High fat diet increases the severity of collagen-induced arthritis in mice by altering the gut microbial community.

OBJECTIVES: Research has demonstrated that obesity may be associated with rheumatoid arthritis (RA). In addition, gut microbiota and its metabolites contribute to the occurrence and development of RA and obesity. However, the mechanism by which obesity affects RA remains unclear. In this study, we aimed to investigate whether gut microbiota and their metabolites alter the effects of high fat diet (HFD) on the severity of collagen-induced arthritis (CIA) in mice. METHODS: Briefly, mice were divided into normal group (N), CIA model group (C), HFD group (T), and HFD CIA group (CT). Hematoxylin and Eosin staining(HE) and Safranin O-fast green staining were conducted, and levels of blood lipid and inflammatory cytokines were measured. 16S rDNA sequencing technique and liquid chromatography-mass spectrometry (LC-MS)-based metabolomics were performed to explore changes in the microbiota structure to further reveal the pathomechanism of HFD on CIA. RESULTS: HFD aggravated the severity of CIA in mice. The CT group had the highest proportion of microbial abundance of Blautia, Oscillibacter, Ruminiclostridium-9, and Lachnospiraceae UCG 006 at the genus level, but had a lower proportion of Alistipes. Additionally, the fecal metabolic phenotype of the combined CT group shows significant changes, with differential metabolites enriched in 9 metabolic pathways, including primary bile acid biosynthesis, arginine biosynthesis, sphingolipid metabolism, purine metabolism, linoleic acid metabolism, oxytocin signaling pathway, aminoacyl-tRNA biosynthesis, the pentose phosphate pathway, and sphingolipid signaling pathway. Correlation analysis revealed that some of the altered gut microbiota genera were strongly correlated with changes in fecal metabolites, total cholesterol (TC), triglyceride (TG), and inflammatory cytokine levels. CONCLUSIONS: This study shows that HFD may aggravate inflammatory reaction in CIA mice by altering the gut microbiota and metabolic pathways.

Effects of acupuncture for Bell's palsy patients in the acute phase and its impact on facial nerve edema: a study protocol for a randomized, controlled trial.

Background: Bell's palsy is an acute peripheral facial neuropathy, which is one of the most common causes of facial palsy of lower motor neurons. Facial nerve swelling is commonly observed in Bell's palsy. Acupuncture therapy has been widely used in the treatment of Bell's palsy. However, whether acupuncture can be effectively used in the acute stage is still controversial. There are no clinical trials conducted previously to evaluate the effect of acupuncture on facial nerve edema in Bell's palsy patients. The study aims to evaluate the potential efficacy of different acupuncture modalities on Bell's palsy patients in the acute phase, its effect on facial nerve edema, and to preliminarily explore its possible mechanism. Methods and analysis: In this randomized, controlled trial, 165 Bell's palsy patients with unilateral onset within 3 days will be recruited and randomly assigned to either the electroacupuncture group (n = 33), the acupuncture group (n = 33), the sham acupuncture group (n = 33), the blank control group (n = 33), or the acupuncture control group (n = 33) in a 1:1:1:1:1 ratio. The participants will receive 4 weeks of treatment and 8 weeks of follow-up. The five groups of participants will receive the following treatments: A: Electroacupuncture + Medication (prednisone acetate tablets, mecobalamin tablets, and vitamin B1 tablets); B: Acupuncture + Medication; C: Sham Acupuncture + Medication; D: Medication only; and E: Acupuncture only. The primary outcome will be the effectiveness rate of different acupuncture modalities in improving facial nerve function after the intervention period. The secondary outcomes will be the recovery speed, the diameter of the facial nerve, the echo intensity and thickness of facial muscles, blood flow parameters of the facial artery, the serum inflammatory level, safety evaluation, and adverse events. Preliminary exploration of its mechanism of action occurs through inflammation and immune response. The difference between groups will be assessed using repeated measure analysis of covariance (ANCOVA) and trend chi-square. Discussion: The trial will evaluate the efficacy and facial nerve edema of acupuncture for Bell's palsy patients in the acute phase and preliminarily explore its possible mechanism. The results thus may provide evidence for clinical application. Clinical trial registration: https://www.chictr.org.cn/bin/project/edit?pid=133211, identifier ChiCTR2100050815.

