Abundance and characteristics of Pisolithus ectomycorrhizas in New Zealand geothermal areas.

Pisolithus is restricted in New Zealand to geothermal areas where it associates with Kunzea ericoides var. microflora (prostrate kanuka) and occasionally Leptospermum scoparium. Here we describe for the first time the ectomycorrhizal morphotypes of three New Zealand Pisolithus species and report the frequency and abundance of these morphotypes against other mycorrhizal fungi associated with these hosts in New Zealand geothermal areas. The three Pisolithus species form typical ectomycorrhizal associations with Kunzea ericoides var. microflora, and one also was observed forming typical ectomycorrhizal associations with Leptospermum scoparium. Although the morphotypes from the three Pisolithus species share many morphological and anatomical characteristics, they vary with regard to the abundance of rhizomorphs. The common occurrence of Pisolithus fruiting bodies at the geothermal sites was matched by frequent and abundant Pisolithus ectomycorrhizas. Pisolithus ectomycorrhizas were frequent (100% of soil cores) and abundant (between 55 and 88% of ectomycorrhizal tips) associates of prostrate kanuka in hot (50 C at 8 cm depth), highly acidic and N depleted soils. The levels of arbuscular mycorrhizal colonization of prostrate kanuka were lower than on K. ericoides and L. scoparium on cooler soils. The stressful conditions where prostrate kanuka dominates probably favor Pisolithus over the mycorrhizal fungi occurring in cooler geothermal areas. Questions about how several genetically similar Pisolithus species co-occur on prostrate kanuka in geothermal areas without mutual competitive exclusion are discussed.