Fate of selenate metabolized by Enterobacter taylorae isolated from rice straw

Rice straw has been successfully tested as an effective organic source and a carrier of selenate [Se(VI)]-reducing bacteria to remove Se(VI) from agricultural drainage water. In this study, an Se(VI)-reducing bacterium identified as Enterobacter taylorae was isolated from rice straw and used to remove Se(VI) from a 0.5% tryptic soy broth (TSB) and high-salt (15.5 dS m(-)(1)) synthetic agricultural drainage water containing Se(VI) in a range of 500-5000 microg/L. Results showed that E. taylorae reduced 81-94% of the added Se(VI) to elemental Se [Se(0)] in the 0.5% TSB solution during a 5-day experiment. In the high-salt drainage water, Se(VI) reduction was rapid during a 9-day experiment. On the final day of the experiment, Se(0) [75%] and Se(-II) [19%] were the major forms of Se in the drainage water with small amounts of Se(VI), Se(IV), and volatile Se released. The pathway of Se(VI) reduction in the drainage water followed the order Se(VI) --> selenite [Se(IV)] --> Se(0) --> selenide [Se(-II)]. This study suggests that E. taylorae may be used to remediate high-salt Se(VI)-contaminated agricultural drainage water.     

Application of redox mediator to accelerate selenate reduction to elemental selenium by Enterobacter taylorae

Acceleration of bacterial reduction of selenate [Se(VI)] to insoluble elemental Se [Se(0)] plays an important role in Se bioremediation. Anthraquinone-2,6-disulfonate (AQDS), a redox mediator, was assessed for its ability to enhance the reduction of Se(VI) (2000 microg/L) to Se(0) by Enterobacter taylorae in various media. The results showed that addition of AQDS did not increase Se(VI) reduction in the media containing 50 and 250 mg/L yeast extract, suggesting that E. taylorae cannot directly use anthrahydroquinone-2,6-disulfonate (AHQDS, a reduced form of AQDS) to respire Se(VI). An increase of yeast extract concentration from 50 to 250 mg/L in the medium dramatically enhanced the AQDS function for rapid reduction of selenite [Se(IV)] to Se(0). During an 8-day experiment, 85-91% of the added Se was reduced to Se(0) in the AQDS-amended medium in comparison to formation of 46% of Se(0) in the medium without AQDS. These results show that redox mediators have great application potential in bioremediation of Se in Se-contaminated water.     

Selenate reduction in river water by Citerobacter freundii isolated from a selenium-contaminated sediment

Bacterial reduction of selenate [Se(VI)] to insoluble elemental Se [Se(0)] is an important remedial technology to remove selenium (Se) from Se-impacted water. Citerobacter freundii, a Se(VI) reducer, isolated from a Se-contaminated sediment was assessed for its ability to reduce Se(VI) in a mineral culture medium and natural river water in a series of laboratory batch experiments. The results showed that a combination of yeast extract and glucose used in the culture medium was more effective than yeast extract alone, yeast extract plus sodium acetate, and yeast extract plus sodium lactate for reduction of Se(VI) to Se(0) by C. freundii. About 89-96% of the added Se(VI) (500-4500 microg/L) was reduced to Se(0) in the culture medium amended with 500 mg/L each of yeast extract and glucose. C. freundii can also survive in natural river water and reduce Se(VI). During an 8-day experiment in both sterile and nonsterile river water, 63-70 and 21-22% of the added Se(VI) was reduced to Se(0) and Se(-II), respectively. These results suggest that C. freundii has great potential for Se(VI) reduction and may be used for remediating Se-impacted water.     

Removal of selenate in river and drainage waters by Citrobacter braakii enhanced with zero-valent iron

A cost-effective remediation method is needed to remove selenium (Se) from Se-contaminated water. In this study, a selenate [Se(VI)]-reducing bacterium, Citrobacter braakii, that is capable of using molasses as a carbon source to reduce Se(VI) from natural river and drainage waters was isolated. During an 8-day experiment, 87-97% of the added Se(VI) in New River water and White River water, California, was reduced to elemental Se [Se(0)] or transformed to organic Se. In highly saline drainage water, removal of Se(VI) by C. braakii was limited, with 20% Se(VI) removal in a 7-day experiment. Addition of zero-valent iron (ZVI) into these waters along with C. braakii inoculation significantly enhanced the removal of Se(VI) and reduced the formation of organic Se. This study suggests that the combination of a bacterial treatment using inexpensive molasses and ZVI can effectively remove Se from natural river water and agricultural drainage waters.     

