Effects of Temperature on Photosynthesis and Respiration in Eelgrass (Zostera marina L)
The short-term temperature responses of the photosynthesis-irradiance (P-I) relationships and respiration of Zostera marina L. (eelgrass) leaves were determined at eight temperatures from 0 to 35°C for plants growing at 20–22°C in Great Harbor, Woods Hole, Massachusetts. Light-saturated, net photosynthesis increased with temperature up to an optimum of 25–30°C and decreased at 35°C. Dark respiration increased with temperature from 5 to 35°C. The initial slopes of the P-I curves were relatively constant between 5 and 30°C, but were greatest at 0 and least at 35°C. The photosynthetic saturation and compensation photon flux densities generally increased with increasing temperature. A Q10 value, determined over the temperature range 0–35°C, of 1.5–1.7 was obtained for light-saturated photosynthesis, while the value for dark respiration was 2.4. Ratios of maximum photosynthetic rates to respiration rates (P : R) were highest at 5°C and declined markedly at higher and lower temperatures. Calculations of daily carbon balances from P : R ratios and daily light regimes indicate that net positive leaf carbon balance could be maintained by Z. marina leaves in Great Harbor under winter temperature and light regimes, while high temperatures (⩾30°C) lead to negative daily carbon balances of leaves which could contribute to mortality or reduced growth of the plants.