Effects of N application on N accumulation of two Erigeron breviscapus populations from different altitudes under enhanced ultraviolet-B radiation

To study intraspecific differences in N utilization in response to enhanced UV-B radiation, field experiments were conducted on two Erigeron breviscapus populations (Huguo and Cangshan), which were respectively obtained from low altitude (UV-B sensitive) and high altitude (UBV-B resistant).The effects of soil nitrogen (N) application (0, 15, 30, 45 g m²) on free amino acid content, the activities of nitrate reductase (NR) and glutamine synthetase (GS), total nitrogen content and N mass in leaves were determined under enhanced UV-B radiation (5 kJ m²) for both populations. The results showed that under enhanced UV-B radiation: (1) increases in total N contents in leaves of the Huguo and Cangshan populations correlated with the amount of N applied. Additionally, leaf biomass of Huguo treated with 15 g m^?2 N application and Cangshan with 30 g m^?2 N application were higher than that of other treatments. Leaf N masses were highest in both E. breviscapus populations treated with 30 g m^?2 N; (2) increases in contents of free amino acids in leaves of both E. breviscapus populations correlated with the amount of applied nitrogen; (3) increases of NR activity in leaves correlated with the amount of applied nitrogen; (4) GS activity in leaves of the Huguo and Cangshan E. breviscapus populations were highest with respective N applications of 15 g m^?2 N and 30 g m^?2 N. In general, under enhanced UV-B radiation, N application might affect NR and GS and change free amino acid content, resulting in changes in total nitrogen content, biomass and N mass. The optimal amount of supplemental N for N accumulation in E. breviscapus was 30 g m^?2 N under enhanced UV-B radiation.