Biomasse microbienne et "statut organique" des sols tropicaux : exemple d'un sol vénézuélien des Llanos sous différents systèmes de culture

National audienc

Mycorrhizal dependency of micropropagated argan tree (Argania spinosa) :I. Growth and biomass production

International audienc

Rôle des mycorhizes dans l'alimentation hydrique et minérale des plantes, notamment des ligneux de zones arides

National audienc

The effect of sewage sludge and sludge compost on soil microflora.

The production of organic wastes is an increasing phenomenon worldwide, while soils are witnessing a progressive reduction of their organic content. The new concern regarding the productivity and sustainability of agro-ecosystems leads to the formulation of a new approach to soil management, which stresses the recycling in soil of waste organic matter. The utilisation of waste organic matter as soil conditioners is meeting with difficulties because of the very particular nature of these wastes. Sewage sludge and related products could in fact be harmful for the environment and human health because of their content of xenobiotic compounds and microbial pathogens. Such hazards can be eliminated, or at least decreased to a very low level, through sanitation treatments and through a better knowledge of the fate of chemical pollutants in soil. The beneficial effects of sewage sludge and sludge compost on the physical soil structure and microbial biomass are summarised together with the possible negative role played by these wastes when heavily contaminated by xenobiotic compounds

Effet de la mycorhization controlée sur la croissance de l'arganier (Argania spinosa) après sa transplantation en sol non infesté

National audienc

Decomposition de corps microbiens dans des sols fumiges au chloroforme: Effets du type de sol et de microorganisme

International audienceve microbial species (Aspergillusflaous, Trichoderma viride, Streptomyces sp., Arthrobacter sp., Achromobacter liquefuciens) were cultivated in liquid media containing ‘Wabelled glucose. The decomposition of these microorganisms was recorded in four different soils after chloroform fumigation by a technique related to that proposed by Jenkinson and Powlson, to determine the mineralization rate of microbial organic matter (K, coefficient). Three treatments were used: untreated soil, fumigated soil alone and fumigated soil suuplied with “C-labelled cells. Total evolved CO, and WO, were measured after 7 and 14 days at 28”6.‘ The labelled microorganisms enabled the calculation of mineralization rate I& (K, = mineralized microbial carbon/supplied microbial carbon). The extent of mineralization of la.belled microbial carbon depended on the type-of soil and on the microbial species. Statistical analysis of results at 7 days showed that 58% of the variance is taken in account by the soil effect and 32% by the microorganism effect. Between 35 and 49% of the supplied microbial C was mineralized in 7 days according to the soil type and the species of microorganism. Our results confirmed that the average value for K, = 0.41 is acceptable, but K, variability according to soil type must be considered. The priming effect on organic C and native microbial biomass mineralization, due to microbial carbon addition was obtained by comparison between the amount of non-labelled CO,-C produced by fumigated soils with or without added labelled microorganisms: this priming effect was generally negligible. These results indicate that the major portion of the error of microbial biomass measurement comes from the K, estimation

Soil microbial biomass and in situ nitrogen mineralization after 20 years of different nitrogen fertilization and forage cropping systems

International audienc

Cumulative Effects of Short-Term Polymetal Contamination on Soil Bacterial Community Structure

In this study we evaluated the short-term effects of copper, cadmium, and mercury, added singly or in combination at different doses, on soil bacterial community structure using the bacterial automated ribosomal intergenic spacer analysis (B-ARISA) fingerprinting technique. Principal-component analysis of B-ARISA profiles allowed us to deduce the following order of impact: (Cu + Cd + Hg) >> Hg ≥ Cd > Cu. These results demonstrated that there was a cumulative effect of metal toxicity. Furthermore, the trend of modifications was consistent with the “hump-backed” relationships between biological diversity and disturbance described by Giller et al. (K. E. Giller, E. Witler, and S. P. McGrath, Soil Biol. Biochem. 30:1389-1414, 1998)

Recherches sur l'arganier

National audienc

Rôle de l'Arganier dans la fertilité des sols

International audienc