Abstract: This paper studied the effects of replacing natural secondary broad-leaved forest with Cunninghamia lanceolata plantation in the south,central and upstate areas of subtropical China on the changes of soil chemical and biological properties.The results showed that after replacing with Cunninghamia lanceolata plantation,the total organic carbon (TOC) content in surface soil decreased by 31.51%～58.24%,and the contents of soil total N and P,pH value,C/N and C/P also decreased to different degree.Soil microbial amount was less than that under natural secondary broad?leaved forest,soil urease,invertase,catalase and dehydrogenase activities decreased,while soil polyphenol oxidase activity increased by 8%～40%.The respiration rate of Cunninghamia lanceolata soil was 51.15%～54.48% lower than that of natural secondary broad?leaved forest soil.The correlation between soil TOC and polyphenol oxidase activity was negative (R=-0.723,n=18), while those between soil TOC,N,P and other enzyme activities were positive.It could be concluded that replacing natural secondary broad?leaved forest with Cunninghamia lanceolata plantation worsened soil quality,and the loss of soil organic matter in Cunninghamia lanceolata plantation ecosystem might be one of the important factors resulted in the decrease of soil nutrients and enzyme activities.

Key words: Rice (Oryza sativa), Genotype, Low P stress, Screening criteria