Trade-offs between water-use related traits,yield components and mineral nutrition of wheat under Free-Air CO2 Enrichment (FACE)

This study investigated trade-offs between parameters determining water use efficiency of wheat under elevated CO₂ in contrasting growing seasons and a semi-arid environment. We also evaluated whether previously reported negative relationships between nutrient content and transpiration efficiency among wheat genotypes will be maintained under elevated CO₂ conditions. Two cultivars of wheat (Triticum aestivum L.), Scout and Yitpi, purportedly differing in water use efficiency related traits (e.g. transpiration efficiency) but with common genetic backgrounds were studied in a high yielding, high rainfall (2013), and in a low yielding, very dry growing season (2014) under Free-Air CO₂ Enrichment (FACE, CO₂ concentration of approximately 550 μmol mol⁻¹) and ambient (approximately 390 μmol mol⁻¹) CO₂. Gas exchange measurements were collected diurnally between stem elongation and anthesis. Aboveground biomass and nutrient content (sum of Ca, K, S, P, Cu, Fe, Zn, Mn and Mg) were determined at anthesis. Yield, yield components and harvest index were measured at physiological maturity. Cultivar Scout showed transiently greater transpiration efficiency (measured by gas exchange) over cultivar Yitpi under both ambient and elevated CO₂ conditions, mainly expressed in the high yielding but not in the low yielding season. Nutrient content was on average 13% greater for the lower transpiration efficiency cultivar Yitpi than the cultivar with higher transpiration efficiency (Scout) in the high yielding season across both CO₂ concentrations. Elevated CO₂ stimulated grain yield to a greater extent in the high yielding season than in the low yielding season where increased aboveground biomass earlier in the season did not translate into fertile tillers in cultivar Yitpi. Yield increased 27 and 33% in the high yielding and 0 and 19% in the low yielding season for cultivars Yitpi and Scout, respectively. Intraspecific variation in CO₂ responsiveness related mechanisms of grain yield were observed. These results suggest CO₂-driven trade-offs between traits governing water use efficiency are related to both growing season and intraspecific variations, and under very dry finishes, the trade-offs may even reverse. The negative relationship between nutrient content and transpiration efficiency among wheat genotypes will be maintained under elevated CO₂ conditions.     

Vulnerability of lodging risk to elevated CO2 and increased soil temperature differs between rice cultivars

Anthropogenic increases in atmospheric carbon dioxide concentration [CO₂], and subsequent increases in surface temperatures, are likely to impact the growth and yield of cereal crops. One potential means for yield reduction is for climate parameters to increase the occurrence of lodging. Using an in situ free-air CO₂ enrichment (FACE) system, two morphologically distinct rice cultivars, KH (Koshihikari) and SY (Shan you 63), were grown at two [CO₂]s (ambient and ambient + 200 μmol mol⁻¹) and two soil temperatures (ambient and ambient ± 1.8 °C) over a two year period to assess and quantify lodging risk. Elevated [CO₂] per se had no effect on lodging resistance for either cultivar. However, elevated [CO₂] and higher soil temperature increased the lodging risk for SY, due to a relatively higher increase in plant biomass and height at the elevated, relative to the ambient [CO₂] condition. Elevated soil temperature per se also increased lodging risk for both cultivars and was associated with longer internodes in the lower portion of the tillers. These findings illustrate that lodging susceptibility in rice, an important cereal crop, can be increased by rising [CO₂] and soil temperature; however, variation observed here between rice cultivars suggests there may be sufficient intraspecific variability to begin choosing rice lines that minimize the potential risk of lodging.     

