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.     

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.     

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.     

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.     

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.     

Elevated CO2 increases wheat cer, leaf and tiller development, and shoot and root growth

Whole-plant responses to elevated CO₂ throughout the life cycle are needed to understand future impacts of elevated atmospheric CO₂. In this study, Triticum aestivum L. leaf carbon exchange rates (CER) and carbohydrates, growth, and development were examined at the tillering, booting, and grain-filling stages in growth chambers with CO₂ concentrations of 350 (ambient) or 700 (high) μmol mol^?1. Single-leaf CER values measured on plants grown at high CO₂ were 50% greater than those measured on plants grown at ambient CO₂ for all growth stages, with no photosynthetic acclimation observed at high CO₂. Leaves grown in high CO₂ had more starch and simple sugars at tillering and booting, and more starch at grain-filling, than those grown in ambient CO₂. CER and carbohydrate levels were positively correlated with leaf appearance rates and tillering (especially third-, fourth- and fifth-order tillers). Elevated CO₂ slightly delayed tiller appearance, but accelerated tiller development after appearance. Although high CO₂ increased leaf appearance rates, final leaf number/culm was not effected because growth stages were reached slightly sooner. Greater plant biomass was related to greater tillering. Doubling CO₂ significantly increased both shoot and root dry weight, but decreased the shoot to root ratio. High CO₂ plants had more spikes plant^?1 and spikelets spike^?1, but a similar number of fertile spikelets spike^?1. Elevated CO₂ resulted in greater shoot, root and spike production and quicker canopy development by increasing leaf and tiller appearance rates and phenology.     

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.     

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.     

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.     

大豆叶片响应CO2浓度升高、干旱及其交互作用的转录组分析

气候变暖及大气CO₂浓度升高成为全球共识,由此增加极端天气气候事件(干旱)发生的频率和强度并对大豆生产带来不确定性。本研究通过大豆表型和叶片转录组测序(RNA-seq)分析,阐释CO₂浓度升高、干旱及其交互条件对大豆基因表达影响,明确CO₂浓度升高影响大豆耐旱性的调控途径,并在两个不同遗传背景品种中验证,从分子水平为未来气候变化背景下大豆抗旱育种提供理论参考。表型结果表明, CO₂浓度升高促进了大豆的生长并缓解干旱胁迫的负面效应。叶片转录组测序分析共筛选到89个CO₂响应基因, KEGG分类显示这些基因主要参与抗氧化物质(萜类、黄酮类等)代谢,同时特异性差异表达基因功能主要集中在细胞组分和生长发育方面。干旱条件下筛选的1006个差异表达(16倍)基因主要参与各类氨基酸(脯氨酸、色氨酸等)代谢途径,绝大多数蛋白质合成与转运相关基因上调,表明干旱胁迫下大豆叶片内物质合成交换过程加强。交互条件下筛选出的8566个差异表达基因主要参与碳水化合物代谢,光合作用-天线蛋白途径的相关基因几乎...     

Effects of soil drought during the vegetative phase of seedling growth on the uptake of 14co2 and the accumulation and translocation of 14C in cultivars of field bean (vicia faba L. Var. Minor) and field pea (pisum sativum L.) Of different drought tolerance

During the vegetative phase of growth of two field bean and two field pea cultivars of different drought tolerance, the effect of short and prolonged soil drought on gas exchange (CO₂ i H₂O), leaf water potential (ψ), stomatal diffusive resistance (r_S), uptake of CO₂, and the distribution and accumulation of ¹⁴C was studied. Differences in the response to drought conditions between resistant and susceptible cultivars were marked. After 5 days of soil drought, the decrease in net photosynthesis and transpiration rate and the increase of stomatal resistance were greater in the drought-resistant cultivars than in the drought-susceptible ones. In contrast, after 10 days of drought the decrease of leaf P_N (CO₂ assimilation rate), E (rate of transpiration) and ψ (water potential) was greater in the susceptible cultivars than in the resistant ones. Significant differences between the resistant and the susceptible cultivars were also observed in the assimilation and translocation of ¹⁴C by the green parts of the plant. The amount of carbon accumulation in roots in drought-susceptible cultivars increased less than in the drought-resistant cultivars. For treatments in which optimal soil watering was resumed after 5 or 10 days of drought there was no evidence of effects of drought on the majority of measurements, but the drought-resistant cultivars showed a general tendency for a more rapid recovery. Our results confirm the existence of genetic variability in drought tolerance among the cultivars of field bean and field pea. The recorded differences in the response to drought of experimental cultivars may indicate that, under water deficit in the soil and in plant tissues, they may use different strategies to avoid the damaging effects of temporary limitation of water supply; for example, the drought-resistant cultivars may more effectively conserve tissue hydration through effective stomatal closure. Also, the observed changes in carbon assimilation and accumulation might be the reason for their different responses to drought. The change in radioactivity losses in the control and stressed plants may result from the differences in demand for energy to maintain cell structure and function. Similarly, the less intense carbon accumulation in the roots of the sensitive cultivars could be caused by more harmful effects of drought on root growth.