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Biocrusts are common living covers found across drylands worldwide, and their photosynthesis substantially contributes to carbon input in these ecosystems. However, direct monitoring of biocrusts’ photosynthetic carbon fixation is challenging due to their scattered distribution, dark pigments, and lower CO2 exchange rate. Current studies have limited monitoring frequency and the results are difficult to extend to a broader spatial scale. Greenness typically functions as an indicator of both vegetation cover and plant photosynthesis. Monitoring biocrust greenness is expected to be able to provide insights into their environmental responses and estimate carbon fixation rates, particularly for moss biocrusts. Here, we monitored greenness, soil moisture and temperature, and gross primary productivity (GPP) of moss biocrusts, as well as climatic factors over two years in the northern China’s Loess Plateau. The results indicated that moss biocrust greenness was highly sensitive to changing environmental conditions and exhibited significant temporal variability. Moss biocrust greenness exhibited a notably higher value in wet season (0.384) than in dry season (0.259). According to these greenness values, we proposed moss biocrust activity and classified it into high (>0.403), medium (0.334–0.403), low (0.271–0.333), and dormancy (

• Current research progress and application of microalgae carbon sequestration are reviewed. • Mechanism of CO 2 sequestration and industrial flue gas pollutants emission reduction by microalgae are summarized. • Prospects and challenges for industrial applications of microalgae CO 2 sequestration are discussed. Global warming caused by the emission of CO 2 in industrial flue gas has attracted more and more attention. Therefore, to fix CO 2 with high efficiency and environmentally friendly had become the hot research field. Compared with the traditional coal-fired power plant flue gas emission reduction technology, carbon fixation and emission reduction by microalgae is considered as a promising technology due to the advantages of simple process equipment, convenient operation and environmental protection. When the flue gas is treated by microalgae carbon fixation and emission reduction technology, microalgae cells can fix CO 2 in the flue gas through photosynthesis, and simultaneously absorb NO x and SO x as nitrogen and sulfur sources required for growth. Meanwhile, they can also absorb mercury, selenium, arsenic, cadmium, lead and other heavy metal ions in the flue gas to obtain microalgae biomass. The obtained microalgae biomass can be further transformed into high value-added products, which has broad development prospects. This paper reviews the mechanisms and pathways of CO 2 sequestration, the mechanism and impacts of microalgal emission reduction of flue gas pollutants, and the applications of carbon sequestration in industrial flue gas by microalgae. Finally, this paper provides some guidelines and prospects for the research and application of green emission reduction technology for industrial flue gas. [ABSTRACT FROM AUTHOR]

Hydrogen sulfide (H2S) performs a crucial role in plant development and abiotic stress responses by interacting with other signalling molecules. However, the synergistic involvement of H2S and rhizobia in photosynthetic carbon (C) metabolism in soybean (Glycine max) under nitrogen (N) deficiency has been largely overlooked. Therefore, we scrutinised how H2S drives photosynthetic C fixation, utilisation, and accumulation in soybean‐rhizobia symbiotic systems. When soybeans encountered N deficiency, organ growth, grain output, and nodule N‐fixation performance were considerably improved owing to H2S and rhizobia. Furthermore, H2S collaborated with rhizobia to actively govern assimilation product generation and transport, modulating C allocation, utilisation, and accumulation. Additionally, H2S and rhizobia profoundly affected critical enzyme activities and coding gene expressions implicated in C fixation, transport, and metabolism. Furthermore, we observed substantial effects of H2S and rhizobia on primary metabolism and C–N coupled metabolic networks in essential organs via C metabolic regulation. Consequently, H2S synergy with rhizobia inspired complex primary metabolism and C–N coupled metabolic pathways by directing the expression of key enzymes and related coding genes involved in C metabolism, stimulating effective C fixation, transport, and distribution, and ultimately improving N fixation, growth, and grain yield in soybeans. Summary Statement: Can H2S effectively modulate photosynthetic C fixation and metabolism in symbiotic soybean‐rhizobia systems? Sufficient and robust data confirmed that H2S synergy with rhizobia promoted the expression of multiple critical enzymes and related coding genes involved in C metabolism to affect crucial primary metabolism and C‐N linked metabolic networks, ensuring efficient C fixation, transport, and allocation and ultimately improving N fixation, growth, and output in N‐deficient soybeans. [ABSTRACT FROM AUTHOR]

