| An in situ N amended experiment has combined with an experiment using the15N-labeling method purpose to explore the rule of N2O release from humid subtropical forest soil and main influencing factors of it, in addition to research the possible N cycle pathway and dominating microbe species to better understand soil N2O emissions from forest of this area. The major resulits are summarized as follows:1) N2O fluxes of natural forest was not raised with the N application level, N2O fluxes of high level N application was lower than low N treatment, exists "inhibition effect". But N2O fluxes of plantation soil rose with higher N application.2) Soil denitrification rate increased when the soil moisture rose above30%, indicating that it could perform at this aerobic condition, perhaps due to soil fungi activity.3) Litter exclusion lead to carbon sources limited for soil microbial, soil N2O fluxes first increases and then decreases with rose of N application level. This phenomenon took place in keep litter treatment of Castanopsis fabric forest prehaps due to polyphenols of it’s litter which restrain soil microbial activity.4) Soil N2O fluxes and soil soluble organic N was significantly correlated (p<0.05) rather than soluble inorganic N, in February SON content was positive correlation with N2O fluxes but in June is negative correlation, demonstrating that soil N2O flux seems to have great relevance with soil organic N content, suggesting that the N2O emissions may be mainly due to fungal co-denitrification process.5) in soils60%of WHC in soil water content, generation of N2O and NO was significantly inhibited by high nitrogen input (p<0.01); while in soils90%WHC in soil water content, a similar phenomenon was observed with the generation of N2O within the first9hours of incubation, but afterwards the trend turned reversely; When NO2-added the inhibitions of high nitrogen input were lifted for all unsterilized soils, addition of NO2" immediately offset the inhibitive effect of high soil N content and triggered off generation of a large amount of N2O and NO, forming a sharp contrast to CK (p<0.01). Such a phenomenon did not last long (for21h only) in soils60%of WHC; but it did quite a long time (over2weeks) in soils90%of WHC, which suggests that high water availability and exogenous NO2-played an important role in offsetting the inhibitive effect of high soil N content.6) In this experiment, N2O was generated mainly in denitrification process of the soil, and what is more, the addition of unlabeled NO2" led to rapid increase of hybrid N2O(14N15NO) molecules within the first21hours of the experiment, demonstrating that denitrification in the forest soil may probably proceed mainly through codenitrification by fungi, which may explain over80%of the denitrification.7) Spearman rank correlation analysis indicates that there is a significantly positive correlation between the NO and N2O production rates (p<0.05) in non-sterilized soils, and the lower the soil water content, the higher the correlation between the two. After addition of NO2-, sterilized soil produced more NO than unsterilized soil, but almost no N2O, which indicates that in acid soils chemical denitrification contributes more to NO than to N2O. |
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