Effects of elevated atmospheric CO2 on grain quality of wheat

Wheat (Triticum aestivum L.) is one of the most important agricultural crops worldwide. Due to its high content of starch and unique gluten proteins, wheat grain is used for many food and non-food applications. Although grain quality is an important topic for food and feed as well as industrial processing, the consequences of future increases in atmospheric carbon dioxide (CO₂) concentrations on quality parameters such as nutritional and bread-making rheological properties are still unclear. Wheat productivity increases under CO₂ enrichment. Concomitantly, the chemical composition of vegetative plant parts is often changed and grain quality is altered. In particular, the decrease in grain protein concentration and changes in protein composition may have serious economic and health implications. Additionally, CO₂ enrichment affects amino acid composition and the concentrations of macro- and micro-elements. However, experimental results are often inconsistent. The present review summarises the results from numerous CO₂ enrichment experiments using different exposure techniques in order to quantify the potential impacts of projected atmospheric CO₂ levels on wheat grain yield and on aspects of grain composition relevant to processing and human nutrition.     

Effects of atmospheric CO2 enrichment on biomass,yield and low molecular weight metabolites in wheat grain

Spring wheat (Triticum aestivum L.) was grown in a free-air carbon dioxide (CO₂) enrichment (FACE) field experiment. Grain and biomass yield and its components were determined at maturity and the grain metabolome was analysed by gas chromatography-mass spectrometry (GC–MS). Elevated CO₂ (537 versus 409 μl l⁻¹) increased biomass production except for leaves. In total, levels of 16 grain metabolites were decreased and four were increased. CO₂ enrichment resulted in significant decreases of amino acids such as o-acetyl-L-homoserine, leucine, arginine, L-homoserine and the group of ornithine, arginine and citrulline and negative trends for norleucine, L-aspartate, proline, L-cysteine and tyrosine. The amines D/L-diaminopimelate and alpha-ketoaminobutyrate and the polyamine putrescine were significantly decreased. In contrast, the polyamine spermidine tended to increase under elevated CO₂. Among sugars and sugar derivatives, ribose-5-P was significantly increased, while gluconate-6-P was decreased. There were also negative CO₂-induced effects on sugar alcohols: significant for glycerol-2-P (P = 0.008) and almost significant for myo-inositol-P (P = 0.066). In contrast, organic acids such as pyruvate and glucuronic acid were significantly increased. Overall, the N-rich metabolites especially were reduced. CO₂ enrichment can markedly affect the physiology and metabolome of mature grains which may in turn lead to changes in nutritional status.     

The impact of free-air CO2 enrichment (FACE) and nitrogen supply on grain quality of rice

Because CO₂ is needed for plant photosynthesis, the increase in atmospheric CO₂ concentration ([CO₂]) has the potential to enhance the growth and yield of rice (Oryza sativa L.), but little is known regarding the impact of elevated [CO₂] on grain quality of rice, especially under different N availability. In order to investigate the interactive effects of [CO₂] and N supply on rice quality, we conducted a free-air CO₂ enrichment (FACE) experiment at Wuxi, Jiangsu, China, in 2001–2003. A long-duration rice japonica with large panicle (cv. Wuxiangging 14) was grown at ambient or elevated (ca. 200 μmol mol⁻¹ above ambient) [CO₂] under three levels of N: low (LN, 15 g N m²), medium (MN, 25 g N m²) and high N (HN, 35 g N m² (2002, 2003)). The MN level was similar to that recommended to local farmers. FACE significant increased rough (+12.8%), brown (+13.2%) and milled rice yield (+10.7%), while markedly reducing head rice yield (−13.3%); FACE caused serious deterioration of processing suitability (milled rice percentage −2.0%; head rice percentage −23.5%) and appearance quality (chalky grain percentage +16.9%; chalkiness degree +28.3%) drastically; the nutritive value of grains was also negatively influenced by FACE due to a reduction in protein (−6.0%) and Cu content (−20.0%) in milled rice. By contrast, FACE resulted in better eating/cooking quality (amylose content −3.8%; peak viscosity +4.5%, breakdown +2.9%, setback −27.5%). These changes in grain quality revealed that hardness of grain decreased with elevated [CO₂] while cohesiveness and resilience increased when cooked. Overall, N supply had significant influence on rice yield with maximum value occurring at MN, whereas grain quality was less responsive to the N supply, showing trends of better appearance and eating/cooking quality for LN or MN-crops as compared with HN-crops. For most cases, no [CO₂] × N interaction was detected for yield and quality parameters. These data suggested that the current recommended rates of N fertilization for rice production should not be modified under projected future [CO₂] levels, at least for the similar conditions of this experiment.     

