Leaf Area Index,Leaf Transpiration and Stomatal Conductance as Affected by Soil Water Deficit and VPD in Processing Tomato in Semi Arid Mediterranean Climate

In order to assess the effects of soil water availability and climatic conditions on leaf growth, leaf transpiration (E) and stomatal conductance (g_s) of processing tomato, under deficit irrigation regimes in the Mediterranean climate, open‐field experiments were carried out in two sites differing from soil and climatic characteristics, in Sicily, South Italy. A wide range of soil water availability from dry, deficit irrigation to full irrigation was examined. Leaf area greatly changed with soil water availability but not with the experimental site. The effect of soil drying on physiological indices was small over a certain range of soil water deficit (from 0 % to approximately 40 %). Within this range, vapour pressure deficit (VPD) strongly affected g_s. To this regard, the adoption of two experimental sites differing in climatic conditions (i.e. air temperature, RH, VPD) has been useful for a better understanding of the mechanisms, which regulate stomatal opening. Therefore, in Mediterranean environment, the combined effect of soil water availability (mostly upon leaf growth) and climatic conditions (mostly upon plant physiology) must be considered in models for biomass production in tomato crop.     

Electron Transport Through Photosystem II Is Not Limited By A Wide Range of Water Deficit Conditions In Field‐Grown Gossypium hirsutum

Despite exhaustive literature describing drought stress effects on photosynthesis in Gossypium hirsutum, the sensitivity of photosynthetic electron flow to water deficit is heavily debated. To address this, G. hirsutum plants were grown at a field site near Camilla, GA under contrasting irrigation regimes, and pre‐dawn water potential (Ψ_PD), stomatal conductance (g_s), net photosynthesis (P_N), actual quantum yield of photosystem II (Φ_PSII) and electron transport rate (ETR) were measured at multiple times during the 2012 growing season. Ψ_PD values ranged from ?0.3 to ?1.1 MPa. Stomatal conductance exhibited a strong (r² = 0.697), sigmoidal response to Ψ_PD, where g_s was ≤0.1 mol m^?2 s^?1 at Ψ_PD values ≤ ?0.86 MPa. Neither Φ_PSII (r² = 0.015) nor ETR (r² = 0.010) was affected by Ψ_PD, despite exceptionally low Ψ_PD values (?1.1 MPa) causing a 71.7 % decline in P_N relative to values predicted for well‐watered G. hirsutum leaves at Ψ_PD = ?0.3 MPa. Further, P_N was strongly influenced by g_s, whereas ETR and Φ_PSII were not. We conclude that photosynthetic electron flow through photosystem II is insensitive to water deficit in field‐grown G. hirsutum.     

Genotypic Variation of Gas Exchange Parameters and Leaf Stable Carbon and Nitrogen Isotopes in Ten Quinoa Cultivars Grown under Drought

Genotypic variations in leaf gas exchange and grain yield were analysed in 10 highland‐adapted quinoa cultivars grown in the field under drought conditions. Trials took place in an arid mountain region of the Northwest of Argentina (Encalilla, Amaicha del Valle, 22°31′S, 65°59′W). Significant changes in leaf gas exchange and grain yield among cultivars were observed. Our data demonstrate that leaf stomatal conductance to water vapour (g_s) is a major determinant of net CO₂ assimilation (A_n) because quinoa cultivars with inherently higher g_s were capable of keeping higher photosynthesis rate. Aboveground dry mass and grain yield significantly varied among cultivars. Significant variations also occurred in chlorophyll, N and P content, photosynthetic nitrogen‐use efficiency (PNUE), specific leaf area (SLA), intrinsic water‐use efficiency (_iWUE) and carboxylation capacity (A_n/C_i). Many cultivars gave promissory grain yields with values higher than 2000 kg ha^?1, reaching for Sayaña cultivar 3855 kg ha^?1. Overall, these data indicate that cultivars, which showed higher photosynthesis and conductances, were also generally more productive. Carbon isotope discrimination (Δ) was positively correlated with the grain yield and negatively with _iWUE, but δ¹⁵N did not show significant correlations. This study provides a reliable measure of specific responses of quinoa cultivars to drought and it may be valuable in breeding programmes.     

