Search

Tropical montane evergreen broad-leaved forests cover the majority of forest areas and have high carbon storage in Xishuangbanna, southwest China. However, stem radial growth dynamics and their correlations with climate factors have never been analyzed in this forest type. By combining bi-weekly microcoring and high-resolution dendrometer measurements, we monitored xylogenesis and stem radius variations of the deciduous species Betula alnoides Buch.-Ham. ex D. Don and the evergreen species Schima wallichii (DC.) Korth. We analyzed the relationships between weekly climate variables prior to sampling and the enlarging zone width or wall-thickening zone width, as well as weekly radial increments and climate factors during two consecutive years (2020 to 2021) showing contrasting hydrothermal conditions in the pre-monsoon season. In the year 2020, which was characterized by a warmer and drier pre-monsoon season, the onset of xylogenesis and radial increments of B. alnoides and S. wallichii were delayed by three months and one month, respectively, compared with the year 2021. In 2020, xylem formation and radial increments were significantly reduced for B. alnoides , but not for S. wallichii. The thickness of enlarging zone and wall-thickening zone in S. wallichii were positively correlated with relative humidity, and minimum and mean air temperature, but were negatively correlated with vapor pressure deficit during 2020 to 2021. The radial increments of both species showed significant positive correlations with precipitation and relative humidity, and negative correlations with vapor pressure deficit and maximum air temperature during two years. Our findings reveal that drier pre-monsoon conditions strongly delay growth initiation and reduce stem radial growth, providing deep insights to understand tree growth and carbon sequestration potential in tropical forests under a predicted increase in frequent drought events. [ABSTRACT FROM AUTHOR]

To understand inter-annual to decadal summer monsoon precipitation variations in Myanmar, we developed new tree-ring chronologies of Tectona grandis (teak) from three sampling sites in north-central Myanmar where the climatic proxy is sparse. A regional chronology (spanning 1700–2016) derived from three site chronologies showed a strongly positive precipitation sensitivity during the summer monsoon (R = 0.71), indicating that slow tree growth was detected in years of deficient precipitation. We reconstructed monsoon precipitation (May–October) for the period 1770–2016, with robust calibration-verification statistics. Our reconstruction revealed 22 (16) extremely dry (wet) years over the past 247 years. Several dry and wet episodes recorded in our reconstruction are consistent with other precipitation proxies from tropical Asia, such as the East Indian drought in 1790–1796 and the Victorian Holocaust drought in 1888–1890. The 2.0–4.0-year high-frequency periodicities revealed from spectral peaks and dominant regions of high spatial correlations indicated the summer precipitation in Myanmar is linked with broader-scale ocean-atmospheric circulations, mainly associated with the El Niño-Southern Oscillation (ENSO) activities due to sea surface temperature variations in the tropical Pacific Ocean. Coherent relationships of our reconstructed series with ENSO-related climate indices further support the dynamics of monsoon precipitation variability in Myanmar is inter-linked with global climate systems. Our reconstruction inferred from teak tree rings may be useful to provide valuable insight into the impacts of extreme weather events associated with monsoon hydroclimate in Myanmar. [ABSTRACT FROM AUTHOR]

Many studies focus on the relationships between plant functional traits and tree growth performances. However, little is known about the ontogenetic shifts of the relationships between functional traits and tree growth. This study examined associations between stem and leaf functional traits and growth rates and their ontogenetic shifts across 20 tropical tree species in a tropical seasonal rainforest in Xishuangbanna, south-west China. For each species, physiological active branches of individual trees belonged to three size classes (i.e. small, diameter at breast height (DBH) 5–10 cm; middle, DBH 10–20 cm; big, DBH >20 cm) were sampled respectively. We measured 18 morphological and structural traits, which characterised plant hydraulic properties or leaf economic spectrum. Associations between diameter growth rates and functional traits were analysed across three size classes. Our results revealed that diameter growth rates of big-sized trees were mainly related to traits related to plant hydraulic efficiency (i.e. theoretical hydraulic conductivity (Ktheo) and leaf vein density (Dvein)), which suggests that the growth of large trees is limited mainly by their xylem water transport capacity. For middle-sized trees, growth rates were significantly related to traits representing leaf economic spectrum (i.e. specific leaf area (SLA), individual leaf mass (ILM), palisade thickness (PT) and spongy thickness (SP)). Diameter growth rates of small-sized trees were not correlated with hydraulic or leaf economic traits. Thus, the associations between tree growth rates and functional traits are size dependent. Our results suggest ontogenetic shift of functional traits which could potential contribute to different growth response to climate change. Plant functional traits can directly reflect plants performance under environmental. We show that traits growth relationships are strongly size-dependent in tropical rainforest in south-west China: diameter growth rates correlated significantly with leaf economic spectrum traits for middle sized trees, but for large sized trees hydraulic efficiency traits play a more important role on growth. This suggests ontogenetic shift of functional traits could potential contribute to different growth response to climate change. [ABSTRACT FROM AUTHOR]

