Photosynthetic responses in spring wheat grown under elevated CO2 concentrations and stress conditions in the European, multiple-site experiment ‘ESPACE-wheat’

Spring wheat cv. Minaret crop stands were grown under ambient and elevated CO₂ concentrations at seven sites in Germany, Ireland, the UK, Belgium and the Netherlands. Six of the sites used open-top chambers and one used a controlled environment mimicking field conditions. The effect of elevated CO₂ for a range of N application regimes, O₃ concentrations, and growth temperatures on flag leaf photosynthesis was studied. Before anthesis, flag leaf photosynthesis was stimulated about 50% by 650 compared with 350 μmol mol⁻¹ CO₂ at all sites, regardless of other treatments. Furthermore, there was no evidence of a decrease in photosynthetic capacity of flag leaves due to growth at elevated CO₂ before anthesis, even for low N treatments. However, photosynthetic capacity, particularly carboxylation capacity, of flag leaves was usually decreased by growth at elevated CO₂ after anthesis, especially in low N treatments. Acclimation of photosynthesis to elevated CO₂ therefore appears to occur only slowly, consistent with a response to changes in sink–source relationships, rather than a direct response. Effect of elevated CO₂ on stomatal conductance was much more variable between sites and treatments, but on average was decreased by ˜10% at 650 compared with 350 μmol mol⁻¹ CO₂. Carboxylation capacity of flag leaves was decreased by growth at elevated O₃ both before and after anthesis, regardless of CO₂ concentration.     

Chlorophyll concentration of potatoes grown under elevated carbon dioxide and/or ozone concentrations

Potato cv. Bintje was grown in open-top-chambers and free-air-CO₂-enrichment systems at 7 sites across Europe for 2 years (1998–99). The effect of different treatments (CO₂ enrichment and O₃ fumigation) on the chlorophyll content of fully expanded upper and lower canopy leaves was investigated collecting Minolta SPAD-502 meter readings. In both CO₂ treated and O₃ fumigated plants, leaves had lower chlorophyll content than those in ambient air controls; season-long chlorophyll averages were 9.3% lower in the ‘CO₂’ treatments, 9.1% lower in ‘O₃’ treatments and 12.3% lower in ‘CO₂+O₃’ treatments. The analysis of chlorophyll content in three different growth phases (Emergence–Tuber Initiation; Tuber Initiation–Maximum Leaf Area; Maximum Leaf Area–Harvest) showed that in the early growth period, i.e. before tuber initiation there was a slight indication for an higher chlorophyll content at elevated CO₂ (+3.8%) or O₃ (+1.7%). However, from tuber initiation onwards the leaves of plants grown under elevated CO₂ or O₃ showed a progressively lower chlorophyll content (−4.8% for CO₂ treatments and −2.6% for O₃ treatments) indicating a faster senescence of leaves that increased during the late growth period (−12.8% for CO₂ treatments and −12.7% for O₃ treatments) and that was enhanced by CO₂–O₃ interaction (−17.8%).     

CO2 and ozone effects on canopy development of potato crops across Europe

This paper describes the effects of elevated CO₂ (550 and 680 μl l⁻¹) and O₃ (60 nl l⁻¹ O₃ as an 8 h mean), alone or in combination, on canopy development and senescence in potato (Solanum tuberosum L. cv Bintje) across a range of European agro-climatic conditions. The assessments were made within the European CHIP project (CHanging climate and potential Impacts on Potato yield and quality) that was conducted for two growing seasons (1998 and 1999) in free air CO₂ enrichment systems (FACE) and open-top chamber facilities (OTCs) at seven European sites. A comparison of chambered and unchambered experimental plots was included to examine the effects of chamber enclosure. Phenological growth stages, plant height, leaf area index (LAI) and the number of green and yellow leaves were recorded non-destructively throughout the growing season and by a destructive intermediate harvest at maximum leaf area (MLA). In the dynamic growth analysis CO₂ and O₃ effects were studied over three developmental stages: canopy expansion, full canopy and canopy senescence. Chamber enclosures promoted potato crop development (taller plants, more leaves) during the initial growth stages and led to a faster decline of LAI and a higher number of yellow leaves. The growth in ambient plots varied between sites and seasons, as did the scale of the treatment responses. Despite the large background variation, some overall treatment effects could be detected across all sites. Both levels of increased CO₂ reduced final plant height in comparison to ambient concentrations, which indicates a premature ending of the active plant growth. At the stage of full canopy and crop senescence the average number of green leaves was significantly (P<0.05) decreased by 680 μl l⁻¹ CO₂ (OTC experiments) and LAI showed the same tendency (P=0.07). As there was however no indication of a decreased leaf formation during initial growth and at full canopy, this must have been due to an earlier leaf fall. In the FACE experiments LAI had already began to decline at the stage of full canopy at 550 μl l⁻¹ CO₂ but not in ambient CO₂ (DAE×CO₂, P<0.05). These observations strongly indicated that elevated CO₂ induced a premature senescence during full canopy. O₃ did not have an overall detrimental effect on crop development during initial growth nor at full canopy, but did induce a faster reduction of LAI during crop senescence (DAE×O₃, P<0.05). Final plant height was not affected by O₃. There were few CO₂×O₃ interactions detected. There was a suggestion (P=0.06) that O₃ counteracted the CO₂-induced decrease of green leaves at full canopy, but on the other hand during crop senescence the decline of LAI due to elevated O₃ was faster at ambient compared to elevated CO₂ (P<0.05). These responses of canopy development to elevated CO₂ and O₃ help to explain the treatment responses of potato yield within the CHIP project at sites across Europe.     