Application of Commercial Coffee for the Remediation of Hexavalent Chromium-Contaminated Water

The potential application of commercial coffee as a source of electron donors for detoxifying hexavalent chromium [Cr(VI)]-contaminated water was investigated. Various amounts of coffee were reacted with 50 mg/L of artificially prepared Cr(VI)-contaminated water, and the Cr(VI) concentration was monitored as a function of the reaction time using the diphenylcarbazide colorimetric method with an Aquamate 8000 UV-Vis spectrophotometer at a 540-nm wavelength. When the ratio of the coffee mass applied to the volume of Cr(VI) solution was 75 g/L, more than 80% of the initial Cr(VI) disappeared within 5 min of reaction time, and the Cr(VI) concentration became lower than the detection limit of 1 mg/L within 20 min. More Cr(VI) disappeared as more coffee was introduced. In general, smaller particles of coffee were more effective at Cr(VI) reduction, but the advantage that particle size conferred disappeared once the coffee particle size was smaller than 125 μm. As a result, the reduction of the Cr(VI) in the solution was not considered to result from the surface catalytic reduction but by the electron transfer from the electron donors released from the applied coffee.     

Cultivation of the Indian fig Opuntia in selenium-rich drainage sediments under field conditions

Growing selenium (Se)-biofortified alternative crops in saline and Se-contaminated agricultural land in arid/semi-arid regions, such as the western United States, depends upon the plant’s ability to tolerate high salinity and accumulate Se. In this field study, we evaluated the ability of five prickly pear cactus clones [Opuntia ficus-indica (L.) Mill., no. 243, 248, 250, 252, and 255] to grow, accumulate and volatilize Se from drainage sediment high in sulphate salinity (∼5 dS/m), soluble B (∼5 mg/L) and Se concentrations (∼0.8 mg/L). After 3 years of growth, all clones exhibited significant decreases up to 20% in height and fruit production compared with control clones. Mean Se concentrations (mg/kg DM) ranged from 4.9 to 9.8 in cladodes, 1.5–2.5 in fruit flesh, and 4.5–10.1 in seeds. Rates of Se volatilization varied from 20 to 80 μg Se/m² per day among the tested clones. The successful growth of prickly pear cactus and its accumulation and volatilization of Se under adverse soil conditions may provide growers with an alternative Se-biofortified crop in the westside of the San Joaquin Valley in central California.     

Selenium Removal from Irrigation Drainage Water Flowing Through Constructed Wetland Cells with Special Attention to Accumulation in Sediments

A flow-through experimental wetland system has been under investigation since 1996 to remove selenium (Se) fromagricultural drainage water in the Tulare Lake Drainage Districtat Corcoran, California, U.S.A. The system consists of ten cellswhich have dimensions of 15 × 76 m continuously flooded andvarious substrates planted. The objectives of this article are topresent the overall performance in Se removal after establishingthe wetland for three years, and to examine factors affecting Seremoval with special attention to accumulation in the sediments.In 1999, The wetland cells reduced Se from inflow water by 32 to65% in concentration and 43 to 89% in mass. Vegetationplays an important role in Se removal as non-vegetated cellshowed the least removal of Se. The inflow drainage water wasdominated by selenate (Se(VI), 91%) with smaller percentages ofselenite (Se(IV), 7%) and organic Se (org-Se(II-), 2%). Theoutflow water from the cells contained an average of 47% Se(VI),32% Se(IV) and 21% org-Se indicating reduction processesoccurring in the wetland cells. The surface sediment appears as alarge sink of Se removal. The highest Se concentration was foundin fallen litter, followed by the fine organic detrital layer onthe sediment surface. The sediment Se concentration dramaticallydecreased with increasing sediment depth. The mass distribution of Se, however, was sediment (0-20 cm) > fine detrital matter >fallen litter. Fractionation of surface sediment (0-5 cm) reveals that elemental Se was the largest fraction (ave. 47%) followedby organic matter-associated Se (34%). Soluble, adsorbed, and carbonate-associated Se accounted for 1.2, 3.1 and 2.5% ofthe total sediment Se, respectively. The major Se sink mechanism in the cells is the reduction of selenate to elemental Se andimmobilization into the organic phase of the sediments.     

