Thermal acclimation and whole-plant carbon balance in Zostera marina L. (eelgrass)

Thermal acclimation in eelgrass Zostera marina L. was investigated in laboratory experiments after growing plants at 10 and 20°C for 21 days under a 12:12 L:D regime. Metabolic rates showed significant shifts in short-term response to temperature in leaves and roots. Growth rates, tissue carbohydrate concentrations and metabolic rates measured at the two growth temperatures were statistically identical, indicating that thermal acclimation was essentially complete at these temperatures. When measured at p O 2 values high enough to achieve capacity rates of respiration, thermal responses of respiration ( Q 10) were lower than previously reported while the thermal response of photosynthesis (measured at p O 2 below air saturation) was similar to previous reports. Daily C budgets constructed from metabolic rate data indicated that H sat periods required for photosynthesis to balance C demand can vary from 3 to > 12 h, depending on the ratios of net photosynthesis: respiration ( P net: R) and shoot: root. Since Z. marina. shows evidence of thermal acclimation, seasonal changes in ambient temperature may not significantly affect H sat requirements and whole-plant C balance. Rapid mortality at high temperatures during summer may result instead from thermal disruption of metabolism while internal C reserves may be important in meeting C demand during winter periods of low light availability, particularly among high-latitude populations.