The Ecotoxicological Effects Of Volatile Organic Compounds From Eucalyptus Grandis Rhizosphere Soil On Eisenia Fetida

The development of Eucalyptus plantations on a large scale yields ecological impacts,such as reduced biological diversity and decreased productivity.Allelopathy has been identified as a potential mechanisms reducing commercial plantation biodiversity.Investigations into the allelopathic effects of Eucalyptus have largely focused on water-soluble allelochemicals that affect other plants,however,investigations into the allelopathy of the VOCs released from the tree species are limited.Additionally,there is lack of research into the allelopathic effects of VOCs on soil biota.Eucalyptus(Eucalyptus grandis),within species fast growing traits and stronger adaptability to different climates and regions have resulted in the extensive use of Eucalyptus in reforestation.Therefore,based on previous studies on the identification of VOCs from rhizosphere soils in E.grandis plantations and their forest age effects,eight volatile organic compounds found in the early studies with relatively high concentrations in the soil(octane,undecane,decane,3-methyl-heptane,2,4-dimethyl-heptane,3,3-dimethyl-octane,2,2,4,6,6-pentamethyl-heptane and 2,4-di-tert-butyl-phenol)were selected to understand the effects on the survival,growth,avoidance behavior,physiological indexes(AChE,SOD,GST),DNA damage,skin and intestinal microstructure of E.fetida for this study.The results would be expected to clarify the allelopathic effects of volatile allelochemicals in the eucalyptus plantations on E.fetida,and served as the theoretical basis for scientific management of the eucalyptus plantations.There were six main results as follows:(1)The results showed that effects of VOCs were concentration dependent and E.fetida survival rate decreased with the increasing of concentration and exposure times.In the present study,the 7-and 14-day LC50 values for undecane were highest as 9.33 and 10.39 ml kg-1 soil,confidence limits(95%)were 6.98-12.41ml kg-1 and 9.19-12.12ml kg-1 by probability regression analysis,respectively.The LC50 values of 2,2,4,6,6-pentamethyl-heptane at the exposure time of 7 and 14d were lowest at 4.53 and 5.07 ml kg-1 soil,the confidence limits(95%)were 4.12-6.08 and 4.69-6.34ml kg-1.The inhibitory effect of octane,2,4-dimethyl-heptane,and 3,3-dimethyl-octane on the survival rate of E.fetida were strongest.(2)The results revealed that E.fetida exhibited significant avoidance behavior with the increasing of concentration.In addition to 2,2,4,6,6-pentamethyl-heptane and octane,the other VOCs produced a significant attraction effect at the lower concentrations(i.e.,C1 or C2).However,with the increasing concentrations,evident avoidance behavior of E.fetida were discovered under octane,decane,and 2,4-dimethyl-heptane treatments than control.(3)The VOCs have significant inhibitory effects on the weight of E.fetida,and the inhibitory effects gradually increased with the increasing dose and exposed time.The growth index of E.fetida exposed to decane,3-methyl-heptane,2,4-dimethyl-heptane and,3,3-dimethyl-octane were inhibited than other VOCs.(4)Under octane,3-methyl-heptane and 3,3-dimethyl-octane treatments,the AChE activities was stimulated during the entire exposure time.However,the activity was inhibited for decane and 2,2,4,6,6-pentametyl-heptane and the effects did not change significantly with the increasing concentrations.With the increasing concentration of 2,4-di-tert-butyl-phenol and 2,4-dimethyl-heptane,the AChE activites of E.fetida were promoted at lower concentration and were inhibited at higher concentration.Undecane and octane have a promotion effect on the SOD activity of E.fetida,but the SOD activity of E.fetida was inhibited by 2,4-di-tert-butyl-phenol.Under 3,3-dimenthyl-heptane and 2,2,4,6,6-pentamethyl-heptane treatment,the SOD activity was promoted at 7d,but was inhibited at 14d.The GST activity of E.fetida was promoted of octane and undecane treatments,but was inhibited under 2,4-diemthyl-heptane treatment.The enzyme activity for undecane and 2,2,4,6,6-pentamethyl-heptane were stimulated at the lowest dose,but was inhibited with increasing concentrations.GST activities were stimulated for 3-methyl-heptane,3,3-dimethyl-octane and 2,4-di-tert-buyl-phenol,2,2,4,6,6-pentamethyl-heptane after 7 d of exposure,but were inhibited at C3 at after 14 d.Among the VOCs,decane,2,4-dimethyl-heptane,2,2,4,6,6-pentamethyl-heptane,and 2,4-di-tert-buyl-phenol exerted stronger effects on enzymatic activities.(5)The tail DNA percentages were significantly increased for all experimental treatments relative to control.However,under the treatments of VOCs,the Olive tail moment content and comet tail length also have an obvious increased than control except for that of octane,undecane and decane treatments.Among the VOCs,3-methyl-heptane,2,4-dimethyl-heptane,2,2,4,6,6-pentamethyl-heptane,and 2,4-di-tert-buylphenol induced a significant increase on the levels of DNA damage.(6)Skin and intestinal epithelium tissue were increasingly damaged under increasing VOC concentrations over the 14-d exposure periods.As concentrations and exposure time increased,the earthworms showed progressively severe signs and symptoms of toxicity such as coiling,curling,mortality,body mass changes,and the damage to skin and intestinal tissue.And 2,4-dimethyl-heptane had the most significant effects on skin and intestinal tissue compared with the other VOCs,and the effects were dose-dependent.In summary,The eight VOCs with relatively high concentrations in rhizosphere soils of E.grandis might exert a significant ecotoxicological impact on E.fetida.among which 2,4-dimethy-lheptane,2,2,4,6,6-pentamethyl-heptane,and 2,4-di-tert-buylphenol have the strongest effects.The observations and related findings will be helpful to achieve a better understanding of the mechanism of allelopathy of the VOCs from E.grandis on soil fauna.