Effect of free air carbon dioxide enrichment combined with two nitrogen levels on growth,yield and yield quality of sugar beet: Evidence for a sink limitation of beet growth under elevated CO2

The increase in atmospheric CO₂ concentration [CO₂] has been demonstrated to stimulate the growth of C₃ crops. However, little information exists about the effect of elevated [CO₂] on biomass production of sugar beet, and data from field experiments are lacking. In this study, sugar beet was grown within a crop rotation over two rotation cycles (2001, 2004) at present and elevated [CO₂] (375 μl l^?1 and 550 μl l^?1) in a free air CO₂ enrichment (FACE) system and at two levels of nitrogen supply [high (N2), and 50% of high (N1)], in Braunschweig, Germany. The objective of the present study was to determine the CO₂ effect on seasonal changes of leaf growth and on final biomass and sugar yield. Shading treatment was included to test whether sugar beet growth is sink limited under elevated [CO₂]. CO₂ elevation did not affect leaf number but increased individual leaf size in early summer resulting in a faster row closure under both N levels. In late summer CO₂ enrichment increased the fraction of senescent leaves under high but not low N supply, which contributed to a negative CO₂ effect on leaf area index and canopy chlorophyll content under high N at final harvest. Petioles contained up to 40% water-soluble carbohydrates, which were hardly affected by CO₂ but increased by N supply. More N increased biomass production by 21% and 12% in 2001 and 2004, respectively, while beet and sugar yield was not influenced. Concentration of α-amino N in the beet fresh weight was increased under low N and decreased under high N by CO₂ enrichment. The CO₂ response of total biomass, beet yield and white sugar yield was unaffected by N supply. Averaged over both N levels elevated [CO₂] increased total biomass by 7% and 12% in 2001 and 2004, respectively, and white sugar yield by 12% and 13%. The shading treatment in 2004 prevented the decrease in leaf area index under elevated [CO₂] and high N in September. Moreover, the CO₂ effect on total biomass (24%) and white sugar yield (28%) was doubled as compared to the unshaded conditions. It is concluded that the growth of the storage root of sugar beet is not source but sink limited under elevated [CO₂], which minimizes the potential CO₂ effect on photosynthesis and beet yield.     

Elevated CO2 affects plant nitrogen and water‐soluble carbohydrates but not in vitro metabolisable energy

The effects of elevated concentrations of atmospheric CO₂ (e[CO₂]) on the nutritive value of wheat vegetative matter and grain as a feedstock for ruminants were investigated in a study undertaken at the Australian grains free‐air CO₂ enrichment (AGFACE) facility. The study included two commercial wheat cultivars (Janz and Yitpi) and two genetic selections from a Seri/Babex population (SB003 and SB062) which had previously been characterised for low and high water‐soluble carbohydrate accumulation efficiency. The trial was grown under ambient (~390 µmol/mol) and elevated (~550 µmol/mol) CO₂ conditions, and plants harvested at tillering, anthesis and physiological maturity. Composition analyses to determine the nutritive value for ruminant feed were undertaken on stems, leaves and grain. Plant and grain nitrogen were reduced in the e[CO₂] treatments, and as expected, the water‐soluble carbohydrates increased. All genotypes responded to e[CO₂] with the effects of altered composition evident within 60 days of sowing. Determinants of ruminant feed quality such as neutral and acid detergent fibre and estimated in vitro metabolisable energy were not significantly affected. The reduced plant and grain N will impact on the nutritive value and supplementation may be required. The impact of e[CO₂] on chemical composition of wheat plants may be greater if the predicted climate change is associated with concomitant abiotic stress such as high ambient temperature or low soil moisture.     

High CO2 effects on postharvest biochemical and textural properties of white asparagus (Asparagus officinalis L.) spears

The effects of high CO₂ concentration (10% CO₂, 17% O₂) on the changes of functional cell wall components (pectic substances, hemicellulose, cellulose, lignin), mechanical properties, content of free soluble sugars (sucrose, glucose, fructose), and respiration activity were studied in harvested white asparagus spears stored at 10 and 20 °C, respectively, for up to 7 d. Spears stored at 2, 10 and 20 °C in air were studied as controls, where the 2 °C condition indicated the effects of cold storage. During storage, respiration activity declined only slightly, irrespective of the CO₂ and temperature regime. Spears stored at 20 °C under both CA and normal air became less stiff and more elastic, however, tissue toughness increased significantly. Changes in toughness were associated primarily with the dynamics of lignin and cellulose, revealing a strong correlation (r² = 0.81). High CO₂ concentration inhibited the synthesis of cellulose and, to some extent, lignin accumulation at 20 °C. Additionally, elevated CO₂ inhibited the degradation of soluble carbohydrates. In contrast, slightly lower temperatures of 10 °C in combination with high CO₂ did not have a pronounced effect on changes in structural carbohydrates (lignin, cellulose, hemicellulose and pectins). The effect low temperature (2 °C) under normal atmosphere conditions resulted in the inhibition of cell wall changes in asparagus spears.     

