SEA ICE MICROBIAL COMMUNITIES. V. THE VERTICAL ZONATION OF DIATOMS IN AN ANTARCTIC FAST ICE COMMUNITY1

A distinct vertical zonation was observed among diatoms in a bottom congelation ice community at McMurdo Sound, Antarctica during the 1981 spring bloom. The bottom 20 cm of ice collected in December from four stations with variable snow cover was subdivided into 5 cm sections for analysis of algal distribution. Algal abundance was inversely related to the depth of snow cover, and generally decreased with increasing distance above the ice-water interface. Most diatoms, including the dominant species Nitzschia stellata Manguin, Amphiprora kufferathii Manguin and Fragilaria islandica var. adeliae Manguin showed peak abundance in the bottom 10 cm of the ice, where the proportion of living to empty cells was also highest. Two species, however, an Auricula Castracane sp. and Navicula glaciei van Heurck, reached highest concentrations at depths 10–20 cm above the ice-water interface. We considered two factors as contributing to the observed vertical zonation: (1) successive blooms at the ice-water interface become spatially stratified within the ice by further accretion below; (2) a differential growth of species occurs along physicochemical gradients within the ice column. A comparison of early versus late season profiles suggests the latter mechanism may prevail once ice accretion has ceased.     

我国冰核活性细菌的优势种类调查与研究

１９８６￣１９９４年,从国内１７个省、市、自治区的６８种植物上分离到了２５０株冰核活性细菌,经鉴定分别属于３个属的１７个种或致病变种。其中出现最多的是菠萝欧文氏菌,共１３３株,占总数的５３．２％,其次是丁香假单胞菌群,共７０株,占２８％,其它种类的冰核活性细菌共４７株,仅占１８．８％。因此,我国冰核活性细菌的优势菌种是Ｅ．ａｎａｎａｓ,其次是Ｐ．ｓｙｒｉｎｇａｅ ｐｖｓ。在低纬度的南方地区中Ｅ．ａ     

冰核细菌(Erwinia ananas 110)冰核基因克隆和序列分析

从作者自行分离的冰核细菌（Erwinia ananas110)中克隆到我国第1个细菌冰核基因,并完成其序列测定和分析,所克隆基因编码区全长3921bp,编码1306aa,氨基酸序列明显分为3个区即N-端（161aa),C-端（41aa)的单一序列区和中部的高度重复序列R区（1104aa)。以16氨基酸为重复单元的R区占整个编码序列的84.5%。序列分析表明我们所克隆的基因为一个新冰核基因,将其命名为iceA。该基因已在GenBank上登录,登录号为：AF387802。     

云南植物上冰核活性细菌鉴定

从云南植物上分离到９２株冰核活性细菌,并进行了鉴定。其中菠萝欧文氏菌６１株,占６６．３％;草生欧文氏菌２株,占２．２％;丁香假单胞菌２１株,占２２．８％;黄瓜角斑病菌２株,占２．２％;菜豆荚斑假单胞菌６株,占６．５％。云南省冰核活性细菌的优势种类是菠萝欧文氏菌,其次是丁香假单胞菌类。     

GROWTH RESPONSES TO SALINITY VARIATION IN FOUR ARCTIC ICE DIATOMS1,2

During spring, extensive blooms of microalgae grow on the underside of arctic sea ice. The brownish, algal layer penetrates ca. 2 cm into the bottom surface of the ice and the algae are potentially exposed to very high salinities. Four diatom species, Melosira juergensii Ag., Porosira glacialis (Grun.) Jørg., Navicula transitans var. derasa (Grun.) Cleve, and Coscinodiscus lacustris Grun., isolated from, sea ice samples taken from the Beaufort and Chukchi seas near Barrow, Alaska, were grown at 11 salinities ranging from 5 to 70‰ at 5 C under constant illumination. All of the species grew at 5‰ except N. transitans whose lower growth limit was 15‰. Growth was high over a broad range of salinities, but none of the species grew at salinities above 60‰. These diatom species appear to be well suited to tolerate the salinities in the brine pockets near the bottom of annual arctic sea ice where they are found. High brine-cell salinity, however, may limit the upward, penetration of ice algae into the bottom of sea ice.     

