The Effect of Changing Sowing Date on Leaf Structure and Gas Exchange Characteristics of Wheat Flag Leaves Grown under Mediterranean Climate Conditions

Comparisons of leaf structure and gas exchange characteristicshave been made between flag leaves of four old genotypes ofcultivated tetraploid wheats and three current varieties ofhexaploid Triticum aestivum grown under Mediterranean climateconditions. For some genotypes the effect of varying the sowingdate was investigated. In the hexaploid wheat Kolibri the effectof sowing date on leaf structure and gas exchange of the penultimateleaf was also studied. Flag leaves differed significantly in photosynthetic capacityand leaf structure characteristics between genotypes, withineach ploidy level. When the mean values for each ploidy levelwere considered, there were no significant differences in valuesfor photosynthesis per unit leaf area, stomatal conductance,intercellular CO₂ concentration, residual CO₂ conductance andwater-use efficiency between the tetraploid and hexaploid wheatssown on the same date. When comparisons were made of leaf structurethe only significant differences observed were in adaxial andabaxial stomatal frequencies and leaf area: mean values of theseparameters were higher in tetraploid than in hexaploid wheats. The changes in leaf structure in response to varying sowingdate were significant and followed the same pattern in all thegenotypes studied: a xeromorphic adaptation was observed inlater sowings in response to warmer climate. Such structuralchanges affected some gas exchange characteristics. For example,the area of flag leaves decreased by 60% in the hexaploid wheatKolibri from first to last sowing, which led to a transpirativeloss of 49% per single leaf, in spite of the fact that transpirationrate per unit leaf area increased by 26%. Penultimate leavesof cv. Kolibri followed a fairly similar adaptive pattern inlater sowings as compared with flag leaves. The adaptive significanceof changes in leaf structure and gas exchange characteristicswith varying sowing date under Mediterranean climate conditionsis discussed. Key words: Photosynthesis, leaf structure, wheat     

Effect of Indol-3-yl Acetic Acid on Photosynthetic Characteristics of Wheat Flag Leaf During Grain Filling

Area and fresh and dry masses of flag leaf show two phases of development during grain filling in Triticum aestivum. The initial large increase in leaf size is mainly due to water intake. Contents of chlorophylls and carotenoids, reducing sugars, and sucrose, Hill reaction rate, and photosynthetic activity increased during leaf growth, but a noticeable decline in these parameters followed throughout leaf senescence. The maximum accumulation of polysaccharides and proteins occurred at the beginning of grain set, but a continuous decline in their absolute values was manifested during grain filling. Grain priming with indol-3-yl acetic acid (IAA) at 25 mg kg^-1 stimulated the flag leaf growth, namely its fresh and dry masses and its area. Furthermore, the stimulatory effect was mainly due to the increase in the pigment formation that in turn increased the photosynthetic activity of flag leaf during grain filling. On the other hand, the highest dose of IAA (50 mg kg^-1) attenuated the growth and physiological activity of flag leaf through its inhibitory action on leaf fresh and dry masses, leaf area, pigments, saccharides and protein formation, as well as its effect on ¹⁴CO₂ assimilation.     

Gas Exchange of Spring Barley and Wheat Grown under Mild Water Shortage

During mild water stress (decrease of full water capacity from 60 to 35 %) net photosynthetic rate (P _N) of four spring barley and wheat genotypes was about twice lower than that for unstressed plants and was mainly limited by non-stomatal factors. Availability of CO₂ from intercellular spaces did not change significantly when stomatal conductance (g _s) decreased from 0.25-0.35 to 0.15-0.20 mol(H₂O) m⁻² s⁻¹. There may be two main processes leading to similar intercellular CO₂ concentration (c _i) in stressed and unstressed seedlings despite of twice lower P _N under mild water stress: (a) lower diffusion of CO₂ through stomata represented by lower g _s, (b) lower consumption of CO₂ by photosynthetic apparatus of stressed plants. Last factor is partially pronounced by lower response of P _N to c _i observed for stressed than for control plants. This revised version was published online in August 2006 with corrections to the Cover Date.     

Gas Exchange of Spring Barley and Wheat Grown under Mild Water Shortage

Photosynthetica - During mild water stress (decrease of full water capacity from 60 to 35 %) net photosynthetic rate (P N) of four spring barley and wheat genotypes was about twice lower than that...     

