Colonisation patterns of supralittoral arthropods in naturally stranded wrack debris on Atlantic sandy beaches of Brazil and Spain

From an ecosystem perspective, wrack debris represents a key element for the maintenance of biodiversity and functioning of sandy beaches. Here, we characterised the colonisation patterns of supralittoral assemblages associated with wrack accumulations (seaweed and mangrove propagules) on multiple Atlantic sandy beaches (southern Brazil and south-western Spain). By using a manipulative field experiment, we sought to determine the temporal changes of the density, diversity and the structure of the whole community during the colonisation of wrack debris, and whether the colonisation patterns in response to the stranding of natural wrack debris were different on local (between beaches) and regional (between Atlantic regions) scales. Our results showed increases in density and diversity during the first 3 days after the stranding of seaweeds and mangrove-propagules debris. Moreover, wrack debris was promptly invaded by a wide range of species (i.e. talitrids, dipterans, coleopterans and spiders), although the colonisation pattern was slower in southern Brazil (16-day period) than in south-western Spain (3-day period). Wrack-debris characteristics (e.g. amount, degradation and composition) combined with biological strategies (e.g. trophic guilds and mobility) of supralittoral species could explain the different colonisation patterns in each Atlantic region. The temporal changes of wrack-associated fauna can have potential effects on the wrack-derived process and food-web structure on sandy beaches.

Characterisation of theFusarium graminearum-Wheat Floral Interaction

Fusarium Ear Blight is a destructive fungal disease of cereals including wheat and can contaminate the crop with various trichothecene mycotoxins. This investigation has produced a newβ-glucuronidase (GUS) reporter strain that facilitates the quick and easy assessment of plant infection. The constitutively expressedgpdA:GUSstrain ofFusarium graminearumwas used to quantify the overall colonisation pattern. Histochemical and biochemical approaches confirmed, in susceptible wheat ear infections, the presence of a substantial phase of symptomless fungal growth. Separate analyses demonstrated that there was a reduction in the quantity of physiologically active hyphae as the wheat ear infection proceeded. A simplified linear system of rachis infection was then utilised to evaluate the expression of severalTRIgenes by RT-qPCR. Fungal gene expression at the advancing front of symptomless infection was compared with the origin of infection in the rachis. This revealed thatTRIgene expression was maximal at the advancing front and supports the hypothesis that the mycotoxin deoxynivalenol plays a role in inhibiting plant defences in advance of the invading intercellular hyphae. This study has also demonstrated that there are transcriptional differences between the various phases of fungal infection and that these differences are maintained as the infection proceeds.

The root surface as the definitive detail for microbial transformation processes in constructed wetlands – a biofilm characteristic

It was the goal of the investigations to characterise the biofilm on the plant roots because of the demonstrable major role of these associated bacteria. The essential criteria for the research were to look at the structure of the microbial colonisation (pattern, density) and to determine properties of the rhizoplane biofilm such as thickness and structure. The root material from a hydroponic system, planted with Glyceria maxima and used for nitrogen removal, has been used for the investigations. Several properties of the bacteria became visible due to the application of specific dyes. The evaluation of the samples was performed by scanning confocal laser microscopy (CLSM). It was shown that the microbial colonisation of the root surface of Glyceria maxima was on an unexpected high level and seems to be related mainly to the permeability and therefore to the age of the plant roots. The thickness of the rhizoplane biofilm is remarkably thin; no inactive layers could be observed in contrast to biofilm growing on technical carrier material. Caused by the untypically two-sided supply with nutrients the whole biofilm is in interaction with the surroundings. This indicates the importance of the plant roots for the microbial transformation processes in wetlands and underlines the especialness of the root as carrier for microorganisms.