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Abstract
Open‐pollinated families from 21 Pinus sylvestris L. clones from a seed orchard in central Sweden were cultivated in growth chambers in mineral wool for two growth periods. Two nitrogen treatments were applied: high N availability, free access to all nutrient elements and low N availability aimed at 1/3 of the potential requirement under prevailing external conditions. The second treatment was realized by daily additions of nutrient solution containing nitrogen in amounts adjusted to plant size and actual growth rate. Two types of nitrogen productivity were estimated for plants from the low‐N treatment‐one called nitrogen productivity, expressed per day and based only on the period of the intensive growth during the second growth period, the other, called nitrogen 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 nitrogen productivity per growth period varied between 247 and 327 mg plant DW (mg needle‐N)−1 (second growth period)−1, and both types showed significant differences between families, with estimated heritabilities of 0.24 and 0.47, respectively. Generally, high N availability resulted in less biomass partitioned to roots, compared with low N availability. There were family differences in growth response to the high N availability. Nitrogen productivity showed moderate and positive genetic correlations with most of the biomass traits, although it was not correlated with the duration of the period of most intensive growth. The results indicate the possibility of maximizing biomas production by breeding for genotypes combining high nitrogen productivity and long growth period.