Wheat Grain Filling Is Limited by Grain Filling Capacity rather than the Duration of Flag Leaf Photosynthesis: A Case Study Using NAM RNAi Plants

It has been proposed that delayed leaf senescence can extend grain filling duration and thus increase yields in cereal crops. We found that wheat (Triticum aestivum) NAM RNAi plants with delayed senescence carried out 40% more flag leaf photosynthesis after anthesis than control plants, but had the same rate and duration of starch accumulation during grain filling and the same final grain weight. The additional photosynthate available in NAM RNAi plants was in part stored as fructans in the stems, whereas stem fructans were remobilised during grain filling in control plants. In both genotypes, activity of starch synthase was limiting for starch synthesis in the later stages of grain filling. We suggest that in order to realise the potential yield gains offered by delayed leaf senescence, this trait should be combined with increased grain filling capacity.     

Leaf Gas Exchange and Water Relations of Grapevines Grown in Three Different Conditions

Diurnal and seasonal changes in the leaf water potential (), stomatal conductance (g _s), net CO₂ assimilation rate (P _N), transpiration rate (E), internal CO₂ concentration (C _i), and intrinsic water use efficiency (P _N/g _s) were studied in grapevines (Vitis vinifera L. cv. Touriga Nacional) growing in low, moderate, and severe summer stress at Vila Real (VR), Pinhão (PI), and Almendra (AL) experimental sites, respectively. In VR and PI site the limitation to photosynthesis was caused more by stomatal limitations, while in AL mesophyll limitations were also responsible for the summer decline in P _N.     

Comparison of the Drought Stress Responses of Tolerant and Sensitive Wheat Cultivars During Grain Filling: Changes in Flag Leaf Photosynthetic Activity,ABA Levels,and Grain Yield

Water status parameters, flag leaf photosynthetic activity, abscisic acid (ABA) levels, grain yield, and storage protein contents were investigated in two drought-tolerant (Triticum aestivum L. cv. MV Emese and cv. Plainsman V) and two drought-sensitive (cvs. GK élet and Cappelle Desprez) wheat genotypes subjected to soil water deficit during grain filling to characterize physiological traits related to yield. The leaf water potential decreased earlier and at a higher rate in the sensitive than in the tolerant cultivars. The net CO₂ assimilation rate (P _N) in flag leaves during water deficit did not display a strict correlation with the drought sensitivity of the genotypes. The photosynthetic activity terminated earliest in the tolerant cv. Emese, and the senescence of flag leaves lasted 7 days longer in the sensitive Cappelle Desprez. Soil drought did not induce characteristic differences between sensitive and tolerant cultivars in chlorophyll a fluorescence parameters of flag leaves during post-anthesis. Changes in the effective quantum yield of PSII (Φ_PSII) and the photochemical quenching (qP) depended on the genotypes and not on the sensitivity of cultivars. In contrast, the levels of ABA in the kernels displayed typical fluctuations in the tolerant and in the sensitive cultivars. Tolerant genotypes exhibited an early maximum in the grain ABA content during drought and the sensitive cultivars maintained high ABA levels in the later stages of grain filling. In contrast with other genotypes, the grain number per ear did not decrease in Plainsman and the gliadin/glutenin ratio was higher than in the control in Emese during drought stress. A possible causal relationship between high ABA levels in the kernels during late stages of grain filling and a decreased grain yield was found in the sensitive cultivars during drought stress.     

Gas Exchange Characteristics in Rice Leaves Grown under the Conditions of Physiologically Low Temperature and Irradiance

The photosynthetic rate measured at 20°C was higher in ricegrown under 20/18°C day/night temperature and 350 µmoIquanta m^–2s^–1 than in rice grown under 25/20°Cand 1,000 µmol quanta m^–2s^–1, whereas therewas no difference in the photosynthetic rate measured at 25°Cbetween rice grown in these two ways. This difference was suggestedto be caused by an enhanced ribulose-l,5-bis-phosphate-regenerationcapacity in the low-temperature/ir-radiance-grown rice. (Received July 14, 1998; Accepted September 25, 1998)     

Biomass Accumulation and Main Stem Elongation of Durum Wheat Grown under Mediterranean Conditions

Detecting and exploiting genetic variation in biomass accumulationis of great importance for increasing wheat yield when the harvestindex is close to its upper limit. This study was undertakento analyse the pattern of biomass accumulation and main stemelongation in 25 durum wheat (Triticum turgidum L. ‘Durum’)genotypes. Field experiments were conducted over 2 years intwo environments contrasting in the amount of available water,in northeastern Spain. Plants were sampled at the main stagesof Zadoks' scale, and dry weight per plant, crop dry weight(CDW) and main stem length were measured at each stage. Measurementsfor growth traits and thermal time from sowing fitted betterto an asymmetric logistic peak curve than to the Richards logisticmodel. Four biological variables were computed from the curve.Differences among curves describing changes in biomass werefound to be greater between irrigated and rainfed sites thanbetween years. Drought stress had less effect on main stem elongationthan on biomass accumulation. Average dry weight per plant andCDW were reduced by drought by 42 and 38%, respectively, duemainly to similar reductions in the mean rate of growth of thetwo variables. In contrast, cycle length from sowing to themaximum values of dry weight per plant and CDW was only slightlymodified by drought. Copyright 2001 Annals of Botany Company Triticum turgidum L. ‘Durum’, durum wheat, biomass, crop dry weight, stem length, rate of growth, modelling, growth analysis, logistic peak curve     

