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1.
Changes in the seawater carbonate chemistry (ocean acidification) from increasing atmospheric carbon dioxide (CO 2) concentrations negatively affect many marine calcifying organisms, but may benefit primary producers under dissolved inorganic carbon (DIC) limitation. To improve predictions of the ecological effects of ocean acidification, the net gains and losses between the processes of photosynthesis and calcification need to be studied jointly on physiological and population levels. We studied productivity, respiration, and abundances of the symbiont‐bearing foraminifer species Marginopora vertebralis on natural CO 2 seeps in Papua New Guinea and conducted additional studies on production and calcification on the Great Barrier Reef (GBR) using artificially enhanced pCO2. Net oxygen production increased up to 90% with increasing pCO2; temperature, light, and pH together explaining 61% of the variance in production. Production increased with increasing light and increasing pCO2 and declined at higher temperatures. Respiration was also significantly elevated (~25%), whereas calcification was reduced (16–39%) at low pH/high pCO2 compared to present‐day conditions. In the field, M. vertebralis was absent at three CO 2 seep sites at pH Total levels below ~7.9 ( pCO2 ~700 μatm), but it was found in densities of over 1000 m ?2 at all three control sites. The study showed that endosymbiotic algae in foraminifera benefit from increased DIC availability and may be naturally carbon limited. The observed reduction in calcification may have been caused either by increased energy demands for proton pumping (measured as elevated rates of respiration) or by stronger competition for DIC from the more productive symbionts. The net outcome of these two competing processes is that M. vertebralis cannot maintain populations under pCO2 exceeding 700 μatm, thus are likely to be extinct in the next century. 相似文献
2.
AbstractThe transporter SbtA is a high affinity Na +-dependent HCO 3 - uptake system present in a majority of cyanobacterial clades. It functions in conjunction with CO 2 uptake systems and other HCO 3 - uptake systems to allow cyanobacteria to accumulate high levels of HCO 3 - used to support efficient photosynthetic CO 2 fixation via the CO 2 concentrating mechanism in these species. The phoA/lacZ fusion reporter method was used to determine the membrane topology of the cyanobacterial bicarbonate transporter, SbtA (predicted size of ~ 39.7 kD), cloned from the freshwater strain, Synechocystis PCC6803. The structure conforms to a model featuring 10 transmembrane helices (TMHs), with a distinct 5 + 5 duplicated structure. Both the N- and C-terminus are outside the cell and the second half of the protein is inverted relative to the first. The first putative helix appears to lack sufficient topogenic signals for its correct orientation in the membrane and instead relies on the presence of later helices. The cytoplasmic loop between helices 5 and 6 is a likely location for regulatory mechanisms that could govern activation of the transporter, and the cytoplasmic loop between helices 9 and 10 also contains some conserved putative regulatory residues. 相似文献
3.
Photosynthetic activity in carbonate‐rich benthic microbial mats located in saline, alkaline lakes on the Cariboo Plateau, B.C. resulted in pCO 2 below equilibrium and δ 13C DIC values up to +6.0‰ above predicted carbon dioxide (CO 2) equilibrium values, representing a biosignature of photosynthesis. Mat‐associated δ 13C carb values ranged from ~4 to 8‰ within any individual lake, with observations of both enrichments (up to 3.8‰) and depletions (up to 11.6‰) relative to the concurrent dissolved inorganic carbon (DIC). Seasonal and annual variations in δ 13C values reflected the balance between photosynthetic 13C‐enrichment and heterotrophic inputs of 13C‐depleted DIC. Mat microelectrode profiles identified oxic zones where δ 13C carb was within 0.2‰ of surface DIC overlying anoxic zones associated with sulphate reduction where δ 13C carb was depleted by up to 5‰ relative to surface DIC reflecting inputs of 13C‐depleted DIC. δ 13C values of sulphate reducing bacteria biomarker phospholipid fatty acids (PLFA) were depleted relative to the bulk organic matter by ~4‰, consistent with heterotrophic synthesis, while the majority of PLFA had larger offsets consistent with autotrophy. Mean δ 13C org values ranged from ?18.7 ± 0.1 to ?25.3 ± 1.0‰ with mean Δ 13C inorg‐org values ranging from 21.1 to 24.2‰, consistent with non‐CO 2‐limited photosynthesis, suggesting that Precambrian δ 13C org values of ~?26‰ do not necessitate higher atmospheric CO 2 concentrations. Rather, it is likely that the high DIC and carbonate content of these systems provide a non‐limiting carbon source allowing for expression of large photosynthetic offsets, in contrast to the smaller offsets observed in saline, organic‐rich and hot spring microbial mats. 相似文献
4.
