The influence of sunlight on the localized corrosion of UNS S31600 in natural seawater

Tests were conducted on the performance of UNS S31600 stainless steel (SS) in a natural day/night cycle vs full darkness under conditions of natural marine biofilm accumulation. In quiescent flowing seawater tests in the laboratory as well as under natural immersion in the sea, diffuse sunlight (～10% of natural) counteracted the influence of marine biofilms and produced substantial inhibition of the corrosion of SS. Thus, the probabilities (percentage attack) and propagation rates (depths of attack) in multiple crevice tests were substantially lower in the day/night cycle than in the dark. A benefit was also observed for welded SS in terms of the time to corrosion initiation and the mass loss. SS in the passive state showed broader passive regions, well-defined breakdown potentials and markedly smaller anodic and cathodic current densities under the diurnal cycle. The overall reduction in corrosion is attributed to a combination of electrochemical photoinhibition and simultaneous photoinactivation of microbially mediated metal redox reactions linked to cathodic kinetics. These data offer fresh insights into the behaviour of SS under practical seawater situations and the proposed potential use of illumination in the mitigation of biologically influenced consequences.     

The influence of sunlight on the localized corrosion of UNS S31600 in natural seawater

Tests were conducted on the performance of UNS S31600 stainless steel (SS) in a natural day/night cycle vs full darkness under conditions of natural marine biofilm accumulation. In quiescent flowing seawater tests in the laboratory as well as under natural immersion in the sea, diffuse sunlight (～10% of natural) counteracted the influence of marine biofilms and produced substantial inhibition of the corrosion of SS. Thus, the probabilities (percentage attack) and propagation rates (depths of attack) in multiple crevice tests were substantially lower in the day/night cycle than in the dark. A benefit was also observed for welded SS in terms of the time to corrosion initiation and the mass loss. SS in the passive state showed broader passive regions, well-defined breakdown potentials and markedly smaller anodic and cathodic current densities under the diurnal cycle. The overall reduction in corrosion is attributed to a combination of electrochemical photoinhibition and simultaneous photoinactivation of microbially mediated metal redox reactions linked to cathodic kinetics. These data offer fresh insights into the behaviour of SS under practical seawater situations and the proposed potential use of illumination in the mitigation of biologically influenced consequences.     

Acclimation of <Emphasis Type="Italic">Salix triandroides</Emphasis> cuttings to incomplete submergence is reduced by low light

A simulated flooding experiment was conducted to evaluate the effects of seasonal flooding on the plant Salix triandroides from the Dongting Lake wetlands in China. The morphology, photosynthetic activity, and anatomy of cuttings in three water conditions (?40 cm, water level 40 cm below soil surface; 0 cm, water level 0 cm at the soil surface; and 40 cm, water level 40 cm above soil surface) and two lights conditions (full sunlight and 10% sunlight) were measured. Plants had a higher survival ratio and biomass accumulation in full sunlight than in 10% sunlight when the water level was ?40 and 0 cm, but there was no difference between these parameters in cuttings grown under the two light conditions in the 40 cm water treatment. In full sunlight, a lower survival ratio and reduced biomass were observed with increasing water level. The same trend was also seen for survival ratio in 10% sunlight. However, there was no difference in biomass among the three water levels in 10% sunlight, except for leaf weight. Branch height, leaf number, adventitious root length, and adventitious root number were different in the three water levels and two light conditions. In water levels of ?40 and 0 cm, plants had lower chlorophyll contents in full sunlight than in 10% sunlight. In full sunlight, there was no difference in chlorophyll content between the water levels, while in 10% sunlight, lower chlorophyll content was observed in ?40 cm than in 0 cm water. Photosynthetic rate, stomatal conductance, and transpiration rate decreased, but water-use efficiency increased in reduced light at all three water levels. Additionally, plants had higher porosity in 40 cm water than in ?40 and 0 cm conditions. Based on the reduced plant growth in the 10% sunlight condition and decreased survival in the 40 cm water level, we conclude that low light significantly decreased plant acclimation to incomplete submergence and that high water levels induced dormancy in the cuttings. Therefore, the height of cuttings used for forestation or reforestation is an important consideration for mitigating the negative effects of seasonal flooding on the survival and growth of S. triandroides in Dongting Lake wetlands.     