Growth rate varies across plant species and represents an important ecological strategy for competition, resource-use and fitness. However, empirical studies often show a low predictability of functional traits to tree growth. We measured stem diameter and height growth rates (DGRs and HGRs) of 96 juvenile trees (2–5 m tall) of eight evergreen and eight deciduous broadleaf tree species over three consecutive years in a subtropical forest in south-western China. We examined the relationships between tree growth rates and 20 leaf/stem traits that are associated with carbon gain, stem hydraulics and nutrient-use efficiency, as well as the difference between evergreen and deciduous trees. We found that cross-species variations of stem DGR/HGR can be predicted by leaf photosynthetic capacity, leaf mass per area, xylem-theoretical-specific hydraulic conductivity, wood density (WD) and photosynthetic-nutrient-use efficiencies. Higher leaf carbon assimilation and lower leaf/stem constructing costs facilitate deciduous species to be more resource acquisitive and consequently faster growth within a relatively shorter growing season, whereas evergreen species exhibit more conservative strategies and thus slower growth. Furthermore, stem growth rates of evergreen species showed were more dependence on leaf carbon gains, whereas stem hydraulic efficiency was more important for deciduous tree growth. Our results suggest that physiological traits (photosynthesis, hydraulics and nutrient-use efficiency) can predict tree diameter and height growth of subtropical tree species. The differential resource acquisition and use strategies and their associations with tree growth between evergreen and deciduous trees provide insights into explaining the coexistence of evergreen and deciduous tree species in subtropical forests. [ABSTRACT FROM AUTHOR]

Tree rings are widely used to reconstruct past climates in regions where observational records of climate are short. In this study, we developed a 294 years-long (1718–2011 CE) ring-width chronology of the Himalayan Silver fir (Abies spectabilis (D.Don, Spach)) from Humla district in western Nepal to reconstruct winter minimum temperature for the remote region of central Himalaya where instrumental records are limited to past three or four decades. Ring-width chronology of the Himalayan Silver fir showed strongest and significant positive correlation with minimum winter temperature prior to the growing season. Based on this relationship, we reconstructed the winter season (previous October–current February) minimum temperature for western Nepal covering the period of 1780–2008 CE. Our reconstruction showed that winter minimum temperature is continuously increasing since the early twentieth century with unprecedented rapid warming in the latter half. The cold episodes in the reconstruction coincided with the major volcanic eruptions in the Northern Hemisphere and tropical regions. The spectral analysis using Multi-Taper Method revealed that the winter temperature in the north-western Himalaya has short- to medium-term periodicities of 2–3, 5.8–6.2, 7.9–8.2, 39–46 and 56–73 years, which suggest possible teleconnections with ENSO (El-Nino Southern Oscillation) and AMO (Atlantic Multidecadal Oscillation). [ABSTRACT FROM AUTHOR]

To develop a high‐resolution paleoclimate proxy record facilitating adaptation measures on drought impacts, we constructed a regional composite tree‐ring chronology of teak (Tectona grandis) by combining three local site chronologies from southern Myanmar. Our regional tree‐ring record is strongly correlated with the November–April self‐calibrated Palmer drought severity index and enabled us to reconstruct drought variability for the period 1802–2016. The reconstruction explained 46.5% of the actual self‐calibrated Palmer drought severity index variance. Over the past two centuries, we detected one extreme (1812) and six severe drought years (1810, 1811, 1816, 1852, 1887, and 1980). Dry periods coincided with six major famines that occurred in India. Spatial correlation analyses revealed that drought occurrence is linked to broader‐scale atmospheric circulations of the Pacific and Indian Oceans, especially during the positive phase of the El Niño–Southern Oscillation. Our reconstruction provides a useful historical perspective for assessing adaptation measures intent on mitigating future drought impacts in Myanmar. Plain Language Summary: We developed a 226‐year‐long ring‐width regional chronology of teak by combining three site chronologies from southern Myanmar. Teak growth is mainly controlled by moisture availability during the dry season, making teak a suitable species for assessing drought variation in southern Myanmar. We reconstructed a 215‐year drought history and find prolonged droughts occurred in 1808–1823, 1837–1843, 1863–1876, 1883–1891, 1895–1901, 1908–1912, 1922–1930, 1941–1945, 1952–1963, 1976–1994, and 2010–2015. We also found a strong association between drought variability in southern Myanmar and sea surface temperatures in the Pacific and Indian Oceans, as well as the El Niño–Southern Oscillation phenomenon. The results are useful to devise necessary policies and strategies for coping with the adverse impacts of drought and protecting the livelihoods of regional populations. Key Points: The radial growth of teak in southern Myanmar is mainly limited by moisture availability during the dry seasonDry episodes in the past 200 years in southern Myanmar coincided with six major famines in India and other regional drought reconstructionsDrought variations in southern Myanmar may be linked to large‐scale climate drivers, mainly tropical SST variations and El Niño events [ABSTRACT FROM AUTHOR]

