No abstract

An inventory of commercial timber species was undertaken in two peri-urban forests of Brazzaville, the continental site of Djoumouna and the Loufézou island site. This inventory was strengthened by the analysis of phytosociological and structural vegetation data. These two habitats have a basal area of 35.7 and 53 m 2 /ha, respectively. The floristic matrix, dominated by Fabaceae, projects a richness of 51 species emanating respectively from 462 and 414 individuals of Ddh ≥ 10 cm. Pentaclethra eetveldeana De Wild. & T. Durand and Pentaclethra macrophylla Benth., dominated the structural framework in the continental forest, both in the basal area and the significance of value index. On the island site, Antiaris toxicaria Lesch var. welwitschii (Engl.) Berg and Ceiba pentandra (L.) Gaertn., on the one hand, and Pterocarpus soyauxii Taub. and Pentaclethra eetveldeana De Wild., on the other hand, take turns for both parameters. The continental site is richer and more diversified compared to its island neighbor. All the same, these two particular habitats project a good structure in commercial timber in relation to the ecological maturity of these forest sites. This feature militates in favour of the elaboration of management plans as a precautionary measure.

Although mechanisms involved in response of Saccharomyces cerevisiae to osmotic challenge are well described for low and sudden stresses, little is known about how cells respond to a gradual increase of the osmotic pressure (reduced water activity; a w) over several generations as it could encounter during drying in nature or in food processes. Using glycerol as a stressor, we propagated S. cerevisiae through a ramp of the osmotic pressure (up to high molar concentrations to achieve testing-to-destruction) at the rate of 1.5 MPa day-1 from 1.38 to 58.5 MPa (0.990-0.635 a w). Cultivability (measured at 1.38 MPa and at the harvest osmotic pressure) and glucose consumption compared with the corresponding sudden stress showed that yeasts were able to grow until about 10.5 MPa (0.926 a w) and to survive until about 58.5 MPa, whereas glucose consumption occurred until 13.5 MPa (about 0.915 a w). Nevertheless, the ramp conferred an advantage since yeasts harvested at 10.5 and 34.5 MPa (0.778 a w) showed a greater cultivability than glycerol-shocked cells after a subsequent shock at 200 MPa (0.234 a w) for 2 days. FTIR analysis revealed structural changes in wall and proteins in the range 1.38-10.5 MPa, which would be likely to be involved in the resistance at extreme osmotic pressure.