Survival and reproduction in some algae under stress conditions

Pithophora oedogonia and Cladophora glomerata survived lowest 60 and 58%, respectively, in June when the pond diurnal water temperature (PDWT) increased to a maximum of 28 degrees C. The lowering of PDWT only by 1 degrees C in July improved survivability of both algae to their almost maximum level of 100 and 96%, respectively. Further lowering of PDWT to 17-22 degrees C in November initiated akinete formation in P. oedogonia. The process of akinete initiation, maturation and germination continued till April when PDWT increased to 20-24 degrees C, but not beyond that in May when PDWT was 21-26 degrees C. By this time, probably all akinetes have germinated in situ, and the alga was entirely vegetative. P. oedogonia population is not synchronous in nature, since during the 5-6-month reproductive season, some filaments were in active vegetative stage, some had akinete initiation, some had completed akinete formation, and some had akinetes germinating. C. glomerata grew dense vegetative in November and initiated (zoo)sporangial primordia formation (to some extent) in February (when PDWT was lowest, viz. 10-14 degrees C) till April. Meanwhile, no (zoo)-sporangial primordia either produced any zoospore or germinated into a germ tube; and all released their cytoplasmic content and died (along with some vegetative cells) with an increase in PDWT to 21-26 degrees C in May. Vaucheria geminata vegetative patches appeared on the soil surface, 2nd week of January by lowering of atmospheric diurnal temperature (ADT) to 9-16 degrees C in the 1st week. The alga started sexual reproduction by the 2nd week of March (when ADT increased to 20-23 degrees C) and completed the process of reproduction by the 1st week of April (when ADT increased to 24-26 degrees C) and died thereafter. P. oedogonia, C. glomerata and V. geminata survived better and longer in submerged conditions than air-exposed (which was true for P. oedogonia and C. glomerata aquatic habitat and also indicated that the soil alga V. geminata could survive to some extent if submerged in rain water). P. oedogonia formed akinetes and C. glomerata (zoo)sporangial primordia only in submerged condition and not when air-exposed on moist soil surface. V. geminata did not complete the life cycle both under submerged and air-exposed conditions. Vegetative survival in P. oedogonia, C. glomerata, V. geminata, Aphanothece pallida, Gloeocapsa atrata, Scytonema millei, Myxosarcina burmensis, Phormidium bohneri, Oscillatoria animalis, O. subbrevis, Lyngbya birgei, L. major, Microcoleus chthonoplastes and Rhizoclonium crassipellitum, reproduction in P. oedogonia, C. glomerata and V. geminata, cell division in A. pallida and G. atrata, heterocyst and false branch formation in S. millei, all, were adversely affected at approximately 28.5 degrees C for t12 h at light intensity of approximately 160 micromol m(-2) s(-1); high intensity does not ameliorate high temperature damage to any algae. The presence of liquid water, than its absence, outside the different algae moderated the severity of heat to some extent but not when the heat was severe.     

Vegetative survival of some wall and soil blue-green algae under stress conditions

Lyngbya major (a wall alga), survived throughout year, maximally to >80 % at atmospheric temperature (AT) of 17-36 degrees C and relative humidity (RH) 60-100 % in rainy and spring seasons, but the survival was 43-64 % in winter when AT decreased to 5 degrees C and RH was 65-98 %, and 15-23 % in summer when AT reached 48 degrees C and RH was 23-60 %. All soil algae (Lyngbya birgei, Aphanothece pallida, Gloeocapsa atrata, Oscillatoria subbrevis, O. animalis) survived >90 % in rainy season when soil moisture content (SMC) was 89-100 %. Lowering of SMC to a minimum of 55 % in spring and 39 % in winter led L. birgei, O. subbrevis and O. animalis to survive from 75, 66, and 65 %, respectively, in spring and 12, 14, and 20 % in winter, and A. pallida and G. atrata not at all in both seasons. All soil algae did not survive in summer when SMC was 12-30 %. Myxosarcina burmensis survived only in rainy and spring seasons when pond water temperature (PWT) was 19-25 degrees C and 18-26 degrees C, respectively, and not in winter and summer when PWT was 2-14 degrees C and 25-36 degrees C, respectively. L. major and A. pallida survived almost equally well under both submerged and air-exposed conditions for 15 d but less if submerged for more time than air-exposed on moist soil surface, while L. birgei, G. atrata, O. subbrevis, and O. animalis survived submergence in liquid medium better and longer than air-exposure on moist soil surface. Pond alga M. burmensis survived submergence better than air-exposure, true to its aquatic habitat. All algae survived less and died without forming any resistant cells when exposed to physical and physiological water stress (imposed by growing them on highly agarized media or in salinized liquid media), light stress (at 0, 2 and 10 mumol m(-2) s(-1) light intensity) or following UV shock (0.96-3.84 kJ/m(2)). A. pallida and G. atrata cells did not divide on 8 % agarized solid media, in >/=0.3 mol/L salinized liquid media, and in darkness. The presence of sheath over L. major and L. birgei filament cells and mucilage cover over A. pallida and G. atrata cells protect them against physical desiccation to some extent but not against UV shock.     