Role of 𝛃 1-4 linked polymers in the biofilm structure of marine Pseudomonas sp. CE-2 on 304 stainless steel coupons

Pseudomonas sp CE-2 cells attach and form biofilms on 304-stainless steel (SS) coupons. A series of experiments were carried out in order to understand the role of exopolysaccharides (EPS) in the formation and maintenance of CE-2 biofilms on SS coupons. The biofilm density and EPS concentration increased over the period of incubation and the highest values for both were recorded after 72 h. Calcofluor and the lectin concanavalin A (Con A) showed a positive interaction with 72-h old biofilms, indicating the presence of β 1-4 linked polymers, and α-d-glucose and α-d-mannose in the biofilm matrix of CE-2. When the CE-2 cells were grown in the presence of calcofluor (200 μg ml^?1), biofilm formation was significantly reduced (～85%). Conversely, the lectins Con A or WGA did not influence the CE-2 biofilms on the SS coupons. Furthermore, treatment with cellulase, an enzyme specific for the degradation of β 1-4 linked polymers, removed substantial amounts of CE-2 biofilm from SS coupons. These results strongly suggest the involvement of β 1-4 linked polymers in the formation and maintenance of Pseudomonas sp. CE-2 biofilms on SS coupons.     

Cathodic behaviour of stainless steel in coastal Indian seawater: calcareous deposits overwhelm biofilms

Type-316 stainless steel (SS) was investigated as the cathode in galvanic couples in full-strength seawater from the Gulf of Mannar on the southeast coast of India. Tests were devised to examine the impact of SS cathodes on anode materials with or without the accrual of marine biofilms. Biofilmed SS cathodes significantly enhanced the rate of corrosion of nickel, causing noble shifts in the couple potentials. With mild steel and zinc as the anodes, calcareous deposits developed quite rapidly on the SS cathodes and led to a significant reduction of bacterial numbers. The calcareous deposits also caused substantial reduction of galvanic corrosion rates for mild steel, whereas there was no difference for zinc. The deposits were identified by XRD as essentially carbonates, oxides and hydroxides of calcium and magnesium. Potentiodynamic polarization performed on the actual couples after disconnection and equilibration provided reasonable interpretations of the galvanic corrosion trends. Data from this work suggest that a potential of about ?0.70 V vs. saturated calomel electrode (SCE) should provide optimum protection of SS in warmer, full-strength seawater that supports the precipitation of calcareous deposits. The criterion commonly recommended for temperate conditions of lower water temperature and estuarine waters of lower alkalinity is ?1.0 V (SCE).     

Virus Decay and Its Causes in Coastal Waters

Recent evidence suggests that viruses play an influential role within the marine microbial food web. To understand this role, it is important to determine rates and mechanisms of virus removal and degradation. We used plaque assays to examine the decay of infectivity in lab-grown viruses seeded into natural seawater. The rates of loss of infectivity of native viruses from Santa Monica Bay and of nonnative viruses from the North Sea in the coastal seawater of Santa Monica Bay were determined. Viruses were seeded into fresh seawater that had been pretreated in various ways: filtration with a 0.2-(mu)m-pore-size filter to remove organisms, heat to denature enzymes, and dissolved organic matter enrichment to reconstitute enzyme activity. Seawater samples were then incubated in full sunlight, in the dark, or under glass to allow partitioning of causative agents of virus decay. Solar radiation always resulted in increased rates of loss of virus infectivity. Virus isolates which are native to Santa Monica Bay consistently degraded more slowly in full sunlight in untreated seawater (decay ranged from 4.1 to 7.2% h(sup-1)) than nonnative marine bacteriophages which were isolated from the North Sea (decay ranged from 6.6 to 11.1% h(sup-1)). All phages demonstrated susceptibility to degradation by heat-labile substances, as heat treatment reduced the decay rates to about 0.5 to 2.0% h(sup-1) in the dark. Filtration reduced decay rates by various amounts, averaging 20%. Heat-labile, high-molecular-weight dissolved material (>30 kDa, probably enzymes) appeared responsible for about 1/5 of the maximal decay. Solar radiation was responsible for about 1/3 to 2/3 of the maximal decay of nonnative viruses and about 1/4 to 1/3 of that of the native viruses, suggesting evolutionary adaptation to local light levels. Our results suggest that sunlight is an important contributing factor to virus decay but also point to the significance of particles and dissolved substances in seawater.     

