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Arctic permafrost environments store large amounts of organic carbon. As a result of global warming, intensified permafrost degradation and release of significant quantities of the currently conserved organic matter is predicted for high latitudes. To improve our understanding of the present and future carbon dynamics in climate sensitive permafrost ecosystems, the present study investigates structure and carbon turnover of the bacterial community in a permafrost-affected soil of the Lena Delta (72°22′N, 126°28′E) in northeastern Siberia. 16S rRNA gene clone libraries revealed the presence of all major soil bacterial groups and of the canditate divisions OD1 and OP11. A shift within the bacterial community was observed along the soil profile indicated by the absence of Alphaproteobacteria and Betaproteobacteria and a simultaneous increase in abundance and diversity of fermenting bacteria like Firmicutes and Actinobacteria near the permafrost table. BIOLOG EcoPlates were used to describe the spectrum of utilized carbon sources of the bacterial community in different horizons under in situ temperature conditions in the presence and absence of oxygen. The results revealed distinct qualitative differences in the substrates used and the turnover rates under oxic and anoxic conditions. It can be concluded that constantly negative redox potentials as characteristic for the near permafrost table horizons of the investigated soil did effectively shape the structure of the indigenous bacterial community limiting its phylum-level diversity and carbon turnover capacity.

Rising atmospheric CO 2 may stimulate future forest productivity, possibly increasing carbon storage in terrestrial ecosystems, but how tropospheric ozone will modify this response is unknown. Because of the importance of fine roots to the belowground C cycle, we monitored fine-root biomass and associated C fluxes in regenerating stands of trembling aspen, and mixed stands of trembling aspen and paper birch at FACTS-II, the Aspen FACE project in Rhinelander, Wisconsin. Free-air CO 2 enrichment (FACE) was used to elevate concentrations of CO2 (average enrichment concentra- tion 535 µl l -1 ) and O 3 (53 nl l -1 ) in developing forest stands in 1998 and 1999. Soil respiration, soil pCO 2 , and dissolved organic carbon in soil solution (DOC) were monitored biweekly. Soil respiration was measured with a portable infrared gas analyzer. Soil pCO 2 and DOC samples were collected from soil gas wells and tension lysimeters, respectively, at depths of 15, 30, and 125 cm. Fine-root biomass averaged 263 g m-2 in con- trol plots and increased 96% under elevated CO 2. The increased root biomass was accompanied by a 39% in- crease in soil respiration and a 27% increase in soil pCO 2 . Both soil respiration and pCO 2 exhibited a strong seasonal signal, which was positively correlated with soil temperature. DOC concentrations in soil solution averaged ~12 mg l -1 in surface horizons, declined with depth, and were little affected by the treatments. A sim- plified belowground C budget for the site indicated that native soil organic matter still dominated the system, and that soil respiration was by far the largest flux. Ozone decreased the above responses to elevated CO2, but effects were rarely statistically significant. We con- clude that regenerating stands of northern hardwoods have the potential for substantially greater C input to soil due to greater fine-root production under elevated CO 2 . Greater fine-root biomass will be accompanied by greater soil C efflux as soil respiration, but leaching losses of C will probably be unaffected.

Predicting ozone-induced reduction of carbon sequestration of forests under elevated tropospheric ozone concentrations requires robust mechanistic leaf-level models, scaled up to whole tree and stand level. As ozone effects depend on genotype, the ability to predict these effects on forest carbon cycling via competitive response between genotypes will also be required. This study tests a process-based model that predicts the relative effects of ozone on the photosynthetic rate and growth of an ozone-sensitive aspen clone, as a first step in simulating the competitive response of genotypes to atmospheric and climate change. The resulting composite model simulated the relative above ground growth response of ozone-sensitive aspen clone 259 exposed to square wave variation in ozone concentration. This included a greater effect on stem diameter than on stem height, earlier leaf abscission, and reduced stem and leaf dry matter production at the end of the growing season. Further development of the model to reduce predictive uncertainty is discussed.

A model to predict global patterns in vegetation physiognomy was developed from physiological considera- tions influencing the distributions of different functional types of plant. Primary driving variables are mean coldest- month temperature, annual accumulated temeprature over 5"C, and a drought index incorporating the seasonality of precipitation and the available water capacity of the soil. The model predicts which plant types can occur in a given environment, and selects the potentially dominant types from among them. Biomes arise as combinations of domi- nant types. Global environmental data were supplied as monthly means of temperature, precipitation and sunshine (interpolated to a global 0.5" grid, with a lapse-rate correc

Current carbon cycle models attribute rising atmospheric CO2 as the major driver of the increased terrestrial carbon sink, but with substantial uncertainties. The photosynthetic response of trees to elevated atmospheric CO2 is a necessary step, but not the only one, for sustaining the terrestrial carbon uptake, but can vary diurnally, seasonally and with duration of CO2 exposure. Hence, we sought to quantify the photosynthetic response of the canopy-dominant species, Quercus robur, in a mature deciduous forest to elevated CO2 (eCO2) (+150 μmol mol−1 CO2) over the first 3 years of a long-term free air CO2 enrichment facility at the Birmingham Institute of Forest Research in central England (BIFoR FACE). Over 3000 measurements of leaf gas exchange and related biochemical parameters were conducted in the upper canopy to assess the diurnal and seasonal responses of photosynthesis during the 2nd and 3rd year of eCO2 exposure. Measurements of photosynthetic capacity via biochemical parameters, derived from CO2 response curves, (Vcmax and Jmax) together with leaf nitrogen concentrations from the pre-treatment year to the 3rd year of eCO2 exposure, were examined. We hypothesized an initial enhancement in light-saturated net photosynthetic rates (Asat) with CO2 enrichment of ≈37% based on theory but also expected photosynthetic capacity would fall over the duration of the study. Over the 3-year period, Asat of upper-canopy leaves was 33 ± 8% higher (mean and standard error) in trees grown in eCO2 compared with ambient CO2 (aCO2), and photosynthetic enhancement decreased with decreasing light. There were no significant effects of CO2 treatment on Vcmax or Jmax, nor leaf nitrogen. Our results suggest that mature Q. robur may exhibit a sustained, positive response to eCO2 without photosynthetic downregulation, suggesting that, with adequate nutrients, there will be sustained enhancement in C assimilated by these mature trees. Further research will be required to understand the location and role of the additionally assimilated carbon.

