Response of Photosynthesis and Water Relations of Rice (Oryza sativa) to Elevated Atmospheric Carbon Dioxide in the Subhumid Zone of Sri Lanka

The objective of the present paper is to determine the response of the physiological parameters related to biomass production and plant water relations in a standard Sri Lankan rice (Oryza sativa) variety (BG‐300) to elevated CO₂ (i.e. 570 µmol/mol). During two seasons, rice crops were grown under three different experimental treatments; namely, at 570 µmol/mol (i.e. ‘elevated’) and 370 µmol/mol (‘ambient’) CO₂ within open top chambers, and at ambient CO₂ under open field conditions. Leaf net photosynthetic rate in the elevated treatment increased by 22–75 % in comparison to the ambient. However, the ratio between intercellular and ambient CO₂ concentrations remained constant across different CO₂ treatments and seasons. CO₂ enrichment decreased individual leaf stomatal conductance and transpiration rate per unit leaf area, and increased both leaf and canopy temperatures. However, the overall canopy stomatal conductance and daily total canopy transpiration rate of the elevated treatment were approximately the same as those achieved under ambient conditions. This was because of the significantly greater leaf area index and greater leaf–air vapour pressure deficit under CO₂ enrichment. The leaf chlorophyll content increased significantly under elevated CO₂; however, the efficiency (i.e. photochemical yield) of light energy capture by Photosystem II (i.e. F_v/F_m) in chlorophyll a did not show a significant and consistent variation with CO₂ enrichment.     

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.     

Genotypic Variation in the Response of Rice (Oryza sativa L.) to Increased Atmospheric Carbon Dioxide and its Physiological Basis

Increasing atmospheric carbon dioxide concentration (C_a) is one aspect of global change that will have a significant impact on the productivity of agricultural crops. Crop yields have been shown to increase with increasing C_a. The magnitude of yield response to increased C_a could vary depending on genotypic and environmental factors. The objective of this study was to determine the genotypic variation of yield response and its physiological basis in rice (Oryza sativa L.) through an initial varietal screening using 16 genotypes. The genotypes were grown under two concentrations of C_a, i.e. 370 ± 28 (ambient) and 570 ± 42 (elevated) μmol mol⁻¹, in open top chambers under lowland field conditions at the Rice Research and Development Institute in Sri Lanka (7°50′N, 80°50′E) from May to August 2001 (yala season) and from November 2001 to March 2002 (maha). C_a within chambers was maintained around target concentrations by a computer‐based real‐time data acquisition and control system. There was significant variation between genotypes in the response of yield to elevated C_a, with absolute increases up to 530 g m⁻² in yala and 347 g m⁻² in maha. In relative terms, percentage yield increases from ambient to elevated C_a ranged from 4 % to 175 % in yala and from 3 % to 64 % in maha. Genotypic variation in yield showed significant positive correlations with light‐saturated net photosynthetic rate of the flag leaf during the grain‐filling stage. This indicated that increased assimilate supply and its genotypic variation contributed to the observed genotypic variation in yield response to elevated C_a. Furthermore, the capacity to develop a larger reproductive sink through increased panicle number per m² and increased number of grains per panicle contributed to greater yield at elevated C_a. There was a significant genotype × season interaction with genotypes responding differentially to increased C_a in the two seasons. This was mainly due to inter‐seasonal variation in incident radiation during the grain‐filling stage. Our results demonstrate the significant genotypic variation that exists within the rice germplasm, in the response to increased C_a of yield and its correlated physiological parameters. A subset of genotypes from screening trials such as the present study can be used for more in‐depth analysis of the influence of elevated C_a on processes responsible for yield determination in rice and for molecular studies to elucidate the genetic basis of the response to increased C_a. This could pave the way for breeding genotypes which are more productive in a future high CO₂ environment, provided that genotypes with greater flexibility in their physiology are selected to counter the genotype × environmental interaction.     

