EFFECTS OF VARIED SOIL-NITROGEN SUPPLY ON NORWAY SPRUCE (PICEA-ABIES [L] KARST) .1. SHOOT AND ROOT-GROWTH AND NUTRIENT-UPTAKE

During a seven-month period the effect of different nitrogen (N) avail ability in soil on growth and nutrient uptake was studied in three-yea r-old Norway spruce (Picea abies [L.] Karst.) trees. The plants were g rown in pots on N-poor forest soil supplied with various amounts and f orms (inorganic and organic) of N. Increasing supply of inorganic N (a s NH4NO3) increased the formation of new shoots and shoot dry weight. The root/shoot dry weight ratio of new growth was drastically decrease d from 1.6 in plants without N supply to 0.5 in plants supplied with h igh levels of NH4NO3. This decrease in root/shoot dry weight ratio was associated with distinct changes in root morphology in favour of shor ter and thicker roots. The addition of keratin as organic N source did neither affect growth nor root morphology of the trees. The amount of N taken up by plants was closely related to the supply of inorganic N , and trees supplied with highest levels of NH4NO3 also had the highes t N contents in the dry matter of needles and roots. In contrast, N co ntents in needles of trees grown without additional N, or with keratin supply, were in the deficiency range. Supply of NH4NO3 decreased the contents of phosphate (P) and potassium (K) and therefore markedly inc reased N/P and N/K ratios in the needles. On the other hand, the conte nts of calcium (Ca), magnesium (Mg), and manganese (Mn) in the needles were increased in the plants supplied with inorganic N, suggesting hi gh soil availability and promotion of uptake of these divalent cations by high nitrate uptake. The observed effects on root/shoot dry weight ratio, root morphology, and mineral nutrient composition of the needl es indicated that high inorganic N supply may increase above-ground pr oductivity but at the same time decrease the tolerance of trees agains t soil-borne (e.g. deficiency of other mineral nutrients) stress facto rs.