Relationships between Grain Yield, Flag Leaf Morphology, Carbon Isotope Discrimination and Ash Content in Irrigated Wheat

The purpose of this study was to examine how differences in leaf angle, leaf rolling (LR) and glaucousness (GL) can modify yield components and leaf physiological traits in wheat. A set of 167 lines derived from a cross between two high‐yielding bread wheat cultivars differing for these traits was grown under flood irrigation and high evaporative demand in the north‐west of Mexico. Area, mass per unit area and chlorophyll content of the flag leaf were assessed. Carbon isotope discrimination (Δ) and ash content (m_a) were also measured. A significant correlation was found between grain yield (GY) and both Δ and m_a suggesting that, despite well‐watered conditions, leaf stomatal conductance was the main yield‐limiting factor. Leaf posture and LR did not significantly affect yield, Δ and m_a. Higher grain weight was noted, however, in lines with droopy flag leaves. Erect leaves had higher mass per unit area. GL was associated with a significant increase in GY and grain weight. Glaucous lines also had higher Δ and m_a, suggesting higher transpiration rate and lower transpiration efficiency. The study confirms that Δ and m_a represent promising criteria for GY in wheat and provides evidence that GL can contribute to higher yield, even under irrigated conditions.     

Carbon Isotope Discrimination, Leaf Ash Content and Grain Yield in Bread and Durum Wheat Grown under Full-Irrigated Conditions

Integrative physiological criteria, such as carbon isotope discrimination (Δ) and (mineral) ash content (m_a) have been found to be very useful, under drought conditions, to elucidate the association between yield gains and variation of photosynthesis‐related traits and orientate future breeding efforts. Information on this association is scarce under irrigated conditions. The relationships between Δ, m_a and yield were studied in bread wheat (Triticum aestivum L.) and durum wheat (Triticum turgidum L. var. durum) under optimal (drip) irrigation in the arid conditions of north‐west Mexico. Carbon isotope discrimination was analysed on leaves at booting stage and anthesis and on grain at maturity, whereas ash content was measured on the flag leaf at anthesis and maturity. At anthesis, there were differences between bread and durum wheat during grain filling for Δ, but not for m_a. No relationship was found between grain yield and Δ. Leaf ash content at anthesis and maturity showed a broad variability within each species and were associated with grain yield. These results suggest that ash content in leaves could be also used as predictive criteria for yield not only under drought, but also under irrigated conditions, particularly when evaporative demand is high.     

Relationship between Carbon Isotope Discrimination and Mineral Content in Wheat Grown under Three Different Water Regimes

Carbon isotope discrimination (Δ) has been proposed as an indirect selection criterion for transpiration efficiency and grain yield in wheat. However, because of the high cost for Δ analysis, attempts have been carried out to identify alternative screening criteria. Ash content (m_a) has been proposed as an alternative criterion for Δ in wheat and barley. A pot experiment was conducted to analyse the relationship between Δ and m_a in flag leaf and grain. Plants of 10 genotypes were cultivated under three different water regimes corresponding to moderate, intermediate and severe drought stress obtained by maintaining soil humidity at 75 %, 55 % and 45 % of the humidity at field capacity, respectively. Δ and m_a in flag leaf and grain showed significant differences between the moderate, intermediate and severe drought stress levels. Significant correlations were found among genotypes for Δ and m_a in flag leaf under severe drought stress, and for Δ and m_a in grain under intermediate and moderate drought stress. In flag leaf at anthesis, Δ was negatively associated to K content and positively to Mg content. At maturity, Δ in grain was negatively correlated with Mg and Ca contents in flag leaf and grain, respectively. These results suggested that these traits may be potentially useful traits, which could be surrogates for Δ.     

