| N2O, being one of main greenhouse gases, plays an important role in global climate warming. Forest ecosystems, being a possibility of an important source in emission of N2O, were rarely studied, especially in sub-tropical soil N2O emissions from a variety of forest types. This study site was located at Dashanchong Forest Park about50km away from Changs ha City, Hunan Province, which as one of typical subtropical regions in South China is the main distribution area of broad-leaved evergreen forests. By the enclosed chamber technique, soil N2O emissions from a variety of forest types were measured once a month within a year. And environmental factors,including temperature and soil moisture, were also simultaneously observed. The samples were plotted at one kind of pure forest (CL) in which species was Cunninghamia lanceolata and three types of mixed forests:PM (composed by Pinus massoniana mainly), CA (composed by Choerospondias axillaria mainly), and CG (composed by Cyclobalanopsis glanca mainly), respectively;1.In general, it was the sink of N2O for the CA plot, and the source of N2O for the rest three kinds of forest types. Surface fluxes of N2O in the growing season was-27.21μg/(m2·h) for the CA plot,34.61μg/(m2-h) for the PM plot,30.48μg/(m2·h) for the CL plot, and5.82μg/(m2·h) for the CG plot, respectively. The growing season that subtropical forest soil N2O flux of years to release a quantity to N2O can absorb or the important influence. However, since the soils in the growing season affects differently the N2O source and sink strength in line with the stand and time, CA appears even obvious phenomenon of N2O emissions. In addition to the differences in forest environmental factors, further researches are urgently needed to study the biological mechanism which causes the differences among the flux of N2O in the soils in the growing season;2.In the growing season, soil N2O flux from PM, CL, CG, and CA were not changed significantly with different slope positions. Soil N2O fluxes was closed correlation with soil properties varied with different forest types. The four kinds of forest soil in flux between N2O does not change significantly, PM soil N2O flux largest in May, June and July are the basic keeps consistent, CG maximum value appeared in July emissions, CL maximum value appeared in the June emissions, CA between June and July are the biggest fluctuations, other change rule is not obvious; 3.Based on the data collected in the growing season, the result of correlation analysis shows there exists a close relationship between different forest of N2O flux and physical and chemical properties including soil humidity and temperature:the soil moisture is the key factor affecting N2O flux in the surface of the forest region, and temperature indirectly influences the quantity of soil N2O emissions by affecting the water in the soil; an obvious positive correlation exists between soil N2O flux and the water in the soils. The influence of the soil water content on soil N2O flux varies with the difference of the stand:soil N2O flux and soil water content were positively associated in PM and CG, in which the soil moisture content is between10%-20%, and the N2O emissions increase with the increase of the soil moisture content, but when the soil moisture content is more than20%, N2O emissions suddenly reduced, and there is no significant correlation in CA and CL;4.Soil N2O fluxes were closely correlated with soil properties varying in different forest types. Also, the soil moisture content was the major factor, not directly but indirectly, affecting soil N2O emissions by influencing soil moisture content in the study area, which differs along with the different forest types. In addition, the influence of temperature on soil N2O are greater in CL and CG than in PM and CA. |
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