Survival and recovery of perennial forage grasses under prolonged Mediterranean drought: II. Water status, solute accumulation, abscisic acid concentration and accumulation of dehydrin transcripts in bases of immature leaves

Effects of ozone on spring wheat ( Triticum aestivum L. cv. Satu) were studied in an open-top chamber experiment during two growing seasons (1992–1993) at Jokioinen in south-west Finland. The wheat was exposed to filtered air (CF), non-filtered air (NF), non-filtered air+35 nl l⁻¹ ozone for 8 h d⁻¹ (NF⁺) and ambient air (AA). Each treatment was replicated five times. Two wk after anthesis, after 4 wk of ozone treatment (NF⁺, 45 nl l⁻¹ 1000–1800 hours, seasonal mean) the net CO₂ uptake of wheat flag leaves was decreased by c . 40% relative to CF and NF treatments, both initial and total activity of Rubisco and the quantity of protein-bound SH groups were decreased significantly. Added ozone also significantly accelerated flag leaf senescence recorded as a decrease in chloroplast size. The effect was significant 2 wk after anthesis, and senescence was complete after 4 wk. In the CF and NF treatments senescence was complete 5 wk after anthesis. The significant effect of ozone on the chloroplasts and net CO₂ uptake 2 wk after anthesis did not affect the grain filling rate. However, since the grain filling period was shorter for ozone fumigated plants, kernels were smaller. The decrease in 1000-grain weight explained most of the yield reduction in the plants under NF⁺ treatment. The results indicate that wheat plants are well buffered against substantial decrease in source activity, and that shortened flag leaf duration is the major factor causing ozone-induced yield loss.     

冬小麦气孔臭氧通量拟合及通量产量关系的比较分析

基于田间原位开顶箱(Open-Top Chambers,OTCs)实验,研究了不同浓度臭氧(O3)处理下(自然大气处理,AA;箱内大气处理,NF;箱内低浓度O3处理,NF+40 nL/L;箱内中等浓度O3处理,NF+80 nL/L;箱内高浓度O3处理,NF+120 nL/L),冬小麦(Triticum aestivum L.)旗叶气孔运动对不同环境因子的响应,并通过剂量反应分析,比较了冬小麦产量损失与累积气孔O3吸收通量(AFstX)和累积O3暴露浓度(AOT40和SUM06)的相关性差异。结果表明:冬小麦旗叶气孔运动的光饱和点和最适温度分别约为400μmol.m-.2s-1和27℃,水汽压差、土壤含水量和O3剂量的气孔限制临界值分别约为1.4 kPa、-100 kPa和20μL.L-.1h-1,超过此临界值时,气孔导度会明显下降。利用Jarvis气孔导度模型对冬小麦旗叶气孔导度和气孔O3吸收通量进行了预测,结果表明Jarvis模型解释了冬小麦实测气孔导度60%的变异性。由于不同时期植物体气孔导度的差异,冬小麦旗叶生长期内累积气孔O3吸收通量(AFstX)呈非线性增加趋势。O3吸收速率临界值(X)为4 nmol.m-.2s-1时,累积O3吸收通量(AFst4)与冬小麦产量的相关性最高(R2=0.76),该数值介于O3暴露指标AOT40和SUM06的剂量反应决定系数(0.74和0.81)之间。与O3浓度指标(AOT40和SUM06)相比,O3通量指标(AFstX)在本试验冬小麦产量损失评价中未表现出明显优势。     

Effects of ozone on zinc and cadmium accumulation in wheat – dose–response functions and relationship with protein,grain yield,and harvest index

Response functions for the effect of ozone on cadmium (Cd) (toxic to humans) and zinc (Zn) (essential nutrient for plants and humans) in wheat grain were derived for the first time. Data from four open‐top chamber (OTC) experiments with field‐grown wheat, performed in southwest Sweden, were used. Ozone exposure was expressed as the phytotoxic ozone dose above a threshold of 6 nmol/m² per sec (POD₆), and AOT40. Grain Zn concentration was significantly enhanced by ozone, while Zn yield was not affected. The positive ozone effect on grain Zn concentration was almost twice as large as the corresponding effect on grain protein concentration, most likely as a result of nitrogen availability being more limiting than Zn availability. Cd concentration was unaffected by ozone, but Cd yield was significantly negatively affected. For the variables studied, correlation was stronger with POD₆ than AOT40, but in several cases, for example, for Zn concentration and Cd yield, there was practically no difference in the performance between the two exposure indices. From the literature, it is obvious that ozone has important adverse effects on wheat yield and certain quality traits. As shown in this study, there are also examples of ozone leading to improved quality, for example, in terms of enhanced Zn concentration of wheat grain. While OTC enclosure did not affect Zn accumulation in wheat grain, Cd accumulation was significantly positively affected, most likely through transpiration being enhanced by the OTC environment, promoting Cd uptake and transport through the plant.     