High‐elevation forests are experiencing high rates of warming, in combination with CO2 rise and (sometimes) drying trends. In these montane systems, the effects of environmental changes on tree growth are also modified by elevation itself, thus complicating our ability to predict effects of future climate change. Tree‐ring analysis along an elevation gradient allows quantifying effects of gradual and annual environmental changes. Here, we study long‐term physiological (ratio of internal to ambient CO2, i.e., Ci/Ca and intrinsic water‐use efficiency, iWUE) and growth responses (tree‐ring width) of Himalayan fir (Abies spectabilis) trees in response to warming, drying, and CO2 rise. Our study was conducted along elevational gradients in a dry and a wet region in the central Himalaya. We combined dendrochronology and stable carbon isotopes (δ13C) to quantify long‐term trends in Ci/Ca ratio and iWUE (δ13C‐derived), growth (mixed‐effects models), and evaluate climate sensitivity (correlations). We found that iWUE increased over time at all elevations, with stronger increase in the dry region. Climate–growth relations showed growth‐limiting effects of spring moisture (dry region) and summer temperature (wet region), and negative effects of temperature (dry region). We found negative growth trends at lower elevations (dry and wet regions), suggesting that continental‐scale warming and regional drying reduced tree growth. This interpretation is supported by δ13C‐derived long‐term physiological responses, which are consistent with responses to reduced moisture and increased vapor pressure deficit. At high elevations (wet region), we found positive growth trends, suggesting that warming has favored tree growth in regions where temperature most strongly limits growth. At lower elevations (dry and wet regions), the positive effects of CO2 rise did not mitigate the negative effects of warming and drying on tree growth. Our results raise concerns on the productivity of Himalayan fir forests at low and middle (<3,300 m) elevations as climate change progresses. [ABSTRACT FROM AUTHOR]

The aim of our study is to determine the pathological changes of white matter microstructure in patients with early post-stroke depression (PSD), and to investigate the association between white matter integrity examined by diffusion kurtosis imaging (DKI) and early PSD. Thirty-eight patients with acute cerebral infarction were selected, including 17 patients with depression (PSD group), and 21 patients without depression (N-PSD group). In addition, 20 normal healthy controls (NORM group) were selected. All were taken DKI scans. The white matter of the frontal lobe, temporal lobe, parietal lobe, occipital lobe, anterior limb of internal capsule, and posterior limb of internal capsule, in addition to the genu of corpus callosum and splenium of corpus callosum was selected as a region of interest (ROI). Selected parameters include fractional anisotropy (FA) and mean kurtosis (MK). Compared with N-PSD group and NORM group, FA value of the left frontal lobe and MK value of the bilateral frontal lobe, bilateral temporal lobe, and genu of corpus callosum in PSD group were decreased (P < 0.05). Our results indicated that the early PSD patients had white matter microstructure abnormalities in the frontal lobe, temporal lobe, and genu of corpus callosum. DKI provides a comprehensive brain imaging reference for detecting early microstructural damage of white matter in PSD patients, which can be used as an imaging biomarker to detect early PSD and its progression potentially. [ABSTRACT FROM AUTHOR]

Atmospheric evaporative demand can be used as a measure of the hydrological cycle and the global energy balance. Its long-term variation and the role of driving climatic factors have received increasingly attention in climate change studies. FAO-Penman-Monteith reference crop evapotranspiration rates were estimated for 644 meteorological stations over China for the period 1960–2011 to analyze spatial and temporal attribution variability. Attribution of climatic variables to reference crop evapotranspiration rates was not stable over the study period. While for all of China the contribution of sunshine duration remained relatively stable, the importance of relative humidity increased considerably during the last two decades, particularly in winter. Spatially distributed attribution analysis shows that the position of the center of maximum contribution of sunshine duration has shifted from Southeast to Northeast China while in West China the contribution of wind speed has decreased dramatically. In contrast relative humidity has become an important factor in most parts of China. Changes in the Asian Monsoon circulation may be responsible for altered patterns of cloudiness and a general decrease of wind speeds over China. The continuously low importance of temperature confirms that global warming does not necessarily lead to rising atmospheric evaporative demand. [ABSTRACT FROM AUTHOR]

