Algal and aquatic plant carbon concentrating mechanisms in relation to environmental change

Abstract

Abstract.Carbon dioxide concentrating mechanisms (also known as inorganic carbon concentrating mechanisms; both abbreviated as CCMs) presumably evolved under conditions of low CO 2 availability. However, the timing of their origin is unclear since there are no sound estimates from molecular clocks, and even if there were, there are no proxies for the functioning of CCMs. Accordingly, we cannot use previous episodes of high CO 2 (e.g. the Palaeocene-Eocene Thermal Maximum) to indicate how organisms with CCMs responded. Present and predicted environmental change in terms of increased CO 2 and temperature are leading to increased CO 2 and HCO 3 -and decreased CO 3 2-and pH in surface seawater, as well as decreasing the depth of the upper mixed layer and increasing the degree of isolation of this layer with respect to nutrient flux from deeper waters. The outcome of these forcing factors is to increase the availability of inorganic carbon, photosynthetic active radiation (PAR) and ultraviolet B radiation (UVB) to aquatic photolithotrophs and to decrease the supply of the nutrients (combined) nitrogen and phosphorus and of any non-aeolian iron. The influence of these variations on CCM expression has been examined to varying degrees as acclimation by extant organisms. Increased PAR increases CCM expression in terms of CO 2 affinity, while increased UVB has a range of effects in the organisms examined; little relevant information is available on increased temperature. Decreased combined nitrogen supply generally increases CO 2 affinity, decreased iron availability increases CO 2 affinity, and decreased phosphorus supply has varying effects on the organisms examined. There are few data sets showing interactions among the observed changes, and even less information on genetic (adaptation) 2 changes in response to the forcing factors. In freshwaters, changes in phytoplankton species composition may alter with environmental change with consequences for frequency of species with or without CCMs. The information available permits less predictive power as to the effect of the forcing factors on CCM expression than for their overall effects on growth. CCMs are currently not part of models as to how global environmental change has altered, and is likely to further alter, algal and aquatic plant primary productivity.Keywords CO 2 concentrating mechanism -combined nitrogen -inorganic carboniron -mixing depth -photosynthetically active radiation -phosphorus -temperature -UVA-UVB Abbreviations CCM CO 2 concentrating mechanism DOC Dissolved organic carbon PAR Photosynthetically active radiation (400-700 nm)Rubisco Ribulose bisphosphate carboxylase-oxygenase UVA Ultraviolet A radiation (320-400 nm) UVB Ultraviolet B radiation (280-320 nm)

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

“…General references on earliest known occurrence of algae: [6][7][8]. References on presence or absence of CO 2 -concentrating mechanisms (CCMs): [9][10][11][12][13][14]. CCM absent in all ?…”

“…Young et al [107] have used molecular phylogenetic evidence to show that there was positive selection of the form ID Rubiscos in some eukaryotes that correspond to low-CO 2 and low-CO 2 /O 2 episodes in the geological record, and that these episodes of positive selection could have corresponded to the time of evolution of CCMs. To be effective, the CCM must maintain a higher CO 2 concentration at the site of Rubisco than would be possible by CO 2 diffusion alone [10].…”

“…A significant increase in oxygen, with oxygenation of the deep ocean, occurred in the Neoproterozoic 0.54-1 Ga [32], with variations in the Phanaerozoic including the highest known level in the Permo-Carboniferous glaciation [33]. Carbon dioxide varied with a general downward trend, with minima generally related to glaciations [10,34]. CO 2 was relatively constant at about 23 (range of estimates 10-100) times the present level between 2.5 and 1.8 Ga, with a very significant decrease between 1.8 and 1.1 Ga [35], further variations in the Neoproterozoic [36][37][38] and relatively well-established changes in the Phanaerozoic with minima in the Permo-Carboniferous and in the Pleistocene glaciations [33,39].…”

“…The mechanistic, including molecular, details of the CCMs of cyanobacteria are now known [51][52][53]56,102]. The CCMs of eukaryotic algae are less clearly understood at both the molecular and the mechanistic levels, although they are clearly polyphyletic [10,13,34,67,79,103,104].…”

Ocean acidification affects competition for space: projections of community structure using cellular automata

“…Marine organisms rely on different forms of dissolved inorganic carbon for different physiological processes. Increased carbon dioxide and bicarbonate availability associated with ocean acidification may boost algal productivity [13,14] (but see [14,15]), however; lower carbonate saturation increases the seawater solubility of carbonate structures, including the shells and skeletons of many marine organisms [16][17][18][19][20][21] (but see [15,22]). The coralline red algae, a group of marine macroalgae (Corallinales, Rhodophyta), make skeletons composed of high-Mg calcite, which is thought to be the mineral form most susceptible to ocean acidification [17,18].…”