Elevated CO2 concentration enhances the role of the ear to the flag leaf in determining grain yield of wheat

Net photosynthetic rate (P _N) of ear and flag leaf during grain filling stage and grain yield of plants with non-darkened or darkened flag leaf or darkened ear were examined in two different CO₂ concentrations: ambient (AC) and AC+200 μmol mol⁻¹ (EC). Ear showed much higher enhancement (56 %) of P _N than flag leaf (23 %) under EC. Moreover, CO₂ enrichment shortened the photosynthetic duration of flag leaf relative to ear. In this way the ratio of ear to flag leaf contribution to grain yield increased from 1.18 (AC) to 1.39 (EC).     

Contribution of the wheat (Triticum aestivum L.) flag leaf to grain yield in response to plant growth regulators

In West-Europe, intensive cereal management uses plant growth regulators (PGRs) especially for wheat. A green-house experiment compared the effects of two PGRs on flag leaf characteristics and yield of winter wheat. Chlormequat chloride + choline chloride (CCC) and chlormequat chloride + choline chloride + imazaquin (CCC+I) were applied to winter wheat at growth stage 5 (Feekes Large scale). CCC and CCC+I significantly increased flag leaf surface area at anthesis. Both treatments also enhanced chlorophyll content of the main stem flag leaf. The grain filling period was extended with PGR application by 2 days. CCC and CCC+I significantly increased net CO₂ assimilation rates during the flag leaf life. No effects of PGR spraying were observed on the pattern of ¹⁴C labelled assimilate distribution. Increased grain yield was due to the increase in average grain weight. The results indicate that PGR treatments increased flag leaf contribution to grain filling. The addition of imazaquin (I) to chlormequat (CCC) improved the effects of CCC.     

Ozone exposure results in various carry-over effects and prolonged reduction in biomass in birch (Betula pendula Roth)

In the first experiment, saplings of ozone-sensitive and a more tolerant clone of Betula pendula Roth were exposed to ambient ozone (control treatment, accumulated exposure over a threshold 40 nmol mol ^{? 1} (AOT40) exposure of 1·0 μmol mol ^{? 1} h) and 1·5 × ambient ozone (elevated-ozone treatment, AOT40 of 17·3 μmol mol ^{? 1} h) over one growing season, 1996. After over-wintering, the dormant elevated-ozone saplings were transferred to the control blocks and assessed for short-term carry-over effects during the following growing season. In the second experiment, three sensitive, four intermediate and three tolerant clones were grown under ambient ozone (control treatment, AOT40 of 0·5–0·8 μmol mol ^{? 1} h per growing season) and 1·6–1·7 × ambient ozone (elevated-ozone treatment, AOT40 of 18·3–18·6 μmol mol ^{? 1} h per growing season) from May 1994 until May 1996, and were assessed for long-term carry-over effects during growing season 1997, after a 12–16 months recovery period. Deleterious short-term carry-over effects of ozone exposure included reduced contents of Rubisco, chlorophyll, carotenoids, starch and nutrients in leaves, lower stomatal conductance, and decreased new shoot growth and net assimilation rate, followed by a 7·5% (shoot dry weight (DW)), 15·2% (root DW) and 23·2% (foliage area) decreased biomass accumulation and yield over the long term, including a reduced root : shoot ratio. However, a slow recovery of relative growth rates during the following two seasons without elevated ozone was apparent. Several long-lasting structural, biochemical and stomatal acclimation, stress-defence and compensation reactions were observed in the ozone-tolerant clone, whereas in the sensitive clone allocation shifted from growth towards defensive phenolics such as chlorogenic acid. The results provide evidence of persistent deleterious effects of ozone which remain long after the ozone episode.     

