•Remotely sensed metrics are effective for monitoring vegetation responses to meteorological drought.•Drought resistance is associated with water balance and vegetation characteristics.•Drought ...impacts are determined by water stress levels and drought resistance among ecosystems.•Arid and semi-arid ecosystems are most susceptible to drought.•Future drought may threaten the survival of mesic ecosystems.
Improving our understanding of present and future impacts of drought on the vegetation in northern China is heightened by expectations that drought would increase its vulnerability and subsequently accelerate land degradation. The response of vegetation activity to drought and the underlying mechanisms are not well known. By using the third-generation Normalized Difference Vegetation Index (NDVI) and the Standardized Precipitation Evapotranspiration Index (SPEI), we investigated the relationship between NDVI and SPEI, across different climate regimes and land cover types, and determined the dominant time-scales at which different biome types respond to drought during the period of 1981–2014. Our results showed that biome response is coupled with drought trends in most regions of northern China. The highest correlation between monthly NDVI and SPEI at different time scales (1–48 months) assessed the impact of drought on vegetation, and the time scales resulting in the highest correlation were an effective indicator of drought resistance, which was related to the interactive roles of mean water balance and divergent drought survival traits and strategies. Diverse responses of vegetation to drought were critically dependent on characteristic drought time-scales and different growing environments. This study highlighted the most susceptible ecosystem types to drought occurrence under current climate, including temperate steppes, temperate desert steppes, warm shrubs and dry forests. Given that drought will be more frequent and severe under future climate scenarios, it may threaten the survival of mesic ecosystems, such as temperate meadows, alpine grasslands, dwarf shrubs, and moist forests not normally considered at drought risk. We propose that future research should be focused on arid and semi-arid ecosystems, where the strongest impact of drought on vegetation is occurring and the need for an early warning drought system is increasingly urgent.
•Drought cumulative and lagged effects on vegetation photosynthesis are measured.•A novel metric for drought sensitivity of vegetation photosynthesis is developed.•Drought sensitivity of vegetation ...photosynthesis has high spatial variability.•Quicker and stronger responses of vegetation photosynthesis to drought are found with increasing dryness.•Regions with high drought sensitivity of vegetation photosynthesis are identified.
Satellite remotely sensed solar-induced chlorophyll fluorescence (SIF) enjoys the intrinsic superiority to the detection of ecosystem-level photosynthetic capacity under drought stress, yet little is known about how drought accumulation and legacy effects shape vegetation photosynthetic activities as approximated by SIF. Hence, we quantified drought sensitivity of vegetation photosynthesis (DSVP) by evaluating the degree and time to which SIF responded to prolonged and previous droughts with standardized precipitation evapotranspiration index (SPEI). Divergent SIF responses to SPEI across bioclimatic zones were examined in northern China for the period of 2000 to 2017. Our results suggested that the accumulation, legacy and their combined effects spread for 9.2, 25.0 and 44.3% of the vegetated land, respectively. The dominant lag and accumulation time of SIF responses to SPEI was 9.1 and 10.5 months for all biomes, respectively. In general, patterns of the cumulative and lagged effects along an aridity gradient were similar, displaying quicker and stronger SIF responses to SPEI in regions with a lower aridity index value, but the changing rate of magnitude and time duration varied among and within biomes. Besides, we detected a nonlinear response to increasing dryness in DSVP as reflected by multiple trend breaks, which were caused by the differences among vegetation types and their drought adaptation and vulnerability. Semi-arid ecosystems were found to be highly sensitive to drought, especially in the farming-pastoral zone with an aridity index value within 0.3–0.4. At the biome level, grasslands responded to prolonged and previous droughts quicker and stronger than croplands and deserts did, whereas forests were the least responsive. This study emphasizes the demand for a prompt assessment of drought impacts on vegetation photosynthesis in a drying climate, and to focus on regions where increasing dryness leads to substantial declines in photosynthetic capacity under global warming.
Satellite‐based solar‐induced chlorophyll fluorescence (SIF) has the potential to offer early detection and accurate impact assessment of meteorological drought on vegetation photosynthesis. However, ...how the response of satellite SIF to meteorological drought varies under different climatic conditions and biome types remains poorly understood. In this study, we determined the drought time‐scale at which the vegetation photosynthesis response was highest based on the standardized precipitation evapotranspiration index (SPEI) and satellite SIF and examined how the sensitivity of SIF signals from different ecosystems to drought varied along an aridity gradient in northern China. The results showed that spatial variability of the annual maximum SIF was constrained by wetness conditions and biome types. Annual maximum SIF was positively correlated with SPEI in 57.9% of vegetated lands (p < .05). About 34.8% of humid ecosystems were characterized by a significant SIF‐SPEI correlation (p < .05). This percentage reached 44, 71.4, and 86.2% for arid, subhumid, and semiarid ecosystems, respectively. The variation of SIF‐SPEI correlations was a Gaussian function of the aridity index (AI), with the highest SIF‐SPEI correlation appearing in the AI bin of 0.4 (0.37–0.46). The drivers for this pattern were vegetation composition and water availability. The variation of SIF time scales in response to SPEI was a linear function of the AI, but the slope varied among biomes. To summarize, with increasing aridity drought‐induced declines in vegetation photosynthesis will be quicker and more significant.
