PHOTOSYNTHESIS BY<i>FONTINALIS ANTIPYRETICA</i>

Abstract

S ummary Rates of net photosynthesis of the aquatic moss Fontinalis antipyretica Hedw. were measured at seven levels of photon irradiance and five or six concentrations of CO 2 at the ambient temperature of the collection site, Esthwaite Water, in four months during a year. The effect of each factor on rates was assessed by fitting the data to models using non‐linear and linear regressions. There was no evidence for photoinhibition. The light compensation point was generally low compared with published values. The CO 2 compensation point was similar to that of C 3 plants. The slope of photosynthesis vs CO 2 concentration increased linearly with temperature in a manner consistent with the effects of boundary‐layer resistance. Other estimated and calculated variables are presented and discussed. Rates of saturated gross photosynthesis, compensation points and indices of degree of saturation varied with the level of the second factor. The results emphasize the interaction between photon irradiance, CO 2 concentration and temperature and the necessity of taking all these into account when studying the effect of one of these factors on photosynthesis.