Involvement of nitrogen and cytokinins in photosynthetic acclimation to elevated CO2 of spring wheat

Acclimation of photosynthetic capacity to elevated CO₂ involves a decrease of the leaf Rubisco content. In the present study, it was hypothesized that nitrogen uptake and partitioning within the leaf and among different aboveground organs affects the down-regulation of Rubisco. Given the interdependence of nitrogen and cytokinin signals at the whole plant level, it is also proposed that cytokinins affect the nitrogen economy of plants under elevated CO₂, and therefore the acclimatory responses. Spring wheat received varying levels of nitrogen and cytokinin in field chambers with ambient (370 μmol mol⁻¹) or elevated (700 μmol mol⁻¹) atmospheric CO₂. Gas exchange, Rubisco, soluble protein and nitrogen contents were determined in the top three leaves in the canopy, together with total nitrogen contents per shoot. Growth in elevated CO₂ induced decreases in photosynthetic capacity only when nitrogen supply was low. However, the leaf contents of Rubisco, soluble protein and total nitrogen on an area basis declined in elevated CO₂ regardless of nitrogen supply. Total nitrogen in the shoot was no lower in elevated than ambient CO₂, but the fraction of this nitrogen located in flag and penultimate leaves was lower in elevated CO₂. Decreased Rubisco: chlorophyll ratios accompanied losses of leaf Rubisco with CO₂ enrichment. Cytokinin applications increased nitrogen content in all leaves and nitrogen allocation to senescing leaves, but decreased Rubisco contents in flag leaves at anthesis and in all leaves 20 days later, together with the amount of Rubisco relative to soluble protein in all leaves at both growth stages. The results suggest that down regulation of Rubisco in leaves at elevated CO₂ is linked with decreased allocation of nitrogen to the younger leaves and that cytokinins cause a fractional decrease of Rubisco and therefore do not alleviate acclimation to elevated CO₂.     

CO2浓度升高与硝化抑制剂对冬小麦田间N2O排放量的影响

以冬小麦中麦175为供试品种,利用农田开放式CO_2浓度增高(FACE)系统,研究未来大气高CO_2浓度对冬小麦田间N_2O排放的影响,以及施用硝化抑制剂(2-氯-6-三氯甲基吡啶)是否可以起到抑制冬小麦田间N_2O的排放量升高的潜能。试验结果表明:CO_2浓度升高显著提高冬小麦田间N2O的排放增幅达到67.6%,追肥灌溉后小麦田N_2O排放量较大,随着冬小麦生育进程的推进N_2O的排放量逐渐减少,硝化抑制剂对中麦175田间N_2O排放量的影响并不明显。因此,在未来高CO_2浓度环境条件下,可以通过采取相应的耕作制度和栽培技术措施等来降低冬小麦田N_2O的排放量。试验结果对冬小麦田间是否选择施用2-氯-6-三氯甲基吡啶来控制N_2O的排放起到一定的参考作用。     

Interactive effects of elevated CO2 and temperature on the anatomical characteristics of leaves in eleven species

The anatomical features of leaves in 11 species of plants grown in a temperature gradient and a temperature + CO₂ gradient were studied. The palisade parenchyma thickness, the spongy parenchyma thickness and the total leaf thickness were measured and analyzed to investigate the effects of elevated temperature and CO₂ on the anatomical characteristics of the leaves. Our results show that with the increase of temperature, the leaf thickness of C₄ species increased while the leaf thickness of C₃ species showed no constant changes. With increased CO₂, seven out of nine C₃ species exhibited increased total leaf thickness. In C₄ species, leaf thickness decreased. As for the trend on the multi-grades, the plants exhibited linear or non-linear changes. With the increase of temperature or both temperature and CO₂ for the 11 species investigated, leaf thickness varied greatly in different plants (species) and even in different branches on the same plant. These results demonstrated that the effect of increasing CO₂ and temperature on the anatomical features of the leaves were species-specific. Since plant structures are correlated with plant functions, the changes in leaf anatomical characteristics in elevated temperature and CO₂ may lead to functional differences. Translated from Acta Ecologica Sinica, 2006, 26(2): 326–333 [译自: 生态学报]     

