No abstract

The method described herein permitted production of three to four micropropagules of Acacia Senegal from one uninodal explant. The explants were taken from plants produced either in a sterile environment or during four years in a greenhouse. Zeatin or 6-benzylaminopurine (BAP) were mixed, at different concentrations, with Murashige and Skoog's medium (MS) of which the amount of macroelements was divided in half (MS mod.). At a concentration of 5.0×10(-5) M, zeatin produced a better multiplication rate after 60 d for the two types of plant stock than did BAP. A two stage process was necessary to obtain a rooting rate of the small cuttings close to 100%. The first stage, called induction, consisted of leaving the cuttings for 6 to 12 d on a Jordan's medium (JN) of which the amount of macroelements was reduced by half (JN mod.) and in which NAA at a concentration of 5.0×10(-5) M was added. The second stage, called root extension, required that the small cuttings be planted on this second hormone-free medium. Roots appeared after a few days. Acclimatization in a greenhouse occured with a survival rate of close to 100% when the rooted in vitro plants were transplanted to pots containing a mixture of vermiculite and top soil (1∶1; v/v).

The relationships between microorganisms and microfauna were studied in an evergreen oak ( Quercus ilex L.) forest floor located in a French Mediterranean region characterized by hot and dry summers. The soil was a brown fersialitic soil with an amphimull, i.e., a mull with a thick litter. A micromorphological study of both litter and organomineral layers was used to observe relationships between white-rot fungi and fauna, such as oribatids, millipedes, enchytraeids, and earthworms. Microbiological properties of the litter and physicochemical properties of the soil were analysed. Enchytraeids comminute the faeces of other animals, whereas earthworms form aggregates. These two opposite actions probably modify aeration and water movements in deeper layers. Brown leaves and animal faeces constitute a nutritional substrate for white-rot fungi and other animals. Inside degraded cells of rootlets and bleached leaves, fungi form calcium oxalate crystals because the absorbent complex is saturated by an excess of calcium. Enzymes such as laccases, manganese peroxidases, cellulases, or xylanases were detected in the litter at significant levels. The high activity values of phosphatases in the litter could reflect a deficiency in available phosphorus. This deficiency could partly explain a low rate of litter degradation and the presence of an OH sublayer.