Network Pharmacology and Experimental Verification of Si Shen Decoction Regulating FABP4/PPARγ/NFκB Pathway in the Treatment of Collagen-induced Arthritis.

AIM: This study aimed to investigate the mechanism of SSD in rats with Collagen- Induced Arthritis (CIA). BACKGROUND: Rheumatoid arthritis (RA) is a complex immune disease characterized by bilateral symmetrical multi-joint pain and swelling. Si Shen Decoction (SSD) has shown good results in treating RA in clinical applications, but its mechanism of action remains unclear. OBJECTIVE: To investigate the mechanism of SSD in rats with Collagen-Induced Arthritis (CIA). METHODS: Bioinformatics and network pharmacology analyses were used to predict the possible treatment targets and signaling pathways. Elisa, Western blotting, and quantitative real-time polymerase chain reaction were used to verify the mechanism of SSD in the treatment of RA. RESULTS: FABP4, MMP9, and PTGS2 were the most common predicted therapeutic targets. SSD treatment significantly reduced synovitis, ankle swelling and bone erosion in CIA rats. The SSD group also significantly reduced the serum secretion of CRP, TNFα, and IL1ß, decreased mRNA levels of FABP4, IKKα, and p65 in the synovial membrane, but increased PPARγ. Western blot showed that SSD treatment could significantly reduce the expression of FABP4, IKKα, and phosphorylated p65 (p-p65) proteins in the synovium. SSD was found to inhibit the FABP4/PPARγ/NFκB signaling pathway and reduce the inflammatory response in CIA rats. The therapeutic effect of SSD was significant with the increase of dose. CONCLUSION: SSD can relieve joint symptoms in CIA rats and alleviate inflammation by inhibiting the FABP4/PPARγ/NFκB signaling pathway. The effect of high-dose SSD was more prominent.

Coix seed oil alleviates synovial angiogenesis through suppressing HIF-1α/VEGF-A signaling pathways via SIRT1 in collagen-induced arthritis rats.

BACKGROUND: Rheumatoid arthritis (RA) is a chronic autoimmune disorder characterized by symmetric arthritis. Coix Seed Oil (CSO) has been shown to reduce inflammation in collagen induced arthritis (CIA) rats. However, the effect of CSO on synovial angiogenesis in RA is unknown. In this study, we aimed to explore whether CSO could inhibit RA synovial angiogenesis and elucidate the underlying mechanisms. METHODS: CIA rat models were established and subjected to different doses of CSO treatments for four weeks in vivo. Arthritis index, paw swelling, and weight were recorded to assess clinical symptoms. Hematoxylin and Eosin staining, Safarnin O fast green staining, Micro-CT, Immunohistochemical, and Immunofluorescence (IF) staining were performed to examined changes in synovial and joint tissues. The serum HIF-1α and VEGF-A levels were evaluated through enzyme-linked immunosorbent assay. Fibroblast-like synoviocytes (FLS) of rats was stimulated with tumor necrosis factor-α (TNF-α) for developing inflammatory model in vitro. Optimal concentrations of CSO and TNF-α for stimulation were measured through Cell Counting Kit-8 test. Wound healing and Transwell migration experiments were employed to determine FLS migratory ability. IF staining was performed to assess HIF-1α nuclear translocation in FLS. Protein levels of SIRT1, HIF-1α, VEGF-A, and CD31 were assessed through Western blot. The isolated aortic rings were induced with recombinant rat VEGF-A 165 (VEGF-A165) to observe the CSO inhibitory impact on angiogenesis ex vivo. RESULTS: CSO attenuated the progression of arthritis in CIA rats, mitigated histopathological deterioration in synovial and joint tissues, significantly inhibited immature vessels labeled with CD31+/αSMA-, and reduced the micro-vessels in VEGF-A165 induced aortic rings. Moreover, it upregulated SIRT1 protein levels in CIA rats and TNF-α induced FLS, but decreased HIF-1α and VEGF-A protein levels. Furthermore, CSO inhibited the migration ability and HIF-1α nuclear translocation of TNF-α induced FLS. Finally, suppressing SIRT1 levels in TNF-α induced FLS enhanced their migration ability, HIF-1α nuclear translocation, and the protein levels of HIF-1α, VEGF-A, and CD31, whereas the inhibitory effect of CSO on TNF-α induced FLS was severely constrained. CONCLUSIONS: This study indicates that CSO can alleviate synovial angiogenesis through suppressing HIF-1α/VEGF-A signaling pathways via SIRT1 in CIA rats.