Survival and reproduction of some blue-green and green algae as affected by sewage water,fertilizer factory effluent,brassica oil,phenol, toluene and benzene

Fourteen blue-green and green algae survived for widely different time periods ranging between 22–102 d in control culture medium. Irrespective of their long or short survival period in control cultures, their pro- or eukaryotic nature, their different morphological types or natural habitats, they all survived for a short time period ranging between 3–8 d in sewage water, 5–10 d in fertilizer factory effluent, ¼-2 d in brassica oil, ½-2 d in phenol, 1–3 d in toluene, and 1–4 d in benzene (showing the relative toxicity of different chemicals to different algae, and the antialgal nature of brassica oil). Dilution decreased the toxicity of these agents very little, indicating that they all were very toxic to algae. None of the agent induced the formation of any reproductive or dormant cells. Sewage water, fertilizer factory effluent, brassica oil and/or benzene favored the formation of necridia cells in Phormidium bohneri, P. foveolarum, Microcoleus chthonoplastes, Lyngbya birgei, and L. major filaments. Scenedesmus quadricauda shed off all spines earlier, Hormidium flaccidum fragmented less or not at all, Scytonema millei formed no false branch and heterocyst, Aphanothece pallida and Gloeocapsa atrata cells did not divide, Cosmarium granatum cells did not form any zygospore and Oedogonium sp. not any oogonia-like cells under all or most of treatments with 25–100 % sewage water, 1–100 % fertilizer factory effluent, 1–100 % brassica oil, 25–100 % phenol, toluene and benzene.     

Biomass and oxygen dynamics of the epiphyte community in a Danish lowland stream

SUMMARY. 1. We examined the abundance and oxygen metabolism of epiphytic organisms on the dominant macrophyte, Potamogeton pectinatus , in headwaters of the eutrophic River Suså. Microbenthic algae were abundant in the stream during spring and macrophytes during summer.
2. The low macrophyte biomass in spring supported a dense epiphyte cover whereas the high macrophyte biomass during summer had a thin epiphyte cover of 10–100-fold lower abundance per unit area of macrophyte surface. The epiphyte community was dominated by microalgae in spring and by heterotrophs, probably bacteria, during summer. This seasonal shift was shown by pronounced reductions of the chlorophyll a content (from 2–3% to 0.1–0.7% of organic DW), the gross photosynthetic rate (from 20–85 to 3–15 mg O₂, g-¹ organic DW h⁻¹) and the ratio of gross photosynthesis to dark respiration in the epiphyte community (from 5–18 to 1). The reduced contributions of epiphytic microalgae correlated with reduced light availability during summer.
3. Both the density and the photosynthetic activity of epiphytic algae were low on a stream area basis relative to those of microbenthic algae and macrophytes. Rapid variations in water velocity and extensive light attenuation in water and macrophyte stands probably constrained the development of epiphytic algae. The epiphyte community was more important in overall stream respiration, contributing c. 10% to total summer respiration and c. 20% to summer respiration within the predominantly heterotrophic microbial communities on sediments and macrophyte surfaces.     

