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Abiotic stresses strongly impair plant development and might impose detrimental effects particularly on seedlings. Irradiance and water deficit are relevant factors, which affect performance of young plants under controlled conditions. In our study, we investigated the influence of water shortage combined with different radiation sources - light emitting diodes (LED) and compact fluorescence lamps (CFL) - on physiological and biochemical parameters of young apple plants. Stress responses were assessed by fluorescence-based indices, while relative water, chlorophyll (Chl), and proline content served as reference parameters. The watering regime had a higher impact on biochemical indicators than the radiation sources. Lower Chl content was determined in plants grown under LED both in control and in water deficit plants. Nitrogen balance index and nitrogen balance index with red radiation excitation showed similar patterns regarding leaf Chl results in relation to the radiation source, being higher under CFL. In contrast, the flavonol index was higher in plants cultivated under LED. Stomatal conductance and maximal photochemical efficiency emphasised a radiation quality effect with higher values for CFL. In conclusion, fluorescence indices related to nitrogen status and flavonol content are promising parameters to sense physiological impairments under the given conditions. However, discrepancies compared to previous studies might be related to the different plant species, the nature of dehydration, and the measuring conditions. [ABSTRACT FROM AUTHOR]