Effects of pH and selenium oxidation state on the selenium accumulation and yield of alfalfa

Experiments were performed in greenhouse sand culture to determine the effect of pH and Se oxidation state on the tissue composition and yield of alfalfa (Medicago sativa L.). Alfalfa was planted and irrigated with nutrient solution containing 0, 0.25, 0.5, 1.0 or 3.0 mg Se L^‐1 as Na₂SeO₃ or Na₂SeO_l4. The solution pH was maintained at 7.0 ± 0.2 or 4.5±0.2. Three harvests were made and the shoots and roots weighed and analyzed for total Se. At the levels tested, additions of Se to the treatment solutions increased the tissue Se concentrations and depressed alfalfa shoot growth regardless of Se oxidation state or pH. Root growth was reduced in the presence of Se(VI) but was unaffected by Se(IV). Selenium was accumulated to higher concentrations in the shoot when supplied as Se(VI) compared to Se(IV) and accumulated to higher concentrations in the root when added as Se(IV) compared to Se(VI). Relative shoot yields were depressed more by Se(IV) then Se(VI) at pH 7, but there was no difference between Se(IV) and Se(VI) at pH 4.5. Relative root yields were depressed by Se(VI) but not by Se(IV).     

Effects of excess boron on growth,gas exchange,and boron status of four orange scion–rootstock combinations

Field observations indicate that boron (B)‐toxicity symptoms may occur in citrus plants from inappropriate foliar spraying or overfertilizing with B especially under low‐rainfall conditions, where B can accumulate to levels that become toxic to plant growth. Previous work has indicated that different rootstocks can greatly influence the scion's tolerance to B toxicity, however, little is known about the response of different citrus scion–rootstock combinations to excess‐B conditions. In the present study, we investigated the effects of excess B on plant growth, gas exchange, B concentration, and distribution of four scion–rootstock combinations, Newhall and Skagg's Bonanza navel orange (Citrus sinensis Osb.) scions grafted on Carrizo citrange (C. sinensis L. Osb. × Poncirus trifoliata L. Raf.) and Trifoliate orange (Poncirus trifoliata L. Raf.) rootstocks. One‐year‐old plants of the four scion–rootstock combinations were grown for 183 d in sand–perlite (1 : 1, v/v) medium under greenhouse conditions. The plants were irrigated with half‐strength Hoagland's nutrient solution containing two B concentrations, 0.25 (control) and 2.50 (excess B) mg L^–1. It was found that, apart from the combination of Newhall grafted on Carrizo citrange, the dry weights in various parts of the other three combinations were reduced by the excess‐B treatment. Furthermore, the plants of Skagg's Bonanza grafted on Carrizo citrange showed the highest growth reduction amongst the four scion–rootstock combinations. In most cases, the greater reductions in dry weight were found in roots as compared to the other plant parts under excess‐B conditions, indicating that roots were more sensitive to B toxicity than the other tissues. In the case of Newhall plants grafted on Carrizo citrange, the entire plant growth was increased by excess‐B treatment. Boron concentrations in all plants parts increased significantly by increasing the B supply in the nutrient solution. Leaves were the dominant sites of B accumulation and showed the greatest increase in B concentration compared to the other plant parts, as B concentration in the nutrient solution increased. Our results indicate that the combination of Newhall grafted on Carrizo citrange was more tolerant to B toxicity, while the combination of Skagg's Bonanza grafted on Carrizo citrange was relatively more sensitive to B toxicity, in comparison with the other scion–rootstock combinations. However, Newhall plants contained more B in leaves and in roots than Skagg's Bonanza plants when they were both grafted on Carrizo citrange, indicating that the mechanism underlying such great differential growth responses of the two scion–rootstock combinations to B toxicity may not be associated with B exclusion from roots or reduced translocation of B to shoots. Furthermore, B distribution in different plant parts implied that the mechanism was also unlikely related to altered distributions of accumulated B in plant tissues. However, inherent ability to tolerate excessive B concentration in plant tissues may be involved in B tolerance.     