Light intensity is a limiting factor to the inland expansion of Cape ivy (<Emphasis Type="Italic">Delairea odorata</Emphasis>)

Cape ivy (Delairea odorata) is a highly invasive climbing perennial vine that is primarily distributed in coastal communities of California and Oregon, with patchy infestations in some inland riparian areas. In this study, we evaluated light as a potential environmental limitation to the spread of Cape ivy into inland regions of the western United States. Cape ivy was collected from four locations representing the north to south range. Plants were grown for 9 to 11 weeks in full sunlight and under two shade regimes (20 and 6% of full sunlight). The experiment was conducted twice at two temperature regimes. Results show some within- and among-population variability, with the southernmost San Diego County population having the highest biomass under the warmer growing conditions and the three northern populations responding most favorably in the cooler growing conditions. Despite the minor differences within and between populations, Cape ivy grew very poorly in full sunlight in both experiments. Although plants growing under 6% light grew better than those in full sunlight, they were far less robust compared to plants growing at 20% light. Our results indicate that while Cape ivy will not persist in areas with prolonged high intensity sunlight, characterized by much of the interior regions of California and Oregon, it is expected to invade and spread in areas with reduced light, including coastal regions frequently exposed to fog or cloudy conditions, or sub-canopy layers of riparian forests or woodlands. These communities should be the target areas for early detection and rapid response programs to prevent further Cape ivy invasion.     

二年生三七农艺和质量性状对环境光强的响应特征

为探究光照强度对二年生三七(Panax notoginseng)农艺性状和质量性状的影响,采用人工遮荫的方法,对三七植株的农艺性状、解剖结构、生物量和皂苷含量进行研究。结果表明,三七生物量积累以透光率为13.5%时最大;三七总皂苷含量在透光率9.2%时最高,透光率为13.5%时单株皂苷含量较大。当透光率降低,三七的叶片和茎部生物量增加;透光率增加时,三七通过增加叶片上表皮厚度、海绵组织厚度、栅栏组织厚度和叶片厚度来减少光捕获。因此,在透光率为9.2%~13.5%时对三七的生长、生物量及皂苷的积累有促进作用。     

Portraying manganese biofilms via a merger of EPR spectroscopy and cathodic polarization

Microbial biofilms on stainless steel surfaces exposed to water from a freshwater pond were dominated by manganese-oxidizing bacteria, as initially diagnosed by microscopy and elemental analysis. The application of electron paramagnetic resonance (EPR) spectroscopy revealed conspicuous sextet (six-line) patterns that intensified with immersion time, implying the gradual accumulation of Mn(II) in the biofilms. Correspondingly, cathodic polarization designated the manganese oxide (MnO_x) reduction peak in the form of a distinctive ‘nose’, which grew increasingly more negative with biofilm growth. The progressive expansion of cathodic current densities and the concurrent area-under-the-curve also allowed the quantification of microbially mediated MnO_x deposition_. Furthermore, the merger of EPR and cathodic polarization techniques yielded key insights, in tandem with Mn speciation data, into the pathways of microbial manganese transformations in biofilms, besides providing meaningful interpretations of prevailing literature. Accordingly, the natural freshwater biofilm was inferred as one supporting a complete manganese cycle encompassing multiple redox states.     

不同光照强度下花魔芋（Amorphophallus konjac）与谢君魔芋（Amorphophallus xiei）光合特性及光保护机制研究

为探讨不同耐光性植物光合特性及光保护机制,本研究以耐高光的喜阴植物花魔芋（Amorphophallus konjac K.Coch）和典型的喜阴植物谢君魔芋（Amorphophallus xiei H.Li & Z.L.Dao）为材料,测定与分析在透光率为100%、15%及2%光照条件下两种魔芋的光合能力、抗氧化酶活性及抗氧化物和光合色素组分的含量。结果表明,花魔芋最大光合速率和气孔导度随着生长环境光照强度降低而显著降低（P<0.05）,谢君魔芋在透光率为15%时最大光合速率达最大值。大部分情况下,花魔芋的超氧化物歧化酶、抗坏血酸过氧化物酶、过氧化氢酶、谷胱甘肽还原酶活性比谢君魔芋高（P<0.05）,而谢君魔芋具有较高的过氧化物酶活性（P<0.05）。总的来看,在中高光照环境下两种植物的抗氧化酶活性较高（P<0.05）。在透光率15%时,花魔芋谷胱甘肽和抗坏血酸显著比谢君魔芋高（P<0.05）。谢君魔芋的光合色素含量在透光率为15%时最高（P<0.05）;相应地,花魔芋的光合色素含量在透光率为2%时含量最低（P<0.05）;在不同光照强度下花魔芋光合色素含量基本上显著高于谢君魔芋（P<0.01）。本研究结果暗示,喜阴植物花魔芋耐受高光可能源于相对较高的光合作用能力和有效的光保护机制。     

