典型河口主要氮转化过程对盐度响应机制的室内外实验研究

Salinity effects on nitrogen transformation processes in a typical estuary:A laboratory-field study

受全球盐水入侵加剧影响,河口区域水环境安全面临巨大的威胁.通过室内水槽控制实验和室外原位微生物培育实验,分别研究盐度作用的不同时间尺度下,不同形态氮(NO_(3)^(-)、NH_(4)^(+)和溶解性N_(2)O)转化及转化过程硝化、反硝化和硝酸异化还原氨(DNRA)功能基因的响应机制.结果表明:①室内实验的NH_(4)^(+)和溶解性N_(2)O浓度与盐度呈正相关,NO_(3)^(-)浓度随盐度上升而降低;室外原位实验的涨潮期,去菌处理组的NH_(4)^(+)和NO_(3)^(-)浓度随盐度上升反而下降,溶解性N_(2)O浓度则随盐度上升呈上升趋势;未去菌处理组和原位对照组的NH_(4)^(+)、NO_(3)^(-)和溶解性N_(2)O浓度均与盐度呈负相关.②室内外实验表明,盐度在21.6以下时,硝化反应、反硝化反应和DNRA反应均得到增强,高盐度条件下(盐度为34.0)硝化反应抑制作用明显.盐度长期作用下主导功能基因为nxrA、nirK、nirS和nrfA,而短期的主导功能基因为amoA-AOA、amoA-AOB、nirK、nirS和nrfA.本研究通过对水体不同组分氮浓度-功能基因对盐度不同作用时间尺度的响应研究,为河口区域盐水入侵和氮源汇转化机制研究提供技术支撑.

Aquatic environments in estuaries are under great threats due to frequent saltwater intrusions at global scales.To explore the effects of saltwater intrusions on the nitrogen cycling and the underlying mechanisms,a salinity-controlling laboratory experiment combined with an in-situ microbial cultivation experiment in Minjiang estuary were conducted.We analyzed how transformation of variable nitrogen forms(e.g.,NH_(4)^(+),NO_(3)^(-)and dissolved N_(2)O)and nitrogen-related functional genes of these transformation processes would respond to salinity changes temporally.Our results suggested that NH_(4)^(+)and dissolved N_(2)O were positively correlated with salinity.In contrast,NO_(3)^(-)decreased with the increase of salinity according to the laboratory experiment.Differently,field measurements during flood periods suggested negative correlations with salinity for NH_(4)^(+)and NO_(3)^(-),but a positive one for dissolved N_(2)O in the sterilized group.However,in both the unsterilized and the controlling groups,all three nitrogen forms(i.e.,NH_(4)^(+),NO_(3)^(-)and dissolved N_(2)O)were negatively correlated with salinity.Both laboratory and field observations showed that nitrification,denitrification and dissimilatory nitrate reduction to ammonia(DNRA)were enhanced when salinity was below 21.6,and nitrification was clearly suppressed if salinity went across 34.0.The dominant functional genes under long-term salinity stress were nxrA,nirK,nirS and nrfA,while in short-term scales,amoA-AOA,amoA-AOB,nirK,nirS and nrfA basically controlled the nitrogen transformation.The findings in this study could inform the alternations of nitrogen between sources and sinks in estuarine regions stressed by saltwater intrusions.