Quantifying Regional Vegetation Cover Variability in North China during the Holocene: Implications for Climate Feedback

<div><p>Validating model simulations of vegetation-climate feedback needs information not only on changes in past vegetation types as reconstructed by palynologists, but also on other proxies such as vegetation cover. We present here a quantitative regional vegetation cover reconstruction for North China during the Holocene. The reconstruction was based on 15 high-quality lake sediment profiles selected from 55 published sites in North China, along with their modern remote sensing vegetation index. We used the surface soil pollen percentage to build three pollen-vegetation cover transfer models, and used lake surface sediment pollen data to validate their accuracy. Our results showed that vegetation cover in North China increased slightly before its maximum at 6.5 cal ka BP and has since declined significantly. The vegetation decline since 6.5 cal ka BP has likely induced a regional albedo change and aerosol increase. Further comparison with paleoclimate and paleovegetation dynamics in South China reproduced the regional cooling effect of vegetation cover decline in North China modelled in previous work. Our discussion demonstrates that, instead of reconstructing vegetation type from a single site, reconstructing quantitative regional vegetation cover could offer a broader understanding of regional vegetation-climate feedback.</p></div

Sample locations and modern NDVI distribution.

<p>Modern NDVI data were acquired by averaging data for August from 1982–2006 of the GIMMS dataset. NDVI in South China is homogeneous at a high level, while that of North China varies widely with precipitation. Samples of NDVI-MAP relationships were randomly chosen from grid points with natural vegetation in our study area (North China) and fitted by a logistic curve. Sites with surface soil pollen, lake surface pollen and sediment profiles are distributed around the 400 mm isohyet; some sites with surface soil pollen samples are located in Mongolia, but in the same biome and precipitation regime. <i>T of China N.</i> and <i>T of China S.</i> indicate the paleotemperature records used in the temperature reconstruction of North China and South China <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0071681#pone.0071681-Fang1" target="_blank">[70]</a>, respectively.</p

Mean reconstructed vegetation cover of each profile for 1–2, 6–7 and 9–10 ka BP.

<p>The circle diameters show the mean values of the reconstruction within 1 ka, while modern NDVI and modern MAP are plotted in the background. Because the heterogeneity between sites is much larger than the variation, the diameters of the circles were plotted according to the relative values compared to the mean value of the entire time series at each site.</p

Reconstructed vegetation cover, related factors and prescribed values in previous studies.

<p><i>Vegetation Cover</i> shows the reconstructed NDVI averaged from 15 sequences, with linear regression after 6.5 ka yr BP showing a decrease of 0.13. The light green area indicates the upper quartile and lower quartile of the 15 sequences, indicating that areas with higher NDVI experience larger fluctuations and were the major contributors to the vegetation decline in <i>Period II</i>. Sand% of AN shows the coarse sand (>63 μm) percentage in sediment cores from Anguli Nuur (inversely scaled). Stalagmite δ¹⁸O of Dongge Cave (as δ¹⁸O, values are negative), coarse sand percentage of Anguli Nuur and reconstructed NDVI are significantly correlated with each other. Prescribed values in the model simulation by Dallmeyer and Claussen (2011) coincide with the vegetation cover at 6.5 cal ka BP as reconstructed here; the colour bar shows the percentage of grass/trees in comparison to the modern vegetation distribution.</p

Result of model reconstruction and verification.

<p>In subplot A, LR, MAT and ANN all performed well in the model construction phase and passed the 0.01 significance level test; in subplot B, when verified by lake surface sediment pollen data, MAT failed to produce a reliable result. ANN was chosen for the reconstruction. All R² data are the adjusted R square.</p

Mechanisms discussed in this study.

<p>Black boxes show the mechanisms discussed in the text, and are further explained by the blue annotations or the corresponding R² in the linear correlation. While vegetation cover in North China is mainly controlled by precipitation, its decline in the past 6500 years might have led to the changes in both land cover albedo and aerosol production, with a resulting regional cooling effect, as model simulations in previous studies and the regional comparison in this study have shown.</p

Three new flavans in dragon's blood from <i>Daemonorops draco</i>

<div><p>Three new flavans were isolated from chloroform extracts of dragon's blood from <i>Daemonorops draco</i>, together with eight known compounds. The structures of the new flavans were determined by 1D and 2D NMR spectroscopic analysis. These compounds are the first examples of 2-methoxyflavans from <i>D. draco</i> and regarded as derivatives of biogenetic intermediates from flavans to chalcones, which are characteristic of the dragon's blood.</p></div

Image1_Association of methylenetetrahydrofolate reductase (MTHFR) rs1801133 (677C>T) gene polymorphism with ischemic stroke risk in different populations: An updated meta-analysis.TIF

Background: Recently, increasing evidence has implicated methylenetetrahydrofolate reductase (MTHFR) gene mutation as a risk factor for ischemic stroke (IS) in the general population. However, studies have been inconclusive and lack evidence on specific populations. We aim to determine whether the rs1801133 (NC_000001.11 (MTHFR):g. 677C>T (p.Ala222Val) variant, we termed as MTHFR rs1801133 (677 C>T), is linked to an increased risk of IS in different age groups and ancestry groups.Methods: The literature relevant to our study was found by searching the PubMed, Cochrane Library, Web of Science, EMBASE, and CNKI databases. A random effect model analysis was used to calculate the pooled odds ratio (OR) and 95% confidence interval (CI) to evaluate any possible association. We conducted a subgroup analysis based on the age and ancestry groups of the included populations.Results: As of March 2022, 1,925 citations had been identified in electronic databases, of which 96 studies involving 34,814 subjects met our eligibility criteria. A strong link was found between IS and the MTHFR gene rs1801133 (677C>T) polymorphism in all genetic models [dominant genetic model (OR = 1.47; 95%CI = 1.33–1.61; p T) variant may increase the risk of IS in Asian, Hispanic, or Latin population, middle-aged, and elderly populations (p Conclusion: Our results implied that mutation of the T allele of MTHFR rs1801133 (677C>T) could be a risk factor for IS. A significant association was found among Asian, Hispanic, or Latin population, middle-aged, and elderly people.</p

Demographic and baseline characteristics, serum levels of PGE₂ and IL-32 from influenza A positive patients and healthy individuals.

<p>Demographic and baseline characteristics, serum levels of PGE₂ and IL-32 from influenza A positive patients and healthy individuals.</p

A model for regulation of pro-inflammatory factors COX-2 and IL-32 expression in response to influenza A virus infection and double-stranded RNA

<p>A model for regulation of pro-inflammatory factors COX-2 and IL-32 expression in response to influenza A virus infection and double-stranded RNA</p