring and autumn months, respectively, compared to ambient conditions. All phenological stages were significantly advanced under elevated temperature but showed a delayed response under elevated [CO2] as compared to ambient conditions.

High CO2 favors ionic homeostasis, photoprotection, and lower photorespiration in salt-stressed cashew plants

The aim of this study was to evaluate the effects of elevated CO2 concentration on acclimation mechanisms related to gas exchange, photochemical activity, photorespiration, and oxidative protection in cashew plants exposed to salinity. Thirty-day-old cashew plants were irrigated with nutrient solution without (control) or with supplemental NaCl (100 mM) for 2 weeks in the greenhouse. Afterward, control and salt-stressed plants were transferred to the growth chamber and supplied with atmospheric (380 µmol mol−1) or high CO2 (760 µmol mol−1) concentrations for 15 days. The results show that elevated CO2 alone reduced the CO2 net assimilation rate (PN) without affecting stomatal conductance (gS) and transpiration rate (E), whereas salinity and NaCl + high CO2 reduced the PN associated with a decrease in gS and E. The potential quantum yield of photosystem II (Fv/Fm) was not altered, but a slight reduction in electron transport rate and photochemical quenching (qP) in response to high CO2 alone or combined with NaCl occurred. However, non-photochemical quenching increased due to the effects of high CO2 and NaCl alone and by their combination. High CO2 alleviated the toxic effects of Na+ favoring the K+/Na+ ratio under salinity. High CO2 coupled with salinity decreased glycolate oxidase activity and the contents of hydrogen peroxide (H2O2), NH4+, and glyoxylate. Furthermore, we observed increase in membrane damage associated with increased thiobarbituric acid-reactive substances levels under high CO2. High CO2 also decreased ascorbate peroxidase activity, but did not affect superoxide dismutase activity. In general, our data suggest that high CO2 could induce acclimation processes in plants independent of salinity, revealing a set of responses that are more associated with acclimation than with protective responses.

Metabolic Effects of Elevated CO2 on Wheat Grain Development and Composition

The increase in the atmospheric CO2 concentration is predicted to influence wheat production and grain quality and nutritional properties. In the present study, durum wheat (Triticum durum Desf. cv. Sula) was grown under two different CO2 (400 versus 700 μmol mol-1) concentrations to examine effects on the crop yield and grain quality at different phenological stages (from grain filling to maturity). Exposure to elevated CO2 significantly increased aboveground biomass and grain yield components. Growth at elevated CO2 diminished the elemental N content as well as protein and free amino acids, with a typical decrease in glutamine, which is the most represented amino acid in grain proteins. Such a general decrease in nitrogenous compounds was associated with altered kinetics of protein accumulation, N remobilization, and N partitioning. Our results highlight important modifications of grain metabolism that have implications for its nutritional quality.

Variable effects of 2°C air warming on yield formation under elevated [CO2] in a Chinese double rice cropping system

Elevated atmospheric CO2 concentration ([CO2]) and temperature can strongly affect rice (Oryza sativa L.) production. However, the impact of warming is variable depending on ambient temperature and cropping system. Little is known about the effect of elevated temperature and its interaction with elevated [CO2] in the Chinese double rice cropping system. To study this issue, field experiments were conducted using open-top chambers (OTC) with varying [CO2] (ambient, ambient+60 μmol mol−1) and varying temperature (ambient, ambient+2 °C) for 4 rotations of double rice from 2013 to 2016. Elevated [CO2] significantly increased grain yield in both early rice and late rice. This could be attributed to greater aboveground biomass, higher panicle number (m-2), spikelet number (per panicle) and 1000-grain weight. Elevated temperature decreased yield in early rice (except for 2016) due to decreases in % filled grains and 1000-grain weight. Elevated temperature increased yield in late rice due to increases in aboveground biomass, number of panicles and spikelets, although % filled grains decreased. We found that warming had positive effects on tiller development and dry matter accumulation during the pre-heading period both in early and late rice, which contributed to yield formation. When elevated temperature and [CO2] were combined, yield changed by −1.9–23.7% in early rice compared with ambient condition as warming partly offset the benefits of CO2 enrichment, while yield increased by 14.3–18.8% in late rice due to a synergy between warming and CO2 enrichment. The benefits of CO2 enrichment for fertile spikelets (m-2) and aboveground biomass could reduce or eliminate the negative impacts of warming. However, there were no significant interactions between elevated temperature and [CO2] in most rice seasons. Our findings indicate that warming by 2 °C is not detrimental to yield formation under CO2 enrichment, and suggest that grain yield may not decrease under future climate change in the Chinese double rice cropping system.

