INTERFAMILY VARIATION IN NITROGEN PRODUCTIVITY OF PINUS-SYLVESTRIS SEEDLINGS

Open-pollinated families from 21 Pinus sylvestris L. clones from a see d orchard in central Sweden were cultivated in growth chambers in mine ral wool for two growth periods. Two nitrogen treatments were applied: high N availability, free access to all nutrient elements and low N a vailability aimed at 1/3 of the potential requirement under prevailing external conditions. The second treatment was realized by daily addit ions of nutrient solution containing nitrogen in amounts adjusted to p lant size and actual growth rate. Two types of nitrogen productivity w ere estimated for plants from the low-N treatment--one called nitrogen productivity, expressed per day and based only on the period of the i ntensive growth during the second growth period, the other, called nit rogen productivity per growth period, based on growth increment during the entire second growth period. Nitrogen productivity varied between 7.8 and 10.3 mg plant DW (mg needle N)(-1) day(-1), whereas the nitro gen productivity per growth period varied between 247 and 327 mg plant DW (mg needle-N)(-1) (second growth period)(-1), and both types showe d significant differences between families, with estimated heritabilit ies of 0.24 and 0.47, respectively. Generally, high N availability res ulted in less biomass partitioned to roots, compared with low N availa bility. There were family differences in growth response to the high N availability. Nitrogen productivity showed moderate and positive gene tic correlations with most of the biomass traits, although it was not correlated with the duration of the period of most intensive growth. T he results indicate the possibility of maximizing biomass production b y breeding for genotypes combining high nitrogen productivity and long growth period.