Respiration and Growth of Sorghum and Sunflower under Predicted Increased Night Temperatures1

Little information exists concerning how crops will respond to the predicted increased night temperatures. The objective of this work was to determine if respiration and growth of sorghum [Sorghum bicolor (L.) Moench], a C, plant, and sunflower (Helianthus annuus L.), a C₃ plant, are affected when the night temperature is increased by 5°C compared to the long-term (19 year) average night temperature in June in Kansas. Sorghum and sunflower were grown in two walk-in growth chambers with either the ambient night temperature (21C) or a high night temperature (26C). Day temperature was the same for all plants (27C). Both sunflower and sorghum had higher respiration rates under the elevated night temperature than under the ambient temperature. The average respiration rate of sunflower grown under elevated night temperature increased by 19% (0.89 vs. 0.75 μmol m^?2 s^?1) and that of sorghum by 44 % (0.52 vs. 0.36μmol m^?2s^?1). After 74 days, sunflower plants grown under the ambient night temperature were 30.2 cm taller than sunflower plants grown under the elevated night temperature; sorghum plants under the ambient temperature were 24.8 cm taller. Sunflower plants grown under the elevated night temperature formed flowers one week earlier than those grown under the ambient temperature. Sorghum formed no flowers by 74 days. Results suggest that, if climate change does increase night temperature, respiration will be increased more in C₄, than C₃ plants.     

Heat,wheat and CO2: The relevance of timing and the mode of temperature stress on biomass and yield

Atmospheric CO₂ enrichment affects C3 crops both directly via increased carbon gain and improved water use efficiency and indirectly via higher temperatures and more frequent climatic extremes. Here we investigated the response of spring wheat (Triticum aestivum L. cv. Triso) to CO₂ enrichment (550 vs. 380 µmol/mol) and heat, applied as a constant +4°C increase or a typical heat wave either before or after anthesis, or as two typical heat waves before and after anthesis. We applied a climate chamber approach closely mimicking ambient conditions. CO₂ enrichment increased above‐ground biomass and yield by c. 7 and 10%, but was not able to compensate for adverse heat stress effects, neither before nor after anthesis, with few exceptions only. Yield depression due to heat stress was most severe when two heat waves were applied (?19%). This adverse effect was, however, compensated by CO₂ enrichment. Applying heat stress before or after anthesis did not exert different effects on yield for both +4°C warming and heat wave application. However, +4°C depressed yield more than a heat wave at ambient CO₂, but not so at elevated CO₂. Thus, the interactive effects were complex and prediction of future wheat yield under CO₂ enrichment and climate extremes deserves more attention.     

Do Increasing Atmospheric CO2 Concentrations Contribute to Yield Increases of German Crops?

The global atmospheric CO₂-concentration is increasing and there has been an increase in Germany of about 30 ppm from 340 ppm to 370 ppm CO₂ during the last two decades. The hectare yield of many crops has also increased during this time period. The objective of the present study was to estimate whether the past and future change in the atmospheric composition significantly contributes to the increase in hectare yield. Different crop species (beans, Phaseolus vulgaris, cv Pfälzer Juni; spring barley, Hordeum vulgare L., cvs. Alexis and Arena; spring wheat, Triticum aestivum L., cvs. Star and Turbo; maize, Zea mays L., cvs. Bonny and Boss) were grown at ambient (372 ppm) and at slightly elevated CO₂-concentrations (459 ppm and 539 ppm) in open-top chambers and the effect of the different CCVconcentrations on the growth and yield of the plants was measured. The past and future CO₂-effect was estimated from the slope of a linear CO₂-yield curve (percentage increase in yield per ppm CO_2′ 100% at 370 ppm) fitted to the data and those from previous studies on wheat and maize. The percentage increase in yield per ppm CO₂ is insignificant for beans, of borderline significance for silage maize (0.06 % per ppm), and 0.35 % per ppm and 0.26 % per ppm for barley and wheat, respectively. The COj-elevation primarily decreases the tiller dieback of the cereals. Considering the increase in CO₂ of 30 ppm and in the hectare yield of 25 % (barley) and 28 % (wheat) from 1970 to 1990, the contribution of CO₂ to the increase in the agricultural production is estimated to be one fourth up to one half of the increase in hectare yield of spring cereals. Given a recent yearly increase of 2 ppm the future CO_:-related increase in hectare yield is estimated to be about 0.5–0.7% per year.     

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.     

