Genetic variation in nitrogen uptake and growth in mycorrhizal and nonmycorrhizal Picea abies (L.) Karst. seedlings

The purpose of this study was to estimate genetic variation in nitrogen uptake and growth of mycorrhizal and nonmycorrhizal seedlings from 30 open-pollinated families of Norway spruce (Picea abies), at two levels of nitrogen (N) supply. Six-week-old seedlings were transplanted into 1.7 L pots filled with pumice, and one-half of them was inoculated with the ectomycorrhizal symbiont Laccaria bicolor. A 2 x 2 factorial combination of the presence or absence of the fungus and two nitrogen concentrations (200 mg N/L and 25 mg N/L) was used during 2 wk of establishment. During the following 10 wk, no water or nutrients were supplied At harvest (week 18) height, shoot and root dry weights, as well as the amount of nitrogen in the shoot and nitrogen acquisition capacity, were determined. There was a strong treatment effect, and most of the traits ranked in increasing order: low N, low N + Mycorrhiza, high N, high N + Mycorrhiza. With low N, plants with mycorrhiza had a shoot dry weight twice that of nonmycorrhizal plants. Significant differences among families were found for most traits in treatments without mycorrhiza, while mycorrhiza strongly reduced the number of significant family differences. The amount of nitrogen in the shoot and all biomass traits showed a significant family x mycorrhiza x nitrogen interaction. Of the two traits related to nitrogen uptake, shoot nitrogen amount showed strong genetic correlations with biomass traits in all treatments (r(g) within the range 0.92 to 0.99) whereas nitrogen acquisition capacity did not (rg within the range -0.53 to +0.23), which implies that the amount of nitrogen in the shoot is a better predictor of growth than nitrogen acquisition capacity.