Nickel speciation in a nickel hyperaccumulating plant (Sebertia acuminata) and its associated soil of southern New Caledonia was studied using various analytical methods. The soil is formed of iron oxides (goethite, hematite), which contain almost all the nickel. The available nickel is probably linked to the organic matter in the litter. Sebertia acuminata, acts as a nickel pump, and concentrates the metal in its leaves. It partitions nickel and silica; nickel is concentrated in the cells (probably in the vacuoles) as organometallic complexes, whereas silica forms the framework of the cells, and the phytolithes. A thorough study of these plants seems essential in order to define the soil–plant relations, and to propose appropriate ways for ecological restoration. To cite this article: N. Perrier et al., C. R. Geoscience 336 (2004).相似文献
This study charts the presence of geography at liberal arts colleges and explores the relationship between the liberal arts and the study of geography. The results of this study reveal a paradox: geography embodies many of the ideals of a liberal arts education and yet this study indicates an absence of degree‐granting geography programs at 93% of institutions. Geography thrives, however, at a select group of liberal arts colleges, and these colleges are disproportionately important as the undergraduate origin for doctorate recipients in geography. 相似文献
The authors investigated the dead fragments of 22 species of submerged plants in the water from three limnological and trophical different water bodies (spring, river and pond). A total of 184 species of aquatic fungi, including 119 zoosporic and 65 conidial species were found on the fragments investigated plants. The most common fungus species were Aphanomyces laevis, Saprolegnia litoralis, Pythium rostratum (zoosporic fungi) and Acrodictys elaeidicola, Anguillospora longissima, Angulospora aquatica, Lemonniera aquatica, Mirandina corticola, Tetracladium marchalianum, Tetracladium maxiliformis, Trinacrium subtile (conidial fungi).
Most fungus species were observed on the specimens of Elodea canadensis (33 fungus species), Hippuris vulgaris f. submersa (33), Myriophyllum spicatum (34) and Potamogeton crispus (33), fewest on Ceratophyllum demersum (24), Fontinalis dalicarlica and Potamogeton nitens (each 25).
The most fungi were growing in the water from River Supraśl (107), the fewest in the water from Pond Dojlidy (99). Some aquatic fungus species were observed in the water of only one of the three water bodies – in Pond Dojlidy (30), in Spring Jaroszówka (32) and in the River Supraśl (39) species. Seventy-five species growing only on fragments of single submerged plants. A number of zoosporic and conidial species (22 and four, respectively) appeared new to Polish waters. Out of these 119 zoosporic species, some are known as parasites or necrotrophs of fish. 相似文献
We present a new three-dimensional SV-wave velocity model for the upper mantle beneath South America and the surrounding oceans, built from the waveform inversion of 5850 Rayleigh wave seismograms. The dense path coverage and the use of higher modes to supplement the fundamental mode of surface waves allow us to constrain seismic heterogeneities with horizontal wavelengths of a few hundred kilometres in the uppermost 400 km of the mantle.The large scale features of our tomographic model confirm previous results from global and regional tomographic studies (e.g. the depth extent of the high velocity cratonic roots down to about 200–250 km).Several new features are highlighted in our model. Down to 100 km depth, the high velocity lid beneath the Amazonian craton is separated in two parts associated with the Guyana and Guapore shields, suggesting that the rifting episode responsible for the formation of the Amazon basin has involved a significant part of the lithosphere. Along the Andean subduction belt, the structure of the high velocity anomaly associated with the sudbduction of the Nazca plate beneath the South American plate reflects the along-strike variation in dip of the subducting plate. Slow velocities are observed down to about 100 km and 150 km at the intersection of the Carnegie and Chile ridges with the continent and are likely to represent the thermal anomalies associated with the subducted ridges. These lowered velocities might correspond to zones of weakness in the subducted plate and may have led to the formation of “slab windows” developed through unzipping of the subducted ridges; these windows might accommodate a transfer of asthenospheric mantle from the Pacific to the Atlantic ocean. From 150 to 250 km depth, the subducting Nazca plate is associated with high seismic velocities between 5°S and 37°S. We find high seismic velocities beneath the Paraná basin down to about 200 km depth, underlain by a low velocity anomaly in the depth range 200–400 km located beneath the Ponta Grossa arc at the southern tip of the basin. This high velocity anomaly is located southward of a narrow S-wave low velocity structure observed between 200 and 500–600 km depth in body wave studies, but irresolvable with our long period datasets. Both anomalies point to a model in which several, possibly diachronous, plumes have risen to the surface to generate the Paraná large igneous province (LIP). 相似文献
13C/12C and 18O/16O ratios of aragonite shells of modern land snails from the southern Great Plains of North America were measured for samples from twelve localities in a narrow east-west corridor that extended from the Flint Hills in North Central Oklahoma to the foothills of the Sangre de Cristo Mountains in Northern New Mexico, USA. Across the study area, shell δ18O values (PDB scale) ranged from −4.1‰ to 1.2‰, while δ13C values ranged from −13.2‰ to 0.0‰. δ18O values of the shell aragonite were predicted with a published, steady state, evaporative flux balance model. The predicted values differed (with one exception) by less than 1‰ from locality averages of measured δ18O values. This similarity suggests that relative humidity at the time of snail activity is an important control on the δ18O values of the aragonite and emphasizes the seasonal nature of the climatic information preserved in the shells. Correlated δ13C values of coexisting Vallonia and Gastrocopta suggest similar feeding habits and imply that these genera can provide information on variations in southern Great Plains plant ecology. Although there is considerable scatter, multispecies, transect average δ13C values of the modern aragonite shells are related to variations in the type of photosynthesis (i.e., C3, C4) in the local plant communities. The results of this study emphasize the desirability of obtaining isotope ratios representing averages of many shells in a locale to reduce possible biases associated with local variations among individuals, species, etc., and thus better represent the “neighborhood” scale temporal and/or spatial environmental variations of interest in studies of modern and ancient systems. 相似文献