CO 2 levels in freshwater systems can fluctuate widely, potentially influencing photosynthetic rates and growth of phytoplankton. Given the right conditions, this can lead to bloom formation and affect water quality. This study investigated the acquisition of dissolved inorganic carbon (DIC ) by six species of microalgae, a cyanobacterium Cylindrospermopsis raciborskii , the diatoms Cyclotella sp., Nitzschia sp., and the green algae Stichococcus sp., Staurastrum sp., and Monoraphidium sp., all isolated from a subtropical reservoir in Australia. Carbon acquisition characteristics, specifically the affinity for DIC , internal pH , and internal DIC concentrations were measured. Affinities for CO 2 () ranged between 0.7 and 6 μM CO 2. This was considerably lower than air‐equilibrated surface water CO 2 concentrations, and below reported affinities for CO 2 of RuBisCO suggesting operation of active carbon dioxide concentrating mechanisms (CCM s) in all species. Internal pH was lowest for Cyclotella sp. at 7.19, and highest for Staurastrum sp., at 7.71. At 180 μM external DIC , ratios of internal:external CO 2 ranged from 2.5 for Nitzschia sp. to 14 in C. raciborskii . Internal HCO 3? concentration showed a linear relationship with surface area to biovolume ratio (SA :Vol). We hypothesized that species with a higher SA :Vol suffer more from diffusive escape of CO 2, thus storage of DIC as bicarbonate is favored in these strains. For C. raciborskii , under stratified summer conditions, its strong CCM , and resilient photosynthetic characteristics may contribute to its bloom forming capacity. 相似文献
5.
Ocean acidification is expected to decrease calcification rates of bivalves. Nevertheless, in many coastal areas high pCO 2 variability is encountered already today. Kiel Fjord (Western Baltic Sea) is a brackish (12–20 g kg ?1) and CO 2 enriched habitat, but the blue mussel Mytilus edulis dominates the benthic community. In a coupled field and laboratory study we examined the annual pCO 2 variability in this habitat and the combined effects of elevated pCO 2 and food availability on juvenile M. edulis growth and calcification. In the laboratory experiment, mussel growth and calcification were found to chiefly depend on food supply, with only minor impacts of pCO 2 up to 3350 μatm. Kiel Fjord was characterized by strong seasonal pCO 2 variability. During summer, maximal pCO 2 values of 2500 μatm were observed at the surface and >3000 μatm at the bottom. However, the field growth experiment revealed seven times higher growth and calcification rates of M. edulis at a high pCO 2 inner fjord field station (mean pCO 2 ca. 1000 μatm) in comparison to a low pCO 2 outer fjord station (ca. 600 μatm). In addition, mussels were able to out‐compete the barnacle Amphibalanus improvisus at the high pCO 2 site. High mussel productivity at the inner fjord site was enabled by higher particulate organic carbon concentrations. Kiel Fjord is highly impacted by eutrophication, which causes bottom water hypoxia and consequently high seawater pCO 2. At the same time, elevated nutrient concentrations increase the energy availability for filter feeding organisms such as mussels. Thus, M. edulis can dominate over a seemingly more acidification resistant species such as A. improvisus. We conclude that benthic stages of M. edulis tolerate high ambient pCO 2 when food supply is abundant and that important habitat characteristics such as species interactions and energy availability need to be considered to predict species vulnerability to ocean acidification. 相似文献
6.