Relationship between Carbon Isotope Discrimination, Ash Content and Grain Yield in Wheat in the Peninsular Zone of India

Carbon isotope discrimination (Δ) and ash content (m_a) have been proposed as indirect selection criteria for grain yield in wheat. The associations between Δ, m_a and grain yield were found, however, to depend highly on the environmental conditions, the organ sampled and the time of sampling. In this study, carried out in the warm conditions of the Peninsular Zone of India, the relationship between Δ, m_a and yield was studied in 30 bread and durum wheat cultivars under residual soil moisture stress (RSMS), post‐anthesis water stress (PAWS) and well‐watered (WW) conditions. Both Δ and m_a were analysed in young seedlings (four‐leaf stage), leaves at anthesis and grain at maturity. Ash content was also evaluated in leaves at booting stage and maturity. Grain Δ was lower under PAWS and RSMS than under WW, while seedling and leaf Δ did not significantly differ among water regimes. Grain yield was positively correlated to grain Δ under PAWS and negatively correlated to grain m_a under RSMS. A significant positive correlation was noted under RSMS and WW treatments between m_aL_m and grain yield. Ash content in leaf at maturity consequently appears to be a useful indirect selection criterion in environments where Δ does not show any correlation with yield. The results highlight the potential of Δ and m_a as indirect selection criteria for wheat yield in the conditions of the Peninsular Zone of India.     

Carbon Isotope Discrimination and Grain Yield Variations among Tetraploid Wheat Species Cultivated under Contrasting Precipitation Regimes

Nineteen accessions belonging to six tetraploid wheat species were evaluated and compared for carbon isotope discrimination and grain yield during two successive cropping seasons (1995 and 1996) under Mediterranean rainfed conditions. The two seasons differed markedly in precipitation regime. A wide variation for the measured traits was observed among the 19 accessions for carbon isotope discrimination and grain yield in both years. Significant differences were also noted between species accessions for Δ and grain yield. In both years, Triticum timopheevi (AG genome) showed lower Δ values than the other tetraploid species (all carrying the AB genome). Positive correlations were observed between Δ and grain yield in both years. The use of carbon isotope discrimination as an indirect selection criterion for yield under stress and the potential benefits of some alien tetraploid species in improving drought tolerance in durum wheat are discussed.     

Relationship between Carbon Isotope Discrimination,Mineral Content and Gas Exchange Parameters in Vegetative Organs of Wheat Grown under Three Different Water Regimes

Carbon isotope discrimination (Δ) has been proposed as an indirect selection criterion for transpiration efficiency and grain yield in wheat. However, because of high cost for Δ analysis, attempts have been made to identify alternative screening criteria. Ash content (m_a) has been proposed as an alternative criterion for Δ in wheat and barley. A pot experiment was conducted to analyse the relationship between Δ, mineral content and gas exchange parameters in seedlings and leaves of bread wheat (Triticum aestivum L.). Plants of 10 genotypes were cultivated under three different water regimes corresponding to moderate (T₃), intermediate (T₂) and severe drought (T₁) stress obtained by maintaining soil humidity at 75 %, 55 % and 45 % of the humidity at field capacity respectively. Δ and m_a in seedlings and leaves showed significant differences among the three water treatments. Significant positive correlations were found between Δ and m_a in seedlings and leaves at elongation and anthesis stages in severe drought stress (T₁). Δ was negatively associated with potassium (K) content in intermediate drought stress (T₂) and positively with magnesium (Mg) content in T₂ and T₃ (moderate drought stress) in flag leaf at anthesis. There were negative correlations between Δ and single‐leaf intrinsic water‐use efficiency (W_T) in T₂ and T₃ at anthesis stage. Stronger positive associations were noted between Δ and stomatal conductance (g_s) in T₁ and T₂ than in T₃ at anthesis. These results suggested that Δ is a good trait as an indirect selection criterion for genotypic improvement in transpiration efficiency, while m_a is a possible alternative criterion of Δ in wheat vegetative organs, especially in stressed environments. Significant association was found between Δ and K, Mg and Ca contents that would merit being better investigated.     

