Fog Drip: A Mechanism of Toxin Transport from Eucalyptus globulus

DEL MORAL, ROGER, and CORNELIUS H. MULLER (University of California, Santa Barbara). Fog drip: a mechanism of toxin transport from Eucalyptus globulus. Bull. Torrey Bot. Club 96: 467-475. 1969.-Fog drip is a mechanism which leaches metabolites of many kinds from foliar crowns. In southern California few herbs of any species are found beneath the canopy of Eucalyptus globulus. Their absence proved not to be attributable to competition for essential resources; but rather allelopathic chemicals were found to be of principal importance. Natural fog drip was collected from beneath Eucalyptus globulus and shown by bioassay with Bromus rigidats to be inhibitory without concentration. Paper chromatography of fog drip revealed the phytotoxins chlorogenie, p-coumarylquinic, and gentisic acid. Artificial fog drip concentrated three fold inhibited several species of grasses in bioassays performed in artificial media. Fog drip was also toxic in soil bioassays. Additional allelopathic mechanisms in Eutcalyptus involving terpenes adsorbed to soil colloids and phenolic acids leached from the leaf litter do exist, but Eucalyptus globulus fog drip acting alone appears to be capable of produeing severe inhibition of growth in some herb species. The importance of fog drip as an agent of metabolite transfer from leaves and deposition in the environment lies in the capacity of these compounds to influence the structure and diversity of a plant community.