三峡库区高岚河甲藻水华的初步研究

2005年2月中下旬,高岚河库湾发生拟多甲藻水华,本文研究了水华爆发期间藻类的生消过程及其基本组成,并分析了环境因子在水华形成和消亡过程中的作用机制。研究结果表明:超高的营养盐,如TN、TP等是此次水华发生的主要原因之一,其他物理条件,如气温、水温的回升等是重要的诱因。而水华消亡的原因是营养盐被不断繁殖的甲藻消耗,以至于不能满足甲藻的营养需求,最终部分甲藻下沉到底层。     

气-水两生型丝孢真菌的多样性与分类研究

气-水两生型真菌通常定植于自然森林生态系统中溪流或池塘沉积的腐枝叶上,菌丝生长于水体底部,当沉积物暴露于空气中时,形成分生孢子并发育成中空的孢子繁殖体,使其能漂浮在水面,附着新的基质,进行生长繁殖。世界范围内已报道约20属116种,大多为无性型的丝孢菌,其独特的生存环境和产孢特点,在真菌的形态、生态和系统演化上有重要研究价值。文中主要从多样性和分类学、采集与分离培养、孢子形态和发育、有性型-无性型关系、系统演化关系等方面对其进行了综述,为该类真菌系统的研究及潜在的应用提供参考。     

香溪河流域浮游植物调查与水质评价

报道了1996年10月～1997年7月和2003年对香溪河流域浮游植物2周年的调查结果。数据显示,香溪河流域的浮游植物主要由硅藻、绿藻和蓝藻组成。1996-1997年硅藻的种类最多,绿藻次之,蓝藻居第3位;2003年绿藻的种类数跃居首位,硅藻次之,其它藻类亦有不同程度的变化。藻类的细胞密度表现出明显的季节变化．最高、最低值分别出现在夏季和冬季。应用Margalef多样性指数和Menkinick多样性指数对香溪河流域的水质进行评价的结果显示：2003年该流域的水质营养等级为中一富营养型,水环境质量较6年前有所下降。     

Associations between lake phytoplankton community and growth factors — a canonical correlation analysis

Canonical correlation analysis was used to study the associations between the most prevalent phytoplankton species and nine physical and chemical growth factors in a polyhumic Finnish lake. The analysis was made (a) to the ten species with the greatest mean biomass in the data over one growth season and (b) to the ten species providing the greatest canonical correlation with the growth factors. The latter species were detected using an exchange type procedure. The analysis showed strong associations within phyla. Especially the most problematic phylum with respect to the use of the lake, the cyanobacteria, had a pronounced mutual association, as they correlated negatively with the N/P ratio as positively with phosphorus.     

Changes in community structure and photosynthetic activities of total phytoplankton species during the growth,maintenance, and dissipation phases of a Prorocentrum donghaiense bloom

The potential interactions between the bloom-forming dinoflagellates and other phytoplankton during the algal bloom cycle are interesting, while the causes for the phytoplankton community changes were not fully understood. We hypothesized that phytoplankton community structure and photosynthetic activities of total phytoplankton have their special characteristics in different phases of the algal blooms. To test this hypothesis, a survey covering the process of a Prorocentrum donghaiense bloom in coastal waters between Dongtou and Nanji Islands was carried out from 9 to 20 May 2016, and the changes in the phytoplankton community and photosynthetic activities of total phytoplankton were determined. Surface seawater was sampled for microscopic analysis of phytoplankton composition and pulse amplitude modulated (PAM) chlorophyll fluorescence analysis of photosynthetic activities of the total phytoplankton species. A total of 25, 31, and 19 phytoplankton species were identified in its growth (9–12 May), maintenance (13–18 May) and dissipation phases (19–20 May), respectively. Diatoms were dominant in terms of species number while dinoflagellates were predominant at cell abundance. Dinoflagellates were the major dominant species during three phases of the bloom based on the dominance (Y) value, whereas the dominant species extended to dinoflagellates and diatoms including P. donghaiense, Coscinodiscus argus, Gonyaulax spinifera, Cyclotella sp. and Scrippsiella trochoidea in the dissipation phase. In the maintenance phase, the average cell abundances of the total phytoplankton and P. donghaiense were consistent with the chlorophyll a (Chla) concentration in the seawater; for the diversity indices of total phytoplankton species, Simpson index (C) was the highest while Shannon index (H′) and Pielou evenness index (J′) were the lowest. Furthermore, photosynthetic activities of the total phytoplankton species represented by the effective quantum yield (F_q'/F_m') and the maximum relative electron transport rate (rETR_max) in the maintenance phase were higher than those in the growth and dissipation phases. The results indicated that the characteristics of phytoplankton community structure and photosynthetic activities could be regarded as criteria in predicting the phases of algal blooms.     