Raman spectroscopy of pigments and oxalates in situ within epilithic lichens: Acarospora from the Antarctic and Mediterranean

The effects of ambient and elevated ozone levels on growth and photosynthesis of beech ( Fagus sylvatica ) were studied by exposing seedlings in open-top chambers for one growing season to three treatments: charcoal-filtered (CF), non-filtered (NF) and non-filtered air with addition of ozone (30 ppb ozone) on clear days for 8–10 h d⁻¹ (NF +). Ambient levels were relatively low and accumulated to an AOT40 (accumulated exposure over a threshold of 40 ppb) of 4055 ppb h (for the period 23 Apr–30 Sept). The NF + chambers received an AOT40 of 8880 ppb h. Throughout the growing season we measured growth and photosynthetic properties. The treatments did not cause strong effects: measurements of gas exchange (light-saturated assimilation rate, CO₂ and light-response curves) and chlorophyll fluorescence showed slight and mostly non-significant reductions of several parameters. No significant differences were found for growth, though in the NF + treatment (AOT40 8880 ppb h) the relative growth rate for diameter increment was at times reduced by 12% compared with the control treatment.     

Concentration‐ and flux‐based dose–responses of isoprene emission from poplar leaves and plants exposed to an ozone concentration gradient

Concentration‐ and flux‐based O₃ dose–responses of isoprene emission from single leaves and whole plants were developed. Two poplar clones differing in O₃ sensitivity were exposed to five O₃ levels in open‐top chambers for 97 d: charcoal‐filtered ambient air (CF), non‐filtered ambient air (NF) and NF plus 20 ppb (NF + 20), 40 ppb (NF + 40) and 60 ppb (NF + 60). At both leaf and plant level, isoprene emission was significantly decreased by NF + 40 and NF + 60 for both clones. Although intra‐specific variability was found when the emissions were up‐scaled to the whole plant, both leaf‐ and plant‐level emissions decreased linearly with increasing concentration‐based (AOT40, cumulative exposure to hourly O₃ concentrations >40 ppb) and flux‐based indices (POD_Y, cumulative stomatal uptake of O₃ > Y nmol O₃ m^?2 PLA s^?1). AOT40‐ and POD₇‐based dose–responses performed equally well. The two clones responded differently to AOT40 and similarly to POD_Y (with a slightly higher R² for POD₇) when the emission was expressed as change relative to clean air. We thus recommend POD₇ as a large‐scale risk assessment metric to estimate isoprene emission responses to O₃ in poplar.     

O3胁迫对冬小麦籽粒果皮光合能力及灌浆的影响

为揭示高浓度O3对冬小麦籽粒发育和干物质累积的影响,通过OTC设置了活性碳过滤空气(CF,4—28 n L/L)、不通风(5H,15—68 n L/L)、环境空气(NF,7—78 n L/L)、100n L/L O3(CF100,96—108 n L/L)和150n L/L O3(CF150,145—160n L/L)等5种O3熏蒸处理,测量了籽粒干物质累积、光合色素含量及果皮的叶绿素荧光特性(IMAGING-PAM)。结果显示,CF100和CF150处理显著降低了冬小麦籽粒的长度、最大宽度、最大厚度、10粒体积、穗粒数、灌浆持续时间和灌浆高峰结束前的平均灌浆速率,其千粒重在整个灌浆过程中均显著低于NF,收获时分别下降了10.7%和17.8%;CF100和CF150的光合色素含量在扬花后8—16d内显著高于其余3组(伴随着较强的光合能力),扬花16d后迅速下降18d后差异达到显著水平。穗粒重下降的主要原因是籽粒体积缩小、灌浆持续时间缩短和穗粒数下降;高浓度O3在灌浆前期延缓了冬小麦的生育进度,在灌浆后期使得植株迅速衰老,灌浆持续时间大幅缩短;籽粒果皮的最大光合能力在灌浆初期受到一定抑制,在灌浆中期表现出较好的适应性,在中后期由于籽粒衰老提前而迅速下降。高浓度O3条件下,果皮绿色层在籽粒干物质累积和营养物合成过程中发挥着更加重要的作用。     

