Cooperation Between Earthworm And AM Fungi On The Degradation And Remediation Of Oxytetracycline In Soil

Oxytetracycline(OTC)introduced into the soil through manure application can negatively affect soil microbial community structure and functions,and plant nutrient uptake.Earthworm and arbuscular mycorrhizal(AM)fungi are two common soil organisms that play important roles in the bioremediation of soil organic pollutants.This thesis uses culture and indoor pot-experiments to study the effect of earthworm and AM fungi on OTC degradation,maize growth and nitrogen uptake in OTC contaminated soils in the drilosphere,rhizosphere and hyphosphere.The main findings are as follows:(1)In the soil-maize system,OTC significantly reduced maize root activity and chlorophyll content,and caused toxic effects in maize by disrupting anti-oxidant enzyme activities such as MDA,SOD and CAT.OTC inhibited maize growth and nitrogen uptake by affecting the soil AOA-amoA and AOB-amoA gene copies,urease activity,and maize root activity.(2)Earthworm altered OTC degradation kinetics,decreased its halflife from 31.50 days to 30.00 days in low OTC concentration and 33.00 days to 20.38 days in high OTC concentration.Two degradation products were identified,which were 4-epi-oxytetracycline(EOTC)and 2-acety1-2-decarboxamido-oxytetracycline(ADOTC).Earthworm was found to accelerate EOTC degradation,which in turn promoted OTC degradation.Earthworm also significantly increased the abundance of bacteria Cystobacter,Caldilinea,and Exiguobacterium,and fungi Trichoderma,Chaetomium,and Cephaliophora,further accelerating OTC degradation.(3)Both AM fungi hyphae and earthworm accelerated OTC degradation in the hyphosphere.Illumina sequencing of the 16S rRNA genes showed that earthworms stimulated the growth of class Anaerolineae,family Flavobacteriaceae,and genus Pseudomonas,reducing OTC residues.AM fungi hyphae significantly increased the abundance of family Pirellulaceae,and genus Glycomyces and Nonomuraea,which promoted EOTC degradation and subsequently accelerated OTC degradation.The coexistence of AM fungi hyphae and earthworm stimulated the growth of Anaerolineae and Flavobacteriaceae in the hyphosphere,accelerating OTC degradation.(4)Rhizosphere results indicated that earthworm and AM fungi could individually or interactively enhance OTC degradation.Earthworm stimulated the growth of Hyphomicrobium and Thielavia,while AM fungi stimulated Bacillus cereus,Thielavia and Chaetomium,which accelerated OTC degradation.Through reducing soil OTC content,earthworm and AM fungi significantly increased maize growth and nitrogen uptake.