Antecedent moderate nitrogen fertilization alleviated the effects of drought on growth and leaf photosynthesis of Schima Superba seedlings.

BACKGROUND

Drought and nitrogen deposition are the major global change factors that alter forest dynamics by affecting tree growth and physiology. However, the impacts of increased nitrogen availability at pre-drought on trees remains poorly understood, and it remains unclear how these responses are coordinated. In this study, we conducted the fertilization-drought microcosm experiment using a widely distributed evergreen broadleaf tree species seedlings (Schima superba) in southern China. The experiment was conducted at 3 stages. First, four levels of N fertilization treatments (without N fertilization-NF, low N fertilization-LF, moderate N fertilization-MF, high N fertilization-HF) were applied for 60 days. Second, all seedlings were allowed to grow under four levels of N fertilization treatments for another 60 days to ensure that the N was absorbed by seedlings. Third, all seedling were subjected to three levels of sustained drought treatments for further 60 days. Traits related to growth and physiology were monitored.

RESULTS

Our findings indicate that drought alone inhibited the growth and leaf photosynthetic rate of S. superba, while N fertilization alone stimulated the growth and leaf photosynthetic rate. Antecedent N fertilization alleviated the drought limitation on growth, due to the increased leaf photosynthetic rate (A) and instantaneous water use efficiency. Moderate N fertilization mitigated the negative effects of drought on A due to improved performance in stomatal conductance, leaf water potential and cell membrane permeability. Additionally, moderate N fertilization increased activities of antioxidant enzymes and osmoprotectants concentration under drought condition.

CONCLUSIONS

Overall, our findings suggest that increased N fertilization prior to drought can alleviate the negative effects of drought on growth and physiology, which is dependent on the magnitude of N fertilization and drought stress.