| Silver nanoparticles?AgNPs? is the simple substance of silver with the particle size of 1-lOOnm. Due to their excellent antimicrobial activity, they are being widely used in a variety of commercial goods, including medical appliances, food storage containers, cleaning products, fiber textile, etc. The wide application of AgNPs increases the likelihood of their inflow into soil. Ammonia-oxidizing microorganisms which carry out ammonia oxidation are ecologically important microorganisms. AgNPs may may disrupt ammonia oxidizers in the terrestrial ecosystem and hence ammonia oxidation. Therefore, it is necessary to study the impact of AgNPs on soil ammonia-oxidizing microorganisms and understand their toxicity. This study evaluated the impact of AgNPs to soil ammonia oxidizers, which will have an important practical significance and provide a theoretical basis and technical support for studying the impact of AgNPs on the nitrogen removal efficiency of constructed wetlands.The activity of soil ammonia-oxidizing microorganisms, ammonium concentration and nitrate concentration under the stress of AgNPs were studied to observe the impact of exposure concentration, exposure time and temperature on them. The results indicated that at normal temperature ?25??, the activity of soil ammonia-oxidizing microorganisms was inhibited and the nitrate concentration was changed significantly at different AgNPs dosages (1,10 and 100?g g-1). The ammonium concentration was changed significantly only at the high dosage. Low temperature ?5?? could reduce the toxicity of AgNPs to ammonia-oxidizing microorganisms.The abundances of soil ammonia-oxidizing microorganisms under the stress of AgNPs were studied. At normal and low temperature ?25? and 5??, the abundances of ammonia-oxidizing bacteria ?AOB? and ammonia-oxidizing archaea ?AOA? were determined with qPCR technology before and after the 37 days of exposure at different AgNPs dosages (1,10 and 100?g g-1). The results indicated that at normal temperature, the abundances of soil ammonia-oxidizing microorganisms decreased at medium and high dosages (10 and 100?g g-1), while at low temperature the abundances decreased only at the high dosage, which suggested the toxicity of AgNPs were reduced at low temperature.The community compositions of soil bacteria, archaea, AOB and AOA after the 37 days of AgNPs exposure (100?g g-1) at normal temperature ?25?? were determined with 454 pyrosequencing, which were represented with 37d-100, and compared with the controls before and after 37 days incubation, which were represented with Od-ck and 37d-ck. It was to study the impact of AgNPs on the community composition and diversity of soil microorganism and ammonia-oxidizing microorganisms. The results indicated that after 37 days, either under the stress of AgNPs or in control, both richness and diversity of the communities of soil bacteria, archaea, AOB and AOA decreased. For bacteria, AOB and AOA, the richness and diversity of the Od-ck were highest, and followed by 37d-ck and 37d-100. For archaea, the richness and diversity of the Od-ck were highest, and followed by 37d-100 and 37d-ck. The community compositions of soil bacteria, archaea, AOB and AOA were changed with AgNPs. AgNPs was the major factor resulting in the changes of bacteria and AOB community and incubation time was the major factor resulting in the changes of archaea and AOA community.The activities of soil urease and dehydrogenase under the stress of AgNPs were studied to observe the impact of exposure concentration, exposure time and temperature on them. The results indicated that at normal temperature ?25??, the activity of urease was inhibited significantly at medium and high dosages (10 and 100?g g-1) and stimulated at low dosage (1?g g-1). At low temperature ?5?? the inhibition decreased. At normal temperature ?25??, the activity of dehydrogenase was inhibited significantly at different AgNPs dosages (1,10 and 100?g g-1). At low temperature ?5??, the inhibition decreased only at the low dosage(1?g g-1). |
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