The rate constant for gas-phase reactions of OH radicals with 1H-heptafluorocyclopentene (cyc-CF2CF2CF2CF═CH-) was measured using a relative rate method at 298 K: (5.20 ± 0.09) × 10-14 cm3 molecule-1 s-1. The quoted uncertainty includes two standard deviations from the least-squares regression, the systematic error from the GC analysis, and the uncertainties of the rate constants of the reference compounds. The OH-radical-initiated oxidation of cyc-CF2CF2CF2CF═CH- gives the main products COF2, CO, and CO2, leading to negligible environmental impact. For consumptions of cyc-CF2CF2CF2CF═CH- of less than 54%, the yield of the formation of ([COF2] + [CO] + [CO2])/5 (based on the conservation of carbon) was 0.99 ± 0.02, which is very close to 100%. A possible degradation mechanism was proposed. The radiative efficiency (RE) of cyc-CF2CF2CF2CF═CH- measured at room temperature was 0.215 W m-2 ppb-1. The atmospheric lifetime of cyc-CF2CF2CF2CF═CH- was calculated as 0.61 year, and the photochemical ozone creation potential (POCP) was negligible. The 20-, 100-, and 500-year time horizon global warming potentials (GWPs) were estimated as 153, 42, and 12, respectively.
New software, Isoclock, focuses on deducing common Pb from reference materials or samples. A novel common Pb correction method has been introduced into the program to process data from hydrothermal/accessory mineral LA-ICP-MS U–Th–Pb dating.
Molecular dynamics (MD) simulation is performed to study the diffusion and phase separation process in binary Lennard-Jones (LJ) liquid. It is found that the growth of phase separation with temperature can be divided into two stages. The first is the fast-growth at high temperatures and the second is the steady-growth at low temperatures. Diffusion activation energy in the phase separation system is not a constant, but a function of temperature and follows the relation of E=a+bTc. The influence of the sizes of the components on the phase separation is also discussed. The results shows that the diffusivity increases when the component size decreases. This facilitates the phase separation.
As a common macroalga living in the intertidal zone, Sargassum thunbergii (Sargassaceae, Phaeophyta) is often exposed to drastic changes in solar photosynthetically active radiation during a diurnal cycle; thus, the potential photosynthetic adaptation processes deserve attention. In this work, we examined the photosynthetic performance and xanthophyll cycle activity of this alga in response to high light (1,200 μmol photons m –2 s –1 , the average in-situ light intensity at noon) by using chlorophyll fluorescence and high-performance liquid chromatography (HPLC). On exposure to high light, a rapid decrease in the effective quantum yield of photosystem II (PSII) (Y(II)) occurred, indicating down-regulation of PSII activity; a corresponding increase in non-photochemical quenching (NPQ) indicated the existence of energy-dissipating cycles. After turning off the light, Y(II) gradually increased to 0.7, accompanied by a decrease in NPQ. However, no complete recovery of NPQ was observed, and its value remained at ≈4, even after an 80-min dark treatment. The size of the xanthophyll cycle pigments pool was quantified using HPLC and was found to be ≈16 mol mol −1 Chl a × 100. The activity of the xanthophyll cycle, characterized by a de-epoxidation state (DPS), could reach up to ≈0.5. Such a large pigments pool and rapid accumulation of zeaxanthin may allow S. thunbergii to induce high values of NPQ (≈10). These results were further complemented by inhibitor (dithiothreitol, DTT) and pre-illumination experiments showing that (1) both NPQ and the xanthophyll cycle could be inhibited by DTT, and there was always a strong positive correlation between NPQ and DPS; (2) the previously formed antheraxanthin exhibited a long retention time and a slow epoxidation; and (3) the long retention of antheraxanthin contributed to a rapid accumulation of zeaxanthin. In conclusion, our present study demonstrated that xanthophyll cycle-induced NPQ can significantly protect S. thunbergii from light fluctuations in the intertidal zone.
Ocean warming is suggested to exert profound effects on phytoplankton physiology and growth. Here, we investigated how the coccolithophore Emiliania huxleyi (BOF 92, a non-calcifying strain) responded to changes in temperature in short- and long-term thermal treatments. The specific growth rate after 10 days of acclimation increased gradually with increasing temperatures (14, 17, 21, 24, 28°C) and peaked at ~23°C, followed by a significant decrease to 28°C. Chlorophyll a content, cell size, photosynthetic rate, and respiratory rate increased significantly from 14°C to 24°C, but the cellular particulate organic carbon (POC) and nitrogen (PON) showed the lowest values at the optimal temperature. In contrast, during long-term thermal treatments at 17°C and 21°C for 656 days (~790 generations for 17°C treatment; ~830 generations for 21°C treatment), the warming significantly stimulated the growth in the first 34 days and the last 162 days, but there was no significant difference in specific growth rate from Day 35 to Day 493. Chlorophyll a content, cell size, cellular POC/PON, and the ratio of POC to PON, showed no significant difference between the warming and control for most of the duration of the long-term exposure. The warming-selected population did not acquire persistent traits in terms of growth and cell quotas of POC and PON, which resumed to the levels in the control temperature treatment after about 9 generations in the shift test. In summary, our results indicate that warming by 4°C (17°C and 21°C) enhanced the growth, but did not result in adaptative changes in E. huxleyi (BOF 92) over a growth period of about 800 generations, reflecting that mild or non-stressful warming treatment to E. huxleyi isolated from cold seas does not alter its phenotypic plasticity.
Zostera marina among seagrass suffering from global decline is a representative species in temperate regions in the Northern Hemisphere. Given our recent findings, the decline of seagrasses may be associated with the photosensitivity of the oxygen-evolving complex (OEC). Therefore, understanding the mechanism of OEC photosensitivity is key to understanding the continued decline in seagrasses. Herein, we explored the screening-based photoprotection function in Z. marina by examining the inactivation spectrum of OEC and the differences in photoresponse pathways following exposure to different spectrums. The OEC inactivation was spectral-dependent. High-energy light significantly reduced the PSII performance, OEC peripheral protein expression, and photosynthetic O release capacity. The increased synthesis of carotenoids under blue light with severe OEC damage implied its weak photoprotection property in Z. marina . However, anthocyanins key synthetic genes were lowly expressed with inefficient accumulation under high-energy light. Furthermore, the acylation modifications of anthocyanins, especially aromatic acylation modifications were insufficient, leading to poor stability and light absorption of anthocyanins. Based on the role of blue light receptors in regulating the synthesis of anthocyanins in vascular plant, we hypothesized that the absence of blue light receptor CRY2 in Z. marina causes the insufficient synthesis of anthocyanins and acyl modifications, reducing the shielding against high-energy light, subsequently causing OEC photoinactivation.
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