Intra-specific variation of wheat grain quality in response to elevated [CO2] at two sowing times under rain-fed and irrigation treatments

In order to investigate the intra-specific variation of wheat grain quality response to elevated atmospheric CO₂ concentration (e[CO₂]), eight wheat (Triticum aestivum L.)cultivars were grown at two CO₂ concentrations ([CO₂]) (current atmospheric, 389 CO₂ μmol mol⁻¹vs. e[CO₂], FACE (Free-Air CO₂ Enrichment), 550  ±  10% CO₂ μmol mol⁻¹), at two water levels (rain-fed vs. irrigated) and at two times of sowing (TOS₁, vs. TOS₂). The TOS treatment was mainly imposed to understand whether e[CO₂] could modify the effects of timing of higher grain filling temperatures on grain quality. When plants were grown at TOS₁, TKW (thousand kernel weight), grain test weight, hardness index, P, Ca, Na and phytate were not significantly changed under e[CO₂]. On the other hand, e[CO₂] increased TKW (16%), hardness index (9%), kernel diameter (6%), test weight (2%) but decreased grain protein (10%) and grain phytate (11%) at TOS₂. In regard to grain Zn, Mn and Cu concentrations and some flour rheological properties, cultivar specific responses to e[CO₂] were observed at both sowing times. Observed genetic variability in response to e[CO₂] in terms of grain minerals and flour rheological properties could be easily incorporated into future wheat breeding programs to enable adaptation to climate change.     

Seasonal changes in the effects of free-air CO2 enrichment (FACE) on phosphorus uptake and utilization of rice at three levels of nitrogen fertilization

Over time, the relative effect of elevated [CO₂] on the photosynthesis and dry matter (DM) production of rice crops is likely to be changed with increasing duration of CO₂ exposure. However, there is no systemic information on interactive effects of elevated [CO₂] and nitrogen (N) supply on seasonal changes in phosphorus (P) nutrient of rice crops. In order to investigate the interactive effects of these two factors on seasonal changes in plant P concentration, uptake, efficiency and allocation, a free-air CO₂ enrichment (FACE) experiment was conducted at Wuxi, Jiangsu, China, in 2001–2003. A japonica cultivar with large panicle was grown at ambient or elevated (ca. 200 μmol mol⁻¹ above ambient) [CO₂] and supplied with three levels of N: low (LN, 15 g N m²), medium (MN, 25 g N m²) and high N (HN, 35 g N m² (2002, 2003)). The MN level was similar to that recommended to local farmers. FACE significantly increased shoot P concentration (dry base) over the season, the average responses varied between 7.3% and 16.2%. Shoot P uptake responses to FACE declined gradually with crop development, with average responses of 57%, 51%, 37%, 26% and 11% on average during the growth periods from transplanting to early-tillering (Period I), early-tillering to mid-tillering (Period II), mid-tillering to panicle initiation (Period III), panicle initiation to heading (Period IV) and heading to grain maturity (Period V), respectively. Seasonal changes in shoot P uptake ratio (i.e., the ratio of shoot P uptake during a given growth period to final shoot P acquisition at grain maturity) responses to FACE followed a similar pattern to that of shoot P uptake, with average responses of 19%, 14%, 3%, −5% and −16% in Periods I, II, III, IV and V of the growth period, respectively. As a result, FACE enhanced shoot P uptake by 33% at grain maturity. P allocation patterns among above-ground organs were not altered by FACE before heading, but it was modified after heading, with a shift in P allocation patterns towards vegetative organ. FACE resulted in the significant decrease in P-use efficiency for biomass across the season and P-use efficiency for grain yield and P harvest index at grain maturity. Generally, there were no interactions between [CO₂] and N supply on above P nutrient variables measured. Data from this study has important implications for P management in rice production systems under future elevated [CO₂] conditions.     

