Nutrient retranslocation in the foliage of Pinus sylvestris L. growing along a heavy metal pollution gradient.

Retranslocation of N, P, K, Ca, Mg, Mn, Fe, Zn, Cu and Ni within the foliage of Scots pine (Pinus sylvestris L.) was studied during autumnal needle senescence along a heavy-metal pollution gradient in western Finland. The stands were located at distances of 0.5 (Har 0.5), 4 (Har 4) and 8 km (Har 8) to the southeast of a copper-nickel smelter at Harjavalta. A background study stand was located at Hämeenkangas (Häm), 60 km northeast of the smelter. During needle senescence, the mobile nutrients N, P and K decreased by 67-88% and needle dry mass decreased by 31-43%. Retranslocation of P and K was less efficient in the stand nearest the smelter (Har 0.5) than in the other stands. During needle senescence at stand Har 0.5, heavy metal content either decreased slightly (Zn, Ni) or increased (Fe, Cu), whereas in the background study stand, retranslocation efficiency of Cu was 75%. Net throughfall (the amount of a nutrient in throughfall minus the amount in open precipitation) was higher in stand Har 0.5 than in stand Har 8 for all of the elements measured, except N and P which were intercepted by the canopy. In stand Har 8, deposition of S, Cu and Ni was intercepted by the canopy, and net throughfall of Fe and Zn was very low. In contrast, S and heavy metal contents of net throughfall in stand Har 0.5 were greater than the decrease in these elements in the needles indicating that accumulation on needle surfaces and subsequent wash-off accounted for a major part of the fluxes. Furthermore, the Cu content in net throughfall during the senescence period was higher than the original Cu content of the needles in July, providing additional evidence that much of the needle Cu content was comprised of dry deposits of Cu on the needle surface.