Experimental study of DOC, nutrients and metals release from forest floors developed under beech (Fagus sylvatica L.) on a Cambisol and a Podzol

Forest floor in acid forest soils is a major source of dissolved organic carbon (DOC), nutrients and metals. We studied the release of DOC, nutrients and metals from two forest floors under beech stands (a moder from a Cambisol and a mor from a Podzol). We analyzed the composition of the solid phase, and we monitored the chemical properties of forest floor leachates through incubation-leaching experiments at 4 and 20 °C. Our data show that the release of DOC, nutrients and metals strongly differed between both forest floors. Whatever the temperature, the release of DOC, DIN, divalent cations and heavy metals, as compared to initial stocks of corresponding elements, were the largest in moder leachates. Instead, the release of K+, Na+, Si, Al and Fe were the largest in mor leachates at 20 °C, and were generally similar for both forest floors at 4 °C. The ionic signature of the leachates was strongly affected by DOC release and nitrogen mineralization, which was mostly directed towards the production of ammonium in mor, and of nitrate in moder. In moder leachates at 20 °C, Ca2+ was the dominant cation, and nitrate the major anion. Instead, in mor leachates, NH4+ was the major cation, and organic anions dominated the anionic charge. Despite the dominance of organic anions in mor leachates, the concentrations of cations and Si were strongly correlated to the concentrations of inorganic anions in leachates from both forest floors. The concentration of Al, Fe, Cu and Pb were strongly correlated to the concentration of organic anions, whereas Zn concentration was poorly correlated with either organic or inorganic anions.