Mechanisms of photoinhibition induced by high light in Hosta grown outdoors

Aims It has long been recognized that photoinhibition of photosynthesis is induced by high light. However, our recent studies are not consistent with this traditional view. Therefore, the objective of this study is to explore the induction of photoinhibition and its mechanisms under full sunlight outdoors.
Methods Changes of leaf morphology, gas exchange, and chlorophyll a fluorescence were measured to investigate the induction and mechanisms of photoinhibition under high light in Hosta, which is a typical shade-tolerant plant.
Important findings Hosta plants grown under full sunlight (HT) and low light (LT) developed sun- and shade-type leaf morphological characteristics, respectively. Under a full sunlight, Hosta plants had lower photosynthetic rate and chlorophyll content than under the LT; whereas, there were only slight difference in the maximum quantum yield of photosystem II (F_v/F_m) between the two treatments, suggesting that Hosta plants could grow normally under full sunlight without severe photoinhibition. After transition from the low to a high light (LHT), the photosynthetic rate and maximum quantum yield of photosystem II decreased sharply, reflecting that the LHT treatment led to irreversibly inactivation of photosystem II. Additionally, the shape of chlorophyll a fluorescence transients also changed significantly; the relative fluorescence yield of the K and J steps were reduced by 24.3% and 34.2%, respectively, indicating that the acceptor side of photosystem II was damaged more severely than the donor side. Consequently, we postulate that photoinhibition in Hosta leaves is mainly induced by the sudden enhancement of light intensity outdoors. Hosta can acclimate to high irradiance through leaf development outdoors. Our finding is of great significance in understanding the acclimation of plants to high light and cultivation of shade-tolerant plants in field.     

Sunlight and the survival of enteric bacteria in natural waters

Escherichia coli and some salmonellas were exposed in seawater and freshwater to natural sunlight, visible light of comparable intensity, and light containing a similar proportion of u.v. as natural sunlight but of a much lower intensity. Direct viable bacterial counts and culturable counts on selective and non-selective media were made at intervals. The rate of decrease in numbers of culturable bacteria was significantly faster in seawater than in freshwater when exposed to natural sunlight. No significant difference was found between the rates of decrease in numbers of culturable bacteria in seawater and those in freshwater when bacteria were exposed to light with a small u.v. component of similar intensity. The effect of salinity no loss of culturability is, therefore, more significant in the presence of u.v. radiation. Direct counts by the acridine orange direct viable count method decreased much more slowly than the culturable counts in seawater but comparably with culturable counts in freshwater in natural sunlight. Direct viable counts and culturable counts decreased at a similar rate in seawater and in freshwater in visible light. This may signify the evolution of enteric bacteria towards a viable but non-culturable form in seawater when exposed to natural sunlight. The presence of humic acids significantly reduced loss of culturability but only in low salinity conditions. Salinity appears to be an important factor influencing culturability in bacteria exposed to sunlight.     

Growth and photosynthetic responses of the federally endangered shrub, Lindera melissifolia (Lauraceae), to varied light environments

Photosynthetic, morphological, and growth responses to light environment can be useful measurements to determine favorable habitat conditions for the conservation of endangered species. For Lindera melissifolia (Walt.) Blume, we compared morphological and photosynthetic responses under natural and controlled light regimes, and growth under three light treatments: 100%, 42%, and 19% full sunlight. Typical sun-shade morphological responses to decreasing light levels included decreased stomatal density, increased specific leaf area, and increased leaf area ratio. Photosynthetic capacity (3-6 μmol CO(2) · m(-2) · s(-1)) was consistent with other shade-tolerant species. Light-saturated rates of photosynthesis of experimental plants increased with increasing light up to 42% sunlight, but declined at 100% sunlight. The 100% light treatment also resulted in lower plant biomass, primarily from a reduction in root biomass. Results indicate that canopy conditions at levels below 40% sunlight are optimal for plant growth and should be considered in management and reintroduction efforts for this species.     

