Canopy leaching of nutrients and metals in a mountain spruce forest

Precipitation and throughfall fluxes of major ions, nutrients (C, N, P), and metals (Al, Fe, Mn), and the chemical composition of litter fall and living plant tissue in Norway spruce stands (the Bohemian Forest; Czech Republic), were used to evaluate how microbial processes and decay of plant tissue in canopies influence canopy leaching (CL) of elements. Proton exchange for Mg2+, Ca2+, and K+ in decaying biomass and co-transport of Ca2+ and K+ out of plant cells with organic acid anions were the most likely processes contributing to CL of base cations. The CL of total P and N (and also NO3−) was minor. Important proportions of the N and P mineral forms were transformed to organic forms by microbial processes (primary and bacterial production), with the respective CL of −13.9 and 16.4 mmol m−2 yr−1 for NH4+ and organic N, and −0.33 and 0.22 mmol m−2 yr−1 for dissolved reactive P (DRP) and organic P. Most of particulate P and N in throughfall (∼90%) originated from microbial DRP and NH4+ transformations, but particulate C mostly came from the fragmentation of plant tissue (58%). Among metals, CL was not observed for Al, was small for Fe (0.3 mmol m−2 yr−1), and greatest for Mn (0.9 mmol m−2 yr−1) due to leaching from decaying tissue by acidic precipitation.