Long-term response of a bahiagrass pasture to elevated CO2 and soil fertility management

Pastures represent a significant portion of the rural landscape in the southeastern US, yet remain understudied agro-ecosystems in terms of the effects of rising atmospheric CO2 concentration. Therefore, in 2005 we initiated a long-term (10 yr) study of bahiagrass (Paspalum notatum Flüggé) response to elevated CO2 using open top field chambers on a Blanton loamy sand (loamy siliceous, thermic, Grossarenic Paleudults). Plants were exposed to ambient or elevated (ambient + 200 μmol mol−1) CO2. After a one-year establishment period, a management (M) treatment was applied where half of all plots received N [(NH4)2SO4] at 90 kg ha−1 three times yearly plus P, K, and lime as recommended by soil testing; the remaining plots received no fertilization. These two treatments represent managed and unmanaged pastures, both of which are common in the Southeast. Prior to M treatment initiation (establishment phase) biomass production was unaffected by CO2 treatment. Harvests after M treatment initiation (Spring 2006) showed strong effects of fertilizer addition on cumulative forage biomass production (˜231.8% increase); the main effect of CO2 was also significant (˜13.8% increase with elevated CO2). Significant M x CO2 interactions showed that CO2 had no impact on bahiagrass production with no fertilizer added (as observed in establishment year); however, forage production was increased (˜15.3%) under elevated CO2 with fertilizer addition. These findings highlight the importance of soil fertility management to enhance pasture productivity under rising atmospheric CO2 levels.

Yield responses to elevated CO2 concentration among Japanese rice cultivars released since 1882

ABSTRACTAtmospheric CO2 concentrations ([CO2]) have increased by more than 100 μmol mol−1 over the last century and are projected to rise further. Breeding cultivars with a greater response to elevated [CO2] (E-[CO2]) can be an effective adaptation to global climate change. We wondered whether E-[CO2]-responsive cultivars have been unintentionally selected through empirical breeding as [CO2] has increased. If so, modern cultivars may respond better to E-[CO2] than old ones. We conducted free-air CO2 enrichment (FACE) experiments in 2 years to examine whether rice cultivars bred in different eras differ in response to E-[CO2] and to determine any associated traits. We tested five Japanese cultivars: Aikoku (released in 1882), Norin 8 (1934), Koshihikari (1956), Akihikari (1976) and Akidawara (2009). The yields of Aikoku and Norin 8 increased by 19.3% and 30.3%, respectively, under E-[CO2], while those of Koshihikari and Akihikari increased by 15.9% and 3.4%, respectively. However, that of Akidawara, the newest cultivar, also increased by 19.0%. Norin 8’s strong response to E-[CO2] was associated with increases in both spikelet density and percentage of ripened grains, both of which were closely related to nitrogen uptake. These results suggest that breeding has not necessarily improved cultivars’ response to E-[CO2], and that selection for traits such as sink capacity and nitrogen uptake can be effective to improve rice productivity under E-[CO2].

An FTIR method for accurate CO2 mole fraction measurements with correction for differences in isotopic composition of gases