Human activities have more impacts on the recent discharge reduction of the largest tributary of the Yellow River relative to last three centuries.

How to quantitatively decouple the impacts of climate change and human activities on river discharge changes is a challenge in current global change research. As the largest tributary of the Yellow River (YR), the Weihe River (WR) is a typical river whose discharge is influenced by climate change and human activities. Here, we first attempt to obtain the normal-flow season and high-flow season discharge in the lower reaches of the WR by using tree rings and historical documents, respectively. The relationship between natural discharge in the two seasons is unstable and complex since 1678. Using an innovative method, we reconstructed the natural discharge from March to October (DM-O), which explains >73 % of the variance in the observed DM-O during the modeling period 1935-1970. There were 44 high-flow years, 6 extremely high-flow years, 48 low-flow years and 8 extremely low-flow years from 1678 to 2008. The contribution of WR annual discharge to the YR is 17 % over the past three centuries, and their natural discharge changes synchronously rise and fall. Human activities, such as the construction of reservoirs and check-dams, agricultural irrigation and domestic and industrial water consumption, have more impacts than climate change on the decrease in the observed discharge. In total, 53.5 % of the discharge reduction since 1971 is due to human activities, and 46.5 % is due to climate change. In addition, this study provides an important model for how to quantify the influences of human activities and nature on discharge reduction and to reconstruct seasonal resolution climate in global change studies.

Kainic acid induced hyperexcitability in thalamic reticular nucleus that initiates an inflammatory response through the HMGB1/TLR4 pathway.

OBJECTIVE: To explore the relationship between the proinflammatory factor high-mobility group box 1 (HMGB1) and glutamatergic alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors in the development of epilepsy. METHODS: Thalamic reticular nucleus (TRN) slices were treated with kainic acid (KA) to simulate seizures. Action potentials and spontaneous inhibitory postsynaptic currents (sIPSCs) were recorded within TRN slices using whole-cell patch clamp techniques. The translocation of HMGB1 was detected by immunofluorescence. The HMGB1/TLR4 signaling pathway and its downstream inflammatory factors (IL-1ß and NF-κB) were detected by RTPCR, Western blot and ELISA. RESULTS: KA-evoked spikings were observed in TRN slices and blocked by perampanel. sIPSCs in the TRN were enhanced by KA and reduced by perampanel. The translocation of HMGB1 in the TRN was promoted by KA and inhibited by perampanel. The expression of the HMGB1/TLR4 signaling pathway was promoted by KA and suppressed by perampanel. CONCLUSION: KA induced hyperexcitability activates the HMGB1/TLR4 pathway, which potentially leading to neuroinflammation in epilepsy.

Insight into spatial-temporal patterns of hydroclimate change on the Chinese Loess Plateau over the past 250 years, using new evidence from tree rings.

