不同氧化还原电位条件下稻田土壤中15N标记硝态氮的反硝化作用

氧化还原状况是影响土壤中反硝化作用的主要环境因子之一通过不同氧化还原条件下１５Ｎ标记硝态氮反硝化作用的培养试验，结合１５Ｎ气态损失的直接测定方法．研究了反硝化作用发生的氧化还原条件，可为进一步阐明稻田土壤中硝化－反硝化作用氮素损失发生机制提供直接依据．结果表明，氧化和还原条件下均能进行硝态氮的反硝化作用；在４周的培养试验期间，直接测得的氧化（Ｅｈ－２９０－３３０ｍＶ）和还原（Ｅｈ－１１４－４２ｍＶ）条件下的１５Ｎ气态损失分别占加入量的６０．２３±８．０４％和８３．８９±４．７９％．但是，氧化条件下反硝化作用速率明显减缓，外加的硝态氮的半衰期延长，显示了溶解Ｑ２对反硝化作用的抑制作用对反硝化作用进程的模型研究表明速率常数及相应的半衰期作为土壤反硝化作用潜在能力的衡量指标可能优于传统的土壤反硝化势表征方法（反硝化作用百分率），而１５Ｎ示踪－质谱计法直接测定与模型研究相结合则有可能对土壤及其他环境中的反硝化作用作出更恰当的评价．

Denitrification of 15N labeled nitrate-N in rice field soil under different redox conditions

Oxidization-reduction status is one of the important factors affecting denitrification in soil. With the incubation experiment of 15N-labeled nitrate-N denitrification under different redox conditions and the direct measurement of the gaseous 15N losses, the redox condition for occurrence of denitrification was studied, so that direct basis could be provid- ed for the future explanation of N loss from nitrification-denitrification in rice field soil. The resresults indicate indicate that the denitrification of nitrate-N can take place under reduction and oxidation conditions. The 15N-nitrate losses directl measured during 4 weeks incubation period are 60.23 8.04 % under oxidation condition (Eh7 290-330 mV ) and 83.89 4.79 % under reduction condition (Eh7-114-42mV). However, under oxidation condition the rate of denitrification is evidently lowered with the half time of added nitrate-N prolonged, showing the inhibition of soluble O2 on the denitrifi- cation. The decrease of 15N abundance of source in the Process of nitrate-N denitrification under oxidation condition indicated that nitrification-denitrification of the ammonium- N from the soill occurred. The results from modeling studies on the Processes of denitrification show that the rate constant and corresponding half bine as the indexes of soil denitrification potential are probably better than the traditional method with the percentage of denitrification as index. With the combination of the direct determination with the 15N tracer-mass spectrometry technique and the modeling method, denitrification in soil and other environmental systems could be more suitably evaluated.