Effect of lowering nutrient solution concentration at night on leaf calcium levels and the incidence of tipburn in lettuce (Var. Gloria)

Butterhead lettuce (var. Gloria) were grown in an evaporatively cooled glasshouse using the nutrient film technique (NFT). During the day all plants received a complete nutrient solution (EC 2 dS/m). Treatments were imposed at night and included: complete nutrient solution (control); tap water (EC 0.19 dS/m); and calcium nitrate solutions containing either 100 mg Ca/L (EC 0.80 dS/m), or 200 mg Ca/L (EC 1.45 dS/m).

Tipburn occurred in the control and its incidence was reduced by the other treatments. This effect was associated with an increase in the concentration of calcium in new leaves, except in the water treatment. The night treatments did not affect the fresh weight of mature lettuce.

Circulation of either water or calcium nitrate (100 mg Ca/L) at night may, therefore, be a commercially acceptable means of reducing tipburn losses in lettuce crops grown using hydroponics.     

Strategy for long term use of saline drainage water for irrigation in semi-arid regions

In arid and semi-arid regions, effluent from subsurface drainage is often saline and in the absence of a natural outlet, its disposal is a serious environmental threat. A field experiment was conducted for 7 years using drainage water of different salinity levels (EC_iw=6, 9, 12 and 18.8 dS/m) for irrigation of wheat during the dry winter season. The objective was to find whether crop production would still be feasible and soil salinity would not be increased unacceptably by this practice. The experimental crop was wheat during the winter season and pearl-millet and sorghum in the rainy season, grown on a sandy loam soil provided with subsurface drainage system. All crops were given a pre-plant irrigation with non-saline canal water and subsequently, saline drainage water of different salinity levels was used for the irrigation of wheat as per the treatment. On an average, the mean yield reduction in wheat yield at different EC_iw was 4.2% at 6, 9.7% at 9, 16.3% at 12 and 22.2% at 18.8 dS/m. Pearl-millet and sorghum yields decreased significantly only where 12 dS/m or higher salinity water was applied to previous wheat crop. The high salinity and sodicity of the drainage water increased the soil salinity and sodicity in the soil profile during the winter season, but these hazards were eliminated by the subsurface drainage during the ensuing monsoon periods. The results obtained provide a promising option for the use of poor quality drainage water for the irrigation of winter wheat without undue yield reduction and soil degradation.     

Nitrogen metabolism in pepper plants applied with different bioregulators

Certain bioregulators were studied in relation to nitrogen metabolism of pepper plants (Capsicum annuum L. cv. Lamuyo). Plants were grown under controlled conditions and submitted to regular fertilization with macro- and micronutrients. Treatments were as follows: nontreated control (T0); fosfonutren [essential amino acids and micronutrients (46.9 mg L(-)(1))] (T1); biozyme [GA(3) (32.2 mg L(-)(1)) plus IAA (32.2 mg L(-)(1)) plus zeatin (83.2 mg L(-)(1)) plus chelated micronutrients] (T2); and GA(3) [16 mg L(-)(1)] (T3). The concentrations of NO(3)(-), organic N, amino acids, and proteins, the activities of nitrate reductase (NR) and nitrite reductase (NiR), and finally the foliar dry weight and yield were analyzed. The results indicated that the application of certain bioregulators, such as fosfonutren (T1), which contain amino acids can cause a negative effect on the efficiency and utilization of NO(3)(-), resulting in a drastic loss in growth and yield, even under the control treatment, in which no bioregulator was applied. On the contrary, the application of certain bioregulators based principally on the combination of different hormones, as in the case of biozyme (T2), increased NO(3)(-) assimilation under our experimental conditions, due possibly to a greater availability of these bioregulators in the leaves and increased NR and NiR activities. This appears to explain why the T2 treatment gave the greatest foliar dry weight and fruit yield per plant in the experiment.     