Effects of Long-Term Fertilization on Leaf Photosynthetic Characteristics and Grain Yield in Winter Wheat

Based on a 20-year fertilization experiment with wheat-maize double cropping system, the effects of different long-term fertilization treatments on leaf photosynthetic characteristics and grain yield in different winter wheat (Triticum aestivum L.) cultivars were studied in the growing seasons of 2000–2001 and 2001–2002. A total of nine fertilization treatments were implemented, i.e. no fertilizer (CK), N fertilizer (N), N and P fertilizers (NP), N and K fertilizers (NK), N, P, and K fertilizers (NPK), only organic manure (M), organic manure and N fertilizer (MN), organic manure and N and P fertilizers (MNP), and organic manure and N, P, and K fertilizers (MNPK). With the treatments of combined organic manure and inorganic fertilizers (TMI), net photosynthetic rate (P _N), maximal activity of photosystem 2, PS2 (F_v/F_m), and chlorophyll content (SPAD value) of flag leaves and leaf area index (LAI) were much higher at the mid grain filling stage (20 or 23 d post anthesis, DPA), and exhibited slower declines at the late grain filling stage (30 DPA), compared with the treatments of only inorganic fertilizers (TI). The maximal canopy photosynthetic traits expressed as P _N×LAI and SPAD×LAI at the mid grain filling stage were also higher in TMI than those in TI, which resulted in different grain yields in TMI and TI. Among the treatments of TMI or among the treatments of TI, both flag leaf and canopy photosynthetic abilities and yield levels increased with the supplement of inorganic nutrients (N, P, and K fertilizers), except for the treatment of NK. Under NK, soil contents of N and K increased while that of P decreased. Hence the unbalanced nutrients in soil from the improper input of nutrients in NK treatment were probably responsible for the reduced flag leaf and canopy photosynthetic characteristics and LAI, and for the fast declining of flag leaf photosynthetic traits during grain filling, resulting in the reduced yield of NK similar to the level of CK.     

浑善达克沙地不同光合途径植物叶片气体交换和水势特征(英文)

以生长于浑善达克沙地上的C3植物白榆(Ulmus pumila)、C4植物沙米(Agriophyllum pungens)和CAM植物钝叶瓦松(Orostachys malacophyllus)3种不同光合途径植物为材料,测定了它们生长期叶片的光合气体交换参数、叶绿素荧光参数和水势,探讨它们对生长环境的生理响应特征.结果表明,白榆和沙米的净光合速率、气孔导度均高于钝叶瓦松,特别是在夏季高温(>40℃)和强光照(>2 100 μmol·m-2·s-1)条件下表现得更加明显.白榆和沙米的光合速率、叶片水势都发生了严重的午休现象,其白天光合速率的降低主要是由于气孔关闭造成的.钝叶瓦松的叶片水势在3种植物中最高,但是白天的光合速率很低;其Fv/Fm值在14:00最低,一天中此时光系统II受伤害最大;CAM物种瓦松的碳固定仅发生在夜间.研究发现,C3植物白榆和C4植物沙米比CAM植物钝叶瓦松对热和高光照有着更强的忍耐力,瓦松固定碳主要发生在生长最快的阶段;CAM植物瓦松为了能够在夏季强光和高温条件下生存,它必须进行高强度的呼吸,仅在早晨和夜间进行碳固定.     

