Diversidade e potencial de infectividade de fungos micorrízicos arbusculares em área de caatinga, na Região de Xingó, Estado de Alagoas, Brasil

The region occupies 2800 km2, in the States of Pernambuco, Alagoas, Sergipe and Bahia, and constitutes a preserved part of the Northeastern semi-arid ecosystem. Evaluation of the diversity and density of propagules of arbuscular mycorrhizal fungi (AMF) in the soil, as well as of the mycorrhizal colonization in plants of the area was carried out by sampling of soil and roots during the dry (August/2000) and rainy (March/2001) seasons, in two subareas (Piranhas and Olho d'Agua do Casado) in Alagoas. More than 95% of the plants, among the 71 examined, formed arbuscular mycorrhiza (580% colonization). Among these 30 phanerogamic species, belonging to 14 families, only Pilosocereus sp. was not colonized. The average percentages of colonization (@ 16-20%) were similar in both sampling periods. There was an inverse relationship between number of spores and the most probable number (MPN) of infective propagules in the area of Olho d'Agua, with lower density of spores (< 2 spores.g-1 of soil) and higher MPN of propagules (4.7 and 11.6 spores.g-1 of soil), in the rainy and dry periods. Number of spores and MPN of propagules were similar in the Piranhas area during the rainy season; in the dry season the number of spores was 1.5 times higher than the MPN. Twenty-four taxa of AMF, mostly of Acaulosporaceaeand Glomaceae, were identified. The AMF are well represented, forming mycorrhizal association with most "caatinga" plants, despite the severe climatic limitations of the region.