Temperature and red algal photosynthesis

The research presented in this thesis was designed to investigate the effects of temperature on photosynthetic physiology in marine red macroalgae. Red macroalgae are important components of most seaweed communities. Despite the fact that thermal variation is known to be an important factor influencing photosynthesis in other groups of plants, little is known about how variations in temperature affect red algal photosynthesis.; Studies employing Chondrus crispus, an ecologically dominant species with a broad geographic distribution in the North Atlantic, indicated that phenotypic acclimation occurred when plants were grown in laboratory culture at winter (5{dollar}spcirc{dollar}C) and summer (20{dollar}spcirc{dollar}C) temperatures. Plants grown at 20{dollar}spcirc{dollar}C acquired increased tolerance of short-term exposure to temperatures above the upper thermal limit for growth, but typical of air temperatures experiences during summer low tides. High temperature grown plants were also able to photosynthesize more efficiently at low light levels because of increases in the sizes of light-harvesting antennae associated with photosystem I and photosystem II, along with decreases in the temperature sensitivity (Q{dollar}sb{lcub}10{rcub}{dollar}) for respiration. These changes counteracted the short-term effects of high temperature on respiration rates with the result that the amount of light necessary to achieve net photosynthesis was similar for plants growing at both temperatures.; Genetic adaptations which enable plants to photosynthesize and grow over different temperatures ranges were discovered between populations (ecotypes) of Chondrus crispus and between Lomentaria baileyana and Lomentaria orcadensis; two closely related species which experience different thermal regimes in their natural ranges. The ecotypes of Chondrus crispus differ in their ability to undergo the thermal acclimation described above. The two Lomentaria species differed in upper thermal tolerance of photosynthesis. This difference was attributable to the relative thermal lability of energy transfer from the light-harvesting antennae, phycobilisomes, to the photosystem II reaction centers.; Photosynthetic metabolism in red algae is very sensitive to environmental temperature and both phenotypic acclimation and genetic adaptation of photosynthetic metabolism to temperature are important in enabling red seaweeds to exploit a wide range of thermal environments. Temperature variation in the natural environment has significant effects on the physiological state of plants and these affect the response of photosynthesis to other factors such as light.