紫甘薯对硒的吸收和累积特征

以紫甘薯为试验材料,采用盆栽试验的方法研究了基施硒酸钠[Se(VI)]和亚硒酸钠[Se(IV)]条件下,紫甘薯对外源硒的吸收累积规律,并比较了施用两种不同价态硒的紫甘薯富硒效果。结果表明:两种硒源均可显著提高紫甘薯各器官含硒量,且紫甘薯含硒量均随施硒量的增加而增大。当土壤施硒量为Se 8 mg/kg时,施用硒酸钠、亚硒酸钠收获期薯块的硒含量(干基)分别达到6.69、0.88 mg/kg。紫甘薯生育期40 d时各器官硒含量叶茎薯块,130 d时硒含量叶薯块茎。当硒酸钠施用量为Se 4 mg/kg时,紫甘薯薯块中的硒累积量最高达923.81μg/株,硒在紫甘薯块根中的分配率可达67%~70%,硒酸钠处理下,紫甘薯对硒的吸收利用率远远高于亚硒酸钠处理。综合紫甘薯含硒量和施硒量对生长的影响结果分析,施用硒酸钠和亚硒酸钠均能增加紫甘薯薯块的硒含量,紫甘薯对硒酸钠敏感性高于亚硒酸钠,生产过程中应充分考虑施用硒酸钠对作物造成的毒害。     

Interactive effects of salinity and iron deficiency on different rice genotypes

Salinity adversely affects plant growth, photosynthesis, and availability of nutrients including iron. Rice (Oryza sativa L.) is susceptible to soil salinity and highly prone to iron (Fe) deficiency due to lower release of Fe‐chelating compounds under saline conditions. In order to investigate the effects of salinity and low iron supply on growth, photosynthesis, and ionic composition of five rice genotypes (KS‐282, Basmati Pak, Shaheen Basmati, KSK‐434 and 99417), a solution culture experiment was conducted with four treatments (control, 50 mM NaCl, Fe‐deficient, and 50 mM NaCl + Fe‐deficient). Salinity and Fe deficiency reduced shoot and root growth, photosynthetic and transpiration rates, chlorophyll concentration, and stomatal conductance. The reduction in all these parameters was more in the interactive treatment of salinity and low Fe supply. Moreover, a significant increase in shoot and root Na⁺ with corresponding decrease in K⁺ and Fe concentrations was also observed in the combined salinity and Fe‐deficiency treatment. Among the tested genotypes, Basmati Pak was the most sensitive genotype both under salt stress and Fe deficiency. The genotype KS‐282 performed better than other genotypes under salinity stress alone, whereas Shaheen Basmati was the best genotype under Fe deficiency in terms of all the studied parameters.     

Effects of boron excess in nutrient solution on growth,mineral nutrition,and physiological parameters of Jatropha curcas seedlings

Jatropha curcas L. has recently attracted the attention of the international research community due to its potential as a biodiesel crop. In addition, its high resistance to drought and salinity is well known. Under arid and semiarid conditions, boron (B) concentrations in irrigation water can be higher than desired when water from industry, urban areas, or desalination is used. However, the growth and physiological responses of J. curcas plants to B excess in the irrigation water are unknown. Therefore, a greenhouse experiment was conducted to study the effects of B excess in the nutrient solution (0.25, 2, 4.5, and 7 mg L^–1 B, applied as H₃BO₃) on plant growth, mineral concentration in the different plant tissues, photosynthesis, water relations, chlorophyll fluorescence, chlorophyll concentration (as SPAD values), and composition of carbohydrates. Plant growth decreased with increasing B concentration in the nutrient solution; growth reduction was higher for roots than for leaves or stems. The B concentration increased in all plant tissues, in the following order: leaf > root > stem. These data indicate that the roots of J. curcas are more sensitive to B toxicity than the leaves and that B has restricted mobility inside these plants, accumulating mainly in the basal and middle leaves via the transpiration stream. Increasing B concentration in leaves decreased the A_CO2 and the stomatal conductance, but the leaf water parameters were not affected. The data for chlorophyll concentration and chlorophyll fluorescence indicated that nonstomatal factors were involved in the A_CO2 decline, whereas decreases in the parameters of PSII photochemistry due to B toxicity suggest that there was structural damage in chloroplasts. There was also a general tendency for a decrease in nonstructural carbohydrates in all plant tissues, possibly due to the decline in A_CO2. With excess B, the concentrations of K and Mg increased in leaves due to a decrease in the growth, while a typical antagonistic effect between B and P was evident from the P concentration decrease in leaves. In summary, J. curcas should be considered a B‐sensitive plant, as a leaf B concentration of 1.2 mg (g dw)^–1 caused a growth decline of approximately 30%.     