小麦旗叶光呼吸对光强和CO2浓度的响应

为给C₃作物光呼吸等光合参数以及光响应模型和CO₂响应模型的研究提供参考,定量研究了小麦花期旗叶光呼吸速率对光强和CO₂浓度的响应。结果表明,在21%和2%O₂下小麦旗叶光饱和点分别为1 960.629和2 030.120 μmol·m^-2·s^-1。在较弱光强(小于800 μmol·m^-2·s^-1)下,小麦的总光呼吸速率(R_pt)与表观光呼吸(R_pa)均随着光强的升高而增大;当光强大于800 μmol·m^-2·s^-1时,R_pt和R_pa趋于稳定;整体上,不同光强下R_pt与R_pa之间差异较小(P>0.05),这主要是由于在380 μmol·mol^-1 CO₂下,光呼吸的CO₂回收利用率较低。饱和光强下,R_pa随着CO₂浓度的增加呈先上升后下降的趋势,R_pa最大值(Rpmax)所对应的外界CO₂浓度为600 μmol·mol^-1,而R_pt则随着CO₂浓度的升高而降低;在低浓度CO₂(小于380 μmol·mol^-1)条件下,R_pt与R_pa之间差异显著(P<0.05)。R_pt与羧化速率的比值(R_pt /Vc)随着胞间CO₂浓度的升高而呈下降的趋势,而不同光强下R_pt /Vc相对稳定,整体上未达到显著水平(P>0.05)。     

Impact of elevated CO2 concentration on inter-subspecific hybrid rice cultivar Liangyoupeijiu under fully open-air field conditions

Hybrid rice cultivar plays an important role in rice production system due to its high yield potential and resistance to environmental stress. Quantification of its responses to rising CO₂ concentration ([CO₂]) will reduce our uncertainty in predicting future food security and assist in development of adaptation strategies. Using free air CO₂ enrichment (FACE), we measured seasonal changes in growth and nitrogen (N) uptake of an inter-subspecific hybrid rice cultivar Liangyoupeijiu grown under two levels of [CO₂] (ambient and elevated by 200 μmol mol⁻¹) and two levels of N fertilization in 2005–2006. Average across the 2 years, FACE increased crop growth rate similarly by 22%, 24% and 23% in the periods from transplanting to panicle initiation (PI), PI to heading and heading to maturity, which was mainly attributed to an increase in green leaf area index rather than the greater net assimilation rate. Grain yield increased greatly under FACE as a result of similar contributions by panicle number per unit area, grain number per panicle and individual grain yield. Final aboveground N acquisition showed a 10.4% increase under FACE, which resulted from enhanced N uptake at both vegetative and reproductive growth stages. Compared with previous FACE studies on final productivity of two inbred japonica cultivars, inter-subspecific hybrid cultivar appears to profit more from elevated [CO₂], which mainly resulted from its greater enhancement in photosynthetic production during reproductive growth due to a lack of N limitations late in the season.     

施氮和大气CO2浓度升高对春小麦拔节期光合作用的影响

为明确高大气CO2浓度下小麦叶片光合作用的适应机制及氮素的调控作用,利用开顶式气室,通过盆栽试验,测定和分析了不同大气CO2浓度和施氮量下小麦拔节期叶片的光合参数、叶绿素含量等指标.结果表明,高大气CO2浓度(760 μmol·mol-1)处理的小麦叶片的叶绿素含量、光合速率(Pn)、气孔导度(G5)和蒸腾速率(Tr)均随着施氮水平的升高而升高,平均增幅分别为31.6%、69.6%和57.6%,而胞间CO2浓度(Ci)和水分利用效率(WUE)随施氮水平的升高而呈先下降后上升的趋势.高大气CO2浓度下小麦叶片Pn、Ci和WUE显著高于正常CO2浓度(400 μmol·mol-1)处理,平均增幅分别为36.8%、74.O%和102.7%.在400 μmol·mol-1 CO2浓度下测定时,与正常大气CO2浓度下生长的小麦相比,高大气CO2浓度下生长的小麦拔节期叶片Pn在高施氮水平(0.2 g N·kg-1土)下未发生下调,而在低、中施氮水平(0和0.1 g N·kg-1土)下叶片Pn明显降低.因此,高大气CO2浓度下施氮可显著提高小麦叶片的Pn和WUE,且充分供氮可使叶片不发生光合适应现象,这可能与较高的施氮水平提高了高大气CO2浓度下小麦叶片的叶绿素含量有关.     