Contribution of biofilm‐dwelling consumers to pelagic–benthic coupling in a large river

1. Over the course of this 17‐month study, we assessed the potential loss of plankton (bacteria, algae, heterotrophic flagellates) to consumers (ciliates and rotifers) within mature biofilms established on natural substrata exposed to the main current of the River Rhine (Germany). Once a month, in flow cells in a bypass system to the River Rhine, we measured the clearance rates of the biofilm‐associated consumers on the different groups within the natural plankton. 2. Ciliates were the most dominant consumers, among which planktivorous groups, particularly peritrichs and (in spring and summer) heterotrichs dominated. Consumer biomass varied with season, with the highest density occurring directly after the appearance of the phytoplankton spring peak. 3. Clearance rates on plankton ranged from 96 to 565 L m^?2 d^?1 for bacteria and 66–749 L m^?2 d^?1 for algae, with a preference for algae in summer and for bacteria in winter. This pattern coincided with seasonal changes in the structures of the grazer communities. The consumers (both ciliates and rotifers with total standing stocks ranging between 19 and 572 mg C m^?2) imported a substantial amount of organic matter (between 15 and 137 mg C m^?2 d^?1) into the biofilm. 4. These results highlight the potential importance of consumers in the biofilm as a trophic link between the plankton and the benthos, a function that has hitherto mostly been attributed to filter‐feeding bivalves. In contrast to bivalves, the biofilm‐dwelling consumers show a more dynamic response towards the plankton density and composition. Such dynamic components need to be considered when estimating total plankton consumption by the benthos.     

The bionomics of the free-living larvae and the transmission of Dictyocaulus filaria between lambs in North-East England.

The bionomics of the free-living larvae of Dictyocaulus filaria on pasture, and the transmission of infection between lambs, were studied during different seasons of the year in North-East England. The rate of development of first-stage larvae to the third stage took 4-9 days in late spring and summer, 1 1/2-4 weeks in autumn and 5 1/2-7 weeks in winter. The proportion of first-stage larvae developing to the third stage ranged from 10-28% in autumn and winter, and 2-25% in spring and summer. The rate of mortality of the third-stage larvae was approximately logarithmic in nature, although the survival time was shorter in spring and summer than in autumn and winter. Third stage larvae were able to survive from autumn until the spring of the following year in sufficient numbers to perpetuate transmission but not to cause clinical disease. In a transmission study, the survival of the infective larvae on the experimental plot was poor in summer, but the larval population increased in the autumn and then declined slowly throughout the winter. Infection in the susceptible lambs was related to the level of infection on the herbage increasing in severity from early summer to late autumn. However, those lambs infected in the summer were resistant to the heavy autumn challenge of larvae on pasture.     

Observations on some environmental factors connected with fertility in heat stressed cows

A field study was performed using 15 Kibutz dairy herds, in which 4195 cows situated in northern Israel were milked to determine the influence of climatological factors and nutritional regimes on the conception rate during the summer period (July-September). The Overall Conception Rate (OCR) during summer was 28.2% (17.3-41.9%) compared to 40% in the spring (May-June). The conception rate from first inseminations (CRl) was 31.3% during summer and 45.3% during spring. The OCR of the nullipara heifers in the same herds was 59.2% in summer and 60.4% in spring. The OCR in summer was negatively correlated with the minimum temperature (r=-0.53), the relative humidity at 0800 hrs. (r=-0.47), and the relative humidity at 1400 hrs (r=-0.49), whereas the CRl during summer was negatively correlated only with the minimum temperature (r=-0.51). In 12 (13) feeding groups of cows examined in 6 herds, no correlation was found between rectal temperatures and the actual milk productions of the cows. In 14 (15) herds, the milk production in summer was lower than in spring; the decrease varied from 0.9%-18.2% (average 7.8%). A highly significant negative correlation was found between the OCR and the various parameters of protein intake: grams of crude protein/cow/day, grams of crude protein/kg FCM/day, and percentage of protein from total dry matter. Particularly high correlations were found between the OCR and the average amounts of protein/kg FCM/day in milk of all cows (r=-0.84).     

