Much has been published on the effects of ocean acidification on plankton since the original Royal Society 2005 report. In addition to direct effects on primary production, it is clear that ocean ...acidification also has profound consequences for biogeochemistry. Furthermore, although ocean acidification can have direct effects of on grazers such as copepods, acidification induces changes in nutritional value of phytoplankton which can be passed on up the food chain. There has also been recognition of the complexity of the interactions between elevated CO2 and other environmental factors and this has seen an upsurge in climate change research involving multifactorial experiments. In particular, the interaction of ocean acidification with global warming resulting from the increasing greenhouse effect has been investigated. There has also been research on acidification and warming effects in inland water plankton. These, combined with novel experimental techniques and long term studies of genetic adaptation, are providing better insights to plankton biology and communities in a future world.
The ins and outs of CO2 Raven, John A; Beardall, John
Journal of experimental botany,
01/2016, Letnik:
67, Številka:
1
Journal Article
Recenzirano
Odprti dostop
It is difficult to distinguish influx and efflux of inorganic C in photosynthesizing tissues; this article examines what is known and where there are gaps in knowledge. Irreversible decarboxylases ...produce CO2, and CO2 is the substrate/product of enzymes that act as carboxylases and decarboxylases. Some irreversible carboxylases use CO2; others use HCO3(-). The relative role of permeation through the lipid bilayer versus movement through CO2-selective membrane proteins in the downhill, non-energized, movement of CO2 is not clear. Passive permeation explains most CO2 entry, including terrestrial and aquatic organisms with C3 physiology and biochemistry, terrestrial C4 plants and all crassulacean acid metabolism (CAM) plants, as well as being part of some mechanisms of HCO3(-) use in CO2 concentrating mechanism (CCM) function, although further work is needed to test the mechanism in some cases. However, there is some evidence of active CO2 influx at the plasmalemma of algae. HCO3(-) active influx at the plasmalemma underlies all cyanobacterial and some algal CCMs. HCO3(-) can also enter some algal chloroplasts, probably as part of a CCM. The high intracellular CO2 and HCO3(-) pools consequent upon CCMs result in leakage involving CO2, and occasionally HCO3(-). Leakage from cyanobacterial and microalgal CCMs involves up to half, but sometimes more, of the gross inorganic C entering in the CCM; leakage from terrestrial C4 plants is lower in most environments. Little is known of leakage from other organisms with CCMs, though given the leakage better-examined organisms, leakage occurs and increases the energetic cost of net carbon assimilation.
Global demand for macroalgal and microalgal foods is growing, and algae are increasingly being consumed for functional benefits beyond the traditional considerations of nutrition and health. There is ...substantial evidence for the health benefits of algal-derived food products, but there remain considerable challenges in quantifying these benefits, as well as possible adverse effects. First, there is a limited understanding of nutritional composition across algal species, geographical regions, and seasons, all of which can substantially affect their dietary value. The second issue is quantifying which fractions of algal foods are bioavailable to humans, and which factors influence how food constituents are released, ranging from food preparation through genetic differentiation in the gut microbiome. Third is understanding how algal nutritional and functional constituents interact in human metabolism. Superimposed considerations are the effects of harvesting, storage, and food processing techniques that can dramatically influence the potential nutritive value of algal-derived foods. We highlight this rapidly advancing area of algal science with a particular focus on the key research required to assess better the health benefits of an alga or algal product. There are rich opportunities for phycologists in this emerging field, requiring exciting new experimental and collaborative approaches.
