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

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

Response of Growth and Yield of Rice (Oryza sativa) to Elevated Atmospheric Carbon Dioxide in the Subhumid Zone of Sri Lanka

Increasing atmospheric CO₂ is recognized as a major aspect of global climate change that would have a significant impact on the productivity of major agricultural crops. Two field experiments were done, with the objective of quantifying the response of a short‐duration rice (Oryza sativa) variety (BG‐300) to elevated atmospheric carbon dioxide, in the low elevation, subhumid zone of Sri Lanka. The experiment contained three treatments. In the elevated CO₂ treatment, rice was grown at a CO₂ concentration of 570 µmol/mol within open top chambers (OTC s). The ambient CO₂ treatment included crops grown within OTC s, but maintained at the ambient CO₂ concentration of 370 µmol/mol. The third treatment was a crop grown in the open field under ambient CO₂ concentration. Grain yields of rice crops grown under elevated CO₂ were 24 % and 39 % greater than the respective ambient treatments in the maha (January – March 2001) and yala (May – August, 2001) seasons. Significant increases in total biomass at harvest (23 % and 39 %, respectively, in maha and yala) were more responsible for the above yield increases than the slight increases in the harvest index (4 % and 2 %). Yields of the ambient and open field treatments did not differ significantly. Among the yield components, the number of panicles per hill was significantly higher in the elevated treatment and showed significant positive correlations with grain yield in both seasons. In addition, grain yield showed significant positive correlations with the percentage of filled grains in maha and the number of grains per panicle in yala. Significant increases in the number of tillers per hill under elevated CO₂ were responsible for its greater leaf area index and the greater numbers of panicles per hill. Crops under elevated CO₂ accumulated biomass faster than those grown under ambient CO₂ during the vegetative and grain‐filling stages. The results of this study demonstrate that elevated CO₂ causes significant yield increases in rice, even when it is grown in warm, subhumid tropical climates.     

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.     

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 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.     

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.     

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.     

Sensitivity of Two Quinoa (ChenopodiumquinoaWilld.) Varieties to Progressive Drought Stress

Quinoa (ChenopodiumquinoaWilld.) is a highly nutritious Andean seed crop which shows great potential to grow under a range of hostile environments. The objective of this study was to investigate the differences of drought tolerance of a Bolivian (Achachino) and a Danish (Titicaca) variety, and especially drought‐related adaption strategies. Soil water status was expressed as the fraction of transpirable soil water (FTSW). Relative stomatal conductance (RSC), relative transpiration (RT) and relative leaf water potential (RLW) were calculated by determining stomatal conductance, transpiration rate and leaf water potential of the drought‐treated plants relative to those of fully irrigated plants. The responses of RSC, RT and RLW to decreasing FTSW were described by a linear‐plateau model. The critical value of FTSW was the threshold of FTSW where the parameters studied decreased. The thresholds increased C_S for stomatal conductance, C_T for transpiration and C_Lfor leaf water potential. Achachino showed significantly lower C_T and C_L when compared with Titicaca, implying that transpiration and leaf water potential were less affected under mild drought conditions in the Bolivian variety. C_S in Achachino was significantly higher than C_L and C_T, which indicated that stomatal conductance declined before transpiration and leaf water potential were reduced. Such difference was found in Titicaca where reduction of leaf area had more effect on transpiration than stomatal closure. Slower growth rate and smaller leaf area in combination with a lower stomatal conductance was found to contribute to drought resistance in Achachino. ABA concentration in the xylem sap tended to increase in both varieties after 2 days onset of drought, prior to decline in leaf water potential. Titicaca showed significantly (P < 0.05) higher ABA concentration when compared with Achachino under both fully irrigated and drought conditions. Titicaca had higher xylem nutrient concentration in comparison with Achachino in both fully‐watered and drought plants at day 2 after onset of soil drying. It was concluded that Titicaca was more sensitive to progressive drought than Achachino which avoided water loss by means of lower growth rate and smaller leaf area.     

