Effects Of SO₂Fumigation On Soil N Gross Transformation Rates And N₂O Fluxes For Castanopsis Carlesii Natural Forests

The SO2effect was investigated of N gross transformation rates and N2O fluxes of topsoil(0-10cm) for a typical mid-subtropical evergreen broad-leaved forest of Castanopsis carlesii located at two different positions in Northern Fujian province, in a short-term lab incubation experiment (68.5h) in which soil was fumigated with gas SO2(CK,0mg S kg-1dry soil; LS,40mg S kg-1dry soil; HS,80mg S kg-1dry soil), and thereafter15N-labeled ammonium nitrate was added according to15N isotpe dilution method. The main results are as follows:1) The more significant changes occurred at the beginning than the late of inorganic N concentration and atom%excess.The trend of CK and LS was similar; while HS treatment significantly promoted NH4+-N concentration and affected15NO3--N atom%excess of Wuyishan soil. The LS treatment only significantly affected the changes of15NO3--N atom%excess in Wuyishan. Compared with CK treatment, the effect of HS on inorganic N changes was more pronounced. This is probably because added SO2amount was not sufficient to cause the change, or its effect was delayed.2) The N gross transformation rate was significantly (p<0.05) larger during24h after addition of the labeling solution than the other time. The trend was leveling off and the difference between the three treatments gradually decreased.This may be related to the added N and effect of SO2on bacterial activity; although S treatment mostly had no significant effect on N transformation excepet the HS treatment on net mineralization rate in Jian’ou, the three treatments had significant differences in some incubation time during the experiment. From the total average point of view, while mostly inhibiting the N transformation rate of Wuyishan, S treatment mostly promoted the N transformation rate of Jian’ou; The N retention capacity of Wuyishan natural soil was larger. S treatment weakened the soil nitrogen retention capacity, the higher level of the sulfur added, the weaker the nitrogen retention capacity for Wuyishan soil. The effects of SO2on N transformation rate showed no common trend.3) The N2O fluxes changes were significantly (p<0.05) larger during the24h after addition of the Labeling solution than the other time. The trend was leveling off and the difference between the three treatments gradually decreased. Statistics show that there was no significant correlation between the SO2added levels and the N2O emission fluxex. So soil acidification caused by SO2can’t singlely influence N2O emission flux changes.