Effects of elevated carbon dioxide and ozone on potato tuber quality in the European multiple-site experiment ‘CHIP-project’

Potato (Solanum tuberosum L cv. Bintje) was exposed to ambient and elevated carbon dioxide (CO₂), to ambient and elevated ozone (O₃) and to elevated levels of both gases during two growing seasons, 1998 and 1999. Experiments in open-top chambers (OTC) were carried out in Finland, Sweden, Ireland, United Kingdom, Germany and Belgium and a FACE (Free Air Carbon dioxide Enrichment) experiment was carried out in Italy. In OTCs the plants were grown under ambient CO₂ concentrations or with 550 and 680 μl l⁻¹ CO₂ alone or in combination with ambient or elevated O₃ concentrations (target seasonal mean of 60 nl l⁻¹ 8 h per day). In the FACE systems the plants were exposed to ambient or 550 μl l⁻¹ CO₂. In the OTC experiments the reducing sugar content of potato tubers decreased significantly with increased concentration of O₃. The starch content of potato tubers decreased, with negative impact on tuber quality, but the ascorbic acid concentration increased as a function of the AOT40 (The sum of the differences between hourly ozone concentration and 40 nl l⁻¹ for each hour when the concentration exceeds 40 nl l⁻¹ during a relevant growing season). However, simultaneous exposure to elevated CO₂ counteracted the ozone effect. With increase in the CO₂ exposure, glycoalkaloid and nitrate concentrations decreased yielding improved quality, while the citric acid concentration decreased causing a higher risk for discoloration after cooking. The amount of dry matter and starch increased significantly in the FACE experiment.     

Climatic conditions and concentrations of carbon dioxide and air pollutants during ‘ESPACE—wheat’ experiments

A major objective of the ESPACE—wheat programme was to perform by means of open-top chambers (OTCs) ‘standardised’ experimental investigations of spring wheat responses to increased atmospheric CO₂ and O₃ concentrations and to other environmental stresses at different locations in Europe, representing a broad range of different climatic conditions. From 1994 to 1996 a total number of 25 OTC experiments were carried out. In addition, four growth chamber experiments focusing on key physiological processes of wheat growth in CO₂-enriched air were performed. According to the specific needs for subsequent modelling purposes, environmental data were collected during experiments, i.e. air temperature, global radiation, humidity and trace gas concentrations. In the present paper results of these measurements are summarised. It was shown, that the OTC-experiments covered a considerable range of growing season mean-air-temperatures (13.0–23.4°C) and global irradiances (10.8–18.1 MJ m⁻² d⁻¹), the most important driving variables for crop growth simulation models. Mean concentrations of CO₂ and O₃ in ambient air and in different treatments illustrated the observed variability of trace gas exposures between different experiments. Implications for subsequent analyses of biological response data are discussed.     

Photosynthetic and stomatal responses of potatoes grown under elevated CO2 and/or O3—results from the European CHIP-programme

