The effect of nitrogen nutrition on growth and on plant hormones content in Scots pine (Pinus silvestris L.) seedlings grown under light of different intensity

Pine seedlings were cultivated in the Ingested nutrient solution containing N as NH₄Cl at concentrations of 0 and 500 ppm, under a 16-hr day, at a light intensity of 1500 and 500 lx and temperature ± 20°C. Measurements of seedlings and determination of plant hormones were performed 8 weeks after sowing. It was found that more intensive light stimulated initiation of needles and lateral roots as well as elongation of needles and roots, and increased the fresh weight and dry matter of these organs. Growth stimulation of needles was correlated with an increase in free gibberellins, cytokinins, an ABA-like inhibitor and with a decrease in auxins and water content of tissues. A similar effect of light on plant hormones (except ABA) was also observed in roots. The level of this inhibitor depended on N nutrition. Nitrogen bad a similar effect as light on the growth and initiation of needles and lateral roots. However, it strongly inhibited elongation of roots and increased the water content of the tissues. In needles N increased the level of GAs and auxins, under both light variants, as well as the level of cytokinins, under more intensive light. It decreased the amount of ABA-like inhibitor. In roots the effect of N nutrition on the level of plant hormones depended upon the light intensity. Under light of low intensity N decreased the level of GAs and ABA, increased the level of auxins and had nonsignificant influence on the level of cytokinins. Under more intensive light it had no effect on the GAs and auxin levels and increased the level of cytoikinins and the ABA-like inhibitor.