Synechococcus is one of the most abundant prokaryotic photosynthetic organisms on Earth and plays a key role in oceanic carbon fixation and transformation. To improve the photosynthetic efficiency of synechococcus, a post-transcriptional regulatory mechanism - Selective RNA Processing and Stabilization (SRPS) was considered. We inactivated the SRPS-enzymes, executor of the SRPS mechanism, to explore their regulation rule of photosynthetic carbon fixation efficiency in Synechococcus. The results showed that the inactivation of SRPS-enzymes mainly affected the growth rate or growth phase. It significantly alters the photosynthetic oxygen evolution rate, pigment content, chlorophyll fluorescence, carbon and nitrogen content, as well as the composition and biological activity of the dissolved organic matter derived from Synechococcus (SOM). Inactivating SRPS-enzymes results in an increase in the expression level of most subunits of the Cytochrome b6-f complex, while the expression levels of most subunits of PSI, PSII, RuBisCO, and NDH decrease. All SRPS-enzymes are involved in the expression regulation of basilic protein complexes in photosynthesis, such as PSI, PSII, Cytochrome b6-f complex, ATP synthase, and RuBisCO. Our results indicate that the inactivation of SRPS-enzymes have a significant influence on carbon sequestration by photosynthesis of Synechococcus sp. PCC7002.

Sargassum golden tides (GT) are common in numerous coastal areas all over the world, and it adversely affects local marine life. Eutrophication is critical for Sargassum GT development. However, its physiological and ecological mechanism remains unclear. To investigate the responses of drifting Sargassum horneri, the species causing GT in the western Pacific, to light and enriched nitrogen, we set three light conditions (Low-light (LL), 10 μmol photons m−2 s−1; Middle-light (ML), 60 μmol photons m−2 s−1; and High-light (HL), 300 μmol photons m−2 s−1) and three nitrogen conditions (Natural seawater, the final concentration of N was 31.8 μmol L−1, including 30.5 μmol L−1 of NO3− and 1.3 μmol L−1 of NH4+; Enrichment of NO3−, final concentration of N was 200 μmol L−1; and Enrichment of NH4+, the final concentration of N was 200 μmol L−1), and grew the thalli under varying conditions for 10 days before determining the growth and utilization of carbon and nitrogen. Based on the accumulated data, the elevated light level led to a higher growth rate of alga. In the LL culture, the higher capacity for carbon utilization, which was reflected by the higher maximum photosynthetic carbon fixation rate (Vmax), resulted in the elevated growth rates of thalli in the nitrogen-enriched media as compared with the natural seawater. Furthermore, a higher growth rate was found in the enrichment of NH4+ despite a low affinity for inorganic carbon indicated by a higher value of the half-saturation constant (K0.5). In the ML treatment, an insignificant difference in growth rate was found in three nitrogen cultures, except for a slight increase in the enrichment of NH4+ than the enrichment of NO3−. In the HL treatment, compared with natural seawater culture, enrichment of NO3− or NH4+ accelerated the growth of alga, with no significant difference between the two nitrogen sources. Such enhancement in growth was related to the more photosynthetic carbon fixation, indicated by the higher value of Vmax and soluble carbohydrates content of alga cultured with NO3− and NH4+ enrichments. Additionally, the uptake and assimilation products of nitrogen, such as pigments and soluble proteins, remained unaffected by nitrogen source enrichment of NO3− or NH4+ at all three light levels. In conclusion, enrichment of NO3− and NH4+ exhibited different influences on the growth of S. horneri at different light levels, which was mainly associated with the capacity and efficiency of photosynthetic carbon utilization. At the HL level, both the enrichment of NO3− and NH4+ dramatically accelerate the growth of alga by stimulating the photosynthetic carbon fixation. Accordingly, we speculated that drifting S. horneri, exposed to HL level on the surface of the sea, were likely to develop rapidly to form GT in eutrophic oceanic areas with upwelled and river plume NO3− or NH4+ nutrients. [ABSTRACT FROM AUTHOR]