The reduction of greenhouse gases (GHG) emissions is important challenge in the wastewater treatment plants. In this way, the present study aimed to evaluate the GHG emissions and carbon dioxide fixation by duckweed ponds (DWP) applied to treat municipal wastewater in a polishing stage. Two pilot DWP (3000 L) were operated in a series with real wastewater receiving a flow rate of 200 L d−1 and organic load rate of 39 g COD ha−1 d−1. Beyond the standard physicochemical parameters for wastewater monitoring, the gases emissions from pond surface were measures by using a static flux chamber with infrared probes installed inside to detect CO2 and CH4 concentration. Operating the DWP with a load of 18.1 kg TN ha−1 d−1 and 2 kg TP ha−1 d−1, across 425 days of monitoring, higher COD and nutrient removal efficiency was identified (79%, 93% and 84% for COD, TN and TP, respectively). The CO2 emission rate ranged from 3048 to 6017 mg CO2 m−2 d−1 and the fixation rate ranged from 19,592 to 42,052 mg CO2 m−2 d−1. Methane emission was not detected (less than 0.1%). Moreover, low abundance of archaeal community was identified in both DWP. The results showed that in presented conditions, under low COD loading rate DWP could fix at least three times more CO2 than it emits, highlighting the sustainability of this natural technology.

Summary Terrestrial primary productivity and carbon cycle impacts of droughts are commonly quantified using vapour pressure deficit (VPD) data and remotely sensed greenness, without accounting for soil moisture. However, soil moisture limitation is known to strongly affect plant physiology.Here, we investigate light use efficiency, the ratio of gross primary productivity (GPP) to absorbed light. We derive its fractional reduction due to soil moisture (fLUE), separated from VPD and greenness changes, using artificial neural networks trained on eddy covariance data, multiple soil moisture datasets and remotely sensed greenness.This reveals substantial impacts of soil moisture alone that reduce GPP by up to 40% at sites located in sub‐humid, semi‐arid or arid regions. For sites in relatively moist climates, we find, paradoxically, a muted fLUE response to drying soil, but reduced fLUE under wet conditions. fLUE identifies substantial drought impacts that are not captured when relying solely on VPD and greenness changes and, when seasonally recurring, are missed by traditional, anomaly‐based drought indices. Counter to common assumptions, fLUE reductions are largest in drought‐deciduous vegetation, including grasslands. Our results highlight the necessity to account for soil moisture limitation in terrestrial primary productivity data products, especially for drought‐related assessments., See also the Commentary on this article by https://doi.org/10.1111/nph.15176.

In this study, a novel on-site torrefaction method was proposed for the pretreatment of wheat straw, in which the wheat straw was placed in an enclosed environment for torrefaction. The effects of different torrefaction conditions on the properties of both solid and gaseous products were investigated. When the temperature of enclosed torrefaction increased from 200 °C to 250 °C, the higher heating value, fixed carbon and C content of wheat straw increased by 12.7%, 80.3% and 18.1%, respectively, and the moisture decreased by 25.0%. Enclosed torrefaction causes more mass loss due to the smoldering of wheat straw, and a strong decomposition of the hemicellulose of wheat straw during the torrefaction process. The gaseous products obtained by enclosed torrefaction have fewer acids and more esters than conventional torrefaction. Compared with conventional torrefaction, enclosed torrefaction performs similarly, or even better, in improving the properties of wheat straw.

The first product of sulfate assimilation in plants, cysteine, is a proteinogenic amino acid and a source of reduced sulfur for plant metabolism. Cysteine synthesis is the convergence point of the three major pathways of primary metabolism: carbon, nitrate, and sulfate assimilation. Despite the importance of metabolic and genetic coordination of these three pathways for nutrient balance in plants, the molecular mechanisms underlying this coordination, and the sensors and signals, are far from being understood. This is even more apparent in C4 plants, where coordination of these pathways for cysteine synthesis includes the additional challenge of differential spatial localization. Here we review the coordination of sulfate, nitrate, and carbon assimilation, and show how they are altered in C4 plants. We then summarize current knowledge of the mechanisms of coordination of these pathways. Finally, we identify urgent questions to be addressed in order to understand the integration of sulfate assimilation with carbon and nitrogen metabolism particularly in C4 plants. We consider answering these questions to be a prerequisite for successful engineering of C4 photosynthesis into C3 crops to increase their efficiency., This review summarizes current knowledge on the coordination of sulfur, nitrogen, and carbon metabolism and discusses sulfate assimilation in the context of evolution of C4 photosynthesis.

Flaveria trinervia C4 phosphoenolpyruvate carboxylase (PEPc) has higher affinity for HCO3− than its closely related Flaveria pringlei C3 PEPc, which drives higher modeled rates of C4 photosynthesis under low CO2 partial pressures., Phosphoenolpyruvate (PEP) carboxylase (PEPc) catalyzes the first committed step of C4 photosynthesis generating oxaloacetate from bicarbonate (HCO3−) and PEP. It is hypothesized that PEPc affinity for HCO3− has undergone selective pressure for a lower KHCO3 (Km for HCO3−) to increase the carbon flux entering the C4 cycle, particularly during conditions that limit CO2 availability. However, the decrease in KHCO3 has been hypothesized to cause an unavoidable increase in KPEP (Km for PEP). Therefore, the amino acid residue S774 in the C4 enzyme, which has been shown to increase KPEP, should lead to a decrease in KHCO3. Several studies reported the effect S774 has on KPEP; however, the influence of this amino acid substitution on KHCO3 has not been tested. To test these hypotheses, membrane-inlet mass spectrometry (MIMS) was used to measure the KHCO3 of the photosynthetic PEPc from the C4Flaveria trinervia and the non-photosynthetic PEPc from the C3F. pringlei. The cDNAs for these enzymes were overexpressed and purified from the PEPc-less PCR1 Escherichia coli strain. Our work in comparison with previous reports suggests that KHCO3 and KPEP are linked by specific amino acids, such as S774; however, these kinetic parameters respond differently to the tested allosteric regulators, malate and glucose-6-phosphate.

The two-cell type C4 photosynthetic pathway requires both anatomical and biochemical specialization to achieve a functional CO2-concentrating mechanism. While a great deal of research has been done on Kranz anatomy and cell-specific expression and activity of enzymes in the C4 pathway, less attention has been paid to partitioning of carbohydrate synthesis between the cell types of C4 leaves. As early as the 1970s it became apparent that, in the small number of species examined at the time, sucrose was predominantly synthesized in the mesophyll cells and starch in the bundle sheath cells. Here we discuss how this partitioning is achieved in C4 plants and explore whether this is a consequence of C4 metabolism or indeed a requirement for its evolution and efficient operation., C4 plants partition starch and sucrose biosynthesis between bundle sheath and mesophyll cells. Here we review why and how this is achieved, and discuss the relevance for C4 photosynthesis.