The low CO 2 concentration in seawater poses severe restrictions on photosynthesis, especially on those species with form II RUBISCO. We found that the potentially toxic dinoflagellate Protoceratium reticulatum Clap. et J. Lachm. possesses a form II RUBISCO. To cast some light on the mechanisms this organism undergoes to cope with low CO 2 availability, we compared cells grown at atmospheric (370 ppm) and high (5000 ppm) CO 2 concentrations, with respect to a number of physiological parameters related to dissolved inorganic carbon (DIC) acquisition and assimilation. The photosynthetic affinity for DIC was about one order of magnitude lower in cells cultivated at high [CO 2]. End‐point pH‐drift experiments suggest that P. reticulatum was not able to efficiently use HCO 3? under our growth conditions. Only internal carbonic anhydrase (CA) activity was detected, and its activity decreased by about 60% in cells cultured at high [CO 2]. Antibodies raised against a variety of algal CAs were used for Western blot analysis: P. reticulatum extracts only cross‐reacted with anti‐ß‐CA sera, and the amount of immunoreactive protein decreased in cells grown at high [CO 2]. No pyrenoids were observed under all growth conditions. Our data indicate that P. reticulatum has an inducible carbon‐concentrating mechanism (CCM) that operates in the absence of pyrenoids and with little intracellular CO 2 accumulation. Calculations on the impact of the CA activity to photosynthetic growth [CO 2] suggest that it is an essential component of the CCM of P. reticulatum and is necessary to sustain the photosynthetic rates observed at ambient CO 2. 相似文献
7.
In the cyanobacteria, mechanisms exist that allow photosynthetic CO 2 reduction to proceed efficiently even at very low levels of inorganic carbon. These inducible, active transport mechanisms enable the cyanobacteria to accumulate large internal concentrations of inorganic carbon that may be up to 1000-fold higher than the external concentration. As a result, the external concentration of inorganic carbon required to saturate cyanobacterial photosynthesis in vivo is orders of magnitude lower than that required to saturate the principal enzyme (ribulose bisphosphate carboxylase) involved in the fixation reactions. Since CO 2 is the substrate for carbon fixation, the cyanobacteria somehow perform the neat trick of concentrating this small, membrane permeable molecule at the site of CO 2 fixation. In this review, we will describe the biochemical and physiological experiments that have outlined the phenomenon of inorganic carbon accumulation, relate more recent genetic and molecular biological observations that attempt to define the constituents involved in this process, and discuss a speculative theory that suggests a unified view of inorganic carbon utilization by the cyanobacteria.Abbreviations C i
Inorganic carbon
- H-cells
Cells grown under high CO 2
- L-cells
Cells grown under low CO 2
- RuBP
Ribulose-1,5-bisphosphate
- WT
Wild type 相似文献
8.
Introducing a carbon‐concentrating mechanism and a faster Rubisco enzyme from cyanobacteria into higher plant chloroplasts may improve photosynthetic performance by increasing the rate of CO 2 fixation while decreasing losses caused by photorespiration. We previously demonstrated that tobacco plants grow photoautotrophically using Rubisco from Synechococcus elongatus, although the plants exhibited considerably slower growth than wild‐type and required supplementary CO 2. Because of concerns that vascular plant assembly factors may not be adequate for assembly of a cyanobacterial Rubisco, prior transgenic plants included the cyanobacterial chaperone RbcX or the carboxysomal protein CcmM35. Here we show that neither RbcX nor CcmM35 is needed for assembly of active cyanobacterial Rubisco. Furthermore, by altering the gene regulatory sequences on the Rubisco transgenes, cyanobacterial Rubisco expression was enhanced and the transgenic plants grew at near wild‐type growth rates, although still requiring elevated CO 2. We performed detailed kinetic characterization of the enzymes produced with and without the RbcX and CcmM35 cyanobacterial proteins. These transgenic plants exhibit photosynthetic characteristics that confirm the predicted benefits of introduction of non‐native forms of Rubisco with higher carboxylation rate constants in vascular plants and the potential nitrogen‐use efficiency that may be achieved provided that adequate CO 2 is available near the enzyme. 相似文献
9.
