The mycorrhizal status of several representative shrub species
(Lavandula spp. and Thymus satureioides) in Moroccan semiarid
ecosystems, was evaluated as well as their contribution to the
mycorrhizal potential of the soil. Furthermore, the rhizosphere soils
collected under these target species were tested for their influence on
the growth of Cupressus atlantica, a tree species whose natural stands
has declined in this area. Soil samples were collected from the
rhizosphere of L. stoechas, L. dentata and of C. atlantica existing in
the experimental area. Control samples were randomly collected from bare
soil sites, away from plant influence. All the target species formed AM
symbiosis and the extent of AM fungal colonization was not signiÞcantly
different between plant species. No signiÞcant difference was detected
between the total number of AM fungal spores of the bare soil and those
recorded in the root zones of target species and C. atlantica. Three
genera of AM fungi (Scutellospora, Glomus and Acaulospora) were present
in the rhizospheres of the plant species and in the bare soil.The number
of mycorrhizal propagules in soil originating from around the four
target plant species was signiÞcantly higher than the one in the bare
soil (Figure 1). The most probable number (MPN) of mycorrhizal
propagules per 100 g of dry soil ranged from 7.82 (bare soil) to 179.7
(L. dentata and C. atlantica) and 244.5 (L. stoechas and T.
satureioides). As the total number of spores was not different for the
soil of different origins, the increase of the mycorrhizal soil
infectivity (MSI) mainly resulted from larger AM mycelial networks that
constituted the main source of AM fungal inoculum. In addition, this MSI
enhancement was linked with changes in the functioning of soil microbial
communities. In a glasshouse experiment, the growth of C. atlantica
seedlings was significantly higher in the C. atlantica and in the shrub
species soils than in the bare soil. Although the AM inoculum potential
is not sufficient to ensure the development of forest trees in
Mediterranean ecosystems, the use of plant nurses such as T.
satureioides or Lavandula spp. could be of great interest to restore a
self-sustaining vegetation cover to act against desertification.