大麦黄矮病毒的冰核活性与作物霜冻的关系

对大麦黄矮病毒(Barley Yellow Dwarf Virus,BYDV)的冰核活性,以及它的侵染与作物霜冻的关系进行了研究.利用人工摸拟霜箱,测试了接种BYDV的小麦等作物植株的霜冻温度,并用ELISA法检测了供试植株的病毒含量.结果表明,接种样品与对照相比,感病品种的霜冻温度升高1—2℃以上,抗病品种的霜冻温度变化不大.离体叶片测定结果表明,“中7902”的叶片中,病毒含量与霜冻温度成正相关,说明BYDV可以起到异源冰核(heterogeneous ice nuclei)的作用,它的侵染能影响作物的抗霜冻能力.用“Vali小液滴冻结法”检测提纯的BYDV,证明BYDV具冰核活性,从而首次发现病毒也能起到生物冰核的作用.     

EFFECTS OF LIGHT AND WAVE DISTURBANCE ON VERTICAL ZONATION OF ATTACHED MICROALGAGE IN A LARGE RESERVOIR1

Experimental field manipulations of artificial substrata were used to examine the mechanisms controlling attached algal zonation down the face of the dam in Lake McConaughy, a large reservoir in western Nabraska. Sets of clay tiles were incubated in the upper (2.5 m depth) and lower (8 m depth) growth zones for two weeks. Five sets tiles were then switched from the upper to the lower growth zone and vice versa. Five additional sets of tiles were switched to the lower zone and artificially disturbed. Diatom cell densities increased rapidly in both the zones; however, wind-induced turbulence caused dramatic declines (up to 61%) in densities in the upper zone. Consequently, cell densities in the upper and lower growth zones were not significantly different after four weeks, despite the 17–30% higher light levels in the upper zone. Based on cell densities and relative abundances on clay tiles and naturally occurring rocks, 26 of the 32 most common diatom taxa had a significant upper (10) or lower (16) zone preference. Of these, 15 taxa exhibited a consistent response to one or both switching manipulations, confirming a growth zone preference, and two showed a clear preference for disturbed substrata. Diatom growth form appeared to play a major role in determining the vertical zonation of attached communities, since actively motile taxa exhibited a lower zone preference and stalked forms occurred primarily in the upper zone. The present study indicates that light attenuation and wave disturbance are primary mechanisms that control the vertical zonation of freshwater epilithic algae.     

Farinose fiavonoids are associated with high freezing tolerance in fairy primrose (Primula malacoides) plants

The deposition of surface(farinose)fiavonoids on aerial parts of some Primula species is a well-documented but poorly understood phenomenon.Here,we show thatfiavonoid deposition on the leaves and winter buds may contribute strongly to preventing freezing damage in these plants.The ice nucleation temperature of fairy primrose(Primula malacoides)leaves covered with naturalfiavone was approximately 6°C lower compared to those that had theirfiavone artificially removed.Additionally,farinosefiavonoids on the leaves reduced subsequent electrolyte leakage(EL)from the cells exposed to freezing temperatures.Interestingly,exogenous application offiavone at4 mg/g fresh weight to P.malacoides leaves,which had the originalfiavone mechanically removed,restored freezing tolerance,and diminished EL from the cells to pretreatment values.Our results suggest that farinosefiavonoids may function as mediators of freezing tolerance in P.malacoides,and exogenous application offiavone could be used to reduce freezing damage during sudden but predictable frost events in other plant species.     

Farinose freezing （Primula flavonoids,are associated with high tolerance in fairy primrose malacoides） plants

The deposition of surface （farinose） flavonoids on aerial parts of some Primula species is a well-documented but poorly understood phenomenon. Here, we show that flavonoid deposition on the leaves and winter buds may contribute strongly to preventing freezing damage in these plants. The ice nucleation temperature of fairy primrose （Primula malacoides） leaves covered with natural flavone was approximately 6~C lower compared to those that had their flavone artificially removed. Additionally, farinose flavonoids on the leaves reduced subse- quent electrolyte leakage （EL） from the cells exposed to freezing temperatures. Interestingly, exogenous application of flavone at 4 mg/g fresh weight to P. malacoides leaves, which had the original flavone mechanically removed, restored freezing tolerance, and diminished EL from the cells to pretreatment values. Our results suggest that farinose flavonoids may function as mediators of freezing tolerance in P. malacoides, and exogenous application of flavone could be used to reduce freezing damage during sudden but predictable frost events in other plant species.     