大气CO2浓度升高对春玉米土壤呼吸的影响

为探讨春玉米不同生育期土壤呼吸速率对大气CO₂浓度升高的响应,以黄土高原旱作春玉米为研究对象,通过改进的开顶式气室（OTC）模拟大气CO₂浓度升高的环境,在田间条件下设置自然大气CO₂浓度（CK）、OTC对照（OTC,CO₂浓度同CK）与CO₂浓度升高（OTC+CO₂,OTC系统自动控制CO₂浓度700 μmol/mol）3种处理。研究了旱区覆膜高产栽培春玉米播前（V0）、六叶期（V6）、九叶期（V9）、吐丝期（R1）、乳熟期（R3）、蜡熟期（R5）及完熟期（R6）土壤呼吸速率对大气CO₂浓度升高的响应特征,以及大气CO₂浓度升高对土壤呼吸速率的温度与水分效应的影响。研究发现,OTC+CO₂处理土壤呼吸速率,与CK相比,在R3和R5期分别增加43%、104%（P<0.05）,与OTC相比,R3和R5期分别提升了63%、109%（P<0.05）;OTC处理与CK相比,在整个生育期对土壤呼吸影响不显著;3种处理条件下,土壤温度和水分随生育期变化趋势基本一致,土壤呼吸速率与土壤温度和水分分别呈指数相关和抛物线型相关;结果表明：大气CO₂浓度升高对土壤呼吸的影响因生育期而异,土壤温度和土壤水分是影响旱地农田土壤呼吸的重要因素,CO₂浓度升高会使土壤呼吸温度效应值（Q₁₀）降低,土壤呼吸对土壤水分响应的阈值提高。     

大气CO2浓度及温度升高对高山灌木鬼箭锦鸡儿(Caragana jubata)生长及抗氧化系统的影响

以CO_2浓度及温度升高为主要标志的全球气候变化将对我国西北地区脆弱的生态系统产生重要影响。利用环境控制实验研究CO_2浓度倍增(eCO_2, C_1:400μmol/mol和C_2:800μmol/mol)和温度升高(eT, T_1:20℃/10℃和T_2:23℃/13℃)对高山灌木鬼箭锦鸡儿(Caragana jubata)生长及抗氧化系统的影响。结果表明:eCO_2和eT表现出相反的生长和生理效应,eT对幼苗生长的影响要大于eCO_2对其的影响。eT使幼苗的总生物量、净光合速率(NAR)和相对生长速率(RGR)降低;但可促进地上部分生长,叶生物量比及叶面积比增加。eCO_2可减缓或补偿由eT引起的总生物量、NAR和RGR的降低,并促进地下部分生长。对抗氧化系统来说,eT使得超氧化歧化酶(SOD)、过氧化物酶(POD)及抗坏血酸过氧化物酶(APX)活性降低,还原型谷胱甘肽(GSH)和抗坏血酸(ASA)含量降低;eCO_2只增加常温下SOD酶活性,并使GSH、ASA整体水平提高。结论:温度升高和CO_2浓度倍增没有协同促进鬼箭锦鸡儿幼苗的生长和光合能力。温度升高将对幼苗生长和抗氧化系统产生不利影响,eCO_2可促进生长并可能通过抗氧剂含量增加来缓解氧化胁迫。因此,未来气候变化,尤其是温度升高将会对高寒区植物产生较大影响,CO_2浓度增加可缓解增温的不利影响。     

Growth, light interception and yield responses of spring wheat (Triticum aestivum L.) grown under elevated CO2 and O3 in open-top chambers

