Effects of mycorrhizal inoculation of shrubs from Mediterranean ecosystems and composted residue application on transplant performance and mycorrhizal developments in a desertified soil

Arbuscular mycorrhizal inoculation and composted residue application are being assayed to aid restoration of desertified areas under Mediterranean climate. The particular objective of the present study was to assess the short-term (8 months) effects on the initial stages of plant performance and on mycorrhizal propagule release, key factors to decide further developments in the restoration process. Mycorrhizal inoculation, with Glomus intraradices, was practised during nursery production of representative shrub species from Mediterranean ecosystems and composted residues were added to soil before transplanting to a desertified area in southern Spain. Pistacia lentiscus, Rhamnus lycioides, Olea europaea subsp. sylvestris and Retama sphaerocarpa, key species from the natural succession in the target area, were the test plants. Mycorrhizal inoculation, and in some cases compost addition, improved the ability for nutrient acquisition by plants upon transplanting in the field. The number of "infective" mycorrhizal propagules was higher in soil around mycorrhiza-inoculated shrubs than that around the corresponding non-inoculated controls. The organic amendment significantly increased propagule production in the rhizosphere of mycorrhiza-inoculated plants. The number of mycorrhizal spores was relatively low in soil around transplants, being hardly affected by treatments. Only three distinguishable glomalean spore morphotypes were found, belonging to the species Glomus geosporum, G. contrictum and Scutellospora calospora, with very few unidentified spores, corroborating the low diversity in degraded ecosystems. An increased development of the extramatrical AM mycelium was found in soil around the roots of the four mycorrhiza-inoculated test plants, probably the main source of AM fungal propagules in the ecosystem at this stage of plant development. In conclusion, the tailored AM inoculation assayed was functioning under field conditions to enhance nutrient acquisition by the target indigenous shrubs and, in interaction with organic amendments, promoted mycorrhizal propagule production in soil, critical factors to benefit further stages of the revegetation process.