Effects of methyl jasmonate on plant growth and leaf properties

Exogenous application of methyl jasmonate (MeJA) can induce anatomical and chemical changes that are components of defence responses in plants. Particularly, MeJA is well‐known to increase leaf trichome density to protect against insect herbivory, but surprisingly little is known about the effects of MeJA on other leaf properties and plant growth. Using sunflower (Helianthus annuus), tomato (Solanum lycopersicum), and soybean (Glycine max) treated with 0.0, 0.1, 0.5, 1.0, and 2.5 mM MeJA, we examined changes in leaf trichome density, stomatal density, cuticle thickness, cuticle composition, plant height, and biomass production. For all three plant species, MeJA (especially at the higher concentrations) caused significant decreases in plant height (up to 39%) and biomass (up to 79%). MeJA caused substantial increases in leaf trichome density (being 1.3–3.5‐times higher) in all three species, with the magnitude of these effects increasing with MeJA concentration. However, we also observed that MeJA resulted in significant changes in cuticle composition and thickness, and stomatal density, although the magnitude of these changes was smaller relative to changes in trichome density. Specifically, high concentrations of MeJA increased the relative content of phenolic compounds and cutin in leaf cuticle while decreasing the relative content of polysaccharide. The changes in stomatal density varied with plant species and MeJA concentration. Also, MeJA increased cuticle thickness in tomato but decreased that in sunflower and soybean. Thus, studies investigating MeJA should also consider the importance of changes in other leaf properties and plant growth.     

Effects of selenium as a beneficial element on growth and photosynthetic attributes of greenhouse cucumber

Selenium (Se) is an essential element for human and livestock with antioxidant and anticancer characteristics. Although Se is not an essential element for plants, it has been reported that it can improve plant growth. This experiment was conducted at the Isfahan University of Technology in winter 2010. The experiment was factorial based on a completely randomized design (CRD) with four replications. Se was added to nutrient solution in four concentrations 2, 4, and 6 mg/L sodium selenite (Na₂SeO₃). Root volume, fresh and dry weights of shoots and roots, number and weight of fruits, chlorophyll content, and photosynthesis traits [photosynthesis rate, stomata internal carbon dioxide (CO₂) concentration, stomata conductance] were measured. Results showed that Se increased root dry weight. Fresh and dry weights of shoot increased in the 2 mg/L Se treatment and decreased at the higher level of Se. Chlorophyll content and photosynthesis rate were not affected by Se. Stomata internal CO₂ concentration and stomata conductance decreased by Se addition. Overall, Se at 2 mg/L application rate was effective in some physiological characteristics of cucumber.     

高温对蓝莓叶片气孔特征和气体交换参数的影响

为探讨不同强度高温对南高丛蓝莓叶片气孔特征及其气体交换参数的影响,利用人工气候箱设置4个温度处理:对照(25℃)、轻度高温(30℃)、中度高温(35℃)和重度高温(40℃)对两年生南高丛蓝莓(Vaccinium corymbosum L.)幼苗(海岸、奥尼尔及蓝脊)进行为期90 d的光照培养实验。研究结果表明:高温增加海岸和蓝脊叶片的气孔密度,但对奥尼尔的气孔密度无影响。中度高温增大奥尼尔和蓝脊叶片气孔的长度、宽度和面积,但海岸的气孔长度比轻度高温减小23.5%(P0.05)。高温使奥尼尔的气孔空间分布更加规则,而对海岸和蓝脊的影响不大。3个品种的叶片净光合反应速率(Pn)、气孔导度(Gs)和蒸腾速率(Tr)均随高温强度先升高后降低,但其最大值随品种发生变化。研究结果表明,南高丛蓝莓具有调整气孔结构特征和优化气孔空间分布格局提高其气体交换效率的功能,但在品种间存在较大的差异,最终导致气体交换参数对高温产生不同的响应,尤其表现在抵抗极端高温能力方面。结果有助于从叶片气孔特征变化角度深入理解不同高温强度对南高丛蓝莓气体交换产生影响的潜在机理,为蓝莓耐高温胁迫选育及引种栽培工作提供理论支持。     