Effects of Increasing Salinity Stress and Decreasing Water Availability on Ecophysiological Traits of Quinoa (Chenopodium quinoa Willd.) Grown in a Mediterranean‐Type Agroecosystem

Quinoa is a native Andean crop for domestic consumption and market sale, widely investigated due to its nutritional composition and gluten‐free seeds. Leaf water potential (Ψ_leaf) and its components and stomatal conductance (g_s) of quinoa, cultivar Titicaca, were investigated in Southern Italy, in field trials (2009 and 2010). This alternative crop was subjected to irrigation treatments, with the restitution of 100 %, 50 % and 25 % of the water necessary to replenish field capacity, with well water (100 W, 50 W, 25 W) and saline water (100 WS, 50 WS, 25 WS) with an electrical conductivity (EC_w) of 22 dS m^?1. As water and salt stress developed and Ψ_leaf decreased, the leaf osmotic potential (Ψ_π) declined (below ?2.05 MPa) to maintain turgor. Stomatal conductance decreased with the reduction in Ψ_leaf (with a steep drop at Ψ_leaf between ?0.8 and 1.2 MPa) and Ψ_π (with a steep drop at Ψ_π between ?1.2 and ?1.4 MPa). Salt and drought stress, in both years, did not affect markedly the relationship between water potential components, RWC and g_s. Leaf water potentials and g_s were inversely related to water limitation and soil salinity experimentally imposed, showing exponential (Ψ_leaf and turgor pressure, Ψ_p, vs. g_s) or linear (Ψ_leaf and Ψ_p vs. SWC) functions. At the end of the experiment, salt‐irrigated plants showed a severe drop in Ψ_leaf (below ?2 MPa), resulting in stomatal closure through interactive effects of soil water availability and salt excess to control the loss of turgor in leaves. The effects of salinity and drought resulted in strict dependencies between RWC and water potential components, showing that regulating cellular water deficit and volume is a powerful mechanism for conserving cellular hydration under stress, resulting in osmotic adjustment at turgor loss. The extent of osmotic adjustment associated with drought was not reflected in Ψ_π at full turgor. As soil was drying, the association between Ψ_leaf and SWC reflected the ability of quinoa to explore soil volume to continue extracting available water from the soil. However, leaf ABA content did not vary under concomitant salinity and drought stress conditions in 2009, while differing between 100 W and 100 WS in 2010. Quinoa showed good resistance to water and salt stress through stomatal responses and osmotic adjustments that played a role in the maintenance of a leaf turgor favourable to plant growth and preserved crop yield in cropping systems similar to those of Southern Italy.     

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.     

Contrasting Water‐Use Efficiency (WUE) Responses of a Potato Mapping Population and Capability of Modified Ball‐Berry Model to Predict Stomatal Conductance and WUE Measured at Different Environmental Conditions

