Northern and Southern Forests of Socorro Island Harbor Different Communities of Arbuscular Mycorrhizal Fungi

Abstract

Arbuscular-mycorrhizal (AM) fungi affect individual plants and the diversity of plant communities. AM interactions are sensitive to the physical properties and nutrient availability of soil. In contrast to the comprehensive knowledge of AM fungi's diversity in many mainland ecosystems, there is a considerable gap in the understanding of the communities of AM fungi on oceanic islands. We surveyed the community of AM fungi in the wet forests of Socorro Island (above an elevation of 600 m). Because of the influence of northerly winds, the island's windward side is presumably more humid than the leeward side, although, above 600 m elevation, fog is common on both sides of the island. Forty-six percent of AM fungi species occurred on only one side of the island. Also, four species common to both sides showed marked differences in abundance, and the abundances of the AM fungi correlated with the abundance of plant life-forms. Beta diversity was similar in the southern and northern forests. However, the contribution of nestedness to beta diversity was three-fold greater in the southern forests than in the northern forests. Root colonization by AM fungi was higher in the northern forests, where phosphorous content was also high. The prevalence of nestedness in beta diversity and the lower mycorrhizal colonization of roots in the southern forests could reflect known perturbations in the southern forests.