Apical Development and Growth of Barley under Different CO2 and Nitrogen Regimes

Increases in atmospheric carbon dioxide (CO₂) concentration have stimulated interest in the response of agricultural crops to elevated levels of CO₂. Several studies have addressed the response of C₃ cereals to CO₂, but the interactive effect of nutrient supply and CO₂ on apical development and spikelet set and survival has not been investigated thoroughly. Hence, an experiment was conducted in the greenhouse to evaluate the effect of high (700 μmol CO₂mol^?1 air) and low (400 μmol mol^?1) levels of atmospheric CO₂ on apical development, spikelet set and abortion, and pre- and post-anthesis growth in spring barley (Hordeum vulgare L.) grown under high N (0.3 g N pot^?1 before sowing ?1–0.11 g N pot^?1 week^?1) and low N (0.3 g N pot^?1) regimes. The plants were grown in 5 L pots. Development of spike was hastened due to CO₂ enrichment, and the C+ plants pollinated few days earlier than the C— plants. Carbon dioxide enrichment had no effect on date of ripening. Development of spike slowed following application of extra N, and plants pollinated 10 days later and matured 2 weeks later when compared with plants under low N. Carbon dioxide enrichment did not affect the number of spikelets at anthesis. Excess N decreased spikelet abortion and the increased maximum number of spikelets under both [CO₂]. Barley plants did not tiller when grown in low [CO₂] and low N. Increased endogenous IAA concentration in those plants, recorded three days before tillers appeared in other treatments, may have contributed to this. Carbon dioxide enrichment increased the C concentration of plants, but decreased the N concentration under high N regime. Both the C and N concentration of plants were increased under high N regime. Carbon dioxide enrichment increased the total dry matter of mature plants by 9 % under high N regime and by 21 % under low N regime. Under high [CO₂] increased kernel number on tiller spikes, and increased kernel weight both on main stem and on tiller spikes resulted in a 23 % increase in kernel yield under low N regime and 76 % increase in kernel yield under high N regime. The rate of N application influenced growth and yield components to a greater extent than CO₂ enrichment. At maturity, plant dry matter, kernel weight, the number of kernels per spike, and the number of spikes per plant were higher under high N regime than under low N regime. Long days (16 h), low light intensity (280 μmol m^?2s^?1), and at constant temperature of 20 °C high [CO₂] increased kernel weight and the number of kernels on tiller spikes under high and low N application rate, but did not increase the number of kernels on main stem spike, or the number of tillers or tiller spikes per plant.     

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.     

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.     

Response of Mung Bean (Vigna radiata (L.) R. Wilczek) to an Increasing Natural Temperature Gradient under Different Crop Management Systems

Increasing temperatures pose a significant threat to crop production in the tropics. A field experiment was conducted with mung bean at three locations in Sri Lanka representing an increasing temperature gradient (24.4–30.1 °C) during two consecutive seasons to (i) determine the response of mung bean to increasing temperature and (ii) test a selected set of crop management practices aimed at decreasing essential inputs such as water, synthetic pesticides and inorganic nitrogen fertilizer. The control treatment (T₁) consisted of standard crop management including irrigation, chemical crop protection and inorganic fertilizer application. Adaptation system 1 (T₂) included mulching with rice straw at 8 t ha^?1 with 30 % less irrigation and crop protection and nutrient management as in T₁. Adaptation system 2 (T₃) included crop protection using a pretested integrated pest management package with water and nutrient management as in T₂. In adaptation system 3 (T₄), 25 % of the crop's nitrogen requirement was given as organic manure (compost) at 0.8 t ha^?1 while 75 % was given as inorganic fertilizer with water management and crop protection as in T₃. Durations of both pre‐ and post‐flowering phases were reduced with increasing temperature. In the warmer (25.4–30.1 °C) yala season, seed yield (Y) of T₁ decreased with increasing temperature at 366 kg ha^?1 °C^?1. However, in maha season, Y did not show a significant relationship across the narrower temperature gradient from 24.4 to 25.8 °C. Pooling the data from both seasons showed a second‐order polynomial response with an optimum temperature of 26.5 °C. In addition to shortened durations, reduced crop growth rates and reduced pod numbers per plant were responsible for yield reductions at higher temperatures. In yala, yields of all adaptation systems at all locations were on par with yields of the respective controls. Furthermore, yala yields of T₂ and T₃ were less sensitive than T₁ to increasing temperatures (265 and 288 kg ha^?1 °C^?1). In maha, T₃ and T₄ had greater yields than the control at the relatively cooler site while having lower yields than the control at the warmer site. Maha yields of T₂ were on par with the control at both temperature regimes. While demonstrating the significant temperature sensitivity of mung bean yields, results of the present work showed that components of the tested adaptation systems could be promoted among smallholder farmers in Asia, especially in view of their long‐term environmental benefits and contributions to sustainable agriculture in a warmer and drier future climate.     