The precision of optically based techniques for long term CO2 monitoring in the atmosphere is approaching the ±0.02 µmol mol−1 level, however biases of potentially up to fifteen times greater than this can arise due to differences in isotopic composition of sample and calibration gases used. We have developed and describe a Fourier transform infrared spectroscopy (FTIR) method for CO2 mole fraction measurements, using an instrument configured with a liquid N2-cooled mid-infrared indium antimonide (InSb) detector and a 10.01 m multipass Whitetype gas cell (0.75 l) and fitting of the 12C16O2 isotopologue absorption in the wavenumber region (3500–3800) cm−1 where the measurement bias resulting from isotopic variation between sample and calibration gases can be corrected for. The method was completed with a comprehensive uncertainty budget from which considerations on the importance of spectroscopic specific biases could be deduced. The method was validated using 29 standards produced by 15 National Metrology Institutes/Designated Institutes, including the Central and a Regional Calibration Laboratory (McClenny et al 2002 J. Air Waste Manag. Assoc. 52 542–62) from the World Meteorological Organization (2011 WMO/TD-No. 1560, Ed.: Hohenpeissenberg Metrological Observatory), with δ13C values in CO2 ranging from −0.4‰ to −67‰ versus VPDB. The standards were all produced with CO2 mole fractions typical of background atmosphere calibration gases (either 380 µmol mol−1 or 480 µmol mol−1), and reference values for each of them were established during a comparison performed with a GC-FID analyzer, insensitive to their isotopic composition. Measurements have confirmed that a Δδ13C of 1‰ between sample and calibration gases can bias the CO2 mole fraction measurements made by FTIR by 4 nmol mol−1 and a Δδ18O of 1‰ by 2 nmol mol−1. These biases can be corrected with the method described here, allowing FTIR based measurements of the CO2 mole fraction with standard uncertainties reaching 0.05 µmol mol−1 to be achieved, even if sample and calibration gases isotopic ratios differ. These findings have significant implications for the use of CO2 calibration mixtures in particular for the atmospheric community, when high accuracy measurements are required.

Genotypic response of wheat under semi-arid conditions showed no specific responsive traits when grown under elevated CO2

ABSTRACTAtmospheric carbon dioxide (CO2) is predicted to reach 550 µmol mol−1 by 2050, increasing from the current ~410 µmol mol−1 concentration, and this will have an impact on wheat production and grain quality. Genetic differences in response to future CO2 levels, which might be exploited for higher yield and sustainable grain quality, were investigated. Twelve diverse genotypes (11 wheat lines and 1 triticale cultivar) were grown in the Australian Grains Free-Air CO2 Enrichment facility under ambient CO2 (~400 µmol mol−1) and elevated CO2 (eCO2) concentrations (550 µmol mol−1) in 2014 and 2015 to test for different responses to CO2. Genotype response to eCO2 for the parameters measured showed strong linear relationships. eCO2 increased plant height (11%), aboveground biomass (31%) and grain yield (32%) as means across all genotypes. Yield response to eCO2 was driven by increases in spike number and weight. The increase in CO2 caused a mean 10% decrease in grain nitrogen content and increased grain weight by 7%. Measures of bread dough quality decreased due to eCO2. Genotypes with large yield response did not show larger than mean reductions in grain %N. The apparent near-universal decline in grain %N under eCO2 might be compensated for by selection of genotypes that are highly responsive to increasing yields but resist dramatic declines in grain %N. Selection for responsiveness to eCO2 for yield and grain %N are likely to involve a range of co-related characteristics that balance sink and source relationships.

Growth and photosynthetic responses in Brassica napus differ during stress and recovery periods when exposed to combined heat, drought and elevated CO2

This study was intended to investigate how an agronomically important crop Brassica napus will be able to cope with the combined impact of a heatwave (21/14 °C vs. 33/26 °C day/night) and drought under ambient or elevated CO2 (800 vs. 400 μmol mol−1) and to what degree their recovery will be ensured after the stress, when additional CO2 is also removed. The obtained results revealed that, in the presence of an adequate water supply, B. napus performed well under heatwave conditions. However, drought fully negated all the advantages gained from hotter climate and led to a slower and incomplete recovery of gas exchange and retarded growth after the stress, regardless mitigating the effect of elevated CO2 during the stress. The mechanism by which the elevated CO2 diminished the adverse effect of a combined heat and drought stress on photosynthetic rate at saturating light (Asat) was attributed to the improved plant water relations. However, it had little effect on the recovery of Asat. In contrast, the mechanism by which photosynthesis was more impaired under the combination of heatwave and drought, compared to single drought treatment, was attributed mainly to the faster soil drying as well as faster and sharper decrease in stomatal conductance and subsequent in Ci/Ca. Keeping in mind that photosynthesis can acclimatize by downregulation to higher CO2, the results of this study, showing a weak memory of mitigating the effect of elevated CO2, highlight a potential risk of more intense and frequent heatwaves and droughts on B. napus.