Effects of free‐air CO2 enrichment and drought on root growth of field grown maize and sorghum

Increasing CO₂ concentration ([CO₂]) is thought to induce climate change and thereby increase air temperatures and the risk of drought stress, the latter impairing crop growth. The objective of this study was to investigate the effects of elevated [CO₂] and drought stress on root growth of one maize genotype (Zea mays cv. Simao) and two sorghum genotypes (Sorghum bicolor cv. Bulldozer and Sorghum bicolor × Sorghum sudanense cv. Inka) under the cool moderate climate of Central Europe. It was hypothesized that root growth stimulation due to elevated [CO₂] compensates for a reduced root growth under drought stress. Therefore, we established an experiment within a f ree‐a ir c arbon dioxide e nrichment system (FACE) in 2010 and 2011. Sorghum and maize genotypes were grown under ambient [CO₂] (385 ppm CO₂) and elevated [CO₂] (600 ppm CO₂) and in combination with restricted and sufficient water supply. Elevated [CO₂] decreased root length density (RLD) in the upper soil layers for all genotypes, but increased it in deeper layers. Higher [CO₂] enhanced specific root length (SRL) of “Simao” and “Bulldozer,” however, did not affect that of “Inka.” “Simao” achieved a higher SRL than the sorghum genotypes, indicating an efficient investment in root dry matter. Although elevated [CO₂] affected the root growth, no interaction with the water treatment and, consequently, no compensatory effect of elevated [CO₂] could be identified.     

Effect of N and CO2 supply on source size per grain at anthesis and its relationship with grain growth in wheat

Rising atmospheric CO₂ concentration ([eCO₂]) increases the yield of wheat mainly by increasing grain number, but effects on single grain weight are variable. It is discussed whether single grain growth is limited by the sink or the source size under a non-stress environment. This study explores the effect of e[CO₂] combined with varying N supply on the source and sink size during grain filling. Source size was defined as the amount of stem reserves per grain (SRG) and the proportion of incident radiation intercepted by the green canopy per grain (f_IRG) at anthesis. Data from a 2-year free-air CO₂ enrichment experiment with wheat with three N levels (on average 38 [Nd], 190 [Nad] and 320 kg N ha⁻¹ [Nex]) and two CO₂ levels (393 and 600 ppm) on SRG, f_IRG and grain filling rate (GFR) and duration (GFD) were evaluated. SRG ranged from 2.5 to 12.9 mg and f_IRG from 4.0 × 0.001% to 6.8 x 0.001%. Rising N supply or e[CO₂] decreased SRG and f_IRG via their increases in grain number. Accordingly, there was a negative linear relationship between grain number and SRG (r² ≥ 0.84) or f_IRG (r² ≥ 0.97). Increasing N supply decreased GFR, but increased GFD, and GFR was increased by e[CO₂] under Nad and Nex. For GFR and final grain weight, there was a strong positive (r² ≥ 0.85), and for GFD, a strong negative linear relationship (r² ≥ 0.76) with f_IRG under Nad and Nex. Under these N levels, f_IRG supplied the largest share (>86%) for grain growth and thus single grain growth was possibly source limited under Nad and Nex. Under high grain number such as under Nex and e[CO₂], there might be a risk for low final grain weight due to the low SRG that is insufficient for buffering assimilate shortage under unfavourable environmental conditions in early grain filling.     