Potatoes (Solanum tuberosum L.) are drought‐sensitive and more efficient water use, while maintaining high yields is required. Here, water‐use efficiency (WUE) of a mapping population comprising 144 clones from a cross between 90‐HAF‐01 (Solanum tuberosum₁) and 90‐HAG‐15 (S. tuberosum₂ × S. sparsipilum) was measured on well‐watered plants under controlled‐environment conditions combining three levels of each of the factors: [CO₂], temperature, light, and relative humidity in growth chambers. The clones were grouped according to their photosynthetic WUE (pWUE) and whole‐plant WUE (wpWUE) during experiments in 2010. Two offspring groups according to pWUE and wpWUE were identified on the basis of experiments conducted in 2010, which in experiments in 2011 again showed significant differences in pWUE (46 %, P < 0.001) and wpWUE (34 %, P < 0.001). The high‐WUE group had a higher net photosynthesis rate (34 %) and dry matter accumulation (55 %, P < 0.001) rather than leaf‐level transpiration rate (?4 %, no significant difference) or whole‐plant water use (16 %). The pWUE correlated negatively to the ratio between leaf‐internal and leaf‐external [CO₂] (R² = ?0.86 in 2010 and R² = ?0.83 in 2011, P < 0.001). The leaf chlorophyll content was lower in the high‐WUE group indicating that the higher net photosynthesis rate was not due to higher leaf‐N status. Less negative value of carbon isotope discrimination (δ¹³C) in the high‐WUE group was only found in 2011. A modified Ball‐Berry model was fitted to measured stomatal conductance (g_s) under the systematically varied environmental conditions to identify parameter differences between the two groups, which could explain their contrasting WUE. Compared to the low‐WUE group, the high‐WUE group showed consistently lower values of the parameter m, which is inversely related to WUE. Differences related specifically to the dependence of g_s on humidity and net photosynthesis rate were only found in 2010. The lower ratio between leaf‐internal and leaf‐external [CO₂] and higher WUE of the high‐WUE group was consistent over a wide range of air vapour pressure deficits from 0.5 to 3.5 kPa. The mapping population was normally distributed with respect to WUE suggesting a multigenic nature of this trait. The WUE groups identified can be further employed for quantitative trait loci (QTL) analysis by use of gene expression studies or genome resequencing. The differences in population WUE indicate a genetic potential for improvement of this trait.     

Effect of Salinity on Growth Parameters,Soil Water Potential and Ion Composition in Cucumis melo cv. Huanghemi in North‐Western China

A field trial conducted on the melon cultivar Huanghemi irrigated with saline water was carried out in Minqin County in the 2‐year period, 2007 and 2008. In three irrigation treatments, different saline water concentrations were applied, that is 0.8 g l^?1 (Control C), 2 g l^?1 (Treatment S₁) and 5 g l^?1 (Treatment S₂), reproducing the natural groundwater concentration in the county. The electrical conductivity of the saline water was as follows: 1.00, 2.66 and 7.03 dS m^?1, respectively. The aims of the study were (i) to monitor water consumption and water potential, (ii) assess, during the whole crop cycle, some growth parameters and their relations for estimating the morpho‐functional plant response irrigated with saline water and (iii) determine the ion concentration in different plant tissues to evaluate which mechanism the plant activates in the presence of high salt concentrations. Under salinity stress, the plants sustained the concentration of Ca, Mg and K, but at a level not sufficient to limit the Na adsorption. Therefore, the melon yield decreased and it was determined by a displacement of the ratio K/Na and by a lower (total potential MPa). Consequently with increasing salinity, a significant reduction was observed in: water consumption (ET c, mm), leaf area duration (LAD, m² d), on shoot dry weight aboveground (W , g plant^?1), on specific leaf area (SLA, cm² g^?1) and on leaf area ratio (LAR, cm² g^?1). In treatment S₂, in addition to these changes which mainly affected the plant morphology with effects on the biomass produced, a moderate reduction was also observed in net assimilation rate (NAR, g m^?2 d^?1), water use efficiency (WUE), a significant reduction in the energy conversion efficiency (ECE, %) and, in short, in a reduction in the relative growth rate (RGR, g g^?1 d^?1).     