Sargassum golden tides (GT) are common in numerous coastal areas all over the world, and it adversely affects local marine life. Eutrophication is critical for Sargassum GT development. However, its physiological and ecological mechanism remains unclear. To investigate the responses of drifting Sargassum horneri, the species causing GT in the western Pacific, to light and enriched nitrogen, we set three light conditions (Low-light (LL), 10 μmol photons m−2 s−1; Middle-light (ML), 60 μmol photons m−2 s−1; and High-light (HL), 300 μmol photons m−2 s−1) and three nitrogen conditions (Natural seawater, the final concentration of N was 31.8 μmol L−1, including 30.5 μmol L−1 of NO3− and 1.3 μmol L−1 of NH4+; Enrichment of NO3−, final concentration of N was 200 μmol L−1; and Enrichment of NH4+, the final concentration of N was 200 μmol L−1), and grew the thalli under varying conditions for 10 days before determining the growth and utilization of carbon and nitrogen. Based on the accumulated data, the elevated light level led to a higher growth rate of alga. In the LL culture, the higher capacity for carbon utilization, which was reflected by the higher maximum photosynthetic carbon fixation rate (Vmax), resulted in the elevated growth rates of thalli in the nitrogen-enriched media as compared with the natural seawater. Furthermore, a higher growth rate was found in the enrichment of NH4+ despite a low affinity for inorganic carbon indicated by a higher value of the half-saturation constant (K0.5). In the ML treatment, an insignificant difference in growth rate was found in three nitrogen cultures, except for a slight increase in the enrichment of NH4+ than the enrichment of NO3−. In the HL treatment, compared with natural seawater culture, enrichment of NO3− or NH4+ accelerated the growth of alga, with no significant difference between the two nitrogen sources. Such enhancement in growth was related to the more photosynthetic carbon fixation, indicated by the higher value of Vmax and soluble carbohydrates content of alga cultured with NO3− and NH4+ enrichments. Additionally, the uptake and assimilation products of nitrogen, such as pigments and soluble proteins, remained unaffected by nitrogen source enrichment of NO3− or NH4+ at all three light levels. In conclusion, enrichment of NO3− and NH4+ exhibited different influences on the growth of S. horneri at different light levels, which was mainly associated with the capacity and efficiency of photosynthetic carbon utilization. At the HL level, both the enrichment of NO3− and NH4+ dramatically accelerate the growth of alga by stimulating the photosynthetic carbon fixation. Accordingly, we speculated that drifting S. horneri, exposed to HL level on the surface of the sea, were likely to develop rapidly to form GT in eutrophic oceanic areas with upwelled and river plume NO3− or NH4+ nutrients.

