NITROGEN UPTAKE OF NORWAY SPRUCE (PICEA-ABIES KARST) SEEDLINGS FROM SIMULATED WET DEPOSITION

The uptake of nitrogen by cloned Norway spruce (Picea abies Karst.) seedlings from wet deposition was studied in a simulation experiment both in greenhouse and in field conditions. The simulation was conducted with ammonium sulphate and sodium nitrate labelled with N-15 isotope (10% of total N). The seedlings were treated separately with labelled ammonium and nitrate as well as a mixture of NH4 and NO3. Furthermore, nitrogen was applied separately to the soil (root pot) and directly on needle foliage. The nitrogen applications corresponded approximately to 10 and 40 kg N ha-1 year-1 wet deposition. The results indicate that Norway spruce seedlings preferred ammonium as the main source of N via soil, if ammonium and nitrate were applied as a mixture. Norway spruce seedlings were also able to take up nitrogen directly via needles and ammonium-N was utilised more readily than nitrate-N by the needles. However, the proportion of the direct foliar N uptake was low compared with the total N uptake of the seedlings. A higher proportion of ammonium than of nitrate assimilated directly in the needles remained in the foliage. The seedling rhizosphere was found to increase the amount of nitrate in the acid sandy soil.