高密度种植条件下去叶对不同株型夏玉米群体及单叶光合性能的调控

当前玉米产量的提高部分归因于种植密度的增加,但过高的种植密度使冠层中下部叶片光照条件变差,致使单株生长速率降低。因此,如何缓解该条件下群体光合与单株光合性能的矛盾成为当前玉米高产栽培中急需解决的问题。为此,在种植密度为105 000株hm–2的大田试验条件下,研究了紧凑型玉米品种郑单958及半紧凑型玉米品种金海5号的群体光合速率(CAP)、叶面积指数(LAI)、穗位叶净光合速率(Pn)及抗氧化酶活性等对不同程度去叶的响应,以期为高密度栽培条件下稳定或提高单株生产力探讨新的技术途径,同时也为耐密高产品种选育提供借鉴。开花后3 d分别2个品种做不同程度去叶处理,包括去除植株顶部2片叶(S1)、4片叶(S2)、6片叶(S3),以不去叶植株为对照(S0)。结果表明,去叶可显著改善玉米生育后期群体透光率(LT),然而S2和S3处理显著降低了LAI,增加了生育后期的漏光损失,不利于光能利用率的提高,致使其实际光化学效率(ΦPSII)和最大光化学效率(Fv/Fm)较低;去除植株顶部两片叶(S1)可显著提高籽粒灌浆期间CAP并延长LAI高值持续期,形成较高的籽粒产量,而过度去叶(S2和S3)则显著降低产量;花后52 d,郑单958 S1处理CAP较对照升高12.49%,而金海5号则升高23.08%;随去叶程度的增强,花后0~26 d内各去叶处理穗位叶Pn、气孔导度(gs)和叶绿素含量明显升高,均显著高于S0,但之后S1处理表现出较优的单叶光合特性。S1处理穗位叶自花后13 d起保持较高的超氧化物歧化酶(SOD)、过氧化物酶(POD)活性及较低的丙二醛(MDA)含量。可见,高密度种植条件下,去除植株顶部2片叶可有效调控两株型玉米生育后期群体光合速率、穗位叶光合特性及活性氧清除能力,能较好地协调高密度群体与个体的关系,获得较高的籽粒产量,且对半紧凑型品种金海5号调控效果更明显。     

Changes in leaf epicuticular wax load and its effect on leaf temperature and physiological traits in wheat cultivars (Triticum aestivum L.) exposed to high temperatures during anthesis

The physiological functions of epicuticular wax (EW) include reflectance of irradiation and the reduction of water loss. When a plant experiences stressful conditions, most notably, high irradiance and temperature, damage to the photosynthetic apparatus can occur and is signalled by a decrease in the F_v/F_max ratio. In this study, we examined the influence of increased EW on physiological function in terms of chlorophyll fluorescence (ChFl), stomatal conductance (g_s), leaf temperature and spectral reflectance indices (SRI) of bread wheat (Triticum aestivum L.) cultivars. The wheat cultivars were subjected to high temperature stress (HT) (38–40°C) under greenhouse conditions when the primary inflorescence was fully emerged to determine its effect on leaf EW deposition. Leaf temperature depression (LTD) was generally lower in control (2.3°C—2012, 0.94°C—2013) compared to HT stress (3.13°C—2012, 4.05°C—2013). Cultivars in control (0.69 to 0.74 F_v/F_max) had significantly higher ChFl compared to HT (0.58 to 0.74 F_v/F_max). HT treatment resulted in higher EW (1.28—2012, 4.59 mg dm^?2—2013) compared to control treatment (1.04—2012 to 4.56 mg dm^?2—2013). Leaves devoid of EW showed significant variation among cultivars at reproductive stages for water index (WI), normalized phaeophytinization index (NPQI) and simple ratio index (SRI). In HT stress conditions, significant correlations were observed between EWL and SRI only at 3DAFE (days after full emergence), suggesting that increased EWL induced by HT and irradiation in early development may provide relief and prevent grain loss. EWL significantly associated with the physiological traits ChFl, g_s, LTD and spike temperature depression (SpTD). These observations suggest that EWL may lessen the effect of high irradiance, thereby, effectively adjusting stomatal conductance, ChFl and leaf temperature, limiting the risk of over excitation of photosystem II.     

Effect of Chemical and Physical Stress Conditions on the Concentration and Composition of Essential Oil Components in Leaves of Full‐Grown Artemisia annua L.

Full‐grown Artemisia annua plants were subjected to chemical and physical stress conditions, and the effect of these on the concentration and chemical composition of essential oil components (EOC) in the leaves was studied. The chemical stress treatments were performed by foliar application of NaCl, H₂O₂, salicylic acid and chitosan oligosaccharide (COS). The EOC of the leaves were extracted with n‐hexane and identified and quantified by GC–MS and GC–FID, respectively. Approximately 96 % of EOC in the extracts were identified and quantified of which β‐pinene, camphene, germacrene D, camphor, coumarin and dihydro‐epi‐deoxyarteannuin B were the major EOC accounting for about 75 % of the total content of EOC in the extracts. The physical stress treatment, sandblasting of the plants resulted in a significant enhancement in the content of α‐pinene, camphene, coumarin and dihydro‐epi‐deoxyarteannuin B. The total yield of identified EOC in non‐treated plants (control) was 86.2 ± 13.8 μg g^?1 fresh weight (FW) compared with 104.0 ± 9.1 μg g^?1 FW in sandblasted plants. The chemical stress treatments did not affect the composition of EOC significantly. The results indicate that chemical stress treatments do not affect the concentration and composition of EOC in full‐grown A. annua plants to the same extent as physical stress treatment by sandblasting.     

