AM fungal abundance and activity in a chronosequence of abandoned fields in a semiarid mediterranean site

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Abstract
When soils of semiarid areas are used for agriculture, their arbuscular mycorrhizal (AM) fungal propagules undergo a series of changes, and when agricultural land is abandoned it is very difficult for these populations and the plant cover to recover. We studied soils that have been abandoned for different lengths of time (3–45 years) in a homogeneous semiarid area in order to observe changes in their physical and chemical properties and in the AM fungi propagules, comparing them with soils that continue to be cultivated and a soil that has never been cultivated. The data we collected clearly showed that agricultural use reduces soil fertility and lowers AM fungi populations compared to the soil kept in its natural state. After abandonment, there is a 5‐year period when the soils undergo a greater degree of degradation after which they slowly recover, with AM fungi propagules reaching values similar to those of the virgin soil after 45 years or so. Although the physical and chemical properties followed a similar pattern of recovery, it 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 not seem to be influenced by position on the landscape, with their recovery appearing to be more influenced by the presence of host plants. In this sense, the rhizosphere o/Anthyllis cytisoides showed normal values of root infection and spore numbers even during the initial stages following abandonment.