Influences of light and temperature on chlorophyll composition in submersed freshwater macrophytes

In three submersed freshwater macrophyte species grown in a greenhouse over broad experimental ranges of light and water temperature, total chlorophyll (a + b) increased with decreasing irradiance and, in two of the three species, with increasing temperature. In contrast, light and temperature had only minor and inconsistent influences on chlorophyll a : b in these species.From results of this and other investigations involving experimentally-controlled light conditions, it appears that total chlorophyll in submersed macrophytes is inversely related to irradiance above photon flux densities minimally required for plant growth. However, the general applicability of this statement to the species investigated here (or others) is uncertain, because thermal gradients in macrophyte dominated littoral zones may promote gradients in macrophyte total chlorophyll with depth in a direction opposite to that expected solely in response to light.