不同温型早籼稻叶片光合及生理性状的差异

本研究旨在明确不同温型早籼稻气冠温差(CTD)与叶片光合及生理性状的关系,为快速筛选优质种质资源以及制定合理的栽培调控措施提供理论依据。选用低温型和高温型早籼稻品种各3个作为试验材料,在相同栽培管理措施下,监测孕穗期、抽穗期各品种冠层温度与大气温度,并测定叶片光合性状、叶绿素相对含量(SPAD)、超氧化物歧化酶(SOD)、过氧化氢酶(CAT)和过氧化物酶(POD)活性、丙二醛、可溶性糖及可溶性蛋白含量,以明确气冠温差与叶片光合及生理性状的关系。结果表明：与高温型品种相比,低温型品种有较高的净光合速率、气孔导度和蒸腾速率,可溶性糖和叶绿素含量也较高,且SOD、CAT、POD活性较强,丙二醛含量较低,但可溶性蛋白含量总体相差不大。相关性分析表明,早籼稻CTD与剑叶净光合速率、气孔导度、蒸腾速率呈显著正相关,与胞间CO₂浓度呈负相关,但未达到显著水平。CTD与叶片可溶性糖含量,SPAD值和SOD酶活性显著正相关,与丙二醛含量呈显著负相关。     

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.     

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.     

氮素对高大气CO2浓度下小麦叶片光合功能的影响

为探讨高大气CO₂浓度下植物光合作用适应现象的光合能量转化和分配的氮素响应及其对C₃植物光合功能的影响,本试验对盆栽小麦进行2个大气CO₂浓度和2个氮水平的组合处理,通过测定小麦光合气体交换参数、叶绿素荧光参数和叶绿素含量等指标,研究施氮对高大气CO₂浓度下小麦叶片光合功能的影响。结果表明,大气CO₂浓度升高后,低氮处理小麦叶片光合速率发生明显的适应性下调,光合速率(P_n)、气孔导度(G_s)、蒸腾速率(T_r)下降;但高氮叶片则无明显的光合作用适应现象发生。高大气CO₂浓度下低氮叶片光化学速率、PSII线性电子传递速率(J_F)、光合电子流的光化学传递速率(J_C)、Rubisco羧化速率(V_C)和TPU下降,并随生育时期推进其下降趋势更为明显,但高氮叶片的上述参数无显著变化;小麦叶片J_C/J_F、V_C/J_C和V₀ /V_C随氮素水平和大气CO₂浓度的变化无显著变化,表明施氮能提高光合机构对光合能量的传递速率,但对光合能量的分配方向无明显影响。施氮提高小麦叶片氮素和叶绿素含量,并且使高大气CO₂浓度下光合氮素利用效率(NUE)明显增加。大气CO₂浓度升高后,施氮增强光合机构的光合能量运转速率,同化力提高,无明显的光合作用适应现象;由于氮素水平与大气CO₂浓度对小麦叶片的光合能量利用存在明显的交互作用,而且高大气CO₂浓度下施氮使得小麦叶片NUE增加、正常大气CO₂浓度下降低,证明高大气CO₂浓度下施氮对光合作用具有直接的影响。     

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

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

瞬时CO2浓度变化对杏属植物光合生理影响研究

为探讨CO2浓度瞬时变化对杏碳同化能力、水分利用能力的影响,进一步了解杏属植物在未来大气CO2浓度升高和全球变暖情况下的生长潜力和生态优势。作者利用Li-6400便携式光合测定仪对15个2年生杏品种进行瞬时CO2浓度倍降和倍升处理的光合参数测定。结果表明,瞬时CO2浓度变化显著影响杏属植物光合作用,在瞬时CO2浓度升高情况下,最大净光合速率(Amax)升高,呼吸速率(Rd)下降,光补偿点(LCP)降低,表光量子效率(AQY)提高,水分利用效率(WUE)显著增强,但光饱和点(LSP)变化不显著,不同品种Gs和Tr反应有一定差异。适当增加CO2浓度能提高杏属植物对弱光和水分的利用能力,促进光合作用,增加同化物积累,加速碳素循环。     

