349 For. Snow Landsc. Res. 80, 3: 349–360 (2006) Availability and toxicity of Cu and Ni to Scots pine in different soils Tiina M. Nieminen 1 *, Liisa Ukonmaanaho 1 , Nicole Rausch 2 and William Shotyk 3 1 Finnish Forest Research Institute, BOX 18, FI-01301 Vantaa, Finland. tiina.nieminen@metla.fi, liisa.ukonmaanaho@metla.fi 2 European Commission Joint Research Center, Institute for Transuranium Elements, Nuclear Chemistry Unit, Analytical Chemistry section, Box 2340, D-76125 Karlsruhe, Germany. rausch@cec.eu.int 3 Institute of Environmental Geochemistry, University of Heidelberg, Im Neuenheimer Feld 236, D-62120 Heidelberg, Germany. shotyk@ugc.uni-heidelberg.de * Corresponding author Abstract We compared the phytoavailability and within plant mobility of Cu and Ni, as well as the plant mortality, in two contrasting substrates: intact smelter-polluted podzol soil profiles and artificially Cu-Ni contaminated quartz-sand media. Both the uptake and the root-to-shoot transport of Cu and Ni by pine seedlings were clearly higher in the artificially contaminated quartz-sand. No pine mortality took place in the smelter-polluted soils at the levels of metal concentration established as the thresholds for lethal toxicity in the artificial contamination series, although the mortality rate was high in the most contaminated smelter-polluted soil. We further compared the exposure doses and mortality rates in these two substrates with those of an old field experiment, in which a predetermined dose of Cu and Ni was applied on a peat bog in 1962. The Cu dose and the pine mortality response observed at the peat bog site were both lower than those obtained from the most polluted smelter-polluted soil, probably partly because the current Cu and Ni concentrations in the topmost peat layer bear little relation to their original exposure dose. Keywords: metal mobility, peat, podzol, root uptake, quartz-sand 1 Introduction Heavy metals from smelting activities have probably affected forest ecosystems since the beginning of metallurgy. The amount of metals accumulated in soil continues to affect vegetation even after emissions have ceased. Increased concentrations of metals in soil can have an effect on plants both by their direct toxicity and by their toxicity to litter decomposing organisms in soil (BAATH 1989; FRITZE et al. 1989; LUKINA and NIKONOV 1995), which leads to impaired soil-nutrient status. Results about the effects of smelter emissions on soil acidity are rather contradictory (DEROME 2000). DEROME and LINDROOS (1998) report displace- ment of base cations from cation-exchange sites by copper (Cu) and nickel (Ni) cations in the vicinity of a Cu-Ni smelter, although no signs of acidification were found. Metal toxicity is dependent on the metal’s availability to the plant, which, for its part, is dependent on the soil characteristics and on the plant species in question. The strength of binding of the metal by the soil controls its availability. The pH of the soil solution, Ca con- tent and the dissolved and solid organic matter content are among the key properties of the soil control (ALLEN 2002). Metals in soils are present in different forms or species with different levels of availability and toxicity. The presence and quality of chelators in nutrient solutions has been shown to affect metal toxicity. For example TAYLOR and FOY (1985)