Dendrochronological methods have been used to reconstruct insect outbreaks, yet the application has been scarce in the high Asia. We compiled tree-ring data from 4 host (Larix potaninii) and 4 non-host (Abies and Picea) sites in the central Hengduan Mountains, southwestern China. We assessed site-specific growth-climate responses and applied two methods to detecting larch insect defoliation events during the past 250 years. Compared with the non-host chronologies, larch trees (host) showed periodic reduction in radial growth, which may be associated with outbreaks of a larch defoliator. Synchronously, growth reductions was found for three low-elevation sites, such as during 1783–1790, 1846–1850, 1860–1865, 1873–1878, 1900–1909, 1939–1945, 1965–1970 and 1981–1986. However, these periods of outbreaks differ from those of a high-elevation site. With spectral analyses, we found 11–13 years frequency domains for three low-elevation larch chronologies, while 7–9 year peaks presented one high-elevation site. Contrastively, no significant frequency domains within the same periodicity were found in ring-width chronologies of co-occurring non-host species. We provide tree-ring evidence that larch trees growing in the central Hengduan Mountains have been infected by insect defoliators repeatedly. We suggest that appropriate approaches should be applied to correct insect-defoliation signals when using larch tree-ring data as a climatic proxy. [ABSTRACT FROM AUTHOR]

Growing evidence indicates that vulnerable carotid plaque rupture is an important cause of stroke. However, the role of novel gemstone spectral imaging (GSI) in the assessment of vulnerable carotid plaques has remained to be sufficiently explored. Therefore, the aim of the present study was to provide a comprehensive evaluation of carotid atherosclerotic plaques using both GSI imaging biomarkers and serological biomarkers, and further explore their possible roles in the atherogenic process. The present study analyzed GSI data, including calcium content of carotid atherosclerotic plaques and spectral curve slope, as well as serum high-sensitivity C-reactive protein (Hs-CRP) and monocyte chemotactic protein-1 (MCP-1) levels in patients with a carotid atherosclerotic plaque using GSI-computed tomographic angiography and immunoturbidimetry. Patients with unstable plaque exhibited a significantly lower calcium content and higher spectral curve slope than those of the stable plaque group. In addition, patients with unstable plaque exhibited an increase in Hs-CRP and MCP-1 levels compared with those of the stable plaque and normal control groups. The alteration in GSI calcium content and spectral curve slope reflects a close link between calcification and plaque instability, while aberrant Hs-CRP and MCP-1 expression are involved in the formation or development of vulnerable plaques. Taken together, the present results strongly support the feasibility of using these serological and newly identified imaging parameters as multiple potential biomarkers relevant to plaque vulnerability or stroke progression. [ABSTRACT FROM AUTHOR]

1. Stem xylem characteristics have a great impact on growth and adult stature of trees because of their role in mechanical support, long-distance water transport and whole-plant carbon allocation. Yet, despite the potential causal link between xylem traits and plant growth/adult stature, most studies have tried to link wood density, an indirect but easy to measure proxy for wood properties, to tree growth and size. 2. To determine whether xylem traits outperform wood density as predictors of tree growth and stature, we evaluated the covariation among wood density, xylem anatomical traits, tree diameter growth rate and adult stature in 40 Asian tropical tree species through principal component analyses and through bivariate correlation, both across species and across phylogenetically independent contrasts. 3. Vessel diameter exhibited a tight negative relationship with vessel frequency. Wood density showed a significant correlation with vessel diameter and density, but not with vessel fraction. Most correlations between functional traits indicate adaptive coordination, demonstrated by significant correlations between phylogenetically independent contrasts. 4. Across species, diameter growth rate and adult stature were positively correlated with vessel lumen diameter and potential hydraulic conductivity, but not with wood density. Thus, our results suggest that xylem anatomical traits that are linked to hydraulic conductivity are better predictors of tree growth rate and adult stature than wood density. 5. Synthesis. We found that xylem anatomical traits have a more significant influence on whole-plant performance due to their direct association with stem hydraulic conductivity, whereas wood density is decoupled from hydraulic function due to complex variations in xylem components. [ABSTRACT FROM AUTHOR]

Monthly mean (TEM), maximum ( Tmax) and minimum ( Tmin) surface air temperatures at 119 meteorological stations on the Yunnan Plateau (YP, Southwest China) were analysed for temporal trends and spatial variation patterns during the period 1961-2004. Linear trend analyses revealed that annual temperature over the YP increased at a rate of 0.3 °C/decade during the period 1961-2004, while warming trend of 0.33 °C/decade and 0.26 °C/decade was observed for winter and summer temperatures, respectively. Warming trends of nighttime minimum temperature are more pronounced than those of daytime maximum temperature, especially during winter season. Consequently, a decreasing trend of diurnal temperature ranges (DTR = Tmax − Tmin) was observed. Five spatial patterns of temperature variability were objectively defined by rotated empirical orthogonal function (EOF) analysis, which are associated with distinct temporal temperature variations and geographical area over the YP. Annual temperature increases were found to be most pronounced in the southern and northwestern (high-elevation) parts of the YP, whereas the hot-dry valleys along the Yangtze and Red River basins experienced cooling during the past four decades. Copyright © 2010 Royal Meteorological Society [ABSTRACT FROM AUTHOR]

