The mycorrhizal status of Phragmites australis in several polluted soils and sediments of an industrialised region of Northern Portugal

Roots of Phragmites australis from three polluted soils and sediments (a pe riodically flooded stream bank containing organic pollutants, a high-pH dry ing sedimentation pond and an acidic, periodically flooded sand polluted by industrial effluents) were sampled over a 1-year cycle of plant growth to assess the degree of colonisation by arbuscular mycorrhizal fungi (AMF). At the dry sedimentation pond, root samples of Juncus effusus and Salix atroc inerea were also taken to assess the presence of AMF throughout the year. R oot colonisation was low (<5% root length colonised) but arbuscule presence peaked in P. australis during the spring and autumn prior to flowering. Th ese changes in arbuscule abundance were also seen in a parallel greenhouse trial using seed taken from one of the sites. Roots of J. effusus contained mainly vesicular colonisation but arbuscule activity peaked during the win ter months (December-March). S. atrocinerea roots were found to be ectomyco rrhizal throughout the year but the fine feeder roots were colonised by AMF The results confirm that semi-aquatics, like P. australis, can become arbu scular mycorrhizal but that this status changes during the year depending o n soil moisture content and plant phenology. The influence of AMF in these polluted soils is uncertain but the potential exists to establish a more di verse plant ecosystem during the landscaping of these areas (phytostabilisa tion) by management of adapted plant and AMF ecotypes.