Deep supercooling enabled by surface impregnation with lipophilic substances explains the survival of overwintering buds at extreme freezing

The frost survival mechanism of vegetative buds of angiosperms was suggested to be extracellular freezing causing dehydration, elevated osmotic potential to prevent freezing. However, extreme dehydration would be needed to avoid freezing at the temperatures down to ?45°C encountered by many trees. Buds of Alnus alnobetula, in common with other frost hardy angiosperms, excrete a lipophilic substance, whose functional role remains unclear. Freezing of buds was studied by infrared thermography, psychrometry, and cryomicroscopy. Buds of A. alnobetula did not survive by extracellular ice tolerance but by deep supercooling, down to ?45°C. An internal ice barrier prevented ice penetration from the frozen stem into the bud. Cryomicroscopy revealed a new freezing mechanism. Until now, supercooled buds lost water towards ice masses that form in the subtending stem and/or bud scales. In A. alnobetula, ice forms harmlessly inside the bud between the supercooled leaves. This would immediately trigger intracellular freezing and kill the supercooled bud in other species. In A. alnobetula, lipophilic substances (triterpenoids and flavonoid aglycones) impregnate the surface of bud leaves. These prevent extrinsic ice nucleation so allowing supercooling. This suggests a means to protect forestry and agricultural crops from extrinsic ice nucleation allowing transient supercooling during night frosts.     

Complex bud architecture and cell‐specific chemical patterns enable supercooling of Picea abies bud primordia

Bud primordia of Picea abies, despite a frozen shoot, stay ice free down to ?50 °C by a mechanism termed supercooling whose biophysical and biochemical requirements are poorly understood. Bud architecture was assessed by 3D—reconstruction, supercooling and freezing patterns by infrared video thermography, freeze dehydration and extraorgan freezing by water potential measurements, and cell‐specific chemical patterns by Raman microscopy and mass spectrometry imaging. A bowl‐like ice barrier tissue insulates primordia from entrance by intrinsic ice. Water repellent and densely packed bud scales prevent extrinsic ice penetration. At ?18 °C, break‐down of supercooling was triggered by intrinsic ice nucleators whereas the ice barrier remained active. Temperature‐dependent freeze dehydration (?0.1 MPa K^?1) caused accumulation of extraorgan ice masses that by rupture of the shoot, pith tissue are accommodated in large voids. The barrier tissue has exceptionally pectin‐rich cell walls and intercellular spaces, and the cell lumina were lined or filled with proteins, especially near the primordium. Primordial cells close to the barrier accumulate di, tri and tetrasaccharides. Bud architecture efficiently prevents ice penetration, but ice nucleators become active inside the primordium below a temperature threshold. Biochemical patterns indicate a complex cellular interplay enabling supercooling and the necessity for cell‐specific biochemical analysis.     

Mesophyll freezing and effects of freeze dehydration visualized by simultaneous measurement of IDTA and differential imaging chlorophyll fluorescence

Infrared differential thermal analysis (IDTA) and differential imaging chlorophyll fluorescence (DIF) were employed simultaneously to study the two-dimensional pattern of ice propagation in leaves and mesophyll freeze dehydration as detected by a significant increase of basic chlorophyll fluorescence (F(0)). IDTA and DIF technique gave different insights into the freezing process of leaves that was highly species-specific. IDTA clearly visualized the freezing process consisting of an initial fast spread of ice throughout the vascular system followed by mesophyll freezing. While mesophyll freezing was homogeneously in Poa alpina, Rhododendron ferrugineum and Senecio incanus as determined by IDTA, DIF showed a distinct pattern only in S. incanus, with the leaf tips being affected earlier. In Cinnamomum camphora, a mottled freezing pattern of small mesophyll compartments was observed by both methods. In IDTA images, a random pattern predominated, while in DIF images, compartments closer to lower order veins were affected earlier. The increase of F(0) following mesophyll freezing started after a species-specific time lag of up to 26 min. The start of the F(0) increase and its slope were significantly enhanced at lower temperatures, which suggest a higher strain on mesophyll protoplasts when freezing occurs at lower temperatures.     

OBSERVATIONS ON WATER LOSS OF SEAWEEDS IN RELATION TO MICROCLIMATE ON A TROPICAL SHORE (GHANA)1

During a 24-hr period (12-13 April, 1966) continuous records of temperature, relative humidity, wind speed, wind direction, salt spray, and evaporative power of the air were made at Nungua beach, Ghana. Water loss from emersed plants of Sargassum vulgare, Bryocladia thyrsigera, and Ulva fasciata was measured during the same period. The daily march of desiccation in these seaweeds follows the curve for evaporative power of the air. At night the 3 species lose relatively little water and very nearly the same percentage in each case. During the day Ulva is most resistant to water loss, Bryocladia next, and Sargassum is least resistant. This behavior is correlated with the upper limits of the zones they occupy on the shore.     