The molecular and isotopic compositions of lipid biomarkers from cultured filamentous cyanobacteria ( Phormidium, also known as Leptolyngbya) have been used to investigate the community and trophic structure of photosynthetic mats from alkaline hot springs of the Lower Geyser Basin at Yellowstone National Park. We studied a shallow‐water coniform mat from Octopus Spring (OS) and a submerged, tufted mat from Fountain Paint Pots (FPP) and found that 2‐methylhopanepolyols and mid‐chain branched methylalkanes were diagnostic for cyanobacteria, whereas abundant wax esters were representative of the green non‐sulphur bacterial population. The biomarker composition of cultured Phormidium‐isolates varied, but was generally representative of the bulk mat composition. The carbon isotopic fractionation for biomass relative to dissolved inorganic carbon (DIC; ? CO2) for cultures grown with 1% CO 2 ranged from 21.4 to 26.1 and was attenuated by diffusion limitation associated with filament aggregation (i.e. cell clumping). Isotopic differences between biomass and lipid biomarkers, and between lipid classes, depended on the cyanobacterial strain, but was positively correlated with overall fractionation. Acetogenic lipids (alkanes and fatty acids) were generally more depleted than isoprenoids (phytol and hopanoids). The δ 13C TOC for OS and FPP mats were somewhat heavier than for cultures (?16.9 and ?23.6, respectively), which presumably reflects the lower availability of DIC in the natural environment. The isotopic dispersions among cyanobacterial biomarkers, biomass and DIC reflected those established for culture experiments. The 7‐methyl‐ and 7,11‐dimethylheptadecanes were from 9 to 11 depleted relative to the bulk organic carbon, whereas 2‐methylhopanols derived from the oxidation‐reduction of bacteriohopanepolyol were enriched relative to branched alkanes by approximately 5–7. These isotopic relationships survived with depth and indicated that the relatively heavy isotopic composition of the OS mat resulted from diffusion limitation. This study supports the suggestion that culture studies can establish valid isotopic relationships for interpretation of trophic structure in modern and ancient microbial ecosystems. 相似文献
10.
Co‐occurring ocean warming, acidification and reduced carbonate mineral saturation have significant impacts on marine biota, especially calcifying organisms. The effects of these stressors on development and calcification in newly metamorphosed juveniles (ca. 0.5 mm test diameter) of the intertidal sea urchin Heliocidaris erythrogramma, an ecologically important species in temperate Australia, were investigated in context with present and projected future conditions. Habitat temperature and pH/ pCO 2 were documented to place experiments in a biologically and ecologically relevant context. These parameters fluctuated diurnally up to 10 °C and 0.45 pH units. The juveniles were exposed to three temperature (21, 23 and 25 °C) and four pH (8.1, 7.8, 7.6 and 7.4) treatments in all combinations, representing ambient sea surface conditions (21 °C, pH 8.1; pCO 2 397; Ω Ca 4.7; Ω Ar 3.1), near‐future projected change (+2–4 °C, ?0.3–0.5 pH units; pCO 2 400–1820; Ω Ca 5.0–1.6; Ω Ar 3.3–1.1), and extreme conditions experienced at low tide (+4 °C, ?0.3–0.7 pH units; pCO 2 2850–2967; Ω Ca 1.1–1.0; Ω Ar 0.7–0.6). The lowest pH treatment (pH 7.4) was used to assess tolerance levels. Juvenile survival and test growth were resilient to current and near‐future warming and acidification. Spine development, however, was negatively affected by near‐future increased temperature (+2–4 °C) and extreme acidification (pH 7.4), with a complex interaction between stressors. Near‐future warming was the more significant stressor. Spine tips were dissolved in the pH 7.4 treatments. Adaptation to fluctuating temperature‐pH conditions in the intertidal may convey resilience to juvenile H. erythrogramma to changing ocean conditions, however, ocean warming and acidification may shift baseline intertidal temperature and pH/ pCO 2 to levels that exceed tolerance limits. 相似文献
11.