Leaf Carbon Isotope Discrimination as an Accurate Indicator of Water‐Use Efficiency in Sunflower Genotypes Subjected to Five Stable Soil Water Contents

Leaf carbon isotope discrimination (CID) has been suggested as an indirect tool for breeding for water‐use efficiency (WUE) in various crops. This work focused on assessing phenotypic correlations between WUE and leaf CID and analysing genotypic variability in four sunflower genotypes grown in a greenhouse in pots with five different stable levels of soil water content (SWC). We measured WUE at whole plant and leaf (intrinsic) level. At whole plant level, WUE was derived from the ratio of total dry aerial biomass (BM) to cumulative water transpired (CWT). At leaf level, intrinsic WUE was calculated as the ratio of light‐saturated CO₂ assimilation to stomatal conductance (A/g_s) in younger expanded leaves. Significant differences among the four genotypes and the five SWCs were observed for whole plant and leaf WUE and CID. Strong negative correlations were observed between whole plant WUE and CID as well as between intrinsic WUE and CID with decreasing water availability. No relationships appeared between BM production and WUE or CID. Our results can help agronomists and breeders to evaluate sunflower lines with high WUE for adaptation to drought conditions and for reducing water consumption and crop water needs. Leaf CID appears to be a pertinent and valuable trait to select sunflower genotypes with high WUE.     

Water Stress, Water Use Efficiency, Carbon Isotope Discrimination and Leaf Gas Exchange Relationships of the Bush Bean

Water use efficiencies for the whole plant (WUE₁) and single leaves (WUE₁) were studied in a greenhouse as a function of soil moisture during four phenological stages of bush bean growth. WUE₁ increased significantly with soil moisture stress and attained its maximum value before the flowering stage. WUE₁ and WUE₁ were linearly related ( r = 0.92), and WUE₁ was correlated with the transpiration rate ( r = -0.87), stomatal conductance ( r = -0.80) and photosynthetic rate ( r = 0.81). Carbon isotope discrimination.), decreased as soil moisture decreased, and) was negatively correlated with both WUE₁ ( r = -0.92) and WUE₁ ( r = -0.88). There were significant differences in leaf N among water regimes.     

The Physiology and Stability of Leaf Carbon Isotope Discrimination as a Measure of Water‐Use Efficiency in Barley on the Canadian Prairies

Temporal and seasonal water deficit is one of the major factors limiting crop yield on the Canadian prairie. Selection for low carbon isotope discrimination (Δ¹³C) or high water‐use efficiency (WUE) can lead to improved yield in some environments. To understand better the physiology and WUE of barley under drought conditions on the Canadian prairie, 12 barley (Hordeum vulgare L.) genotypes with contrasting levels of leaf Δ¹³C were investigated for performance stability across locations and years in Alberta, Canada. Four of those genotypes (‘CDC Cowboy’, ‘Niobe’, ‘170011’ and ‘Kasota’) were also grown in the greenhouse under well‐watered and water‐deficit conditions to examine genotypic variations in leaf Δ¹³C, WUE, gas exchange parameters and specific leaf area (SLA). The water‐deficit treatment was imposed at the jointing stage for 10 days followed by re‐watering to pre‐deficit level. Genotypic ranking in leaf Δ¹³C was highly consistent, with ‘170011’, ‘CDC Cowboy’ and ‘W89001002003’ being the lowest and ‘Kasota’‘160049’ and ‘H93174006’ being the highest leaf Δ¹³C. Under field and greenhouse (well‐watered) conditions, leaf Δ¹³C was significantly correlated with stomatal conductance (g_s). Water deficit significantly increased WUE, with ‘CDC Cowboy’– a low leaf Δ¹³C genotype with significantly higher WUE and lower percentage decline in assimilation rate (A) and g_s than the other three genotypes (‘Niobe’, ‘170011’ and ‘Kasota’). We conclude that leaf Δ¹³C is a stable trait in the genotypes evaluated. Low leaf Δ¹³C of ‘CDC Cowboy’ was achieved by maintaining a high A and a low g_s, with comparable biomass and grain yield to genotypes showing a high g_s under field conditions; hence, selection for a low leaf Δ¹³C genotype such as ‘CDC Cowboy’ maybe important for maintaining productivity and yield stability under water‐limited conditions on the Canadian prairie.     