The climate aridity since the mid-20th century has raised concerns about water resources on the Chinese Loess Plateau (CLP). A lack of extended observation-like precipitation records for the eastern CLP (ECLP) means that it remains unclear whether or not the current arid state of the CLP is unprecedented, and the spatial-temporal characteristics of hydroclimatic variability across the CLP over past centuries are not well understood. Here we present a regional hydrological-year precipitation reconstruction for the Heichashan Mountains, which successfully captures hydroclimate changes on the ECLP since 1773 CE. The reconstruction explains 48.72 % of the observed variance for 1957-2019 CE and reveals a wetting trend since the early 2000s and shows 2014-2020 CE to have been the second wettest period over the past 248 years. 1910-1932 CE was the longest and driest period over the past centuries. Furthermore, the 19th century was relatively wet, whereas the 20th century was dry. We demonstrate that droughts tend to occur in warm periods. Combining our new reconstruction with previously published hydroclimatic reconstructions, we find that hydroclimate has changed synchronously on the ECLP and the western CLP (WCLP) for most of the past two centuries. Some regional differences do exist, for example in the 1890s-1920s, when aridity gradually intensified across the ECLP, no similar drying is evident in records for the WCLP, although the 1920s megadrought occurred in both the ECLP and WCLP. Another difference is in the onset of the 20th-century aridity, which began in the 1950s on the ECLP, around 20 years later than it began on the WCLP. In addition to the known influences of the Asian Summer Monsoon and related large-scale circulations, this work highlights a major finding that the 1920s megadrought may be related to a regime shift in Northern Hemisphere temperature.

Abnormal Ventral Somatomotor Network Homogeneity in Patients With Temporal Lobe Epilepsy.

Background: Abnormalities of functional connectivity in the somatomotor network have been thought to play an essential role in the pathophysiology of epilepsy. However, there has been no network homogeneity (NH) study about the ventral somatomotor network (VSN) in patients with temporal lobe epilepsy (TLE). Therefore, we explored the NH of the VSN in TLE patients in this study. Methods: The sample included 52 patients with left temporal lobe epilepsy, 83 patients with right temporal lobe epilepsy, and 68 healthy controls. The NH method was utilized to analyze the resting-state functional magnetic resonance imaging data. Results: Compared to the controls, rTLE patients had significantly higher NH in the bilateral postcentral gyrus, and significantly lower NH in the bilateral Rolandic operculum and the right superior temporal gyrus (STG). The NH values of the left postcentral gyrus were significantly higher in lTLE patients than in the healthy controls, and lTLE patients had lower NH in the right Rolandic operculum. The altered NH in the postcentral gyrus was negatively correlated with the illness duration, and the decreased NH in the left Rolandic operculum was negatively correlated with the executive control reaction time (ECRT). Conclusion: Our findings suggest that altered NH of the postcentral gyrus, Rolandic operculum and STG might be associated with the pathophysiology of TLE, and thus, highlight the contribution of the VSN to the pathophysiology of TLE.

Abnormal Degree Centrality as a Potential Imaging Biomarker for Right Temporal Lobe Epilepsy: A Resting-state Functional Magnetic Resonance Imaging Study and Support Vector Machine Analysis.

Previous studies have reported altered neuroimaging features in right temporal lobe epilepsy (rTLE). However, the alterations in degree centrality (DC) as a diagnostic method for rTLE have not been reported. Therefore, we aimed to explore abnormalities in the DC of the rTLE and whether such alterations could be applied to the diagnosis of rTLE. Resting-state functional magnetic resonance imaging (fMRI) was used to scan 82 patients with rTLE and 69 healthy controls. The DC and support vector machine (SVM) methods were used for an analysis of the imaging data. Compared to the control group, the rTLE patients exhibited lower DC values in the right hippocampus, right superior temporal gyrus, and right caudate. Compared to the control group, the rTLE patients showed higher DC values in the right medial superior frontal gyrus (SFGmed), left dorsolateral superior frontal gyrus (SFGdor), right inferior parietal lobule (IPL), and the left postcentral. The highest diagnostic accuracy of 99.34% (150/151), based on SVM analysis, was demonstrated for the combination of abnormal DC in the right IPL and the left SFGdor, along with a sensitivity of 100% (82/82), and a specificity of 98.55% (68/69) for the differentiation of rTLE patients from healthy controls. The study demonstrated abnormal functional connectivity in rTLE patients. Thus, a distinctive DC pattern may serve as an imaging marker for the diagnosis of rTLE patients.