Spring wheat cv. Minaret was grown to maturity under three carbon dioxide (CO₂) and two ozone (O₃) concentrations in open-top chambers (OTC). Green leaf area index (LAI) was increased by elevated CO₂ under ambient O₃ conditions as a direct result of increases in tillering, rather than individual leaf areas. Yellow LAI was also greater in the 550 and 680 μmol mol^–1 CO₂ treatments than in the chambered ambient control; individual leaves on the main shoot senesced more rapidly under 550 μmol mol^–1 CO₂, but senescence was delayed at 680 μmol mol^–1 CO₂. Fractional light interception (f) during the vegetative period was up to 26% greater under 680 μmol mol^–1 CO₂ than in the control treatment, but seasonal accumulated intercepted radiation was only increased by 8%. As a result of greater carbon assimilation during canopy development, plants grown under elevated CO₂ were taller at anthesis and stem and ear biomass were 27 and 16% greater than in control plants. At maturity, yield was 30% greater in the 680 μmol mol^–1 CO₂ treatment, due to a combination of increases in the number of ears per m^–2, grain number per ear and individual grain weight (IGW). Exposure to a seasonal mean (7 h d^–1) of 84 nmol mol^–1 O₃ under ambient CO₂ decreased green LAI and increased yellow LAI, thereby reducing both f and accumulated intercepted radiation by ≈ 16%. Individual leaves senesced completely 7–28 days earlier than in control plants. At anthesis, the plants were shorter than controls and exhibited reductions in stem and ear biomass of 15 and 23%. Grain yield at maturity was decreased by 30% due to a combination of reductions in ear number m^–2, the numbers of grains per spikelet and per ear and IGW. The presence of elevated CO₂ reduced the rate of O₃-induced leaf senescence and resulted in the maintenance of a higher green LAI during vegetative growth under ambient CO₂ conditions. Grain yields at maturity were nevertheless lower than those obtained in the corresponding elevated CO₂ treatments in the absence of elevated O₃. Thus, although the presence of elevated CO₂ reduced the damaging impact of ozone on radiation interception and vegetative growth, substantial yield losses were nevertheless induced. These data suggest that spring wheat may be susceptible to O₃-induced injury during anthesis irrespective of the atmospheric CO₂ concentration. Possible deleterious mechanisms operating through effects on pollen viability, seed set and the duration of grain filling are discussed.     

Carbon isotope discrimination and stomatal responses of mature Pinus sylvestris L. trees exposed in situ for three years to elevated CO2 and temperature

The Climate Change Experiment (CLIMEX) is a unique large scale facility in which an entire undisturbed catchment of boreal vegetation has been exposed to elevated CO₂ (560 ppm) and temperature (+3°C summer, +5°C winter) for the past three years with all the soil-plant-atmosphere linkages intact. Here, carbon isotope composition and stomatal density have been analysed from sequential year classes of needles of mature Scots pine trees (Pinus sylvestris L.) to investigate the response of time-integrated water-use efficiency (UWE) and stomatal density to CO₂ enrichment and climate change. Carbon isotope discrimination decreased and WUE increased in cohorts of needles developing under increased CO₂ and temperature, compared to needles on the same trees developing in pretreatment years. Mid-season instantaneous gas exchange, measured on the same trees for the past four years, indicated that these responses resulted from higher needle photosynthetic rates and reduced stomatal conductance. Needles of P. sylvestris developing under increased CO₂ and temperature had consistently lower stomatal densities than their ambient grown counterparts on the same trees. The stomatal density of P. sylvestris needles was inversely correlated with δ¹³C-derived WUE, implying some effect of this morphological response on leaf gas exchange. Future atmospheric CO₂ and temperature increases are therefore likely to improve the water economy of P. sylvestris, at least at the scale of individual needles, by affecting stomatal density and gas exchange processes.     