Metabolite profiling has uncovered unexpected diversity of Calvin–Benson cycle operation in C3 species, but also conserved features that may be important in the fluctuating conditions found in the field., Improving photosynthesis is a promising avenue to increase crop yield. This will be aided by better understanding of natural variance in photosynthesis. Profiling of Calvin–Benson cycle (CBC) metabolites provides a top-down strategy to uncover interspecies diversity in CBC operation. In a study of four C4 and five C3 species, principal components analysis separated C4 species from C3 species and also separated different C4 species. These separations were driven by metabolites that reflect known species differences in their biochemistry and pathways. Unexpectedly, there was also considerable diversity between the C3 species. Falling atmospheric CO2 and changing temperature, nitrogen, and water availability have driven evolution of C4 photosynthesis in multiple lineages. We propose that analogous selective pressures drove lineage-dependent evolution of the CBC in C3 species. Examples of species-dependent variation include differences in the balance between the CBC and the light reactions, and in the balance between regulated steps in the CBC. Metabolite profiles also reveal conserved features including inactivation of enzymes in low irradiance, and maintenance of CBC metabolites at relatively high levels in the absence of net CO2 fixation. These features may be important for photosynthetic efficiency in low light, fluctuating irradiance, and when stomata close due to low water availability.

Global warming has become a serious issue nowadays as the trend of CO2 emission is increasing by years. In Malaysia, the electricity and energy sector contributed a significant amount to the nation’s CO2 emission due to fossil fuel use. Many research works have been carried out to mitigate this issue, including carbon capture and utilization (CCUS) technology and biological carbon fixation by microalgae. This study makes a preliminary effort to screen native microalgae species in the Malaysian coal-fired power plant’s surrounding towards carbon fixation ability. Three dominant species, including Nannochloropsis sp., Tetraselmis sp., and Isochrysis sp. were identified and tested in the laboratory under ambient and pure CO2 condition to assess their growth and CO2 fixation ability. The results indicate Isochrysis sp. as the superior carbon fixer against other species. In continuation, the optimization study using Response Surface Methodology (RSM) was carried out to optimize the operating conditions of Isochrysis sp. using a customized lab-scale photobioreactor under simulated flue gas exposure. This species was further acclimatized and tested under actual flue gas generated by the power plant. Isochrysis sp. had shown its capability as a carbon fixer with CO2 fixation rate of 0.35 gCO2/L day under actual coal-fired flue gas exposure after cycles of acclimatization phase. This work is the first to demonstrate indigenous microalgae species' ability as a carbon fixer under Malaysian coal-fired flue gas exposure. Thus, the findings shall be useful in exploring the microalgae potential as a biological agent for carbon emission mitigation from power plants more sustainably.

With the emerging need of nutrient recycling in resource recovery facilities, the use of microalgae-bacteria flocs has received considerable attention in the past few years. However, although the main biological processes are already known, the complex interactions occurring between algae and bacteria are not fully understood. In this work, a combined respirometric-titrimetric unit was used to assess the microorganisms' kinetics within microalgae-bacteria flocs under different growth regimes (i.e. photoautotrophic, heterotrophic and mixotrophic) and different ratios of inorganic (IC) to organic carbon (OC) (IC:OC-ratios). Using this respirometric-titrimetric data, a new model was developed, calibrated and successfully validated. The model takes into account the heterotrophic growth of bacteria, the photoautotrophic, heterotrophic and mixotrophic growth of algae and the production and consumption of extracellular polymeric substances (EPS) by both bacteria and algae. As such, the model can be used for detailed analysis of the carbon fluxes within microalgae-bacteria flocs in an efficient way. Model analysis revealed the high importance of the EPS regulatory mechanism. Firstly, under heterotrophic growth conditions, OC-uptake occurred during the first 10–15 min. This was linked with internal OC storage (49% of added OC) and EPS production (40%), as such providing carbon reserves which can be consumed during famine conditions. Moreover, the algae were able to compete with bacteria for OC. Secondly, under photoautotrophic conditions, algae used the added IC to grow (57% of added IC) and to produce EPS (29%), which consecutively stimulated heterotrophic bacteria growth (20%). Finally, under mixotrophic conditions, low IC:OC-ratios resulted in an extensive OC-storage and EPS production (50% of added C) and an enhanced microalgal CO2 reuse, resulting in an increased algal growth of up to 29%.

A combined increase in seawater [CO2 ] and [H(+) ] was recently shown to induce a shift from photosynthetic HCO3 (-) to CO2 uptake in Emiliania huxleyi. This shift occurred within minutes, whereas acclimation to ocean acidification (OA) did not affect the carbon source. To identify the driver of this shift, we exposed low- and high-light acclimated E. huxleyi to a matrix of two levels of dissolved inorganic carbon (1400, 2800 μmol kg(-1) ) and pH (8.15, 7.85) and directly measured cellular O2 , CO2 and HCO3 (-) fluxes under these conditions. Exposure to increased [CO2 ] had little effect on the photosynthetic fluxes, whereas increased [H(+) ] led to a significant decline in HCO3 (-) uptake. Low-light acclimated cells overcompensated for the inhibition of HCO3 (-) uptake by increasing CO2 uptake. High-light acclimated cells, relying on higher proportions of HCO3 (-) uptake, could not increase CO2 uptake and photosynthetic O2 evolution consequently became carbon-limited. These regulations indicate that OA responses in photosynthesis are caused by [H(+) ] rather than by [CO2 ]. The impaired HCO3 (-) uptake also provides a mechanistic explanation for lowered calcification under OA. Moreover, it explains the OA-dependent decrease in photosynthesis observed in high-light grown phytoplankton.

Summary Coccolithophores are globally distributed unicellular marine algae that are characterized by their covering of calcite coccoliths. Calcification by coccolithophores contributes significantly to global biogeochemical cycles. However, the physiological requirement for calcification remains poorly understood as non‐calcifying strains of some commonly used model species, such as Emiliania huxleyi, grow normally in laboratory culture.To determine whether the requirement for calcification differs between coccolithophore species, we utilized multiple independent methodologies to disrupt calcification in two important species of coccolithophore: E. huxleyi and Coccolithus braarudii. We investigated their physiological response and used time‐lapse imaging to visualize the processes of calcification and cell division in individual cells.Disruption of calcification resulted in major growth defects in C. braarudii, but not in E. huxleyi. We found no evidence that calcification supports photosynthesis in C. braarudii, but showed that an inability to maintain an intact coccosphere results in cell cycle arrest.We found that C. braarudii is very different from E. huxleyi as it exhibits an obligate requirement for calcification. The identification of a growth defect in C. braarudii resulting from disruption of the coccosphere may be important in considering their response to future changes in ocean carbonate chemistry., See also the Commentary on this article by https://doi.org/10.1111/nph.15409.

With rapid technology progress and cost reduction, clean hydrogen from water electrolysis driven by renewable powers becomes a potential feedstock for CO2 fixation by hydrogen-oxidizing bacteria. Cupriavidus necator (formally Ralstonia eutropha), a representative member of the lithoautotrophic prokaryotes, is a promising producer of polyhydroxyalkanoates and single cell proteins. This paper reviews the fundamental properties of the hydrogen-oxidizing bacterium, the metabolic activities under limitation of individual gases and nutrients, and the value-added products from CO2, including the products with large potential markets. Gas fermentation and bioreactor safety are discussed for achieving high cell density and high productivity of desired products under chemolithotrophic conditions. The review also updates the recent research activities in metabolic engineering of C. necator to produce novel metabolites from CO2.

