Phosphorus and aquatic bryophytes in the Swale–Ouse river system, north-east England. 2. Phosphomonoesterase and phosphodiesterase activities of Fontinalis antipyretica

Surface phosphatase activities of the aquatic moss Fontinalis antipyretica were studied at sites on the Swale–Ouse system and adjacent catchments. A total of 27 sites were sampled on some occasions (eight main river; tributaries: 10 Swale, five Eden, four Tees), including a direct comparison for 20 of them during a short period in August 1997. Measurements were made on 2-cm shoot tips for phosphomonoesterase (PMEase) and phosphodiesterase (PDEase) at pH 5.5. The ratio of PDEase:PMEase was highest in the upland tributaries and decreased on passing down the main river. There was a positive significant relationship (P<0.01) between the ratio and altitude and possible reasons for this are discussed. Kinetic studies also showed differences between PMEase and PDEase. Km values for PMEase were similar all down the river, but PDEase showed marked differences between the headwaters and downstream sites. Laboratory studies with P-limited shoots in the presence of DNA and phytic acid showed that both substrates could provide a source of P. Utilisation was an order of magnitude lower than enzyme hydrolysis.