开放式空气CO2浓度升高对稻米品质的影响

了解大气CO₂浓度升高对粳稻和籼稻稻米品质的影响,为今后合理筛选育种材料提供依据。以粳稻Asominori与籼稻IR24为材料,田间试验,于2003年和2004年连续2年在FACE（Free Air CO₂ Enrichment,大气CO₂浓度增加200μmol/mol）和正常大气CO₂浓度（约370μmol/mol）下,分析了稻米的加工品质、外观品质和蒸煮食味品质。与对照相比,两年内IR24和Asominori的糙米率、精米率和整精米率等加工品质都显著降低了,降低幅度分别为-3.14%~-0.21%和-3.14%~-0.33%;FACE对水稻粒长、粒宽以及粒形无显著影响;但与对照相比,IR24和Asominori的垩白米率却由对照下的29.63%和30.81%显著降低至18.93%和24.78%;FACE对两品种精米中直链淀粉含量无显著影响,但对RVA(Rapid Viscosity Analyzer)谱中各指标影响显著,其中FACE处理显著提高了两品种的最高粘度,而崩解值、消减值和糊化温度由于受到其它互作效应的影响两年的变化趋势不尽相同,蒸煮食味品质变化复杂;此外,IR24和Asominori的粗蛋白含量由对照下的11.77%和10.23%显著降低至10.97%和9.91%。两年内,IR24和Asominori除加工品质和食味品质表现趋势相同外,外观品质和蒸煮品质表现出籼稻IR24对CO₂浓度升高的响应程度大于粳稻Asominori。     

The Alleviating Effect of Elevated CO2 on Heat Stress Susceptibility of Two Wheat (Triticum aestivum L.) Cultivars

This study analysed the alleviating effect of elevated CO₂ on stress‐induced decreases in photosynthesis and changes in carbohydrate metabolism in two wheat cultivars (Triticum aestivum L.) of different origin. The plants were grown in ambient (400 μl l^?1) and elevated (800 μl l^?1) CO₂ with a day/night temperature of 15/10 °C. At the growth stages of tillering, booting and anthesis, the plants were subjected to heat stress of 40 °C for three continuous days. Photosynthetic parameters, maximum quantum efficiency of photosystem II (PSII) photochemistry (F_v/F_m) and contents of pigments and carbohydrates in leaves were analysed before and during the stress treatments as well as after 1 day of recovery. Heat stress reduced P_N and F_v/F_m in both wheat cultivars, but plants grown in elevated CO₂ maintained higher P_N and F_v/F_m in comparison with plants grown in ambient CO₂. Heat stress reduced leaf chlorophyll contents and increased leaf sucrose contents in both cultivars grown at ambient and elevated CO₂. The content of hexoses in the leaves increased mainly in the tolerant cultivar in response to the combination of elevated CO₂ and heat stress. The results show that heat stress tolerance in wheat is related to cultivar origin, the phenological stage of the plants and can be alleviated by elevated CO₂. This confirms the complex interrelation between environmental factors and genotypic traits that influence crop performance under various climatic stresses.     

Does interspecific competition change the barley's response and recovery from heat wave?

Different species have different sensitivity to heat waves; therefore, interspecific competition may affect the crop response to heat waves. We investigated the effects of heat waves on spring barley (Hordeum vulgare L.) grown with and without wild mustard (Sinapis arvensis L.) as well as the recovery of barleys from stress. The plants were exposed to a 7‐day 35/28ºC (day/night) heat wave at ambient CO₂ (400 μmol/mol) and elevated CO₂ (800 μmol/mol). All seedlings were rehydrated and returned to control conditions (21/14ºC, CO₂ 400 μmol/mol) after the cease of heat wave and grown for a 7‐day period of recovery. Heat wave had more pronounced negative effect on the barley's aboveground biomass under competition with mustard, whereas the response of root biomass was not influenced by the presence of weeds. The heat wave induced reductions in barley's photosynthetic rate, stomatal conductance and water use efficiency under interspecific competition were higher compared to monocultured conditions. Interspecific competition impaired and delayed the recovery of barley's biomass production and leaf gas exchange parameters after heat wave. Elevated CO₂ slightly mitigated negative heat wave impact on the growth and leaf gas exchange parameters but had no effect during the recovery period.     

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.     