The different categories of samples and their treatments at the radiocarbon (14C) laboratory in Jena, Germany, are described. The Jena 14C laboratory is dedicated to studying the global carbon cycle through the analysis of soil, plant, gas, charcoal, and wood samples. The respective preparation procedures for different samples types are presented, including wet-chemistry pretreatments for soil decalcification, charcoal purification using an acid–base–oxidation procedure (ABOx), and α-cellulose extraction from wood and leaves. In particular, investigations of the background corrections for each sample type are emphasized. Furthermore, an investigation of the contamination resulting from the storage of graphite is presented. Four storage conditions are investigated for storage times up to 30 months.

Lack of glycogen synthases results in the lethal accumulation of their substrate, ADP-glucose, but providing an alternative metabolic sink restores cell viability and the nutrient deprivation response., Cyanobacteria are widely distributed photosynthetic organisms. During the day they store carbon, mainly as glycogen, to provide the energy and carbon source they require for maintenance during the night. Here, we generate a mutant strain of the freshwater cyanobacterium Synechocystis sp. PCC 6803 lacking both glycogen synthases. This mutant has a lethal phenotype due to massive accumulation of ADP-glucose, the substrate of glycogen synthases. This accumulation leads to alterations in its photosynthetic capacity and a dramatic decrease in the adenylate energy charge of the cell to values as low as 0.1. Lack of ADP-glucose pyrophosphorylase, the enzyme responsible for ADP-glucose synthesis, or reintroduction of any of the glycogen synthases abolishes the lethal phenotype. Viability of the glycogen synthase mutant is also fully recovered in NaCl-supplemented medium, which redirects the surplus of ADP-glucose to synthesize the osmolite glucosylglycerol. This alternative metabolic sink also suppresses phenotypes associated with the defective response to nitrogen deprivation characteristic of glycogen-less mutants, restoring the capacity to degrade phycobiliproteins. Thus, our system is an excellent example of how inadequate management of the adenine nucleotide pools results in a lethal phenotype, and the influence of metabolic carbon flux in cell viability and fitness.

The purpose of this study was to evaluate the carbon equivalences (CE) of whole-chain soybean oil production, starting from plantation until production of soybean oil. Appropriate approaches for the reduction of carbon emissions were also evaluated. Following a carbon-balanced model, total carbon emissions from soybean oil production were found to be +711 ± 14 kg CE/ton soybean oil. Cultivation, threshing, and industrial phases were responsible for 63%, 3%, and 34% of overall emissions, respectively. The highest equivalent carbon emissions in the cultivation process come from use of diesel fuel for watering and spraying chemical fertilizers. Meanwhile, the most significant emission from soybean oil production was found to be due to fuel oil used for steam production, contributing to 52% of total emissions in industrial phase. In addition, emissions from soybean meal, a co-product from soybean oil industry is equal to 169 kg CE/ton soybean meal. It involves fixed carbon as valuable protein sources sent to feed mills. From the complete carbon cycle scenarios of soybean oil production, the carbon fixation efficiency is computed to be equal to 74.7%. This indicates that soybean oil production still continues to emit carbon into the atmosphere. However, nutrients fixed in plant residues remaining in cultivation areas help reduce carbon emissions of about 175 ± 23.8 kg CE/ha from decreasing amount chemical fertilizers to be applied. From the selected scenarios, potential reductions of carbon emissions from soybean oil production were found to be 87% as compared to existing conditions. Moreover, cost saving from selected approaches to reduction of carbon emissions were estimated to be 7.4 Baht/kg soybean oil (0.21 USD/kg soybean oil). Based on emitted CE, the unit cost of soybean oil production was found to be 49.6 Baht/kg CE (1.41 USD/kg CE).

Bark beetle outbreaks are widespread in western North American forests, reducing primary productivity and transpiration, leading to forest mortality across large areas and altering ecosystem carbon cycling. Here the carbon isotope composition (δ(13) C) of soil respiration (δJ ) was monitored in the decade after disturbance for forests affected naturally by mountain pine beetle infestation and artificially by stem girdling. The seasonal mean δJ changed along both chronosequences. We found (a) enrichment of δJ relative to controls (

Microalgae have been considered as promising alternative for CO2 fixation and wastewater purification. In our previous work, a hybrid microalgae CO2 fixation concept has been put forward, which initially used carbonate solution absorb CO2, and then provided obtained bicarbonate as nutrition for microalgae growth to avoid the challenge of low CO2 solubility and carbon fixation efficiency in the conventional process. In this work, the proposed hybrid system was further intensified via integrating soybean wastewater nutrition removal with bicarbonate-carbon (NH4HCO3 and KHCO3) conversion. The investigation results indicated that the maximum biomass productivity (0.74 g L−1) and carbon bioconversion efficiency (46.9%) were achieved in low-NH4HCO3 concentration system with pH adjusted to 7. pH adjustment of different bicarbonate systems also enhanced total nitrogen (TN), total phosphorus (TP) and chemical oxygen demand (COD) removal efficiency up to 87.5%, 99.5% and 77.6%, respectively. In addition, maximum neutral lipid (14.4 mg L−1·d−1) and polysaccharide (14.5 mg L−1·d−1) productivities could be obtained in the KHCO3 systems, while higher crude protein productivity (48.1 mg L−1·d−1) was yielded in the NH4HCO3 systems.

In this study, the techno-economic, energy consumption (EC), and environmental performances of biomass-to-hydrogen (BTH) production with/without methane tri-reforming (MTR) from corn straw were studied. The techno-economic analysis includes an assessment of the energy efficiency, MTR operating conditions, total capital investment (TCI), production cost (PC), and payback period. The BTH energy efficiency with MTR is 17.08% higher than that without MTR. The Claus unit is the largest contribution unit of energy loss. The reaction temperature and operating pressure of one MTR unit are 800 °C and 0.1 MPa, respectively. Compared with BTH without MTR, the TCI of BTH with MTR increased by 10.97%, and the PC decreased by 10.12%. The static payback period of BTH with MTR is approximately 4.72 yr. BTH without MTR exhibits 3.09% less EC and 7.85% greenhouse gas emissions than that of BTH with MTR. The life cycle analysis of the BTH process illustrates that the BTH with MTR can realize negative carbon dioxide (CO2) emissions when considering the natural carbon cycle. The evaluation method combines a thermodynamic analysis with a life cycle assessment, which is significant for the development of clean hydrogen production technology with low carbon and high energy savings.