Der Beitrag einzelner Blätter an der Pflanze zur Photosynthese des gesamten Blattapparates im Laufe der Pflanzenentwicklung

Plants ofPlectranthus fructicosus were grown in two controlled environments -“spring” and “summer” conditions - differing in temperature and air humidity (day/night 20/15 and 27/22 °C; 80/98 and 50/80 % relative humidity) in order to study the influence of environmental conditions on the development of photosynthetic characteristics of individual leaves. The contribution of individual leaves to plant photosynthesis was very similar in both environments, the maximum shifting from bottom leaves to leaves of middle insertion levels during plant ontogenesis. On integrating the values of leaf photosynthesis for the whole vegetation period, the 5th leaf in “spring” conditions and the 4th leaf in “summer” conditions showed the highest contribution to plant photosynthesis (29 % resp. 25% of total net CO₂ influx). The “photosynthetically mature” leaves of middle insertion levels played the main role in CO₂ uptake of whole plant.     

Survival of Bemisia tabaci adults under different climatic conditions

The ability of the sweet potato whitefly, Bemisia tabaci Gennad., to survive a range of environmental conditions was investigated in the laboratory. The range of temperature and humidity investigated corresponds to the normal climatic range during B. tabaci's summer migration in Israel. Adult whiteflies confined to small test cages were exposed to combinations of temperature (25, 30, 35, and 41 °C) and relative humidity (20, 50, 80, and 100%) for periods of 2, 4, or 6 h.A logistic regression model describing the four-dimensional surface defining percent survival as a function of time, temperature, and humidity was developed. Using stepwise regression to exclude non-significant terms, the linear predictor included temperature, and the products of temperature and time, and humidity and time. The model accounted for 75% of the variance. A reparameterization of the fitted regression model suggests that survival potential is conditioned by temperature conditions prevailing during the previous 10 h.Whitefly survival after 2 h exposure ranged from 90% survival at 20°C and 100% RH, to <2% survival at 41°C and 20% r.h.. No whiteflies survived more than 2 h exposure at these latter extremes of temperature and humidity. Survival rates decreased slightly after experimental whiteflies were kept in a cage with food a further 20 h at 25±2°C, 55±5% r.h. Investigations of the effects of hunger and virus infection, showed that both increased mortality.     

引种地被石竹光合特征与生理生态因子的关系

以上海地区引种的一年生地被石竹实生苗为材料,研究其苗高生长变化、生物量积累和分配、光合特性及其变化规律,并分析主要生理生态因子对其净光合速率的影响。结果表明:(1)3～6月份为地被石竹苗高生长速生期,生长量为年生长量的65.93%,实生苗各部分器官的生物量总体呈现上升的趋势;3～6月份苗木以地上部分生物量积累为主,其占总生物量的比例从46.89%升至65.60%,6月份以后地下部分生物量所占比例从34.40%升至53.11%。(2)地被石竹叶片净光合速率(Pn)日变化在春季和秋季呈单峰曲线型,而在夏季表现为双峰曲线,且具有典型的光合"午睡"现象。(3)影响光合变化的主要决定生理生态因子:春季为蒸腾速率和气温,夏季为气孔导度和大气CO2摩尔分数,秋季为胞间CO2摩尔分数和光合有效辐射;限制地被石竹Pn日变化生理生态因子:春季为胞间CO2摩尔分数和光合有效辐射,夏季为蒸腾速率和空气相对湿度,秋季为气孔导度和气温。(4)地被石竹具有较高水平的光补偿点(56.94μmol·m-2·s-1)和光饱和点(780.07μmol·m-2·s-1),应属于喜光植物。     

Dynamics of long-leaved sundew Drosera intermedia populations at two extremes of a hydrological gradient

Densities of Drosera intermedia were low in two studied habitats (10–25 ramets m⁻¹), a path through a wet heath (short inundation in spring, low soil moisture in summer) and a pool edge (longlasting inundation, high soil moisture in summer). The low densities could be explained by the observed low recruitment and high adult mortality.
The low recruitment resulted from: (1) a high first year mortality of the large number of seedlings that emerged each year in the path population, caused by summer drought and cover with algae after heavy rainfall; (2) the absence in two years out of three of seedling emergence at the pool edge, due to the longlasting inundation. In neither population any seedlings survived to flower; (3) low vegetative reproduction rate.
Adult mortality during the growing season was caused by drought, which did not occur at the pool edge. Rapid senescence in autumn, caused by summer drought on the path and by a rapid submersion after heavy rainfall at the pool edge, was associated with a high winter mortality.     

