EFFECTS OF VARIED SOIL-NITROGEN SUPPLY ON NORWAY SPRUCE (PICEA-ABIES [L] KARST) .2. CARBON METABOLISM IN NEEDLES AND MYCORRHIZAL ROOTS

The response of carbohydrate metabolism in 3-year-old Norway spruce pl ants to an increased amount of nitrogen supply to a N-poor forest soil was investigated in a pot experiment. After 7 months of treatment we found a decreased amount of starch in both needles and roots, together with decreased amounts of sucrose in needles of those plants grown un der an enhanced inorganic N supply. In addition, the activity and the protein amount of the anaplerotic enzyme phosphoenolpyruvate carboxyla se (PEPC) and the activity of NADP-dependent isocitrate dehydrogenase (IDH) were clearly increased. The activity of sucrose phosphate syntha se (SPS) and the pool size of fructose 2,6-bisphosphate (F26BP) were n ot affected by high supply of inorganic N. These data indicate a shift of carbon flow from starch formation towards an enhanced provision of carbon skeletons for N assimilation and shoot growth. In parallel, we found decreased contents of fungus-specific compounds (ergosterol, ma nnitol, trehalose) in roots, which are indicators of a decreased colon ization by ectomycorrhizal fungi, probably as a result of a changed al location and partitioning of photoassimilates due to an increased N su pply.