In relation to the disappearance of aRuppia maritima population near the effuent of an electrical generating station on the Patuxent River, Maryland, a broad study of temperature effects on respiration and photosynthesis of aquatic plants was begun.
A Gilson differential respirometer was used to investigate respiratory variation in leaves ofPotamogeton perfoliatus at 25, 30, 35, 40, and 45 C. This species grows withRuppia maritima, appears to be more tolerant of high temperatures and plant material was readily available. Plants growing in heated and non-heated water were compared. The data indicate thatP. perfoliatus is capable of physiological adjustment to higher temperatures as the leaf matures, since only older leaves tended to respire less at the elevated temperatures. Death of plant material occurred at 45 C.