The physiological effects of elevated CO₂ and/or O₃ on Solanum tuberosum cv. Bintje were examined in Open-Top Chambers during 1998 and 1999 at experimental sites across Europe as part of the EU ‘Changing Climate and Potential Impacts on Potato Yield and Quality’ programme (CHIP). At tuber initiation (≈20 days after emergence, DAE) elevated CO₂ (680 μl l⁻¹) induced a 40% increase in the light saturated photosynthetic rate (A_sat) of fully expanded leaves in the upper canopy. This was 16% less than expected from short-term exposures of plants grown under ambient CO₂ (360 μl l⁻¹) to elevated CO₂, indicating that photosynthetic acclimation began at an early stage of crop growth. This effect resulted from a combination of a 12% reduction in stomatal conductance (g_s) and a decline in photosynthetic capacity, as indicated by the significant reductions in the maximum carboxylation rate of Rubisco (Vc_max) and light-saturated rate of electron transport (J_max) under elevated CO₂. The seasonal decline in the promotion of photosynthesis by elevated CO₂ reflected the concurrent decrease in g_s. Vc_max and J_max were both reduced in plants grown under elevated CO₂ until shortly after maximum leaf area (MLA) was attained. Although non-photorespiratory mitochondrial respiration in the light (R_d) increased during the later stages of the season, net photosynthesis was consistently increased by elevated CO₂ during the main part of the season. Photosynthetic rate declined more rapidly in response to elevated O₃ under ambient CO₂, and the detrimental impact of O₃ was most obvious after MLA was attained (DAE 40–50). Several exposure indices were compared, with the objective of determining the critical ozone level required to induce physiological effects. The critical O₃ exposure above which a 5% reduction in light saturated photosynthetic rate may be expected (expressed in terms of cumulative exposure above 0 nl l⁻¹ O₃ between emergence and specific dates during the season (AOT0-cum)) was 11 μl l⁻¹ h; however this value should only be extrapolated beyond the CHIP dataset with caution. The interaction between O₃ and stomatal behaviour was more complex, as it was influenced by both long-term and daily exposure levels. Elevated CO₂ counteracted the adverse effect of O₃ on photosynthesis, perhaps because the observed reduction in stomatal conductance decreased O₃ fluxes into the leaves. The results are discussed in the context of nitrogen deficiency, carbohydrate accumulation and yield.     

Effect of climatic conditions on tuber yield (Solanum tuberosum L.) in the European ‘CHIP’ experiments

The main objective of the CHIP project was to perform ‘standardised’ investigations of potato (Solanum tuberosum L. cv Bintje) responses to increased O₃ and CO₂ concentrations by means of open-top chambers (OTC) and free air carbon dioxide enrichment (FACE) systems. The experimental sites are located across Europe representing a broad range of different climatic conditions. In 1998 and 1999 a total number of 12 OTC experiments and four FACE experiments were conducted. According to the specific needs for subsequent modelling purposes, environmental data were collected during experiments, i.e. air temperature, global radiation, air humidity (vapour pressure deficit (VPD)), soil moisture and trace gas concentrations. In the present paper, the results of these measurements are summarised. It was shown that the experiments covered a considerable range of growing season mean air temperatures (13.8–19.9 °C) and global irradiances (12.0–21.3 MJ m⁻² per day), the most important driving variables for crop growth simulation models. Analysis of the soils used during the experiments demonstrated that in most cases sufficient nutrient elements were available to guarantee an undisturbed growth. Mean concentrations of CO₂ and O₃ in ambient air and in different treatments illustrate the observed variability of trace gas exposures between different sites and experiments. However, the effects of these parameters on growth and yield are subject of separate papers. The general climatic conditions across Europe are also causing important growth and yield effects. Comparison of marketable tuber yields revealed an increase at higher latitudes. This result was associated with lower temperatures and VPD and longer day lengths at the higher latitudes, which in turn were associated with longer growing seasons.     

Growth and marketable-yield responses of potato to increased CO2 and ozone

Central to the CHanging climate and potential Impacts on Potato yield and quality project (CHIP) was the consideration of the potential impacts of ozone and CO₂ on growth and yield of future European Potato crops. Potato crops, cv. Bintje, were exposed to ambient or elevated ozone; targeted daily average, 60 nl l⁻¹ for 8 h, and ambient or elevated CO_2; targeted 680 μl l⁻¹ averaged over the full growing season, in open top chambers (OTCs) at six European sites in 1998 and 1999, or to elevated CO₂ (550 μl l⁻¹) in Free Air Carbon dioxide Enrichment facilities (FACE) at two sites in both years. Some OTC experiments included 550 μl l⁻¹. Above and below ground biomass were measured at two destructive harvests; at maximum leaf area (MLA) and at final-harvest. Final-harvest fresh weight yields of marketable-size tubers, >35 mm diameter, from ambient conditions ranged from 1 to 12 kg m⁻². There was no consistent (P>0.1) CO₂×O₃ interaction for growth or yield variables at either harvest. No consistent effects of ozone were detected at the maximum-leaf-area harvest. However, at final harvest, ozone had reduced both above-ground biomass and tuber dry weight (P<0.05), particularly of the largest (>50 mm) size class. These yield losses showed linear relationships both with accumulated ozone exposure; AOT40 expressed as nl l⁻¹ h over 40 nl l⁻¹, and with yields from chambered ambient-ozone treatments (P<0.05) but, because of partial confounding between the treatment AOT40s and the ambient-ozone yields in the data, the two relationships were not completely independent. Yields from ambient-ozone treatments, however, explained a significant (P<0.01) amount of the residual variation in ozone effects unexplained by AOT40. When averaged over all experiments, mean dry weights and tuber numbers from both harvests were increased by elevated CO₂. Only green leaf number at the MLA harvest was reduced. The CO₂ responses varied between sites and years. For marketable-size tubers, this variation was unrelated to variation in ambient-CO₂ treatment yields. Yield increases resulting from the 680 μl l⁻¹ and 550 μl l⁻¹ treatments were similar. Thus elevating [CO₂] from 550 to 680 μl l⁻¹ was less effective than elevating [CO₂] from ambient to 550 μl l⁻¹. On average, CO₂ elevation to 680 μl l⁻¹ increased the dry weight of marketable-size tubers by about 17%, which far exceeded the average ozone-induced yield loss of about 5%. The net effect of raising CO₂ and O₃ concentrations on the European potato crop would be an increase marketable yield.     