Rice (Oryza sativa L.) as the staple food is widely grown, but the current high tropospheric ozone (O 3) pollution has seriously threatened the rice production. We performed an experiment on four rice cultivars widely grown in the Yangtze River Delta region of China, which were exposed to five O 3 treatments under open top chambers. The effects of O 3 on leaf physiology, growth, yield and grain quality of rice were comprehensively explored, and the results showed that (i) elevated O 3 reduced the light-saturated rate of CO 2 assimilation (A sat) and stomatal conductance (g s), and the O 3 -induced decrease in A sat was mainly attributed to stomatal limitation under low O 3 treatment whereas stomatal and biochemical co-limitation under high O 3 treatment; (ii) elevated O 3 did not affected the harvest index since the inhibition of shoot biomass and yield was the same extent, which indicated that O 3 does not alter the remobilization of carbon assimilates from vegetative organs to grains; (iii) only ambient air plus 60 ppb O 3 treatment (NF60) significantly reduced the yield of rice, which was caused by the combined reduction of individual grain weight, grain number, and panicle number; (iv) elevated O 3 did not significantly affect the concentration of mineral nutrients in grains, while the effect of O 3 on the concentration of amino acids was consistent with biphasic O 3 -response profile. NF60 had a greater reduction in the concentration of essential amino acids than non-essential amino acids; (v) NF60 significantly reduced the accumulation of mineral nutrients and amino acid in grain due to a decrease in grain yield. These results are conducive to a comprehensive understanding of the impacts of O 3 on rice, and also indicated that the risk assessment of O 3 on crops would need to consider both crop yield and grain quality. • Four rice cultivars were exposed to five O 3 levels in 15 open-top chambers. • The inhibition of low O 3 treatment on rice A sat is attributed to a decrease in g s. • Only NF60 reduced rice yield and the accumulation of grain nutrients and amino acids. • O 3 did not alter the harvest index of four rice cultivars. • NF60 reduced concentration of essential amino acids more than non-essential ones. [ABSTRACT FROM AUTHOR]

Environmental pollutants interfere with plant photosynthesis, thus reduce the crop yield and carbon storage capacity of farmland. This study comparatively explored the effects and mechanisms of polycyclic aromatic hydrocarbons (PAHs, e.g., phenanthrene, pyrene, and benzo[a]pyrene) and cadmium (Cd) on the carbon fixation capacity of rice throughout the growth period. Cd posed severer inhibition on the net carbon fixation of rice than PAHs, with the inhibition rates of 1.40–14.8-fold over PAHs at the concentrations of 0.5 or 5 mg/kg soil. Ribulose diphosphate carboxylase/oxygenase (Rubisco) involved in the Calvin cycle was identified as the common target of these pollutants to inhibit the photosynthetic carbon fixation. Further investigation demonstrated that the different inhibitory effects of Cd and PAHs was resulted from their different interference on the dual catalysis function (carboxylation and oxygenation) of Rubisco. Cd disturbed the balance of the intercellular CO 2 /O 2 , thus promoting the oxygenation and inhibiting the carboxylation of the substrate of Rubisco. Under the stress of Cd, the downstream metabolites (e.g. glycolate, glyoxylate, and serine) of Rubisco oxygenation were upregulated by over 2.01–3.24-fold, whereas the carboxylation efficiency (V cmax) was decreased by 5.58–29.3%. Comparatively, PAHs inhibited both the carboxylation and oxygenation by down-regulating the expression of Rubisco coding gene (OsRBCS2 , Log 2 FC < −2). This study broadens the understanding of the mechanisms of different environmental pollutants on the carbon fixation, providing valuable information for the quantitative estimation of their impacts on the farmland carbon sink. The results would be constructive to develop strategies for eliminating the adverse effects of contaminants and assist the carbon-neutral programs. [Display omitted] • Cd posed severer effects on carbon fixation of rice than PHEN, PY, and BaP. • Rubisco was a common target of PAHs and Cd. • Cd unbalanced the dual catalytic activities of Rubisco by stomatal closure. • PAHs downregulated the expression of Rubisco-coding gene (OsRBCS2) directly. [ABSTRACT FROM AUTHOR]