Effects of different application methods of selenite and selenate on selenium distribution within wheat

Abstract

The objective of this sand culture experiment was to determine how fertilization methods (i.e., fertigation rates of 0.5, 1, and 2?mg Se·pot^?1, foliar rates of 5, 10, and 20?mg Se· L^?1) and fertilizer type (i.e., selenate or selenite) affected wheat Se concentrations. The results showed that the fertigation and foliar treatments both increased wheat Se content. In the fertigation and foliar treatment total Se content of wheat was greatest in the selenate treatments. In the fertigation treatment, the Selenite had mainly accumulated in the roots, while the Selenate was majority transported to shoot. In the foliar treatment, we found that most of Se was transported to grain. In addition, the organic Se concentration was the most than other Se fractions. In conclusion, selenate was more effective than selenite in both the fertigated and the foliar application treatments. And the foliar application was better than fertigation.     

The effect of cobalt stress on growth and physiological traits and its association with cobalt accumulation in barley genotypes differing in cobalt tolerance

Cobalt (Co) is beneficial for legume plants and not an essential element for most plants. There is no sufficient information about the effect of Co stress on barley growth. The current experiment was carried out to investigate the effects of different Co levels (25, 50, 75, and 100 µM) on growth and physiological traits of three barley genotypes (B325, J36, and B340) differing in Co tolerance. The results showed that Co stress inhibited plant growth, decreased chlorophyll content and photosynthetic rate, and enhanced oxidative stress. However, the effects differed among genotypes, with B325 and B340 being the most and the least affected, respectively. Co stress caused decrease and increase of manganese (Mn) and phosphorus (P) concentrations in both roots and shoots, respectively; iron (Fe) concentration had little change in shoots and a significant decrease in roots. The current results showed a close association of Co tolerance and its accumulation in plant tissues.     

Effects of foliar selenium application on some physiological and phytochemical parameters of Vitis vinifera L. cv. Sultana under salt stress

Abstract

In this research the effect of foliar application of selenium (Se) at four levels (Na₂OSe₄; 0, 5, 10 and 20?mg L^?1) was evaluated on some phytochemical characteristics of Sultana grapevine under different salinity levels (NaCl; 0 or 75?mM). The vines were fed twice a week with Hoagland nutrient solution and Se was foliar applied twice with 24 intervals. During growing period, plant height, leaf number and leaf area were recorded. Moreover, at the end of experiment, mature leaves from middle nods of canes were used for measurement of some phytochemical indices. According to results, Se application had a positive effect on plant height, leaf numbers, leaf area and photosynthetic pigments content especially at 5?mg L^?1 and to some extent 10?mg L^?1 Se levels. Under salinity stress, foliar application of Se at 5?mg L^?1 considerably decreased vines leaves electrolyte leakage and lipid peroxidation values compared to non se-treated plants under salinity stress condition. Selenium had an additive effect on salinity stress (75?mM NaCl) induced accumulation of total phenol, total flavonoid, soluble sugars and proline content in leave of vines. Moreover, the interaction of salinity and Se at 5 and 10?mg L^?1 improved leaves antioxidant enzymes activities in Sultana grapevine. Likewise, foliar application of Se improved leaf mineral content in 75?mM NaCl -treated vines. Totally, foliar application of selenium (Se at 5 or 10?mg L^?1) increased salt tolerance through improvement in nutritional balance and by enzymatic and non-enzymatic antioxidant capacity in grapevine leaves.     

