Occurrence of arbuscular mycorrhiza and ectomycorrhiza on Leptospermum scoparium from the Rakaia catchment, Canterbury

Leptospermum is one of only three New Zealand genera that are colonised by ectomycorrhizal (EM) fungi, and L. scoparium is one of the very few New Zealand species that can be colonised by both arbuscular mycorrhizal (AM) and EM fungi. This study examined AM and EM colonisation on L. scoparium growing within AM grassland ecosystems or adjoining Nothofagus forest in the Rakaia catchment, Canterbury. Very low AM colonisation was found (<4%) in all samples, while EM colonisation ranged from 7 to 55% of root length colonised. These results contradict an earlier report that L. scoparium is mostly colonised by AM fungi. We suggest the montane environment of the study sites would favour EM rather than AM colonisation. EM colonisation was higher in mature plants than in saplings. Lowest EM colonisation (7–15%) was recorded on root samples that were from either young or mature plants occurring as separate individuals in grassland distant from other indigenous EM species, while highest colonisation (49–55%) was recorded on samples from mature closed canopy L. scoparium stands, irrespective of distance from other indigenous EM sources.