The effects of climatic variation in Europe on the yield response of spring wheat cv. Minaret to elevated CO2 and O3: an analysis of open-top chamber experiments by means of two crop growth simulation models

In the ESPACE-Wheat programme, 25 open-top chamber experiments were carried out in 1994, 1995 and 1996, on nine locations, divided over eight European countries. In most experiments, spring wheat cv. Minaret was subjected to two levels of atmospheric CO₂ and two levels of ozone. Grain yields in the control treatments (ambient levels of CO₂ and O₃) varied strongly between sites. Also, yield response to elevated CO₂ and O₃ showed great variation. The present study was conducted to determine whether climatic differences between sites could account for the observed variation.

Two simulation models were used for the analysis: AFRCWHEAT2-O3 and LINTULCC. AFRCWHEAT2-O3 simulates phenology, canopy development and photosynthesis in greater detail than LINTULCC. Both models account for the effects of radiation and temperature on crop growth. New algorithms were developed to simulate the effects of CO₂ and O₃. Weather data that were measured in the experiments were used as input, and simulated growth responses to CO₂ and O₃ were compared with measurements. No attempt was made to merge the two models. Thus two independent tools for analysis of data related to climate change were developed and applied.

The average measured grain yield in the control treatment, across all 25 experiments, was 5.9 tons per hectare (t ha⁻¹), with a standard deviation (SD) of 1.9 t  ha⁻¹. The models predicted similar average yields (5.5 and 5.8 t ha⁻¹ for AFRCWHEAT2-O3 and LINTULCC, respectively), but smaller variation (SD for both models: 1.2 t ha⁻¹). Average measured yield increase due to CO₂-doubling was 30% (SD 22%). AFRCWHEAT2-O3 expected a slightly lower value (24%, SD 9%), whereas LINTULCC overestimated the response (42%, SD 11%). The average measured yield decrease due to nearly-doubled O₃ levels was 9% (SD 11%). Both models showed similar results, albeit at lower variation (7% yield decrease at SDs of 6 and 4%). Simulations accounted well for the observation that, at elevated CO₂, the percentage yield loss due to O₃ was lower than at ambient CO₂.

The models predicted lower variation among sites and years than was measured. Yield response to CO₂ and O₃ was predicted to depend on the climate, with a predominant effect of temperature on the response to CO₂. In the measurements, these climatic effects were indeed observed, but a greater part of the variation was not related to light intensity, temperature, CO₂, or O₃. This unexplained variability in the measured dataset was probably caused by factors not accounted for in the models, possibly related to soil characteristics.

We therefore conclude that even perfect information on the climate variables examined in ESPACE-Wheat, i.e. light intensity and temperature, by itself would be insufficient for accurate prediction of the response of spring wheat to future elevated levels of CO₂ and O₃.     

Effects on nutrients and on grain quality in spring wheat crops grown under elevated CO2 concentrations and stress conditions in the European, multiple-site experiment ‘ESPACE-wheat’

Nutrient element concentrations and grain quality were assessed in spring wheat grown under elevated CO₂ concentrations and contrasting levels of tropospheric ozone at different nitrogen supply rates at several European sites. Carbon dioxide enrichment proved to affect nutrient concentrations in a complex manner. In green leaves, all elements (with exception of phosphorus and iron) decreased. In contrast, effects on the element composition of grains were restricted to reductions in nitrogen, calcium, sulphur and iron. Ozone exposure resulted in no significant effects on nutrient element concentrations in different tissues in the overall analysis. The nitrogen demand of green tissues was reduced due to CO₂ enrichment as shown by reductions in the critical leaf nitrogen concentration and also enhanced nitrogen use efficiency. Reductions in the content of ribulose-bisphosphate carboxylase/oxygenase and repression of the photorespiratory pathway and reduced nitrogen allocation to enzymes driving the photosynthetic carbon oxidation cycle were chiefly responsible for this effect. Thus, nitrogen acquisition by the crop did not match carbon acquisition under CO₂ enrichment. Since crop nitrogen uptake from the soil was already completed at anthesis, nitrogen allocated to the grain after anthesis originated from vegetative pools—causing grain nitrogen concentrations to decrease under CO₂ enrichment (on average by 15% when CO₂ concentrations increased from 360 to 680 μmol mol⁻¹). Correspondingly, grain quality was reduced by CO₂ enrichment. The Zeleny value, Hagberg value and dry/wet gluten content decreased significantly with increasing [CO₂]. Despite the beneficial impact of CO₂ enrichment on growth and yield of C₃ cereal crops, declines in flour quality due to reduced nitrogen content are likely in a future, [CO₂]-rich world.     