Yield formation of CO2-enriched hybrid rice cultivar Shanyou 63 under fully open-air field conditions

Hybrid indica rice (Oryza sativa L.) cultivars play an important role in rice production system due to its heterosis, resistance to environmental stress, large panicle and high yield potential. However, no attention has been given to its yield responses to rising atmospheric [CO₂] in conjunction with nitrogen (N) availability. Therefore we conducted a free air CO₂ enrichment (FACE) experiment at Yangzhou, Jiangsu, China (119°42′0′′E, 32°35′5′′N), in 2004–2006. A three-line hybrid indica rice cv. Shanyou 63 was grown at ambient and elevated (ca. 570 μmol mol⁻¹) [CO₂] under two levels of supplemental N (12.5 g Nm⁻² and 25 g Nm⁻²). Elevated [CO₂] had no effect on phenology, but substantially enhanced grain yield (+34%). The magnitude of yield response to [CO₂] was independent of N fertilization, but varied among different years. On average, elevated [CO₂] increased the panicle number per square meter by 10%, due to an increase in maximum tiller number under enrich [CO₂], while productive tiller ratio remained unaffected. Spikelet number per panicle also showed an average increase of 10% due to elevated [CO₂], which was supported by increased plant height and stem dry weight per tiller. Meanwhile, elevated [CO₂] caused a significant enhancement in both filled spikelet percentage (+5%) and individual grain weight (+4%). Compared with the two prior FACE studies on rice, hybrid indica rice cultivar appears to profit much more from elevated [CO₂] than japonica rice cultivar (ca. +13%), not only due to its stronger sink generation, but also enhanced capacity to utilize the carbon sources in a high [CO₂] environment. The above data has significant implication with respect to N strategies and cultivar selection under projected future [CO₂] levels.     

小麦水分利用效率对CO2浓度响应的模型研究

为了定量研究水分利用效率(water use efficiency, WUE)对CO_2浓度的响应,在植物光合作用对CO_2响应模型的基础上构建了WUE(分为内禀水分利用效率和瞬时水分利用效率,即WUE_i和WUE_(inst))对CO_2(包括大气CO_2浓度和胞间CO_2浓度,即C_a和C_i)的响应模型,并应用新构建的模型对小麦(Triticum aestivum L.)测量数据进行了拟合。结果表明,新构建的模型不仅可以很好地拟合小麦叶片WUE对CO_2浓度的响应曲线(包括WUE_i-C_a、WUE_i-C_i、WUE_(inst)-C_a和WUE_(inst)-C_i曲线),而且还可以直接给出小麦的最大WUE_i和WUE_(inst)以及相对应的饱和C_a和C_i。以小麦WUE_i-C_a和WUE_(inst)-C_a曲线拟合结果为例,得到的最大WUE_i和WUE_(inst)分别为176.29μmol·mol~(-1)和8.65 mol·mmol~(-1),其对应的观测值分别为172.96μmol·mol~(-1)和8.62 mol·mmol~(-1);拟合得到的饱和CO_2浓度分别为1 410.52和1 399.73μmol·mol~(-1),对应的观测值分别为1 294.05和1 332.84μmol·mol~(-1)。拟合值与观测值之间均无显著差异。由此可见,新建模型拟合得到的这些参数与观测值高度相符,可用于植物WUE对未来CO_2增加响应规律研究。     

玉米作为地质封存CO_2泄漏耐受植物的评估

二氧化碳的捕获与储存(CO2capture and storage,CCS)是全球CO_2减排最重要技术战略,其存在CO_2泄漏的风险,会对周围农田生态产生重要影响。深入认识植物对高浓度CO_2的响应并筛选对CO_2的耐受植物,为CCS项目区农业生产决策提供参考数据。本文设置玉米对不同CO_2浓度的响应情形,选择株高、鲜重、干重、净光合速率、蒸腾速率、气孔导度和胞间CO_2浓度作为玉米耐受的观测指标。结果表明,当CO_2浓度为10 000、20 000μmol/mol时,玉米株高增高7%～12%,生物量增加10%～15%,净光合速率增加高达60%左右;当CO_2浓度为40 000、80 000μmol/mol时,玉米株高度减少9%～12%,生物量减少10%～17%,净光合速率减少35%～45%左右。一定程度CO_2浓度的增加,对玉米生长发育具有"施肥"效应;在更高CO_2浓度下,会抑制其生长发育,并未出现植株死亡的现象。通过CO_2耐受指数法(LCTI)计算得出,玉米可以作为地质封存CO_2泄漏的耐受植物。     

