Selected Metals in Various Fractions of Soil and Fungi in a Swedish Forest

The patterns of uptake and distribution of Co, Ni, Cu, Zn, Cd, and Pb in the soil-mycelium-sporocarps compartments in various transfer steps are presented. I attempted to find out whether there is a difference between the uptake of metals from soil to fungi (mycelium/soil ratio) and transport within fungal thalli (sporocarps/mycelium ratio). The concentration of Cu, Zn, and Cd increased in the order bulk soil < soil-root interface (or rhizosphere) < fungal mycelium < fungal sporocarps. The concentration of Co, Ni, and Pb decreased in the order bulk soil (or rhizosphere) < fungal mycelium < soil-root interface < fungal sporocarps. The uptake of Cu, Zn, and Cd during the entire transfer process in natural conditions between soil and sporocarps occurred against a concentration gradient. Mycorrhizal fungi (mycelium and sporocarps) only absorbed Co, Ni, and Pb but did not accumulate these elements in their thalli. Metal accumulation within fungal mycelium biomass in the top forest soil layer (0–5？cm) may account for about 5% of the total amount of Co, 4% Ni, 7% Cu, 8% Zn, 24% Cd, and 3% Pb. 1. Introduction Ectomycorrhizal fungi are major components of fungal community in the soils of most boreal and temperate forests. The mycelium of soil fungi plays a crucial role in nutrient cycling and nutrient uptake into plants from soil via the formation of symbiotic mycorrhizal associations [1]. Mycorrhizal fungi increase the surface absorbing area of roots and enhance nutrient uptake into the host plant: this is due to the physical geometry of the mycelium and its ability to mobilise nutrients from organic substrates through the action of extracellular catabolic enzymes [2]. Mycorrhizal mycelia have the ability to take up mineral nutrients [3] and mycorrhizal fungi acquire both essential macronutrients, such as phosphorus [4], and are efficient at taking up and accumulating microelements [3]. This includes the accumulation of both nonessential elements and trace metals [5, 6], such as the heavy metal cadmium (Cd), an element of concern for food quality as its behaviour is analogous to essential metals, and essential nutrient elements such as zinc (Zn) and the trace element copper (Cu). Cd, Zn, and Cu accumulate in mushroom thalli [7, 8]. Sporocarps of many macrofungi might contain extremely high levels of heavy metals, with Cd being among the most intensively accumulated metal [9–13]. Relatively high Cu and Zn concentrations (bioaccumulation values higher than 1) in certain species of wild growing fungi are also reported [8, 11, 12, 14]. Thus, soil fungi, especially