Sesuvium sesuvioides represents a young C4 lineage with C4-like metabolism: CO2 compensation points range between C4 and C3–C4 intermediate values, and Rubisco was detected in bundle sheath and mesophyll., Sesuvium sesuvioides (Sesuvioideae, Aizoaceae) is a perennial, salt-tolerant herb distributed in flats, depressions, or disturbed habitats of southern Africa and the Cape Verdes. Based on carbon isotope values, it is considered a C4 species, despite a relatively high ratio of mesophyll to bundle sheath cells (2.7:1) in the portulacelloid leaf anatomy. Using leaf anatomy, immunocytochemistry, gas exchange measurements, and enzyme activity assays, we sought to identify the biochemical subtype of C4 photosynthesis used by S. sesuvioides and to explore the anatomical, physiological, and biochemical traits of young, mature, and senescing leaves, with the aim to elucidate the plasticity and possible limitations of the photosynthetic efficiency in this species. Assays indicated that S. sesuvioides employs the NADP-malic enzyme as the major decarboxylating enzyme. The activity of C4 enzymes, however, declined as leaves aged, and the proportion of water storage tissue increased while air space decreased. These changes suggest a functional shift from photosynthesis to water storage in older leaves. Interestingly, S. sesuvioides demonstrated CO2 compensation points ranging between C4 and C3–C4 intermediate values, and immunocytochemistry revealed labeling of the Rubisco large subunit in mesophyll cells. We hypothesize that S. sesuvioides represents a young C4 lineage with C4-like photosynthesis in which C3 and C4 cycles are running simultaneously in the mesophyll.

An air-lift-type microbial carbon capture cell (ALMCC) was constructed for the first time by using an air-lift-type photobioreactor as the cathode chamber. The performance of ALMCC in fixing high concentration of CO2, producing energy (power and biodiesel), and removing COD together with nutrients was investigated and compared with the traditional microbial carbon capture cell (MCC) and air-lift-type photobioreactor (ALP). The ALMCC system produced a maximum power density of 972.5 mW·m(-3) and removed 86.69% of COD, 70.52% of ammonium nitrogen, and 69.24% of phosphorus, which indicate that ALMCC performed better than MCC in terms of power generation and wastewater treatment efficiency. Besides, ALMCC demonstrated 9.98- and 1.88-fold increases over ALP and MCC in the CO2 fixation rate, respectively. Similarly, the ALMCC significantly presented a higher lipid productivity compared to those control reactors. More importantly, the preliminary analysis of energy balance suggested that the net energy of the ALMCC system was significantly superior to other systems and could theoretically produce enough energy to cover its consumption. In this work, the established ALMCC system simultaneously achieved the high level of CO2 fixation, energy recycle, and municipal wastewater treatment effectively and efficiently.

Bamboo forests provide important ecosystem services and play an important role in terrestrial carbon cycling. Of the approximately 500 bamboo species in China, Moso bamboo (Phyllostachys pubescens) is the most important one in terms of distribution, timber value, and other economic values. In this study, we estimated current and potential carbon stocks in China's Moso bamboo forests and in their products. The results showed that Moso bamboo forests in China stored about 611.15 ± 142.31 Tg C, 75% of which was in the top 60 cm soil, 22% in the biomass of Moso bamboos, and 3% in the ground layer (i.e., bamboo litter, shrub, and herb layers). Moso bamboo products store 10.19 ± 2.54 Tg C per year. The potential carbon stocks reach 1331.4 ± 325.1 Tg C, while the potential C stored in products is 29.22 ± 7.31 Tg C a(-1). Our results indicate that Moso bamboo forests and products play a critical role in C sequestration. The information gained in this study will facilitate policy decisions concerning carbon sequestration and management of Moso bamboo forests in China.

Highlight Multigene manipulation of levels of Calvin cycle enzymes, together with the introduction of a putative cyanobacterial inorganic carbon transporter, results in substantial improvements in biomass yield. This study demonstrates that this approach has the potential to produce crop plants to meet the food requirements of a growing population., Over the next 40 years it has been estimated that a 50% increase in the yield of grain crops such as wheat and rice will be required to meet the food and fuel demands of the increasing world population. Transgenic tobacco plants have been generated with altered combinations of sedoheptulose-1,7-bisphosphatase, fructose-1,6-bisphosphate aldolase, and the cyanobacterial putative-inorganic carbon transporter B, ictB, of which have all been identified as targets to improve photosynthesis based on empirical studies. It is shown here that increasing the levels of the three proteins individually significantly increases the rate of photosynthetic carbon assimilation, leaf area, and biomass yield. Furthermore, the daily integrated measurements of photosynthesis showed that mature plants fixed between 12–19% more CO2 than the equivalent wild-type plants. Further enhancement of photosynthesis and yield was observed when sedoheptulose-1,7-bisphosphatase, fructose-1,6-bisphosphate aldolase, and ictB were over-expressed together in the same plant. These results demonstrate the potential for the manipulation of photosynthesis, using multigene-stacking approaches, to increase crop yields.

Flue gas refers to the gas emitting from the combustion processes, and it contains CO2 , NOx , SOx and other potentially hazardous compounds. Due to the increasing concerns of CO2 emissions and environmental pollution, the cleaning process of flue gas has attracted much attention. Using microalgae to clean up flue gas via photosynthesis is considered a promising CO2 mitigation process for flue gas. However, the impurities in the flue gas may inhibit microalgal growth, leading to a lower microalgae-based CO2 fixation rate. The inhibition effects of SOx that contribute to the low pH could be alleviated by maintaining a stable pH level, while NOx can be utilized as a nitrogen source to promote microalgae growth when it dissolves and is oxidized in the culture medium. The yielded microalgal biomass from fixing flue gas CO2 and utilizing NOx and SOx as nutrients would become suitable feedstock to produce biofuels and bio-based chemicals. In addition to the removal of SOx , NOx and CO2 , using microalgae to remove heavy metals from flue gas is also quite attractive. In conclusion, the use of microalgae for simultaneous removal of CO2 , SOx and NOx from flue gas is an environmentally benign process and represents an ideal platform for CO2 reutilization.

A recent unprecedented epidemic of beetle-induced tree mortality has occurred in the lodgepole pine forests of Western North America. Here, we present the results of studies in two subalpine forests in the Rocky Mountains, one that experienced natural pine beetle disturbance and one that experienced simulated disturbance imposed through bole girdling. We assessed changes to soil microclimate and biogeochemical pools in plots representing different post-disturbance chronosequences. High plot tree mortality, whether due to girdling or beetle infestation, caused similar alterations in soil nutrient pools. During the first 4 years after disturbance, sharp declines were observed in the soil dissolved organic carbon (DOC) concentration (45-51 %), microbial biomass carbon concentration (33-39 %), dissolved organic nitrogen (DON) concentration (31-42%), and inorganic phosphorus (PO4(3-)) concentration (53-55%). Five to six years after disturbance, concentrations of DOC, DON, and PO4(3-) recovered to 71-140 % of those measured in undisturbed plots. Recovery was coincident with observed increases in litter depth and the sublitter, soil O-horizon. During the 4 years following disturbance, soil ammonium, but not nitrate, increased to 2-3 times the levels measured in undisturbed plots. Microbial biomass N increased in plots where increased ammonium was available. Our results show that previously observed declines in soil respiration following beetle-induced disturbance are accompanied by losses in key soil nutrients. Recovery of the soil nutrient pool occurs only after several years following disturbance, and is correlated with progressive mineralization of dead tree litter.