Phenological development, leaf emergence, tillering and leaf area index, and duration of spring wheat across Europe in response to CO2 and ozone

Phenological development, leaf emergence, tillering and leaf area index (LAI), and duration (LAD) of spring wheat cv. Minaret, grown in open-top chambers at different sites throughout Europe for up to 3 years at each site, were investigated in response to elevated CO₂ (ambient CO₂×2) and ozone (ambient ozone ×1.5) concentrations.

Phenological development varied among experiments and was partly explained by differences in temperature among sites and years. There was a weak positive relationship between the thermal rate of development and the mean daylength for the period from emergence to anthesis. Main stems produced on average 7.7 leaves with little variation among experiments. Variation was higher for the thermal rate of leaf emergence, which was partly explained by differences in the rate of change of daylength at plant emergence among seasons. Phenological development, rate of leaf emergence and final leaf number were not affected by CO₂ and ozone exposure. Responses of tillering and LAI to CO₂ and ozone exposure were significant only in some experiments. However, the direction of responses was consistent for most experiments. The number of tillers and ears per plant, respectively, was increased as a result of CO₂ enrichment by about 13% at the beginning of stem elongation (DC31), at anthesis and at maturity. Exposure to ozone had no effect on tillering. LAI was increased as a result of CO₂ elevation by about 11% at DC31 and by about 14% at anthesis. Ozone exposure reduced LAI at anthesis by about 9%. No such effect was observed at DC31. There were very few interactive effects of CO₂ and ozone on tillering and LAI. Variations in tillering and LAI, and their responses to CO₂ and ozone exposure, were partly explained by single linear relationships considering differences in plant density, tiller density and the duration of developmental phases among experiments. Consideration of temperature and incident photosynthetically active radiation in this analysis did not reduce the unexplained variation. There was a negative effect of ozone exposure on leaf area duration at most sites. Direct effects of elevated CO₂ concentration on leaf senescence, both positive and negative, were observed in some experiments. There was evidence in several experiments that elevated CO₂ concentration ameliorated the negative effect of ozone on leaf area duration. It was concluded from these results that an analysis of the interactive effects of climate, CO₂ and ozone on canopy development requires reference to the physiological processes involved.     

Interactive effects of elevated atmospheric CO2 concentrations and plant available soil water content on canopy evapotranspiration and conductance of spring wheat

The present study was conducted to investigate the possible interactive effects of rising atmospheric CO₂ concentration [CO₂] and drought stress on water use of wheat. Spring wheat (Triticum aestivum cv. “Minaret”) was grown either in 1 m diameter lysimeters with 0.4 m soil depth (1998) or in the field (1999) in open-top chambers under two CO₂-concentrations (ambient, ambient + 280 ppm) and two watering regimes (well-watered = WW with a plant available water content PAW > 40 mm and drought stressed = DS, 10 mm < PAW < 30 mm) beginning after first node stage. Canopy evapotranspiration (E_C) was measured continuously from first the node stage until the beginning of flag leaf senescence using four open-system canopy chambers (0.78 m³). Seasonal changes of the absorption of photosynthetically active radiation (APAR) of the canopy and root growth (1999) were also measured.

In both growing seasons leaf area index increased in response to elevated [CO₂] in both water treatments. The related effects of [CO₂] on canopy radiation absorption (APAR) were, however, smaller. E_C was linearily related to APAR in both growing seasons. While elevated [CO₂] reduced the slope of this relation under WW conditions by ca. 20% in both growing seasons, it was not reduced (1998) and even increased (1999) under drought. Canopy conductance (G_C) calculated as E_C divided by vapour pressure deficit of air, showed a non-linear relationship to APAR that was best explained by saturation curves. Under WW conditions, elevated [CO₂] reduced the initial slope of G_C versus APAR as well as G_C at saturating light conditions (ca. −30%), while under DS conditions no effect of elevated [CO₂] could be detected. Under high light conditions (PAR > 400 μmol m⁻² s⁻¹) a critical “threshold value” of PAW (T_PAW, ca. 40 mm) could be identified above which G_C did not respond to PAW. While in 1998 G_C did not respond to elevated [CO₂] at PAW < T_PAW, it was slightly increased at low PAW values in the field experiments of 1999. The reduction of T_PAW by elevated [CO₂] may be explained by enhanced root growth (1999) that would have given the plants better access to soil water resources. The present results suggest that below a critical soil water content elevated [CO₂] will not reduce canopy water loss of wheat or may even enhance it.     

