Mycorrhizal colonisation of exotic conifers in kānuka and mānuka shrublands

Mycorrhizal colonisation of Douglas-fir and Corsican pine seedlings in soil from kānuka and mānuka dominated shrublands in Canterbury was studied using a bait plant technique. Soil cores were collected from 10 sites of each shrubland, transferred to a glasshouse, and sown with seed of both tree species. Mycorrhizal colonisation was examined after 19 weeks’ growth. Overall, seedlings of Douglas-fir were larger than those of Corsican pine, but the amount of Corsican pine seedlings that were colonised (56%) was about twice that of Douglas-fir (29%). Across the sites, 7–61% of Douglas-fir and 16–81% of Corsican pine seedlings had mycorrhizas. Colonisation of the two tree species was correlated in soil cores from kānuka stands, but not from mānuka stands. Colonisation was significantly greater in kânuka than mânuka stands in Douglas-fir, but not in Corsican pine. Kānuka stands were of a lower overall elevation than mānuka stands and had higher levels of soil available phosphorus. Both factors may have contributed to the greater mycorrhizal colonisation of Douglas-fir in kānuka stands. Differences in colonisation between sites could be partially explained by the proximity of sources of spores of mycorrhizal fungi. It is concluded that low numbers of mycorrhizal propagules may constrain mycorrhizal formation in environments distant from a spore source, but are ultimately unlikely to preclude it, or limit successful seedling establishment