氮肥后移对抽穗后水分胁迫下冬小麦光合特性及产量的影响

采用子母桶栽土培法模拟冬小麦抽穗后不同的水分胁迫状态,研究了氮肥后移对冬小麦光合特性及产量的影响.设置3个氮肥处理,分别为N₁(基肥∶拔节肥∶开花肥=10∶0∶0)、N₂(6∶4∶0)和N₃(4∶3∶3),模拟冬小麦抽穗后2种水分胁迫(渍水胁迫、干旱胁迫),设正常供水为对照.结果表明：相同供水条件下,N₂和N₃处理较N₁处理显著提高冬小麦灌浆期旗叶的SPAD和光合速率,确保了收获时较高的穗数、穗粒数和地上部分生物量;氮肥后移处理显著提高了冬小麦的耗水量,但其籽粒产量和水分利用效率也显著提高.相同氮肥条件下,干旱胁迫和渍水胁迫处理较正常供水显著降低了冬小麦开花期和灌浆期旗叶的光合速率、千粒重、穗粒数和产量.与正常供水相比,各氮肥条件下干旱胁迫和渍水胁迫处理花后旗叶光合速率及籽粒产量的减小幅度均表现为N₁＞N₂＞N₃.表明氮肥后移通过提高旗叶SPAD、减缓花后旗叶光合速率的下降幅度、增加地上部分干物质积累量,调控产量及其构成要素,以减轻逆境灾害(干旱和渍水胁迫)对产量的影响.     

Involvement of abscisic acid and cytokinins in the senescence and remobilization of carbon reserves in wheat subjected to water stress during grain filling

This study investigated the possibility that abscisic acid (ABA) and cytokinins may mediate the effect of water deficit that enhances plant senescence and remobilization of pre‐stored carbon reserves. Two high lodging‐resistant wheat (Triticum aestivum L.) cultivars were field grown and treated with either a normal or high amount of nitrogen at heading. Well‐watered (WW) and water‐stressed (WS) treatments were imposed from 9 d post‐anthesis until maturity. Chlorophyll (Chl) and photosynthetic rate (Pr) of the flag leaves declined faster in WS plants than in WW plants, indicating that the water deficit enhanced senescence. Water stress facilitated the reduction of non‐structural carbohydrate in the stems and promoted the re‐allocation of prefixed ¹⁴C from the stems to grains, shortened the grain filling period and increased the grain filling rate. Water stress substantially increased ABA but reduced zeatin (Z) + zeatin riboside (ZR) concentrations in the stems and leaves. ABA correlated significantly and negatively, whereas Z + ZR correlated positively, with Pr and Chl of the flag leaves. ABA but not Z + ZR, was positively and significantly correlated with remobilization of pre‐stored carbon and grain filling rate. Exogenous ABA reduced Chl in the flag leaves, enhanced the remobilization, and increased grain filling rate. Spraying with kinetin had the opposite effect. The results suggest that both ABA and cytokinins are involved in controlling plant senescence, and an enhanced carbon remobilization and accelerated grain filling rate are attributed to an elevated ABA level in wheat plants when subjected to water stress.     

Differential ozone sensitivity of rice cultivars as indicated by visible injury and grain yield

Surface ozone pollution may cause reductions in rice ( Oryza sativa L.) yield. Ozone sensitivity in rice cultivars is often evaluated based on visible leaf injury at an early growth stage. However, it is not clear whether reduction in grain yield is related to visible injury. Therefore, visible damage and grain yield reduction were examined in Japanese and Asian rice cultivars exposed to ozone. In experiment 1, 3-week-old rice seedlings were exposed to ozone (min.: 20 nl·l⁻¹, max.:120 nl·l⁻¹) for 12 h in open-top chambers (OTCs). Visible leaf injury was quantified according to a leaf bronzing score. In experiment 2, rice plants were exposed to ozone in OTCs throughout the cropping season until grain harvest. Daily mean ozone concentrations were maintained at 2, 23, 28, 42, and 57 nl·l⁻¹ with a regular diurnal pattern of exposure. After harvest, grain yield was determined. Based on visible injury to the uppermost fully expanded leaf, the indica cultivar 'Kasalath' was most tolerant, and the japonica cultivar 'Kirara 397' was most sensitive to ozone. However, grain yields for both 'Kasalath' and 'Kirara 397' were significantly decreased after ozone exposure. The indica cultivar 'Jothi' suffered severe injury after ozone exposure but had no reduction in grain yield. Therefore, ozone sensitivity of rice cultivars evaluated by visible injury did not coincide with that evaluated by the reductions in grain yield. These results suggest that mechanisms that induce acute leaf injury do not relate to chronic ozone toxicity that reduces yield.     

Photosynthetic characteristics and enzymatic antioxidant capacity of flag leaf and the grain yield in two cultivars of Triticum aestivum (L.) exposed to warmer growth conditions

Using late sowing practice, the reproductive growth (anthesis and kernel filling) phase of two wheat cultivars, HD 1553 and HD 2307 was exposed to warmer growth conditions, and the effect on grain yield was examined. The grain weight declined in late-sown plants of both cultivars, but the number of grains per spike decreased drastically in HD 1553 plants. In this cultivar exposure to warmer temperature during reproductive phase led to 67% fewer grains per spike. Examination of photosynthetic and enzymatic antioxidant capacity in flag leaves of late-sown plants revealed a marked reduction in chlorophyll and carotenoid pigmentation in addition to a decline in the activity of H2O2 metabolising enzymes in HD 1553 cultivar. The photo-oxidative pigment loss due to warmer growth conditions in late-shown HD 1553 plants could lead to a reduction in flag leaf photosynthesis and contribute to poor grain yield.     

