Microresonator solitons are critical to miniaturize optical frequency combs to chip scale and have the potential to revolutionize spectroscopy, metrology and timing. With the reduction of resonator ...diameter, high repetition rates up to 1 THz become possible, and they are advantageous to wavelength multiplexing, coherent sampling, and self-referencing. However, the detection of comb repetition rate, the precursor to all comb-based applications, becomes challenging at these repetition rates due to the limited bandwidth of photodiodes and electronics. Here, we report a dual-comb Vernier frequency division method to vastly reduce the required electrical bandwidth. Free-running 216 GHz "Vernier" solitons sample and divide the main soliton's repetition frequency from 197 GHz to 995 MHz through electrical processing of a pair of low frequency dual-comb beat notes. Our demonstration relaxes the instrumentation requirement for microcomb repetition rate detection, and could be applied for optical clocks, optical frequency division, and microwave photonics.
N-alkane-based proxies are widely employed to reconstruct paleoclimate and paleoenvironment in lacustrine environments. However, little is known about the influence of microbially mediated ...alkane-degradation on n-alkane-derived proxies. In this study, the chemical composition of n-alkanes and microbially mediated n-alkane degradation potential were investigated in the surface sediment samples collected from seven lakes with a range of salinity from freshwater to salt saturation on the northern Qinghai-Tibetan Plateau (QTP). The results showed that the chemical composition of n-alkanes differed among the studied QTP lakes. Significant correlations were observed between salinity and some n-alkane-based paleoclimate and paleoenvironment proxies, such as ratio of C21−/C22+, average chain length (ACL) and carbon preference index (CPI). This suggested that salinity may affect the validity of some n-alkane-based paleoclimate and paleoenvironment proxies. Alkane-degrading bacteria were abundant and widespread in the studied freshwater and saline/hypersaline lakes but were minor or absent in salt-saturation lakes. The obtained alkane-degrading bacterial strains showed active ability to degrade n-hexadecane. This suggested that the salinity influence on the n-alkane distribution may be partially related to microbial degradation, which awaits further in-situ investigation. So salinity variation should be taken into account when using n-alkane-based proxies for reconstructing paleoclimate and paleoenvironment in lakes.
•Chemical composition of n-alkanes differed among the studied lakes of different salinity•Salinity may affect the validity of n-alkane-based paleoclimate proxies.•Alkane-degrading bacteria showed active ability to degrade n-hexadecane.•Microbial degradation may partially account for salinity influence on n-alkane distribution.•Salinity variation should be taken into account when using n-alkane-based proxies.
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•Molecular composition of DOM differs significantly with lake salinity.•Oxidation state of carbon of DOM increases with lake salinity.•Molecular weight and number of carbon atoms in ...DOM decrease with lake salinity.•Environmental and microbial factors shape DOM composition in saline lakes.•Microbes explain lake DOM composition better than environmental factors.
Increased knowledege of the molecular composition of dissolved organic matter (DOM) is of great importance for an improved understanding of carbon cycling in lakes. However, such information remains limited for saline lakes. Here, DOM molecular compositions and microbial community structures were investigated in saline lakes with a full range of salinity from freshwater to hypersaline. An integrated approach, including Fourier transform-ion cyclotron resonance mass spectrometry and Illumina sequencing was employed. The results showed that in the studied saline lakes, aliphatic compounds, highly unsaturated and oxygen poor/rich compounds were the dominant DOM molecules. With increasing salinity, the molecular weight and carbon contents of the DOM molecules decreased, while their oxygen contents and carbon oxidation states increased. DOM molecular composition was significantly correlated with multiple environmental variables (i.e., chlorophyll a, salinity, pH) and with microbial components. The synergy of environmental and microbial factors exhibited great importance in explaining the variation of DOM molecular composition. Comparatively, microbial factors alone gave a much better explanation than environmental factors alone of the variation of DOM molecular composition, emphasizing the tight connection between DOM molecular composition and microbial communities. Taken together, these findings help improve our understanding of the molecular composition of DOM and its influencing factors in saline lakes.
Millimetre-wave (mmWave) technology continues to draw great interest due to its broad applications in wireless communications, radar, and spectroscopy. Compared to pure electronic solutions, ...photonic-based mmWave generation provides wide bandwidth, low power dissipation, and remoting through low-loss fibres. However, at high frequencies, two major challenges exist for the photonic system: the power roll-off of the photodiode, and the large signal linewidth derived directly from the lasers. Here, we demonstrate a new photonic mmWave platform combining integrated microresonator solitons and high-speed photodiodes to address the challenges in both power and coherence. The solitons, being inherently mode-locked, are measured to provide 5.8 dB additional gain through constructive interference among mmWave beatnotes, and the absolute mmWave power approaches the theoretical limit of conventional heterodyne detection at 100 GHz. In our free-running system, the soliton is capable of reducing the mmWave linewidth by two orders of magnitude from that of the pump laser. Our work leverages microresonator solitons and high-speed modified uni-traveling carrier photodiodes to provide a viable path to chip-scale, high-power, low-noise, high-frequency sources for mmWave applications.
