研究生知识库

纳米技术的快速发展使部分纳米颗粒在生产、使用及排放过程中进入环境并在土壤中大量累积，对土壤系统带来一定的生态压力。水稻土作为我国分布最广、面积最大的农业土壤类型，纳米材料在农业保护产品中的应用及施肥灌溉的过程中不可避免的进入稻田土壤，造成农业生态及人类健康风险。水稻土在水稻生长期内大多处于淹水条件，因而有机质的分解主要为厌氧过程并最终产生CH4和CO2，这使得水稻土成为全球重要的温室气体CH4的主要释放源之一。本文选用两种水稻土，分别添加两个浓度的纳米Fe3O4（Fe3O4 NPs）和多壁碳纳米管（MWCNTs），模拟纳米颗粒进入水稻土生态系统后对有机质厌氧分解过程产生的生态效应，探讨Fe3O4 NPs和MWCNTs对水稻土中微生物群落结构和多样性以及种群丰度的影响，并试图解释Fe3O4 NPs和MWCNTs对分解过程和微生物的作用机制。培养过程中定期测定CH4和CO2的累积产生量，发现Fe3O4 NPs和MWCNTs均抑制CH4和CO2的产生，且抑制程度随纳米颗粒浓度升高而增加。培养结束后测定体系理化性质发现，Fe3O4 NPs和MWCNTs的添加降低了体系的pH值，由于体系中Fe（Ⅱ）含量无明显改变推测Fe3O4 NPs在培养体系并未发生显著的还原作用。溶解性有机碳（DOC）含量在纳米颗粒处理中没有表现出显著的增加，说明有机质厌氧分解在大分子水解成可溶态有机质的过程就受到了抑制作用，因而推测Fe3O4 NPs和MWCNTs可能附着在土壤有机质颗粒表面阻碍其与微生物的相互作用。最终，有机质含量高的贵阳水稻土分解量降低多达51.1%，有机质含量较低的富阳水稻土分解量也降低了33.1%，而MWCNTs的抑制作用高于Fe3O4 NPs，低浓度处理即可大幅度的抑制有机质分解速率。和MWCNTs可能由于比表面积大于Fe3O4 NPs，与微生物及有机质的结合更紧密，使其对土壤有机质分解的抑制作用更强。同时，本研究利用高通量测序揭示了Fe3O4 NPs和MWCNTs对水稻土微生物群落的影响。结果发现Fe3O4 NPs和MWCNTs影响了微生物群落结构及多样性，水稻土中的三类优势细菌菌群 Acidobacteria、Chloroflexi、Proteobacteria在Fe3O4 NPs和MWCNTs处理中丰度均降低，而另外两类优势细菌菌群Bacteroidetes和Firmicutes经Fe3O4 NPs和MWCNTs处理后相对含量升高。参与有机质水解发酵过程的初级发酵菌和次级发酵菌对Fe3O4 NPs和MWCNTs具有一定的耐受性，而产甲烷菌相对比较敏感。另一方面Fe3O4 NPs和MWCNTs使氨氧化菌及铁还原、硫还原菌的丰度比例发生改变。综上所述，我们的研究结果表明Fe3O4 NPs和MWCNTs可能通过减少有机质与微生物的相互作用以及对微生物细胞的毒性作用抑制土壤有机质的厌氧分解。

With the rapid development of nanotechnology, some nanoparticles enter the environment in the process of production, use and emission, and accumulate in a large amount in the soil, which brings certain ecological pressure to the soil system. Paddy soil is the most widely distributed and largest type of agricultural soil in China. The application of nano-materials in agricultural protection products and the process of fertilization and irrigation inevitably enter paddy soil, causing agricultural ecological and human health risks. Paddy soils are mostly submerged during the rice growing period, so the decomposition of organic matter is mainly anaerobic and ultimately produces CH4 and CO2, which makes paddy soils become one of the major sources of greenhouse gas CH4 in the world. In this paper, two kinds of paddy soils were added with two concentrations of nano-Fe3O4 (Fe3O4 NPs) and multi-walled carbon nanotubes (MWCNTs) to simulate the ecological effects of nanoparticles on the anaerobic decomposition of organic matter in paddy soil ecosystem. The effects of Fe3O4 NPs and MWCNTs on the structure and diversity of microbial communities and population abundance in paddy soil were discussed, and an attempt was made to explain mechanism of Fe3O4 NPs and MWCNTs on decomposition process and microbial.The cumulative production of CH4 and CO2 was measured periodically during culture. It was found that both Fe3O4 NPs and MWCNTs inhibited the production of CH4 and CO2, and the degree of inhibition increased with the increase of nanoparticle concentration. pH value of the system was decreased with addition of Fe3O4 NPs and MWCNTs after culture. Because the content of Fe (II) did not change significantly, it was inferred that Fe3O4 NPs had no significant reduction effect in the culture system. The content of dissolved organic carbon (DOC) did not increase significantly in the treatment of nanoparticles, indicating that the process of anaerobic decomposition of organic matter into soluble organic matter was inhibited. Therefore, it is speculated that Fe3O4 NPs and MWCNTs may adhere to the surface of soil organic matter particles and hinder their interaction with microorganisms. Finally, the decomposition amount of Guiyang paddy soil with high organic matter content decreased by 51.09%, and that of Fuyang paddy soil with low organic matter content also decreased by 33.11%. The inhibition effect of MWCNTs was higher than that of Fe3O4 NPs, and the decomposition rate of organic matter could be greatly inhibited by low concentration treatment. The specific surface area of MWCNTs is larger than that of Fe3O4 NPs, and the combination of MWCNTs with microorganisms and organic matter is closer, which makes the inhibition of soil organic matter decomposition stronger.Meanwhile, the effects of Fe3O4 NPs and MWCNTs on microbial communities in paddy soils were revealed by high throughput sequencing. The results showed that Fe3O4 NPs and MWCNTs affected the microbial community structure and diversity. The abundance of three dominant bacterial groups Acidobacteria, Chloroflexi and Proteobacteria in paddy soil decreased in Fe3O4 NPs and MWCNTs treatments, while the relative content of the other two dominant bacterial groups Bacteroidetes and Firmicutes increased after Fe3O4 NPs and MWCNTs treatments. The primary and secondary fermentation bacteria involved in the process of hydrolysis and fermentation of organic matter were tolerant to Fe3O4 NPs and MWCNTs, while methanogens were relatively sensitive. On the other hand, Fe3O4 NPs and MWCNTs changed the abundance ratio of ammonia oxidizing bacteria, iron reducing bacteria and sulfur reducing bacteria. In conclusion, our results suggest that Fe3O4 NPs and MWCNTs may inhibit the anaerobic decomposition of soil organic matter by reducing the interaction between organic matter and microorganisms and their toxicity to microbial cells.