Soybean (Glycine max (L.) Merr.) growth and development response to CO2 enrichment under different temperature regimes

The carbon dioxide (CO₂) concentration of the global atmosphere has increased during the last decades. This increase is expected to impact the diurnal variation in temperature as well as the occurrence of extreme temperatures. This potentially could affect crop production through changes in growth and development that will ultimately impact yield. The objective of this study was to evaluate the effect of CO₂ and its interaction with temperature on growth and development of soybean (Glycine max (L.) Merr., cv. Stonewall). The experiment was conducted in controlled environment chambers at the Georgia Envirotron under three different temperatures and two CO₂ regimes. The day/night air temperatures were maintained at 20/15, 25/20 and 30/25 °C, while the CO₂ levels were maintained at 400 and 700 ppm, resulting in six different treatments. Plants were grown under a constant irradiance of 850 μmoles m⁻² s⁻¹ and a day length of 12 h; a non-limiting supply of water and mineral nutrients were provided. Five growth analyses were conducted at the critical development stages V4, R3, R5, R6 and R8. No differences in start of flowering were observed as a function of the CO₂ level, except for the temperature regime 25/20 °C, where flowering for the elevated CO₂ level occurred 2 days earlier than for the ambient CO₂ level. For aboveground biomass, an increase in the CO₂ level caused a more vigorous growth at lower temperatures. An increase in temperature also decreased seed weight, mainly due to a reduction in seed size. For all temperature combinations, final seed weight was higher for the elevated CO₂ level. This study showed that controlled environment chambers can be excellent facilities for conducting a detailed growth analysis to study the impact on the interactive effect of changes in temperature and CO₂ on soybean growth and final yield.     

Atmospheric CO2 enrichment affects potatoes: 1. Aboveground biomass production and tuber yield

Despite its economic and environmental importance, information about effects of future atmospheric carbon dioxide (CO₂) enrichment on aboveground biomass production and tuber yield of potato is still rare. Responses of potato (Solanum tuberosum L. cv. Bintje) were thus investigated in two full growing seasons under 380, 550 or 680 μmol mol^?1 CO₂ in open-top chambers (OTCs). When averaged over both years, aboveground stem biomass at canopy maturity was negatively related to CO₂ enrichment. Aboveground-to-belowground biomass ratio was negatively related to CO₂ enrichment as there was a positive relationship between CO₂ and total dry yield of potato tubers. The stimulation was mainly related to an increase in the tuber size fraction for commercial yield (tubers > 35 mm). For the largest size class (tubers > 50 mm), which is important for industrial processing, large CO₂-induced impacts were observed too, although these effects were not significant. Elevated CO₂ concentrations will thus affect biomass allocation of potato plants and result in improvements concerning the market value of the commercial tuber yield.     

Effects of Free‐Air Carbon Dioxide Enrichment on Sap Flow and Canopy Microclimate of Maize Grown under Different Water Supply

The rise of atmospheric CO₂ concentration ([CO₂]) affects stomatal conductance and thus transpiration and leaf temperature. We evaluated the effect of elevated [CO₂] levels under different water supply on daily sap flow and canopy microclimate (air temperature (Tc) and vapour pressure deficit (VPD)) of maize. The crop was cultivated in circular field plots under ambient (AMB, 378 μmol mol^?1) and elevated [CO₂] (FACE, 550 μmol mol^?1) using free‐air CO₂ enrichment with sufficient water in 2007, while in 2008 a DRY semicircle received only half as much water as compared to the WET semicircle from mid of July. In 2007, sap flow was measured in WET simultaneously under AMB and FACE conditions and was significantly decreased by elevated [CO₂]. In 2008, sap flow was measured in all four treatments but not simultaneously. Therefore, data were correlated with potential evaporation and the slopes were used to determine treatment effects. Drought reduced whole‐plant transpiration by 50 % and 37 % as compared to WET conditions under AMB and FACE, respectively. Moreover, CO₂ enrichment did not affect sap flow under drought but decreased it under WET by 20 % averaged over both years. The saving of water in the period before the drought treatment resulted in a displacement of dry soil conditions under FACE as compared to AMB. Under WET, CO₂ enrichment always increased Tc and VPD during the day. Under DRY, FACE plots were warmer and drier most of the time in August, but cooler and damper short after the start of drought in July and from the end of August onwards. Thus, the CO₂ effect on transpiration under drought was variable and detectable rather easy by measuring canopy microclimate.     