Phloem transport of arsenic species from flag leaf to grain during grain filling

? Strategies to reduce arsenic (As) in rice grain, below concentrations that represent a serious human health concern, require that the mechanisms of As accumulation within grain be established. Therefore, retranslocation of As species from flag leaves into filling rice grain was investigated. ? Arsenic species were delivered through cut flag leaves during grain fill. Spatial unloading within grains was investigated using synchrotron X-ray fluorescence (SXRF) microtomography. Additionally, the effect of germanic acid (a silicic acid analog) on grain As accumulation in arsenite-treated panicles was examined. ? Dimethylarsinic acid (DMA) and monomethylarsonic acid (MMA) were extremely efficiently retranslocated from flag leaves to rice grain; arsenate was poorly retranslocated, and was rapidly reduced to arsenite within flag leaves; arsenite displayed no retranslocation. Within grains, DMA rapidly dispersed while MMA and inorganic As remained close to the entry point. Germanic acid addition did not affect grain As in arsenite-treated panicles. Three-dimensional SXRF microtomography gave further information on arsenite localization in the ovular vascular trace (OVT) of rice grains. ? These results demonstrate that inorganic As is poorly remobilized, while organic species are readily remobilized, from leaves to grain. Stem translocation of inorganic As may not rely solely on silicic acid transporters.     

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.     

Evidence of widespread effects of ozone on crops and (semi‐)natural vegetation in Europe (1990–2006) in relation to AOT40‐ and flux‐based risk maps

Records of effects of ambient ozone pollution on vegetation have been compiled for Europe for the years 1990–2006. Sources include scientific papers, conference proceedings, reports to research funders, records of confirmed ozone injury symptoms and an international biomonitoring experiment coordinated by the ICP Vegetation. The latter involved ozone‐sensitive (NC‐S) and ozone‐resistant (NC‐R) biotypes of white clover (Trifolium repens L.) grown according to a common protocol and monitored for ozone injury and biomass differences in 17 European countries, from 1996 to 2006. Effects were separated into visible injury or growth/yield reduction. Of the 644 records of visible injury, 39% were for crops (27 species), 38.1% were for (semi‐) natural vegetation (95 species) and 22.9% were for shrubs (49 species). Owing to inconsistencies in reporting effort from year to year it was not possible to determine geographical or temporal trends in the data. Nevertheless, this study has shown effects in ambient air in 18 European countries from Sweden in the north to Greece in the south. These effects data were superimposed on AOT40 (accumulated ozone concentrations over 40 ppb) and POD3_gen (modelled accumulated stomatal flux over a threshold of 3 nmol m^?2 s^?1) maps generated by the EMEP Eulerian model (50 km × 50 km grid) that were parameterized for a generic crop based on wheat and NC‐S/NC‐R white clover. Many effects were found in areas where the AOT40 (crops) was below the critical level of 3 ppm h. In contrast, the majority of effects were detected in grid squares where POD3_gen (crops) were in the mid‐high range (>12 mmol m^?2). Overall, maps based on POD3_gen provided better fit to the effects data than those based on AOT40, with the POD3_gen model for clover fitting the clover effects data better than that for a generic crop.     

CO(2) enrichment enhances flag leaf senescence in barley due to greater grain nitrogen sink capacity

