MULTI-FUNCTIONALITY AND BIODIVERSITY IN ARBUSCULAR MYCORRHIZAS

Plant roots in natural ecosystems are typically colonized by a wide ra nge of fungi. Some of these are pathogenic, others appear to be opport unistic and have no apparent impact, while mycorrhizal fungi are gener ally regarded as mutualistic. Of the various types of mycorrhizal fung i, the arbuscular mycorrhizal (AM) association is by far the most abun dant and widespread. While the most widely accepted model of AM functi on depends upon plants benefiting from the facilitation of phosphorus uptake, recent data from field-based studies in temperate ecosystems i ndicate that only plant species with poorly branched root systems bene fit from AM fungi in this way: species with highly branched root syste ms may benefit in other ways, such as by being protected against root pathogenic fungi. These two responses apparently represent extremes al ong a continuum of AM benefit determined by root system architecture.