Transferring sediment containing intact seed banks: a method for studying plant community ecology

The experimental study of the ecology of natural plant communities is necessary to demonstrate the effects of environmental factors on plant growth. It allows one to make predictions of the likely effects of environmental changes on plant communities. Manipulating an entire ecosystem is complicated, and is rarely attempted. An alternative method is applied here for the submerged plant communities of the seasonally-flooded oligohaline marshes of the Camargue. It consists of collecting undisturbed sediment samples with their contained intact seed bank, and submitting them to different salinities. The study of total biomass and of the biomass of the more frequent species was carried out using parametric tests. The precision of the results depended on the frequency of the species in the replicates. When the frequency was low, non-parametric statistics were necessary. The method seems to be particularly suitable for the study of communities of annual species in aquatic environments.

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Résumé L'étude expérimentale de l'écologie des communautés naturelles de plantes est nécessaire pour démontrer les relations de cause à effet entre les facteurs environnementaux et l'abondance des plantes. Elle l'est également pour faire des prédictions réalistes sur les effets de modifications envisagées de l'environnement sur des communautés de plantes. La manipulation de l'écosystème complet est complexe, ce qui rend son utilisation rare. Une méthode alternative a été utilisée pour l'étude de la composition spécifique des communautés de plantes submergées des marais temporaires de Camargue. Elle consiste à prélever des échantillons non perturbés de sédiment, avec leur stock de semences intact, et à les soumettre à des conditions de salinité. L'étude de la biomasse totale et de la biomasse des espèces les plus fréquentes est faite au moyen de test paramétriques. La précision attendue des résultats dépend de la fréquence de l'espèce dans les réplicats. Lorsque la fréquence n'est pas élevée l'emploi de statistiques non paramétriques est indispensable. La méthode se révéle particulièrement bien adaptée à l'étude des communautés d'annuelles en milieu aquatique.

     

Avoidance of egg parasitism through submerged oviposition by tandem pairs in the water strider, Aquarius paludum insularis (Heteroptera: Gerridae)

Abstract.  1. Females of the water strider Aquarius paludum insularis (Motschulsky) (Heteroptera: Gerridae) carry males on their backs and oviposit under water after copulation. This study focuses on the benefit  A. paludum insularis receives by ovipositing in tandem.
2. Males guarded females in tandem through to the end of oviposition in 85% of copulations. Females in tandem dived deeper than single females, and the density of A. paludum insularis eggs increased with water depth. The proportion of eggs parasitized by a scelionid wasp, Tiphodytes gerriphagus Marchal (Hymenoptera: Scelionidae) decreased with increasing water depth.
3. These results suggest that during oviposition guarding by males is beneficial for females, because it enables pairs to dive and lay eggs deeper and in oviposition sites where the risk of egg parasitism is lower.     

Secondary productivity (3H-Leucine and 3H-Thymidine incorporation), abundance and biomass of the epiphytic bacteria attached to detritus of Typha domingensis pers. in a tropical coastal lagoon

Senescent, naturally dried leaves of Typha domingensis were incubated inthe littoral region of a coastal lagoon and epiphytic bacterial volume,abundance, biomass and secondary productivity were measured during 127 daysof decomposition. The peak of cell abundance was registered at t =127 days when expressed per leaf surface area (10.07×10⁷cells cm^-2; 7.26 µgC cm^-2), and at t= 26 days when expressed per biofilm dry mass (38.10 ×10⁷ cells (mgDM biofilm)^-1, 30.52 µgC(mgDM biofilm)^-1). The highest values of bacterial biovolumesand lower turnover time were usually obtained in the beginning of thecolonization. Leu:Tdr ratios were also higher in the beginning of thecolonization, when bacterial community presented unbalanced metabolism.Consequently, the highest discrepancies between the bacterial secondaryproduction estimated by leu and Tdr incorporation were observed in the first2 days of decomposition. On average, the bacterial secondary productivityestimated by leu incorporation was 2.1 times higher than the valuesestimated by Tdr incorporation when the empirical factor for Tdr wasobtained from the relationship between Tdr and biomass increment. Thisdifference increased to 4.2 when the empirical factor was obtained from therelationship between Tdr and cell numbers increment. An average of bothmethods (0.0037 to 0.1397 µgC cm^-2 h^-1)produced results that fall within the range reported in the literature forepiphytic bacteria of freshwater ecosystems.     

Alien aquatic vascular plants in Hungary (Pannonian ecoregion): Historical aspects,data set and trends

Estimating the extent of biological invasions is critical in predicting the effect of exotic species. We investigated the occurrence and number of alien freshwater plants and give information on the composition of alien aquatic flora, their trend in time, invasion pathway, and their invasive character.     

