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The dispersal capacity of vegetative propagules of riparian fen species
No full textFlowing water can disperse a high number of seeds and vegetative propagules over long distances and is therefore a very important dispersal vector in wetland habitats. Although the dispersal of seeds is relatively well studied, the dispersal of vegetative propagules has received less attention. However, in riparian and aquatic systems where many species have clonal growth forms, it can be very important. The relative importance of vegetative propagules in the dispersal of fen species was assessed first by determining their relative abundance in the field and second, by determining the buoyancy of plant fragments of ten fen species experimentally. On average, vegetative propagules made up 3.2–58.9% of the total propagule number (mainly Elodea nutallii). Buoyancy of the tested species ranged from 25 days to over 6 months. Surprisingly, the propagules of Stratiotes aloides and Hydrocharis morsus-ranae increased buoyancy when spring started (after ca. 100 days). The results demonstrate that vegetative propagules of riparian and aquatic fen species have a high capacity to disperse over long distances via water and are therefore likely to play an important role in the colonisation of new habitats. Especially because in nine out of the ten species tested, over 50% of the propagules were still viable after 6 months of floating.
Isolation of Arthrobacter species from the phyllosphere and demonstration of their epiphytic fitness
No full textBacteria of the genus Arthrobacter are common inhabitants of the soil environment, but can also be recovered from leaf surfaces (the phyllosphere). Using enrichment cultures on 4-chlorophenol, we succeeded in specifically isolating Arthrobacter bacteria from ground cover vegetation in an apple orchard. Based on 16S rRNA gene sequencing, the isolates were found to belong to at least three different species of Arthrobacter. Compared to the model bacterial epiphyte Pantoea agglomerans, the Arthrobacter isolates performed as well or even better in a standardized laboratory test of phyllosphere fitness. A similar performance was observed with the well-characterized soil isolate Arthrobacter chlorophenolicus A6. These findings suggest that the frequently reported presence of Arthrobacter strains on plant foliage can be explained by the capacity to multiply and persist in the phyllosphere environment. As bacteria from the genus Arthrobacter are known for their ability to degrade a wide variety of organic pollutants, their high phyllosphere competency marks them as a promising group for future studies on phyllosphere-based bioremediation, for example, as foliar bioaugmentation on ground cover or buffer-zone vegetation to prevent pesticides from reaching soil, surface-, or groundwater.
Alternative states and population crashes in a resource-susceptible-infected model for planktonic parasites and hosts
No full text1. Despite the strong impact parasites can have, only few models of phytoplankton ecology or aquatic food webs have specifically included parasitism.
2. Here, we provide a susceptible-infected model for a diatom-chytrid host–parasite system that explicitly includes nutrients, infected and uninfected hosts, reproduction of the parasite on the hosts and free-living infective stages.
3. A distinguishing feature of the model is that parasite reproduction on host increases with nutrient availability to the infected host, as has been observed for many parasites and viruses.
4. It follows from this assumption that the parasite’s basic reproduction number, R0, increases with nutrient concentration, because at higher nutrient concentrations, infected hosts consume more nutrients that are used for the reproduction of the parasite.
5. Another important result is that there may be two alternative states to which population densities can converge: one with only the host and one with host and parasite co-existing. In the latter, the parasite can invade a host population only if it is introduced above a threshold density.
6. Furthermore, the model shows a strong tendency for host–parasite cycles, which may be chaotic. Nutrient enrichment leads to increasing amplitude of these cycles, which may cause host or parasite population extinction caused by stochastic fluctuations during periods of low population density, which is the Paradox of Enrichment.
7. Finally, if alternative states and cycles co-occur, increased population cycle amplitude may drive the parasite below its threshold density for successful invasion, causing parasite extinction in a ‘deterministic Paradox of Enrichment’. Published results confirm that host–parasite cycles and collapse of host–parasite systems may occur in real plankton communities.
8. Our results underline that ecological detail in host–parasite models may have consequences for disease dynamics that may be overlooked when ecological interactions between environment, host and parasite are not explicitly taken into account.
Draft Genome Sequence of the Phyllosphere Model Bacterium Pantoea agglomerans 299R
No full textBacteria belonging to the genus Pantoea are common colonizers of plant leaf surfaces. Here, we present the draft genome sequence of Pantoea agglomerans 299R, a phyllosphere isolate that has become a model strain for studying the ecology of plant leaf-associated bacterial commensals.
