The effects of quantity and duration of simulated pollutant nitrogen deposition on root‐surface phosphatase activities in calcareous and acid grasslands: a bioassay approach

A field and laboratory based bioassay has been developed to investigate the effects of the quantity and duration of simulated pollutant nitrogen (N) deposition on root‐surface phosphomonoesterase (PME) activities in calcareous and acid grasslands. Seedlings of Plantago lanceolata were transplanted to a calcareous grassland and Agrostis capillaris seedlings were grown in microcosms containing soil from an acid grassland that had received either 7 yr (long‐term) N additions or 18 months (short‐term) N and phosphorus (P) additions. The bioassay revealed that short‐term N treatments had little effect on the enzyme activity, whereas long‐term N additions significantly increased PME activity within 7 d of transplanting into the field plots. Root‐surface PME activity of A. capillaris was significantly reduced in soil that received additions of P. In the plots receiving long‐term additions of N, a strong relationship was observed between extractable soil ammonium and root‐surface PME activity. Soil ammonium concentrations accounted for 67% of the variation in PME activity of P. lanceolata in the calcareous grassland, and 86% of the variation in PME activity of A. capillaris in the acid grassland. These results provide evidence that N deposition may have considerable effects on the demand and turnover of P in ecosystems that are approaching or have reached N saturation.