Objective The mixed-broadleaved Korean pine (Pinus koraiensis) forest is a zonal climax in mountainous area in eastern part of northeastern China, however, due to the unreasonable utilization in the 1950s, most of the mixed-broadleaved Korean pine forests in China were replaced by natural secondary forests, over-cutting forests and planted forests. The recovery of understory Korean pine and succession process of mixed-broadleaved Korean pine forests can be accelerated by artificial promotion of natural regeneration of P. koraiensis, so it is very important to study the photosynthetic physiological mechanism of P. koraiensis.
Method In order to explore the feasibility of artificial promotion of natural regeneration of P. koraiensis and the physiological effects of different cutting intensities on transplanted P. koraiensis seedlings, three sample plots with different cutting intensities (the cutting intensities of the sample plots were 0, 17% and 35%) were selected in this study, and the photosynthetic physiology of the transplanted P. koraiensis seedlings and the natural P. koraiensis seedlings was compared.
Result (1) There was no significant difference in photosynthetic efficiency and most chlorophyll fluorescence parameters between 6-year-old transplanted seedlings of P. koraiensis and 6-year-old natural seedlings of P. koraiensis, including net photosynthetic rate, water use efficiency, carbon assimilation quantum efficiency, maximum photochemical efficiency, actual photochemical efficiency, electron transfer efficiency, open PSII excitation energy capture efficiency, and non-photochemical quenching coefficient. (2) From the perspective of light response parameters, the light compensation point and dark respiration rate of transplanted P. koraiensis seedlings were higher than those of natural P. koraiensis seedlings, but the difference was not significant. (3) The maximum photochemical efficiency of transplanted and natural P. koraiensis seedlings under 35% cutting intensity (canopy density 0.6) was the lowest (P < 0.05), indicating that the two P. koraiensis seedlings were subjected to a certain degree of stress under 35% cutting intensity. (4) The net photosynthetic rate, maximum net photosynthetic rate, photochemical quenching coefficient and light saturation point of the transplanted seedlings of P. koraiensis increased first and then decreased with the increase of cutting intensity, reaching the maximum at 17% cutting intensity (canopy density 0.8).
Conclusion There is no significant difference in photosynthetic physiology between 6-year-old transplanted seedlings of P. koraiensis and 6-year-old natural seedlings of P. koraiensis. The transplanted P. koraiensis seedlings under canopy could well adapt to the forest environment; the regeneration of P. koraiensis under canopy does not advocate afforestation under the condition of post-cutting canopy density of 0.6, and P. koraiensis seedlings can be transplanted under the condition of post-cutting canopy density of 0.8.
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