The evolution of organisms capable of oxygenic photosynthesis paralleled a long-term reduction in atmospheric CO2 and the increase in O2. Consequently, the competition between O2 and CO2 for the ...active sites of RUBISCO became more and more restrictive to the rate of photosynthesis. In coping with this situation, many algae and some higher plants acquired mechanisms that use energy to increase the CO2 concentrations (CO2 concentrating mechanisms, CCMs) in the proximity of RUBISCO. A number of CCM variants are now found among the different groups of algae. Modulating the CCMs may be crucial in the energetic and nutritional budgets of a cell, and a multitude of environmental factors can exert regulatory effects on the expression of the CCM components. We discuss the diversity of CCMs, their evolutionary origins, and the role of the environment in CCM modulation.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
Oxygenic photosynthesis evolved at least 2.4 Ga; all oxygenic organisms use the ribulose bisphosphate carboxylase-oxygenase (Rubisco)—photosynthetic carbon reduction cycle (PCRC) rather than one of ...the five other known pathways of autotrophic CO 2 assimilation. The high CO 2 and (initially) O 2 -free conditions permitted the use of a Rubisco with a high maximum specific reaction rate. As CO 2 decreased and O 2 increased, Rubisco oxygenase activity increased and 2-phosphoglycolate was produced, with the evolution of pathways recycling this inhibitory product to sugar phosphates. Changed atmospheric composition also selected for Rubiscos with higher CO 2 affinity and CO 2 /O 2 selectivity correlated with decreased CO 2 -saturated catalytic capacity and/or for CO 2 -concentrating mechanisms (CCMs). These changes increase the energy, nitrogen, phosphorus, iron, zinc and manganese cost of producing and operating Rubisco—PCRC, while biosphere oxygenation decreased the availability of nitrogen, phosphorus and iron. The majority of algae today have CCMs; the timing of their origins is unclear. If CCMs evolved in a low-CO 2 episode followed by one or more lengthy high-CO 2 episodes, CCM retention could involve a combination of environmental factors known to favour CCM retention in extant organisms that also occur in a warmer high-CO 2 ocean. More investigations, including studies of genetic adaptation, are needed.
Phosphorus (P) is the proximate (immediate) limiting element for primary productivity in some habitats, and is generally the ultimate limiting element for primary productivity. Although RNA can ...account for over half of the non-storage P in photosynthetic organisms, some primary producers have more ribosomes than the minimum needed for the observed rate of net protein synthesis; some of this RNA may be needed for protein turnover. Two cases of protein turnover which can occur at a much faster rate than the bulk protein turnover are those of photodamaged photosystem II and O2-damaged nitrogenase. While RNA involved in photosystem II repair accounts for less than 1% of the non-storage P in photosynthetic organisms, a maximum, of 12% of non-storage P could occur in RNA associated with replacement of damaged nitrogenase and/or O2 damage avoidance mechanism in diazotrophic (N2 fixing) organisms. There is a general trend in published data towards lower P use efficiency (g dry matter gain per day per mol P in the organism) for photosynthetic diazotrophic organisms growing under P limitation with N2 as their nitrogen source, rather than with NH4+, urea or NO3−. Additional work is needed to examine the generality of a statistically verified decrease in P use efficiency for diazotrophic growth relative to growth on other nitrogen sources and, if this is confirmed, further investigation of the mechanism is needed. The outcome of such work would be important for relating the global distribution of diazotrophy to P availability. There are no known P acquisition mechanisms specific to diazotrophs. Phosphorus (P) is the proximate (immediate) limiting element for primary productivity in some habitats, and is generally the ultimate limiting element for primary productivity. Although RNA can account for over half of the non-storage P in photosynthetic organisms, some primary producers have more ribosomes than the minimum needed for the observed rate of net protein synthesis; some of this RNA may be needed for protein turnover. Two cases of protein turnover which can occur at a much faster rate than the bulk protein turnover are those of photodamaged photosystem II and O2-damaged nitrogenase. While RNA involved in photosystem II repair accounts for less than 1% of the non-storage P in photosynthetic organisms, a maximum, of 12% of non-storage P could occur in RNA associated with replacement of damaged nitrogenase and/or O2 damage avoidance mechanism in diazotrophic (N2 fixing) organisms. There is a general trend in published data towards lower P use efficiency (g dry matter gain per day per mol P in the organism) for photosynthetic diazotrophic organisms growing under P limitation with N2 as their nitrogen source, rather than with NH4+, urea or NO3−. Additional work is needed to examine the generality of a statistically verified decrease in P use efficiency for diazotrophic growth relative to growth on other nitrogen sources and, if this is confirmed, further investigation of the mechanism is needed. The outcome of such work would be important for relating the global distribution of diazotrophy to P availability. There are no known P acquisition mechanisms specific to diazotrophs.
