Antecedent Moderate Nitrogen Fertilization Alleviated the Effects of Drought on Growth and Leaf Photosynthesis of Schima Superba Seedlings

Abstract

Drought and nitrogen deposition are major global change factors that alter forest dynamics by affecting tree growth and physiology. However, the impact of increased nitrogen availability on tree responses to drought remains poorly understood. In this study, we conducted a fertilization-drought microcosm experiment using a widely distributed evergreen broadleaf tree species (Schima superba) in southern China. One-year old S. superba seedings were exposed to four levels of nitrogen (N) fertilization treatments for 120 days, and then subjected to three levels of sustained drought treatments for another 60 days. Traits related to growth and physiology were monitored. Our findings indicate that drought alone inhibited the growth and leaf photosynthetic rate of S. superba, while N fertilization alone stimulated growth and leaf photosynthetic rate. Antecedent N fertilization alleviated the drought limitation on growth. Furthermore, moderate N fertilization mitigated the negative effects of drought on photosynthetic rate, associated with improved performance in stomatal conductance, leaf water potential, chlorophyll concentration and cell membrane. Additionally, moderate N fertilization stimulated the increase in activities of antioxidation enzymes and osmoprotectants concentration under drought condition. Overall, our findings suggest that increased N fertilization prior to drought can alleviate the negative effects of drought on growth, and moderate N fertilization mitigated the negative effects of drought on photosynthetic rate. However, how increased N availability would alter the physiological responses to drought is dependent on the magnitude of N fertilization and drought stress.

Keywords: Drought, fertilization, growth, gas exchange, Biochemical traits