高浓度CO2对树木生理生态的影响研究进展

大气CO2浓度升高已成为世界范围内的重要环境问题。CO2浓度升高势必会对植物的生理生态变化产生重要影响。综述了国内外有关高浓度CO2对树木生理生态影响研究的最新进展,具体包括高浓度CO2对树木生长发育、光合和呼吸作用、抗氧化系统、树木代谢物质、挥发性有机化合物以及树木凋落物等方面的影响。高浓度CO2一般会促进树木地上植株的生长和发育,但也因树种差异而有所不同。最新研究表明,高浓度CO2促进了树木细根周转,树木根系生长在大气CO2浓度升高条件下表现为促进作用,这种作用加快了全球森林生态系统的C循环。高浓度CO2虽然在一定程度上促进树木光合速率的增加,但长期熏蒸也往往会发生光合驯化,这种现象产生的生理学机制目前仍无定论。高浓度CO2对树木呼吸作用尤其是根系呼吸的影响将是未来研究的重点和难点。高浓度CO2一般会提高树木抗氧化酶活性与抗氧化剂含量,但不同树种响应高浓度CO2的过程和机理也有所差异。研究表明,高浓度CO2一般对树木凋落物的分解产生不利影响,但也因树种而异。需要强调的是,目前关于树木地下部分、树木对高浓度CO2的适应机理和重要过程(碳氮水耦合及基因调控等)以及多个树种包括不同类型树种及不同品种之间比较研究较少;关于某一重要生理生态机制(如根系生理代谢)尤其是多个生态因子复合条件下缺乏长期深入的研究。在此基础上给出了大气CO2浓度升高下树木生理生态学研究的未来发展方向,包括高CO2浓度条件下树木根系生理代谢及机制、树木碳氮水耦合的生理过程及机制、不同生态因子复合作用对树木生理影响机制以及树木分子作用机理等方面的研究。这些研究不仅将丰富森林树木应对未来气候变化的有关科学理论,也为全球气候变化背景下实现森林树种生态功能的优化选择及森林生态系统的可持续发展与经营提供重要的生理生态学理论依据和参考。     

地质封存CO2泄漏对玉米根系形态的影响

碳捕集与封存（Carbon Capture and Storage,CCS）是应对全球气候变化、实现煤炭清洁利用的有效手段之一,但是地质封存的CO₂存在泄漏的风险,可能对农田生态系统产生重大威胁,影响我国粮食安全。根系生长是地上部和地下部相互作用、相互促进的统一过程,其形态特征对作物生产力有显著影响,但CCS泄漏对植物根系的影响评估尚不多见。本文以玉米为研究对象,采用盆栽底部通入CO₂的方法模拟不同CO₂泄漏情景,研究CK（0 g m^-2 d^-1）和G1000（1000 g m^-2 d^-1）和G2000（2000 g m^-2 d^-1）三种泄漏情景下CO₂对玉米根系形态的影响。结果表明：CO₂泄漏对玉米根系形态有明显的影响,随着泄漏量的增大总根长从40290.81 cm减少至21448.18 cm,减少46.77%,其中细根大幅减少;CO₂泄漏造成玉米明显减产,最大减产率达26.64%;玉米的地上部生物量较地下部生物量对CO₂泄漏更加敏感。综合来看,随着CO₂泄漏量增大,对玉米根的生长、地上部生物量、地下部生物量以及产量有显著的抑制作用。作物根系形态对封存CO₂泄漏的响应可为CCS泄漏监测和生态修复提供系统科学依据。     

