Abstract: An incubation experiment was conducted to investigate the effects of the additions of different nitrogen forms on nitrogen transformation in red soils of subtropical forest under soil moisture conditions with 40%, 70% and 110% of water holding capacity (WHC). The results showed that soil net mineralization and ammonification rates were maximum at 70% WHC and minimum at 40% WHC. Compared with the control, the addition of NO₃^--N decreased the soil net mineralization and ammonification rates by 56.1% and 43.0% under 70% WHC condition, and decreased by 68.2% and 19.0% under 110% WHC, respectively. However, the proportion of ammonification to mineralization increased at 70% and 110% WHC, which suggested that nitrate addition inhibited the nitrification. With addition of NO₃^--N at 110% WHC, the net nitrification rate was lowest while N₂O emission was highest with the concomitant decrease of nitrate content, indicating that N₂O emission was largely derived from denitrification. However, at 40% WHC and 70% WHC, the maximum N₂O flux was found at the early stage of incubation. Even with addition of NH₄⁺-N and NO₃^--N, N₂O flux did not change much at the latter stage of incubation, indicating that autotrophic nitrification was dominant for N₂O production at the early stage of incubation. Under 40% WHC condition, soluble organic carbon increased more and it increased largely with NH₄⁺-N addition, which meant NH₄⁺-N addition could enhance the mineralization of soil organic matter. Under 40% and 110% WHC conditions, the addition of NH₄⁺-N increased significantly the soil soluble organic nitrogen (SON) by 73.6% and 176.6% compared with the control, respectively. A significant increase of 78.7% for SON was only found at 40% WHC under addition of NO₃^--N  compared with the control. These results showed that high soil moisture condition and addition of NH₄⁺-N were of benefit to SON formation.