SHORT- AND LONG-TERM EFFECTS OF ELEVATED CO₂ ON PHOTOSYNTHESIS AND RESPIRATION IN THE MARINE MACROALGA HIZIKIA FUSIFORMIS (SARGASSACEAE, PHAEOPHYTA) GROWN AT LOW AND HIGH N SUPPLIES

• Published in: Journal of phycology 2011-02, Vol.47 (1), p.87-97
• Main Authors: Zou, Dinghui, Gao, Kunshan, Luo, Hanjin
• Format: Article
• Language: English
• Subjects: Algae; brown algae; CO2; Hizikia; Hizikia fusiformis; marine macroalgae; Phaeophyta; photosynthesis; respiration; Sargassaceae
• ISSN: 0022-3646; 1529-8817
• DOI: 10.1111/j.1529-8817.2010.00929.x

The short-term and long-term effects of elevated CO₂ on photosynthesis and respiration were examined in cultures of the marine brown macroalga Hizikia fusiformis (Harv.) Okamura grown under ambient (375 μL · L⁻¹) and elevated (700 μL · L⁻¹) CO₂ concentrations and at low and high N availability. Short-term exposure to CO₂ enrichment stimulated photosynthesis, and this stimulation was maintained with prolonged growth at elevated CO₂, regardless of the N levels in culture, indicating no down-regulation of photosynthesis with prolonged growth at elevated CO₂. However, the photosynthetic rate of low-N-grown H. fusiformis was more responsive to CO₂ enrichment than that of high-N-grown algae. Elevation of CO₂ concentration increased the value of K₁/₂(Ci) (the half-saturation constant) for photosynthesis, whereas high N supply lowered it. Neither short-term nor long-term CO₂ enrichment had inhibitory effects on respiration rate, irrespective of the N supply, under which the algae were grown. Under high-N growth, the Q₁₀ value of respiration was higher in the elevated-CO₂-grown algae than the ambient-CO₂-grown algae. Either short- or long-term exposure to CO₂ enrichment decreased respiration as a proportion of gross photosynthesis (Pg) in low-N-grown H. fusiformis. It was proposed that in a future world of higher atmospheric CO₂ concentration and simultaneous coastal eutrophication, the respiratory carbon flux would be more sensitive to changing temperature.