Highlight text Combining experimental and theoretical approaches to characterize the carbon acquisition of a cyanobacterium, this paper improves interpretations of C isotope fractionation by accounting for the important role of intracellular C cycling., To predict effects of climate change on phytoplankton, it is crucial to understand how their mechanisms for carbon acquisition respond to environmental conditions. Aiming to shed light on the responses of extra- and intracellular inorganic C (Ci) fluxes, the cyanobacterium Trichodesmium erythraeum IMS101 was grown with different nitrogen sources (N2 vs NO3 –) and pCO2 levels (380 vs 1400 µatm). Cellular Ci fluxes were assessed by combining membrane inlet mass spectrometry (MIMS), 13C fractionation measurements, and modelling. Aside from a significant decrease in Ci affinity at elevated pCO2 and changes in CO2 efflux with different N sources, extracellular Ci fluxes estimated by MIMS were largely unaffected by the treatments. 13C fractionation during biomass production, however, increased with pCO2, irrespective of the N source. Strong discrepancies were observed in CO2 leakage estimates obtained by MIMS and a 13C-based approach, which further increased under elevated pCO2. These offsets could be explained by applying a model that comprises extracellular CO2 and HCO3 – fluxes as well as internal Ci cycling around the carboxysome via the CO2 uptake facilitator NDH-14. Assuming unidirectional, kinetic fractionation between CO2 and HCO3 – in the cytosol or enzymatic fractionation by NDH-14, both significantly improved the comparability of leakage estimates. Our results highlight the importance of internal Ci cycling for 13C composition as well as cellular energy budgets of Trichodesmium, which ought to be considered in process studies on climate change effects.

Through supplying 13C to leaves, the effect of the transportation of respired CO2 on measured leaf respiration is shown., High concentrations of inorganic carbon in the xylem, produced from root, stem, and branch respiration, travel via the transpiration stream and eventually exit the plant through distant tissues as CO2. Unlike previous studies that focused on the efflux of CO2 from roots and woody tissues, we focus on efflux from leaves and the potential effect on leaf respiration measurements. We labeled transported inorganic carbon, spanning reported xylem concentrations, with 13C and then manipulated transpiration rates in the dark in order to vary the rates of inorganic carbon supply to cut leaves from Brassica napus and Populus deltoides. We used tunable diode laser absorbance spectroscopy to directly measure the rate of gross 13CO2 efflux, derived from inorganic carbon supplied from outside of the leaf, relative to gross 12CO2 efflux generated from leaf cells. These experiemnts showed that 13CO2 efflux was dependent upon the rate of inorganic carbon supply to the leaf and the rate of transpiration. Our data show that the gross leaf efflux of xylem-transported CO2 is likely small in the dark when rates of transpiration are low. However, gross leaf efflux of xylem-transported CO2 could approach half the rate of leaf respiration in the light when transpiration rates and branch inorganic carbon concentrations are high, irrespective of the grossly different petiole morphologies in our experiment.

We examined the effects of three ectomycorrhizal (ECM) symbionts on the growth and photosynthesis capacity of Japanese black pine (Pinus thunbergii) seedlings and estimated physiological and photosynthetic parameters such as the light compensation point (LCP), biomass, and phosphorus (Pi) concentration of P. thunbergii seedlings. Through this investigation, we documented a new role of ectomycorrhizal (ECM) fungi: enhancement of the survival and competitiveness of P. thunbergii seedlings under low-light condition by reducing the LCP of seedlings. At a CO2 concentration of 400 ppm, the LCP of seedlings with ECM inoculations was 40–70 μmol photons m−2 s−1, significantly lower than that of non-mycorrhizal (NM) seedlings (200 μmol photons m−2 s−1). In addition, photosynthetic carbon fixation (Pn) increased with light intensity and CO2 level, and the Pn of ECM seedlings was significantly higher than that of NM seedlings; Pisolithus sp. (Pt)- and Laccaria amethystea (La)-mycorrhizal seedlings had significantly lower Pn than Cenococcum geophilum (Cg)-mycorrhizal seedlings. However, La-mycorrhizal seedlings exhibited the highest fresh weight, relative water content (RWC), and the lowest LCP in the mycorrhizal group. Concomitantly, ECM seedlings showed significantly increased chlorophyll content of needles and higher Pi concentrations compared to NM seedlings. Overall, ECM symbionts promoted growth and photosynthesis while reducing the LCP of P. thunbergii seedlings. These findings indicate that ECM fungi can enhance the survival and competitiveness of host seedlings under low light.

Bamboo forest is characterized by large carbon sequestration capability and it plays an important role in mitigating climate change and global carbon cycling. Previous studies have mostly focused on carbon cycling and carbon stocks in bamboo forest ecosystems, whereas the carbon footprints of bamboo products have not received attention. China is the largest exporting country of bamboo flooring in the world. Estimating the carbon footprint of bamboo flooring is of essential importance for the involved enterprises and consumers to evaluate their own carbon footprints. In this study, we investigated the production processes of bamboo scrimber flooring for outdoor use, a typical bamboo flooring in China. Based on business-to-business (B2B) evaluation method, we assessed CO2 emission and carbon transfer ratio in each step of the production process, including transporting bamboo culms and producing and packing the products. We found that to produce 1 m3 of bamboo scrimber flooring, direct carbon emissions from fossil fuels during transporting raw materials/semi-finished products, from power consumptions during production, and indirect emissions from applying additives were 30.94 kg CO2 eq, 143.37 kg CO2 eq, and 78.34 kg CO2 eq, respectively. After subtracting the 267.54 kg CO2 eq carbon stocks in the product from the 252.65 kg CO2 eq carbon emissions derived within the defined boundary, we found that the carbon footprint of 1 m3 bamboo scrimber flooring was &minus, 14.89 kg CO2 eq. Our results indicated that the bamboo scrimber flooring is a negative carbon-emission product. Finally, we discussed factors that influence the carbon footprint of the bamboo flooring and gave suggestions on carbon emission reduction during production processes. This study provided a scientific basis for estimating carbon stocks and carbon footprints of bamboo products and further expanded knowledge on carbon cycling and lifespan of carbon in the bamboo forest ecosystem.

