|Heuck, C; Smolka, G; Whalen, E; Frey, S; Gundersen, P; Moldan, F; Fernandez, IJ; Spohn, M: Effects of long-term nitrogen addition on phosphorus cycling in organic soil horizons of termperate forests, Biogeochemistry, 141(2), 167–181 (2018), doi:10.1007/s10533-018-0511-5|
High atmospheric nitrogen (N) deposition is expected to impair phosphorus (P) nutrition of temperate forest ecosystems. We examined N and P cycling in organic soil horizons of temperate forests exposed to long-term N addition in the northeastern USA and Scandinavia. We determined N and P concentrations, phosphatase activities and net N and P mineralization rates in organic soil horizons of two deciduous (Harvard Forest, Bear Brook) and two coniferous (Klosterhede, Gårdsjön) forests which had received experimental inorganic N addition between 25 and 150 kg N ha-1yr-1 for more than 25 years. Long-term N addition increased the activity of phosphatase (+180%) and the activity of carbon (C)- and N-acquiring enzymes (cellobiohydrolase: +70%, chitinase: +25%). Soil N enrichment increased the N:P ratio of organic soil horizons by up to 150%. In coniferous organic soil horizons, net N and P mineralization were small and unaffected by N addition. In deciduous organic soil horizons, net N and P mineralization rates were significantly higher than at the coniferous sites, and N addition increased net N mineralization by up to 290%. High phosphatase activities concomitant with a 40% decline in P stocks of deciduous organic soil horizons indicate increased plant P demand. In summary, projected future global increases in atmospheric N deposition may induce P limitation in deciduous forests, impairing temperate forest growth.