Elevated [CO2] and warming increase the macronutrient use efficiency and biomass of Stylosanthes capitata Vogel under field conditions

Stylosanthes capitata Vogel is a C3 forage legume widely cultivated in tropical and subtropical pastures. However, the nutrient dynamics of this species under future climate change is unknown. Therefore, this study aimed to evaluate the nutrient content, nutrient accumulation, nutrient use efficiency and growth of S. capitata exposed to increased [CO₂] and temperature under field conditions using two levels of atmospheric [CO₂] (ambient and elevated—600 ppm) and two canopy temperature (ambient and elevated—2°C). Treatments were applied at field conditions, for 30 days, using a free-air carbon dioxide enrichment (FACE) and a free-air temperature-controlled enhancement (T-FACE) systems. Warming showed no effects on macronutrient content, but increased the accumulation of nitrogen, potassium, calcium, magnesium and sulphur, the nutrient use efficiency and root dry mass. Elevated [CO₂] alone had no effect on most of the parameters evaluated. However, the combination of elevated [CO₂] with warming improved the nutrient accumulation, nutrient use efficiency and whole-plant growth more than under isolated conditions of elevated [CO₂] or warming. Based on our short-term results, we concluded that an increment of atmospheric [CO₂] and temperature will benefit S. capitata growth, suggesting no alterations in the actual fertilizer programs for this species.     

Effect of elevated carbon dioxide and temperature on phosphorus uptake in tropical flooded rice (Oryza sativa L.)

A field experiment was carried out to assess the impact of elevated carbon dioxide (CO₂) and temperature on phosphorous (P) nutrition in relation to organic acids exudation, soil microbial biomass P (MBP) and phosphatase activities in tropical flooded rice. Rice (cv. Naveen) was grown under chambered control (CC), elevated CO₂ (EC, 550 μmol mol⁻¹) and elevated CO₂ + elevated temperature (ECT, 550 μmol mol⁻¹ and 2 °C more than CC) in a tropical flooded soil under open top chambers (OTCs) along with unchambered control (UC) for three years. Root exudates were analyzed at different growth stages of rice followed by organic acids determination. Rhizospheric soil was used for analysis of soil phosphatase, MBP and available P. The total organic carbon (TOC) in root exudates was increased by 27.5% and 30.2% under EC and ECT, respectively over CC. Four different types of organic acids viz. acetic acid (AA), tartaric acid (TA), malic acid (MA) and citric acid (CA) were identified and quantified as dominant in root exudates, concentration of these was in the order of TA > MA > AA > CA. The TA, MA, AA and CA content were increased by 34.4, 31.1, 38.7 and 58.3% under ECT compared to that of UC over the period of 3 years. The P uptake in shoot, root and grain under elevated CO₂ increased significantly by 29, 28 and 22%, respectively than CC. Soil MBP, acid and alkaline phosphatase activity was significantly higher under elevated CO₂ by 35.1%, 27 and 36%, respectively, compared to the CC. Significant positive relationship exists among the organic acid exudation, MBP, phosphatase activities and P uptake by rice. The enhanced organic acid in root exudates coupled with higher soil phosphatase activities under elevated CO₂ resulted in increased rate of soil P solubilization leading to higher plant P uptake.     

Elevated CO2 modulates the effects of drought and heat stress on plant water relations and grain yield in wheat

To investigate the interactive effects of drought, heat and elevated atmospheric CO₂ concentration ([CO₂]) on plant water relations and grain yield in wheat, two wheat cultivars with different drought tolerance (Gladius and Paragon) were grown under ambient and elevated [CO₂], and were exposed to post‐anthesis drought and heat stress. The stomatal conductance, plant water relation parameters, abscisic acid concentration in leaf and spike, and grain yield components were examined. Both stress treatments and elevated [CO₂] reduced the stomatal conductance, which resulted in lower leaf relative water content and leaf water potential. Drought induced a significant increase in leaf and spike abscisic acid concentrations, while elevated [CO₂] showed no effect. At maturity, post‐anthesis drought and heat stress significantly decreased the grain yield by 21.3%–65.2%, while elevated [CO₂] increased the grain yield by 20.8% in wheat, which was due to the changes of grain number per spike and thousand grain weight. This study suggested that the responses of plant water status and grain yield to extreme climatic events (heat and drought) can be influenced by the atmospheric CO₂ concentration.     

