脱水时长对间歇性河流生物膜反硝化功能的影响

Effects of drought duration on the denitrification of biofilms in intermittent river

以人工河道模拟培养的生物膜为研究对象,探究了短期干旱25d和长期干旱90d在复水20d后生物膜反硝化功能对干湿交替的动态响应.结果表明,生物膜的含水率及微观形态在干旱和复水期间均发生了显著变化,含水率在干旱第3d~第7d间发生陡降,从(74.96±3.57)%下降至(2.38±0.37)%.长短期干旱组的反硝化速率在复水后均表现为持续增长,短期干旱组反硝化速率在复水后期表现出显著增加(P<0.05),从(3.26±0.12)上升至(5.35±1.18)μmol N_(2)-^(15)N/(L·h),而长期干旱组则集中在复水前期,由(2.14±0.19)上升到(4.15±0.89)μmol N_(2)-^(15)N/(L·h)(P<0.05).经历了短期干旱的生物膜复水后能够恢复到初始水平,但长期干旱组生物膜的反硝化速率难以恢复到初始水平(P<0.05),表明长期干旱对生物膜反硝化速率造成了不可逆的影响.反硝化功能酶活在各复水阶段也表现出不同的变化.短期干旱显著增加了反应路径末端一氧化氮还原酶活性(P<0.05),而直接影响反硝化速率的亚硝酸盐还原酶、氧化亚氮还原酶经历长期干旱后,也难以恢复到初始水平(P<0.05).以上研究结果均表明长期干旱会显著改变河流生物膜驱动的生物地球化学循环过程(反硝化功能).

This study took the biofilms cultivated in artificially simulated rivers as the test subjects,and explored the dynamic response of biofilms denitrification to rewetting process after short-term drought(25days)and long-term drought(90days).The results showed that the water content and macro-microscopic morphology of biofilm changed significantly during both drought and rewetting,and the water content dropped sharply in the 3d to 7d,from(74.96±3.57)% to(2.38±0.37)%.The denitrification rate of both short and long term drought groups showed a continuous increase after rewetting.The short-term drought group showed a significant increase(P<0.05),from(3.26±0.12)to(5.35±1.18)μmol N_(2)-^(15)N/(L·h),while the long-term drought group was concentrated in the late rewetting period,from(2.14±0.19)to(4.15±0.89)μmol N_(2)-^(15)N/(L·h)(P<0.05).Biofilms that experienced short-term drought were able to recover to the initial denitrification rate level through the rewetting process,while those that experienced long-term drought had difficulty achieving it(P<0.05),indicating that long-term drought had an irreversible effect on the denitrification rate of biofilm.The activities of denitrification functional enzymes also showed different changes during each rehydration stage.Short-term drought significantly increased the nitric oxide reductase activity at the end of the reaction pathway(P<0.05).While the nitrite reductase and nitrite oxide reductase,which directly affect the denitrification rate,also had difficulty in recovering to their initial levels after experiencing long-term drought(P<0.05).The above results show that prolonged drought significantly alters the biogeochemical cycle driven by river biofilms(denitrification function).