Testing the Stress Gradient Hypothesis in herbivore communities: facilitation peaks at intermediate nutrient levels
No full textThe role of positive interactions in structuring plant and animal communities is increasingly recognized but the generality of current theoretical models has remained practically unexplored in animal communities. The Stress Gradient Hypothesis predicts a linear increase in the intensity of facilitation as environmental conditions become increasingly stressful, whereas other theoretical models predict a maximum at intermediate environmental stress. We tested how competition and facilitation between herbivores change over a manipulated gradient of nutrient availability. We studied the effect of grazing by pond snails (Lymnaea stagnalis L.) as bulk grazers on aquatic caterpillars (Acentria ephemerella Denis & Schiffermüller) as small specialist grazers along an experimental gradient of environmental nutrient concentration. Higher nutrient levels increased overall total plant biomass but induced a shift towards dominance of filamentous algae at the expense of macrophytes. Facilitation of caterpillars by snail presence peaked at intermediate nutrient levels. Both caterpillar biomass and caterpillar grazing on macrophytes were highest at intermediate nutrient levels. Snails facilitated caterpillars possibly by removing filamentous algae and increasing access to the macrophyte resource, whereas they did not affect macrophyte biomass or C:nutrient ratios, a measure of food quality. We conclude that competition and facilitation in herbivore communities change along nutrient availability gradients that affect plant biomass and community composition. Understanding how interspecific interactions may change in strength and direction along environmental gradients is important to predict how the diversity and structure of communities may respond to the introduction or removal of herbivore species in ecosystems.
Read More: http://www.esajournals.org/doi/abs/10.1890/12-1175.1
Methylomonas paludis sp. nov., the first acid-tolerant member of the genus Methylomoas, from an acidic wetland
No full textAn aerobic methanotrophic bacterium was isolated from an acidic (pH 3.9) Sphagnum peat bog in north-eastern Russia and designated strain MG30T. Cells of this strain are Gram-negative, pale-pink-pigmented, non-motile, thick rods that are covered by large polysaccharide capsules and contain an intracytoplasmic membrane system typical of type I methanotrophs. They possess a particulate methane monooxygenase enzyme (pMMO) and utilize only methane and methanol. Carbon is assimilated via the ribulose-monophosphate pathway; nitrogen is fixed via an oxygen-sensitive nitrogenase. Strain MG30T grows in a pH range of 3.8-7.3 (optimum pH 5.8-6.4) and at temperatures between 8 and 30°C (optimum 20-25°C). The major cellular fatty acids are C16:1ω5t, C16:1ω8c, C16:1ω7c, and C14:0; the DNA G+C content is 48.5 mol%. The isolate belongs to the family Methylococcaceae of the class Gammaproteobacteria and displays 94.7-96.9% 16S rRNA gene sequence similarity to members of the genus Methylomonas. However, strain MG30T differs from all taxonomically characterized members of this genus by the absence of motility, the ability to grow in acidic conditions, and low DNA G+C content. Therefore, we propose to classify this strain as a novel, acid-tolerant species of the genus Methylomonas, Methylomonas paludis sp. nov. Strain MG30T (=DSM 24973T = VKM B-2745T) is the type strain.
What is the influence on water quality in temperate eutrophic lakes of a reduction of planktivorous and benthivorous fish? A systematic review protocol
Get PDFCase study on the efficacy of a lanthanum-enriched clay (Phoslock®) in controlling eutrophication in Lake Het Groene Eiland (The Netherlands)
Get PDFLake Het Groene Eiland was created in the beginning of 2008 by construction of dikes for isolating it from the surrounding 220-ha water body. This so-called claustrum of 5 ha was treated using lanthanum-modified clay (Phoslock®) to control eutrophication and mitigate cyanobacterial nuisance. Cyanobacteria chlorophyll-a were significantly lower in the claustrum than those in the reference water body, where a massive bloom developed in summer, 2008. However, PO4-P and TP did not statistically differ in these two waters. TN and NO3-N were significantly lower in the claustrum, where dense submerged macrophytes beds developed. Lanthanum concentrations were elevated after the applications of the modified clay in the claustrum, but filterable lanthanum dropped rapidly below the Dutch standard of 10.1 μg l−1. During winter, dozens of Canada geese resided at the claustrum. Geese droppings contained an average of 2 mg PO4-P g−1 dry weight and 12 mg NH3-N g−1 dry weight and might present a growing source of nutrients to the water. Constructing the claustrum enabled unrestricted bathing in subsequent three summers, as no swimming bans had to be issued due to cyanobacteria blooms. However, the role of the modified clay in this positive outcome remains unclear, and longevity of the measures questionable.