Abnormal Fractional Amplitude of Low-Frequency Fluctuation as a Potential Imaging Biomarker for First-Episode Major Depressive Disorder: A Resting-State fMRI Study and Support Vector Machine Analysis.

Objective: Major depressive disorder (MDD) is a psychiatric disorder with serious negative health outcomes; however, there is no reliable method of diagnosis. This study explored the clinical diagnostic value of the fractional amplitude of low-frequency fluctuation (fALFF) based on the support vector machine (SVM) method for the diagnosis of MDD. Methods: A total of 198 first-episode MDD patients and 234 healthy controls were involved in this study, and all participants underwent resting-state functional magnetic resonance imaging (fMRI) scanning. Imaging data were analyzed with the fALFF and SVM methods. Results: Compared with the healthy controls, the first-episode MDD patients showed higher fALFF in the left mid cingulum, right precuneus, and left superior frontal gyrus (SFG). The increased fALFF in these three brain regions was positively correlated with the executive control reaction time (ECRT), and the increased fALFF in the left mid cingulum and left SFG was positively correlated with the 17-item Hamilton Rating Scale for Depression (HRSD-17) scores. The SVM results showed that increased fALFF in the left mid cingulum, right precuneus, and left SFG exhibited high diagnostic accuracy of 72.92% (315/432), 71.76% (310/432), and 73.84% (319/432), respectively. The highest diagnostic accuracy of 76.39% (330/432) was demonstrated for the combination of increased fALFF in the right precuneus and left SFG, along with a sensitivity of 84.34% (167/198), and a specificity of 70.51% (165/234). Conclusion: Increased fALFF in the left mid cingulum, right precuneus, and left SFG may serve as a neuroimaging marker for first-episode MDD. The use of the increased fALFF in the right precuneus and left SFG in combination showed the best diagnostic value.

Machine learning forecasting of active nematics.

Active nematics are a class of far-from-equilibrium materials characterized by local orientational order of force-generating, anisotropic constitutes. Traditional methods for predicting the dynamics of active nematics rely on hydrodynamic models, which accurately describe idealized flows and many of the steady-state properties, but do not capture certain detailed dynamics of experimental active nematics. We have developed a deep learning approach that uses a Convolutional Long-Short-Term-Memory (ConvLSTM) algorithm to automatically learn and forecast the dynamics of active nematics. We demonstrate our purely data-driven approach on experiments of 2D unconfined active nematics of extensile microtubule bundles, as well as on data from numerical simulations of active nematics.

Effects of external application of compound Qingbi granules on acute gouty arthritis with dampness-heat syndrome: a randomized controlled trial.