Carbon Isotope Discrimination and Productivity in Field-Grown Barley Genotypes

Five barley genotypes of different origins were used to examine the relationships between carbon isotope discrimination (Δ) and grain yield, yield components, dry aerial biomass and harvest index under rainfed and irrigated Mediterranean conditions. High positive correlations were found between Δ and grain yield and harvest index under both water conditions, suggesting that Δ may represent efficiency of dry matter partitioning to the grain. This hypothesis was also supported by the positive correlation found between Δ and thousand-grain weight when all the data were considered. The two drought-tolerant genotypes LM2887 and Tadmor presented the smallest difference between the two treatments for traits related to productivity as well as the highest Δ values. These results highlight the potential of Δ as a selection criterion in barley breeding in Mediterranean regions. They also encourage the study of the genetics of Δ and the identification of molecular markers linked to its variation in available progenies derived from crosses between the genotypes used in the present paper.     

玉米水分利用效率、碳稳定同位素判别值和叶面积之间的关系

通过盆栽试验,研究了水分胁迫对玉米各生育期叶面积(LA)、比叶面积(SLA)、水分利用效率(WUE)和碳稳定同位素判别值(Δ¹³C)的影响以及不同水分条件下WUE、茎叶Δ¹³C和SLA之间的关系。试验设4个水分处理, 分别为田间持水量的75%~100%(W1)、50%~75%(W2)、30%~50%(W3)和0~30%(W4)。W2和W3处理对生物量干重的影响在玉米拔节期明显,而W4处理导致各生育期生物量干重的极大降低。在W2和W3处理下,玉米各生育期的WUE随着水分胁迫程度的增加而增加;而W4处理下,WUE在孕穗期后则显著降低。SLA在孕穗期达到最大。玉米各生育期叶片Δ¹³C在W1、W2和W3处理中呈随水分胁迫的增加而降低的趋势,而W4处理下的叶片Δ¹³C则高于W2和W3处理。玉米叶片光合同化物质往茎秆转移时没有发生碳同位素的分馏作用。在玉米的各生育期,叶片Δ¹³C、茎秆Δ¹³C和玉米WUE呈一致性的负相关;各生育期的SLA与Δ¹³C呈正相关关系,而与WUE呈显著的负相关。     

Relationship of Carbon Isotope Discrimination to Water Use Efficiency and Productivity of Barley Under Field and Greenhouse Conditions

This study was conducted to evaluate the application of carbon isotope discrimination (CID) as a selection criterion for improving water use efficiency (WUE) and productivity of barley (Hordeum vulgare L.) under field and drought‐stress conditions in a greenhouse. A total of 54 genotypes were screened for variability in CID under field conditions, while 23 genotypes were evaluated under water‐deficit conditions in the greenhouse. A survey of leaf CID of 54 genotypes at two field locations showed more than 2.14‰ difference between extreme genotypes. Significant (P ≤ 0.05) genotypic variation was found in WUE and CID that had a negative strong correlation. There was a negative correlation between leaf CID and aerial biomass in the greenhouse and among six‐row genotypes in the field. Correlations between leaf CID across field locations and across irrigation regimes in the greenhouse were significant (experiment 1, r = 0.79 and 0.94 for six‐ and two‐row genotypes), suggesting stability of the CID trait across different environments. Overall, these results indicate the potential of leaf CID as a reliable method for selecting for high WUE and productivity in barley breeding programmes in the Canadian prairies. Further work is currently underway to determine heritability/genetics of leaf CID and application of molecular marker‐assisted selection for the traits in barley breeding programmes.     

