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Ammonia-oxidizing bacteria(AOB)and the newly discovered ammonia-oxidizing archaea(AOA)play a key biochemical role in the global nitrogen cycle.Knowledge on AOA in forest soils,especially acidic forest soils,is very limited.Large area of Masson pine forests were transformed to Eucalypt plantations in Guangdong Province,South China in the last 30 years.We studied AOA community characteristics and soil nutrient levels at different soil depths in Masson pine(Pinus massoniana)plantation and Eucalypt(Eucalyptus urophylla)plantation.The results showed both soils were acidic(pH 3.85-4.12),and land use change from Masson pine to Eucalypt plantation decreased soil nutrient levels.AOA were the only ammonia oxidizers in both plantations(no AOB were detected).The detected AOA were affiliated with the genera Nitrosotalea that constantly occur in acidic soils and Nitrososphaera that occur widely in various soils.A decrease of AOA abundance and an increase of their diversity were evident from Masson pine to Eucalypt plantation.This study demonstrated land use change from Masson pine to Eucalypt plantation had driven AOA community shift,which could potentially have an effect on atmospheric environment and soil health.