ZONATION OF DEEP WATER BENTHIC ALGAE IN THE GULF OF MAINE1

Algal community structure is described for a deep-water rock pinnacle in the Gulf of Maine. Three depth zones of algal dominance were apparent consisting of 1) leathery macrophytes (to 40 m), 2) foliose red algae (to 50 m) and 3) crustose algae (fleshy crusts to 55 m and coralline crusts to 63 m). Microscopic filamentous and erect calcareous algae were also present but inconspicuous. Upright macroscopic filamentous and thin sheet-like forms were not observed on the pinnacle. Sea anemones (Metridium senile) dominated some vertical faces and abrupt prominences in the shallowest regions of the pinnacle (to 24 m) and locally appeared to set the upper vertical limits of kelp and possibly foliose reds. Laminaria sp. formed an open park-like canopy from 24 to 30 m whereas Agarum cribrosum, the deepest kelp, grew as isolated individuals to 40 m. Peyssonnelia sp. and Leptophytum laeve were the deepest occurring fleshy (to 55 m) and calcareous crusts (to 63 m), respectively. The occurrence of these algae at record depths for the Gulf of Maine and for cold water marine environments may be the result of an absence of large herbivores and the high productivity potential of the benthos in these relatively clear waters. By compiling data on depth distribution patterns world-wide, it is evident that the three zone structure of algal morphologies observed in the Gulf of Maine is a global phenomenon.     

几种海藻和赤潮藻的DCMU增益荧光比率及其与增殖速率的关系

本文研究了红藻梅膜(Halymenia sinensis),绿藻孔石莼(Ulva pertusa),褐藻裙带(Underia pinnatifida)及蓝藻钝顶螺旋藻(Spir~dulina platensis)的DCMU增益荧光比率(F_D/F_N)。其中海膜的比率最高(3.9),石莼及螺旋藻次之(2.5和2.8),裙带(采自夏季)的比率最低(1.7)。脱水及热处理下和藻体老化时,F)D/F_N值显著下降。在实验室条件下分批培养的两种赤潮藻海洋原甲藻(Prorocentrum micans)和微小角毛藻(Chaetocersa minutissmus),其增殖过程中最大增益荧光比率较最大增殖速率出现早,这一结果为赤潮的预报提供了依据。     

ALGAL ASSEMBLAGES IN ANTARCTIC PACK ICE AND IN ICE-EDGE PLANKTON1

A significant amount of the primary production in the Southern Ocean and other ice-covered oceans takes place in localized ice edge plankton blooms. The dynamics of these blooms appear to be closely related to seasonal melting of sea ice. Algal cells released from the ice are a possible source of ice edge planktonic assemblages, but evidence for this “seeding” has been equivocal. We compared algal assemblages in ice and water in the Weddell Sea during the austral spring of 1983 at a receding ice edge with a well-developed ice edge bloom. The high degree of similarity between ice and water column assemblages, the spatial and temporal patterns in the distribution and abundances of species, and preliminary evidence for the viability and growth of ice-associated species provide evidence for seeding from sea ice of some species in Antarctica.     

RATES OF PHOTOADAPTATION IN SEA ICE DIATOMS FROM MCMURDO SOUND,ANTARCTICA1

Sea ice microalgae are released from their relatively stable light environment to the water column seasonally, and any subsequent growth in a vertically mixed water column may depend, in part, on their photoadaptation rates. In this study we followed the time course of photoadaptation in natural sea ice algal communities from bottom ice and surface ice by measuring their photophysiological response to an artificial shift in the ambient irradiance field. Microalgae from under-ice habitats, were incubated under full sunlight (LL-HL) and microalgae from surface ice habitats were incubated under artificial light to mimic under-ice irradiance (HL-LL). During 3- to 4-day time course studies, opposite shifts in chlorophyll: carbon, α, P^B_m, and I_k were observed, depending on the direction of the irradiance change. First-order rate constants (k) ranged from 0.0067 to 0.29 h^?1 for photosynthetic parameters, although P^B_m did not always show a clear change over time. Rates of photoadaptation for ice algae are comparable to k values reported for temperate phytoplankton, suggesting that sea ice algae may be equally capable of adapting to the light conditions experienced in a vertically mixed water column. This study presents the first evidence that sea ice microalgae are physiologically capable of adapting to a planktonic life and thus could serve as a seed population for polar marine phytoplankton blooms.     

