Abstract
The effects of cerium oxide nanoparticles (CeO(2)-NPs) on (15)N/(14)N ratio (δ(15)N) in wheat and barley were investigated. Seedlings were exposed to 0 and 500 mg CeO(2)-NPs/L (Ce-0 and Ce-500, respectively) in hydroponic suspension supplied with NH(4)NO(3), NH(4) (+), or NO(3) (-). N uptake and δ(15)N discrimination (i.e. differences in δ(15)N of plant and δ(15)N of N source) were measured. Results showed that N content and (15)N abundance decreased in wheat but increased in barley. Ce-500 only induced whole-plant δ(15)N discrimination (-1.48‰, P ≤ 0.10) with a simultaneous decrease (P ≤ 0.05) in whole-plant δ(15)N (-3.24‰) compared to Ce-0 (-2.74‰) in wheat in NH(4) (+). Ce-500 decreased (P ≤ 0.01) root δ(15)N of wheat in NH(4)NO(3) and NH(4) (+) (3.23 and -2.25‰, respectively) compared to Ce-0 (4.96 and -1.27‰, respectively), but increased (P ≤ 0.05) root δ(15)N of wheat in NO(3) (-) (3.27‰) compared to Ce-0 (2.60‰). Synchrotron micro-XRF revealed the presence of CeO(2)-NPs in shoots of wheat and barley regardless of N source. Although the longer-term consequences of CeO(2)-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.