Bacteria and phosphorus regeneration in lakes. An experimental study

The aerobic decomposition of the green alga Chlamydomonas reinhardii by a mixed population of lake bacteria was studied in batch and chemostat cultures. Bacterial chemostats were supplied with continuously heatkilled algae. The dead algae rapidly released most of their phosphorus as SRP. In the batch experiments bacteria acted as consumers of the released algal phosphorus. This phosphorus uptake was dependent on the C:P ratio of the algae. During the death phase of the bacteria most of the bacterial phosphorus itself was released. The continuous supply of energy in form of dead algae in the chemostat experiments prevented the death phase of the bacteria and thus any net regeneration of phosphorus. The influence of the C:P stoichiometry of algae and bacteria on the regeneration of algal phosphorus is discussed.     

Transplant experiments. Growth-limiting factors for diatoms and bluegreen algae in Norwegian lakes

Population densities and total phosphorus concentrations in samples from different lakes of south-eastern Norway were determined. In addition some transplant experiments with dilute phytoplankton populations were carried out. A laboratory batch culture method was used.The diatoms studied may be divided into three ecological groups based on their cell densities and total phosphorus concentrations in the samples. This classification was supported by the experimental results. Cyclotella spp., Asterionella formosa and Tabellaria fenestrata did not grow or had low growth rates above pH 9. Synedra cf. acus and Fragilaria crontonensis had often high growth rates within the pH 9–10 range, but were not able to grow at pH values above 10. High pH-values had no effect on the growth rate of Oscillatoria. Oscillatoria, Synedra and Stephanodiscus were severely growth-limited in filtered water from oligotrophic lakes. Maximum growth rates of all the populations studied were often obtained after addition of phosphate and chelated iron (FeEDTA) in combination to filtered water samples from oligotrophic/mesotrophic lakes.     

Succession of phytoplankton species in indoor reservoir models varying in sediment composition and water inlet site

Using four continuous-flow indoor reservoir models, the combined effects of varying water inlet depth and sediment composition on phytoplankton species composition and its succession pattern were studied. Species which are known to bloom in eutrophicated reservoirs were dominant in the species succession in each tank. At any one time, a step-like pattern was observed in the composition of the dominant species of each tank, wherein all the species which appeared in a tank with a lower phosphorus concentration were included in the species composition of the tank with a higher phosphorus concentration in an additive relationship.     

Penetration and Postinfection Development of Meloidogyne incognita on Cotton as Affected by Glomus intraradices and Phosphorus

The influence of the vesicular-arbuscular mycorrhizal fungus Glomus intraradices (Gi) and superphosphate (P) on penetration, development, and reproduction of Meloidogyne incognita (Mi) was studied on the Mi-susceptible cotton cultivar Stoneville 213 in an environmental chamber at 28 C. Plants were inoculated with Mi eggs at planting or after 28 days and destructively sampled 7, 14, 21, and 28 days after nematode inoculation. Mi penetration after 7 days was similar in all treatments at either inoculation interval. At 28 days, however, nematode numbers were least in mycorrhizal root systems and greatest in root systems grown with supplemental P. The rate of development of second-stage juveniles to ovipositing females was unaffected by Gi or P when Mi was added at planting, but was delayed in mycorrhizal root systems when Mi was added 28 days after planting. Nematode reproduction was lower in mycorrhizal than in nonmycorrhizal root systems at both Mi inoculation intervals. Nematode reproduction was stimulated by P when Mi was added at planting, but was similar to reproduction in the low P nonmycorrhizal treatment when Mi was added 28 days after planting. Eggs per female were increased by P fertility when Mi was added at planting.     

Photosynthetic characteristics of the submerged macrophyte Ceratophyllum demersum

The photosynthetic and growth characteristics of Ceratophyllum demersum L. were investigated under laboratory conditions which simulated those encountered in the plants' normal environment. The carbon fixation rate of C. demersum measured with ¹⁴C at light and carbon saturation at pH 8.0 was 4.48 mg C (g ash-free dry weight)⁻¹ h⁻¹. It was lower at pH 6.5 than at pH 8.0. The light use efficiencies in quiescent plants and actively growing plants were 6.3 and 8.7 × 10⁻⁹ kg CO₂ J⁻¹, respectively, with corresponding maximum photosynthetic rates of 2.67 and 4.36 mg C (g ash-free dry weight)⁻¹ h⁻¹. Photorespiration in actively growing plants consumed 24% of the carbon fixed. Incubation with DCMU demonstrated that about one-third was refixed. The optimum temperature for carbon fixation was 25°C. The C₃-photosynthetic pathway was the main operational route as indicated by the early photosynthetic products (largely C₃-acids) and the absence of Krantz anatomy and the chlorophyll a:b ratio (2.7). The maximum relative growth rates ranged from 0.025 to 0.041 g ash-free dry weight (g ash-free dry weight)⁻¹ day⁻¹ in the field (Lake Vechten, 1 to 3 m depth classes).     

Daphnia curvirostris Eylmann in Japanese high mountain waters (Cladocera: Daphniidae)

A species of Daphnia, Daphnia curvirostris Eylmann, found in high mountain lakes and ponds in central Japan is described. Although there were some differences in the shape of the male rostrum and the chromosome number between European populations as described by Johnson (1952) and Trentini (1980), and Japanese ones collected from high mountain waters, Japanese specimens had many characteristics similar to the taxon D. curvirostris of Europe.     

人体急性缺氧性意识障碍

实验分为低压组(低压舱7,000米)与常压组(吸入7.6％低氧混合气),每组受试者各为12名,有7名参加了两组实验。每组各有4名平均经15分23秒发生了意识模糊或丧失(通称意识障碍)。障碍者的肺泡氧分压为29.9±0.8mmHg。障碍发生前,呈现严重无力,觉醒度降低,反应迟钝,脑波特征是高幅6波(100-300μV)占优势。障碍发生时,高幅δ波丧失节律,幅度衰减,波型不规则,额枕失同步;呼吸循环代偿功能增强程度明显高于障碍前。本工作对于预测和评价人体急性缺氧引起的意识障碍有意义。