SOIL-CONDITIONS AFFECT THE OCCURRENCE OF CLUSTER ROOTS IN MYRICA-GALE L IN THE FIELD

Roots of Myrica gale L. from 12 field sites in central Maine were examined for extent of cluster (proteoid) root formation and mycorrhizal infection. Cluster roots were abundant (30-66% of total fine root weight) at all 12 sites and leaf P concentrations were consistently low (490-900 mug Pg-1). Extent of cluster root formation was negatively correlated (r = -0.59) with the amount of available (extractable) soil P and the amount of organic matter (r = -0.79) in the soil and was greater on mineral soils than on organic soils. Extent of cluster root formation was not correlated with leaf P concentration or soil pH. Mycorrhizas probably contributed little or nothing to the P nutrition of M. gale at these sites because only small amounts of fungal infection were found. The infections were intracellular but probably did not represent functional vesicular-arbuscular mycorrhizas because no arbuscules were seen. Cluster roots probably allow M. gale to obtain sufficient P from wet, nutrient poor soils in the absence of significant mycorrhizal infection.