Characteristics Of Soil Acidification,Response Of Earthworms On Soil Acid Stress And Impacts Of Earthworms On Soil Aluminum Fractions In Southern China

Soil acidification and aluminum(Al)toxicity is an ecological and environmental problem that can not be ignored.Soil remediation of acidification and aluminum(Al)toxicity in mining area has attracted abroad attention.Earthworms play an important role in soil ecosystem,but the response of earthworms on soil acidity and the precise tolerance threshold value of earthworms to soil acid stress have not yet been revealed.Earthworms can play an important role in the transformations of soil chemical elements.However,the impact of earthworms on soil Al toxicity and fractions is not clear yet.Three experiments were included in this study.Firstly,soils collected from mining and no-mining area were taken as the research object.Some soil acidic indexes,such as pH value and Al fractions were measured to clarify the difference of acidification and Al fractions characteristics between the soils collected from mining and no-mining areas,it could provide a theoretical basis for the remediation of soil acidification in mining soils.Secondly,the responses of different soil pH levels on earthworm growth and biochemical indexes was studied,and the threshold of earthworms to soil pH levels was determined by biphasic model,so as to allow more accurate assessments of the real field effects of acid stress onto earthworms.Finally,the objectives were to investigate the impacts of different earthworm species in South China on soil pH,Al form and exchangeable base ions,so as to evaluate the impacts of earthworm on changing Al fractions,reducing soil acidity and Al toxicity.The main results were as follows:(1)The acidity characteristics between mining and no-mining soils were significantly different.Soils of mining area were more acidic than that of no-mining.Compared with the mining soils,the soil of non-mining area had higher pH(H₂O),contents of CEC,organic bound aluminum(Al _Or)and weak organic bound aluminum(Al _Orw).The soil group with pH<3.50 had higher contents of Ex-Al,Ex-H,Ex-Q and Al _Ex.(2)The soil pH value had significant inhibitory effects on the survival,growth and reproduction of earthworms beginning with 3.0,4.0 and 3.4,respectively.The dose-response models(J-shaped and inverted U-shaped curves)statistics indicated that the critical values(EC_ZEP)of the GSH-PX,SOD,POD,CAT,TP and MT inhibited by soil acid stress were 3.63,3.56,3.44,3.60,3.53 and 3.88(average 3.60),respectively.In the present study,the fitting curves analysis showed that the responses of the CAT activities,TP and MT contents in earthworm in response to soil pH have the behavior of Hormesis.(3)P.corethrurus,A.robustus and A.aspergillum significantly increased the pH(H₂O)values of lateritic red soil,altered Al fractions,reduced the toxicity of Al and promoted the release of exchangeable calcium(Ca _Ex)and magnesium(Mg _Ex),especially P.corethrurus.Compared to control soil,the casts of P.corethrurus,the pH value were increased 0.79 units,the Al _Excontent were decreased 61.7%,the contents Ca _Exand Mg _Exwere increased 78.7%and 12.1%,respectively.P.corethrurus,A.robustus and A.aspergillum casts and no-ingested soil differ in the characteristics of the soil pH,Al fractions and exchangeable base cations release.In conclusion,soils of mining area were more acidic than that of no-mining.Compared with the mining soils,the soil of non-mining area had higher pH(H₂O),CEC contents of organic bound aluminum(Al _Or),weak organic bound aluminum(Al _Orw).The critical value inhibited by soil acid stress was 3.60,and the fitting curves analysis showed that the responses of the CAT activities,TP and MT contents in earthworm in response to soil pH had the behavior of Hormesis.Earthworms could reduced soil acidity and Al toxicity,altered Al fractions and promoted the release of exchangeable base cations.