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Directing CO2 conversion using photosynthetic microorganisms offers a promising route to couple CO2 sequestration with petrochemical replacement. However, the low-flux shikimate pathway remains largely unexploited for the synthesis of valuable aromatics. In addition, it is unclear how an enhanced low-flux pathway would influence the photosynthetic chain. We created a powerful metabolic sink by introducing the 2-phenylethanol pathway and an artificial feedback-inhibition-resistant cassette to Synechococcus elongatus. More than 30 % of the fixed carbon was redirected to the shikimate pathway for aromatic synthesis, and carbon fixation and O2 evolution increased significantly. A "self-remodeling" mechanism of the photosynthetic chain was discovered, which accelerates electron transport and reduces energy waste. This study represents a significant step toward the industrial viability of CO2 conversion into aromatic compounds and provides design guidance for improving photosynthetic efficiency.

In C3 plants, photorespiration is an energy-expensive process, including the oxygenation of ribulose-1,5-bisphosphate (RuBP) by ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco) and the ensuing multi-organellar photorespiratory pathway required to recycle the toxic byproducts and recapture a portion of the fixed carbon. Photorespiration significantly impacts crop productivity through reducing yields in C3 crops by as much as 50% under severe conditions. Thus, reducing the flux through, or improving the efficiency of photorespiration has the potential of large improvements in C3 crop productivity. Here, we review an array of approaches intended to engineer photorespiration in a range of plant systems with the goal of increasing crop productivity. Approaches include optimizing flux through the native photorespiratory pathway, installing non-native alternative photorespiratory pathways, and lowering or even eliminating Rubisco-catalyzed oxygenation of RuBP to reduce substrate entrance into the photorespiratory cycle. Some proposed designs have been successful at the proof of concept level. A plant systems-engineering approach, based on new opportunities available from synthetic biology to implement in silico designs, holds promise for further progress toward delivering more productive crops to farmer's fields.

This research article describes and analyses the use of seaweeds residue as pellets. Pellets are 12 mm in diameter and 15 mm in length and were obtained from eight marine seaweeds collected from Galician beaches. Different parameters, such as moisture content, heating power, volatile matter, ash content, and fixed carbon, were determined to analyze the suitability of using these pellets in boilers. From the results, it can be concluded that the obtained pellets are not suitable for using directly in boilers. Moreover, the results suggest that the seaweeds pellets have similar properties than straw pellets. The classification based on obtained results after testing seaweeds residue as pellets is D12, A10.0+, and BD700+. © 2015 American Institute of Chemical Engineers Environ Prog, 34: 1187–1190, 2015

This study examined root production and turnover in a California grassland during the third year of a long-term experiment with ambient (LO) and twice-ambient atmospheric CO2 (HI), using harvests, ingrowth cores, and minirhizotrons. Based on one-time harvest data, root biomass was 32% greater in the HI treatment, comparable to the stimulation of aboveground production during the study year. However, the 30–70% increase in photosynthesis under elevated CO2 for the dominant species in our system is considerably larger than the combined increase in above and belowground biomass. One possible explanation is, increased root turnover, which could be a sink for the additional fixed carbon. Cumulative root production in ingrowth cores from both treatments harvested at four dates was 2–3 times that in the single harvested cores, suggesting substantial root turnover within the growing season. Minirhizotron data confirmed this result, demonstrating that production and mortality occurred simultaneously through much of the season. As a result, cumulative root production was 54%, 47% and 44% greater than peak standing root length for the no chamber (X), LO, and HI plots, respectively. Elevated CO2, however, had little effect on rates of turnover (i.e. rates of turnover were equal in the LO and HI plots throughout most of the year) and cumulative root production was unaffected by treatment. Elevated CO2 increased monthly production of new root length (59%) only at the end of the season (April–June) when root growth had largely ceased in the LO plots but continued in the HI plots. This end-of-season increase in production coincided with an 18% greater soil moisture content in the HI plots previously described. Total standing root length was not affected by CO2 treatment. Root mortality was unaffected by elevated CO2 in all months except April, in which plants grown in the HI plots had higher mortality rates. Together, these results demonstrate that root turnover is considerable in the grassland community and easily missed by destructive soil coring. However, increased fine root turnover under elevated CO2 is apparently not a major sink for extra photosynthate in this system.

The amount of carbon released into soil through root exudation byDigitaria adscendens Herrm. andAmbrosia artemisiifolia L. var.elatior Desc., which often predominate at the early stages of secondary succession, was evaluated in a laboratory experiment conducted over a 60-day period. Differences in the amount of exuded carbon between these species and between the developmental stages were examined. The amount of carbon exuded increased with growth in both species. The percentage of exuded carbon to photosynthetically net fixed carbon, which was higher at younger stages (13%) inD. adscendens, decreased to 3.1% with time. On the other hand, no reduction in the amount of carbon exuded was observed inA. artemisiifolia (4.7–8.1% range). The total amount of carbon released through root exudation inD. adscendens andA. artemisiifolia was estimated at 3.1% and 6.9% of photosynthetically net fixed carbon, respectively. These results suggest the possibility that wild plants exude a considerable amount of carbon from their roots to the soil, and emphasizes the necessity for considering root exudation in the carbon cycle.