CO2浓度升高条件下内生真菌感染对宿主植物的生理生态影响

以内蒙古草原常见伴生种、感染内生真菌的天然禾草羽茅为研究对象,通过比较不同CO₂浓度和不同养分供应条件下,带内生真菌和不带菌植物在种子发芽和幼苗生长等方面的差异,探讨带内生真菌的天然禾草对CO₂浓度增加的响应。结果表明:CO₂浓度增加对带菌种子发芽率和发芽速度均无显著影响,但CO₂浓度增加显著降低了不带菌种子的发芽率和发芽速度,即CO₂浓度升高加大了带菌和不带菌种子发芽率之间的差异;内生真菌感染显著提高了宿主植物的最大净光合速率和水分利用效率;羽茅的营养生长受CO₂浓度和养分供应的交互影响,高CO₂浓度对生长的促进作用只出现在充足养分供应条件下;CO₂浓度升高和内生真菌感染对植物根系形态有显著的交互作用,在正常CO₂浓度下,带菌植株根径>1.05 mm的根系比例显著高于不带菌植株,随着CO₂浓度的升高,带菌植株上述根径根系所占比例无显著变化而不带菌植株所占比例显著升高,CO₂浓度升高导致带菌和不带菌不同根径根系分配之间的差异缩小。     

Above- and below-ground responses of C3–C4 species mixtures to elevated CO2 and soil water availability

We evaluated the influences of CO₂[Control, ～ 370 µ mol mol ^{? 1}; 200 µ mol mol ^{? 1} above ambient applied by free‐air CO₂ enrichment (FACE)] and soil water (Wet, Dry) on above‐ and below‐ground responses of C₃ (cotton, Gossypium hirsutum) and C₄ (sorghum, Sorghum bicolor) plants in monocultures and two density mixtures. In monocultures, CO₂ enrichment increased height, leaf area, above‐ground biomass and reproductive output of cotton, but not sorghum, and was independent of soil water treatment. In mixtures, cotton, but not sorghum, above‐ground biomass and height were generally reduced compared to monocultures, across both CO₂ and soil water treatments. Density did not affect individual plant responses of either cotton or sorghum across the other treatments. Total (cotton + sorghum) leaf area and above‐ground biomass in low‐density mixtures were similar between CO₂ treatments, but increased by 17–21% with FACE in high‐density mixtures, due to a 121% enhancement of cotton leaf area and a 276% increase in biomass under the FACE treatment. Total root biomass in the upper 1.2 m of the soil was not influenced by CO₂ or by soil water in monoculture or mixtures; however, under dry conditions we observed significantly more roots at lower soil depths ( > 45 cm). Sorghum roots comprised 81–85% of the total roots in the low‐density mixture and 58–73% in the high‐density mixture. CO₂‐enrichment partly offset negative effects of interspecific competition on cotton in both low‐ and high‐density mixtures by increasing above‐ground biomass, with a greater relative increase in the high‐density mixture. As a consequence, CO₂‐enrichment increased total above‐ground yield of the mixture at high density. Individual plant responses to CO₂ enrichment in global change models that evaluate mixed plant communities should be adjusted to incorporate feedbacks for interspecific competition. Future field studies in natural ecosystems should address the role that a CO₂‐mediated increase in C₃ growth may have on subsequent vegetation change.     

Growth responses of yellow-poplar(Liriodendron tulipifera L.) exposed to 5 years of O3 aloneor combined with elevated CO2

Field‐grown yellow‐poplar (Liriodendron tulipifera L.) werefumigated from May to October in 1992–96 within open‐topchambers to determine the impact of ozone (O₃) aloneor combined with elevated carbon dioxide (CO₂) on saplinggrowth. Treatments were replicated three times and included: charcoal‐filteredair (CF); 1 × ambient ozone (1 × O₃);1·5 × ambient ozone (1·5 × O₃);1·5 × ambient ozone plus 350 p.p.m.carbon dioxide (1·5 × O₃ + CO₂)(target of 700 p.p.m. CO₂); and open‐air chamberlessplot (OA). After five seasons, the total cumulative O₃ exposure (SUM₀₀ = sumof hourly O₃ concentrations during the study) rangedfrom 145 (CF) to 861 (1·5 × O₃) p.p.m. × h (partsper million hour). Ozone had no statistically significant effecton yellow‐poplar growth or biomass, even though total root biomasswas reduced by 13% in the 1·5 × O₃‐exposedsaplings relative to CF controls. Although exposure to 1·5 × O₃ + CO₂ hada stimulatory effect on yearly basal area growth increment aftertwo seasons, significant increases in shoot and root biomass (～ 60% increaserelative to all others) were not detected until the fifth season.After five seasons, the yearly basal area growth increment of saplingsexposed to 1·5 × O₃ + CO₂‐air increasedby 41% relative to all others. Based on this multi‐yearstudy, it appears that chronic O₃ effects on yellow‐poplargrowth are limited and slow to manifest, and are consistent withprevious studies that show yellow‐poplar growth is not highly responsiveto O₃ exposure. In addition, these results show thatenriched CO₂ may ameliorate the negative effects of elevatedO₃ on yellow‐poplar shoot growth and root biomass underfield conditions.     