Marine calcifying eukaryotic phytoplankton (coccolithophores) is a major contributor to the pelagic production of CaCO 3 and plays an important role in the biogeochemical cycles of C, Ca and other divalent cations present in the crystal structure of calcite. The geochemical signature of coccolithophore calcite is used as palaeoproxy to reconstruct past environmental conditions and to understand the underlying physiological mechanisms (vital effects) and precipitation kinetics. Here, we present the stable Sr isotope fractionation between seawater and calcite (Δ 88/86Sr) of laboratory cultured coccolithophores in individual dependence of temperature and seawater carbonate chemistry. Coccolithophores were cultured within a temperature and a pCO 2 range from 10 to 25°C and from 175 to 1,240 μatm, respectively. Both environmental drivers induced a significant linear increase in coccolith stable Sr isotope fractionation. The temperature correlation at constant pCO 2 for Emiliania huxleyi and Coccolithus braarudii is expressed as Δ 88/86Sr = ?7.611 × 10 ?3 T + 0.0061. The relation of Δ 88/86Sr to pCO 2 was tested in Emiliania huxleyi at 10 and 20°C and resulted in Δ 88/86Sr = ?5.394 × 10 ?5 pCO 2 – 0.0920 and Δ 88/86Sr = ?5.742 × 10 ?5 pCO 2 – 0.1351, respectively. No consistent relationship was found between coccolith Δ 88/86Sr and cellular physiology impeding a direct application of fossil coccolith Δ 88/86Sr as coccolithophore productivity proxy. An overall significant correlation was detected between the elemental distribution coefficient ( DSr) and Δ 88/86Sr similar to inorganic calcite with a physiologically induced offset. Our observations indicate (i) that temperature and pCO 2 induce specific effects on coccolith Δ 88/86Sr values and (ii) that strontium elemental ratios and stable isotope fractionation are mainly controlled by precipitation kinetics when embedded into the crystal lattice and subject to vital effects during the transmembrane transport from seawater to the site of calcification. These results provide an important step to develop a coccolith Δ 88/86Sr palaeoproxy complementing the existing toolbox of palaeoceanography. 相似文献
12.
Unicellular green algae and cyanobacteria have mechanism(s) to actively concentrate dissolved inorganic carbon (DIC) into the cells, only if they are grown with air levels of CO 2. The DIC concentration mechanisms are environmental adaptations to actively transport and accumulate inorganic carbon into the chloroplasts of green algae or into the carboxysomes of cyanobacteria. The current working model of cyanobacterial carbon concentration mechanism consists of at least two basic components: an active C i transport system and a Rubisco-rich polyhedral carboxysome. In case of unicellular green algae, the working model for DIC concentration mechanism includes several isoforms of carbonic anhydrase (CA), and ATPase driven active bicarbonate transporters at the plasmalemma and at the inner chloroplast envelopes. In the past twenty years, significant progress has been made in isolating and characterizing the isoforms of carbonic anhydrase. However, active transporters are yet to be characterized. This mini-review summarizes the current status of research on DIC-pumps including its significance and possible application to increase the productivity of plants of economic importance. 相似文献
13.
