The plant growth inhibitor nagilactone does not work directly in a stabilized Podocarpus nagi forest

Nagilactones isolated from Podocarpus nagi are known for poisonous physiolo gical activities to organisms. To clarify the allelopathic potential of nag ilactone to wild plants, the seasonal changes in nagilactone contents in th roughfall, leaf litter, and soil were monitored monthly in a podocarp fores t at Mt. Mikasa, Nara City, central Japan. The average annual nagilactone c oncentrations in throughfall, leaf litter, and surface soil at 0-10 cm dept h were 4.7 x 10(-12) g/ml, 3.8 x 10(-4) g/g and 3.1 x 10(-7) g/g, respectiv ely. The nagilactone flux from canopy leaves to the forest Root via through fall was 5.2 x 10(-2) g/ha/yr, which was far smaller than that via leaf lit terfall: 765.3 g/ha/year. The disappearance of nagilactones from leaf litte r and the nagilactone accumulation in the Ao layer and mineral soil were al so studied. Nagilactone in leaf litter rapidly disappeared and its relative disappearance rate was 5.8/yr. Nagilactone concentration in mineral soil a lso decreased rapidly with an increase in soil depth and could not be detec ted in soil at 40-100 cm depth. The total mass of nagilactones was 177.3 g/ ha in the Ao layer and 105.0 g/ha in mineral soil. These quantities in nagi lactone dynamics give a very rapid turnover time of 0.37 year (4.4 months) in a soil nagilactone pool, implying the possibility of the reabsorption of nagilactone by P. nagi, while the allelopathic effects of nagilactone to o ther plants in the podocarp forest are questionable.