Long-term nitrogen deposition increases phosphorus limitation of bryophytes in an ombrotrophic bog

Here we investigate the effect of 4 years simulated atmospheric deposition of ammonium (NH4) and nitrate (NO3), applied alone or in combination with phosphorus and potassium (PK), on the surface phosphatase activities and nutrient acquisition behaviour of two species of moss (Sphagnum capillifolium and Hypnum jutlandicum) from an ombrotrophic peatland. Phosphatase activity was significantly enhanced by both the NH4 and NO3 treatments, particularly for Sphagnum, but the activity decreased when exposed to additions of PK. Regression analysis revealed that phosphatase activity on Sphagnum was positively related with tissue N and negatively related to tissue P concentrations. For Hypnum, a negative relationship between shoot P concentration and phosphatase activity was observed. Using a 32P tracer, mosses removed from plots receiving PK in combination with NH4 maintained their affinity for increased phosphorus uptake. These findings suggest that enhanced nutrient supply, even at modest doses, significantly alter the nutrient recycling behaviour of bryophytes.