Photosynthetic responses to elevated CO2and O3 in field-grown potato(Solanum tuberosum)

Potato plants (Solanum tuberosum L. cv. Bintje) were grown to maturity in open-top chambers under three carbon dioxide (CO₂; ambient and 24 h d⁻¹ seasonal mean concentrations of 550 and 680 μmol mol⁻¹) and two ozone levels (O₃; ambient and an 8 h d⁻¹ seasonal mean of 50 nmol mol⁻¹). Chlorophyll content, photosynthetic characteristics, and stomatal responses were determined to test the hypothesis that elevated atmospheric CO₂ may alleviate the damaging influence of O₃ by reducing uptake by the leaves. Elevated O₃ had no detectable effect on photosynthetic characteristics, leaf conductance, or chlorophyll content, but did reduce SPAD values for leaf 15, the youngest leaf examined. Elevated CO₂ also reduced SPAD values for leaf 15, but not for older leaves; destructive analysis confirmed that chlorophyll content was decreased. Leaf conductance was generally reduced by elevated CO₂, and declined with time in the youngest leaves examined, as did assimilation rate (A). A generally increased under elevated CO₂, particularly in the older leaves during the latter stages of the season, thereby increasing instantaneous transpiration efficiency. Exposure to elevated CO₂ and/or O₃ had no detectable effect on dark-adapted fluorescence, although the values decreased with time. Analysis of the relationships between assimilation rate and intercellular CO₂ concentration and photosynthetically active photon flux density showed there was initially little treatment effect on CO₂-saturated assimilation rates for leaf 15. However, the values for plants grown under 550 μmol mol⁻¹ CO₂ were subsequently greater than in the ambient and 680 μmol mol⁻¹ treatments, although the beneficial influence of the former treatment declined sharply towards the end of the season. Light-saturated assimilation was consistently greater under elevated CO₂, but decreased with time in all treatments. The values decreased sharply when leaves grown under elevated CO₂ were measured under ambient CO₂, but increased when leaves grown under ambient CO₂ were examined under elevated CO₂. The results obtained indicate that, although elevated CO₂ initially increased assimilation and growth, these beneficial effects were not necessarily sustained to maturity as a result of photosynthetic acclimation and the induction of earlier senescence.     

