Photosynthesis and canopy characteristics in genetically defined families of silver birch (Betula pendula).

Net photosynthetic rates (A) of leaves in upper and lower crown layers (A(upper) and A(lower)), leaf area index (LAI), mean tilt angle (MTA), several leaf characteristics, and volume growth were observed in fast- and slow-growing families of a 14-year-old full-sib and half-sib family progeny test of Betula pendula Roth. Each measure of net photosynthetic rate was calculated after correcting measured net photosynthesis for the effects of environmental variables. The differences in A(upper) and LAI among families were significant. The proportions of the total variance assigned to family for A(upper), A(lower) and LAI were 33.64, 28.93 and 54.99%, respectively. The mean A(upper) and LAI of the fast-growing families were significantly higher than those of the slow-growing families, whereas the mean A(lower) of the fast-growing families was significantly lower than that of the slow-growing families. There were also significant differences among families in leaf size, leaf shape, and the ratios leaf fresh weight/area and leaf dry weight/area. Between 27.55 and 54.55% of the total variance in these characteristics could be assigned to the family effect. Volume growth was positively correlated with A(upper) and LAI, but it was most strongly correlated with A(upper) x LAI.