Due to various activities associated with nuclear industry, uranium is migrated to aquatic environments like groundwater, ponds or oceans. Uranium forms stable carbonate complexes in the oxic waters of pH 7–10 which results in a high degree of uranium mobility. Microorganisms employ various mechanisms which significantly influence the mobility and the speciation of uranium in aquatic environments. Uranyl bioremediation studies, this far, have generally focussed on low pH conditions and related to adsorption of positively charged UO 2 2+ onto negatively charged microbial surfaces. Sequestration of anionic uranium species, i.e. [UO 2(CO 3) 2 2? ] and [UO 2(CO 3) 3 4? ] onto microbial surfaces has received only scant attention. Marine cyanobacteria are effective metal adsorbents and represent an important sink for metals in aquatic environment. This article addresses the cyanobacterial interactions with toxic metals in general while stressing on uranium. It focusses on the possible mechanisms employed by cyanobacteria to sequester uranium from aqueous solutions above circumneutral pH where negatively charged uranyl carbonate complexes dominate aqueous uranium speciation. The mechanisms demonstrated by cyanobacteria are important components of biogeochemical cycle of uranium and are useful for the development of appropriate strategies, either to recover or remediate uranium from the aquatic environments. 相似文献
14.
Previous studies have demonstrated that coral and algal calcification is tightly regulated by the calcium carbonate saturation state of seawater. This parameter is likely to decrease in response to the increase of dissolved CO 2 resulting from the global increase of the partial pressure of atmospheric CO 2. We have investigated the response of a coral reef community dominated by scleractinian corals, but also including other calcifying organisms such as calcareous algae, crustaceans, gastropods and echinoderms, and kept in an open‐top mesocosm. Seawater pCO 2 was modified by manipulating the pCO 2 of air used to bubble the mesocosm. The aragonite saturation state ( Ωarag) of the seawater in the mesocosm varied between 1.3 and 5.4. Community calcification decreased as a function of increasing pCO 2 and decreasing Ωarag. This result is in agreement with previous data collected on scleractinian corals, coralline algae and in a reef mesocosm, even though some of these studies did not manipulate CO 2 directly. Our data suggest that the rate of calcification during the last glacial maximum might have been 114% of the preindustrial rate. Moreover, using the average emission scenario (IS92a) of the Intergovernmental Panel on Climate Change, we predict that the calcification rate of scleractinian‐dominated communities may decrease by 21% between the pre‐industrial period (year 1880) and the time at which pCO 2 will double (year 2065). 相似文献
15.
The increases in atmospheric pCO 2 over the last century are accompanied by higher concentrations of CO 2(aq) in the surface oceans. This acidification of the surface ocean is expected to influence aquatic primary productivity and may also affect cyanobacterial nitrogen (N)‐fixers (diazotrophs). No data is currently available showing the response of diazotrophs to enhanced oceanic CO 2(aq). We examined the influence of pCO 2 [preindustrial∼250 ppmv (low), ambient∼400, future∼900 ppmv (high)] on the photosynthesis, N fixation, and growth of Trichodesmium IMS101. Trichodesmium spp. is a bloom‐forming cyanobacterium contributing substantial inputs of ‘new N’ to the oligotrophic subtropical and tropical oceans. High pCO 2 enhanced N fixation, C : N ratios, filament length, and biomass of Trichodesmium in comparison with both ambient and low pCO 2 cultures. Photosynthesis and respiration did not change significantly between the treatments. We suggest that enhanced N fixation and growth in the high pCO 2 cultures occurs due to reallocation of energy and resources from carbon concentrating mechanisms (CCM) required under low and ambient pCO 2. Thus, in oceanic regions, where light and nutrients such as P and Fe are not limiting, we expect the projected concentrations of CO 2 to increase N fixation and growth of Trichodesmium. Other diazotrophs may be similarly affected, thereby enhancing inputs of new N and increasing primary productivity in the oceans. 相似文献
16.