长期弱光对苦草幼苗生长发育的影响

用遮光法研究弱光(5%、1%、0.5%、0.1%全光照)对苦草幼苗生长发育的影响,统计了苦草的生物学参数,测定了叶片叶绿素荧光参数。结果表明:1)0.1%组无新株萌发,随着实验时间的延长其余组新株萌发逐渐被抑制。2)随着实验时间增加和光照强度降低,老株叶片形成受到的抑制程度呈增大趋势;前20d时新株叶片形成未被抑制,但随着实验时间延长显著被抑制。3)老株、新株的叶宽均受到显著抑制。4)老株叶片的伸长显著被抑制,且随着光强降低叶片伸长的幅度呈显著降低趋势;前20天时新株叶长被促进,随着实验时间延长叶片伸长显著被抑制。5)随实验天数的增加,老株叶片光化学最大量子产量(Fv/Fm)呈显著降低趋势,第80天时相对电子传递速率(rETR)和非光化学淬灭(NPQ)显著降低。6)新、老植株根、茎、叶的鲜重均显著低于对照,且随着光照强度降低老株的茎重/株重和根重/株重呈增加趋势,而叶重/株重呈显著的降低趋势。第80天时苦草植株仍具有一定的光合能力,地下茎的生物量比例较高,因此,≤1%全光照下苦草植株具有较强的耐受能力。     

Sunlight and the survival of enteric bacteria in natural waters

Escherichia coli and some salmonellas were exposed in seawater and freshwater to natural sunlight, visible light of comparable intensity, and light containing a similar proportion of u.v. as natural sunlight but of a much lower intensity. Direct viable bacterial counts and culturable counts on selective and non-selective media were made at intervals. The rate of decrease in numbers of culturable bacteria was significantly faster in seawater than in freshwater when exposed to natural sunlight. No significant difference was found between the rates of decrease in numbers of culturable bacteria in seawater and those in freshwater when bacteria were exposed to light with a small u.v. component of similar intensity. The effect of salinity on loss of culturability is, therefore, more significant in the presence of u.v. radiation. Direct counts by the acridine orange direct viable count method decreased much more slowly than the culturable counts in seawater but comparably with culturable counts in freshwater in natural sunlight. Direct viable counts and culturable counts decreased at a similar rate in seawater and in freshwater in visible light. This may signify the evolution of enteric bacteria towards a viable but non-culturable form in seawater when exposed to natural sunlight. The presence of humic acids significantly reduced loss of culturability but only in low salinity conditions. Salinity appears to be an important factor influencing culturability in bacteria exposed to sunlight.     

Demonstration of biofilm removal from type 304 stainless steel using pulsed-waveform electropolishing

Abstract

This article describes an electrochemical method to remove bacterial biofilm from a stainless steel (SS) surface using a potential pulse/reverse pulse technique. This technique employs a periodic waveform that consists of anodic and cathodic pulses. The pulses can effectively strip a thin layer of metal off the SS surface, along with the adherent biofilm, in a saline solution. Not only can the pulses effectively remove biofilm from the SS surface, but they also regenerate the original mirror-like shiny surface. The importance of this electrochemical biofilm removal method is its wide applicability for any types of biofilms. That is, instead of directly removing the biofilm, it removes a very thin layer of the metal under the biofilm. Thus, the removal process is independent to the nature of the biofilms. Furthermore, this electrochemical biofilm removal method is rapid (less than 30?s of potential pulse time) and does not require hazardous chemicals.     

