Physiology of inorganic C acquisition and implications for resource use efficiency by marine phytoplankton: relation to increased CO₂ and temperature

Abstract

Abstract. Photosynthesis by many marine phytoplankton algae is saturated by the inorganic C concentration in air‐equilibrated sea water. These organisms appear to use an active inorganic C transport process (CO2‐concentrating mechanism) which increases the CO2 concentration around rubisco and saturates this enzyme with CO2 and suppresses its oxygenase activity. A minority of marine phytoplankton algae have photosynthetic characteristics more suggestive of diffusive CO2 entry; the inorganic C concentration present in sea water does not saturate photosynthesis by these organisms. Theoretical considerations, tested when possible against observation, suggest that the organisms with a CO2‐concentrating mechanism could have a lower cost of photons, nitrogen, iron, manganese and molybdenum to achieve a given rate of carbon accumulation by the cells than is the case for the organisms with diffusive CO2 entry. Zinc and selenium costs may show the reverse effect. The increased sea‐surface inorganic C, and CO2 concentrations which will result from anthropogenic increases in atmospheric CO2 content are predicted to increase the rate of photosynthesis, and of growth when other resources are abundant, and to reduce, or reverse, the higher resource (photons, nitrogen, iron, manganese and molybdenum) cost of a given rate of CO2 assimilation in organisms with CO2 diffusion relative to those which have CO2 concentrating mechanisms and do not repress them at higher inorganic C concentrations. These effects may well alter species composition, and overall resource cost of growth, of phytoplankton; any influence that these effects may have on CO2 removal from the atmosphere are severely constrained by other trophic levels and, especially, oceanic circulation patterns. Changed sea‐surface temperatures are unlikely to qualitatively alter these conclusions.

Interactions between CCM and N2 fixation in Trichodesmium

“…In Dunaliella tertiolecta and Chlorella emersonii, however, affinities for CO 2 were enhanced under N depletion (Beardall et al 1991;Young and Beardall 2005). This type of CCM regulation may serve to improve the N use efficiency by reducing the N requirement for synthesis of RubisCO (Beardall et al 1991;Raven 1991). By suppressing photorespiration, up-regulation of CCMs under N-limitation may also prevent the exudation of downstream products such as glycolate and thus the loss of N .…”

Algal evolution in relation to atmospheric CO 2 : carboxylases, carbon-concentrating mechanisms and carbon oxidation cycles

“…As Raven [66,[68][69][70] points out, the effects on Rubisco demand additional nitrogen in the enzyme itself and in related enzymes, more iron and manganese in additional thylakoid redox agents, and more phosphorus in the RNA needed to make the additional protein, if the rate of photosynthesis is to be maintained. More energy input as NADPH and ATP is also needed to run CO 2 assimilation [66,69,70]. For oxygen damage to nitrogenase, there is generally synthesis of 'reserve' nitrogenase in addition to what is needed in the absence of oxygen damage to satisfy the combined nitrogen requirements of cell growth.…”

“…These characteristics would minimize the nitrogen needed to produce the machinery associated with a given rate of CO 2 fixation, and thus the phosphorus in RNA needed to synthesize the proteins [66]. Costs in energy, nitrogen, phosphorus, iron and manganese will be considered below in the context of decreasing CO 2 and increasing O 2 [66][67][68][69][70][71][72][73][74].…”

Extra and intracelular activities of carbonic anhydrase of the marine microalga Tetraselmis gracilis (Chlorophyta)

“…As the atmospheric levels of carbon dioxide are continuously increasing in the atmosphere, it is interesting to know what effects this changes can bring for organisms that posseses mechanisms of concentrating carbon in their cells, especially because marine phytoplankton is responsible for almost 40% of the planetary photosynthesis (28).…”