Biological soil crusts (biocrusts) cover soil surfaces in many drylands globally. The impacts of 10 years of elevated atmospheric CO 2 on the cyanobacteria in biocrusts of an arid shrubland were examined at a large manipulated experiment in Nevada, USA. Cyanobacteria‐specific quantitative PCR surveys of cyanobacteria small‐subunit (SSU) rRNA genes suggested a reduction in biocrust cyanobacterial biomass in the elevated CO 2 treatment relative to the ambient controls. Additionally, SSU rRNA gene libraries and shotgun metagenomes showed reduced representation of cyanobacteria in the total microbial community. Taxonomic composition of the cyanobacteria was similar under ambient and elevated CO 2 conditions, indicating the decline was manifest across multiple cyanobacterial lineages. Recruitment of cyanobacteria sequences from replicate shotgun metagenomes to cyanobacterial genomes representing major biocrust orders also suggested decreased abundance of cyanobacteria sequences across the majority of genomes tested. Functional assignment of cyanobacteria‐related shotgun metagenome sequences indicated that four subsystem categories, three related to oxidative stress, were differentially abundant in relation to the elevated CO 2 treatment. Taken together, these results suggest that elevated CO 2 affected a generalized decrease in cyanobacteria in the biocrusts and may have favoured cyanobacteria with altered gene inventories for coping with oxidative stress. 相似文献
17.
This study tested the interactive effects of increased seawater temperature and CO2 partial pressure (pCO2) on the photochemistry, bleaching, and early growth of the reef coral Pocillopora damicornis. New recruits were maintained at ambient or high temperature (29 or 30.8 °C) and pCO2 (~ 500 and ~ 1100 μatm) in a full-factorial experiment for 3 weeks. Neither a sharp decline in photochemical efficiency (Fv/Fm) nor evident bleaching was observed at high temperature and/or high pCO2. Furthermore, elevated temperature greatly promoted lateral growth and calcification, while polyp budding exhibited temperature-dependent responses to pCO2. High pCO2 depressed calcification by 28% at ambient temperature, but did not impact calcification at 30.8 °C. Interestingly, elevated temperature in concert with high pCO2 significantly retarded the budding process. These results suggest that increased temperature can mitigate the adverse effects of acidification on the calcification of juvenile P. damicornis, but at a substantial cost to asexual budding.
相似文献
18.
Rising concentrations of atmospheric CO 2 are changing the carbonate chemistry of the oceans, a process known as ocean acidification (OA). Absorption of this CO 2 by the surface oceans is increasing the amount of total dissolved inorganic carbon (DIC) and bicarbonate ion (HCO 3
−) available for marine calcification yet is simultaneously lowering the seawater pH and carbonate ion concentration ([CO 3
2−]), and thus the saturation state of seawater with respect to aragonite (Ω ar). We investigated the relative importance of [HCO 3
−] versus [CO 3
2−] for early calcification by new recruits (primary polyps settled from zooxanthellate larvae) of two tropical coral species,
Favia fragum and Porites astreoides. The polyps were reared over a range of Ω ar values, which were manipulated by both acid-addition at constant pCO 2 (decreased total [HCO 3
−] and [CO 3
2−]) and by pCO 2 elevation at constant alkalinity (increased [HCO 3
−], decreased [CO 3
2−]). Calcification after 2 weeks was quantified by weighing the complete skeleton (corallite) accreted by each polyp over the
course of the experiment. Both species exhibited the same negative response to decreasing [CO 3
2−] whether Ω ar was lowered by acid-addition or by pCO 2 elevation—calcification did not follow total DIC or [HCO 3
−]. Nevertheless, the calcification response to decreasing [CO 3
2−] was nonlinear. A statistically significant decrease in calcification was only detected between Ω ar = <2.5 and Ω ar = 1.1–1.5, where calcification of new recruits was reduced by 22–37% per 1.0 decrease in Ω ar. Our results differ from many previous studies that report a linear coral calcification response to OA, and from those showing
that calcification increases with increasing [HCO 3
−]. Clearly, the coral calcification response to OA is variable and complex. A deeper understanding of the biomineralization
mechanisms and environmental conditions underlying these variable responses is needed to support informed predictions about
future OA impacts on corals and coral reefs. 相似文献
19.