Association between Yield and Carbon Isotope Discrimination Value in Different Organs of Durum Wheat Under Drought

Carbon isotope discrimination (Δ) has been proposed as a selection criterion for transpiration efficiency and grain yield in drought‐prone environments for several C³ species, including cereals. Δ analysis, however, has mainly been concerned with grain or culm tissues and little work has been devoted to other organs. The objective of this study was to describe Δ variation in different organs and to examine the relationships between Δ and grain yield across environments. Six durum wheat genotypes with contrasted grain Δ were cultivated under rainfed conditions during three successive years at Montpellier (South of France). Δ was measured on flag leaf, stalk, awns, chaff and rachis sampled at anthesis and maturity, and on mature grain. Higher genotypic variation and closer correlation with yield were noted for grain Δ compared to other plant parts. The genotype ranking across years was more consistent for grain Δ than for other organs. Consequently, the grain seems the most effective plant part for Δ analysis in durum wheat under Mediterranean conditions. The study of Δ variation in other organs may be useful, however, to evaluate the contribution of those organs to grain filling and final yield according to environmental conditions.     

大豆和小麦不同基因型的碳同位素分馏作用及水分利用效率

26个大豆基因型和18个小麦基因型的叶片和种子的稳定碳同位素分馏值(△13C)在正常供水和缺水的田间条件下皆有明显的基因型差别。土壤干旱降低△13C值，提高水分利用效率(WUE)并增大了不同基因型间的差值。抗旱性不同的基因型的叶片和种子的△13C平均值及相应的WUE与抗旱性大小之间表现一定的规律性变化，抗旱性强的基因型的     

Water Use Efficiency, Carbon Isotope Discrimination and Biomass Production of Two Sugar Beet Varieties Under Well-Watered and Dry Conditions

Two sugar beet (Beta vulgaris sp.) varieties, which were supposed to differ in drought tolerance, were exposed to drought stress in a growth chamber and a container experiment in field. The aim was to test for (i) differences between the varieties in water use efficiency (WUE), biomass production and distribution and (ii) the relationship between WUE and carbon isotope discrimination (Δ), and between biomass production and Δ. Significant differences in WUE were detected between plants of well‐watered and drought treatments in both experiments, but not between the varieties. Production losses due to drought were large for both varieties in both experiments. Losses in the growth chamber were up to 50 % of plant dry weight and the corresponding value in the field was 24 %, when plants were given 60 and 30 %, respectively, of the full‐watered treatments. Significant negative correlations between WUE and Δ were found, but not between biomass production and Δ, when both varieties were included. Negative correlations between WUE and Δ were also found for each variety separately. The results suggest that Δ estimates from leaf tissue of sugar beet may provide a useful tool for genetic selection of drought‐tolerant sugar beet varieties.     

A Prominent Role for Leaf Calcium as a Yield and Quality Determinant in Upland Cotton (Gossypium hirsutum L.) Varieties Grown Under Irrigated Mediterranean Conditions

Seven cotton (Gossypium hirsutum L.) accessions were tested over 2 years under irrigated Mediterranean conditions on a loamy soil with nitrogen (N) as the only nutrient input. The study aimed to identify the critical nutritional and physiological factors determining seedcotton yield and fibre quality. A suite of leaf physiological traits [chlorophyll content (assessed by SPAD), carbon isotope discrimination (Δ), ¹⁵N natural abundance (δ¹⁵N), leaf water potential, N and C concentrations, C/N ratio, K, Na, Ca and Mg concentrations, their sum and ratios] was assessed, and their interrelationships then analysed. It was found that physiological indices such as SPAD, Δ and δ¹⁵N failed to discern genotypes for yield and did not relate with fibre quality traits. At the same time, leaf Ca concentration was the trait that showed the strongest correlation with both seedcotton (SY) and lint yield (LY). An increase of K/Na ratio up to 5.74 was beneficial for SY but higher ratios impacted yield adversely. In this line, exclusion of K in favour of Ca (lower K/Ca ratios) increased both SY and LY. The above results could be explained by Ca²⁺ control over activity of tonoplast and plasma membrane cation channels, resulting in redistribution of K⁺ between cell compartments. It is suggested that Ca²⁺‐rich plants are more efficient in sequestering higher K⁺ quantities in leaf vacuoles, at the expense of cytosolic K⁺. Under K⁺‐limiting conditions, such redistribution may trigger programmed cell death and enhance leaf senescence. This would remobilize and translocate nutrients (e.g. N) and organic substances to sinks (seedcotton), contributing to higher yields reported in the present work.     