大豆主要株型和产量指标对大气CO2和温度升高的响应

针对当前气候变暖和大气CO_2浓度升高同步发生现实,以高光效大豆品种黑农41(HN41)和3个常规对照品种周豆16号(ZD16)、中豆35号(ZD35)和桂黄豆2号(GHD2)为研究对象,通过开顶式气室模拟高CO_2浓度(650μL/L)和温度升高(±0.5—0.6℃)研究了大气CO_2和温度升高对大豆的生长发育与产量影响。结果表明,CO_2浓度升高对株高、茎粗、单株干重和单株籽粒重影响极显著;温度、CO_2与品种互作极显著地影响单株籽粒重。CO_2浓度升高有增加大豆株高、茎粗、干重和单株籽粒重的趋势,且高温下CO_2浓度升高对株高和茎粗的促进作用更大,而正常温度水平下高CO_2浓度升高更有利于干物质积累。与对照CO_2浓度比,高CO_2浓度显著促进了高温下HN41、ZD16和GHD2的株高,并显著提高了正常温度下HN41、ZD16、ZD35和GHD2的单株干重。与正常温度相比,高温仅显著提高了高CO_2处理下HN41的茎粗,并显著提高了对照CO_2处理下HN41的单株籽粒重。此外,同一CO_2浓度和温度处理下,高光效大豆HN41的茎粗、根冠比和单株籽粒重等都显著高于ZD16、ZD35和GHD2;而仅在正常温度与高CO_2浓度处理下HN41的单株干重显著高于ZD16和GHD2。CO_2浓度和温度升高显著影响了高光效大豆的生长,其中,高温下CO_2浓度升高有利于其生长势,正常温度下CO_2浓度升高有利于其光合产物积累。     

Genetic and physical characterization of theLR1 leaf rust resistance locus in wheat (Triticum aestivum L.)

The objective of this study was to characterize the leaf rust resistance locusLr1 in wheat. Restriction fragment length polymorphism (RELP) analysis was performed on the resistant lineLr1/6^*Thatcher and the susceptible varieties Thatcher and Frisal, as well as on the segregating F₂ populations. Seventeen out of 37 RFLP probes mapping to group 5 chromosomes showed polymorphism betweenLr1/6^*Thatcher and Frisal, whereas 11 probes were polymorphic between the near-isogenic lines (NILs)Lr1/6^*Thatcher and Thatcher. Three of these probes were linked to the resistance gene in the segregating F₂ populations. One probe (pTAG621) showed very tight linkage toLr1 and mapped to a single-copy region on chromosome 5D. The map location of pTAG621 at the end of the long arm of chromosome 5D was confirmed by the absence of the band in the nulli-tetrasomic line N5DT5B of Chinese Spring and a set of deletion lines of Chinese Spring lacking the distal part of 5DL. Twenty-seven breeding lines containing theLr1 resistance gene in different genetic backgrounds showed the same band asLr1/6^*Thatcher when hybridized with pTAG621. The RFLP marker was converted to a sequence-tagged-site marker using polymerase chain reaction (PCR) amplification. Sequencing of the specific fragment amplified from both NILs revealed point mutations as well as small insertion/deletion events. These were used to design primers that allowed amplification of a specific product only from the resistant lineLr1/6^*Thatcher. This STS, specific for theLr1 resistance gene, will allow efficient selection for the disease resistance gene in wheat breeding programmes. In addition, the identification of a D-genome-specific probe tightly linked toLr1 should ultimately provide the basis for positional cloning of the gene.     

6种草本植物对干旱胁迫和CO2浓度升高交互作用的生长响应

以CO2浓度升高为主要标志的全球气候变化及由其引起的极端气候变化对陆地生态系统产生了重要的影响。利用步入式CO2生长室模拟研究了CO2浓度变化(400和700μL/L)和干旱胁迫(水分充足CK:100%FC(田间持水量);中度干旱MS:40%FC;重度干旱SS:20%FC)的交互作用对草本植物网果酸模(Rumex chalepensis)、野豌豆(Vicia sepium)、泥胡菜(Hemmistepta lyrata)、风轮菜(Clinopodium chinense)、藜(Chenopodium album)和玉米石(Sedum album)生长特性的影响。结果表明:CO2浓度升高总体上刺激了网果酸模、野豌豆、泥胡菜、风轮菜和藜这5种C3植物在任何水分条件下的生长,也刺激了玉米石在水分条件较好下的生长;干旱胁迫总体上抑制了所有6种植物的生长,但中度干旱胁迫有刺激CAM植物玉米石生长的趋势。CO2浓度升高能否缓解干旱的负面影响具有明显的种间差异:CO2浓度升高减缓了干旱胁迫对泥胡菜和风轮菜的负面影响,这种缓解作用在网果酸模和野豌豆中显著降低,对藜没有明显的促进作用,对干旱下的玉米石的生长却起到了抑制作用。CO2浓度升高总体上增加了根质量分数和干物质含量;干旱胁迫明显提高了6种草本植物的根生物量的分配比例,降低了干物质含量;但CO2浓度升高和干旱胁迫的交互作用可导致不同的物种产生不同的响应,说明植物能够通过调节生物量分配和植株本身的水分含量保持能力来适应CO2浓度和干旱胁迫的交互影响,这种调节能力取决于植物在碳的吸收和水分散失之间的平衡"trade-off"。研究结果有助于增进草本植物对未来气候变化的适应性理解,为评估和预测全球气候和水文变化对植物的生理生态影响提供理论依据。     

