Combined effects of carbon and phosphorus levels on the invasive cyanobacterium, Cylindrospermopsis raciborskii

Abstract

Wu Z., Zeng B., Li R. and Song L. 2012. Combined effects of carbon and phosphorus levels on the invasive cyanobacterium, Cylindrospermopsis raciborskii. Phycologia 51: 144–150. DOI: 10.2216.10.87.1

The invasive cyanobacterium, Cylindrospermopsis raciborskii, was cultured semicontinuously for 18 days at different carbon and phosphorus levels. Growth and photosynthesis were measured to study the combined effects of CO₂ and phosphorus availabilities. The results showed that enrichment of CO₂ or inorganic phosphorus (Pi) levels in the culture medium significantly increased specific growth rate (μ), light-saturated photosynthesis (P_m) and photosynthetic efficiency (α), but tended to decrease dark respiratory rate (R_d), saturating irradiance for photosynthesis (E_k) and the light compensation point (E_c). However, photosynthetic responses to inorganic carbon concentration in C. raciborskii were affected by interactions between CO₂ and Pi. At high Pi concentration, elevated CO₂ significantly increased the inorganic carbon-saturated photosynthesis rate (V_max) and substrate concentration giving half-maximal photosynthetic rate [K_0.5 (DIC)], whereas at low Pi levels, elevated CO₂ slightly decreased the values of V_max and K_0.5 (DIC). Additionally, enrichment with Pi significantly increased K_0.5 (DIC) and V_max regardless of the CO₂ level, suggesting that Pi plays a role in photosynthetic carbon fixation in C. raciborskii. Furthermore, when C. raciborskii was batch cultured in different carbon and phosphorus concentrations for 72 h, the uptake rate of nitrogen increased with enrichment of both CO₂ and Pi, while the uptake rate of phosphorus was enhanced only by increases in Pi concentration. The results suggest that the availability of CO₂ and phosphorus have combined and independent effects on photosynthesis and nutrient uptake in C. raciborskii, reflecting that changes in environmental factors could influence the dominance of this invasive cyanobacterium. These combined effects need to be considered when generalizing this species response to changing CO₂ levels.

Key Words::

• CO₂
• Cylindrospermopsis raciborskii
• Growth
• Phosphorus
• Photosynthesis

ACKNOWLEDGMENTS

The study was supported by the National Natural Science Foundation of China (30800123), the State Key Basic Research and Development Plan of China (2008CB418002) and the Doctoral Foundation Project of China SWU (SWU110065).