Growth and yield responses of spring wheat to increasing carbon dioxide, ozone and physiological stresses: a statistical analysis of ‘ESPACE-wheat’ results

One of the major goals of the European Stress Physiology and Climate Experiment (ESPACE-wheat) was to investigate the sensitivity of wheat growth and productivity to the combined effects of changes in CO₂ concentration, ozone and other physiological stresses. Experiments were performed at different sites throughout Europe, over three consecutive growing-seasons using open-top chambers. This paper summarizes the main experimental findings of the effects of CO₂ enrichment and other factors i.e. ozone (O₃), drought stress or nitrogen supply on the biomass and yield of spring wheat (Triticum aestivum cv. Minaret). Final harvest data from different sites and seasons were statistically analysed: (1) to identify main effects and interactions between experimentally controlled factors; and (2) to evaluate quantitative relationships between environmental variables and biological responses. Generally, ‘Minaret’ wheat did not respond significantly to O₃, suggesting that this cultivar is relatively tolerant to the O₃ levels applied. The main effect of CO₂ was a significant enhancement of grain yield and above-ground biomass in almost all experiments. Significant interactions between CO₂ and other factors were not common, although modifications in different N- and water supplies also led to significant effects on grain yield and biomass. In addition, climatic factors (in particular: mean air temperature and global radiation) were identified as important co-variables affecting grain yield or biomass, repectively. On average, the yield increase as a result of a doubling of [CO₂] was 35% compared with that observed at ambient CO₂ concentrations. However, linear regressions of grain yield or above-ground biomass for individual experiments revealed a large variability in the quantitative responses of ‘Minaret’ wheat to CO₂ enrichment (yield increase ranging from 11 to 121%). Hence, CO₂ responsiveness was shown to differ considerably when the same cultivar of wheat was grown at different European locations. Multiple regression analyses perfomed to evaluate the relative importance of the measured environmental parameters on grain yield indicated that although yield was significantly related to five independent variables (24 h mean CO₂ concentration, 12 h mean O₃ concentration, temperature, radiation, and drought stress), a large proportion of the observed variability remained unexplained.     

Plant oil emulsion modifies internal atmosphere, delays fruit ripening, and inhibits internal browning in Chinese pears

'Laiyang Chili’ and ‘Ya Li’ (Pyrus bertschneideri Reld) pears were treated with 3, 6, and 9% emulsions of commercial or refined (reduced -tocopherol levels) plant (soybean, corn, peanut, linseed, and cottonseed) oils at harvest an stored at 0°C for 6 months. Effects of oil treatments on ethylene production, respiration, fruit firmness, fruit color, soluble solid content (SSC), titratable acids (TA), internal browning (IB), and internal CO₂, O₂, and ethanol were studied. At the same concentration, oil treatments induced similar responses regardless of their sources or their -tocopherol concentrations. In both cultivars, ethylene production and respiration in fruit treated with 9% oils were lower in early storage and higher in late storage than that in the controls. Oils at 6% reduced IB, at 9% inhibited IB completely, and at 3% was not effective after 6 months at 0°C and 7 days at 20°C. Plant oil treatment maintained fruit color, firmness, SSC, and TA in a concentration-dependent manner during storage. In the first 4 months storage, 9% corn oil-treated fruit contained similar partial pressure of CO₂ and O₂ as the controls. After 5 months storage, oil-treated fruit contained higher partial pressure of CO₂ and lower levels of O₂ than the controls. When held at 20°C for 7 days, changes of internal CO₂ and O₂ were slower but partial pressure of CO₂ were higher, and O₂ were lower, in 9% corn oil-treated fruit than in the controls. Internal ethanol was not affected by oil treatment compared with control, either during storage or 7 days at 20°C. No off-flavor was detected in either oil-treated and control fruit by sensory evaluation.     

Mortality of eggs and third instar larvae of Anastrepha ludens and A. obliqua with insecticidal controlled atmospheres at high temperatures

The in vitro mortality of eggs and third instar larvae of Anastrepha ludens and A. obliqua was determined after exposure to 21 treatments of air or controlled atmospheres (CA) at high temperatures and 50% RH. Air at 44°C for 160 min caused very low mortality, which increased significantly by CA. Higher temperatures caused a more rapid kill. One hundred percent mortality was achieved for third instar larvae of both species in air or CA at 48°C for 220 min. A 100% mortality of eggs of A. ludens was achieved in air at 51°C for 240 min or in CA at 52°C for 240 min, and 100% mortality of eggs of A. obliqua was achieved in air or in CA at 55°C for 240 min. A. obliqua was slightly more tolerant than A. ludens, and eggs were more tolerant than third instar larvae in both species. CA had a synergistic effect at <50°C, but was slightly less effective than air at higher temperatures. Low O₂ concentrations were more effective than high CO₂ levels. The mean estimated temperatures for 50, 99 and 99.9968% mortality (LT₅₀s, LT₉₉s, LT_99.9968s) of eggs of A. obliqua (the most tolerant) exposed to 0 kPa O₂+50 kPa CO₂ for 240 min were 49.4, 54.8 and 60.9°C, respectively. We conclude that dry hot air at ≥44°C and 50% RH in CA (0 kPa O₂+50 kPa CO₂), for 160 min or longer, is effective in increasing mortality of eggs and third instar larvae of A. ludens and A. obliqua.     