遮荫和全光下生长的棉花光合作用和叶绿素荧光特征

 遮荫条件下（遮荫下光强相当于自然光强的40％左右）棉花(Gossypium hirsutum)叶片光合速率明显降低,仅为自然光强下生长叶片的30%～40％,叶片中RuBP羧化酶活性降低,而表观量子效率(AQY)较高。不同光照条件下生长的棉花叶片对短时间持续光强的光合诱导过程有明显的差异,由弱光转到强光下,自然光强下生长的叶片的Pn、Gs、ΦPSⅡ及非光化学猝灭系数(NPQ)都能在较短的时间内达到最大值,而遮荫叶片需要的时间较长;遮荫下生长的棉花叶片的实际光化学效率,随光强的增加下降幅度较大,而自然光照下生长的叶片下降幅度较小;自然光照下生长的叶片的NPQ随光强的升高达到较高水平,而遮荫叶片在较低的光强下即达到最大值,此时NPQ较低,遮荫叶片依赖于叶黄素循环的能量耗散水平较低。遮荫叶片较低的光合速率以及过剩光能耗散能力是其转入自然强光后光抑制严重的主要原因。     

无机碳供应与光照条件对坛紫菜光合功能的影响

海藻群体密度过大常引起海水中CO_2供应和光照强度降低,为探讨这两种环境条件对坛紫菜光合作用的影响,在4种条件下培养坛紫菜,即390μL·L^-1(正常空气)+全日光、20μL·L^-1(低CO_2供应)+全日光、390μL·L^-1+低日光(光照强度为全日光的20%)、20μL·L^-1+低日光,测定藻体的碳酸酐酶活性、光合速率,以及不同温度下开放状态光系统Ⅱ最大量子产量(F_ v'/F _m').结果表明:低CO_2供应和低日光下生长的坛紫菜具有较高的碳酸酐酶活性,并且低日光能够提高海藻最大碳饱和光合放氧速率(V _max).在低日光下,生长在低CO_2海水中的坛紫菜V _max显著低于正常CO_2海水中生长的海藻V _max;在全日光下,低CO_2下生长的海藻V _max却高于正常CO_2下生长的海藻V _max.生长在低CO_2和低日光条件下的海藻在低温(10℃)和高温(30℃)下,藻体的F_ v'/F _m'变化不明显;而生长在390μL·L^-1+全日光环境中的海藻在高温环境下200 min后,藻体的F_ v'/F _m'相比40 min时的F_ v'/F _m'降低76.4%.低CO_2和低日光提高坛紫菜光合无机碳利用能力以及适应短期温度变化的能力,而低CO_2对海藻光合速率的影响与海藻所处光照环境有关.     

Solar UV radiation does not inactivate marine birnavirus in coastal seawater

We examined the inactivation kinetics of marine birnavirus (MABV) in a coastal sea, in seawater samples collected from 50 cm depth. MABV was added to both natural and autoclaved seawater at a concentration of 6 x 10(6.43) TCID50 (50% tissue culture infectious dose) ml(-1), put in dialysis tubes and incubated at the original depth. The inactivation of MABV by solar UV radiation was examined using light and dark tubes. The infectivity titer of MABV was measured by the TCID50 method using CHSE-214 cells. Virus infectivity in natural seawater decreased quickly and was below the detection limit by 270 min in both light and dark conditions; however, virus infectivity was maintained in the autoclaved seawater until 420 min. These results suggest that the loss of virus infectivity is not caused by sunlight UV radiation.     

Role of beta 1-4 linked polymers in the biofilm structure of marine Pseudomonas sp. CE-2 on 304 stainless steel coupons

Pseudomonas sp CE-2 cells attach and form biofilms on 304-stainless steel (SS) coupons. A series of experiments were carried out in order to understand the role of exopolysaccharides (EPS) in the formation and maintenance of CE-2 biofilms on SS coupons. The biofilm density and EPS concentration increased over the period of incubation and the highest values for both were recorded after 72 h. Calcofluor and the lectin concanavalin A (Con A) showed a positive interaction with 72-h old biofilms, indicating the presence of beta 1-4 linked polymers, and alpha-d-glucose and alpha-d-mannose in the biofilm matrix of CE-2. When the CE-2 cells were grown in the presence of calcofluor (200 microg ml(-1)), biofilm formation was significantly reduced (approximately 85%). Conversely, the lectins Con A or WGA did not influence the CE-2 biofilms on the SS coupons. Furthermore, treatment with cellulase, an enzyme specific for the degradation of beta 1-4 linked polymers, removed substantial amounts of CE-2 biofilm from SS coupons. These results strongly suggest the involvement of beta 1-4 linked polymers in the formation and maintenance of Pseudomonas sp. CE-2 biofilms on SS coupons.