Objective  Under the background of the change of precipitation pattern caused by global warming, the study of the impact of throughfall reduction (rain reduction) on soil organic carbon (SOC) concentration and chemical composition of Castanopsis hystrix plantations in the southern subtropical region was carried out, and it will provide a scientific basis for accurately predicting the potential impact of climate change on the SOC sequestration function of plantation ecosystem.

  Method  In 2012, in the Guangxi Youyiguan Forest Ecosystem Research Station, three throughfall reduction treatment sample plots and three control sample plots were randomly selected in a 29 years old C. hystrix plantation, each sample plot was 20 m × 20 m. In the sixth year of throughfall reduction treatment, the SOC concentration and chemical composition, total amount and components of litter, fine root biomass, soil microbial biomass and functional gene abundance in dry season (samplings in March) and wet season (samplings in July) were measured, respectively. The effects of throughfall reduction on SOC concentration and chemical stability were analyzed.

  Result  (1) Throughfall reduction significantly decreased soil water content in dry season and fine root biomass in dry and wet season, but there were no differences in the total litter, litter components and soil microbial biomass in dry and wet seasons. (2) In the dry season, throughfall reduction significantly reduced the soil alkyl C and alkyl C/O-alkyl C, but significantly increased the soil aromatic C and aromatic C/alkyl C. In the wet season, throughfall reduction had no effect on SOC concentration and chemical compositions. (3) Litterfall played a major role in the change of chemical compositions of SOC.

  Conclusion  After six years of throughfall reduction treatment, although the content of SOC doesn’t change significantly, the proportion of soil alkyl C with high stability decreases and the aromatization degree of SOC is improved in dry season. Therefore, the projected precipitation reduction scenario may reduce the chemical stability of SOC in C. hystrix plantations in the southern subtropical region.