Coccolithophores are unicellular phytoplankton that produce calcium carbonate coccoliths as an exoskeleton. Emiliania huxleyi, the most abundant coccolithophore in the world's ocean, plays a major role in the global carbon cycle by regulating the exchange of CO 2 across the ocean‐atmosphere interface through photosynthesis and calcium carbonate precipitation. As CO 2 concentration is rising in the atmosphere, the ocean is acidifying and ammonium (NH 4+) concentration of future ocean water is expected to rise. The latter is attributed to increasing anthropogenic nitrogen (N) deposition, increasing rates of cyanobacterial N 2 fixation due to warmer and more stratified oceans, and decreased rates of nitrification due to ocean acidification. Thus, future global climate change will cause oceanic phytoplankton to experience changes in multiple environmental parameters including CO 2, pH, temperature and nitrogen source. This study reports on the combined effect of elevated pCO 2 and increased NH 4+ to nitrate (NO 3?) ratio (NH 4+/NO 3?) on E. huxleyi, maintained in continuous cultures for more than 200 generations under two pCO 2 levels and two different N sources. Herein, we show that NH 4+ assimilation under N‐replete conditions depresses calcification at both low and high pCO 2, alters coccolith morphology, and increases primary production. We observed that N source and pCO 2 synergistically drive growth rates, cell size, and the ratio of inorganic to organic carbon. These responses to N source suggest that, compared to increasing CO 2 alone, a greater disruption of the organic carbon pump could be expected in response to the combined effect of increased NH 4+/NO 3? ratio and CO 2 level in the future acidified ocean. Additional experiments conducted under lower nutrient conditions are needed prior to extrapolating our findings to the global oceans. Nonetheless, our results emphasize the need to assess combined effects of multiple environmental parameters on phytoplankton biology to develop accurate predictions of phytoplankton responses to ocean acidification. 相似文献
20.
Global emissions of atmospheric CO 2 and tropospheric O 3 are rising and expected to impact large areas of the Earths forests. While CO 2 stimulates net primary production, O 3 reduces photosynthesis, altering plant C allocation and reducing ecosystem C storage. The effects of multiple air pollutants can alter belowground C allocation, leading to changes in the partial pressure of CO 2 ( pCO 2) in the soil , chemistry of dissolved inorganic carbonate (DIC) and the rate of mineral weathering. As this system represents a linkage between the long- and short-term C cycles and sequestration of atmospheric CO 2, changes in atmospheric chemistry that affect net primary production may alter the fate of C in these ecosystems. To date, little is known about the combined effects of elevated CO 2 and O 3 on the inorganic C cycle in forest systems. Free air CO 2 and O 3 enrichment (FACE) technology was used at the Aspen FACE project in Rhinelander, Wisconsin to understand how elevated atmospheric CO 2 and O 3 interact to alter pCO 2 and DIC concentrations in the soil. Ambient and elevated CO 2 levels were 360±16 and 542±81 l l –1, respectively; ambient and elevated O 3 levels were 33±14 and 49±24 nl l –1, respectively. Measured concentrations of soil CO 2 and calculated concentrations of DIC increased over the growing season by 14 and 22%, respectively, under elevated atmospheric CO 2 and were unaffected by elevated tropospheric O 3. The increased concentration of DIC altered inorganic carbonate chemistry by increasing system total alkalinity by 210%, likely due to enhanced chemical weathering. The study also demonstrated the close coupling between the seasonal 13C of soil pCO 2 and DIC, as a mixing model showed that new atmospheric CO 2 accounted for approximately 90% of the C leaving the system as DIC. This study illustrates the potential of using stable isotopic techniques and FACE technology to examine long- and short-term ecosystem C sequestration. 相似文献
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