土壤氮磷化学计量特征对小麦光合气体交换参数和叶绿素荧光参数的影响

选取‘镇麦168’为实验对象,采用盆栽实验,设置16个不同土壤氮磷梯度,测定不同土壤氮磷化学计量比处理下小麦叶片叶绿素含量、光合气体交换参数和叶绿素荧光参数的响应特征,以揭示不同土壤氮磷化学计量关系对小麦叶片光合特性影响的生理生态机制。结果表明:(1)不同生育期内小麦叶片叶绿素含量均随土壤速效N或速效P含量的增加而增加。(2)随着土壤化学计量比N∶P下降,小麦叶片净光合速率(Pn)在土壤中低氮水平(≤258.4mg·kg~(-1))下持续增加,在高氮水平(308.4mg·kg~(-1))下则呈现先增后降的趋势。(3)在土壤速效N相同水平处理下,土壤化学计量比N∶P的降低显著提高了小麦叶片叶绿素荧光参数最小荧光(F0,7.27%~20.00%)、最大荧光(Fm,5.28%~16.15%)、光化学猝灭系数(qP,6.64%~20.92%)及实际光化学效率(ΦPSⅡ,6.95%~18.82%),显著降低了非光化学猝灭系数(NPQ,7.42%~25.63%,P0.05)。研究认为,在中、高氮磷养分水平下,土壤化学计量比N∶P为2.88时,‘镇麦168’叶片净光合速率和实际光化学效率均达到最高水平,表现出较强的光能利用能力。     

The Occurrence of Cell Wall Appositions in Flag Leaves of Spring Wheats, Susceptible and Partially Resistant to Wheat Leaf Rust

In two experiments, the presence of cell wall appositions in flag leaves of spring wheat genotypes susceptible and partially resistant to wheat leaf rust was studied. More cell wall appositions were observed near aborted infection structures than in estabhshed colonies. There was not a marked difference in the number of cell wall appositions per colony between susceptible and partially resistant genotypes. More cell wall appositions per unit area colony were present in partially resistant genotypes. It was concluded that the low number of cell wall appositions could not be responsible for the observed difference in colony size between susceptible and partially resistant genotypes. Partial resistance in wheat to wheat leaf rust can be divided into two phases. The first phase is pre-haustorial and results in a reduction of the number of colonizing infection structures. In the second phase a post-haustorial retardation of fungal growth rate occurs. The latter appears to be the more important phase.     

Changes in the Number and Size of Chloroplasts during Senescence of Primary Leaves of Wheat Grown under Different Conditions

Changes in the number and size of chloroplasts in mesophyllcells were investigated in primary leaves of wheat from fullexpansion to yellowing under different growth conditions. Thenumber of chloroplasts per cell decreased slowly, although thedecrease was steady and statistically significant, until thelast stage of leaf senescence, when rapid degradation of chloroplaststook place. Rates of leaf senescence, or the decline in thenumber of chloroplasts, varied greatly among plants grown atdifferent seasons of the year, but about 20% of chloroplastsalways disappeared during the phase when steady loss of chloroplastsoccurred. The area of chloroplast disks also decreased graduallybut significantly, with a rapid decrease late in senescence.Thus, the total quantity of chloroplasts per mesophyll celldecreased substantially during leaf senescence. Yellowed leavescontained numerous structures that resemble oil drops but nochloroplasts. Decreases in rates of photosynthesis that occurduring senescence may, therefore, be largely due to decreasesin the quantity of chloroplasts. However, a better correlationwas found between the decrease in the maximum capacity for photosynthesisand the degradation of RuBP carboxylase. When plants had beengrown with a sufficient supply of nutrients, the number of chloroplastsdecreased steadily but at a reduced rate and the reduction inthe area of chloroplast disks was strongly suppressed. Thus,the quantitative decrease in chloroplasts in senescing leavesappears to be regulated by the requirements for nutrients (nitrogen)of other part of the plant. ³Present address: Department of Biology, Faculty of Science,Toho University, Miyama, Funabashi, Chiba, 274 Japan     

A Comparative Study ofMiscanthus floridulus(Labill) Warb andM. transmorrisonensisHayata: Photosynthetic Gas Exchange, Leaf Characteristics and Growth in Controlled Environments

The relationship between temperature and the distribution ofMiscanthusfloridulus(Labill) Warb andM. transmorrisonensisHayata alongaltitudinal gradients in central Taiwan was examined. Responsesof biomass accumulation, leaf characteristics and photosyntheticgas exchange to growth temperature (from 10 to 30 °C) ofM.floridulusfrom an altitude of 390 m and ofM. transmorrisonensisfrom2700 m were determined. There were differences between the twospecies in above-ground biomass, CO₂uptake characteristics andleaf chlorophyll contents in response to growth temperature.The optimal temperatures for biomass accumulation were 30/25(day/night temperature) and 25/20 °C forM. floridulusandM.transmorrisonensis,respectively. Light saturated photosyntheticrates (A_max) were largest in plants grown at the optimal temperature.Growth at 15/10 and 10/10 °C compared to the optima reducedaccumulated biomass, leaf chlorophyll content and photosyntheticrate in both species with a greater reduction inM. floridulusthaninM. transmorrisonensis.We concluded that growth ofM. floridulusathigh altitude is limited by an inability to grow at temperatureslower than 15 °C, whileM. transmorrisonensisis able to growin chilling temperatures at higher altitudes.Copyright 1998Annals of Botany Company Miscanthus floridulus;M. transmorrisonensis; C₄plants; chlorophyll content; leaf growth; photosynthetic gas exchange; biomass accumulation; temperature response.     

