Survival of inocula and native AM fungi species associated with shrubs in a degraded Mediterranean ecosystem

Reconstitution of the potential of soil mycorrhizal inoculum is a key step in revegetation programs for semiarid environments. We tested the effectiveness of inoculation with native arbuscular mycorrhizal (AM) fungi or with an allochthonous AM fungus, Glomus claroideum, with respect to the growth of four shrub species, the release of mycorrhizal propagules in soil, within and outside the canopy, and the improvement of soil structural stability. Two years after outplanting, the mixture of native endophytes was more effective than, for Olea europaea subsp. sylvestris, Retama sphaerocarpa and Rhamnus lycioides, or equally as effective as, for Pistacia lentiscus, the non-native AM fungus Glomus claroideum, with respect to increasing shoot biomass and foliar NPK contents. The increases in glomalin concentration and structural stability produced by inoculation treatments in the rhizosphere soil of the all shrub species, except R. lycioides, ranged from about 55 to 173% and 13 to 21%, respectively. The mixture of native AM fungi produced the highest levels of mycorrhizal propagules in soil from the center of the canopy of P. lentiscus and R. lycioides, while plants of O. europaea and R. sphaerocarpa inoculated with G. claroideum had more mycorrhizal propagules than did those inoculated with the mixture of native fungi. The number of mycorrhizal propagules in soil outside the canopy of the four shrub species was 5–35 times higher in inoculation treatments than in soil of the non-inoculated plants.