Bio-fixation of carbon dioxide (CO2) by microalgae has been recognised as an attractive approach to offset anthropogenic emissions. Biological carbon mitigation is the process whereby autotrophic organisms, such as microalgae, convert CO2 into organic carbon and O2 through photosynthesis; this process through respiration produces biomass. In this study Dunaliella tertiolecta was cultivated in a semicontinuous culture to investigate the carbon mitigation rate of the system. The algae were produced in 1.2-L Roux bottles with a working volume of 1 L while semicontinuous production commenced on day 4 of cultivation when the carbon mitigation rate was found to be at a maximum for D. tertiolecta. The reduction in CO2 between input and output gases was monitored to predict carbon fixation rates while biomass production and microalgal carbon content are used to calculate the actual carbon mitigation potential of D. tertiolecta. A renewal rate of 45 % of flask volume was utilised to maintain the culture in exponential growth with an average daily productivity of 0.07 g L(-1) day(-1). The results showed that 0.74 g L(-1) of biomass could be achieved after 7 days of semicontinuous production while a total carbon mitigation of 0.37 g L(-1) was achieved. This represented an increase of 0.18 g L(-1) in carbon mitigation rate compared to batch production of D. tertiolecta over the same cultivation period.

Symbiotic nitrogen fixation (SNF) involves global changes in gene expression and metabolite accumulation in both rhizobia and the host plant. In order to study the metabolic changes mediated by leaf–root interaction, photosynthesis was limited in leaves by exposure of plants to darkness, and subsequently gene expression was profiled by real-time reverse transcription–PCR (RT–PCR) and metabolite levels by gas chromatography–mass spectrometry in the nodules of the model legume Lotus japonicus. Photosynthetic carbon deficiency caused by prolonged darkness affected many metabolic processes in L. japonicus nodules. Most of the metabolic genes analysed were down-regulated during the extended dark period. In addition to that, the levels of most metabolites decreased or remained unaltered, although accumulation of amino acids was observed. Reduced glycolysis and carbon fixation resulted in lower organic acid levels, especially of malate, the primary source of carbon for bacteroid metabolism and SNF. The high amino acid concentrations together with a reduction in total protein concentration indicate possible protein degradation in nodules under these conditions. Interestingly, comparisons between amino acid and protein content in various organs indicated systemic changes in response to prolonged darkness between nodulated and non-nodulated plants, rendering the nodule a source organ for both C and N under these conditions.

Parenchyma cells from tubers of Solanum tuberosum L. convert several externally supplied sugars to starch but the rates vary largely. Conversion of glucose 1-phosphate to starch is exceptionally efficient. In this communication, tuber slices were incubated with either of four solutions containing equimolar [U-C-14]glucose 1-phosphate, [U-C-14]sucrose, [U-C-14]glucose 1-phosphate plus unlabelled equimolar sucrose or [U-C-14]sucrose plus unlabelled equimolar glucose 1-phosphate. C-14-incorporation into starch was monitored. In slices from freshly harvested tubers each unlabelled compound strongly enhanced C-14 incorporation into starch indicating closely interacting paths of starch biosynthesis. However, enhancement disappeared when the tubers were stored. The two paths (and, consequently, the mutual enhancement effect) differ in temperature dependence. At lower temperatures, the glucose 1-phosphate-dependent path is functional, reaching maximal activity at approximately 20 degrees C but the flux of the sucrose-dependent route strongly increases above 20 degrees C. Results are confirmed by in vitro experiments using [U-C-14]glucose 1-phosphate or adenosine-[U-C-14]glucose and by quantitative zymograms of starch synthase or phosphorylase activity. In mutants almost completely lacking the plastidial phosphorylase isozyme(s), the glucose 1-phosphate-dependent path is largely impeded. Irrespective of the size of the granules, glucose 1-phosphate-dependent incorporation per granule surface area is essentially equal. Furthermore, within the granules no preference of distinct glucosyl acceptor sites was detectable. Thus, the path is integrated into the entire granule biosynthesis. In vitro C-14-incorporation into starch granules mediated by the recombinant plastidial phosphorylase isozyme clearly differed from the in situ results. Taken together, the data clearly demonstrate that two closely but flexibly interacting general paths of starch biosynthesis are functional in potato tuber cells.

The objective of the present study was to set up a small-scale pilot reactor at ONGC Hazira, Surat, for capturing CO2 from vent gas. The studies were carried out for CO2 capture by either using microalgae Chlorella sp. or a consortium of microalgae (Scenedesmus quadricauda, Chlorella vulgaris and Chlorococcum humicola). The biomass harvested was used for anaerobic digestion to produce biogas. The carbonation column was able to decrease the average 34 vol.% of CO2 in vent gas to 15 vol.% of CO2 in the outlet gas of the carbonation column. The yield of Chlorella sp. was found to be 18 g/m2/day. The methane yield was 386 l CH4/kg VSfed of Chlorella sp. whereas 228 l CH4/kg VSfed of the consortium of algae.

Natural polymers such as starch, protein, and algae are renewable and sustainable materials. They are used in many industrial applications such as polymeric blends for films, fibers, and injection molded articles. However, biodegradability of these materials in anaerobic sludge digestion is largely unreported. Extensive laboratory results were acquired to elucidate biodegradability and biodegradation kinetics of the selected materials according to ASTM D5210. There was no remarkable difference in biodegradability of wheat, native corn, and modified corn starches. For the protein samples, wheat gluten biodegraded to a great extent than soy protein isolate. For the algal samples, Spirulina biodegraded to a great extent than Nannochloropsis . A first order kinetic equation was used to fit all experimental data. A separate set of 14 C data examined if the carbon source, which is a building-block for all plant polymers, was bio-based (recent carbon) or fossil-based. The former is a part of global carbon cycle, and the latter is believed to cause adverse greenhouse gas effects resulting in global warming.

A snow addition experiment in moist acidic tussock tundra at Toolik Lake, Alaska, increased winter snow depths 2–3 m, and resulted in a doubling of the summer active layer depth. We used radiocarbon (∆14C) to (1) determine the age of C respired in the deep soils under control and deepened active layer conditions (deep snow drifts), and (2) to determine the impact of increased snow and permafrost thawing on surface CO2 efflux by partitioning respiration into autotrophic and heterotrophic components. ∆14C signatures of surface respiration were higher in the deep snow areas, reflecting a decrease in the proportion of autotrophic respiration. The radiocarbon age of soil pore CO2 sampled near the maximum mid-July thaw depth was approximately 1,000 years in deep snow treatment plots (45–55 cm thaw depth), while CO2 from the ambient snow areas was ~100 years old (30-cm thaw depth). Heterotrophic respiration ∆14C signatures from incubations were similar between the two snow depths for the organic horizon and were extremely variable in the mineral horizon, resulting in no significant differences between treatments in either month. Radiocarbon ages of heterotrophically respired C ranged from

This paper presents a discussion of the status of the field of coral geochemistry as it relates to the recovery of past records of ocean chemistry, ocean circulation, and climate. The first part is a brief review of coral biology, density banding, and other important factors involved in understanding corals as proxies of environmental variables. The second part is a synthesis of the information available to date on extracting records of the carbon cycle and climate change. It is clear from these proxy records that decade time-scale variability of mixing processes in the oceans is a dominant signal. That Western and Eastern tropical Pacific El Niño-Southern Oscillation (ENSO) records differ is an important piece of the puzzle for understanding regional and global climate change. Input of anthropogenic CO 2 to the oceans as observed by 13 C and 14 C isotopes in corals is partially obscured by natural variability. Nonetheless, the general trend over time toward lower δ 18 O values at numerous sites in the world’s tropical oceans suggests a gradual warming and/or freshening of the surface ocean over the past century.