Survival of Botrytis cinerea in Soil in South-Eastern Spain

The survival of Botrytis cinerea in sterile and unsterile soil at different temperatures and relative air humidities was investigated in south‐eastern Spain. Conidia survived only 7 days at 40^°C but, depending on relative humidity, for 30–90 days at 22^°C. High air humidity (95%) was needed to maintain soil humidity (8%) at a level that favoured conidial survival. Conidia survived better in sterile soil than in unsterile soil, probably because of the presence in the latter of soil microorganisms antagonistic to B. cinerea. Survival of conidia in environmental conditions simulating those in a greenhouse was less than 28 days. Results showed that B. cinerea conidia cannot survive over summer in south‐eastern Spain, and other primary sources of inocula are discussed.     

浙江早稻谷中稻水象甲的存活研究

研究了早稻收获和储藏期间稻水象甲Lissorhoptrus oryzophilus Kuschel一代成虫的数量动态及其存活时间与温湿度的关系。早稻收割时尚未迁离稻田的象甲中,仅3～13%的个体随脱落操作落入稻谷中,且这些个体经太阳曝晒2天后存活率不足1%;收割时残留于稻草中的虫量为稻谷中的5.1～12.3倍。储藏1个月的稻谷中所有成虫均死亡,但储藏相同时间的秕谷和稻草中存活成虫分别达到250头/50 kg秕谷和17头/50 kg稻草。成虫在≥90% RH下的存活时间显著长于35～75%RH下,在玻璃管中的存活时间显著长于稻谷中。在稻谷中,温度对成虫存活时间的影响不明显,但在玻璃管中,20℃（恒温）下的存活时间显著长于27.0～33.2℃（室温）下。利用生存分析的指数模型分析了成虫存活与湿度、温度和存放基质的关系,表明在75～98% RH之间,湿度越低则成虫死亡风险越大,较高温度（27.0～33.2℃）和处于稻谷中其死亡风险亦高。这些结果为开展稻谷中稻水象甲的检疫提供了依据。     

Use of Coating to Protect Lyophilized Bacillus popilliae from Moisture

Lyophilized cells of Bacillus popilliae were protected from moisture when suspended in pellets of tung oil polymer which were then coated with paraffin wax. The survival of the protected cells at various levels of relative humidity (RH) and under various storage conditions was determined. During 6 months of storage, moisture appeared to have little effect on survival of the cells when the RH level was 22% or less; but, at higher RH levels, survival declined upon storage. Viable cells were recovered when pellets were stored for 3 months at 33% RH, 2 months at 42% RH, 1 month at 50% RH, and 4 days in distilled water. Under field conditions, some cells survived at least 1 week of storage.     

PHOTOSYNTHETIC CHARACTERISTICS AND POTENTIAL MOISTURE STRESS FOR THE ACTINORHIZAL SHRUB,MYRICA CERIFERA (MYRICACEAE), ON A VIRGINIA BARRIER ISLAND

Seasonal variations in photosynthesis and water relations parameters were quantified for Myrica cerifera, the dominant woody species on the barrier islands along the eastern shore of Virginia. From June through September of 1989, maximum values were 35 μmol m^−-2 sec^−-1 for net CO₂ assimilation, 10.5 mm sec^−-1 for stomatal conductance to water vapor diffusion, and –0.3 MPa for xylem pressure potential at the field site on Hog Island. Midday minimum xylem pressure potential often was less than –1.5 MPa. Data from the field and measurements on glasshouse plants indicated that stomatal opening and photosynthesis were sensitive to leaf water potential (<–0.8 MPa) and the leaf-to-air humidity deficit (>1.5 kPa). Using meteorological data and derived photosynthetic responses, predictions indicated that M. cerifera photosynthesis would have been limited at the field site due to nonoptimal air temperatures and humidity deficits on at least 90% of the days during the relatively wet summer of 1989. By comparison, these parameters were expected to limit photosynthesis on all but 2 d, or more than 98% of the time during the relatively dry summer of 1990. The sensitivity of Myrica cerifera to atmospheric humidity and plant moisture status may explain the distributional preference for the more mesic swale sites of barrier islands.     

