Initial Sterilization of Soil Affected Interactions of Cerium Oxide Nanoparticles and Soybean Seedlings (Glycine max (L.) Merr.) in a Greenhouse Study

Cerium oxide nanoparticles (CeO₂NPs) have exhibited strong impacts on many physiological and biochemical processes in agricultural crops. However, almost all previous studies directly linked the responses of plants to the impact of ENPs, ignoring the potential role of local organisms in the rhizosphere. The primary goal of this study was to assess the effects of the rhizosphere biocommunity on the interactions of CeO₂NPs with soybeans, including CeO₂NPs transformation in the rhizosphere and in plant tissues. Soybean seedlings grown in initially sterilized soil or unsterilized soil were exposed to different concentrations of CeO₂NPs (0, 100, and 500 mg/kg) in a growth chamber for 27 days. Initial sterilization significantly affected the interactions of CeO₂NPs and soybeans, compared with the unsterilized soil (p ≤ 0.05). For example, the net photosynthesis rate of soybean seedlings exposed to 100 mg/kg of CeO₂NPs for 25 days was 122% higher in sterilized soil than in unsterilized soil. However, at 500 mg/kg, the net photosynthesis rate was 67.2% lower in sterilized soil than in unsterilized soil. Cerium accumulation in soybean tissues was affected by the exposure concentration and soil type, although strong interaction between the two factors was not observed. The presence of 100 mg/kg of CeO₂NPs significantly increased the nodule numbers on soybean roots to about 12 in sterilized soil, while only one or two nodules were observed in unsterilized soil at the same concentration, indicating significant impact of soil treatment (p ≤ 0.05). Higher CeO₂NPs concentrations and soil treatment also influenced the number of soil nematodes and their viability. In summary, the soil biocommunity strongly affected the physiological impact of CeO₂NPs on soybean seedlings, the nematode population and the Ce accumulation in soybean tissues.