Why are Halophytophthora species well adapted to mangrove habitats?

Halophytophthora species are commonly isolated from fallen mangrove leaves from early to late stages of decay. In this study we show that these organisms are well adpted to mangrove habitats as they have a wide tolerance to varying levels of pH, salinity and temperature. They also produce, abundant zoospores, and are chemotactically attracted to decaying mangrove leaves, and can readily attach to suitable substrata. In general, the four tested isolates (H. vesicula, H. avicennae, H. kandeliae and H. bahamensis) grew at pH 6-9, with maximum growth recorded at neutral pH. Vegetative growth and sporulation were observed over a wide range of salinities (from freshwater to marine) and temperatures, although optimum requirements varied from species to species. Zoospores of Halophytophthora spp. were chemotactically attracted to mangrove leaf-extracts and some other compounds that are common to the surrounding environment. The zoospores attached and germinated on both artificial (glass coverslips and polycarbonate membranes) and natural (mangrove leaves) substrata. Scanning electron micrographs show that newly attached zoospores, cysts, and germinating cystospores of H. vesicula produced fibrillar adhesive mucilage for attachement as was evident by debris sticking to their tips. More adhesive mucilage was produced by encysted and germinating cystospores on natural as compared to artificial substrata. Cystospores and germlings of H. vesicula and H. avicennae were also found to attach firmly to a perspex disc even after being subjected to a high shear stress of 3.19 Newton per square meter (Nm-2). Enzyme treatment and staining of attached cystospores indicate that the adhesive produced is composed of acidic polysaccharide with α-1, 4 linkages, and with either sulphate or phosphate functional groups. Once the cystospores were attached to the substratum, they could not be readily dislodged, and successful germination and colonization followed

Grain-scale pressure variations and chemical equilibrium in high-grade metamorphic rocks

ISSN:0263-4929ISSN:1525-131

Fungal endophytes associated with Kandelia candel (Rhizophoraceae) in Mai Po Nature Reserve, Hong Kong

We examined the endophytic fungi associated with the dominant mangrove plant, Kandelia candel, in Mai Po Nature Reserve, Hong Kong. Bark, woody tissue and leaves from four mature healthy trees were sampled for fungal endophytes in April and June, 2001. A total of 880 isolates was obtained, 595 from the June sampling. The highest number of fungal endophytes was cultured from bark (674 isolates) with only 63 from leaves. Three taxa of ascomycetes, 18 of anamorphic fungi and 29 mycelial morphotypes were identified. These results indicate a degree of tissue recurrence with similar endophytic fungal assemblages in bark and wood, and a different assemblage in the leaf samples. Dominant sporulating fungi of K. candel were Phomopsis sp., Pestalotiopsis sp., Guignardia sp. and Xylaria sp., which are cosmopolitan and common endophytic species. © 2008 by Walter de Gruyter

Chemical, petrological and structural analysis of syn-kinematic migmatites: insights from the Western Gneiss Region, Norway.

International audienceMigmatites in the inner part of collisional orogens are markers of past partial melting during burial and/or exhumation of their crustal root. If melt production has a softening effect as soon as the very first percents of melt are produced, as suggested by experimental data, then the exact timing of partial melting initiation and the complete duration of the melting event need to be estimated. The Western Gneiss Region (WGR), a basement window within the Norwegian Caledonides, presents excellent exposures of migmatites associated with (ultra)-high pressure (UHP) eclogites and amphibolitic gneisses, appropriate for a field study on the relationships between partial melting, (U)HP metamorphism and subsequent retrogression. Chemical analyses of natural leucosomes in the WGR define a trend from trondhjemitic to granitic compositions. Their relative chronology allows correlation between trondhjemitic compositions and early melting stages in one hand, and granitic compositions and late melting stages in the other hand (Labrousse et al., 2011). A broader sampling of leucosomes in the WGR and their systematic chemical analysis allows an expansion of the observed trend in space and time. The natural trondhjemitic to granitic trend of the leucosome compositions is comparable to experimental results obtained in vapor present partial melting experiments in piston-cylinder (Labrousse et al., 2011), implying that water-present partial melting may have occurred at depth in the Caledonides. While bulk compositions of leucosomes relate to the partial melting conditions and the beginning of partial melting episode, their petrography is relevant for the determination of their retrograde equilibration stage and the termination of the partial melting. The petrography of the leucosomes displays a great diversity in terms of mineral assemblages and compositions. However, early and late leucosomes have different mineral compositions, implying different retrograde PT paths. First results of syn-kinematic partial melting experiments on a natural gneiss from the low temperature realm of the WGR in a Paterson apparatus at ISTO Orléans indicate that partial melting does not occur at temperature below 850°C (i.e. maximum temperature estimate for the peak conditions in the WGR) without free water. Higher temperature and/or fluid present deformation experiments show partial melting textures with melts segregated in a vein network parallel to uniaxial stress. Both piston-cylinder and Paterson experiments suggest that the Caledonian syn-kinematic partial melting event in the WGR is due to vapor present melting reactions. Even if such a reaction is known and expected for the late stages of melting at amphibolite facies conditions, its relevance at higher pressures has strong implications on the hydration state of the continental crust at depth. Keywords: migmatite, leucosome, partial melting, Paterson experiments, Western Gneiss Region, (U)HP. Labrousse L., Prouteau G. and Ganzhorn A.-C., 2011, Continental exhumation triggered by partial melting at ultrahigh pressure: Geology, v. 39, n°12, p. 1171-1174, doi: 10.1130/G32316.1