BACKGROUND AND AIM: The use of anti-inflammatory and analgesic drugs such as nonsteroidal anti-inflammatory drugs(NSAIDs) for treating acute gout has limitations, such as adverse reactions in the gastrointestinal tract and toxicity in the liver, kidney, and heart. Hence, a new safe and effective treatment approach needs to be explored to reduce the use of anti-inflammatory and analgesic drugs, incidence of adverse reactions, and patients' burden. This randomized controlled clinical trial aimed to investigate the clinical efficacy and safety of the external application of compound Qingbi granules (CQBG) in treating acute gouty arthritis(AGA), providing evidence for designing a safe, effective, and optimized protocol for AGA comprehensive treatment. METHODS: A total of 90 patients in line with the diagnostic standard of AGA were recruited and randomly divided into control, T1, and T2 groups (30 in each group). All the participators in the three groups all received Western-medicine-basic treatment (low-purine diet, drinking water more than 2000 mL/days, oral loxoprofen, and NAHCO3). Besides, the T1 group received an external application of diclofenac diethylamine emulgel, while the T2 group received an external application of CQBG. The participants in the control group received single-use Western-medicine-basic treatment. With a treatment course of 7 days and a follow-up of 7 days, the three groups were compared in terms of primary outcome indicators, including swelling, pain improvement, and change in pain duration and secondary outcome indicators, including serum C-reactive protein (CRP) level, uric acid (UA) level, and change in the thickness of the inflammatory synovium of joints under ultrasound. Meanwhile, the safety of the protocol was evaluated. RESULTS: The three groups of patients had no apparent differences in age, body mass index, history of gout, complications, and so on before recruitment. A comparison between pretreatment and post-treatment revealed remarkable reductions in the arthralgia visual analog scale score(VAS) and the swelling score in the three groups after the treatment and the improvements in the T2 group were more significant than those in the T1 and control groups (P < 0.05). Regarding the onset time of pain improvement and pain duration, the T2 group had more significant efficacy compared with the other two groups (P < 0.05). The serum CRP and blood UA levels in the three groups significantly decreased after the treatment, but with no significant intergroup difference. The improvement in the thickness of the inflammatory synovium in joints tested by ultrasound was more significant in the T2 group than in the control group (P < 0.05). For safety evaluations, no significant difference in the incidence of adverse events was found. CONCLUSIONS: The external application of CQBG combined with Western-medicine-basic treatment in patients with AGA improved arthralgia and swelling, shortened the period of taking NSAIDs, and reduced the levels of CRP and serum UA. Its therapeutic effect was significantly better than the effect of single-use Western-medicine-basic treatment. The study provided evidence for the clinical application of CQBG combined with Western medicine in treating AGA. TRIAL REGISTRATION: ChiCTR, ChiCTR1800018020. Registered 27 August 2018, https://www.chictr.org.cn/showproj.aspx?proj=27138.

Delayed warming in Northeast China: Insights from an annual temperature reconstruction based on tree-ring δ18O.

Global warming has had an unprecedented impact on environmental changes and thus human life in mid-high latitude regions. As one of the areas most affected by global warming, Northeast China has suffered from a series of ecological crises, including warming-induced water deficits, permafrost thaw, and extended growing seasons. The change in annual average temperature (annual T) variations in Northeast China since the Industrial Revolution are still not fully understood, mainly because of the lack of long-term instrumental data and high-resolution annual T reconstructions. Here, we present the first annual T reconstruction (r = -0.683, p < .001, n = 60) for 1818-2012 in Northeast China, which may also be the first temperature reconstruction based on tree-ring δ18O in China. The reconstruction is significantly related to temperature variations over mid-high latitude Eurasia and agree (p < .01) with several long-term hydroclimatic reconstructions in the surrounding area. When the internal variability in the reconstruction was high, the decadal to multidecadal cycles were significant. Further analysis found that the reconstruction was mainly affected by the East Asian Summer Monsoon (EASM) and North Atlantic Oscillation (NAO). The reconstruction was significantly negatively correlated with several time series of annual T in the Northern Hemisphere, which showed that there is a substantial difference in annual T between Northeast China and other regions of the Northern Hemisphere. The difference mainly existed before the 1950s. From the 1850s to the 1950s, the annual T in Northeast China decreased slightly. However, extreme warming began in the 1950s in Northeast China, and this warming has been unprecedented during the past two centuries. If the warming trend since the 1950s continues, then it will lead to devastating disasters to forest and permafrost ecosystems in Northeast China.

Recent anthropogenic curtailing of Yellow River runoff and sediment load is unprecedented over the past 500 y.

