Abstract: By using close chamber-GC method, the N₂O fluxes in defarming grassland, bush land,Pinus massoniana forestland, and broadleaved forestland in central Guizhou were measured in situ in 2006 and 2007 to investigate the seasonal change patterns of soil N₂O flux under different vegetations in karst region of southwest China. The results indicated that in a whole year round, the soils in all test sites played the source of atmospheric N₂O, only acting as a N₂O sink in exceptional months. The soil type and the vegetation had obvious effets on the N₂O flux from soil. Yellow soil had a smaller N₂O flux than calcareous soil, except for broadleaved forestland. The N₂O fluxes from defarming grassland and bush land were higher in spring and lower in autumn and winter, and varied within the range of -20.7-103.09 μg N·m^-2·h^-1 and -33.0-67.3 μg N·m^-2·h^-1, respectively; while those from P. massoniana forestland and broadleaved forestland were the highest in spring but had no definite change patterns in other seasons, and varied within the range of -5.3-35.0 μg N·m^-2·h^-1 and -14.4-152.8 μg N·m^-2·h^-1, respectively. The correlation analysis showed that there existed a negative correlation between soil moisture content and N₂O flux, suggesting that soil moisture was the main factor driving the seasonal change of N₂O flux. Temperature indirectly affected the soil N₂O flux through affecting soil moisture.

Key words: spore density, drainage, carbon accumulation, C/N