Abstract: High-resolution proxy data are still scarce in the southeastern Tibetan Plateau, which limit our understanding of climatic variability before instrumental records. In this study, we developed 595-year tree ring-width chronology from Larix speciosa near the timberlines of the Gaoligong Mountains, southeastern Tibetan Plateau. Ring-width site chronologies and a well-replicated regional chronology (RC) showed significant positive correlations with warm season temperatures from May to August. Using RC as predictor, we reconstructed mean May–August temperature for the study region that extends back to A.D. 1585. Cold conditions prevailed during the periods 1600s, 1620–30, 1640–50s, 1700s, 1730–40s, 1760s, 1810–20s, 1850s, 1900–10s and 1955–70. Warm episodes occurred during 1610s, 1660–1680s, 1710–20s, 1750s, 1780–90s, 1820–40, 1920–50 and 1980–present. Spatial correlations with gridded land surface temperatures revealed that our reconstruction represents regional temperature signal for the southern Tibetan Plateau. Comparison with other tree ring-based temperature reconstructions from surrounding areas implies a high degree of confidence for our reconstruction. [ABSTRACT FROM AUTHOR]

Abstract: Variations in ring width and wood density of Picea brachytyla were used to develop high-resolution climate proxy data to extend the existing climate record in the central Hengduan Mountains, north-western Yunnan Province, China. Growth–climate response analyses showed that the total ring width (TRW) and maximum latewood density (MXD) in the sub-alpine zone are mainly influenced by summer temperature variability. Based on a MXD regional chronology derived from two high elevation sites, we developed a warm season (April–September) temperature reconstruction for the period A.D. 1750–2006. The climate/tree-growth model accounts for 41% of the instrumental temperature variance during the period 1958–2004. Warm summers occurred during 1750s, 1820–50s, 1880–1890s, 1930–1950s and 1990–present; while the periods of 1790–1810s, 1860–1870s, 1900–1920s, and 1960–1985 were relatively cold. Spatial climate correlation analyses with gridded land surface data revealed that our warm season temperature reconstruction contains a strong regional temperature signal for the Hengduan Mountain ranges. Our reconstruction successfully captured recent abrupt climatic changes and agreed in general with other tree ring-based temperature reconstructions from nearby regions on a decadal timescale. In addition, reconstructed summer temperature variations were consistent with recorded glacier fluctuations in the surrounding high mountains. [Copyright &y& Elsevier]

The article discusses the 1st International Workshop on Liana Forest Ecology, which focused on the impact of lianas on carbon and water cycling in tropical forests. Lianas, woody vines that climb trees, are increasing in abundance due to forest disturbance and climate change. The workshop brought together scientists from 14 countries to discuss topics such as liana distribution, hydraulics, life histories, reproductive phenology, and the role of lianas in carbon and nutrient cycling. The workshop highlighted the need for further research to understand the ecological consequences of increasing liana density in tropical forests. [Extracted from the article]

Climate change and other anthropogenic disturbances are increasing liana abundance and biomass in many tropical and subtropical forests. While the effects of living lianas on species diversity, ecosystem carbon, and nutrient dynamics are receiving increasing attention, the role of dead lianas in forest ecosystems has been little studied and is poorly understood. Trees and lianas coexist as the major woody components of forests worldwide, but they have very different ecological strategies, with lianas relying on trees for mechanical support. Consequently, trees and lianas have evolved highly divergent stem, leaf, and root traits. Here we show that this trait divergence is likely to persist after death, into the afterlives of these organs, leading to divergent effects on forest biogeochemistry. We introduce a conceptual framework combining horizontal, vertical, and time dimensions for the effects of liana proliferation and liana tissue decomposition on ecosystem carbon and nutrient cycling. We propose a series of empirical studies comparing traits between lianas and trees to answer questions concerning the influence of trait afterlives on the decomposability of liana and tree organs. Such studies will increase our understanding of the contribution of lianas to terrestrial biogeochemical cycling, and help predict the effects of their increasing abundance. [ABSTRACT FROM AUTHOR]

CD4+CD25+ regulatory T cells (Tregs) play an important role in maintaining immune homeostasis in multiple sclerosis (MS). Hence, we aimed to explore the therapeutic efficacy and safety of adoptive cell therapy (ACT) utilizing induced antigen-specific Tregs in an animal model of MS, that is, in an experimental autoimmune encephalomyelitis (EAE) model. B cells from EAE model that were activated with soluble CD40L were used as antigen-presenting cells (APCs) to induce the differentiation of antigen-specific Tregs from naïve CD4 precursors, and then, a stepwise isolation of CD4+CD25highCD127low Tregs was performed using a flow sorter. All EAE mice were divided into Treg-treated group (2 × 104 cells in 0.2 mL per mouse, n = 14) and sham-treated group (0.2 mL normal saline (NS), n = 20), which were observed daily for clinical assessment, and for abnormal appearance for 6 weeks. Afterward, histological analysis, immunofluorescence and real-time PCR were performed. Compared to sham-treated mice, Treg-treated mice exhibited a significant decrease in disease severity scores and reduced inflammatory infiltration and demyelination in the spinal cord. Additionally, Tregs-treated mice demonstrated higher CCN3 protein and mRNA levels than sham-treated mice. The results of this preclinical study further support the therapeutic potential of this ACT approach in the treatment of MS. [ABSTRACT FROM AUTHOR]

