Formation of stable aggregates in rhizosphere soil of Juniperus oxycedrus: Effect of AM fungi and organic amendments

The effects of mycorrhizal inoculation, with an arbuscular mycorrhizal (AM) fungus (Glomus intraradices Schenck and Smith) or with a mixture of three AM fungi (G. intraradices, G. deserticola (Trappe, Bloss. and Menge) and G. mosseae (Nicol and Gerd.) Gerd. and Trappe), and addition of composted sewage sludge or Aspergillus niger-treated dry olive cake (DOC) residue on aggregate stabilisation of the rhizosphere soil of Juniperus oxycedrus were studied. The influence of such structural improvements on the establishment of J. oxycedrus was evaluated. Six months after planting, the inoculation with the mixture of three AM fungi and the combination of G. intraradices with both organic amendments had significantly enhanced the structural stability. Water soluble C and carbohydrates values were increased only with the addition of composted sewage sludge or fermented DOC. The addition of both organic amendments, particularly fermented DOC, decreased significantly the dehydrogenase, urease, protease and β-glucosidase activities. Rhizosphere soil from the inoculation treatments had higher dehydrogenase and β-glucosidase activities than control soil. Both the organic amendments addition and the mycorrhizal inoculation treatments increased significantly shoot biomass in J. oxycedrus. AM inoculation treatments were more effective with respect to increasing shoot biomass than the addition of organic amendments alone, and there were no significant differences between the two mycorrhization treatments (on average, about 53% higher with respect to control plants and about 18% higher with respect to plants grown in the amended soil).