Role of Arbuscular Mycorrhiza in Alleviating Salinity Stress in Wheat (Triticum aestivum L.) Grown Under Ambient and Elevated CO2

Plant growth and development are influenced by future elevated atmospheric CO₂ concentration and increased salinity stress. AM (arbuscular mycorrhiza) symbiosis has been shown to improve plant growth and resistance to environmental stresses. The aim of this study was to investigate the potential role of AM fungus in alleviating salinity stress in wheat (Triticum aestivum L.) plants grown under ambient and elevated CO₂ concentrations. Wheat plants inoculated or not inoculated with AM fungus were grown in two glasshouses with different CO₂ concentrations (400 and 700 μmol l^?1) and salinity levels (0, 9.5 and 19.0 dS m^?1). Results showed that salinity stress decreased and elevated CO₂ increased AM colonization. AM inoculation increased plant dry weight under elevated CO₂ and salinity stress. Stomatal conductance, density, size and aperture of AM plants were greater than non‐AM plants. AM fungi enhanced NUE by altering plant C assimilation and N uptake. AM plants had higher soluble sugar concentration and [K⁺]: [Na⁺] ratio compared with non‐AM plants. It is concluded that AM symbiosis improves wheat plant growth at vegetative stages through increasing stomatal conductance, enhancing NUE, accumulating soluble sugar, and improving ion homeostasis in wheat plants grown at elevated CO₂ and salinity stress.     

Effect of Phosphorus Nutrition on Growth and Physiology of Cotton Under Ambient and Elevated Carbon Dioxide

Phosphorous deficiency in soil limits crop growth and productivity in the majority of arable lands worldwide and may moderate the growth enhancement effect of rising atmospheric carbon dioxide (CO₂) concentration. To evaluate the interactive effect of these two factors on cotton (Gossypium hirsutum) growth and physiology, plants were grown in controlled environment growth chambers with three levels of phosphate (Pi) supply (0.20, 0.05 and 0.01 mm ) under ambient and elevated (400 and 800 μmol mol^?1, respectively) CO₂. Phosphate stress caused stunted growth and resulted in early leaf senescence with severely decreased leaf area and photosynthesis. Phosphate stress led to over 77 % reduction in total biomass across CO₂ levels. There was a below‐ground (roots) shift in biomass partitioning under Pi deficiency. While tissue phosphorus (P) decreased, tissue nitrogen (N) content tended to increase under Pi deficiency. The CO₂ × Pi interactions were significant on leaf area, photosynthesis and biomass accumulation. The stimulatory effect of elevated CO₂ on growth and photosynthesis was reduced or highly depressed suggesting an increased sensitivity of cotton to Pi deficiency under elevated CO₂. Although, tissue P and stomatal conductance were lower at elevated CO₂, these did not appear to be the main causes of cotton unresponsiveness to elevated CO₂ under severe Pi‐stress. The alteration in the uptake and utilization of N was suggested due to a consistent reduction (18–21 %) in the cotton plant tissue N content under elevated CO₂.     

Free Air CO2 Enrichment (FACE) of grapevine (Vitis vinifera L.): II. Growth and quality of grape and wine in response to elevated CO2 concentrations

A FACE (Free Air CO₂ Enrichment) experiment was carried out on Grapevine (Vitis vinifera L.) in 1996 and 1997 in an existing vineyard in Italy. Four FACE arrays were used to fumigate adults plants, while two arrays were used as control. Three CO₂ exposure levels were used in these arrays (ambient, 550 and 700 μmol mol⁻¹). Dynamics of vegetative and reproductive biomass and grape quality compounds (sugar and acid concentrations) were monitored during the two growing seasons. Chemical analyses of the main wine quality compounds were made after fermentations. Elevated atmospheric CO₂ levels had a significant effect on biomass components (total and fruit dry weight) with increases that ranged from 40 to 45% in the 550 μmol mol⁻¹ treatment and from 45 to 50% in 700 μmol mol⁻¹ treatment. Acid and sugar contents were also stimulated by rising CO₂ levels up to a maximum increase in the middle of the ripening season (8–14%); however, as the grapes reached the maturity stage the CO₂ effect on both quality parameters almost completely disappeared. Wine quality was not significantly affected by elevated CO₂. Furthermore, no significant differences were detectable among the plants grown in the two enriched treatments (550 and 700 μmol mol⁻¹), and the effects of elevated CO₂ concentration were similar in the two growing seasons. The absence of any further stimulation of the highest CO₂ treatment (700 μmol mol⁻¹) on grapevine growth and yield quality (i.e. grapes and wine) may be explained as a result of transport and/or sink limitations. We can conclude that the expected rise in CO₂ concentrations may strongly stimulate grapevine production without causing negative repercussions on quality of grapes and wine.     

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.     

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.