The effect of CO2 and 1-methylcyclopropene on the regulation of postharvest senescence of mint,Mentha longifolia L.

The regulatory effects of 5 kPa CO₂ and of the ethylene action inhibitor, 1-methylcyclopropene (1-MCP) at 0.5 μmol/l on the senescence of harvested mint, Mentha longifolia L. were assessed. Visual parameters of senescence including yellowing, browning, decay and leaf abscission were recorded and scored on scales linking the onset and progression of senescence to marketability. The effects of plant age on the rate of postharvest senescence and on the efficacy of the CO₂ and 1-MCP treatments were also investigated. All experiments were repeated with and without the presence of exogenous ethylene. Two experimental formats were used, with 6 days storage at room temperature representing local market conditions, and 6 days cold storage at 1.5 °C followed by 4 days at room temperature representing export market conditions. Sprigs from old plants were no longer of marketable quality after 6 days storage at room temperature. Exogenous ethylene accelerated the onset of senescence causing unacceptably high rates of leaf abscission. Raised levels of CO₂ in a controlled atmosphere system were found to be more effective in inhibiting senescence without the presence of exogenous ethylene than pre-treatment with 1-MCP, and no additive effect was found. However in the presence of exogenous ethylene, a combined treatment with 1-MCP together with raised CO₂ levels resulted in a significant additive effect in nullifying the ethylene-induced leaf abscission. Respiration rates as measured by CO₂ production, and ethylene production, were recorded throughout all experiments. While CO₂ levels were not affected by any experimental treatment, ethylene production was elevated in mint sprigs exposed to an initial dose of gaseous 1-MCP, and was further increased under a combined treatment of 1-MCP together with 5 kPa CO₂. However in the presence of exogenous ethylene, CO₂ strongly suppressed the 1-MCP induced ethylene production.     

Can additional N fertiliser ameliorate the elevated CO2‐induced depression in grain and tissue N concentrations of wheat on a high soil N background?

Elevated CO₂ stimulates crop yields but leads to lower tissue and grain nitrogen concentrations [N], raising concerns about grain quality in cereals. To test whether N fertiliser application above optimum growth requirements can alleviate the decline in tissue [N], wheat was grown in a Free Air CO₂ Enrichment facility in a low‐rainfall cropping system on high soil N. Crops were grown with and without addition of 50–60 kg N/ha in 12 growing environments created by supplemental irrigation and two sowing dates over 3 years. Elevated CO₂ increased yield and biomass (on average by 25%) and decreased biomass [N] (3%–9%) and grain [N] (5%). Nitrogen uptake was greater (20%) in crops grown under elevated CO₂. Additional N supply had no effect on yield and biomass, confirming high soil N. Small increases in [N] with N addition were insufficient to offset declines in grain [N] under elevated CO₂. Instead, N application increased the [N] in straw and decreased N harvest index. The results suggest that conventional addition of N does not mitigate grain [N] depression under elevated CO₂, and lend support to hypotheses that link decreases in crop [N] with biochemical limitations rather than N supply.     

Field experiments and simulation to evaluate rice cultivar adaptation to elevated carbon dioxide and temperature in sub-tropical India