不同价态外源硒对小白菜生长及养分吸收的影响

采用土壤外源加入两种不同价态的硒 [Se(Ⅳ)和 Se(Ⅵ)]的盆栽试验,研究了其对小白菜生长、营养元素和硒吸收的影响。结果表明,施硒对小白菜的生长均表现出低浓度(5 mg/kg)促进,高浓度(5 mg/kg)抑制趋势。Se(Ⅵ)处理小白菜地上部硒含量大于地下部;而Se(Ⅳ)处理则与Se(Ⅵ)相反。硒从根部转运到地上部的转移因子Se(Ⅵ)处理大于Se(Ⅳ)。两种价态硒处理,小白菜对氮、磷、钾、硫、镁和锌的吸收也表现出低浓度时为促进作用,高浓度为抑制作用。Se(Ⅵ)显著增加了钙的吸收,Se(Ⅳ)却无显著影响;Se(Ⅳ)和Se(Ⅵ)均能促进小白菜对铁的吸收。相同浓度下, Se(Ⅵ)对各个营养元素吸收的影响显著大于Se(Ⅳ)。综合硒对生长和养分吸收的影响看出,小白菜施硒量以Se(Ⅵ)不超过2.5 mg/kg或Se(Ⅳ)不超过5 mg/kg为宜。     

Effects of salt stress on plant growth characteristics and mineral content in diverse rice genotypes

ABSTRACT

When rice is grown under moderate salinity (6?dS m^?1), yields are reduced by up to 50%. The development of salt-tolerant varieties is a key strategy for increasing yields. We conducted an experiment using a hydroponic system with ion components similar to seawater to determine useful parameters for assessing salt tolerance. Two-week-old seedlings were grown for 7 days on Yoshida hydroponic solution. The treatment group then additionally received an artificial seawater solution (electrical conductivity, 12 dS m^?1). After a 2-week period of salt stress, standard evaluation scores (SES) of visual salt injuries were assessed. The K, Na, Mg, and Ca contents were then determined in the roots, sheaths, and leaves of each plant. Following the SES results, we divided the 37 genotypes into four groups: salt-tolerant groups (STGs), moderately salt-tolerant groups, salt-sensitive groups (HSSGs), and highly salt-sensitive groups (HSSGs). In the control, STGs had the highest sheath K content (30.1 mg g^?1 dried weight [DW]), whereas HSSGs had the lowest (21.4 mg g^?1 DW). Sheath K was also highly and negatively correlated with SES. This suggests that sheath K may be useful for identifying salt-tolerant varieties under non-saline conditions. Plant growth was significantly affected under salt stress, but STGs had the smallest decrease in sheath DW. SES was significantly correlated with sheath and leaf Na, sheath K and Mg, and sheath and leaf Na/K and Na/Mg ratios. The results suggested that sheath K, Na/K, and Na/Mg may be useful indicators for genetic analyses of salt-tolerant varieties under salt-stress conditions. The salt-tolerant cultivars, KCR20, KCR124, and KCR136, are possible candidates for such studies because they had high sheath K content (31.19, 31.21, 29.44 mg g^?1 DW, respectively) under non-saline conditions and low SES (3.3, 3.6, 3.9, respectively), and low sheath Na/K (0.64, 0.52, 0.92, respectively) and Na/Mg ratios (2.96, 2.27, 3.03, respectively) under salt-stress conditions.     

钾对不同基因型玉米生长、体内钾循环和分配的影响

钾素循环和再利用对维持植物生长和提高钾利用效率非常重要。本文以杂交玉米豫玉23和兴农998为供试作物,采用供应高钾（1.85 mmol/L）和低钾（0.1 mmol/L）营养液的石英砂培养方法,研究不同基因型玉米各器官干重和钾积累及分配、 体内钾在木质部和韧皮部中的循环、 流动及钾效率等。结果表明,低钾处理10 d后,与高钾处理相比,低钾降低两玉米品种各器官干重净增量、 钾浓度、 钾积累量、 钾吸收效率和木质部中钾的运输量,增加钾利用效率和源叶中韧皮部输出的钾,提高钾通过韧皮部的再循环量及占木质部运输总量的比例。低钾处理的豫玉23和兴农998上部叶均为钾库,钾积累量的38.5%和70.3%是由各自中、 下部叶韧皮部输出的钾供给,但体内光合产物和钾向上部叶的运输是不完全同步的过程。两品种比较,低钾处理下的豫玉23较兴农998干重净增量提高,在于前者具有较大根量、 较高钾吸收速率和较多钾素吸收量,木质部中有更多的钾通过叶片韧皮部输出进行循环运输进入上部叶;但豫玉23对介质中钾的吸收大于体内钾的再利用。钾营养高效基因型玉米应该具有较强的吸收和利用体内钾的能力。     