微咸水滴灌对黄瓜产量及灌溉水利用效率的影响

试验主要研究了华北半湿润地区微咸水滴灌条件下,滴头正下方0.2 m深度土壤基质势分别控制在－10～－50 kPa时,不同盐分浓度微咸水(2.2～4.9 dS/m)对黄瓜产量、灌水量及灌溉水利用效率(IWUE)的影响。研究发现当灌溉水电导率(EC)大于1.1 dS/m时,黄瓜的产量随着EC的增大而降低。当滴头下0.2 m深度土壤基质势控制在－25～－35 kPa时,黄瓜表现出来的耐盐性最强,EC每升高1 dS/m产量大约降低3%。总的趋势是土壤基质势控制越高(－10 kPa)处理的灌溉量越多,IWUE越低,而土壤基质势控制越低(－50 kPa)处理的灌溉量越少,IWUE越高。通过研究,在年降雨量大约为600 mm的半湿润地区,当没有足够的淡水用于作物灌溉时,可以在采用一系列灌溉与栽培管理措施条件下,利用2.2～4.9 dS/m的微咸水来灌溉黄瓜等对盐分中等敏感的作物。     

滨海重度盐碱地微咸水滴灌水盐调控及月季根系生长响应研究

滨海盐碱地是滨海地区重要的土地资源,随着滨海地区城镇化进程及生态文明建设的发展,迫切需要低成本、快速、可持续的滨海盐碱地原土植被构建技术。针对滨海盐碱地原土建植与咸水/微咸水资源的利用,该研究以月季(Rosa chinensis)为例,采用微咸水滴灌技术进行滨海盐碱地水盐调控植被构建。试验在渤海湾曹妃甸区吹沙造田形成的典型沙质滨海盐渍土上进行,设计了灌溉水电导率(ECiw)为0.8、3.1、4.7、6.3、7.8 dS/m的5个处理,研究滴灌水盐调控对土壤盐分淋洗及月季根系生长和分布特征的影响。结果表明:在渤海湾滨海地区气候条件下,先进行淡水滴灌盐分强化淋洗和缓苗灌溉,随后采用7.8 dS/m的微咸水滴灌,0～100 cm土层土壤盐分得到了有效的淋洗,尤其是根层0～40 cm土壤盐分经过一个月左右,由初始28.33 dS/m降低到均小于4 dS/m,一个低盐适生的土壤环境得到快速营造;随着ECiw的增加,0～40 cm土层土壤最终趋于稳定的盐分呈增加趋势,土壤脱盐过程可以被logistic方程描述,脱盐过程可划分为快速脱盐、缓慢脱盐和盐分趋于稳定3个阶段;94%以上的月季根系主要分布在0～20cm的表层土壤中,随着ECiw的增加,根系生物量显著降低,根系受盐分胁迫生理干旱影响向土壤深处生长以扩大水分空间。研究认为,采用短期淡水滴灌盐分强化淋洗和缓苗淡水滴灌、随后进行微咸水滴灌的方法,可以实现土壤盐分的快速淋洗并维持在较低水平,但受盐分对根系生长的影响会作用于植物地上部分生长及植物存活,因此需要结合植物耐盐性及生产目标(产量、景观)确定适宜灌溉水矿化度阈值。     

Bioreduction of chromium (VI) by Bacillus sp. isolated from soils of iron mineral area

Extensive use of chromium in industry has caused environmental contamination. Chromium-resistant bacteria are capable of reducing toxic Cr (VI) to less toxic Cr (III). Eight isolates, which can grow on LB agar containing 500 mg/L of Cr (VI), were isolated from soil samples of iron mineral area. The bacterial isolates were identified as Bacillus sp. by the 16S rRNA gene sequences. Phylogenetic tree analysis indicates the isolates can be divided into two groups. The bacterial isolates can be resistant to other heavy metals and reduce Cr (VI) at different levels. One bacterial isolate (MDS05), which can tolerate 2500 mg/L Cr (VI) and was able to reduce almost 100% of Cr (VI) at the concentration of 10 mg/L in 24 h, was selected to study the effects of some environmental factors such as pH, temperature, and time on Cr (VI) reduction and growth. The cell growth of MDS05 was affected by the presence of Cr (VI), especially at the concentration of 100 mg/L. It reduced more amount of Cr (VI) under a wide range of concentrations from 5 to 50 mg/L, and reduction was optimum at 37 °C and pH 8. MDS05 showed great promise for use in Cr (VI) detoxification under a wide range of environmental conditions.     