Summary: Understanding how intra‐annual stem growth responds to atmospheric and soil conditions is essential for assessing the effects of climate extremes on forest productivity. In species‐poor forests, such understanding can be obtained by studying stem growth of the dominant species. Yet, in species‐rich (sub‐)tropical forests, it is unclear whether these responses are consistent among species.We monitored intra‐annual stem growth with high‐resolution dendrometers for 27 trees belonging to 14 species over 5 yr in a montane subtropical forest. We quantified diel and seasonal stem growth patterns, verified to what extent observed growth patterns coincide across species and analysed their main climatic drivers.We found very consistent intra‐annual growth patterns across species. Species varied in the rate but little in the timing of growth. Diel growth patterns revealed that – across species – trees mainly grew before dawn when vapour pressure deficit (VPD) was low. Within the year, trees mainly grew between May and August driven by temperature and VPD, but not by soil moisture.Our study reveals highly consistent stem growth patterns and climatic drivers at community level. Further studies are needed to verify whether these results hold across climates and forests, and whether they can be scaled up to estimate forest productivity. [ABSTRACT FROM AUTHOR]

Tropical forests are experiencing increases in vapour pressure deficit (D), with possible negative impacts on tree growth. Tree‐growth reduction due to rising D is commonly attributed to carbon limitation, thus overlooking the potentially important mechanism of D‐induced impairment of wood formation due to an increase in turgor limitation. Here we calibrate a mechanistic tree‐growth model to simulate turgor limitation of radial stem growth in mature Toona cilitata trees in an Asian tropical forest. Hourly sap flow and dendrometer measurements were collected to simulate turgor‐driven growth during the growing season. Simulated seasonal patterns of radial stem growth matched well with growth observations. Growth mainly occurred at night and its pre‐dawn build‐up appeared to be limited under higher D. Across seasons, the night‐time turgor pressure required for growth was negatively related to previous midday D, possibly due to a relatively high canopy conductance at high D, relative to stem rehydration. These findings provide the first evidence that tropical trees grow at night and that turgor pressure limits tree growth. We suggest including turgor limitation of tree stem growth in models also for tropical forest carbon dynamics, in particular, if these models simulate effects of warming and increased frequency of droughts. [ABSTRACT FROM AUTHOR]

We reconstructed summer (June–September) minimum temperature for eastern Nepal over the past 288 years (1733–2020 CE), using a total tree-ring width chronology of Himalayan Larch (Larix griffithiana (Lindl. and Gord.)) from Kanchanjunga Conservation Area (KCA). This study is the first minimum temperature reconstruction for the eastern Himalaya region of Nepal. We examined the response of the Larix ring-width chronology to different climate variables including precipitation, and minimum, maximum and mean temperatures. Of all climatic variables, minimum temperature has the strongest correlation with tree-ring chronology. This response revealed that the growth of the L. griffithiana is limited by temperature-induced physiological behaviors during summer season. The reconstruction shows fluctuating warm and cool periods during the entire period and captures warming during recent decades. This increasing warming trend appears to be unprecedented in the context of the past 288 years. We observed short (2.5 years) and multidecadal (35, 43, 71 and 100 years) cyclicity, which suggests possible atmospheric teleconnection with the broader circulation system of Atlantic Multidecadal Oscillation (AMO). This possible teleconnection is further revealed in spatial field correlation and also supported by temporal comparison of the reconstruction with instrumental- and proxy-based AMO records. [ABSTRACT FROM AUTHOR]

The climate of Southeast Asia is influenced by the Asian monsoon systems, and inter-annual hydroclimate variability exerts a significant impact on forest ecosystems and agricultural productivity in this region. To improve our understanding of long-term drought variability, this study established ring-width chronologies for Pinus latteri trees at three sites in southern Laos. Site chronologies show negative correlations with temperature and positive correlations with precipitation, the self-calibrated Palmer Drought Severity Index (scPDSI), and the Standardized Precipitation-Evapotranspiration Index (SPEI) during the dry and wet months. The regional composite chronology shows the strongest correlation (r = 0.657, p < 0.001) with SPEI during March–August, indicating that the radial growth of P. latteri in southern Laos is primarily influenced by moisture conditions during the dry-to-wet season. A well-calibrated regression model was employed to reconstruct the variability of March–August SPEI for the period 1885–2019, explaining 43.1 % of the observed SPEI variance during the calibration period 1960–2019. The reconstruction records inter-annual to decadal-scale drought variability in southern Laos including eleven extreme dry years and seven extreme wet years. Notably, the frequency of extreme dry and wet events has increased since the 1970s. The reconstruction shows spectral peaks with periodicities of 2.3–3.1 years and displays negative correlations with sea surface temperatures (SSTs) in the tropical Pacific and Indian oceans, indicating that hydroclimatic variations in southern Laos are driven by large-scale ocean-atmospheric circulations. • Pinus latteri growth in southern Laos is mainly limited by March–August moisture. • March-to-August SPEI was reconstructed for the period 1885–2019 in southern Laos. • Drought variability is teleconnected to SSTs in tropical Pacific and Indian oceans. • Extreme dry and wet events have increased in frequency since the 1970s. [ABSTRACT FROM AUTHOR]