Enhanced biological phosphorus removal (EBPR) is predicated on exposing bacteria to cyclical anaerobic/aerobic environments while providing volatile fatty acids (VFAs). Combined, this environment enriches for phosphorus accumulating organisms (PAOs) and induces metabolisms to ensure excess phosphorus removal. Crude glycerol (CG), a byproduct of biodiesel manufacturing, is an alternate waste stream that could be substituted to achieve excess phosphorus removal; research into the use of CG yielded unexpected findings. While CG was an excellent substrate to accomplish and/or help achieve excess phosphorus removal, CG-fed bacteria did not consistently exhibit theoretical EBPR metabolisms. Specifically, anaerobic phosphorus release was not required for successful EBPR; however, carbon cycling patterns were consistent with theory. Analysis of results suggests that PAOs will first leverage carbon to generate energy anaerobically; only as needed will the bacteria utilize polyphosphate reserves anaerobically. Results also demonstrated that excess phosphorus removal can be achieved with a small fraction of PAOs.

The extent of biological CO2 fixation was evaluated for outdoor cultures of the cyanobacterium Anabaena sp. ATCC 33047. Culture conditions were optimized indoors in bubble-column photochemostats operating in continuous mode, subjected to irradiance cycles mimicking the light regime outdoors. Highest values achieved for CO2 fixation rate and biomass productivity were 1 and 0.6gL-1day-1, respectively. The comparison among different reactors operating simultaneously - open pond, horizontal tubular reactor and vertical flat-panel - allowed to assess their relative efficiency for the outdoor development of Anabaena cultures. Despite the higher volumetric CO2 fixation capacity (and biomass productivity) exhibited by the tubular photobioreactor, yield of the flat-panel reactor was 50% higher than that of the tubular option on a per area basis, reaching values over 35g CO2 fixed m-2d-1. The flat-panel reactor actually represents a most suitable system for CO2 capture coupled to the generation of valuable biomass by Anabaena cultures

Summary In young and mature plants of the CAM species Agave angustifolia, the day/night pattern of CO2 exchange was highly conserved under a range of environmental conditions., Agaves exhibit the water-conserving crassulacean acid metabolism (CAM) photosynthetic pathway. Some species are potential biofuel feedstocks because they are highly productive in seasonally dry landscapes. In plants with CAM, high growth rates are often believed to be associated with a significant contribution of C3 photosynthesis to total carbon gain when conditions are favourable. There has even been a report of a shift from CAM to C3 in response to overwatering a species of Agave. We investigated whether C3 photosynthesis can contribute substantially to carbon uptake and growth in young and mature Agave angustifolia collected from its natural habitat in Panama. In well-watered plants, CO2 uptake in the dark contributed about 75% of daily carbon gain. This day/night pattern of CO2 exchange was highly conserved under a range of environmental conditions and was insensitive to intensive watering. Elevated CO2 (800 ppm) stimulated CO2 fixation predominantly in the light. Exposure to CO2-free air at night markedly enhanced CO2 uptake during the following light period, but CO2 exchange rapidly reverted to its standard pattern when CO2 was supplied during the subsequent 24h. Although A. angustifolia consistently engages in CAM as its principal photosynthetic pathway, its relatively limited photosynthetic plasticity does not preclude it from occupying a range of habitats, from relatively mesic tropical environments in Panama to drier habitats in Mexico.

Sugar-derived reactive carbonyls (RCs), including methylglyoxal (MG), are aggressive by-products of oxidative stress known to impair the functions of multiple proteins. These advanced glycation end-products accumulate in patients with diabetes mellitus and cause major complications, including arteriosclerosis and cardiac insufficiency. In the glycolytic pathway, the equilibration reactions between dihydroxyacetone phosphate and glyceraldehyde 3-phosphate (GAP) have recently been shown to generate MG as a by-product. Because plants produce vast amounts of sugars and support the same reaction in the Calvin cycle, we hypothesized that MG also accumulates in chloroplasts. Incubating isolated chloroplasts with excess 3-phosphoglycerate (3-PGA) as the GAP precursor drove the equilibration reaction toward MG production. The rate of oxygen (O2) evolution was used as an index of 3-PGA-mediated photosynthesis. The 3-PGA- and time-dependent accumulation of MG in chloroplasts was confirmed by HPLC. In addition, MG production increased with an increase in light intensity. We also observed a positive linear relationship between the rates of MG production and O2 evolution (R = 0.88; P < 0.0001). These data provide evidence that MG is produced by the Calvin cycle and that sugar-derived RC production is inevitable during photosynthesis. Furthermore, we found that MG production is enhanced under high-CO2 conditions in illuminated wheat leaves.

Pacing of the marine carbon cycle by orbital forcing during the Pliocene and Pleistocene Ice Ages [past 2.5 million years (Myr)] is well known. As older deep-sea sediment records are being studied at greater temporal resolution, it is becoming clear that similar fluctuations in the marine carbon system have occurred throughout the late Mesozoic and Tertiary, despite the absence of large continental ice sheets over much of this time. Variations in both the organic and the calcium carbonate components of the marine carbon system seem to have varied cyclically in response to climate forcing, and carbon and carbonate time series appear to accurately characterize the frequency spectrum of ancient climatic change. For the past 35 Myr, much of the variance in carbonate content carries the “polar” signal of obliquity [41,000 years (41 kyr)] forcing. Over the past 125 Myr, there is evidence from marine sediments of the continued role of precessional (≈21 kyr) climatic cycles. Repeat patterns of sedimentation at about 100, 400, and 2,400 kyr, the modulation periods of precession, persistently enter into marine carbon cycle records as well. These patterns suggest a nonlinear response of climate and/or the sedimentation of organic carbon and carbonates to precessional orbital perturbations. Nonlinear responses of the carbon system may help to amplify relatively weak orbital insolation anomalies into more significant climatic perturbations through positive feedback effects. Nonlinearities in the carbon cycle may have transformed orbital-climatic cycles into long-wavelength features on time scales comparable to the residence times of carbon and nutrient elements in the ocean.