Abstract:By using a Li-6400 portable photosynthesis system, this paper studied the heterogeneity of light intensity in four different size gaps of a broadleaved Korean pine forest in Changbai Mountains, and analyzed the diurnal change of the photosynthesis of Pinus koraiensis saplings in the gaps. In the nine orientations within the gaps, the peak value of the photosynthetically active radiation (PAR) varied in the sequence of west of actual gap, north of extended gap, gap center＞south of actual gap, south of extended gap, east of extended gap, east of actual gap＞west of extended gap, north of actual gap. Light distribution was dissymmetry in the orientations of east-west and south-north, with the variation in west and north being more significant than that in other orientations. There was no significant difference in the average PAR among the positions within specific orientations. The average PAR of the four gaps from I to IV was 2185, 4557, 6602, and 2348 μmol·m-2·s-1, respectively, and the difference was statistically significant (P＜005). PAR had a significant positive correlation with net photosynthetic rate (Pn), and the correlation coefficient increased with increasing PAR. With the increase of gap size, both the PAR and the Pn of P. koraiensis saplings increased first and decreased then, with the maximum values appeared at 267 m2 of gap size .