The effect of plant light environment on mycorrhizal colonisation in field‐grown seedlings of podocarp‐angiosperm forest tree species

Abstract

To test the possibility that the development of mycorrhizas in seedlings may be limited under shaded conditions, arbuscular mycorrhizal colonisation was measured in gap and understorey seedlings from mixed podocarp/angiosperm forests in North Okarito, south Westland, and Blue Duck Scientific Reserve, Marlborough, New Zealand. Mean percentage colonisation of seedlings of podocarp and angiosperm tree species ranged from 66 to 97% of root length, and no seedlings were non‐mycorrhizal. Plant light environment had no significant overall effect on percentage mycorrhizal colonisation within cortical cells. Levels of colonisation of seedlings at North Okarito forest, which experiences high annual rainfall and grows on a poorly drained gley‐podzol soil, were similar to those of seedlings from Blue Duck Scientific Reserve, a podocarp‐angiosperm forest of comparable structure, which experiences much lower annual rainfall and grows on soils dominated by yellow‐brown earths of moderate to high fertility. This result indicates that all podocarp and angiosperm seedlings in forests of this type in New Zealand are likely to support heavy arbuscular mycorrhizal colonisation, regardless of regional climatic conditions and soil type.