Effects Of Light Intensity Heterogeneity In Gaps Of Broadleaved Korean Pine Forest In Changbai Mountains On Main Species Saplings Photosynthesis

With a Li-6400 portable photosynthesis system,the light heterogeneity among four gaps;distinguished in size,were studied in a broadleaved Korean pine forest in Changbai Mountain,and the diurnal dynamics of photosynthesis of Pinus koraiensis saplings in nine orientations within the sites were analyzed from July to Augest,2007.The results showed that:The maximum of photosynthetically active radiation(PAR) varied with both orientation and time;the PAR peaks occurred in the sequence as follows:West of actual gap,North of expanded gap,Gap center＞South of actual gap,South of expanded gap,East of expanded gap,East of actual gap＞West of expanded gap,North of actual gap. Light distribution was dissymmetry in both orientations of east-west and south-north,with variations in west and north sides more significant comparing with that in other orientations.In contrast,the average PAR showed no significant difference among positions within specific orientations.Average PAR of the four gaps fromâ… toâ…£were 21.85,45.57,66.02 and 23.48μmol·m^-2·s^-1,respectively,and the difference was statistically significant(P＜0.05).PAR and net photosynthetic rate(P_n) showed significantly positive correlation which was-closer with the increase of PAR.Both PAR and P_n of P.koraiensis saplings increased at first then decreased with the increase of gap size,and the maximum values appeared at 267 m².With a Li-6400 portable photosynthesis system,the light heterogeneity among three gaps,distinguished in age,and understory were studied in a broadleaved Korean pine forest in Changbai Mountain,and the diurnal dynamics of photosynthesis of P.koraiensis saplings and other three species within the sites were analyzed from July to Augest,2008.The results showed that:The Average photosynthetically active radiation(PAR) occurred in the sequence as follows:early aged gap＞middle aged gap＞old aged gap＞understory,and were 71.58,38.10,26.18,21.80μmol·m^-2·s^-1,respectively. Average PAR as well as its single peak in gaps were significantly higher than that in understory,and were 45.29μmol·m^-2·s^-1,21.80μmol·m^-2·s^-1,respectively.The intrinsic quantum efficiency for CO₂ uptake(α) and The maximum of net photosynthetic rate(P_max) in gaps and understory occurred in the sequence as follows:T.amurensis＞Q.mongolica＞A.mono.Theαof T.amurensis and Q.mongolica in gaps were higher than that in understory,while the a of A.mono showed opposite result.Among three gaps,distinguished in age,Average PAR of four species in gaps were higher than that in understory. Average PAR of P.koraiensis and A.mono were higher than that of T.amurensis and Q.mongolica in young and middle aged gaps.Average PAR of T.amurensis and Q.mongolica were higher than that of P. koraiensis and A.mono in old aged gap,the same trend as that in understory.