MYCORRHIZIC STATUS AND ITS VARIATION ON LEGUMES OF THE SONORAN DESERT

Leguminous trees of the Sonoran desert, plays a key role as nurse plants for some cactus and shrubs. The rhizospheres of three representativelegumes (Olneya tesota, Prosopis juliflora, and Parkinsonia microphylla)were sampled during four seasons, to evaluate the relationship with their associated arbuscular mycorrhizal fungi. The lower values of mycorrhizal colonization were founded in O. tesota (1.2%) and the highest in P. microphylla with 57% in spring and autumn respectively. Spores density ranged from 2,130 to 22,530 spores/dm(3) in P. microphylla and P. juliflora respectively. Mycelium biomass in soil was similar among the plants studied, ranging from 27-414 mg/dm(3), showing the lowest values on winter and gradually increasing in the following seasons, reaching the highest value in autumn. The seasonal behavior of mycorrhizae showed differences throughout the year, seasonality was the most significant factor to explain the plant-AMF interaction, suggesting that mycorrhizal association in these plants is defined by a strong interaction between climate, soil and biological factors.