Free-Radical Scavenging Activity of Submerged Mycelium Extracts from Higher Basidiomycetes Mushrooms

Twenty-four Basidiomycetes strains were evaluated to determine their free-radical scavenging capacity in submerged cultivation. The scavenging capacity of the extracts varied from 1 to 85% depending on the mushroom species, solvent used, and concentration. A calculation of EC₅₀ of extracts from several wood-rotting Basidiomycetes showed high scavenging abilities at low effective concentration.     

Optimization of Nutritional Factors for Exopolysaccharide Production by Submerged Cultivation of the Medicinal Mushroom Oudemansiella radicata

Summary Effects of nutritional factors on exopolysaccharide production by submerged cultivation of the medicinal mushroom Oudemansiella radicata were investigated in shake flasks. Sucrose and peptone were optimal carbon and nitrogen sources for cell growth and exopolysaccharide production. The exopolysaccharide production was increased with an increase in initial sucrose concentration within the range of 10–40 g l⁻¹ and initial peptone concentration within the range of 1–3 g l⁻¹. To enhance further exopolysaccharide production, the effect of carbon/nitrogen ratios was studied using central composite design (CCD) and response surface analysis. The maximum exopolysaccharide production of 2.67 ± 0.15 g l⁻¹ was achieved in medium with optimized carbon and nitrogen sources, i.e. 39.3 g sucrose l⁻¹ and 3.16 g peptone l⁻¹ in the same cultivation conditions. The information obtained is helpful for the hyperproduction of exopolysaccharide by submerged cultivation of O. radicata on a large scale.     

Impacts of a submerged plant (Elodea canadensis) on interactions between roach (Rutilus rutilus) and its invertebrate prey communities in a lake littoral zone

1. Using 5‐m² field enclosures, we examined the effects of Elodea canadensis on zooplankton communities and on the trophic cascade caused by 4–5 year old (approximately 16 cm) roach. We also tested the hypothesis that roach in Elodea beds use variable food resources as their diet, mainly benthic and epiphytic macroinvertebrates, and feed less efficiently on zooplankton. Switching of the prey preference stabilises the zooplankton community and, in turn, also the fluctuation of algal biomass. The factorial design of the experiment included three levels of Elodea (no‐, sparse‐ and dense‐Elodea) and two levels of fish (present and absent). 2. During the 4‐week experiment, the total biomass of euplanktonic zooplankton, especially that of the dominant cladoceran Daphnia longispina, decreased with increase in Elodea density. The Daphnia biomass was also reduced by roach in all the Elodea treatments. Thus, Elodea provided neither a favourable habitat nor a good refuge for Daphnia against predation by roach. 3. The electivity of roach for cladocerans was high in all the Elodea treatments. Roach were able to prey on cladocerans in Elodea beds, even when the abundance and size of these prey animals were low. In addition to cladocerans, the diet of roach consisted of macroinvertebrates and detrital/plant material. Although the biomass of macroinvertebrates increased during the experiment in all Elodea treatments, they were relatively unimportant in roach diets regardless of the density of Elodea beds. 4. Euplanktonic zooplankton species other than Daphnia were not affected by Elodea or fish and the treatments had no effects on the total clearance rate of euplanktonic zooplankton. However, the chlorophyll a concentration increased with fish in all the Elodea treatments, suggesting that fish enhanced algal growth through regeneration of nutrients. Thus, our results did not unequivocally show that Elodea hampered the trophic cascade of fish via lowered predation on grazing zooplankton. 5. In treatments with dense Elodea beds (750 g FW m^?2), chlorophyll a concentration was always low suggesting that phytoplankton production was controlled by Elodea. Apparently, the top‐down control of phytoplankton biomass by zooplankton was facilitated by the macrophytes and operated simultaneously with control of phytoplankton production by Elodea.     

Changes in the allocation of some chemical compounds in structures of Oryza glumaepatula (Steud) in an Amazonian lake subjected to an anthropic impact (Lake Batata, Porto Trombetas)

Lake Batata is a typical clear water lake of the Amazon, located at the right margin of the Trombetas River, at the town of Porto Trombetas (PA). It is subjected to a large and predictable variation of the water level, greater than 6 m, being in the floodplain of the Trombetas River. For 10 years (1979–1989) Lake Batata has received the tailings of bauxite processing from the activities of Mineração Rio do Norte S.A. These tailings impacted about 30% of its total area with an effluent of fine granulometry. Nowadays, two different areas can be observed at Lake Batata, one impacted by the bauxite tailings and one where the natural characteristics have been preserved. The aquatic macrophyte Oryza glumaepatula (Steud), known as wild rice, is one of the species found in the two areas, impacted and natural. The goal of this research was to evaluate the concentration of organic matter, organic carbon, N, P, lipids, soluble carbohydrates, and cell-wall fraction in three structures of O. glumaepatula (leaves and culm, adventitious roots, and basal roots), as well as to identify the possible differences in the allocation of these compounds between individuals in the natural and impacted areas. While the differences between the different structures of the plant are preliminary data for studies on the detritus chain and herbivory, the differences between the natural and impacted areas show the probable impact of the tailings on O. glumaepatula.