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 2185, 4557, 6602, and 2348 μmol·m-2·s-1, respectively, and the difference was statistically significant (P＜005). PAR had a significant positive correlation with net photosynthetic rate (Pn), and the correlation coefficient increased with increasing PAR. With the increase of gap size, both the PAR and the Pn of P. koraiensis saplings increased first and decreased then, with the maximum values appeared at 267 m2 of gap size .

Key words: paddy soil chronosequence, cultivation age, organic carbon, particle size distribution.