Location specific adaptation option is required to minimize adverse impact of climate change on rice production. In the present investigation, we calibrated genotype coefficients of four cultivars in the CERES-Rice model for simulation of rice yield under elevated CO₂ environment and evaluation of the cultivar adaptation in subtropical India. The four cultivars (IR 36, Swarna, Swarn sub1, and Badshabhog) were grown in open field and in Open Top Chamber (OTC) of ambient CO₂ (≈390 ppm) and elevated CO₂ environment (25% higher than the ambient) during wet season (June–November) of the years 2011 and 2012 at Kharagpur, India. The genotype coefficients; P1 (basic vegetative phase), P2R (photoperiod sensitivity) and P5 (grain filling phase) were higher, but G1 (potential spikelet number) was lower under the elevated CO₂ environment as compared to their open field value in all the four cultivars. Use of the calibrated model of elevated CO₂ environment simulated the changes in grain yield of −13%, −17%, −4%, and +7% for the cultivars IR 36, Swarna, Swarna sub1, and Badshabhog, respectively, with increasing CO₂ level of 100 ppm and rising temperature of 1 °C as compared to the ambient CO₂ level and temperature and they were comparable with observed yield changes from the OTC experiment. Potential impacts of climate change were simulated for climate change scenarios developed from HadCM3 global climate model under the Intergovernmental Panel on Climate Change Special Report on Emission Scenarios (A2 and B2) for the years 2020, 2050, and 2080. Use of the future climate data simulated a continuous decline in rice grain yield from present years to the years 2020, 2050 and 2080 for the cultivars IR 36 and Swarna in A2 as well as B2 scenario with rising temperature of ≥0.8 °C. Whereas, the cultivar Swarna sub1 was least affected and Badshabhog was favoured under elevated CO₂ with rising temperature up to 2 °C in the sub-tropical climate of India.     

Controlled atmosphere treatment for control of grape mealybug,Pseudococcus maritimus (Ehrhorn) (Hemiptera: Pseudococcidae), on harvested table grapes

Controlled atmosphere (CA) treatments with ultralow oxygen (ULO) alone and in combinations with 50% carbon dioxide were studied to control grape mealybug, Pseudococcus maritimus (Ehrhorn) on harvested table grapes. Two ultralow oxygen levels, 30 and <0.01 μL L⁻¹, were tested in both ULO and ULO + 50% CO₂ treatments. The ULO treatments with the lower oxygen level were more effective than the ULO treatments at the higher oxygen level. The ULO + 50% CO₂ treatments were more effective than the ULO treatments. Grape mealybug eggs were significantly more tolerant of ULO and ULO + CO₂ treatments than nymphs and adults. A 14 day ULO treatment with 30 μL L⁻¹ O₂ at 2 °C did not achieve 100% mortalities of any life stage. In the presence of 50% CO₂, the 14 d treatment achieved complete mortality of all life stages of the grape mealybug. A 3 d ULO treatment with <0.01 μL L⁻¹ O₂ at 2 °C resulted in 93.3% mortality of nymphs and adults. The 3 d ULO treatment in combination with 50% CO₂ treatments, however, achieved complete control of grape mealybug nymphs and adults and caused 70.5% relative egg mortality. Complete egg mortality was achieved in a 10 d ULO + 50% CO₂ treatment with <0.01 μL L⁻¹ O₂ at 2 °C. Both the 14 d CA treatment with 30 μL L⁻¹ O₂ and 50% CO₂ and the 10 d CA treatment with <0.01 μL L⁻¹ O₂ and 50% CO₂ were tested on table grapes and grape quality was evaluated after two weeks of post-treatment storage. The CA treatments did not have a significant negative impact on grape quality and were safe for table grapes. The study indicated that CA treatments have potential to be developed for postharvest control of grape mealybug on harvested table grapes.     

Multivariate analysis of modifications in biosynthesis of volatile compounds after CA storage of ‘Fuji’ apples

Emission of aroma volatile compounds and some related enzyme activities (LOX, PDC, ADH, and AAT) were assessed in ‘Fuji’ apples (Malus × domestica Borkh.) during shelf life at 20 °C following cold storage under air or under three different CA conditions (3 kPa O₂:2 kPa CO₂; 1 kPa O₂:1 kPa CO₂; or 1 kPa O₂:2 kPa CO₂). Data were used for principal component analysis (PCA) and partial least-square regression (PLSR) analysis of results. LOX activity was partly inhibited by hypoxic conditions, and thus could have contributed to differentiation between air- and CA-stored fruit. Accordingly, emission of straight-chain esters was also higher in air- than in CA-stored fruit. In contrast, PDC activity was responsible for part of the differences between low (3 kPa) and ultra-low (1 kPa) O₂ storage conditions, probably by providing substrates for AAT action. AAT activity afforded no satisfactory differentiation between samples, and therefore it is suggested that substrate availability is a more decisive factor than enzyme activity for volatile production after storage. The PCA and PLSR models developed in this work were not useful for discrimination between the two studied ultra-low O₂ conditions.     