• We studied stem growth and xylogenesis of Toona ciliata and their climate drivers. • Stem radial increment of T. ciliata mainly occurred during March to October. • T. ciliata trees at a wetter site showed higher rates and longer duration of growth. • Stem growth and xylogenesis of T. ciliata were mainly controlled by precipitation. • We highlights the strong influence of soil water capacity on tropical tree growth. Climate extremes will increasingly influence ecosystem productivity of tropical forests, but little is known about their effects on tree stem radial growth, a major component of forest productivity. To analyze the role of climatic drivers and local site differences on tree growth at sub-annual timescales, we studied the timing, magnitude and climatic drivers of stem growth and xylem formation at two tropical forest sites with contrasting soil water availability in southwestern China. We combined high-resolution point dendrometer recordings and microcoring to investigate intra-annual stem radius variation and xylem formation of Toona ciliata over three consecutive years (2018–2020). Stem radial increment of T. ciliata derived from dendrometer data showed distinct seasonal patterns, with growth mainly occurring during March to October. The start day of stem radial growth coincided with the occurrence of the cell enlarging phase, and its end day occurred concomitantly with the cessation of cell enlarging as identified from microcores. Toona ciliata trees at the tropical ravine rainforest site with higher soil water availability showed higher mean annual stem radial increment, higher daily growth rates, and longer duration of xylem productivity than that at the tropical karst forest site. Weekly stem radial growth rates increased with precipitation and air temperature at the wetter ravine rainforest site, while relative humidity had a positive effect at the drier karst forest site. Our findings indicate that drought stress advances and shortens the growing season for T. ciliata. Our study highlights the strong influence of soil water capacity mediating the impact of climate, so response to drought is site-specific, which should be considered in growth models. [Display omitted] [ABSTRACT FROM AUTHOR]

• Pine radial growth across Southwest China was limited by moisture availability • Moisture sensitivity of P. kesiya species decreased from dry to humid sites • Temperature sensitivity of P. yunnanensis decreased from cold to warm sites • Climate sensitivity of two pine species varies with site environmental conditions A better understanding of tree growth-climate sensitivity across regions and species may reduce uncertainties in simulating forest carbon budgets. We studied the spatial heterogeneity of growth-climate sensitivity of Pinus yunnanensis and Pinus kesiya across temperature and moisture gradients in the complex mountain regions of Southwest China. We developed tree ring-width chronologies from 22 sites for P. yunnanensis and 20 sites for P. kesiya , totaling 903 trees (1684 cores). We applied generalized additive mixed models (GAMMs) on basal area increment (BAI) series to remove the age and size effects on tree growth, and correlated BAI residual chronologies with climate variables. Radial growth of P. yunnanensis and P. kesiya at most sites (> 75%) were positively correlated with precipitation and one-month Standardized Precipitation-Evapotranspiration Index (SPEI1) during the early growing season. In contrast, high precipitation and SPEI1 during the late growing season reduced tree growth of both pine species. The growth-climate sensitivity of both pine species varied along the temperature and moisture gradients, i.e., moisture sensitivity of tree growth decreased along a dry-to-humid moisture gradients for P. kesiya during early growing season, whereas temperature sensitivity of P. yunnanensis shifted from positive (beneficial) to negative (limitative) along cold-to-warm gradients. Our results indicate that the growth-climate sensitivity of both pine species varies with site-specific environmental conditions. These findings contribute to improve our understanding about the spatial patterns of tree growth-climate responses of these economically important conifer species in Southwest China. [ABSTRACT FROM AUTHOR]