用SahysMod模型研究不同灌排管理情景土壤水盐动态

银北灌区是宁夏土地整治和高标准灌溉绿洲农田建设的重点区域。该区域耕荒地交错分布、土壤盐渍化严重。通过模型分区模拟,在土地整治过程中建立完整、配套的灌排系统是解决区域土壤盐渍化的有效措施。该研究以银北灌区典型区域-西大滩为例,综合考虑荒地与耕地土壤属性的空间变异性,以2015—2016年土壤盐分数据进行率定,2017年盐分数据作为验证,利用SahysMod探索在土地整治过程中不同灌排管理下未来10 a内土壤水盐动态变化。结果表明,现有灌排管理下(即灌水量为670 mm,灌溉水电导率为1.05 dS/m,排水沟深1.5 m),荒地土壤盐分在预测初期(2017—2022年)逐年升高,预测后期(2023—2027年)变化平缓;耕地土壤盐分在预测初期变化缓慢,预测后期逐年增加。加大灌水量是解决土壤盐渍化的一个重要途径,可以有效延迟耕地盐分累积到障碍水平的时间;在灌溉水电导率为0.6 dS/m情况下,未来10 a内耕地都不会受到盐害胁迫;现有灌排管理下,在2024年以后作物生长就会受到盐害胁迫,当灌溉水电导率继续增加时,作物生长受到胁迫的时间相应提前。通过土地整治,加深排水沟深度可以延迟土壤盐分达到障碍水平的时间。在整治过程中深为2.2 m的排水沟,可保证未来10 a内耕地盐分小于1.7 dS/m,区域内玉米可正常生长。研究可为在土地整治过程中的灌排管理及土壤盐渍化防治提供建议。     

咸水灌溉棉田保证棉花优质高产的土壤盐度指标控制

为了探索由咸水灌溉引发的次生盐渍化棉田适宜的土壤盐度控制指标,试验于2012年在5个不同次生盐渍化水平的小区开展,0~60 cm深土层的初始土壤电导率(土水质量比为1∶5)分别为0.29、0.32、0.55、0.79、0.99 d S/m,分别以处理1~5表示。研究分析了盐分对棉花"三桃"比例、产量和纤维品质的影响,并建立了棉花价格模型,最后通过拟合分段式作物耐盐函数得出土壤盐度控制指标。结果显示,在平水年时降雨基本满足棉花需水要求,而且土壤中很大一部分盐分被降雨淋洗出0~60 cm深土层,并被控制在100 cm以下的土层中,与试验初始相比,处理1~5的最大脱盐率分别为9.6%、19.8%、36.4%、42.4%和45.7%,最终脱盐率分别为9.4%、1.8%、21.0%、24.5%和31.7%。当0~60 cm深土层初始土壤电导率低于0.79 d S/m时,没有显著降低成铃数和籽棉产量,仅会改变"三桃"比例,随土壤盐度进一步增高,成铃数和籽棉产量显著降低。棉花衣分率和纤维品质指标受到采摘时间和土壤盐度的共同影响,仅马克隆值在3次调查中都随着土壤盐度增加呈增大的趋势。由棉花净收益决定的土壤盐度指标低于由籽棉产量决定的土壤盐度指标,证明考虑纤维品质指标的必要性。在与处理1的净收益相比不降低的情况下,棉花播种初始和生育期平均土壤电导率应该分别控制在0.71和0.67 d S/m以下。该研究为改善次生盐渍化棉田土壤盐度控制指标的确定方法提供了理论参考。     

灌溉水盐度和施氮量对棉花产量和水氮利用的影响

淡水资源不足和盐渍化是干旱半干旱地区农业生产的重要限制因素,因此提高水、 肥利用效率和作物产量,减少根区盐分积累和地下水污染风险是这些地区水分养分优化管理的重要目标。通过田间试验研究了滴灌条件下灌溉水盐度和施氮量对棉花产量和水、 氮利用率的影响。试验设置灌溉水盐度和施氮量两个因素,灌溉水盐度（电导率,EC）设3个水平,为0.35（淡水）、 4.61（微咸水）和 8.04（咸水）dS/m,分别用SF、 SM和SH表示;施氮（N）量设4个水平,为0、 240、 360和480 kg/hm2,分别以N0、 N1、 N2和N3表示。研究结果表明,棉花干物质重、 氮素吸收量和氮肥利用率受灌溉水盐度、 施氮量及二者交互作用的影响显著。咸水灌溉处理（SH）棉花干物质重、 氮素吸收量、 产量和氮肥表观利用率均显著降低,而微咸水灌溉（SM）对棉花氮素吸收量和氮肥表观利用率影响不大,但干物质重和产量有所降低。施氮肥可显著促进棉花生长,增加干物质重、 氮素吸收量和产量,但随着灌溉水盐度的增加,其促进效应明显受到抑制。微咸水和咸水灌溉会导致水分渗漏增加、 蒸散量降低,增施氮肥则可显著降低水分渗漏、 增加蒸散量。微咸水灌溉水分利用率最高,其次是淡水灌溉,咸水灌溉最低;增施氮肥则可显著提高水分利用率。因此滴灌条件下,高盐度的咸水不宜用于灌溉。而短期的微咸水灌溉不会对棉花产量和水、 氮利用率产生严重的负面影响;同时,合理的配施氮肥也有助于促进棉花生长,提高棉花产量和水分利用率。     