The Yellow River (YR) is the fifth-longest and the most sediment-laden river in the world. Frequent historical YR flooding events, however, have resulted in tremendous loss of life and property, whereas in recent decades YR runoff and sediment load have fallen sharply. To put these recent changes in a longer-term context, we reconstructed natural runoff for the middle reach of the YR back to 1492 CE using a network of 31 moisture-sensitive tree-ring width chronologies. Prior to anthropogenic interference that started in the 1960s, the lowest natural runoff over the past 500 y occurred during 1926 to 1932 CE, a drought period that can serve as a benchmark for future planning of YR water allocation. Since the late 1980s, the low observed YR runoff has exceeded the natural range of runoff variability, a consequence of the combination of decreasing precipitation and increasing water consumption by direct and indirect human activities, particularly agricultural irrigation. This reduced runoff has resulted in an estimated 58% reduction of the sediment load in the upper reach of the YR and 29% reduction in the middle reach.

Tree-ring evidence of the impacts of climate change and agricultural cultivation on vegetation coverage in the upper reaches of the Weihe River, northwest China.

Comprehending the characteristics and causes of vegetation coverage in history is of practical significance for studying ecological and environmental changes. As a typical region of the semi-arid and semi-humid climatic zone in northwest China, the upper reaches of the Weihe River have relatively fragile ecological environment. Based on tree-ring width chronologies, the vegetation coverage represented by the normalized difference vegetation index was reconstructed from 1630 to 2006 using a regression model. There were 64 years with high vegetation coverage and 56 years with low vegetation coverage over the past 377 years. At low frequencies, the coverage was relatively higher in the 1650s and from the 1880s to 1890s, while the coverage was lower in the 1720s and from the 1760s to 1770s. While precipitation and temperature had positive and negative influences on the changes of vegetation coverage, respectively, during the past several centuries, the agricultural cultivation played an important role on coverage changes. Along with the land reclamation expansion in history, the forest cover gradually declined, and vegetation coverage decreased. The vegetation coverage was lower when there were more arable lands reclaimed from woodlands. Regardless of the land reclamation policy during the historical period or the current conversion project of cropland to forest, they affected the vegetation coverage by influencing cover ranges of woodland and farmland.

The 600-mm precipitation isoline distinguishes tree-ring-width responses to climate in China.

The numerous temperature and precipitation reconstructions in China based on tree-ring-width data have played significant roles in furthering the understanding of past climate changes. However, the geographical variability in the responses of trees to climate variations in China remains largely undetermined. Here, we describe an important spatial boundary in the response of trees to climate variations, namely the 600-mm annual precipitation isoline. We found that, to the north of this line, tree-ring widths are usually positively correlated with precipitation and negatively correlated with growing-season temperature. To the south of this line, the tree-ring widths respond positively to temperature, and winter half-year temperatures are the main reconstructed parameters, especially on the third topographical step of China. We also found that precipitation reconstructions based on tree-ring data and the Palmer Drought Severity Index almost exclusively fall in the region of the 200- to 600-mm annual precipitation isolines, not other regions. Our findings indicate that, when using multiple tree-ring-width chronologies for large-scale past climate reconstructions, the climatic signal of each tree-ring-width series should be carefully considered.

Elements content in tree rings from Xi'an, China and environmental variations in the past 30years.

Using inductively coupled plasma mass spectrometry (ICP-MS) and inductively coupled plasma atomic emission spectroscopy (ICP-AES), the characteristics of chemical elements were analyzed in white poplar (Populus bonatii Levl.) and ailanthus (Ailanthus altissima (Mill.) Swingle) from three sites in the town of Xi'an, China. The results indicated that the concentration variations of Pb and Cd in tree rings were consistent with that of the environment where the trees were growing. P and Zn were translocated within tree rings to a certain degree, which led to an inaccurate pollution reconstruction. We also found that white poplar had a stronger absorptive capacity of Cd and Zn than ailanthus, which could make white poplar better as a species in environmental remediation. From this research we can see the great potential of tree rings for studying the history of different element pollution in the environment, showing that dendrochemical methods could be used as a powerful component in environmental monitoring programmes, to reconstruct past pollution history at the time when monitoring systems were not yet installed.