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 fas t- and slow-growing families of a 14-year-old full-sib and half-sib fa mily progeny test of Betula pendula Roth. Each measure of net photosyn thetic rate was calculated after correcting measured net photosynthesi s for the effects of environmental variables. The differences in A(upp er) and LAI among families were significant. The proportions of the to tal 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 famil ies was significantly lower than that of the slow-growing families. Th ere were also significant differences among families in leaf size, lea f shape, and the ratios leaf fresh weight/area and leaf dry weight/are a. Between 27.55 and 54.55% of the total variance in these characteris tics could be assigned to the family effect. Volume growth was positiv ely correlated with A(upper) and LAI, but it was most strongly corrrel ated with A(upper) X LAI.