Wheat grain quality under increasing atmospheric CO2 concentrations in a semi-arid cropping system

We investigated wheat (Triticum aestivum) grain quality under Free Air CO₂ Enrichment (FACE) of 550 ± 10% CO₂ μmol mol⁻¹. In each of two full growing seasons (2008 and 2009), two times of sowing were compared, with late sowing designed to mimic high temperature during grain filling. Grain samples were subjected to a range of physical, nutritional and rheological quality assessments. Elevated CO₂ increased thousand grain weight (8%) and grain diameter (5%). Flour protein concentration was reduced by 11% at e[CO₂], with the highest reduction being observed at the late time of sowing in 2009, (15%). Most of the grain mineral concentrations decreased under e[CO₂] - Ca (11%), Mg (7%), P (11%) and S (7%), Fe (10%), Zn (17%), Na (19%), while total uptake of these nutrients per unit ground area increased. Rheological properties of the flour were altered by e[CO₂] and bread volume reduced by 7%. Phytate concentration in grains tended to decrease (17%) at e[CO₂] while grain fructan concentration remained unchanged. The data suggest that rising atmospheric [CO₂] will reduce the nutritional and rheological quality of wheat grain, but at high temperature, e[CO₂] effects may be moderated. Reduced phytate concentrations at e[CO₂] may improve bioavailability of Fe and Zn in wheat grain.     

Physicochemical and antioxidant properties of extruded corn grits with corn fiber by CO2 injection extrusion process

Corn grits and corn fiber mixed at different mass ratios (0/100, 15/85 and 30/70) were extruded at different melt temperature (90, 105 and 120 °C) using extrusion with and without CO₂ injection. The L value, reducing sugar content and antioxidant properties decreased after extrusion with or without CO₂ injection. The color and antioxidant properties were relatively stable in the extrusion with CO₂ injection at higher melt temperature (120 °C) in comparison with the extrusion without CO₂ injection. Higher corn fiber content resulted in less loss of total phenolic content. The b, ΔE values and water absorption index increased after extrusion. The increase of the water absorption index was higher after the extrusion process with the CO₂ injection especially at the lower melt temperature. The addition of corn fiber decreased L, b, and ΔE values, but significantly increased antioxidant properties under the same extrusion conditions.     

Seasonal changes in the effects of free-air CO2 enrichment (FACE) on nitrogen (N) uptake and utilization of rice at three levels of N fertilization

Over time, the relative effect of elevated [CO₂] on the photosynthesis and dry matter (DM) production of rice crops is likely to be changed with increasing duration of CO₂ exposure, but the resultant [CO₂] effects on rice N concentration, uptake, efficiency and allocation remain unclear, especially under different soil N availability. Therefore, we conducted a free-air CO₂ enrichment (FACE) experiment at Wuxi, Jiangsu, China, in 2001–2003. A japonica cultivar with large panicle was grown at ambient or elevated (ca. 200 μmol mol⁻¹ above ambient) [CO₂] under three levels of N: low (LN, 15 g N m²), medium (MN, 25 g N m²) and high N (HN, 35 g N m² (2002, 2003)). The MN level was similar to that recommended to local farmers. Averaged across all N levels and years, shoot N concentration (dry base) was lower under FACE by 1.8%, 6.1%, 12.2%, 14.3%, 12.1%, and 6.9% at early-tillering, mid-tillering, panicle initiation (PI), booting, heading and grain maturity, respectively. Shoot N uptake under FACE was enhanced by 46%, 38%, 6% and 16% on average during the growth periods from transplanting to early-tillering (period 1), early-tillering to mid-tillering (period 2), mid-tillering to PI (period 3) and heading to grain maturity (period 5), respectively, but slightly decreased by 2% in the period from PI to heading (period 4). Seasonal changes in crop response to FACE in ratio of shoot N uptake during a given growth period to that over the whole season followed a similar pattern to that of shoot N uptake, with average responses of 33%, 26%, −3%, −11% and 10% in periods 1–5 of the growth period, respectively. As a result, FACE increased final aboveground N uptake by 9% at maturity. FACE greatly reduced the ratio of leaf to shoot N content over the season, while allocation of N to stems and spikes showed an opposite trend. FACE treatment resulted in the significant increase in N use efficiency for biomass (NUEp) over the season except at early-tillering and in N use efficiency for grain yield (NUEg) at grain maturity. These results indicate that, in order to maximize grain output in a future high [CO₂] environment, the recommended rates, proportion and timing across the season of N application should be altered, in order to take full advantage of strong N uptake capacity during the early growth period and facilitate N uptake after that.     