Simulation of growth and development processes of spring wheat in response to CO2 and ozone for different sites and years in Europe using mechanistic crop simulation models

The response of crop growth and yield to CO₂ and ozone is known to depend on climatic conditions and is difficult to quantify due to the complexity of the processes involved. Two modified mechanistic crop simulation models (AFRCWHEAT2-O3 and LINTULCC), which differ in the levels of mechanistic detail, were used to simulate the effects of CO₂ (ambient, ambient ×2) and ozone (ambient, ambient ×1.5) on growth and developmental processes of spring wheat in response to climatic conditions. Simulations were analysed using data from the ESPACE-wheat project in which spring wheat cv. Minaret was grown in open-top chambers at nine sites throughout Europe and for up to 3 years at each site.

Both models closely predicted phenological development and the average measured biomass at maturity. However, intermediate growth variables such as biomass and leaf area index (LAI) at anthesis, seasonal accumulated photosynthetically active radiation intercepted by the crop (ΣIPAR), the average seasonal light use efficiency (LUE) and the light saturated rate of flag leaf photosynthesis (A_sat) were predicted differently and less accurately by the two models. The effect of CO₂ on the final biomass was underestimated by AFRCWHEAT2-O3 due to its poor simulation of the effect of CO₂ on tillering, and LAI.LINTULCC overestimated the response of biomass production to changes in CO₂ level due to an overprediction of the effect of CO₂ on LUE. The measured effect of ozone exposure on final biomass was predicted closely by the two models. The models also simulated the observed interactive effect of CO₂ and ozone on biomass production. However, the effects of ozone on LAI, ΣIPAR and A_sat were simulated differently by the models and less accurately with LINTULCC for the ozone effects on LAI and ΣIPAR. Predictions of the variation between sites and years of growth and development parameters and of their responses to CO₂ and ozone were poor for both AFRCWHEAT2-O3 and LINTULCC. It was concluded that other factors than those considered in the models such as chamber design and soil properties may have affected the growth and development of cv. Minaret. An analysis of the relationships between growth parameters calculated from the simulations supported this conclusion. In order to apply models for global change impact assessment studies, the difficulties in simulating biomass production in response to CO₂ need to be considered. We suggest that the simulation of leaf area dynamics deserves particular attention in this regard.     

Combined effects of 1-methylcyclopropene, calcium chloride dip, and/or atmospheric modification on quality changes in fresh-cut strawberries

The aim of this study was to determine the effects of 1-methylcyclopropene, 1-MCP (1 μL L⁻¹ for 24 h at 5 °C) on quality attributes and shelf life of fresh-cut strawberries. The 1-MCP was applied before (whole product) and/or after cutting (wedges), followed by storage in a continuous flow of air or air +1 μL L⁻¹ C₂H₄. The combined effects of 1-MCP and CaCl₂ dips (1% for 2 min) and/or CA (3 kPa O₂ + 10 kPa CO₂) were also examined. The application of only 1-MCP before and/or after cutting did not have a significant effect on firmness and appearance quality during storage for up to 12 days at 5 °C. The exposure to a continuous flow of 1 μL L⁻¹ C₂H₄ in air during storage did not increase the softening rate. 1-MCP applied before cutting or both before and after cutting of the strawberries increased respiration rates but reduced C₂H₄ production rates. Exposure to 1-MCP had a synergistic effect when combined with CaCl₂ plus CA. The combined treatment of 1-MCP + CaCl₂ + CA slowed down softening, deterioration rates, TA and microbial growth. Compared to the control, which had a 6-day shelf life, the shelf life of fresh-cut strawberries subjected to the combination treatment was extended to 9 days at 5 °C.     