The Fate of the Dry Matter, Carbohydrates and 14C Lost from the Leaves and Stems of Wheat during Grain Filling

In a field study with six winter wheat genotypes losses of drymatter from the stems between 30 June and maturity averaged172 g m^–2 (range 82–236), there being significantdifferences in loss between genotypes. Respiration from thestems during the same period was estimated to amount to 106g m^–2 (range 104–225). The amount of dry mattermobilized from the stems, calculated by difference, was estimatedas 66 g m^–2. The loss of ethanol- and water-soluble carbohydratefrom the stems (170 g m^–2; range 124–215) was verysimilar to the dry weight loss. Carbon-14 labelling was used to trace the time course and theamount of the movement of assimilates from the vegetative organsto the grain. Only 14•3 per cent (range 10•3–21•0)of the products of photosynthesis over the period 21 May-20June were relocated to the grains. This relocation amountedto an average of 7 per cent (range 5•7–11•4)of the final grain weight. It was estimated that during the18 days following anthesis on 20 June photosynthesis contributed48 per cent (range 39–55) of the final grain dry weight.Of this, about half was translocated to the grain within 10days of initial assimilation. The remainder appeared to be storedtemporarily in the stems and leaves and translocated to thegrains during the period 17–29 July. In general, relocationof dry matter from the vegetative organs to the grains, assessedby carbon-14 labelling, was greatest in those genotypes (Hobbitand Sportsman) which lost most dry weight from the stems andleaves.     

Investigation of Water Dynamics and the Effect of Evapotranspiration on Grain Yield of Rainfed Wheat and Barley under a Mediterranean Environment: A Modelling Approach

Agro-hydrological models have increasingly become useful and powerful tools in optimizing water and fertilizer application, and in studying the environmental consequences. Accurate prediction of water dynamics in such models is essential for models to produce reasonable results. In this study, detailed simulations were performed for water dynamics of rainfed winter wheat and barley grown under a Mediterranean climate over a 10-year period. The model employed (Yang et al., 2009. J. Hydrol., 370, 177-190) uses easily available agronomic data, and takes into consideration of all key soil and plant processes in controlling water dynamics in the soil-crop system, including the dynamics of root growth. The water requirement for crop growth was calculated according to the FAO56, and the soil hydraulic properties were estimated using peto-transfer functions (PTFs) based on soil physical properties and soil organic matter content. Results show that the simulated values of soil water content at the depths of 15, 45 and 75 cm agreed with the measurements well with the root of the mean squared errors of 0.027 cm³ cm^-3 and the model agreement index of 0.875. The simulated seasonal evapotranspiration (ET) ranged from 208 to 388 mm, and grain yield was found to correlate with the simulated seasonal ET in a linear manner within the studied ET range. The simulated rates of grain yield increase were 17.3 and 23.7 kg ha^-l for every mm of water evapotranspired for wheat and barley, respectively. The good agreement of soil water content between measurement and simulation and the simulated relationships between grain yield and seasonal ET supported by the data in the literature indicates that the model performed well in modelling water dynamics for the studied soil-crop system, and therefore has the potential to be applied reliably and widely in precision agriculture. Finally, a two-staged approach using inverse modelling techniques to further improve model performance was discussed.     

林下与全光下地枫皮叶片形态和光合特性的比较

测量了林下与全光下地枫皮的叶片形态和光合-光响应曲线,探讨光强对地枫皮的形态和生理特性的影响。结果表明：林下与全光下地枫皮叶片净光合速率（Pn）、气孔导度（Gs）、蒸腾速率（Tr）和水分利用效率（WUE）对光强的响应趋势均基本一致,但全光下的Pn、Gs和Tr值较高,林下WUE值较高。全光下地枫皮的最大净光合速率、光饱和点和光补偿点均极显著高于林下,但弱光下的量子效率无显著差异;林下地枫皮的叶长、叶宽、干物质重、叶面积和比叶面积等叶片形态参数均极显著大于全光。推断地枫皮为耐阴性较弱的阳生植物,其光合能力和光饱和点较低,是对干旱环境的适应性反应;全光下地枫皮叶片狭小降低了吸光面积,有利于避免过高光强对叶光合器官的损伤。