Impacts of ocean acidification (OA) on noncalcifying organisms and the possibly responsible mechanism have aroused great research interests with the intensification of global warming. The present study focused on a noxious, noncalcifying, bloom-forming dinoflagellate, Karenia mikimotoi (K. mikimotoi), and its variation of growth patterns exposed to different periods of seawater acidification with stressing gradients was discussed. The dinoflagellates under short-time acidifying stress (2d) with different levels of CO2 presented significant growth inhibition (p < 0.05). The cell cycle was obviously inhibited at S phase, and the photosynthetic carbon fixation was also greatly suppressed (p < 0.05). Apoptosis was observed and the apoptotic rate increased with the increment of pCO2. Similar tendencies were observed in the key components of mitochondrial apoptotic pathway (the mitochondrial membrane potential (MMP), Caspase-3 and -9, and Bax/Bcl-2 ratio). However, under prolonged stressing time (8 d and 15 d), the growth of dinoflagellates was recovered or even stimulated, the photosynthetic carbon fixation was significantly increased (p < 0.05), the cell cycle of division presented little difference with those in the control, and no apoptosis was observed (p > 0.05). Besides, acidification adjusted by HCl addition and CO2 enrichment resulted in different growth performances, while the latter had a more negative impact. The results of present study indicated that (1) the short-time exposure to acidified seawater led to reduced growth performance via inducing apoptosis, blocking of cell cycle, and the alteration in photosynthetic carbon fixation. (2) K. mikimotoi had undergone adaptive changes under long-term exposure to CO2 induced seawater acidification. This further demonstrated that K. mikimotoi has strong adaptability in the face of seawater acidification, and this may be one of the reasons for the frequent outbreak of red tide. (3) Ions that dissociated by the dissolved CO2, instead of H+ itself, were more important for the impacts induced by the acidification. This work thus provides a new perspective and a possible explanation for the dominance of K. mikimotoi during the occurrence of HABs.

Sedoheptulose-1,7-bisphosphatase (SBPase) is a critical enzyme involved in photosynthetic carbon fixation in the Calvin cycle. Here, we report the effects of SBPase overexpression on the tolerance to chilling-induced oxidative stress in transgenic tomato ( Solanum lycopersicum ) plants. In transgenic plants overexpressing SBPase, CO 2 fixation and carbohydrate accumulation were increased in comparison with equivalent wild-type plants. SBPase was found to be susceptible to oxidative stress and the activity was substantially inhibited by reactive oxygen species both in vivo and in vitro . In response to chilling stress, production of H 2 O 2 was increased in parallel with the reduction in SBPase activity in tomato plants, however, transgenic plants maintained significantly higher SBPase activity than wild-type plants did. Under chilling stress, compared with wild-type plants, transgenic plants were found to have increased CO 2 fixation and reduced electrolyte leakage. The overall tolerance could be ascribed to the enhancement of photosynthetic carbon fixation, the reductions in the level of H 2 O 2 and the increased accumulation of carbohydrate in transgenic plants. Collectively, our data suggest that high level of SBPase activity gives an advantage to photosynthetic carbon fixation and tolerance to chilling-induced oxidative stress in tomato plants. This work presents a case study that an individual enzyme in the Calvin cycle may be a useful target for genetically engineering stress tolerance in horticultural crops. [ABSTRACT FROM AUTHOR]

Background: Microalgae, which can absorb carbon dioxide and then transform it into lipid, are promising candidates to produce renewable energy, especially biodiesel. The paucity of genomic information, however, limits the development of genome-based genetic modification to improve lipid production in many microalgae. Here, we describe the de novo sequencing, transcriptome assembly, annotation and differential expression analysis for Chlorella sorokiniana cultivated in different conditions to reveal the change of genes expression associated with lipid accumulation and photosynthetic carbon fixation. Results: Six cultivation conditions were selected to cultivate C. sorokiniana. Lipid content of C. sorokiniana under nitrogen-limited condition was 2.96 times than that under nitrogen-replete condition. When cultivated in light with nitrogen-limited supply, C. sorokiniana can use carbon dioxide to accumulate lipid. Then, transcriptome of C. sorokiniana was sequenced using Illumina paired-end sequencing technology, and 244,291,069 raw reads with length of 100 bp were produced. After preprocessed, these reads were de novo assembled into 63,811 contigs among which 23,528 contigs were found homologous sequences in public databases through Blastx. Gene expression abundance under six conditions were quantified by calculating FPKM value. Ultimately, we found 385 genes at least 2-fold up-regulated while 71 genes at least 2-fold down-regulated in nitrogen-limited condition. Also, 204 genes were at least 2-fold up-regulated in light while 638 genes at least 2-fold down-regulated. Finally, 16 genes were selected to conduct RT-qPCR and 15 genes showed the similar results as those identified by transcriptomic analysis in term of differential expression. Conclusions: De novo transcriptomic analyses have generated enormous information over C. sorokiniana, revealing a broad overview of genomic information related to lipid accumulation and photosynthetic carbon fixation. The genes with expression change under different conditions are highly likely the potential targets for genetic modification to improve lipid production and CO2 fixation efficiency in oleaginous microalgae. [ABSTRACT FROM AUTHOR]