Abstract
In wind erosion models, previous parameters related to vegetation morphology and density are limited in describing the spatial distribution of vegetation that influences surface ...heterogeneity. Thus, it is not fully understood how spatial vegetation patterns affect wind erosion on a field-scale. Based on an investigation of 36 plots of vegetation in Alxa Plateau, northwestern China, we established a multivariate linear model for temporally and spatially averaged aerodynamic roughness length (
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) incorporating the height, roughness density, regularity of vegetation patches (curvature) and spacing between patches (connectivity). The curvature positively interacted with the connectivity in affecting the mean
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, while it was the most important factor affecting the standard deviation of
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. The connectivity modulated the roughness density in affecting the standard deviation of
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. The spatial-related terms contributed 37% and 62% to the model variance of the mean and standard deviation of
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, respectively. Our results validate the importance of spatial vegetation structure in the vegetation-airflow interactions, with a suggestion of estimating the heterogeneity of surface erodibility by intuitive spatial parameters. Based on that spatial vegetation patterns reflect the ecosystem states, a strengthened linkage between wind erosion and vegetation stability may be useful in erosion regulation in drylands.
Dryland mountain ecosystems regulate global terrestrial carbon cycling and show high sensitivity to climate variability. The Qilian Mountains (QLMs) typify dryland mountain ranges in northern ...temperate belts and offer fundamental ecosystem services including forage production and water conservation. However, dominant controls on the interannual trend and variability of net primary productivity (NPP) in this region are unknown. Thus, we examined magnitude and direction of the NPP trend and quantified NPP sensitivity to temperature and precipitation under different biomes and altitudes using ground and remote sensing data. Our results showed that 12% of the QLMs had a reversed NPP trend from increasing to decreasing from 2000 to 2016, particularly in the western and southern parts, where NPP reductions were related to precipitation deficits. About 34% of the QLMs showed accelerated or persistent increasing NPP trends, mainly from the mid‐altitude between 3,100 and 4,300 m. The growth rate of NPP was higher in deserts and grasslands than in forests and increased in deserts but decreased in forests and grasslands with increasing elevation. Precipitation showed a stronger effect on the interannual variability in NPP than temperature did. The temperature sensitivity of NPP was similar along elevation gradients in forest steppes but decreased with increasing elevation in alpine deserts. The precipitation sensitivity of NPP reached highest in shrubby meadows when compared with coniferous forests and alpine deserts. This research provides new insights into climate controls of the NPP over the QLMs and to present drought as a growing threat to shrubby meadows and alpine deserts.
Lipoprotein lipase (LPL) is a rate-limiting enzyme that catalyzes hydrolysis of the triglyceride (TG) core of circulating TG-rich lipoproteins including chylomicrons (CM), low-density lipoproteins ...(LDL) and very low-density lipoproteins (VLDL). A variety of parenchymal cells can synthesize and secrete LPL. Recent studies have demonstrated that complicated processes are involved in LPL biosynthesis, secretion and transport. The enzyme activity of LPL is regulated by many factors, such as apolipoproteins, angiopoietins, hormones and miRNAs. In this article, we also reviewed the roles of LPL in atherosclerosis, coronary heart disease, cerebrovascular accident, Alzheimer disease and chronic lymphocytic leukemia. LPL in different tissues exerts differential physiological functions. The role of LPL in atherosclerosis is still controversial as reported in the literature. Here, we focused on the properties of LPL derived from macrophages, endothelial cells and smooth muscle cells in the vascular wall. We also explore the existence of crosstalk between LPL and those cells when the molecule mainly plays a proatherogenic role. This review will provide insightful knowledge of LPL and open new therapeutic perspectives.
•We have reviewed these complicated processes involved in biosynthesis, secretion, and transportation of LPL.•We explored the relationship of LPL and macrophages, endothelial cells, and vascular smooth muscle cells.•We reviewed its role of LPL in Atherosclerosis and other diseases.
