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. K-m 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. (C) 1998 Elsevier Science B.V.