Effect of Shading on Gas Exchange of Cotton Leaves Under Conditions of Different Soil Water Contents1

Effect of different shading levels (no-shading, 80% shading, and 40% shading) on photosynthetic and stomatal responses in cotton leaves were investigated under onditions of different soil water contents in summer midday. All cotton leaves exhibited similar basic responses to shading, including decreased netphotosynthetic rates, a tendency to decrease in transpiration rates, and increased stomatal conductance and intercellular CO2 concentration. The leaf conductance of 80% shaded and 40% shaded plants increased by 28% and 16.7% compared with no-shaded plants at high water, respectively, but the net photosynthetic rates of 80% shaded and 40% shaded plants declined by 50% and 14.73%, respectively. Results showed that combined effect of soil moisture and shading on photosynthetic and stomatal responses in cotton leaves was very remarkable.     

水分和CO2对玉米光合性能及水分利用率的影响

利用环境生长室探讨不同CO₂浓度和土壤水分亏缺处理下玉米植株生物量、气孔形态与分布特征、叶片气体交换参数、叶绿素荧光参数等生长及生理指标的变化规律。以‘郑单958’ 玉米品种为试材,利用环境生长室设置2个CO₂浓度和4个土壤水分梯度对玉米进行CO₂浓度和水分处理。结果表明：1）不同程度土壤水分亏缺均显著降低玉米地上生物量（P<0.05）,但CO₂浓度升高增加了轻度水分亏缺条件下玉米地上生物量（P<0.01）和总生物量（P<0.01）。2）大气CO₂浓度升高导致轻度和中度水分亏缺条件下玉米的净光合速率（P_n）分别提高15.8%（P<0.05）和25.7%（P=0.001）,而CO₂浓度升高却降低了玉米叶片蒸腾速率（P<0.001）和气孔导度（P<0.001）,最终导致玉米瞬时水分利用效率均显著提高（P<0.001）。3）不同水分处理对玉米叶片气孔密度和单个气孔形态特征均造成显著影响（P<0.01）。因此,大气CO₂浓度升高可以增加轻度水分亏缺条件下玉米叶片氮含量、叶片非结构性碳水化合物含量和光合电子传递速率,从而提高玉米植株的生物量累积以及叶片碳同化能力和水分利用效率。研究结果将为深入理解气候变化背景下玉米对大气CO₂浓度升高和土壤水分亏缺的生理生态响应机制提供科学依据。     

Impact of water availability on root growth of sugar beet varieties

On average, sugar beet yield in the UK is reduced by 10% due to water limitation. The root system of a plant is responsible for water uptake and hence an extensive root system is crucial to mitigate drought stress. There might be varietal differences when it comes to plant root system architecture but so far none have been reported in sugar beet. This study shows the results of 2 years of field experiments, examining the rooting patterns and overall plant growth of sugar beet under both rainfed and irrigated conditions. In the first year, three varieties were assessed, and in the second year, five varieties. No significant yield differences were found between the rainfed and irrigated treatments, which is likely due to the applied drought stress only being mild in both years. There were, however, significant varietal differences in plant growth and rooting patterns in rainfed plants which were most distinct when plants were subjected to mild drought stress. Varietal differences observed might indicate the possibility of breeding for certain root traits to mitigate drought stress in sugar beet in the future.     