Interactive effects of CO2 and nitrogen supply on growth and physiological traits of millet cultivars under drought stress

ABSTRACTAn experiment was conducted to evaluate the effects of irrigation regimes (irrigation after 40 and 75% depletion of available soil water) and nitrogen levels (0 and 85 mg N kg−1 soil) on millet cultivars (Bastan and Pishahang) under two atmospheric CO2 concentrations (390 ± 50 and 700 ± 50 µmol mol−1). Evaluation of different biochemical traits at 50% flowering stage and measurement of dry matter weight at milk stage revealed that water shortage reduced shoot dry weight as the consequence of decreasing chlorophyll and carotenoid contents, leaf area, membrane stability index, and root dry weight but it increased not only the production of H2O2 but also MDA and antioxidant enzyme activities. Drought conditions with elevated levels of CO2 and nitrogen supply, however, partly relaxed limitations observed under water shortage conditions so that H2O2 and MDA production decreased but chlorophyll content and leaf area increased, leading to reduced loss of shoot dry weight. Increased CO2 had a greater effect on the reduction of ascorbate peroxidase and catalase in Bastan, while in Pishahang it had more effect on the reduction of malondialdehyde. Results showed that elevated CO2 and nitrogen supply depended for their effects on both irrigation regime and the genotype grown.

Elevated CO2-induced changes in cytokinin and nitrogen metabolism are associated with different responses in the panicle architecture of two contrasting rice genotypes

The yield response of Yangdao6 (YD6, Oryza sativa L. ssp. indica) to an enriched CO2 concentration was at least 30% higher, an approximately twofold increase, compared with that of Wuyunjing23 (WYJ23, Oryza sativa L. ssp. japonica). The differences in grain yield response levels between these two contrasting rice genotypes were mainly attributed to the disparities in the number of spikelets per panicle in response to elevated CO2. The number of spikelets per panicle was significantly increased by ~ 11.3% for YD6, but that of WYJ23 was decreased by 6.0% under elevated CO2 conditions. The increase in the differentiated spikelet number and decrease in the percentage of degenerated spikelet number on secondary branches were the key factors accounting for this phenomenon. To clarify the underlying physiological mechanisms corresponding to the above phenotype, the cytokinin content and nitrogen assimilation enzymes were assayed in the panicles and roots of YD6 and WYJ23 under ambient and elevated CO2 conditions (+ 200 µmol mol− 1). The results showed that locally synthesized cytokinins in panicles under elevated CO2 increased the differentiated spikelet number on secondary branches for YD6. Elevated CO2 also caused the enhanced or stabilized catalytic activity of most nitrogen assimilation enzymes in the panicles of YD6 but caused only a slight increase, or even a significant decrease, in the panicles of WYJ23. The increased activity of nitrogen assimilation enzymes in the panicles may reduce the degenerated spikelet number of YD6. These findings have significant implications for the utilization of germplasm resources in ensuring food security under future elevated CO2 conditions.

Improve Plant Photosynthesis by a New Slow-Release Carbon Dioxide Gas Fertilizer.

In the natural state, the concentration of carbon dioxide in the atmosphere is about 300 μmol mol–1. Plants need a suitable balance of CO2 to achieve optimal growth. The optimum CO2 content corresponding to a high photosynthesis rate is between 0.1 and 1.0% by volume. However, air has only a CO2 content of 0.03% by volume, so plants cannot use all of their growth potential. The use of fertilizer to assist in the supply of CO2 increases the rate of photosynthesis. In this work, a slow-release CO2 gas fertilizer inspired by polyphenol chemistry was prepared to provide sustainable CO2 that could improve plant photosynthetic capacity and get a higher crop yield. The core–shell structure was designed to confer gas fertilizers slow-release property. Micron-sized calcium carbonate particles with uniform particle size and regularity morphology, as carbon sources for plant photosynthesis, was a core, and tannic acid was coated on it as a shell via oxidative oligomerization and cross-linked by polyetherimide. The structure and morphology of fertilizers were characterized by scanning electron microscopy, X-ray energy dispersive spectroscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, and thermogravimetric analysis. In vitro experiments, the prepared fertilizers were proved to have slow-release properties. And then through net photosynthesis rate, chlorophyll fluorescence parameters, chlorophyll content, leaf area, leaf mass per area, and dry matter to study the effects of slow-release CO2 gas fertilizers on plant physiology of Brassica chinensis. The results revealed that the slow-release CO2 gas fertilizers not only had good slow-release properties but also can well improve plant photosynthesis.