CARBON/NUTRIENT BALANCE IN RELATION TO BIOMASS PRODUCTION AND HALOGENATED COMPOUND CONTENT IN THE RED ALGA ASPARAGOPSIS TAXIFORMIS (BONNEMAISONIACEAE)1

We tested how the availability of carbon and nitrogen determines both the production of Asparagopsis taxiformis (Delile) V. Trevis. and content of the two major halocarbons, bromoform and dibromoacetic acid. The halogenated secondary metabolites of Asparagopsis species are particularly interesting from an applied perspective due to their remarkable antimicrobial activity. Terrestrial ecologists named the relationship between resources and secondary metabolites as the carbon (C)/nutrient balance (CNB) hypothesis. This relationship was tested both in the laboratory, with a factorial analysis using different concentrations of total ammonia (TAN) and dissolved inorganic carbon (DIC), and in an integrated aquaculture system where TAN and DIC fluxes of fish effluent were manipulated. The total C/N content of A. taxiformis biomass cultivated in laboratory was highly significantly linearly related to the content of both halocarbons, as predicted by the CNB hypothesis. A. taxiformis cultivated at low levels of carbon and high levels of nitrogen (N) (lowest C/N ratio) had the lowest content in both halogenated metabolites. Increased availability of CO₂ in the medium resulted in a general higher halocarbon content in the biomass, even though the effect was only statistically significant for bromoform at high levels of N. The farm experiments supported the results of the laboratory experiments. DIC fluxes had the highest effect on the production of both bromoform and biomass, as shown by multiple regression analysis. In A. taxiformis integrated aquaculture, C, rather than N, is the most important factor affecting the production of biomass and of valuable halocarbon secondary metabolites.     

PHOTOADAPTATION,GROWTH AND PRODUCTION OF BOTTOM ICE ALGAE IN THE ANTARCTIC1

Biomass, chemical composition, growth rates and the photosynthetic response of natural populations of sea ice algae in McMurdo Sound, Antarctica were followed over most of the spring bloom to examine temporal variability under a relatively constant incident irradiance (ca. 1500–1700 μE · m^-2· s^-1 at solar noon). Collection were restricted to bottom 20 cm of the ice sheet in an area with little or no snow (0–5 cm). At low temperature and irradiance these algae normally exhibited low assimilation numbers (ca. 0.1–0.4 mg C · mg Chl^-1· h^-1). Average growth rates (0.02–0.45 d^-1), based on changes in standing stocks, were also low. Biomass, biochemical composition, growth rates, assimilation numbers and photosynthetic efficiencies (mg C · mg Chl^-1· h^-1 (μE · m^-2· s^-1)^-1) displayed large fluctuations over periods of several days during the growth season. On the other hand, I_k which is an index of photoadaptation, and I_m, the optimal irradiance for photosynthesis, were relatively constant with less than twofold variation throughout our study. Substantial nutrient fluxes (3.3–8.0 mmol Si or N · m^-2· d^-1) were necessary to satisfy the minimum nutrient demand for the observed biomass levels and population growth rates; over the 41 days of our study, integrated nutrient demand represented 69–150 mmol N or Si · m^-2, Only 5–25% of this total demand could be met by all of the nutrients in the ice sheet, if they were readily available. However, adequate amounts were present in the top few meters of the water column. With small nutrient gradients in surface waters below the sea ice, vertical eddy diffusivities on the order of 3.8–9.3 cm²· s^- should supply sufficient nutrients to meet algal demand.     

Ice Nucleation Activity in the Freezing-Tolerant Antarctic NematodePanagrolaimus davidi

Ice nucleation spectrometry was used to look for the presence of ice nucleating agents (INAs), and their inhibitors, in cultures ofPanagrolaimus davidi, an Antarctic nematode which survives intracellular freezing. INA activity was absent in both nematode suspensions and homogenates. The nematodes produce a substance which inhibits the nucleation activity of organic INAs but not of an inorganic INA (AgI). The nucleation inhibitor is both released from the nematode by homogenization and excreted by them into the medium, but the former was more effective at inhibiting nucleation. The inhibitory activity was destroyed by heating. A thermal hysteresis protein, or a similar ice-active substance, may be responsible for the nucleation inhibition.