ARBUSCULAR MYCORRHIZAL FUNGI IN SUCCESSIONAL STAGES OF CAATINGA IN THE SEMI-ARID REGION OF BRAZIL

Caatinga is an exclusively Brazilian biome with areas in accentuated process of desertification. Arbuscular mycorrhizal fungi (AMF) act in plant succession by favoring the establishment of plant species typical of successional stages and by accelerating recovery leading to a climax stage. The objective of the present work was to evaluate the occurrence and diversity of AMF in successional stages of caatinga in the semi-arid region of Paraiba State. Experimental plots (30 x 60 m) were delimitated in 2007 in areas corresponding to different caatinga successional stages: early caatinga succession (natural revegetation during the previous 15 years); intermediate (natural revegetation for about 35 years); late (mature caatinga with more than 50 years without major disturbances;) and also in pasture areas fenced and protected to represent the initial phase of succession. Plots of all four stages were implemented with three replicates. Soil and root samples were collected in the experimental plots, from the 0-15 cm soil layer in the dry and in the rainy seasons. All areas presented low infectivity potential suggesting that the introduction of mycorrhizal seedlings may accelerate the process of revegetation of degraded soils in this region. Except for the areas of late stage, the glomalin reservoirs increased along with the advancement of the succession process. Areas in the late stage of succession presented greater richness of AMF species, indicating that the establishment of the vegetation also exerts a significant effect in the fungal community. Glomus and Acaulospora species were predominant in both seasons, possibly because they are well adapted to semi-arid conditions.