Antioxidant status in herbaceous plants growing under elevated CO2 in mini-FACE rings

Here we present studies on the antioxidant status of a semi-natural grassland community, permanently growing in mini-FACE rings under elevated concentrations of atmospheric CO₂ (560 μmol mol⁻¹). In general, in leaves of Dactylis glomerata L. and Trifolium repens L., no differences between ambient and elevated CO₂ were detected as concerns protein content, activity of oxidant-scavenging enzymes (catalase, superoxide dismutase, ascorbate peroxidase and guaiacol peroxidase), and lipid peroxidation. The activity of antioxidant-regenerating enzymes (monodehydroascorbate reductase, dehydroascorbate reductase and glutathione disulfide reductase) and the content of antioxidants (ascorbic acid, dehydroascorbic acid, reduced glutathione and glutathione disulfide) showed remarkable variability between leaves from plants grown in ambient and CO₂-enriched mini-FACE rings. Thus, in general it can be concluded that the effects of elevated CO₂ at environmentally relevant concentrations on the leaf antioxidant status of a grassland community are extremely variable, species-specific and rather limited.     

Effects of elevated CO2 and O3 on the rate and duration of grain growth and harvest index in spring wheat (Triticum aestivum L.)

Wheat (Triticum aestivum L.) cv. Minaret was grown in open-top chambers (OTCs) in 1995 and 1996 under three carbon dioxide (CO₂) and two ozone (O₃) levels. Plants were harvested regularly between anthesis and maturity to examine the rate of grain growth (dG/dt; mg d^–1) and the rate of increase in harvest index (dHI/dt;% d^–1). The duration of grain filling was not affected by elevated CO₂ or O₃, but was 12 days shorter in 1995, when the daily mean temperature was over 3 °C higher than in 1996. Season-long exposure to elevated CO₂ (680 μmol mol^–1) significantly increased the rate of grain growth in both years and mean grain weight at maturity (MGW) was up to 11% higher than in the chambered ambient air control (chAA; 383 μmol mol^–1). However, the increase in final yield obtained under elevated CO₂ relative to the chAA control in 1996 resulted primarily from a 27% increase in grain number per unit ground area. dG/dt was significantly reduced by elevated O₃ under ambient CO₂ conditions in 1995, but final grain yield was not affected because of a concurrent increase in grain number. Neither dG/dt nor dHI/dt were affected by the higher mean O₃ concentrations applied in 1996 (77 vs. 66 nmol mol^–1); the differing effects of O₃ on grain growth in 1995 and 1996 observed in both the ambient and elevated CO₂ treatments may reflect the contrasting temperature environments experienced. Grain yield was nevetheless reduced under elevated O₃ in 1996, primarily because of a substantial decrease in grain number. The data obtained show that, although exposure to elevated CO₂ and O₃ individually or in combination may affect both dG/dt and dHI/dt, the presence of elevated CO₂ does not protect against substantial O₃-induced yield losses resulting from its direct deleterious impact on reproductive processes. The implications of these results for food production under future climatic conditions are considered.