Effects of pine wilt disease invasion on soil properties and Masson pine forest communities in the Three Gorges reservoir region,China

Pine wilt disease (PWD) has caused significant Masson pine mortality in the Three Gorges reservoir region in central China. In this study, five uniform Masson pine stand types infected by PWD were selected and surveyed on slopes and aspects with similar environmental conditions. In sites that had been infected, soil bulk density was reduced, and the difference among the groups was statistically significant (P < 0.05) at the 0–10 cm and 10–20 cm soil layers, but not at 20–40 cm. Other soil water‐related physical properties, excluding noncapillary porosity, significantly differed among the groups in all soil layers. Additionally, the values of available phosphorus, sodium, potassium, calcium, and magnesium were higher in the invaded stands, but the total nitrogen and organic matter contents were lower. Masson pine does not become reestablished following PWD‐induced mortality but is instead replaced by broad‐leaved tree species. Among the 19 examined environmental variables, five were found to be significantly related with the ordination of plant community structure: Masson pine stumps (MPS), K⁺, capillary water holding capacity (CWHC), capillary porosity (CP), and soil water content (SWC). Among these factors, the plant community structure was principally related to MPS and K⁺. The findings of this study show that the outbreak of PWD has impacted Masson pine forest soil properties and altered forest community composition. The disease is negatively related with the presence of Masson pine and positively associated with that of broad‐leaved tree species.     

Influence of nutrient status and grazing pressure on the fate of Francisella tularensis in lake water

The natural reservoir of Francisella tularensis , the causative agent of tularaemia, is yet to be identified. We investigated the possibility that Francisella persists in natural aquatic ecosystems between outbreaks. It was hypothesized that nutrient-rich environments, with strong protozoan predation, favour the occurrence of the tularaemia bacterium. To investigate the differences in adaptation to aquatic environments of the species and subspecies of Francisella , we screened 23 strains for their ability to survive grazing by the ciliate Tetrahymena pyriformis . All the Francisella strains tested were consumed at a low rate, although significant differences between subspecies were found. The survival and virulence of gfp -labelled F. tularensis ssp. holarctica were then studied in a microcosm experiment using natural lake water, with varying food web complexities and nutrient availabilities. High nutrient conditions in combination with high abundances of nanoflagellates were found to favour F. tularensis ssp. holarctica . The bacterium was observed both free-living and within the cells of a nanoflagellate. Francisella tularensis entered a viable but nonculturable state during the microcosm experiment. When studied over a longer period of time, F. tularensis ssp. holarctica survived in the lake water, but loss of virulence was not prevented by either high nutrient availability or the presence of predators.     

Monolayer–multilayer transitions in a lung surfactant model: IR reflection–absorption spectroscopy and atomic force microscopy

A hydrophobic pulmonary surfactant protein, SP-C, has been implicated in surface-associated activities thought to facilitate the work of breathing. Model surfactant films composed of lipids and SP-C display a reversible transition from a monolayer to surface-associated multilayers upon compression and expansion at the air/water (A/W) interface. The molecular-level mechanics of this process are not yet fully understood. The current work uses atomic force microscopy on Langmuir–Blodgett films to verify the formation of multilayers in a dipalmitoylphosphatidylcholine, dipalmitoylphosphatidylglycerol, cholesterol, and SP-C model system. Isotherms of SP-C-containing films are consistent with exclusion and essentially complete respreading during compression and expansion, respectively. Multilayer formation was not detected in the absence of SP-C. Most notable are the results from IR reflection–absorption spectroscopy (IRRAS) conducted at the A/W interface, where the position and intensity of the Amide I band of SP-C reveal that the predominantly helical structure changes its orientation in monolayers versus multilayers. IRRAS measurements indicate that the helix tilt angle changed from approximately 80° in monolayers to a transmembrane orientation in multilayers. The results constitute the first quantitative measure of helix orientation in mixed monolayer/multilamellar domains at the A/W interface and provide insight into the molecular mechanism for SP-C-facilitated respreading of surfactant.     

Relationships Between Rotifers,Phytoplankton and Bacterioplankton in the Corumbá Reservoir,Goiás State,Brazil

This study evaluates the relationships between rotifers and phytoplankton and rotifers and bacterioplankton in a tropical reservoir. Fourteen stations in the reservoir were sampled, including in its arms and tributaries, in the dry and rainy seasons. The highest rotifer density was found in the dry season, mainly in the upper and intermediary stretches of the reservoir. Brachionus calyciflorus, Polyarthra vulgaris, Keratella tropica, K. cochlearis, K. americana and Pompholyx complanata were the most abundant species. Densities of B. calyciflorus and bacteria were significantly correlated. On the other hand, there was an inverse relationship between P. vulgaris and bacteria. Diatoms (Bacillariophyceae) were observed to be associated to K. americana. We suggest that the rotifer populations play a part in microbial and herbivory food webs.     