Infrared Thermal Imaging as a Rapid Tool for Identifying Water‐Stress Tolerant Maize Genotypes of Different Phenology

The main task of this research was to evaluate canopy temperature and Crop Water Stress Index (CWSI) by assessing genotype variability of maize performance for different water regimes. To that end, three hundred tropical and subtropical maize hybrids with different phenology in terms of date of anthesis were evaluated. The influence of phenology on the change in canopy temperatures and CWSI was not equal during the three dates of measurement. At the end of vegetative growth (82 days after sowing, DAS) and at the blister stage (DAS 97), a high significant difference in temperatures and CWSI (P < 0.001) were obtained between the early‐ and late‐maturity genotypes. During anthesis (DAS 89), phenology had a significant effect (P < 0.01) only for the well‐watered genotypes, while under water‐stress conditions, no differences were found between early and late genotypes in terms of canopy temperature and CWSI. High significant differences (P < 0.001) in stomatal conductance (g_s) between early and late genotypes for different treatments were observed. A relationship (R² = 0.62) between g_s and canopy temperature was obtained. Under a water‐stress canopy, temperature was measured at anthesis, which was negatively correlated with grain yield of the early (r = ?0.55)‐ and late (r = ?0.46)‐maturity genotypes in the water‐stressed condition.     

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.     

Rapid Assessment of Specific Leaf Area and Leaf Nitrogen in Peanut (Arachis hypogaea L.) using a Chlorophyll Meter

The present study investigates the potential use of a hand-held portable SPAD chlorophyll meter for rapid assessment of specific leaf area (SLA) and specific leaf nitrogen (SLN), which are surrogate measures of transpiration efficiency (TE) in peanut ( Arachis hypogaea L.). The effects of sampling (leaf position, time of sampling and leaf water status) and climatic factors (solar radiation and vapour pressure deficit, VPD) on SLA and SPAD chlorophyll meter reading (SCMR) were studied in a range of peanut genotypes grown under field and greenhouse conditions. The correlation between SLA and SCMR was significant (r=−0.77, P < 0.01) for the second leaf from the apex but the correlation declined for leaves sampled from lower nodal positions. The diurnal fluctuation in SLA ranged from −20 % to +10 %, whereas SCMR was relatively unaffected by these diurnal changes. Solar radiation and VPD during the sampling period had a significant influence on the relationship between SLA and SCMR, largely through their effects on SLA. However, standardization of SLA for these environmental factors significantly improved the relationship between SLA and SCMR from −0.50 to −0.80 (P < 0.01), suggesting that, when protocols for leaf sampling and SLA measurements are followed, SCMR can be a surrogate measure of SLA. There were significant relationships between SLN and SCMR (r=0.84, P < 0.01) and SLN and SLA (r=−0.81, P < 0.01). These significant interrelationships amongst SLA, SLN and SCMR suggested that SCMR could be used as a reliable and rapid measure to identify genotypes with low SLA or high SLN (and hence high TE) in peanut.     

