Short-term variations of bacterioplankton in Antarctic zone: Terre Adelie area.

Previous studies on Antarctic seawater have demonstrated the presence of significant numbers of bacteria, but their in situ activity has not been demonstrated. In order to demonstrate this hypothetical activity, a scheduled survey was conducted from January to February 1986 in a coastal area of Adelie Land. Seawater samples were collected in a selected station every day or every hour during a 17 hour period. Bacterial communities in each sample were studied by measuring direct and viable counts, frequency of dividing cells estimation, taxonomic analysis, and heterotrophic potential. Complementary studies used batch cultures with artificial nutrient supplements. The results clearly suggest a strong potential activity of the natural Antarctic bacterial microflora.

[Effect of application of a herbicide propyzamide into the soil by study of mineralization of glucose 14C(U) and distribution of radioactivity in various fractions of the soil (laboratory and open field tests)]. / Influence de l'application d'un herbicide le propyzamide dans le sol par l'étude de la minéralisation du glucose 14C(U) et de la répartition de la radioactivité dans différentes fractions du sol (essais en laboratoire et en plein champ).

The effects of the herbicide PROPYZAMIDE are studied in laboratory and field conditions. The modifications involved are characterized by measurement of 14C-glucose mineralization and radioactivity incorporation into the soil fractions. In laboratory conditions, temperature and moisture are kept stable and the experiment is performed during less than 24 hours. In these conditions, Kerb 50 (commercial formulation of propyzamide) and the emulsifier (material used in propyzamide formulation) exert little effect on 14CO2 evolution. In field conditions, propyzamide andKerb 50 are applied once at two different doses: at field rate (1,5 kg/ha) and twentyfold this rate. Essays are duplicated. The herbicide (propyzamide in Celanol and Kerb 50) and the emulsifiers alone (Celanol and the material used in propyzamide formulation) are applied on the soil surface (application date: 3.02.81). Two weeks later and then every month during four months, samples are taken to the depth of about 5 cm (Propyzamide migrates very slowly in the first centimeters of the soil). The characterization experiment is performed on 10 g soil samples by 14C-glucose incubation at 28 degrees C during two hours. 14CO2 evolved is measured after incubation and acidification with HCl. Then radioactivity distribution in the soil is counted after chemical fractionation of soil. This distribution is about 10-16.5% as 14CO2, 22-37% in the acid-soluble fraction, 10-25% in the alkali-soluble fraction and 15-45% in the human fraction (measured as 14CO2 evolved after combustion). This distribution is little modified by the herbicides or the emulsifiers but its evolution is significantly related to environmental conditions (temperature). Nevertheless a few modifications are observed. They can be due to the herbicide propyzamide itself but the emulsifiers and the degradation products of propyzamide can also influence the measurement (After forty days in the soil, 70-95% of the starting active ingredient have disappeared). They can also be a result of the initial effects of the products (modification of the microflora and of the environment).