The hypothesis that nitrogen and phosphorus can have a positive effect on the bloom formation of Ulva prolifera along the southern coast of the Yellow Sea was examined. The nutrient enrichment on the growth and photosynthetic carbon assimilation of U. prolifera were investigated in laboratory. Four nitrogen and phosphorus treatments were established: high nitrogen and high phosphorus (HNHP), high nitrogen and low phosphorus, low nitrogen and high phosphorus, and low nitrogen and low phosphorus (LNLP). Fresh weights, relative growth rate (RGR), chlorophyll fluorescence parameters, photosynthetic rate, and the uptake of dissolved inorganic carbon (DIC) in U. prolifera were measured. The results showed that nitrogen and phosphorus enrichment significantly increased RGR of U. prolifera. The chlorophyll fluorescence parameters all reached maximum values under the HNHP treatment. The photosynthetic rate under the HNHP treatment also was the highest, which was 1.52 times that of the LNLP treatment. The DIC uptake under the HNHP treatment was 1.63 times greater than under the LNLP treatment. The photosynthesis and carbon fixation were significantly promoted by N and P enrichment. This work may further clarify the mechanisms of U. prolifera bloom formation and decline in the Yellow Sea. [ABSTRACT FROM AUTHOR]

• TCONS_00093333、 TaBBX25 and TaOBFl , which are associated with pollen development and male fertility, are up-regulated in the expression of fertile anthers of KTM3315A. • TCONS_00093333、 TaBBX25 and TaOBFl were silenced by BMSV mediated VIGS technique, and the final results showed that they showed impaired fertility and affected the male fertility of KTM3315A. • TCONS_00093333 regulates the expression of key genes in photosynthetic carbon fixation pathways with B-box zinc protein 25 and OCS element-binding factor 1, and participates in the fertility conversion in thermo-sensitive cytoplasmic male-sterility wheat. An increasing number of studies have shown that long non-coding RNAs (lncRNAs) play an important role in regulating plant fertility, however, they are less studied in wheat. Here, we analyzed lncRNA sequencing data and showed that the fixation carbon sequestration pathway was closely associated with pollen development and fertility conversion in KTM3315A, and eight differentially expressed genes under different fertility conditions were significantly regulated by TCONS_00093333 (designed as TaHTMAR) and transcription factors TaBBX25 and TaOBF1. Among them, TaBBX25 and TaOBF1 were located in the nucleus and expressed in the early stage of fertile anther development. Gene silencing experiments of TaHTMAR showed that TaHTMAR positively regulated the expression of TaBBX25 and TaOBF1 under fertile conditions, thereby reducing male fertility of KTM3315A. This study confirms the effective roles of TaHTMAR, TaBBX25 , and TaOBF1 in the regulation of male fertility in wheat and provides a valuable molecular basis for hybrid wheat breeding. [ABSTRACT FROM AUTHOR]