The Alleviating Effect of Elevated CO2 on Heat Stress Susceptibility of Two Wheat (Triticum aestivum L.) Cultivars

This study analysed the alleviating effect of elevated CO₂ on stress‐induced decreases in photosynthesis and changes in carbohydrate metabolism in two wheat cultivars (Triticum aestivum L.) of different origin. The plants were grown in ambient (400 μl l^?1) and elevated (800 μl l^?1) CO₂ with a day/night temperature of 15/10 °C. At the growth stages of tillering, booting and anthesis, the plants were subjected to heat stress of 40 °C for three continuous days. Photosynthetic parameters, maximum quantum efficiency of photosystem II (PSII) photochemistry (F_v/F_m) and contents of pigments and carbohydrates in leaves were analysed before and during the stress treatments as well as after 1 day of recovery. Heat stress reduced P_N and F_v/F_m in both wheat cultivars, but plants grown in elevated CO₂ maintained higher P_N and F_v/F_m in comparison with plants grown in ambient CO₂. Heat stress reduced leaf chlorophyll contents and increased leaf sucrose contents in both cultivars grown at ambient and elevated CO₂. The content of hexoses in the leaves increased mainly in the tolerant cultivar in response to the combination of elevated CO₂ and heat stress. The results show that heat stress tolerance in wheat is related to cultivar origin, the phenological stage of the plants and can be alleviated by elevated CO₂. This confirms the complex interrelation between environmental factors and genotypic traits that influence crop performance under various climatic stresses.     

转2-Cys Prx基因烟草抗氧化酶和PSII电子传递对盐和光胁迫的响应

以转2-Cys Peroxiredoxins (2-Cys Prx)基因的烟草(Nicotiana tabacum)为材料,非转基因烟草为对照,调查盐和光胁迫对转基因烟草幼苗叶片抗氧化酶和叶绿素荧光特性的影响,揭示2-Cys Prx基因在植物抗逆方面的功能。结果表明,弱光(200 μmol m^–2 s^–1)下,随着盐浓度增大,转基因烟草和对照的SOD活性皆增加,APX活性变化不大,H₂O₂含量稍有升高;强光(1000 μmol m^–2 s^–1)下,随着盐浓度增大,转基因烟草SOD活性增强,APX活性下降,H₂O₂含量增加缓慢,而对照的H₂O₂含量迅速升高,转基因烟草叶片的PSII电子传递速率(ETR)、最大光化学效率(F_v/F_m)和实际光化学效率(Ф_PSII)均高于对照,而且PSII电子受体侧的受抑制程度明显低于对照。结果暗示在强光和盐胁迫使APX活性降低的情况下,2-Cys Prx可有效清除细胞中过量H₂O₂,增强光合电子传递链的稳定性,特别是PSII电子受体侧的电子传递,有效减轻盐和高光胁迫引起的PSII光抑制。     

Differences in Ion Accumulation and Salt Tolerance among Glycine Accessions

Salinity reduces crop yield by limiting water uptake and causing ion‐specific stress. Soybean [Glycine max (L.) Merr.] is sensitive to soil salinity. However, there is variability among soybean genotypes and wild relatives for salt tolerance, suggesting that genetic improvement may be possible. The objective of this study was to identify differences in salt tolerance based on ion accumulation in leaves, stems and roots among accessions of four Glycine species. Four NaCl treatments, 0, 50, 75 and 100 mm , were imposed on G. max, G. soja, G. tomentella and G. argyrea accessions with different levels of salinity tolerance. Tolerant genotypes had less leaf scorch and a greater capacity to prevent Na⁺ and Cl^? transport from soil solution to stems and leaves than sensitive genotypes. Magnitude of leaf injury per unit increase in leaf Na⁺ or Cl^? concentrations was lower in tolerant than in susceptible accessions. Also, plant injury was associated more with Na⁺ rather than with Cl^? concentration in leaves. Salt‐tolerant accessions had greater leaf chlorophyll‐meter readings than sensitive genotypes at all NaCl concentrations. Glycine argyrea and G. tomentella accessions possessed higher salt tolerance than G. soja and G. max genotypes.     

Is Discrimination of 13C in Potato Leaflets and Tubers an Appropriate Trait to Describe Genotype Responses to Restrictive and Well‐Watered Conditions?

