NUTRIENT CYCLING IN PINUS-SYLVESTRIS STANDS IN EASTERN FINLAND

Nutrient cycling within three Pinus sylvestris stands was studied in e astern Finland. The aim of the study was to determine annual fluxes an d distribution of N, P, K, Ca, Mg, Mn, Zn, Fe, B, and Al in the resear ch stands. Special emphasis was put on determining the importance of d ifferent fluxes, especially the internal cycle within the trees in sat isfying the tree nutrient requirements for biomass production. The fol lowing nutrient fluxes were included, input; free precipitation and th roughfall, output; percolation through soil profile, biological cycle; nutrient uptake from soil, retranslocation within trees, return to so il in litterfall, release by litter decomposition. The distribution of nutrients was determined in above- and belowground tree compartments, in ground and field vegetation, and in soil. The nitrogen use efficie ncies were 181, 211 and 191 g of tree aboveground dry matter produced per g of N supplied by uptake and retranslocation in the sapling, pole stage and mature stands, respectively. Field vegetation was more effi cient in nitrogen use than trees. Stand belowground/aboveground and fi ne root/coarse root biomass ratios decreased with tree age. With only slightly higher fine root biomass, almost three times more nitrogen ha d to be taken-up from soil for biomass production in the mature stand than in the sapling stand. The annual input-output balances of most nu trients were positive; throughfall contained more nutrients than was l ost in mineral soil leachate. The sulphate flux contributed to the lea ching of cations, especially magnesium, from soil in the mature stand. Retranslocation supplied 17-42% of the annual N, P and K requirements for tree aboveground biomass production. Precipitation and throughfal l were important in transferring K and Mg, and also N in the sapling s tand. Litterfall was an important pathway for N, Ca, Mg and micro nutr ients, especially in the oldest stands.