Storage characteristics and relationships between microbial growth parameters and shelf life of MAP sliced onions

Microbial proliferation and sensory quality aspects of sliced onions were tested at different temperatures (−2, 4 and 10 °C) and atmospheric conditions (with or without 40% CO₂ + 59% N₂ + 1% O₂). The relationships among microorganism growth parameters (the initial cell number (N₀), the maximum cell number (N_max), the maximum specific growth rate (μ_max) and lag-phase (λ)) and the microbial or sensory shelf life were determined. The microorganism growth parameters were obtained by fitting the modified Gompertz equation to the microbial counts. The results showed that color intensity (yellowness), sensory scores and microbial counts increased, and firmness decreased during storage. The total plate counts (TPC) provided the best indication of the spoilage organism growth capacity under tested temperatures and atmospheric conditions. The microbial shelf lives of the tested onions in 40% CO₂ + 59% N₂ + 1% O₂, or at −2, 4 and 10 °C, were 12.5, 9.5, 7, 12, 9 and 6 days, respectively, and their sensory shelf lives were 12, 8, 5, 10.5, 7 and 5 days, respectively. The lag time (λ) of the TPC, coliforms, pseudomonads and yeasts correlated well with the microbial and sensory shelf life results. The correlations between microbial and sensory shelf life, and the μ_max of TPC, lactic acid bacteria (LAB) and coliforms were between (−0.61 and −0.85). The initial microbial counts (N₀) of the five microorganisms showed a slight correlation, and the maximum microbial counts (N_max) of this group showed no obvious correlation with onion shelf life, apart from the LAB and yeasts.     

小麦脱植基相关基因在春性小麦叶片叶绿素降解过程中的作用分析

小麦叶片的衰老会导致产量的损失,而叶绿素降解是小麦叶片衰老的明显特征,分析小麦叶绿素降解过程中脱植基反应的相关基因叶绿素酶（TaCLH）和脱镁叶绿素水解酶（TaPPH）在春性小麦叶片衰老过程中的作用,为解析小麦叶绿素降解的分子机制提供参考。以10个春性小麦品种为参试材料,对衰老过程中TaCLH和TaPPH的相对表达量进行测定,结合不同品种在开花后不同时期的相对叶绿素含量（SPAD）、功能绿叶面积（GLAD）和叶绿素荧光参数的变化规律,研究叶片衰老过程中TaCLH和TaPPH与SPAD、GLAD和叶绿素荧光参数的相关关系。结果表明,TaPPH的相对表达量与GLAD、SPAD及叶绿素荧光参数[ETR、F_v/F_m、Y(Ⅱ)]等生理指标之间存在极显著负相关关系,与TaCLH相对表达量存在极显著正相关关系,表明TaPPH在春小麦叶绿素降解过程的脱植基反应中起主要作用。     

The effect of delays in establishment of a static or dynamic controlled atmosphere on the quality of ‘Hass’ avocado fruit

The effect of delays of 1, 5, 10 or 15 d after harvest in establishing a static controlled atmosphere (SCA) or dynamic controlled atmosphere (DCA) on the quality of ‘Hass’ avocados (Persea americana Mill.) was investigated. Fruit were stored at 5 °C in SCA (5% O₂/5% CO₂) or DCA (<3% O₂/0.5% CO₂) for 6 weeks and compared with fruit stored in air. In addition, to determine whether increasing the CO₂ in the DCA would affect the fruit quality, DCA-stored fruit were compared with fruit held in a DCA with 5% CO₂ (DCA + CO₂) established 1 d after harvest. The quality of fruit was assessed at the end of storage and after ripening at 20 °C. DCA-stored fruit ripened in 4.6 d compared with 7.2 d for SCA-stored fruit, or 4.8 d for air-stored fruit. In addition, the incidences of stem end rot (SER), body rot (BR) and vascular browning (VB) were lower in DCA-stored fruit (35%, 29% and 29%, respectively) than in SCA-stored fruit (57%, 52% and 49%, respectively), or air-stored fruit (76%, 88% and 95%, respectively). Delaying the establishment of both SCA and DCA for 15 d resulted in significantly more advanced skin colour at the end of storage (average rating score 11.9) compared with other delay periods (4.6–5.1). There was no significant effect of delay on the time to ripen, skin colour when ripe or any ripe fruit disorder incidence. The incidence of diffuse flesh discolouration (DFD) was not only <1% when averaged over all delays but only occurred at >0.5% incidence in the 15 d delay treatment in DCA (4.8%) and not in SCA. The incidence of diffuse flesh discolouration was 62% in air-stored fruit. Inclusion of 5% CO₂ in DCA retarded fruit ripening from 4.7 to 6.9 d and increased the incidence of rots at the end of storage from 5% to 14%, and increased the incidence in ripe fruit of SER from 30% to 56% and of BR from 27% to 55%. It is concluded that fruit quality was better after CA storage than after air storage, and that DCA storage was better than SCA. The effect of DCA is to independently reduce the time to ripen after storage and the incidence of rots when ripe. Delaying the application of SCA or DCA did not affect the expression of rots, but may increase the incidence of DFD. Inclusion of CO₂ at 5% in CA retarded fruit ripening but stimulated rot expression and should not be used for CA storage of New Zealand grown ‘Hass’ avocados.