A study of Lough Corrib,western Ireland and its phytoplankton

During 1980/1981, a twelve month study was carried out on the phytoplankton of Lough Corrib, a large freshwater lake in western Ireland. Cell counts indicated low phytoplankton productivity and this was reflected in low chlorophyll a values and high Secchi readings. Diatoms predominated in spring and were succeeded by blue-green algae in late summer. The spring diatom crop was apparently limited by either silicate or nitrogen. Mineral uptake by rooting macrophytes and benthic algae and phosphate recycling as a result of bottom sediment disturbance may be important elements in the nutrient cycling regime of the lake. Differences in morphology between the upper and lower basins of the lake are reflected, to some extent, in species composition and areal productivity.     

Nitrate removal in two relict oxbow urban wetlands: a 15N mass-balance approach

A ¹⁵N-tracer method was used to quantify nitrogen (N) removal processes in two relict oxbow wetlands located adjacent to the Minebank Run restored stream reach in Baltimore County (Maryland, USA) during summer 2009 and early spring 2010. A mass-balance approach was used to directly determine the flow of ¹⁵NO₃ ^? to plants, algae, and sediments, with unaccounted for ¹⁵N assumed to be denitrified. During the summer, plant and algal uptake accounted for 42%, of the added ¹⁵NO₃ ^? in oxbow 1, less than 1% remained in the water column and 57% was unaccounted for. In oxbow 2 during the summer, plant and algal uptake accounted for 63% of the added ¹⁵NO₃ ^?, with <1% remaining in the water column and 38% unaccounted for. During the early spring, plant and algal uptake were much lower in both oxbows, ranging from 0.05 to 13.3% of the ¹⁵N added, with 97 and 87% was unaccounted for in oxbow 1 and 2, respectively. The amount of unaccounted for ¹⁵N was equivalent to estimated areal denitrification rates of 12 and 6 mg N m^?2 d^?1 in the summer and 78 and 15 mg N m^?2 d^?1 in the spring, in oxbow 1 and oxbow 2, respectively. However, the uncertainty of these estimates is high as it was difficult to detect accumulation of ¹⁵N in the sediments which could have accounted for a very large percentage of the added ¹⁵N. Our results suggest that the two relict oxbow wetlands are sinks for NO₃ ^? during both summer and spring but that the pathways of removal vary with plants and algae playing a major role in summer but not in spring.     

大兴安岭地区紫貂的活动节律

借助无线电遥测技术,对４只紫貂全年的活动节律进行了研究,结果表明,紫貂的活动节律春季和冬季的高峰是在晨昏二个阶段,夏秋二季的活动高峰在白昼。春季总体活动节律与夏季相比有明显差异（Ｆ＝４．４９９,ｄｆ＝１,２２,２３;Ｐ＝０．０４５）,春季与秋季的活动节律也有差异（Ｆ＝７．０３９;ｄｆ＝１,２２,２３;Ｐ＝０．０１５）。其总体平均活动强度,春季活动量最小（１７．５３％）,夏季最高（３８．２９％）,其     

Role of Relative Humidity in the Survival of Airborne Mycoplasma pneumoniae

Aerosols of Mycoplasma pneumoniae were studied at several relative humidities at a controlled temperature of 27 C. Production of an experimentally reproducible aerosol required preatomization of the organism in its suspending fluid and was dependent on the type of fluid used in atomization as well as on the procedures used to produce an aerosol. The airborne particles studied were within the range of epidemiological significance, with most being 2 mum or less in diameter. Survival of the airborne mycoplasma in these particles was found to be best at very low and at very high humidities. The most lethal relative humidity levels were at 60 and 80%, at which levels fewer than 1% of the organisms survived over a 4-hr observation period. However, survival of the organism at most relative humidity levels was such that long-term infectivity could be expected from aerosols of M. pneumoniae. Because of the extreme sensitivity of M. pneumoniae at critical humidity levels, control of the airborne transmission of these organisms may be possible in selected spaces.