Does N deposition mitigate the adverse impacts of drought stress on plant seed germination and seedling growth?

Large amounts of nitrogen (N) enter ecosystems via N deposition. The increased drought stress has incurred serious threats to plant seed germination and seedling growth (SGe-SGr). It is significant to characterize the combined impacts of N deposition and drought stress on SGe-SGr of plants to enable a further explanation of the response mechanism of SGe-SGr to N deposition and drought stress. This study aims to explore the combined impacts of N deposition with a concentration gradient and drought stress (mimicked using PEG 6000) with different levels on SGe-SGr of wheat. N treatment raises seedling growth of wheat mainly due to the increased levels of available N and the decreased level of peroxidation of the cell cytoplasm membrane of wheat. Drought stress declines SGe-SGr of wheat mostly due to the progressively enlarged osmotic pressure triggered by water deficit and the advanced level of peroxidation of the cell cytoplasm membrane of wheat. N treatment regardless of the concentration dramatically mitigates the adverse impacts of drought stress on seedling growth of wheat. This may be owed to the improved competitive ability for sunlight acquisition and leaf photosynthetic area via the deactivation of nutrition limits (wheat can absorb more N nutrients and improve its drought resistance ability) implemented by N addition. This may also due to the down-regulated level of peroxidation of the cell cytoplasm membrane of wheat under the combined N and drought stress. However, the combined treatments of the high level of N supply and light drought stress decline seed germination of wheat. This may be due to the promoted osmotic pressure contributed by the high level of N supply under water deficit. Thus, N deposition mitigates the adverse impacts of drought stress on seedling growth of wheat but aggravates the adverse impacts of drought stress on seed germination of wheat mostly.