Uncovering the limiting factors for benthic algal distributions in lakes is of great importance to understanding of their role in global carbon cycling. However, limited is known about the benthic ...algal community distribution and how they are influenced by geographic distance and environmental variables in alpine lakes. Here, we investigated the benthic algal community compositions in the surface sediments of six lakes on the Qinghai-Tibetan Plateau (QTP), China (salinity ranging from 0.8 to 365.6 g/L; pairwise geographic distance among the studied lakes ranging 8-514 km) employing an integrated approach including Illumina-Miseq sequencing and environmental geochemistry. The results showed that the algal communities of the studied samples were mainly composed of orders of
,
,
,
,
,
, and
. The benthic algal community compositions in these QTP lakes were significantly (
< 0.05) correlated with many environmental (e.g., dissolved inorganic and organic carbon, illumination intensity, total nitrogen and phosphorus, turbidity and water temperature) and spatial factors, and salinity did not show significant influence on the benthic algal community structures in the studied lakes. Furthermore, geographic distance showed strong, significant correlation (
= 0.578,
< 0.001) with the benthic algal community compositions among the studied lakes, suggesting that spatial factors may play important roles in influencing the benthic algal distribution. These results expand our current knowledge on the influencing factors for the distributions of benthic alga in alpine lakes.
Priming effect (PE) is a key biogeochemical process regulating organic carbon mineralization. However, the impacts of climate change-related factors on PE remain largely unclear in lakes with a large ...salinity range. The patterns of PE induced by algal (13C-labeled Chlorella vulgaris) and terrestrial grass (13C-labeled Festuca ovina) organic matter (OM) at 8 °C and 18 °C were investigated in lake sediments with a salinity range from 0.7 to 376.3 g L−1. The results showed that the intensities of early (7th day) and late (42nd day) PEs in the studied lake sediments ranged −51.0%–3833.7% and −55.2%–1874.5% of basal respiration, respectively; positive PE predominated over negative PE. Climate-related factors (e.g., salinity, temperature, OM types) exhibited significant influences on the intensity and/or direction of PE. Positive PE was more likely to occur in the sediments of hypersaline lakes than in freshwater/saline lakes, while negative PE showed an inverse trend. PE intensity induced by algal OM was significantly different at 8 °C and 18 °C, but no temperature influence was observed for that induced by grass OM. The effect of temperature increase on PE induced by algal OM was negative and positive in the early and late stages of incubation, respectively. The types of OM (algal OM vs. grass OM) supply significantly (P < 0.05) affected PE intensity except for the late PE intensity at 8 °C. Overall, these results suggest that organic carbon mineralization in lake sediments may be enhanced by positive PEs induced by the increased input of both allochthonous and autochthonous OM, and the autochthonous OM-induced PE is more susceptible to climate warming than that by allochthonous OM. These results help understand the carbon cycle in lakes under global climate change.
Exploring functional gene composition is essential for understanding the biogeochemical functions of lakes. However, little is known about the diversity and composition of biogeochemical cycling ...genes and their influencing factors in saline lakes. In this study, metagenomic analysis was employed to characterize the diversity and composition of microbial functions predicted from genes involved in carbohydrate metabolisms, nitrogen, and sulfur cycles in 17 surface sediments of Qinghai-Tibetan lakes with salinity ranging from 0.7 to 31.5 g L
. The results showed that relative abundances of carbohydrate-active enzyme (CAZy), nitrogen, and sulfur cycling genes were 92.7-116.5, 15.1-18.7, 50.8-63.9 per 1,000 amino acid coding reads, respectively. The Shannon diversity indices of CAZy and sulfur cycling genes decreased with increasing salinity, whereas nitrogen cycling gene diversity showed an opposite trend. Relative abundances of many CAZy (i.e., carbohydrate-binding module and carbohydrate esterase), nitrogen (i.e., anammox and organic degradation and synthesis) and sulfur (i.e., dissimilatory sulfur reduction and oxidation, link between inorganic and organic sulfur transformation, sulfur disproportionation and reduction) cycling gene categories decreased with increasing salinity, whereas some CAZy (i.e., auxiliary activity), nitrogen (i.e., denitrification) and sulfur (i.e., assimilatory sulfate reduction and sulfur oxidation) gene categories showed an increasing trend. The compositions of CAZy, nitrogen, and sulfur cycling genes in the studied lake sediments were significantly (
< 0.05) affected by environmental factors such as salinity, total organic carbon, total nitrogen, and total phosphorus, with salinity having the greatest influence. Together, our results suggest that salinity may regulate the biogeochemical functions of carbohydrate metabolisms, nitrogen, and sulfur cycles in lakes through changing the diversity and composition of microbial functional genes. This finding has great implications for understanding the impact of environmental change on microbial functions in lacustrine ecosystems.
