Abstract: Allelopathy is regarded as one of the main mechanisms for the ecological problems of Eucalyptus plantations. In the present study, a chronosequence of Eucalyptus grandis plantations (2, 4, 6, 8, 10 years old) in Danling County, Sichuan Province was selected to evaluate the allelopathic effects of soils on earthworm. The growth indicators (growth rate, survival rate) and physiological indicators (protein, superoxide dismutase (SOD), acetylcholinesterase (AChE), glutathione Stransferase (GST), malondialdehyde (MDA)) of Eisenia foetida were measured in the soils from various aged E. grandis plantations. The survival rate of E. fetida did not change significantly with the plantation age and exposure time. The weight inhibition of E. foetida increased ignificantly with exposure time, whereas the weight inhibition rate increased at 7-14th day and then decreased with exposure time. At the exposure time of 7^th and 14^th day, the weight inhibition rate increased firstly (2-6 years old) and then decreased (6-10 years old); however, the weight inhibition rate had no significant changes with plantation age at the 21^th and 28^th days of exposure. E. foetida represented no significant avoidance responses with the increasing E. grandis plantation age. After the exposure time of 28 days, there were no significant effects on the protein content and AChE activity under the treatments of soils from 2-8 years old E. grandis plantations and then increased with plantation age. SOD activity of E. foetida decreased significantly in the soils of 4 and 10 years old stands, but was stable in other treatments. Overall, GST activity increased significantly with plantation age, especially for 6-8 years old stands, and was stable for other aged plantations. MDA content was stable in the soil of 2-4 years old stands, increased significantly in the soil of 6 years old stand and then was stable with increasing E. grandis plantation age.

Key words: tidal action, net ecosystem CO₂ exchange, drying and wetting cycle, salt marsh.