The Strait of Malacca (SoM), the world's busiest sea-route, is increasingly polluted as the rapid development of world trades, affecting phytoplankton primary productivity therein. The variations of surface phytoplankton biomass, size-structure and carbon fixation were investigated across the SoM during the spring period (May 4 to 9, 2011). Chlorophyll a concentration increased from 0.12 µg/L at the northwest entrance of the SoM to a maximal 0.63 µg/L at narrowest section, and decreased to 0.10 µg/L at the southeast entrance. Photosynthetic carbon fixation by phytoplankton coincided well with Chl a biomass, and increased from 10.8 to 22.3 µg C/(L·d), then decreased to 9.21 µg C/(L·d); while the carbon fixation rate showed an inverse pattern to the changes of Chl a, and decreased from 87.1 to 35.5 µgC/(µgChla·d) and increased thereafter to 95.3 µg C/(µg Chl a·d). Picophytoplankton cells (<3 µm) contributed to more than 60% and 50% of the total Chl a and carbon fixation at both the entry waters; while the contributions of pico-cells decreased sharply to the minimum of 18.3% and 27.5% at the narrowest part of the SoM. In particular, our results showed that the silicate concentration positively regulated Chl a biomass and carbon fixation, reflecting that the higher silicate favoured the growth of phytoplankton and thus led to higher primary production in this strait. [ABSTRACT FROM AUTHOR]

Abstract: Phytoplankton cells in estuary waters usually experience drastic changes in chemical and physical environments due to mixing of fresh and seawaters. In order to see their photosynthetic performance in such dynamic waters, we measured the photosynthetic carbon fixation by natural phytoplankton assemblages in the Jiulong River estuary of the South China Sea during April 24–26 and July 24–26 of 2008, and investigated its relationship with environmental changes in the presence or the absence of UV radiation. Phytoplankton biomass (Chl a) decreased sharply from the river-mouth to seawards (17.3–2.1μgL−1), with the dominant species changed from chlorophytes to diatoms. The photosynthetic rate based on Chl a at noon time under PAR-alone increased from 1.9μgC (μg Chl a)−1 L−1 in low salinity zone (SSS<10) to 12.4μgC (μg Chl a)−1 L−1 in turbidity front (SSS within 10–20), and then decreased to 2.1μgC (μg Chl a)−1 L−1 in mixohaline zone (SSS>20); accordingly, the carbon fixation per volume of seawater increased from 12.8 to 149μgCL−1 h−1, and decreased to 14.3μgCL−1 h−1. Solar UVR caused the inhibition of carbon fixation in surface water of all the investigated zones, by 39% in turbidity area and 7–10% in freshwater or mixohaline zones. In the turbidity zone, higher availability of CO2 could have enhanced the photosynthetic performance; while osmotic stress might be responsible for the higher sensitivity of phytoplankton assemblages to solar UV radiation. [Copyright &y& Elsevier]

Photosynthetic performance of the terrestrial cyanobacterium Nostoc flagelliforme (M. J. Berkeley et M. A. Curtis) Bornet et Flahault during rehydration and desiccation has been previously characterized, but little is known about the effects of solar UV radiation (280–400 nm) on this species. We investigated the photochemical activity during rehydration and subsequent desiccation while exposing the filamentous colonies to different solar radiation treatments. Photochemical activity could be reactivated by rehydration under full-spectrum solar radiation, the species being insensitive to both ultraviolet-A radiation (UVAR; 315–400 nm) and ultraviolet-B radiation (UVBR). When the rehydrated colonies were exposed for desiccation, the effective PSII photochemical yield was inhibited by visible radiation (PAR) at the initial stage of water loss, then increased with further decrease in water content, and reached its highest value at the water content of 10%–30%. However, no significant difference was observed among the radiation treatments except for the moment when they were desiccated to critical water content of about 2%–3%. At such a critical water content, significant reduction by UVBR of the effective quantum yield was observed in the colonies that were previously rehydrated under indoor light [without ultraviolet radiation (UVR)], but not in those reactivated under scattered or direct solar radiation (with UVR), indicating that preexposure to UVR during rehydration led to higher resistance to UVR during desiccation. The photosynthetic CO2 uptake by the desiccated colonies was enhanced by elevation of CO2 but was not affected by both UVAR and UVBR. It increased with enhanced desiccation to reach the maximal values at water content of 40%–50%. The UV-absorbing compounds and the colony sheath were suggested to play an important role in screening harmful UVR. [ABSTRACT FROM AUTHOR]

