Assessment of natural mycorrhizal potential in a desertified semiarid ecosystem.

A survey of the natural mycorrhizal potential has been carried out in a representative area of a desertified semiarid ecosystem in the southeast of Spain. Many indigenous plants from the field site were mycorrhizal, including the dominant Anthyllis cytisoides, which had high levels of colonization by arbuscular mycorrhizal fungi (AMF). Low numbers of AMF spores were present in the soil, although a range of species, including Scutellospora calospora, Glomus coronatum, Glomus constrictum, and several Acaulospora species, was represented. Soil infectivities, as determined by a soil dilution method, were similar for most plants tested but were significantly lower for Anthyllis cytisoides. Nevertheless, when a less disruptive method to determine soil infectivity was used, the importance of the mycelial network in maintaining the infectivity of soil under perennial shrubs, such as Anthyllis cytisoides, was highlighted. Seasonal variations in the mycorrhizal infectivity showed that it was higher towards the end of the summer period than in midwinter. In screening trials in a greenhouse, the indigenous AMF did not significantly improve the growth of plants compared with that of noninoculated controls. Augmentation of the soil with an inoculum of Glomus intraradices resulted in improved growth of Anthyllis cytisoides in both sterile and nonsterile conditions, in contrast to results obtained following inoculation with Glomus mosseae or another Glomus sp. Our findings suggest that the indigenous inoculum levels of AMF are inadequate to support an extensive revegetation program in the absence of an additional mycorrhizal inoculum.