EFFECTS OF LIGHT CONDITIONS AT DIFFERENT GROWTH STAGES ON GROWTH AND PHOTOSYNTHETIC CHARACTERISTICS OF PINUS SYLVESTRIS VAR. SYLVESTRIFORMIS SEEDINGS.

Pinus sylvestris var. sylvestriformis is an endemic plant in Changbai Mountain area of China. Five different light levels were simulated and designed with control experiments: full sunlight (CK), light shading (light transmittance was 10%) (LA), light and moderate shading (light transmittance was 20%) (LB), moderate shading (light transmittance was 40%) (LC), and severe shading (light transmittance was 60%) (LD). The optimal light levels and the main physiological and ecological factors affecting photosynthesis in different growth stages were discussed. The results showed that the phenotypic index and photosynthetic physiological and ecological indicators were the highest when the light transmittance was 40%. In the early growth phase, the physiological factors intercellular CO₂ concentration (C_i) and ecological factors transmittance (Tran) and air temperature (Temp) jointly affected the changes of net photosynthetic rate (P_n). In the peak growth phase, transpiration rate (T_r), air humidity (RH), and Tran had greater direct positive effects on P_n, and C_i and stomatal conductance (G_s) had direct negative effects on P_n. In the later growth phase, T_r and C_i had large direct positive effects on P_n. The research results could provide important references for the scientific cultivation and popularization of P. sylvestris var. sylvestriformis. [ABSTRACT FROM AUTHOR]