Relationship between Carbon Isotope Discrimination and Grain Yield in Spring Wheat under Different Water Regimes and under Saline Conditions in the Ningxia Province (North-west China)

The relationship between grain yield and carbon isotope discrimination (Δ) was analysed in wheat grown under different water regimes in the Ningxia Province (north‐west of China). When the association was significant, the relationships between grain yield, Δ and other drought tolerance related traits, such as leaf ash content (m_a), chlorophyll concentration (Chl), relative water content (RWC), stomatal conductance (g_S) and the ratio of internal CO₂ leaf concentration to ambient CO₂ concentration (C_i/C_a), were also examined. Using correlation analysis, the relationships were determined during two consecutive years in a set of 20 spring wheat cultivars (landraces, improved varieties and advanced lines) under rainfed and irrigated conditions, including saline conditions. The relationship between Δ and yield within environments highly depended on the quantity of water stored in the soil at sowing, the quantity and distribution of rainfall during the growth cycle, and the irrigation before anthesis. Δ predicted grain yield under limited irrigation (post‐anthesis water stress) but not under pre‐anthesis water stress (rainfed conditions), fully irrigated and saline conditions. Under limited irrigation, grain Δ correlated significantly to grain yield leaf m_a at heading and maturity. It also significantly positively correlated to Chl, RWC, g_S and C_i/C_a assessed at anthesis. A precise characterization of the timing and intensity of the abiotic constraints experienced by the crop is consequently needed before implementing the use of Δ in wheat breeding programmes.     

退化草地碳动态及固碳潜力

草地是陆地生态系统中最重要的生态系统之一,在维持陆地碳平衡,减缓气候变化中起着重要作用。笔者论述了草地退化的驱动因子及草地退化中的碳变化效应。从草地生态系统中植物生长和土壤性质2个方面分析了土壤固碳潜力与机制,并结合国内外研究动态,提出未来草地的主要研究方向。     

Effect of Glaucousness on Carbon Isotope Discrimination and Grain Yield in Durum Wheat

The effect of glaucousness on yield and transpiration efficiency was studied in durum wheat under Mediterranean conditions. Two groups of 16 genotypes, with contrasting glaucousness, were compared over 2 years for flag leaf and kernel carbon isotope discrimination, residual transpiration, specific leaf dry weight, biomass and grain yield. Significantly higher carbon isotope discrimination and lower specific leaf dry weight were noted in the glaucous lines. No significant effect of glaucousness was found on residual transpiration. Glaucous genotypes also exhibited higher grain yield, which was strongly correlated to the carbon isotope discrimination values. Results suggest that glaucousness has a negative effect on transpiration efficiency, which could be related to modifications of leaf energy balance. Higher stomatal conductance, reflected by the high carbon isotope discrimination, could mainly explain the higher grain yield found in the glaucous lines.     

氯钾离子共体诱导后黄瓜叶片内几种物质含量变化

在黄瓜幼苗子叶期及第一真叶期用浓度为0.2%,0.5%,1.0%,1.5%,2.0%的氯钾离子共体液进行诱导处理,结果表明:诱导后可溶性糖含量均显著高于对照,且呈先升高后降低的趋势,15 d后各处理达到最大值;叶绿素含量也呈先升高后降低的趋势,诱导初期对照和各处理变化平缓,10 d后急剧升高,15 d达到最大值,各处理均高于对照;单宁含量诱导后即开始升高,15 d达到峰值,阿魏酸含量前期变化平缓,15 d后急剧升高,20 d后达到峰值,绿原酸含量诱导后急剧升高,5 d后即达到最大值;木质素的含量各处理均高于对照。在诱导物浓度为0.5%~1.5%的范围内,黄瓜叶片内各生理生化指标较对照差异最大。