ATP-binding cassette transporter A1 (ABCA1) plays a critical role in maintaining cellular cholesterol homeostasis. The purpose of this study is to identify the molecular mechanism(s) underlying ABCA1 ...epigenetic modification and determine its potential impact on ABCA1 expression in macrophage-derived foam cell formation and atherosclerosis development. DNA methylation induced foam cell formation from macrophages and promoted atherosclerosis in apolipoprotein E-deficient (apoE-/-) mice. Bioinformatics analyses revealed a large CpG island (CGI) located in the promoter region of ABCA1. Histone methyltransferase enhancer of zeste homolog 2 (EZH2) downregulated ABCA1 mRNA and protein expression in THP-1 and RAW264.7 macrophage-derived foam cells. Pharmacological inhibition of DNA methyltransferase 1 (DNMT1) with 5-Aza-dC or knockdown of DNMT1 prevented the downregulation of macrophage ABCA1 expression, suggesting a role of DNA methylation in ABCA1 expression. Polycomb protein EZH2 induced DNMT1 expression and methyl-CpG-binding protein-2 (MeCP2) recruitment, and stimulated the binding of DNMT1 and MeCP2 to ABCA1 promoter, thereby promoting ABCA1 gene DNA methylation and atherosclerosis. Knockdown of DNMT1 inhibited EZH2-induced downregulation of ABCA1 in macrophages. Conversely, EZH2 overexpression stimulated DNMT1-induced ABCA1 gene promoter methylation and atherosclerosis. EZH2-induced downregulation of ABCA1 gene expression promotes foam cell formation and the development of atherosclerosis by DNA methylation of ABCA1 gene promoter.
A strategy for the synthesis of isoquinolylselenocyanates and quinolylselenocyanates through electrophilic selenocyanogen cyclization has been developed. The feature of this reaction is that the ...sequential process was induced directly by generated in situ pseudohalogen (SeCN)2 generated in situ. Additionally, the obtained selenocyanates allowed functional group diversification, which could be potential intermediates for valuable compounds.
A Sb‐embedded polyoxoniobate has been originally synthesized under hydrothermal conditions. Particularly, the peanut‐like Sb2Nb24O7218− cluster cage in 1 with C2h symmetry is composed of two ...9‐nuclear {SbNb9O33} motifs and one {Nb6O24} crown‐shaped ring. The compound 1 present the novel structure of Sb‐substituted sandwich‐type polyoxoniobate with antimoniobate cluster cage. Decomposition catalytic studies indicate that compound 1 exhibits good hydrolytic activity and stability on the degradation of nerve agent simulant dimethylphosphonate (DMMP).
A Sb‐embedded polyoxoniobate, H4Na8K6Sb2Nb24O72 ⋅ 30H2O, composed of the largest peanut‐like antimony‐niobate cluster cage with C2h symmetry, exhibits good hydrolytic activity and stability in the degradation of nerve agent simulant DMMP.
Abstract Rationale Macrophage accumulation of cholesterol leads to foam cell formation which is a major pathological event of atherosclerosis. Recent studies have shown that microRNA (miR)-19b might ...play an important role in cholesterol metabolism and atherosclerotic diseases. Here, we have identified miR-19b binding to the 3′UTR of ATP-binding cassette transporter A1 (ABCA1) transporters, and further determined the potential roles of this novel interaction in atherogenesis. Objective To investigate the molecular mechanisms involved in a miR-19b promotion of macrophage cholesterol accumulation and the development of aortic atherosclerosis. Methods and results We performed bioinformatics analysis using online websites, and found that miR-19b was highly conserved during evolution and directly bound to ABCA1 mRNA with very low binding free energy. Luciferase reporter assay confirmed that miR-19b bound to 3110-3116 sites within ABCA1 3′UTR. MiR-19b directly regulated the expression levels of endogenous ABCA1 in foam cells derived from human THP-1 macrophages and mouse peritoneal macrophages (MPMs) as determined by qRT-PCR and western blot. Cholesterol transport assays revealed that miR-19b dramatically suppressed apolipoprotein AI-mediated ABCA1-dependent cholesterol efflux, resulting in the increased levels of total cholesterol (TC), free cholesterol (FC) and cholesterol ester (CE) as revealed by HPLC. The excretion of3 H-cholesterol originating from cholesterol-laden MPMs into feces was decreased in mice overexpressing miR-19b. Finally, we evaluated the proatherosclerotic role of miR-19b in apolipoprotein E deficient (apoE−/− ) mice. Treatment with miR-19b precursor reduced plasma high-density lipoprotein (HDL) levels, but increased plasma low-density lipoprotein (LDL) levels. Consistently, miR-19b precursor treatment increased aortic plaque size and lipid content, but reduced collagen content and ABCA1 expression. In contrast, treatment with the inhibitory miR-19b antisense oligonucleotides (ASO) prevented or reversed these effects. Conclusion MiR-19b promotes macrophage cholesterol accumulation, foam cell formation and aortic atherosclerotic development by targeting ABCA1.
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