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To better constrain Li dynamics in the tropics, we sampled critical zone compartments of a small forested andesitic catchment in Guadeloupe (soils, parent rock, atmospheric dust, plants, soil solutions, stream and rain waters). The aims of this study are to identify the origin of Li in the different compartments and to better characterize the behavior of Li and its isotopes during water–rock interaction in a highly cation-depleted soil. The Li isotope signature (δ 7 Li) of throughfall samples varies between + 11.2‰ and + 26.4‰. As this is lower than the seawater signature (31‰) and vegetation does not fractionate Li isotopes, our data indicate that Saharan dust (− 0.7‰) significantly contributes to the throughfall signature. Li isotope composition measured in a 12.5 m deep soil profile varies from + 3.9‰ near the surface to − 13.5‰ at 11 m depth. Compared to unweathered andesite (+ 5‰), the deep soil signature is in agreement with preferential incorporation of light Li into secondary minerals. In the top soil however, our results also emphasized that atmospheric deposition (wet and dry) is a main source of Li to the soil. The decreasing δ 7 Li with increasing depth is consistent with a vertical gradient of incorporation of heavy atmospheric Li, this input being maximal near the surface. At the catchment scale, throughfall and total atmospheric inputs (sea salts + Saharan dust) provide 12.1 and 23.9 g Li yr − 1 respectively to the Quiock Creek catchment. These fluxes represent 34% and 67%, respectively, of Li exported at the outlet indicating that atmospheric deposition is one of the main Li inputs to the critical zone. Li concentration and isotopic mass balance at the catchment scale indicate that in addition to atmospheric deposition, secondary mineral phase dissolution is a major solute source and that andesite no longer participates in significant production of Li. [ABSTRACT FROM AUTHOR]

The detection of mitochondrial DNA (mtDNA) in living human cells could be useful for understanding mitochondrial behaviour during cellular processes and pathological mtDNA depletions. However, until now, human mtDNA has not been visualized in living cells with fluorescence microscopy, although it has been easily detected in organisms with larger mtDNA. Previous reports have stated that mtDNA staining results in homogeneous fluorescence of mitochondria or that animal mitochondria are refractory to DAPI staining. This paper shows that mtDNA of cultured green monkey kidney CV-1 can be stained using a very low concentration of DAPI, then detected by a cooled Photometrics CCD camera with 14-bit resolution detection. Indeed, under these conditions CV-1 cells have small fluorescent spots in the cytoplasm that colocalize with mitochondria, even after mitochondrial movements, uncoupling by carbonyl cyanide p-(trifluoromethoxy)phenylhydrazone and swelling. These observations have been reproduced for the human fibroblast foreskin cell line HS68. These results and known properties of DAPI as a specific DNA stain strongly suggest that mtDNA can be detected and visualized by fluorescence microscopy in human living cells, with potential developments in the study of mtDNA in normal and pathological situations. [ABSTRACT FROM AUTHOR]

Oxidation of particulate organic carbon (POC) during fluvial transit releases CO2 to the atmosphere and can influence global climate. Field data show large POC oxidation fluxes in lowland rivers; however, it is unclear if POC losses occur predominantly during in-river transport, where POC is in continual motion within an aerated environment, or during transient storage in floodplains, which may be anoxic. Determination of the locus of POC oxidation in lowland rivers is needed to develop process-based models to predict POC losses, constrain carbon budgets, and unravel links between climate and erosion. However, sediment exchange between rivers and floodplains makes differentiating POC oxidation during in-river transport from oxidation during floodplain storage difficult. Here, we isolated inriver POC oxidation using flume experiments transporting petrogenic and biospheric POC without floodplain storage. Our experiments showed solid phase POC losses of 0%–10% over ∼10³ km of fluvial transport, compared to ∼7% to >50% losses observed in rivers over similar distances. The production of dissolved organic carbon (DOC) and dissolved rhenium (a proxy for petrogenic POC oxidation) was consistent with small POC losses, and replicate experiments in static water tanks gave similar results. Our results show that fluvial sediment transport, particle abrasion, and turbulent mixing have a minimal role on POC oxidation, and they suggest that POC losses may accrue primarily in floodplain storage. [ABSTRACT FROM AUTHOR]