Seasonal changes in the surface phosphatase kinetics of aquatic mosses in northern England

The widespread occurrence of surface phosphatase activity in aquatic mosses, presumably synthesized to utilize organic phosphates in the environment, suggests the likelihood of strategies to optimize this process. Here we report seasonal changes in the kinetics of surface phosphatase in six moss populations, representing four species (Fontinalis antipyretica, Fontinalis squamosa, Rhynchostegium riparioides and Warnstorfia fluitans) from N. E. England. Kinetic parameters of shoots assayed within a few hours of sampling from the streams showed a summer/autumn increase in K(m) and V(max) corresponding to seasonal decrease in phosphate supply. The detection of phosphomonoesterases and phosphodiesterases with both low and high substrate affinities in all the populations studied confirms the widespread existence of this phenomenon in mosses. Similar two-phase kinetics were found for clonal, axenic isolates of two of the species (Rhynchostegium and Warnstorfia), indicating that any influence of epiphytes on the results with stream material was negligible. The seasonal changes in the kinetic parameters indicate that surface phosphatase activity is a dynamic response to seasonal changes in nutrient supply and/or requirement.