氮素对不同生育期小麦植株累积硒的影响

【目的】施用氮肥是农业生产上最重要的增产措施之一,但增施氮肥对不同生育期小麦植株中硒累积、 转运和分配的影响尚不明确。本研究通过盆栽试验研究不同氮水平对小麦生长过程中植株各器官硒累积的影响,为合理施氮提高小麦硒含量提供理论参考。【方法】 试验设置N 100 mg/kg和200 mg/kg 两个水平,每个氮水平设置低硒 (Se 0.81 mg/kg)和高硒 (Se 5.02 mg/kg) 处理,分别在小麦苗期、 拔节期、 孕穗期、 抽穗期、 扬花期、 灌浆期和成熟期取样,分析不同生育期小麦对土壤外源硒的吸收速率,探讨不同硒水平下施氮量对小麦各器官硒累积、 转运和分配的影响。【结果】 1)与低氮相比,高氮促进了小麦籽粒产量增加,低硒的促进作用大于高硒,低硒和高硒时的高氮处理小麦籽粒产量较低氮处理分别提高了21.7%和13.7%。低硒时的高氮处理能提高小麦穗(特别是籽粒)和老叶中的硒含量,籽粒和颖壳硒含量较低氮处理分别提高了31.2%和13.6%,但高硒时高氮处理却导致小麦各器官(特别是籽粒和根)中硒含量下降,其中籽粒和根部硒含量较低氮处理分别下降了13.2%和17.8%。 2)相同硒水平下,高氮处理小麦根部硒占植株总硒的比例较低氮处理下降了约1/4; 在营养生长阶段,低硒时高氮处理能促进硒向小麦地上部转运,而在生殖生长阶段其能促进硒从小麦茎叶向颖壳和籽粒中转运,使得籽粒中硒占总硒比例提高了18.4%; 但高硒时高氮处理却促进硒从茎叶转运到颖壳中,致使籽粒中硒占总硒比例下降了8.0%。3)小麦根部硒含量在苗期和拔节期,抽穗期和扬花期之间增长幅度最大,说明此期间是小麦硒吸收的敏感期。【结论】小麦硒含量因生育期和外源硒水平的不同而异,施氮量也影响着小麦硒累积、 转运和分配。增施氮肥能提高硒的利用效率,建议低硒地区农业生产中补硒时要结合氮的合理施用。     

土壤水分及环境因子对刺楸叶片气体交换的影响

通过测定不同土壤水分条件下,3a生盆栽刺楸苗木的气体交换参数及其周围环境因子,探讨土壤水分及微气候因子对光合速率、蒸腾速率、气孔导度等气体交换参数的影响规律。结果表明:随着水分胁迫的加剧,刺楸叶片蒸腾速率、净光合速率和气孔导度总体上表现出减小的趋势,且随着胁迫的加剧,下降的幅度越大,蒸腾速率、净光合速率和气孔导度在重度、中度、轻度胁迫下日均值分别比对照下降6 6 % ,2 5 %和16 % ,81% ,30 %及5 1% ,70 % ,17%和14 %。随着土壤水分的减少,净光合速率下降逐渐由气孔限制转变为非气孔限制,水分利用效率并未完全表现出下降的趋势,日平均值表现为对照>中度>轻度>重度。逐步回归分析表明,刺楸苗木叶片水气交换参数,不仅受土壤水分的影响,同时也受外界环境因子的综合影响,且影响程度差异较大,回归方程相关系数较好     

Effects of Plant-Growth-Promoting Rhizobacteria on Yield,Growth, and Some Physiological Characteristics of Wheat and Barley Plants

In 2009 a greenhouse experiment was conducted to determine the effects of boron (B) and plant growth-promoting rhizobacteria (PGPR) treatments, applied either alone or in combination, on yield, plant growth, leaf total chlorophyll content, stomatal conductance, membrane leakage, and leaf relative water content of wheat (Triticum aestivum L. cv. Bezostiya) and barley (Hordeum vulgare L. cv. Tokak) plants. Results showed that alone or combined B (0, 1, 3, 6, 9 kg ha^?1) and PGPR (Bacillus megaterium M3, Bacillus subtilis OSU142, Azospirillum brasilense Sp245, and Raoultella terrigena) treatments positively affected dry weight and physiological parameters searched in both species. Statistically significant differences were observed between bacterial inoculation and B fertilizer on root and shoot dry weight under non-cold-stress (NCS) and cold-stress (CS) conditions. Leaf total chlorophyll content (LTCC), stomatal conductance (SC), leaf relative water content (LRWC), and membrane leakage (ML) were negatively affected by CS conditions and decreased with reduced temperatures of media, but B and PGPR application alleviate the low-temperature deleterious effect in both species. The greatest SC and LRWC, and the lowest ML, were obtained by 6 kg B ha^?1 combined with R. terrigena treatment. The greatest LTCC in both NCS and CS conditions was observed with B. megaterium M3 application alone.