Abstract
Utilizing waste heat from engine exhausts to decompose methanol into a hydrogen (H
2
) and carbon monoxide (CO) mixture, subsequently reintroduced into the engine, offers a significant ...potential to enhance engine efficiency and reduce emissions. The efficacy of the catalyst is crucial, as it directly influences the composition of the decomposition gases, thereby impacting energy conservation and emissions reduction. This study investigates the impact of various preparation methods for the self-developed Cu/Ni/Zr catalyst for methanol hydrogenation decomposition. These techniques include the co-precipitation method, co-impregnation method, and citrate complexation method, evaluated within a temperature spectrum of 220 °C–320 °C. Employing analytical methods such as x-ray Photoelectron Spectroscopy (XPS), x-ray Diffraction (XRD), Thermogravimetric Analysis-Differential Scanning Calorimetry (TGA-DSC), Brunauer–Emmett–Teller (BET), Temperature-Programmed Reduction (TPR), and Scanning Electron Microscopy (SEM) analysis, the study elucidates the mechanism of methanol decomposition catalyzed by Cu/Ni/Zr. The findings indicate that the catalyst’s activity, in terms of decomposition rate and hydrogen content, ranks in descending order from the co-impregnation method, followed by the citrate complexation method, to the co-precipitation method.
Uncovering microbial response to salinization or desalinization is of great importance to understanding of the influence of global climate change on lacustrine microbial ecology. In this study, to ...simulate salinization and desalinization, sediments from Erhai Lake (salinity 0.3–0.8 g/L) and Chaka Lake (salinity 299.3–350.7 g/L) on the Qinghai–Tibetan Plateau were transplanted into different lakes with a range of salinity of 0.3–299.3 g/L, followed by
in situ
incubation for 50 days and subsequent geochemical and microbial analyses. Desalinization was faster than salinization in the transplanted sediments. The salinity of the transplanted sediment increased and decreased in the salinization and desalinization simulation experiments, respectively. The TOC contents of the transplanted sediments were lower than that of their undisturbed counterparts in the salinization experiments, whereas they had a strong negative linear relationship with salinity in the desalinization experiments. Microbial diversity decreased in response to salinization and desalinization, and microbial community dissimilarity significantly (
P
< 0.01) increased with salinity differences between the transplanted sediments and their undisturbed counterparts. Microbial groups belonging to
Gammaproteobacteria
and
Actinobacteria
became abundant in salinization whereas
Bacteroidetes
and
Chloroflexi
became dominant in desalinization. Among the predicted microbial functions, hydrogenotrophic methanogenesis, methanogenesis through CO
2
reduction with H
2
, nitrate/nitrogen respiration, and nitrification increased in salinization; in desalinization, enhancement was observed for respiration of sulfur compounds, sulfate respiration, sulfur respiration, thiosulfate respiration, hydrocarbon degradation, chemoheterotrophy, and fermentation, whereas depressing was found for aerobic ammonia oxidation, nitrate/nitrogen respiration, nitrification, nitrite respiration, manganese oxidation, aerobic chemoheterotrophy, and phototrophy. Such microbial variations could be explained by changes of transplantation, salinity, and covarying variables. In summary, salinization and desalinization had profound influence on the geochemistry, microbial community, and function in lakes.
Assembly processes of prokaryotic and microeukaryotic community is an important issue in microbial ecology. However, unclear remains about the relative contribution of deterministic and stochastic ...processes to the shaping of prokaryotic and microeukaryotic communities in saline lake water. Here, we systematically investigated the assembly processes governing the prokaryotic and microeukaryotic communities in Qinghai Lake with the use of Illumina sequencing and a null model. The results showed that both deterministic and stochastic processes play vital roles in shaping the assemblies of prokaryotic and microeukaryotic communities, in which stochastic processes appeared to dominate (> 70%). Prokaryotic communities were mainly governed by non-dominant processes (60.4%), followed by homogeneous selection (15.8%), variable selection (13.6%) and dispersal limitation (10.2%), whereas microeukaryotes were strongly driven by non-dominant processes (68.9%), followed by variable selection (23.6%) and homogenizing dispersal (6.3%). In terms of variable selection, nutrients (e. g., ammonium, dissolved inorganic carbon, dissolved organic carbon and total nitrogen) were the major factors influencing prokaryotic and microeukaryotic community structures. In summary, prokaryotes and microeukaryotes can be predominantly structured by different assembly mechanisms, in which stochasticity is stronger than deterministic processes. This finding helps to better comprehend the assembly of prokaryotic and eukaryotic communities in saline lakes.
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