关键词: 扩张, 西洞庭湖, 杨树人工林, 影响因子, 时空特征

Abstract: Volatile halogenated organic compounds (VOX) are known as atmospheric pollutants which contribute to stratospheric ozone depletion and global warming. Although ocean is considered to be the major source and sink of VOX, VOX from forest ecosystems still have significant effect on global VOX cycle. Increasing global nitrogen deposition plays a great role in structure and function of forest ecosystems, leading to changing of VOX uptake and emission from forest floor. Static chamber coupled with preconcentratorGC-MS technique was employed to study the responses of VOX fluxes from forest floor with simulated elevated nitrogen deposition in two major forests, namely pine forest (PF) and monsoon evergreen broadleaf forest (BF) in Dinghushan. The results showed that PF floor acted as sink for VOX at the control sites, with the maximum uptake rate of -428.32 pmol·m^-2·s^-1 for 1,1,2trichloroethane. The uptake rates of VOX decreased with enhanced nitrogen deposition, and the medium nitrogen addition had a significant influence on VOX flux in PF, with the change from sink to source. BF floor acted as source for VOX at the control sites. The emission rates of VOX decreased with enhanced nitrogen deposition, with a significant difference between the control and nitrogen addition sites, and BF forest floor changed from source to sink for some VOXs. Significant differences were found between forests at the control sites, but the difference diminished or even disappeared with nitrogen addition. Significant correlations were observed between vinylchloride and 1,2dichloropropane and 1,1,2trichloroethane at nitrogen addition sites in PF. In BF, significant correlations were also found between chloromethane and vinylchloride, chloroethane and chlorobenzene, and between chlorobenzene and most tested VOXs. These results indicated the same mechanism of response of the tested VOXs to nitrogen deposition in forest floor. There were no obvious diurnal variations for VOX fluxes at the control site, but a small emission peak appeared at 07:00 and the highest uptake rates were observed at 13:00 for most of the VOXs at high nitrogen addition sites in BF.

Key words: West Dongting Lake, spatio-temporal characteristics, influential factors., poplar plantation, expansion