萌芽前叶面喷施硒酸钠提高茶叶含硒量及品质

【目的】探究在茶树不同生育时期叶面喷施不同硒肥对夏茶产量、品质及硒含量的影响,为生产富硒茶提供技术依据。【方法】田间试验在浙江嵊州进行,供试茶树品种为‘中茶108’。试验采用二因素列区设计,主处理为硒肥种类(A因素),副处理为硒肥喷施时期(B因素)。主处理设喷施清水对照(A0)、硒酸钠(A1)、亚硒酸钠(A2)和酵母硒(A3);副处理设夏茶顶芽萌发前(5月12日,B1)与1芽1叶期(5月20日,B2)两个喷施时期。硒肥喷施浓度均为Se 50 mg/L,硒肥溶液喷施量为1.8 L/m2。当茶树蓬面1芽2叶占比达30%左右时,每个小区随机选取30 cm×30 cm茶蓬,调查蓬面新梢总数、1芽2叶数量、1芽2叶长度和百芽重。同时,取1芽2叶新梢样品,测定茶多酚、儿茶素、咖啡碱、游离氨基酸、花青素以及硒含量。【结果】与A0B1处理相比,A3B1处理茶树萌展值显著降低了0.14,但对茶树蓬面新梢总数无明显影响;A2B1处理茶树1芽2叶新梢长度和百芽重分别显著降低了1.04 cm和1.94 g。A1B2和A3B2处理茶树蓬面新梢总数分别显著降低了17.66和22.33,但不影响其萌展值;A1B2显...     

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).     

Selenium content and distribution in cow's milk supplemented with two dietary selenium sources

The effect of two sources of Se, selenized yeast (Se-Y) and sodium selenite, added to total mixed rations (TMR) fed to cows on Se milk content and distribution in milk components was studied on three farms for 6 weeks. The maximal increase in milk Se was attained with Se-Y supplemented at 0.3 microg g(-1). The effect was immediate, with an increase of 9 microg L(-1) being observed after only 5 days, and remained steady until the last sample at day 40 of Se supplementation. Se distribution in milk components was constant, 53.6, 42.6, and 9.3% in whey, casein, and fat, respectively, and was unaffected by the form of supplementation. The effect of the level of Se-Y supplementation on milk Se was studied on two farms. Increasing dietary Se-Y from 0 to 0.5 microg g(-1) elevated milk Se content from 20 to 39 microg L(-1). Se-enriched cow's milk at different levels can be produced by varying dietary Se supplementation in the form of selenized yeast.     

ALA对冬小麦叶片气体交换和水分利用效率的影响

以冬小麦“百农矮抗58”为材料,研究了在始穗期喷施不同浓度(10 、30、50 mg/L)的5-氨基乙酰丙酸（5-aminolevulinic acid, ALA)对冬小麦叶片气体交换和水分利用效率的影响。结果表明,10～50 mg/L ALA处理的叶片气孔导度高于不喷施的对照,但在开花期和乳熟期对气孔导度的促进作用大于腊熟期; 叶片净光合速率也明显高于对照。在开花期和乳熟期,ALA提高叶片的净光合速率主要是由于减少了光合的气孔限制; 而在腊熟期则主要是由于减少了光合的非气孔限制。在开花期和乳熟期,10～50 mg/L ALA处理的叶片水分利用效率与对照没有显著性差异,但在腊熟期,叶片水分利用效率较对照有显著性提高。与对照相比,10～50 mg/L ALA处理冬小麦的穗粒数、千粒重和产量显著增加,其中以30 mg/L ALA处理增产效果最大。