AM FUNGAL ABUNDANCE AND ACTIVITY IN A CHRONOSEQUENCE OF ABANDONED FIELDS IN A SEMIARID MEDITERRANEAN SITE

When soils of semiarid areas are used for agriculture, their arbuscula r mycorrhizal (AM) fungal propagules undergo a series of changes, and when agricultural land is abandoned it is very difficult for these pop ulations and the plant cover to recover. We studied soils that have be en abandoned for different lengths of time (3-45 years) in a homogeneo us semiarid area in order to observe changes in their physical and che mical properties and in the AM fungi propagules, comparing them with s oils that continue to be cultivated and a soil that has never been cul tivated. The data we collected clearly showed that agricultural use re duces soil fertility and lowers AM fungi populations compared to the s oil kept in ifs natural state. After abandonment, there is a 5-year pe riod when the soils undergo a greater degree of degradation after whic h they slowly recover, with AM fungi propagules reaching values simila r to those of the virgin soil after 45 years or so. Although the physi cal and chemical properties followed a similar pattern of recovery, if was not possible to establish significant correlations between these parameters and the recovery of the AM fungi. Except in isolated cases, the distribution of AM fungi did nor seem to be influenced by positio n on the landscape, with their recovery appearing to be more influence d by the presence of host plants. In this sense, the rhizosphere of An thyllis cytisoides showed normal values of root infection and spore nu mbers even during the initial stages following abandonment.