Thylakoids are flattened sacs isolated from other membranes; cristae are attached to the rest of the inner mitochondrial membrane by the crista junction, but the crista lumen is separated from the ...intermembrane space. The shape of thylakoids and cristae involves membranes with small (5–30 nm) radii of curvature. While the mechanism of curvature is not entirely clear, it seems to be largely a function of Curt proteins in thylakoids and Mitochondrial Organising Site and Crista Organising Centre proteins and oligomeric FOF1 ATP synthase in cristae. A subordinate, or minimal, role is attributable to lipids with areas of their head group area greater (convex leaflet) or smaller (concave leaflet) than the area of the lipid tail; examples of the latter group are monogalactosyldiglyceride in thylakoids and cardiolipin in cristae. The volume per unit area on the lumen side of the membrane is less than that of the chloroplast stroma or cyanobacterial cytosol for thylakoids, and mitochondrial matrix for cristae. A low volume per unit area of thylakoids and cristae means a small lumen width that is the average of wider spaces between lipid parts of the membranes and the narrower gaps dominated by extra-membrane components of transmembrane proteins. These structural constraints have important implications for the movement of the electron carriers plastocyanin and cytochrome c6 (thylakoids) and cytochrome c (cristae) and hence the separation of the membrane-associated electron donors to, and electron acceptors from, these water-soluble electron carriers. The donor/acceptor pairs, are the cytochrome fb6Fenh complex and P700+ in thylakoids, and Complex III and Complex IV of cristae. The other energy flux parallel to the membranes is that of the proton motive force generated by redox-powered H+ pumps into the lumen to the proton motive force use in ATP synthesis by H+ flux from the lumen through the ATP synthase. For both the electron transport and proton motive force movement, concentration differences of reduced and oxidised electron carriers and protonated and deprotonated pH buffers are involved. The need for diffusion along a congested route of these energy transfer agents may limit the separation of sources and sinks parallel to the membranes of thylakoids and cristae.
CO₂-concentrating mechanisms (CCMs), based either on active transport of inorganic carbon (biophysical CCMs) or on biochemistry involving supplementary carbon fixation into C₄ acids (C₄ and CAM), ...play a major role in global primary productivity. However, the ubiquitous CO₂-fixing enzyme in autotrophs, Rubisco, evolved at a time when atmospheric CO₂ levels were very much higher than today and O₂ was very low and, as CO₂ and O₂ approached (by no means monotonically), today’s levels, at some time subsequently many organisms evolved a CCM that increased the supply of CO₂ and decreased Rubisco oxygenase activity. Given that CO₂ levels and other environmental factors have altered considerably between when autotrophs evolved and the present day, and are predicted to continue to change into the future, we here examine the drivers for, and possible timing of, evolution of CCMs. CCMs probably evolved when CO₂ fell to 2–16 times the present atmospheric level, depending on Rubisco kinetics. We also assess the effects of other key environmental factors such as temperature and nutrient levels on CCM activity and examine the evidence for evolutionary changes in CCM activity and related cellular processes as well as limitations on continuity of CCMs through environmental variations.
Ensuring that global warming remains <2 °C requires rapid CO
emissions reduction. Additionally, 100-900 gigatons CO
must be removed from the atmosphere by 2100 using a portfolio of CO
removal (CDR) ...methods. Ocean afforestation, CDR through basin-scale seaweed farming in the open ocean, is seen as a key component of the marine portfolio. Here, we analyse the CDR potential of recent re-occurring trans-basin belts of the floating seaweed Sargassum in the (sub)tropical North Atlantic as a natural analogue for ocean afforestation. We show that two biogeochemical feedbacks, nutrient reallocation and calcification by encrusting marine life, reduce the CDR efficacy of Sargassum by 20-100%. Atmospheric CO
influx into the surface seawater, after CO
-fixation by Sargassum, takes 2.5-18 times longer than the CO
-deficient seawater remains in contact with the atmosphere, potentially hindering CDR verification. Furthermore, we estimate that increased ocean albedo, due to floating Sargassum, could influence climate radiative forcing more than Sargassum-CDR. Our analysis shows that multifaceted Earth-system feedbacks determine the efficacy of ocean afforestation.
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