LAUNONEN, TM, DH ASHTON & PJ KEANE.
School of Botany, La Trobe University, Bundoora, 3083 Victoria, AUSTRALIA.
The regeneration of E. regnans forests in Australia is dependent on major disturbance, such as fire. The changes in soil microflora caused by heating may contribute to the stimulation of seedling growth after regeneration burns. This study was designed to separate direct nutrient effects from biological effects. In two experiments, E. regnans seedlings were grown either in differentially heated soil (red burnt, black burnt and unburnt) collected from logging coupes and adjacent forests or in sterilised soil/gravel mix inoculated with the mycorrhizal roots of the seedlings grown in heated soils. The seedling dry weight, phosphorus, zinc, iron and nitrogen content, mycorrhizae and root ergosterol concentration were determined. The soils were analyzed for extractable phosphorus. The seedling growth and phosphorus acquisition were enhanced in all black burnt soils compared with unburnt controls. Root ergosterol concentration was promoted only in seedlings grown in black burnt soils which had relatively low levels of soil phosphorus. Also the root inocula from these black burnt soils stimulated seedling growth. The mycorrhizae were morphologically different in differentially heated soils. These results suggest that both biological and direct nutrient effects may contribute to seedling growth promotion after regeneration burns.