Impacts of early-season square abscission on the growth and yield of transgenic Bt cotton under elevated CO2

A field study was carried out to quantify the compensation capacity of Bacillus thuringiensis (Bt)-transgenic cotton to simulated damage by manually removing squares during the early growing season in 2004 and 2005 in combination with CO₂ levels (ambient CO₂ and elevated CO₂). Treatments included: initial squares were wholly (100%) removed manually for 1 week (i.e., SR1 treatment) and for 2 consecutive weeks (i.e., SR2 treatment). Plant leaf area was measured every 2 weeks, and plant root, stem, leaf, shatters, boll dry weight and lint yield and maturity were measured at harvest. Significantly higher leaf area per plant was observed on each sampling date for SR1 and SR2 treatments compared with control (SR0) treatment in 2004 and 2005 under elevated CO₂. Significantly higher lint yield and maturity were observed for SR0, SR1 and SR2 treatments under elevated CO₂ in 2004 and 2005. CO₂ concentration and square removal significantly affected plant lint yield and maturity. Moreover, the interaction between CO₂ concentration × square removal had a significant effect on plant leaf dry weight, lint yield and maturity. Our results indicated that transgenic cotton plants can compensate for the manual removal of 100% of the initial squares for 1 and 2 weeks under ambient and elevated CO₂.     

Simulation of the effects of genotype and N availability on rice growth and yield response to an elevated atmospheric CO2 concentration

The objective of this study was to identify physiological processes that result in genotypic and N fertilization effects on rice yield response to elevated atmospheric CO₂ concentrations ([CO₂]). This study conducted growth and yield simulations for 9 rice genotypes grown at 4 climatically different sites in Asia, assuming the current atmospheric [CO₂] (360 ppm) and elevated [CO₂] (700 ppm) using 5 levels of N fertilizer (4, 8, 12, 16, 20 g m⁻² N fertilizer). A rice growth model that was developed and already validated for 9 different genotypes grown under 7 sites in Asia was used for the simulation, integrating additional components into the model to explain the direct effect of [CO₂] on several physiological processes. The model predicted that the relative yield response to elevated [CO₂] (RY, the ratio of yield under 700 ppm [CO₂] to that under 360 ppm [CO₂]) increased with increasing N fertilizer, ranging from 1.12 at 4 g m⁻² N fertilizer to 1.22 at 20 g m⁻² N fertilizer, averaged overall genotypes and locations. The model also predicted a large genotypic variation in RY at the 20 g N treatment, ranging from 1.08 for ‘WAB450-I-B-P-38-HB’ to 1.41 for ‘Takanari’ averaged overall locations. Combining all genotypes grown at the 5N fertilization conditions, a close 1:1 relationship was predicted between RY and the relative [CO₂] response in spikelet number for crops with a small number of spikelets (less than 30,000 m⁻²) under the current atmospheric [CO₂] (n = 18, r = 0.89^***). In contrast, crops with a large number of spikelets under the current atmospheric [CO₂] showed a significantly larger RY than the relative [CO₂] response for spikelet number per unit area. The model predicted that crops with a larger number of spikelets under the current atmospheric [CO₂] derived great benefit from elevated [CO₂] by directly allocating increased carbohydrate to their large, vacant sink, whereas crops with a smaller number of spikelets primarily required an increased spikelet number to use the increased carbohydrate to fill grains. The simulation analyses suggested that rice with a larger sink capacity relative to source availability under the current atmospheric [CO₂] showed a larger yield response to elevated [CO₂], irrespective of whether genotype or N availability was the major factor for the large sink capacity under the current [CO₂]. The model predicted that the RY response to nitrogen was brought about through the N effects on spikelet number and non-structural carbohydrate accumulation. The genotypic variation in RY was related to differences in spikelet differentiation efficiency per unit plant N content. Further model validation about the effects of [CO₂] on growth processes is required to confirm these findings considering data from experimental studies.     

