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Acacia trees play an important role in the restoration and maintenance of soil fertility. The aims of this study were to evaluate natural nodulation and arbuscular mycorrhizal fungi (AMF) colonization of the roots of three Acacia species (Acacia tortilis, A. ehrenbergiana, A. negrii) growing in South-western Saudi Arabia. Mycorrhizal status was assessed by microscopic observation of root fragments after trypan blue staining. Spore density was quantified and was expressed as the total number of spores per 100 g of soil. The occurrence of natural nodulation was also investigated. Mycorrhizal and nodulation intensity varied greatly between species. The roots of A. negrii had the highest AMF root colonization and nodulation (47±2.2 % and 27 nodules, respectively). Rhizosphere soils harbored AMF fungal spores ranging from 161.3 spore per 100 g of soil in A. tortilis to 423.3 spore per 100 g of soil in A. negrii. Thus, Acacia species investigated in this study are potentially useful for replanting degraded unfertile soils prevalent in most regions of Saudi Arabia.
Keywords: Arbuscular Mycorrhizal Fungi, Acacia, nodulation, Saudi Arabia