Energy Sciences

The effects of cerium oxide nanoparticles (CeO₂-NPs) on ¹⁵N/¹⁴N ratio (δ¹⁵N) in wheat and barley were investigated. Seedlings were exposed to 0 and 500 mg CeO₂-NPs/L (Ce-0 and Ce-500, respectively) in hydroponic suspension supplied with NH₄NO₃, NH₄ ⁺, or NO₃ ^-. N uptake and δ¹⁵N discrimination (i.e. differences in δ¹⁵N of plant and δ¹⁵N of N source) were measured. Results showed that N content and ¹⁵N abundance decreased in wheat but increased in barley. Ce-500 only induced whole-plant δ¹⁵N discrimination (-1.48‰, P ≤ 0.10) with a simultaneous decrease (P ≤ 0.05) in whole-plant δ¹⁵N (-3.24‰) compared to Ce-0 (-2.74‰) in wheat in NH₄ ⁺. Ce-500 decreased (P ≤ 0.01) root δ¹⁵N of wheat in NH₄NO₃ and NH₄ ⁺ (3.23 and -2.25‰, respectively) compared to Ce-0 (4.96 and -1.27‰, respectively), but increased (P ≤ 0.05) root δ¹⁵N of wheat in NO₃ ^- (3.27‰) compared to Ce-0 (2.60‰). Synchrotron micro-XRF revealed the presence of CeO₂-NPs in shoots of wheat and barley regardless of N source. Although the longer-term consequences of CeO₂-NP exposure on N uptake and metabolism are unknown, the results clearly show the potential for ENMs to interfere with plant metabolism of critical plant nutrients such as N even when toxicity is not observed.