SUMMARY The allocation of carbon in two montane grasses was followed using 14C labelling and gas exchange measurements. Both grasses showed similar total non-structural carbohydrate contents and net allocation of carbon. A six-compartmental model (with root and shoot each composed of soluble, storage and structural material) was used to summarize the data, to provide estimates of carbohydrate turnover rates, and to produce complete carbon budgets. Storage carbohydrate was heavily labelled and turned over rapidly, with half-times of 25 h in Festuca ovina and 15 h in Nardus stricta. This does not support the idea that storage carbohydrates are deposited only to be mobilized in response to environmental perturbations. It is suggested that the small relative growth rates in these species are not the result of inefficient use of fixed carbon, but of slow rates of photosynthesis; the respiratory costs of growth are similar to those for barley. The large flux of carbon through storage carbohydrate is suggested to ensure a readily available supply of sugars for metabolism, independent of environmental conditions.

The net photosynthetic rates of nine genotypes of the cultivated peanut (Arachis hypogaea L.) grown under controlled conditions were measured at six different light intensities: 180, 255, 526, 784, 1098, and 1546 µE m−2 sec−1 (E = einsteins). All genotypes evidenced an endogenous, circadian rhythm in photosynthetic rate. No genotype photosaturated at the highest intensity used, which was slightly less than full sunlight. Genotypes differed significantly in photosynthetic rate at similar light intensities; net photosynthetic rates of several of the genotypes exceeded 50 mg dm−2 hr−1. Soybean (Glycine max (L.) Merr., cv. ‘Bragg’) and tomato (Lycopersicum esculentum L., cv. ‘Marion’), grown similarly to peanut in growth chambers, showed considerably lower photosynthetic potential and photosaturated at much lower light levels (~250 to 500 µE m−2 sec−1). The peanut's photosynthetic response can help explain its adaptation to the dissimiliar light conditions in humid, semihumid, and arid regions. Its high rate of photosynthesis at any light level indicates that it is one of the more efficient species in converting solar energy to fixed carbon. Lowering ambient oxygen concentration to 1.5% increased net photosynthetic rate 35%. No correlation between specific leaf weight and net photosynthesis of the peanut was found.

Coal is successfully gasified in the presence of a pilot flame in a modified fluidized bed. Except for the pilot flame, no external heat is required to operate this gasifier. The results showed that increasing the solid-to-air ratio in the feed increased the temperature and the products, carbon monoxide and hydrogen. About 95% of the volatile materials and 80% of the fixed carbon of the feed coal could be gasified by this pilot-flame gasification method. The ash could be efficiently separated during gasification by a distributor within the dead-zone collector of this gasifier. On a reussi a gazeifier du charbon en presence d'une flamme pilote dans un lit fluidise modifie. A l'exception de la flamme pilote, aucune chaleur externe n'est necessaire pour faire fonctionner ce gazogene. L'experience montre que le fait d'augmenter le rapport solide-air dans l'alimentation accroit la temperature ainsi que l'oxyde de carbone et l'hydrogene produits. Environ 95% des materiaux volatiles et 80% du carbone fixe presents dans le carbone d'alimentation peuvent ětre gazeifies par cette methode. La cendre peut ětre efficacement separee lors de la gazeification par un distributeur situe a l'interieur de la zone morte du collecteur de ce gazogene.

In productivity studies of Cladophora by the light—and—dark—bottle method, errors may arise from CaCo3 precipitation, self—shading, pH/Co2 limitation, or variations in the condidtion of the alga. Precipitation of CaCo3 and MgCo3 by Cladophora may equal one—third of production at pH 9.3 to 10.4, resulting in overestimation of photosynthesis by either the 14C or pH method. The calcification is readily removed by acid rinse without loss of fixed carbon. Consideration of such errors in relation to a recent study leads to the refutation of the conclusion the Cladophora shows an unusual ability to utilize low light intensities. See full-text article at JSTOR

SUMMARY Wheat and bailey plants were grown for 3 weeks in a constant environment chamber containing approximately atmospheric concentrations of carbon dioxide (0.03%) labelled with 14C. The roots of the plants were maintained under sterile or non-sterile conditions in soil contained in sealed pots which were regularly flushed with air. This enabled the quantities of 14C-labelled carbon dioxide produced in the soil by plant and microbial activity to be separately assessed. At harvest, the 14C and total carbon contents of the roots and shoots and of the water-soluble and insoluble material present in the soil were measured. These procedures enabled both the amounts of organic materials released into soil by the roots of growing plants and the effects of micro-organisms on the process to be determined. Under sterile conditions between 5 and 10% of the photosynthetically fixed carbon may be released by roots compared with 12–18% by the roots of plants growing in unsterilized soil. These latter values are equivalent to 18–25% of the dry matter increments of the plants. The results indicate also that the increased evolution of carbon dioxide by cropped as compared to fallow soils can largely be ascribed to the immediate utilization by micro-organisms of substances released by roots.

Some of the sources of error in measuring the excretion rate of phytoplankton are discussed. Among those factors are: damage to cells during handling, contaminant C/sub 14/, errors resulting from aliquoting, variable storage times, and incubation time. These sources of error are discussed in regard to a previous paper which had argued that the release of fixed carbon was substantial. The conclusion reached is that indeed, the release (excretion) of organic material by phytoplankton is of substantial magnitude. 10 references.