Do arbuscular mycorrhizal fungi play a role in the ability of rare plant species to colonize abandoned fields?

While some plant species colonize abandoned agricultural fields and dry grasslands with similar frequency (generalists), others are absent or underrepresented in abandoned fields (specialists). We tested if inoculation with dry grassland or abandoned field soil could improve specialist performance in an abandoned field and compared the effects of inoculation in the stage of sown seeds and transplanted seedlings. Arbuscular mycorrhizal fungi from abandoned field had higher root colonization potential. This could explain the higher performance of the sown specialists inoculated with the abandoned field inoculum compared to those inoculated with dry grassland inoculum. This difference disappeared when specialists were transplanted instead of sown. The results do not provide any support for higher performance of specialists inoculated with dry grassland inoculum. Transplantation, however, seems to be an efficient way to introduce specialists into the abandoned fields.     

Bacterial communities and toxin profiles of Ostreopsis (Dinophyceae) from the Pacific island of Okinawa,Japan

Variations in toxicity of the benthic dinoflagellate Ostreopsis Schmidt 1901 have been attributed to specific molecular clades, biogeography of isolated strains, and the associated bacterial community. Here, we attempted to better understand the biodiversity and the basic biology influencing toxin production of Ostreopsis. Nine clonal cultures were established from Okinawa, Japan, and identified using phylogenetic analysis of the ITS-5.8S rRNA and 28S rRNA genes. Morphological analysis suggests that the apical pore complex L/W ratio could be a feature for differentiating Ostreopsis sp. 2 from the O. ovata species complex. We analyzed the toxicity and bacterial communities using liquid chromatography-mass spectrometry, and PCR-free metagenomic sequencing. Ovatoxin was detected in three of the seven strains of O. cf. ovata extracts, highlighting intraspecies variation in toxin production. Additionally, two new potential analogs of ovatoxin-a and ostreocin-A were identified. Commonly associated bacteria clades of Ostreopsis were identified from the established cultures. While some of these bacteria groups may be common to Ostreopsis (Rhodobacterales, Flavobacteria-Sphingobacteria, and Enterobacterales), it was not clear from our analysis if any one or more of these plays a role in toxin biosynthesis. Further examination of biosynthetic pathways in metagenomic data and additional experiments isolating specific bacteria from Ostreopsis would aid these efforts.     

Fungicidal Activity of Volatiles from Selected Cruciferous Plants against Resting Propagules of Soil-borne Fungal Pathogens

The efficacy of volatiles evolved from tissues of nine cruciferous plants against resting propagules of Fusarium oxysporum var radicis f. sp. lycopersici, Sclerotium cepivorum, and Sclerotinia sclerotiorum was tested. The cruciferous plants released biocidal compounds, mainly isothiocyanates, produced during the enzymatic degradation of glucosinolates present in the plant cells. Among the plants investigated, the highest fungicidal activity and also the highest concentration of isothiocyanates were found in Brassica juncea. The resting propagules of tested fungi differed significantly in their sensitivity towards volatiles released from plant tissues.     

LETTER TO THE EDITOR

SUMMARY

A two-year limnological survey between 1973 and 1975 showed that the Roodeplaat Dam is a warm monomictic impoundment which has stable thermal stratification during summer. Oxygen supersaturation of the surface waters and anaerobic conditions in the hypolimnion were encountered during summer. Water transparency was seasonal and related to existing phytoplankton populations and allochthonously-introduced clay material. Chemical stratification during summer was prominent and appeared to be caused not only by mineralization processes in the hypolimnion, but also by dilution in the surface layers during summer flooding. Because of the morphometry of the impoundment and the fact that sewage effluents are discharged into the major inflow, considerable horizontal variation in most chemical and biological characteristics was found. On the basis of the nutrient content of the waters and the magnitude of the phytoplankton populations observed, Roodeplaat Dam may be classified as a highly eutrophic water body.