carbon dioxide formula and photosynthesis

fascicularis (originally obtained under CITES no. MATERIALS AND METHODSįragments of a captive-bred specimen of the encrusting coral G. fascicularis, flow stimulates photosynthesis through a more efficient uptake of carbon dioxide rather than through a decrease in photorespiration, whereas respiration is stimulated by flow through an increased uptake of oxygen. The applied values for pH and oxygen saturation are within the range experienced by corals in nature: natural diel fluctuations in pH (8.7–7.8) and oxygen saturation (27–247%) have been reported for reef flats and tropical lagoons ( Ohde and Van Woesik, 1999). (1) How does the ambient oxygen concentration in seawater affect photosynthesis in corals? (2) Does water flow stimulate photosynthesis in corals through stimulating the uptake of carbon dioxide or through reducing the negative effects of oxygen? To answer these questions, we studied the effect of flow on net photosynthesis and dark respiration in the stony coral Galaxea fascicularis (Linnaeus 1767) under three different levels of dissolved oxygen (hypoxia, 20% saturation normoxia, 100% saturation and hyperoxia, 150% saturation) and two different values for dissolved carbon dioxide (9.5 and 19.1 μmol l −1), as reflected by two corresponding values for pH (8.1 and 7.84). The contradicting views on the effects of dissolved oxygen on photosynthesis and photorespiration in corals and, consequently, on the mechanism that underlies flow-enhanced photosynthesis prompted us to address the following research questions. Hence, photorespiration decreases the efficiency of the photosynthesis process. Although 3PG can be regenerated from 2PG, this process requires several reaction steps, which consume more metabolic energy than regenerated 3PG can return after its uptake in the CBB cycle ( Peterhansel et al., 2010). RuBisCO then converts oxygen and ribulose bisphosphate into 2-phosphoglycerate (2PG), instead of converting carbon dioxide and ribulose bisphosphate into 3-phosphoglycerate (3PG). Photorespiration is a reaction in which oxygen instead of carbon dioxide binds to RuBisCO, the initial carbon dioxide-fixing enzyme in the Calvin–Benson–Bassham (CBB) cycle ( Peterhansel et al., 2010). (2010) concluded that a flow-induced, enhanced efflux of oxygen out of the coral tissue increases the efficiency of photosynthetic carbon fixation by reducing the rate of photorespiration. This decrease in internal oxygen was accompanied by an increase in the rate of net photosynthesis. (2010) demonstrated that the onset of flow led to a decrease of oxygen supersaturation from 500% to 200% inside illuminated tissue of the scleractinian coral Favia veroni. However, it remains unclear whether this flow effect relates to a higher influx of carbon dioxide into the coral tissue ( Dennison and Barnes, 1988 Lesser et al., 1994) or to a higher efflux of oxygen out of the coral tissue ( Nakamura et al., 2005 Finelli et al., 2006 Mass et al., 2010 Schutter et al., 2011). (2011) found an instantaneous increase in photosynthesis upon an increase in flow velocity from 5 to 20 cm s −1, which supports the idea that the effects of flow on photosynthesis are related to an improved exchange of dissolved gases.

In a flume experiment with Galaxea fascicularis, Schutter et al. Several authors have reported positive effects of water flow on photosynthesis in corals ( Dennison and Barnes, 1988 Lesser et al., 1994 Nakamura et al., 2005 Finelli et al., 2006 Mass et al., 2010 Schutter et al., 2011). Rates of net photosynthesis measured in this study are among the highest ever recorded for scleractinian corals and confirm a strong scope for growth. fascicularis, increased uptake of carbon dioxide rather than increased efflux of oxygen explains the beneficial effect of water flow on photosynthesis.

These results indicate that for this individual of G. Flow and pH had a synergistic effect on net photosynthesis: at high flow, a decrease in pH stimulated net photosynthesis by 14%. Oxygen saturation did not influence net photosynthesis: neither hypoxia nor hyperoxia affected net photosynthesis, irrespective of flow and pH, which suggests that hyperoxia does not induce high rates of photorespiration in this coral. Dark respiration was enhanced by increased flow and increased oxygen saturation in an interactive way, which relates to improved oxygen influx into the coral tissue. Rates of dark respiration and net photosynthesis were measured for six replicate clonal fragments of the stony coral Galaxea fascicularis (Linnaeus 1767), which were incubated under 12 different combinations of dissolved oxygen (20%, 100% and 150% saturation), dissolved carbon dioxide (9.5 and 19.1 µmol l −1) and water flow (1–1.6 versus 4–13 cm s −1) in a repeated measures design.

Carbon dioxide formula and photosynthesis