Ecological strategies of ectomycorrhizal fungi of Salix repens: root manipulation versus root replacement

The ecological significance of a range of ectomycorrhizal fungal species, associated with Salix repens, was investigated under controlled conditions. Different ectomycorrhizas increased plant benefits in various ways. Effects of 12 ectomycorrhizal fungi on short-term (12 weeks) and long-term (20 and 30 weeks) plant performance were compared. Different fungi increased plant benefits in different ways and none exerted the full range of mycorrhizal benefits. Two strategies of EcM fungi were recognized, root manipulation and root replacement. Species (Hebeloma, Cortinarius spp.) with a root manipulation strategy strongly increased root length and had a more effective nitrogen economy than species with the root replacement strategy (Laccaria, Paxillus spp.). As a consequence of these different strategies two parameters of nutrient acquisition, viz. nutrient inflow per unit root length (efficiency) and total shoot nutrient uptake (effectiveness) were not correlated. Differences in magnitude of mycorrhizal response were not related to the amount of root colonization. Only in the short term was plant nutrient content positively correlated with root length colonized. Over a whole growing season plant nutrient content could not be predicted from root length colonized. Effects of mycorrhizal fungi on root manipulation also occurred with aqueous extracts of the fungus and, hence, were partly independent of the formation of ectomycorrhizas.