Canopy uptake of N deposition in spruce (Picea abies L Karst) stands

In order to quantify the total deposition and canopy uptake of N in spruce, plastic Christmas trees were established next to real spruce trees of appr oximately similar height in clearings of the Strengbach catchment (Vosges m ountains, France). Bulk precipitation and throughfall (TF) composition unde r the artificial trees, the real spruce trees, and in 3 spruce stands aged 15, 35 and 90 years were monitored during 8.5 months. Fluxes of inorganic N , SO42- and Na+ in throughfall below plastic trees were 50% (N) to 30% (Na) higher to there in bulk precipitation, whereas. the flux of water was 30% lower. Net throughfall (NTF) fluxes of NH4+ were higher below the plastic trees than below the real trees, whereas the reverse was true for NO3-. The ratio between total inorganic nitrogen and Na+ (or SO42-) in NTF was highe r below plastic trees than below closed spruce stands. Assuming that foliar leaching of Na+ (or SO42-) was negligible, the ration between Na+ (or SO42 -) fluxes in net throughfall under living and plastic canopies were used as deposition indexes, and dry + occult deposition of N was computed for the real spruce trees in the clearings as well as in the 3 closed stands. Resul ts confimed a significant canopy uptake of dry + occult deposited N and esp ecially NH4+ by spruce stands.