Document: CAT-3-54-5

Growth responses to mycorrhizal colonization of rainforest seedlings vary with light intensity and plant species.

GEHRING, C.A.* ^1,2

Australian National University, Canberra, ACT 0200 Australia ¹
Northern Arizona University, Flagstaff, AZ 86011, USA ²

Abstract:
Both light intensity and root colonization by mycorrhizal fungi are considered important factors affecting the performance of rainforest plants, yet few studies have examined how these two factors interact. I determined whether mycorrhizal colonization altered growth or biomass allocation in four Australian rain forest seedling species (Flindersia brayleana, Acmena resa, Cryptocarya mackinnoniana and Cryptocarya angulata) grown in a glasshouse under light conditions that mimicked the shaded understory (3% PAR) and small light gaps (10% PAR). Seedlings were grown in sterilized field soil and were either inoculated with vesicular-arbuscular mycorrhizal fungi or provided sterile inoculum. Three major findings emerged. First, variation in light intensity had similar effects on seedling dry mass and biomass allocation in all species; increased light intensity resulted in greater seedling biomass, greater root length and a lower leaf area ratio. Second, in all species, mycorrhizal colonization was significantly lower at 3% PAR than at 10% PAR. However, the magnitude of this difference varied among species, ranging from 25-82%. Third, growth responses to mycorrhizal inoculation varied with light intensity and plant species. Mycorrhizal colonization promoted growth in both light regimes in only one species, F. brayleana, while it had no effect on either growth or biomass allocation in C. angulata in either light regime. Responses of the two other species were intermediate - mycorrhizal colonization promoted growth only in high light in A. resa, while it increased the leaf area ratio and decreased the root length of C. mackinnoniana in both light regimes. The finding that mycorrhizal growth responses were observed in only one of four species in shaded understory light conditions, and in only two of four species in small gap light conditions, suggests that some rain forest seedling species may not benefit from mycorrhizal colonization, at least in terms of growth, in the low light environments characteristic of rain forest habitats.

Keywords: mycorrhiza, light intensity, seedling, rainforest

This abstract is being presented at: 11:45 AM in session:
Oral Session #8: Mycorrhizal Fungi.