Abstract: An incubation test was conducted with the paddy soil samples collected from three national longterm experiment stations in Hunan Province to study the characteristics of organic carbon mineralization under different fertilization treatments and its relationships with organic carbon fractions, i.e., total organic carbon (TOC), microbial biomass carbon (MBC), and watersoluble organic carbon (WSOC). The results showed that in all fertilization treatments, the cumulative-amounts of CO₂ and CH₄ ranged from 448.64 to 1 516.77 μg·g^-1 and from 15.60 to 33.34 μg·g^-1, respectively. In the 58 days of incubation, the mineralized carbon accounted for 3.59%-557% of TOC. The CO₂ production rate was higher in the early phase of incubation, decreased rapidly then, and tended to stable afterwards; while the CH₄ production rate had a slow increase first and declined rapidly then. A combined application of chemical fertilizers and manure or straw increased the cumulative amounts of CO₂ and CH₄ significantly. In all fertilization treatments, the cumulative mineralized C had significant correlations with TOC, MBC and WSOC, but less correlation with its percentage in TOC.

Key words: high temperature stress, CH₄ emission rate, plant leaf, subtropics.