Objective This paper aims to explore the effects of various nitrogen (N) addition levels on photosynthetic and fluorescence characteristics of the seedlings of four main tree species at different succession stages of broadleaved-Korean pine forest. To reveal the response mechanisms of different tree species seedlings to N addition, this paper provides some reference for the application of artificial afforestation tree species, and to make predictions on the forest succession situation in Northeast China against the background of increased N deposition.

Method Betula platyphylla, Quercus mongolica, Tilia amurensis and Pinus koraiensis were selected as the research objects in Shulan City of Jilin Province of northeastern China. The levels of N addition were 0, 50, 100 kg/(year·ha), respectively. The plant photosynthetic parameters, spectral reflectance parameters, fluorescence parameters and other indicators under different N treatments were measured, and variance analysis and mean multiple comparison were performed.

Result The net photosynthetic rate of B. platyphylla remained the highest under different N conditions, and was less affected by N. The net photosynthetic rate of Q. mongolica increased significantly under LN due to the increase of chlorophyll content, and decreased significantly under HN due to the restriction of stomata and electron transport ability. T. amurensis had low maximum quantum yield (F_v/F_m), poor electron transport activity, and it was strongly inhibited by light, the net photosynthetic rate was the lowest under different N conditions, and there was no significant difference under different N treatments. The net photosynthetic rate of P. koraiensis decreased under N application due to the reduced electron transport rate.

Conclusion It is speculated that the growth of Q. mongolica will occupy a great advantage under LN concentration, while the broadleaved-Korean pine forest will still be dominated by B. platyphylla in the early stage under high N concentration, while Q. mongolica will be suppressed in the middle stage, T. amurensis will occupy the advantage, and the growth of P. koraiensis will also be inhibited by high N in the later stage.