Summary The guard cell chloroplast is the site of perception of blue light and of photosynthetically active radiation, and of at least one of the mechanisms sensing CO2 in the guard cell. The guard cell chloroplast has been the focus of intense controversy over its capacity for light sensing and photosynthetic carbon fixation, and the osmoregulatory mechanisms mediating stomatal movements. It is argued here that a primary reason behind these long-lived controversies is the remarkable plasticity of the guard cell, which has resulted in responses being generalized as basic properties when opposite responses appear to be the norm under different environmental or experimental conditions. Examples of guard cell plasticity are described, including variation of chlorophyll fluorescence transients over a daily course, acclimation of the guard cell responses to blue light and CO2 , the shift from potassium to sucrose in daily courses of osmoregulation and the transduction of red light into different osmoregulatory pathways. Recent findings on the properties of the guard cell chloroplast are also presented, including the role of the chloroplastic carotenoid, zeaxanthin, in blue light photoreception, the blue-green reversibility of stomatal movements, and the involvement of phytochrome in the stomatal response to light in the orchid, Paphiopedilum . [ABSTRACT FROM AUTHOR]

Impacts of ocean acidification (OA) on noncalcifying organisms and the possibly responsible mechanism have aroused great research interests with the intensification of global warming. The present study focused on a noxious, noncalcifying, bloom-forming dinoflagellate, Karenia mikimotoi (K. mikimotoi), and its variation of growth patterns exposed to different periods of seawater acidification with stressing gradients was discussed. The dinoflagellates under short-time acidifying stress (2d) with different levels of CO2 presented significant growth inhibition (p < 0.05). The cell cycle was obviously inhibited at S phase, and the photosynthetic carbon fixation was also greatly suppressed (p < 0.05). Apoptosis was observed and the apoptotic rate increased with the increment of pCO2. Similar tendencies were observed in the key components of mitochondrial apoptotic pathway (the mitochondrial membrane potential (MMP), Caspase-3 and -9, and Bax/Bcl-2 ratio). However, under prolonged stressing time (8 d and 15 d), the growth of dinoflagellates was recovered or even stimulated, the photosynthetic carbon fixation was significantly increased (p < 0.05), the cell cycle of division presented little difference with those in the control, and no apoptosis was observed (p > 0.05). Besides, acidification adjusted by HCl addition and CO2 enrichment resulted in different growth performances, while the latter had a more negative impact. The results of present study indicated that (1) the short-time exposure to acidified seawater led to reduced growth performance via inducing apoptosis, blocking of cell cycle, and the alteration in photosynthetic carbon fixation. (2) K. mikimotoi had undergone adaptive changes under long-term exposure to CO2 induced seawater acidification. This further demonstrated that K. mikimotoi has strong adaptability in the face of seawater acidification, and this may be one of the reasons for the frequent outbreak of red tide. (3) Ions that dissociated by the dissolved CO2, instead of H+ itself, were more important for the impacts induced by the acidification. This work thus provides a new perspective and a possible explanation for the dominance of K. mikimotoi during the occurrence of HABs. [ABSTRACT FROM AUTHOR]

The author gives an account of his life and work in scientific research. At the prompting of Govindjee, this is a quite personal account and, I hope, not too serious. The circumstances surrounding the discovery of C photosynthesis are mentioned together with some aspects of the subsequent development of this field. Since it seems to be expected on such occasions, there is also some reminiscences and some unsolicited advice. I hope there are no gross or libelous inaccuracies. [ABSTRACT FROM AUTHOR]