Selection for drought tolerance entails prioritizing plant traits that integrate critical physiological processes occurring during crop growth. Discrimination against ¹³C (?) in leaflets (?_leaflet) and tubers (?_tuber) was compared under two water regimes in two potato‐improved varieties selected to maintain yield under drought conditions (Unica and Sarnav) and one drought susceptible European cultivar (Désirée). In the control treatment, soil water content was kept at field capacity over the whole growth cycle, while in the drought treatment water supply was restricted after tuber initiation (50 % of field capacity). Gas exchange and N content per unit leaf area (N_area) as well as ? were assessed at different stages. Sarnav showed the highest tuber yield in both water conditions, suggesting that yield in the water restriction treatment was largely driven by yield potential in this genotype. Higher stomatal conductance (g_s) and N_area and lower ?_leaflet in well‐watered Sarnav suggested higher photosynthetic capacity. Under water restriction, Sarnav maintained higher g_s indicating that carbon diffusion was a key factor for biomass accumulation under water restriction. Our results suggest the use of ? determined after tuber initiation as an indirect selection indicator for tuber yield under both well‐watered and restricted soil water availability conditions.     

Salt‐Induced Regulation of Some Key Antioxidant Enzymes and Physio‐Biochemical Phenomena in Five Diverse Cultivars of Turnip (Brassica rapa L.)

A greenhouse experiment was carried out to examine the differential morpho‐physiological responses of five cultivars of turnip (Brassica rapa L.) to salt stress. Five diverse cultivars of turnip (shaljum desi surakh, shaljum purple top, shaljum golden bal, neela shaljum, and peela shaljum) were subjected for 6 weeks to varying levels of NaCl, i.e. 0, 80 and 160 mm in Hoagland’s nutrient solution in sand culture. Imposition of varying levels of salt substantially decreased shoot and root fresh and dry weights, chlorophyll contents, leaf osmotic potential, relative water contents, different gas exchange attributes, total phenolics, malondialdehyde, activities of superoxide dismutase, peroxidase catalase, and leaf and root K⁺ levels while enhanced the proline contents, membrane permeability, level of H₂O₂, leaf and root Na⁺ and Cl^? and leaf Ca²⁺ in all turnip cultivars under study. Of all cultivars, peela shaljum and neela shaljum were consistently higher in their growth than the other turnip cultivars at all salt concentrations of the growth medium. Photosynthetic capacity (A) and stomatal conductance (g_s) were higher in high biomass‐producing cultivars, i.e. peela shaljum and neela shaljum, which provide to be potential selection criteria of salt tolerance in turnip. However, the regulation of antioxidant system was cultivar‐specific under saline conditions.     

Effects of Free‐Air Carbon Dioxide Enrichment on Sap Flow and Canopy Microclimate of Maize Grown under Different Water Supply

The rise of atmospheric CO₂ concentration ([CO₂]) affects stomatal conductance and thus transpiration and leaf temperature. We evaluated the effect of elevated [CO₂] levels under different water supply on daily sap flow and canopy microclimate (air temperature (Tc) and vapour pressure deficit (VPD)) of maize. The crop was cultivated in circular field plots under ambient (AMB, 378 μmol mol^?1) and elevated [CO₂] (FACE, 550 μmol mol^?1) using free‐air CO₂ enrichment with sufficient water in 2007, while in 2008 a DRY semicircle received only half as much water as compared to the WET semicircle from mid of July. In 2007, sap flow was measured in WET simultaneously under AMB and FACE conditions and was significantly decreased by elevated [CO₂]. In 2008, sap flow was measured in all four treatments but not simultaneously. Therefore, data were correlated with potential evaporation and the slopes were used to determine treatment effects. Drought reduced whole‐plant transpiration by 50 % and 37 % as compared to WET conditions under AMB and FACE, respectively. Moreover, CO₂ enrichment did not affect sap flow under drought but decreased it under WET by 20 % averaged over both years. The saving of water in the period before the drought treatment resulted in a displacement of dry soil conditions under FACE as compared to AMB. Under WET, CO₂ enrichment always increased Tc and VPD during the day. Under DRY, FACE plots were warmer and drier most of the time in August, but cooler and damper short after the start of drought in July and from the end of August onwards. Thus, the CO₂ effect on transpiration under drought was variable and detectable rather easy by measuring canopy microclimate.