Yield dilution of grain Zn in wheat grown in open-top chamber experiments with elevated CO2 and O3 exposure

Wheat (Triticum aestivum L.) grain Zn data from six open-top chamber experiments performed in south-west Sweden were combined to study the relationship between Zn accumulation and grain yield, grain protein, and yield components. Treatments included, in addition to open-top chamber controls, elevated CO₂, elevated O₃, combined CO₂ and O₃ exposure, combined elevated CO₂ and supplemental irrigation, supplemental irrigation, and ambient air comparison plots. The grain Zn concentration was strongly correlated with grain protein (R² = 0.90) over the range of the experimental treatments, representing non-soil factors. A significant yield dilution effect was found for Zn. For a 10% increase in grain yield, Zn yield was increased by 6.8% on average. Effects on Zn yield correlated strongly with effects on grain protein yield, with a slope close to unity, showing that yield dilution effects for grain Zn and grain protein were similar. Treatment effects on grain Zn concentration were related to effects on grain weight (P < 0.01) and grain number (P < 0.05), but not to harvest index. It was concluded that yield stimulation caused by rising CO₂ concentrations is likely to lead to reduced Zn concentrations of wheat grain, thus reducing the nutritional quality.     

低温条件下小麦返白系叶片中H2O2累积的原因初探

为了研究低温处理下小麦叶色阶段性白化品种返白系与对照品种矮变1号叶片的H_2O_2含量是否存在差异,并初步分析导致差异的原因,采用DAB组织染色法检测返白系和矮变1号在4℃低温处理90 d、25℃下恢复培养10 d时叶片H_2O_2含量的动态变化,测定4℃低温处理下返白系和矮变1号中表征光合电子传递效率的荧光参数F_v/F_m和qP,并采用qRT-PCR方法分析返白系和矮变1号中几个光合电子传递体基因及质体H_2O_2清除相关基因的表达模式。结果显示,低温处理下,矮变1号叶片中H_2O_2含量变化不大,返白系叶片中H_2O_2会大量累积;低温处理下,返白系叶片的叶绿素荧光参数F_v/F_m、qP都明显低于矮变1号。同时,低温下返白系光合电子传递链中部分电子传递体亚基基因petD、petN、ndhB和ndhK,以及质体H_2O_2清除相关基因 APX4和 HO1的表达量低于矮变1号。这些结果表明,低温处理下,相较于矮变1号,返白系叶片中会累积大量的H_2O_2。返白系质体中光合电子传递受阻引起电子泄露,同时质体中清除活性氧的能力下降,可能是导致返白系叶片中积累大量H_2O_2的原因。     

重铬酸钾对黑麦的细胞遗传毒性及硅的缓解作用

为了解K2Cr2O7的细胞遗传毒性及硅对铬毒害的缓解作用,采用常规染色体压片技术,观察不同浓度的K2Cr2O7(20、40、60、80、100、120mg.L-1)对黑麦根尖细胞有丝分裂的影响以及硅对铬胁迫缓解效应。结果表明,细胞有丝分裂指数、微核率和染色体畸变率均随K2Cr2O7浓度的升高呈先升后降趋势,在K2Cr2O7浓度为40.0mg.L-1时均达到最大值。与蒸馏水对照相比,6个不同浓度K2Cr2O7胁迫处理的微核率和染色体畸变率均有显著升高。对40mg.L-1 K2Cr2O7胁迫的黑麦根尖分别进行60、120和180mg.L-1的Na2SiO3处理,细胞有丝分裂指数、微核率和染色体畸变率均显著降低,且随硅浓度的增加呈下降趋势。说明K2Cr2O7对黑麦根尖细胞有丝分裂在低浓度时促进,高浓度时抑制,高低浓度处理均对染色体具有明显的致畸效应。外源硅可有效缓解K2Cr2O7对黑麦根尖细胞有丝分裂的不利影响。