二氧化钛纳米颗粒对沼泽土壤反硝化和N2O排放的影响

近年来，二氧化钛纳米颗粒（TiO₂NPs）环境释放量不断增加，并通过多种途径进入湿地生态系统，不可避免地影响到湿地生态系统环境和功能。然而，关于TiO₂NPs对沼泽土壤反硝化作用和氧化亚氮（N₂O）排放的影响机及制尚不明确。选择典型沼泽土壤，通过室内培养实验研究土壤理化性质、反硝化酶活性、反硝化速率（DNR）和N₂O排放对不同剂量TiO₂NPs 0 mg/kg （CK）、10 mg/kg （A10）、100 mg/kg （A100）、1000 mg/kg （A1000）输入的响应，探讨TiO₂NPs输入对沼泽土壤反硝化作用和N₂O排放影响的内在机制。结果表明：不同剂量TiO₂NPs处理显著降低了土壤pH （P<0.05），A10处理显著降低土壤总有机碳（TOC）含量（P<0.01），A1000处理显著降低硝态氮（NO₃^--N）和亚硝态氮（NO₂^--N）含量（P<0.05）。TiO₂NPs处理抑制硝酸盐还原酶（NAR）活性，促进一氧化氮还原酶（NOR）和氧化亚氮还原酶（NOS）活性（P<0.01），A1000处理先促进后抑制了亚硝酸盐还原酶（NIR）活性（P<0.05）。不同剂量TiO₂NPs处理抑制了土壤DNR，促进了N₂O排放，TiO₂NPs处理通过抑制NIR活性，降低土壤DNR，同时通过促进NOR活性，提高N₂O排放。综上，TiO₂NPs输入通过影响反硝化还原酶活性改变沼泽土壤反硝化过程，导致沼泽土壤N₂O排放增加，改变湿地氮的源、汇功能，影响全球气候变化。为TiO₂NPs输入的湿地环境风险评估研究提供理论基础。

Effects of TiO2 nanoparticles on the denitrification and N2O emissions of marsh soil

In recent years, with the rapid development of nanotechnology, the increasing production and application of titanium dioxide nanoparticles (TiO₂NPs) will lead to their release and accumulation in the environment. Owing to that the wetland is located in a relatively lower water catchment environment, TiO₂NPs may enter the wetland ecosystem through multiple pathways, once it enters the wetland ecosystem, it will affect environment and the function of wetland ecosystem and change the process of soil nitrogen transformation inevitably. However, little is known about the effects and mechanism of TiO₂NPs input on the denitrification and nitrous oxide (N₂O) emissions of marsh soil. In this study, in order to explore the effects and its mechanism of TiO₂NPs input on soil denitrification and N₂O emissions, marsh soils were collected from typical field and an indoor cultivated experiment with different addition of TiO₂NPs was conducted, exposure experiments were conducted to investigate the effects of TiO₂NPs (0 mg/kg (CK), 10 mg/kg (A10), 100 mg/kg (A100), 250 mg/kg (A250), and 1000 mg/kg (A1000)) on soil physical and chemical properties, denitrifying enzyme activity, denitrification rate and N₂O emissions of marsh soil. The results showed that (1) all the addition of TiO₂NPs significantly reduced soil pH (P<0.05), the treatments of A10 significantly reduced the content of soil total organic carbon (TOC) (P<0.01), the treatments of A1000 significantly reduced the content of soil nitrate nitrogen (NO₃^--N) and nitrite nitrogen (NO₂^--N) (P<0.05). (2) The addition of TiO₂NPs inhibited the activity of nitrate reductase (NAR) and promoted the activity of nitric oxide (NOR) and nitrous oxide (NOS) (P<0.01), the treatments of A1000 promoted the activity of nitrite reductase (NIR) in initial stage of inhibition, then the trend was opposite (P<0.05), but with the extension of the culture time, the inhibitory effect of TiO₂NPs gradually weakened. (3) The addition of TiO₂NPs significantly inhibited denitrification rate (DNR) and promoted N₂O emissions. (4) DNR was positively correlated with the activity of NIR(P<0.01), N₂O was positively correlated with the activity of NOR(P<0.01). The addition of TiO₂NPs reduced the DNR of marsh soil by inhibiting the activity of NIR, addition of TiO₂NPs improved the N₂O emissions of marsh soil by promoting the activity of NIR. Overall, addition of TiO₂NPs interfered the denitrification process of marsh soil by affecting denitrification reductase activity, resulting in increased N₂O emissions, thus the function of nitrogen source or sink in wetland and global climate will be changed. This study provides a theoretical basis for the assessment of environmental risks of TiO₂NPs input in wetland.