Soil Nitrogen Oxides Emission Of Different Vegetation Types And Their Response To S Deposition

The emission fluxes of nitrogen oxides(N2O, NO, NO2)and seasonal variation of N2O were studied for different vegetation types (natural forest, fir plantation forest and orchard) in mid-subtropics with closed static chamber Method. Meanwhile, the effect of enhanced S deposition on soil nitrogen oxides emissions was also studied by simulating atmospheric SO2 dry deposition in September. The main results were as follows:(1) The monthly average soil N2O emission fluxes in the observation period in Altingia gracilies(ALG) natural forest, Castanopsis carlesii (CAC) natural forest, Cunninghamia lanceolata (CUL) plantation and Orchard were 25.77±19.65,22.65±16.56,19.67±11.31, 29.60±16.81μg·m-2·-1, respectively. There were no significant differences in the fluxes between the different vegetation types (P>0.05).(2) The monthly variation trend of soil N2O fluxes for all the vegetation types were generally similar. Much higher soil N2O emission fluxes were observed in spring and summer (from April to July) and lower fluxes in autumn and winter (from August to October), but there was no data for the orchard in spring.(3) The soil fluxes of three kinds of nitrogen oxides were in the order of magnitude: N2O>NO>NO2 in the summer for the forests of CAC, CUL and orchard, and N2O fluxes were significantly higher than those of NO and NO2(P<0.05). But, the NO flux for ALG was significantly higher than those of N2O and NO2(P<0.05). The soil NO2 fluxes were very low, and most of which were negative values in the observation period, suggesting a net uptake of NO2 existed for these vegetation types in this study.(4) There was no significant effect of temperature on soil nitrogen oxides emission, but a significant linear positive correlation between soil N2O(P<0.01), NO(P<0.05) emission fluxes and soil water content, and a negative correlation between soil NO2 fluxes and water content, which suggest that soil water content is the important factor to soil nitrogen oxides emission and can be used to explain the N2O fluxes monthly variation in this mid-subtropical region.(5) The SO2 dry deposition significantly increased the soil N2O and NO emission fluxes, but it had no significant influence on the NO2 fluxes. Different forest soils responsed differently to SO2 deposition. In CAC and orchard, soil N2O emission fluxes peaked after 72h, while the other forests reached a peak value within 6h after S deposition treatment, and soil NO emission fluxes reached a peak value within 6h for all the forest lands. With S deposition, soil N2O emission fluxes in ALQ CAC, CUL and orchard were 2.3,2.1, 12.6 and 4.1 times those in control plots, respectively, and soil NO emission fluxes were 3.4,25.3,9.8,12.2 times those in control plots, respectively.