Effect of non-conventional atmospheres and bio-based packaging on the quality and safety of Listeria monocytogenes-inoculated fresh-cut celery (Apium graveolens L.) during storage

The increased consumption of fresh-cut celery has led to the need to explore packaging alternatives for fresh-cut celery that can meet consumer, market, and industry needs. In this study, the effect of bio-based packaging and non-conventional atmospheres on the quality and safety of chlorine-sanitized celery sticks stored at 7 °C was investigated. Two materials differing in permeability [a bio-based polyester (polylactic acid (PLA)) and a petroleum-based polyolefin (polypropylene/low density polyethylene (PP/PE)] and four initial gas compositions [air (A-PLA or A-PP/PE), 95 kPa O₂ + 5 kPa N₂ (O₂-PLA), 99 kPa N₂ + 1 kPa O₂ (N₂-PLA), and 6 kPa O₂ + 12 kPa CO₂ + 82 kPa N₂ (CO₂-PLA)] were evaluated. Changes in headspace composition, weight loss, surface and cut end color, texture, ethanol content, appearance, and growth of Listeria monocytogenes on inoculated celery sticks were assessed during 21 d of storage. Active MAP (CO₂-PLA) out-performed passive MAP (A-PLA) in maintaining celery stick quality but not safety. Conventional active MAP (CO₂-PLA) out-performed non-conventional active MAPs (O₂-PLA and N₂-PLA) in maintaining celery stick quality throughout storage, but O₂-PLA suppressed L. monocytogenes growth while CO₂-PLA promoted growth during the first 10 d of storage. PLA and PP/PE materials affected celery stick quality but not Listeria growth. This study shows that the initial gas composition and packaging material both impact the quality and safety of celery sticks. Overall, the combination PLA and 95 kPa O₂ proved most beneficial in maximizing both the safety and quality of celery sticks during one week of storage at 7 °C.     

The combined effects of aqueous chlorine dioxide,fumaric acid,and ultraviolet-C with modified atmosphere packaging enriched in CO2 for inactivating preexisting microorganisms and Escherichia coli O157:H7 and Salmonella typhimurium inoculated on buckwheat sprouts

The combined effects of a sanitizer mixture, ultraviolet-C (UV-C), and modified atmosphere packaging (MAP) on the quality of non-inoculated and inoculated (Escherichia coli O157:H7 and Salmonella typhimurium) buckwheat sprouts were examined. Buckwheat sprouts were treated with a sanitizer mixture (comprising 100 mg L⁻¹ aqueous ClO₂ and 0.3% fumaric acid) and 2 kJ m⁻² UV-C, packaged under two different conditions (air and CO₂ gas) and storage for 8 d at 4 °C. The combination of the sanitizer mixture and UV-C treatment reduced the initial counts of preexisting microorganisms in the buckwheat sprouts by 1.9 log CFU g⁻¹ and reduced the initial inoculated counts of E. coli O157:H7 and S. typhimurium on buckwheat sprouts by 3.0 and 2.3 log CFU g⁻¹, respectively. The preexisting microorganisms and inoculated pathogens in buckwheat sprouts packaged under CO₂ gas were significantly reduced during storage following the combined treatment compared to those of the control by above 95%. Differences in Hunter L^*, a^*, and b^* values among the treatments were negligible. The combined sanitizer mixture and UV-C treatment increased the sprout rutin content by 147%, but there was no significant difference in 2,2-diphenyl-1-picrylhydrazyl radical scavenging activity between treatments during storage. Therefore, the combination of sanitizer mixture made from aqueous ClO₂ and fumaric acid, UV-C irradiation, and MAP can improve the microbial safety and quality of buckwheat sprouts.