Plankton richness in a eutrophic reservoir (Barra Bonita Reservoir,SP, Brazil)

Species richness of plankton was studied in a eutrophic reservoir (Barra Bonita Reservoir) of the Middle Tietê River, São Paulo State, Brazil, during the period 1985–1986. This reservoir is formed by two rivers: the Tietê and the Piracicaba (the main tributaries), of which the Tiête is more eutrophic, having conductivity and nutrient concentration values twice those of the Piracicaba. In addition, the reservoir is fed by 114 smaller tributaries. Monthly sampling was carried out at three stations representing different environmental conditions: St1 on the Tietê, S2 on the Piracicaba, and St3 at the confluence of the two rivers. For the phytoplankton community, the Piracicaba River (St2) proved the richest site, with a listed 72 species with abundance of Chlorophyta, while St1 and St3 registered 59 and 50 species, respectively, with abundance of Cyanophyta. For the zooplankton community a great difference was not registered in species number at the three stations but the species composition and dominant species of rotifers and copepods were quite different. The occurrence of Mesocyclops meridianus and Metacyclops mendocinus, specific for St2;Mesocyclops ogunnus and Notodiaptomus iheringi, specific for St1, and that of these two species plus Mesocyclops meridianusat St3 shows that the conditions combining at this station were favorable to Mesocyclops meridianus but not to Metacyclops mendocinus. Both for phytoplankton and zooplankton, high values found of species richness were compared to species richness of natural lakes, e.g., Dom Helvecio, a monomictic stable lake in eastern Brazil, and another fifteen lakes in the same region.In conclusion, this work shows that environmental gradients are strong selective factors that enhance plankton richness in eutrophic reservoirs exhibiting environmental instability. This fact could explain the presence of a high number of plankton species associated with a high number of individuals in Barra Bonita Reservoir, supporting the effects of the intermediate disturbance hypothesis.     

Morphological Variation in Daphnia Cucullata Sars with Progressive Eutrophication of a Polymictic Lowland Reservoir

Morphological variation in Daphnia cucullata Sars was studied from 1994 to 2001 when fast increasing water trophy of the Siemianówka Reservoir was related to high TP and chlorophyll concentrations. During this period, D. cucullata biomass, as well as its contribution to the total cladocerans biomass clearly decreased. We found that among the six morphological parameters analyzed in D. cucullata, body length, height of the head and length of the tail spine had a tendency to decrease. The maximum values of these traits and carapace length also decreased. The morphology of D. cucullata appeared to be influenced by factors such as food availability, fish predation and an exclusive presence of D. cucullata among Daphniidae species. Increased water mixing in the reservoir may have also affected the changes in the head inclination of D. cucullata.     

How parasites affect interactions between competitors and predators

We present a synthesis of empirical and theoretical work investigating how parasites influence competitive and predatory interactions between other species. We examine the direct and indirect effects of parasitism and discuss examples of density and parasite-induced trait-mediated effects. Recent work reveals previously unrecognized complexity in parasite-mediated interactions. In addition to parasite-modified and apparent competition leading to species exclusion or enabling coexistence, parasites and predators interact in different ways to regulate or destablize the population dynamics of their joint prey. An emerging area is the impact of parasites on intraguild predation (IGP). Parasites can increase vulnerability of infected individuals to cannibalism or predation resulting in reversed species dominance in IGP hierarchies. We discuss the potential significance of parasites for community structure and biodiversity, in particular their role in promoting species exclusion or coexistence and the impact of emerging diseases. Ongoing invasions provide examples where parasites mediate native/invader interactions and play a key role in determining the outcome of invasions. We highlight the need for more quantitative data to assess the impact of parasites on communities, and the combination of theoretical and empirical studies to examine how the effects of parasitism scale up to community-level processes.     

Drifting plankton from a reservoir subsidize downstream food webs and alter community structure

Subsidy between ecosystems has been considered in many natural ecosystems, and should alter food webs and communities in human-impacted ones. We estimated how drifting plankton from a reservoir contribute to downstream food webs and showed that they alter community structures over a 10-km reach below the dam. To estimate the contribution of the drifting plankton to macroinvertebrates, we used C and N isotopes and an IsoSource mixing model. In spring and autumn, contributions of plankton to collector-filterer species were highest 0.2 km downstream of the dam, and clearly decreased from 0.2 to 10 km. At 0.2 km, the contribution of plankton to a predator stonefly was remarkably high. These results indicated that drifting plankton from a dam reservoir could subsidize downstream food webs and alter their energy base, but the importance of this subsidy decreased as distance from the reservoir increased. The general linear models indicated that the abundance of collector-filterers and predators was related positively to zooplankton density in stream water. Thus, food source alteration by drifting plankton also influenced the community structures downstream of the dam.     

Metals,trace elements,and organochlorine compounds in bottom sediment of Tuttle Creek Lake,Kansas, U.S.A.

Bottom-sediment cores were used to investigate the occurrence of 44 metals and trace elements, and 15 organochlorine compounds in Tuttle Creek Lake, a reservoir with an agricultural basin in northeast Kansas, U.S.A. On the basis of U.S. Environmental Protection Agency sediment-quality guidelines, concentrations of Ag, As, Cr, Cu, Ni, and Zn frequently or typically exceeded the threshold-effects levels for toxic biological effects. Organochlorine compounds either were not detected or were detected at concentrations generally below the threshold-effects levels. Statistically significant positive depositional trends were determined for several elements. However, because the vertical profiles of element concentrations typically indicated a bimodal distribution and much of the variability could be attributable to analytical variance, the statistical trends may not represent actual trends. DDE concentrations reflected the history of DDT use. Substantial increases in grain corn and soybean production, irrigated land, and hog production in the basin have not had a discernible effect on sediment quality in the reservoir. Future research focused on small impoundments throughout the basin may enhance understanding of the effects of human activity on sediment quality within the Tuttle Creek Lake system and elsewhere.