Simulated pollutant nitrogen deposition increases P demand and enhances root-surface phosphatase activities of three plant functional types in a calcareous grassland

The effects of 7 yr enhanced nitrogen (N) deposition (3.5-14 g N m(-2) yr(-1)) in combination with phosphorus (P) additions, on growth, shoot N and P content, and root-surface phosphomonoesterase (PME) activities were determined along with mycorrhizal infection rates in seedlings of a sedge (Carex flacca), grass (Koeleria macrantha) and forb (Leontodon hispidus). Seedlings were grown for 14-28 d in mesh-walled cores inserted into turfs from treated field plots enabling complete root recovery. After 14 d, root-surface PME activity was typically more than doubled by 3.5 and 14 g N m(-2) yr(-1), and by 28 d the N treatments consistently gave dose-dependent effects. PME activity was reduced by P additions in the sedge and grass by 55 and 65%, respectively, and correlated with soil and shoot N and P concentrations, again most strongly in the sedge and grass. Mycorrhizal infection was least in the sedge (1%) and greater in the grass (49%) and forb (76%). Long-term N enrichment of calcareous grassland stimulates root-surface PME in representatives of the three major higher-plant functional types. PME response to P additions was greatest in least mycorrhizal-dependant species with roots more adapted for direct P uptake.