Spatial heterogeneity of photosynthetic characteristics of Castanopsis fargesii canopy

The vertical and horizontal differences in the energy transmission,photosynthetically active radiation,and micrometeorological characteristics of forest canopy can lead to a considerable heterogeneity,which should be analyzed when estimating forest primary productivity.With Castanopsis fargesii,the dominant species in the subtropical evergreen broad-leaved forest in Tiantong National Forest Park of Zhejiang Province as test object,this paper studied the vertical and horizontal variations of photosynthetic characteristics of its canopy.Vertically,the photosynthetic indices such as maximum photosynthetic rate(Amax),light saturation point(LSP),and carboxylation efficiency(CCE)of north-facing leaves in the canopy all declined in the sequence of top canopymid-canopybottom canopy.The mean values of light compensation point(LCP),respiration in light(Rd),and Amax from top canopy to bottom canopy reduced by 19.4%,18.1% and 37.1%,respectively.The LSP and CCE of south-facing leaves followed the pattern of top canopybottom canopymid-canopy.These two indices decreased by 12.3% in bottom canopy and 71.4% in mid-canopy,compared with those in top canopy.The apparent quantum yield(AQY)of leaves followed the sequence of bottom canopytop canopymid-canopy,being 1.1 and 1.3 times higher at bottom canopy than at top-and mid-canopy,respectively.Horizontally,the Amax,LSP and CCE of south-facing leaves at top-and bottom canopy were 0.9%-31.5% higher than those of north-facing leaves.In mid-canopy however,the values of test six indices of north-facing leaves were 9.6%-63.2% higher than those of south-facing leaves.It was suggested that in order to estimate and model forest primary productivity accurately,the vertical and horizontal heterogeneity of photosynthetic characteristics of forest canopy should be analyzed.