Senescence is a highly regulated process which is under genetic control. In monocarpic plants, the onset of fruit development is the most important factor initiating the senescence process. During senescence, a large fraction of plant nutrients is reallocated away from vegetative tissues into generative tissues. Senescence may therefore be regarded as a highly effective salvage mechanism to save nutrients for the offspring. CO(2) enrichment, besides increasing growth and yield of C(3) plants, has often been shown to accelerate leaf senescence. C(3) plants grown under elevated CO(2) experience alterations in their nutrient relations. In particular their tissue nitrogen concentrations are always lower after exposure to elevated CO(2). We used a monocarpic C(3) crop - spring barley (Hordeum vulgare cv. Alexis) - grown in open-top field chambers to test the effects of CO(2) enrichment on growth and yield, on nitrogen acquisition and redistribution, and on the senescence process in flag leaves, at two applications of nitrogen fertilizer. CO(2) enrichment (650 vs. 366 μmol mol(-1)) caused an increase both in biomass and in grain yield by 38% (average of the two fertilizer applications) which was due to increased tillering. Total nitrogen uptake of the crops was not affected by CO(2) treatment but responded solely to the N supply. Nitrogen concentrations in grains and straw were significantly lower (-33 and -24%) in plants grown at elevated CO(2). Phenological development was not altered by CO(2) until anthesis. However, progress of flag leaf senescence as assessed by chlorophyll content, protein content and content of large and small subunit of RubisCO and of cytochrome b559 was enhanced under elevated CO(2) concentrations by approximately 4 days. We postulate that CO(2) enhanced flag leaf senescence in barley crops by increasing the nitrogen sink capacity of the grains.     

施氮量对超高产冬小麦灌浆期旗叶光响应曲线的影响

为冬小麦超高产栽培的氮肥管理提供技术支撑,在大田条件下研究了施氮量对超高产冬小麦灌浆期旗叶光响应曲线的影响.采用开放式气路测定了小麦旗叶的净光合速率、气孔导度、胞间二氧化碳浓度、蒸腾速率等相关指标,并运用"米式方程"对旗叶净光合速率进行了模拟,计算了光响应曲线的特征参数.结果表明,在0～300kg/hm2施氮范围内,随着光照强度的增加,各处理的旗叶净光合速率、气孔导度、蒸腾速率均随之增加,而胞间二氧化碳浓度却随之降低,但是在375kg/hm2施氮水平下旗叶的净光合速率、气孔导度、蒸腾速率的增加和胞间二氧化碳浓度的降低反而低于300kg/hm2施氮水平,表明合理的氮素水平对超高产小麦灌浆期旗叶的光响应曲线有明显的调节作用.在合理的施氮范围内,增施氮肥小麦旗叶在整个灌浆期内的最大净光合速率随之增加.在本试验条件下,超高产麦田的适宜施氮量为300kg/hm2.     

灌水模式对冬小麦光合特性、水分利用效率和产量的影响

试验于2013—2014和2014—2015年连续2个生长季在自动控制干旱棚内的隔离池中进行,拔节期设3个灌水梯度,灌水量分别为0(J_0)、37.5(J_1)、75 mm(J_2),扬花期设3个灌水梯度,灌水量分别为0(F_0)、37.5(F_1)、75 mm(F_2),灌浆期所有处理均按75 mm灌溉,共9个处理,研究不同灌溉模式对小麦中后期不同生育阶段植株生长、耗水量、水分利用效率、光合特性和产量构成因素的影响.结果表明:拔节期干旱(0和37.5 mm)显著降低了小麦扬花期的净光合速率和拔节后的叶面积,扬花期的灌水量直接影响扬花期后的旗叶净光合速率;拔节期干旱扬花期补水和扬花期干旱灌浆期补水都可以有效提高植株的干物质量;拔节期灌水量越多,全生育期耗水量越大;除J_1F_2外,全生育期灌水量越大,耗水量越大,产量也越高;J_1F_2处理产量和水分利用效率最高.扬花期充足的灌水量使J_1F_2处理具有较高的花后旗叶净光合速率,此期补偿性灌溉加快了干物质积累,也保证了较高的穗粒数,使其最终产量高于J_2F_2处理或与之持平,同时J_1F_2拔节期较低的灌水量降低了小麦生育中后期的耗水量,其水分利用效率也显著高于其他处理.综上,J_1F_2是小麦生育中期理想的水分处理组合.     

不同植物生长调节剂对小麦衰老及产量构成的调节效应

研究了叶面喷施GA3、NBT、6－BA、TIBA、PP333对小麦旗叶衰老过程中若干生理指标的影响,分析了它们对成产要素的不同作用。结果表明：不同生长调节剂可以以不同的方式调节小麦旗叶的衰老,影响小麦产量构成因素水平。其中6－BA和PP333能够提高单位面积穗数,明显延缓叶片衰老,增加了穗粒数和千粒重,使成产3因素间比例协调合理,产量较高;TIBA可以明显提高叶绿素含量并显著提高千粒重。GA3和NBT对延缓旗叶衰老有一定作用,但增产效果不显著。研究指出,根据小麦生育状况有选择性地使用生长调节剂,协调成产因素关系,是一个有效的增产途径。