叶面肥“天达-2116植物细胞膜稳态剂”对烟草叶片气体交换特征的影响

摘要：为了揭示叶面肥“天达-2116”对烟草光合速率的影响,本试验对比分析了喷施和不喷施叶面肥“天达-2116”两种处理下,旺长期叶片的光合速率、蒸腾速率、气孔导度以及水分利用率对光强响应特征。结果表明：喷施叶面肥时烟草的光合速率、蒸腾速率、气孔导度都随光强的增强而逐渐增大。不喷施条件下,蒸腾速率和气孔导度随光强的增强而逐渐增大,而在高光强（>1200μmol s-1m-2）下,会产生光饱和现象。喷施叶面肥“天达-2116”条件下的光合速率、蒸腾速率、气孔导度均高于不喷施的,但并未改变水分利用效率。因此,适量喷施叶面肥“天达-2116”可以显著改善烟草叶片的的光合生理性状和气体交换能力。     

不同供水条件下小麦不同绿色器官的气孔特性研究

为了考察小麦叶片与非叶器官气孔结构特性的差异及其对供水条件的反应，本研究设置不同灌水处理，利用电镜观察小麦灌浆期不同绿色器官的气孔分布和结构特征，并分析其与气孔特性指标间的关系。结果表明，在不同灌水处理下看到各非叶器官（穗、旗叶鞘和穗下节间）均分布着气孔，但其数目少于旗叶叶片。护颖仅在远轴面存在气孔；外稃在多水条件下（4水处理）近轴面出现较多气孔，而远轴面看不到气孔，但在水分胁迫（无水处理）条件下，气孔却出现在远轴面而不在近轴面；在不同水分处理下均观察到芒上明显的气孔分布。从气孔大小看，穗各部分（护颖、外稃、内稃和芒）略小于其他器官。随着灌水次数的减少，各器官气孔密度呈增大趋势，气孔器及气孔孔径表现出长度增加、宽度减小的特征。限水灌溉下非叶器官（穗、旗叶鞘和穗下节间）在籽粒灌浆期气孔导度、蒸腾速率和光合速率的稳定性高于叶片。相关分析表明，不同器官的气孔导度与蒸腾速率均呈显著正相关，非叶器官气孔导度与光合速率的相关程度明显低于叶片。说明在干旱少水条件下，叶与非叶器官蒸腾作用均会减弱，叶片光合速率亦相应降低，而非叶器官光合速率可能保持相对稳定，可相对提高其水分利用效率。     

Leaf Area Index,Leaf Transpiration and Stomatal Conductance as Affected by Soil Water Deficit and VPD in Processing Tomato in Semi Arid Mediterranean Climate

In order to assess the effects of soil water availability and climatic conditions on leaf growth, leaf transpiration (E) and stomatal conductance (g_s) of processing tomato, under deficit irrigation regimes in the Mediterranean climate, open‐field experiments were carried out in two sites differing from soil and climatic characteristics, in Sicily, South Italy. A wide range of soil water availability from dry, deficit irrigation to full irrigation was examined. Leaf area greatly changed with soil water availability but not with the experimental site. The effect of soil drying on physiological indices was small over a certain range of soil water deficit (from 0 % to approximately 40 %). Within this range, vapour pressure deficit (VPD) strongly affected g_s. To this regard, the adoption of two experimental sites differing in climatic conditions (i.e. air temperature, RH, VPD) has been useful for a better understanding of the mechanisms, which regulate stomatal opening. Therefore, in Mediterranean environment, the combined effect of soil water availability (mostly upon leaf growth) and climatic conditions (mostly upon plant physiology) must be considered in models for biomass production in tomato crop.     

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

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

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

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

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.