Aim Xylem structures are closely related to a tree's hydraulic efficiency and mechanical stability, both of which affect the life history and ecological strategy of a species. Although mechanical strength and hydraulic capacity can be shaped by the environment, no such associations between hydraulic efficiency and climatic variables have been reported across a wide range of tree species. Location Yunnan, south-west China. Methods We compiled a data set for vessel density, vessel diameter ( D), potential hydraulic conductivity ( Kp), wood density ( WD), modulus of rupture ( MOR) and modulus of elasticity ( MOE) from 316 angiosperm tree species. Our objective was to examine the correlations among xylem traits and climatic variables. We hypothesized that both hydraulic efficiency and mechanical strength would vary along climatic gradients, but that a trade-off would occur between them. Results All xylem traits varied significantly across species, but the magnitudes of variation were greater for vessel traits than for mechanical properties. Values for Kp and D increased with mean annual temperature ( MAT) in both evergreen and deciduous trees, but they were significantly correlated with aridity index ( AI) in evergreen species only. Both WD and MOR were significantly correlated with MAT only in evergreen trees. MOR decreased with increasing AI in the evergreens, but not in deciduous trees. These findings indicated that xylem development in evergreens is more sensitive to environmental changes than in deciduous trees. However, stem hydraulic traits are independent of mechanical properties. Main conclusions Consistent with our hypothesis, both hydraulic efficiency and mechanical strength of angiosperm trees are influenced by the environment, with temperature having a more important effect on hydraulic efficiency than precipitation. However, no trade-off exists between efficiency and strength. This absence of a link is explained because angiosperms have xylem tissue that specifically functions in either mechanical strength or water transport. [ABSTRACT FROM AUTHOR]

• Nitrogen allocation to each organ and nitrogen resorption of an epiphytic orchid were quantified. • The leaf accounted for the largest proportion of both exogenous and pseudobulb-stored nitrogen among all organs. • High dependence of reproduction process on the pseudobulb-stored nitrogen was observed regardless of exogenous nitrogen addition. As the main organ for storing water and nutrients, pseudobulbs are of central importance to the growth and survival of orchids. Quantifying nitrogen allocation and resorption of pseudobulbs is important for understanding the survival and adaptation strategies of orchids, but studies in this area are still lacking due to the complicated integration effect between pseudobulbs of different ages. In this study, nitrogen allocation to each organ and nitrogen resorption of Pleione aurita , an epiphytic orchid characterized by annually renewed pseudobulbs, were examined quantitatively under three nitrogen levels using 15N labeling. We found the old pseudobulb can act as a sink for exogenous nitrogen, although it had a much lower sink activity than the developing new pseudobulb. The single leaf accounted for the largest proportion of both exogenous and pseudobulb-stored nitrogen among all organs and in three nitrogen treatments, and the fruit tended to use pseudobulb-stored nitrogen preferentially regardless of exogenous nitrogen supply. The resorption of nitrogen in the leaf and pseudobulb was highly efficient, but decreased with increasing nitrogen supply. Overall, positive biomass accumulation was only observed in plants with exogenous nitrogen supply, while all fruit-bearing plants lost more than 30% of their biomass after a growing season regardless of nitrogen supply. The P. aurita plants exhibited a strong low nitrogen tolerance with only a slight loss of biomass for those nitrogen deficient and fruitless plants. Surprisingly, an increase in the nitrogen pool of the whole-plant was always observed regardless of biomass loss in fruit-bearing plants after nitrogen addition. Our results suggest an important role of the pseudobulb in the nitrogen economy of P. aurita , and the high dependence of the reproduction process on the pseudobulb-stored nitrogen. The findings will help to understand the adaptive strategies of orchids, and contribute to the conservation of endangered species. [ABSTRACT FROM AUTHOR]

Cypripedium subtropicum is the only known winter-green species in the genus Cypripedium , whereas the other nearly 50 species keep their leaves for less than half the year. Life form has an important effect on carbon acquisition and adaptation of plants. However, the physiological mechanism behind it remains unclear. In this study, we investigated vegetative anatomy and photosynthetic performance of C. subtropicum across with its leaf ages. These anatomical and photosynthetic traits were also compared with typical Cypripedium spp. and other members of subfamily Cypripedioideae. The obtained results confirmed that this species exhibited many characters of shade plants, such as thin leaves, extremely low photosynthetic rate and light saturation point and high chlorophyll content. Unlike the strategy adopted by typical Cypripedium spp. that quickly achieve annual carbon gain with a high assimilation rate in a short growing season, C. subtropicum obtains its carbon through a low assimilation rate but a much longer leaf lifespan. The local climate and favourable light condition guaranteed the comparable carbon income in winter to compensate for its low photosynthetic capacity. The long-lived, thin leaves of C. subtropicum , differing from the long-lived, thick leathery leaves in conduplicate-leaved genera, represent a distinct adaptive strategy in subfamily Cypripedioideae. Our findings shed light on the divergent and convergent evolution in slipper orchids, and we hope these findings will contribute to the conservation of such an endangered orchid. [ABSTRACT FROM AUTHOR]

• Leaf mass-based photosynthetic rate was more enhanced in evergreen trees with eCO2. • Branch hydraulic efficiency was more enhanced in deciduous trees with eCO2. • eCO2 strengthens the coordination of stem hydraulics with leaf gas exchange. Elevated CO 2 concentration (eCO 2) in the atmosphere is expected to impact plant water relations and growth in several ecosystems across the globe. However, we still know little about such impact on tree species in subtropical regions. The present study investigated the impact of eCO 2 on leaf gas exchange, nitrogen and phosphorus concentrations, leaf and stem hydraulic conductivity, and growth of seedlings of four evergreen and four deciduous tree species from a subtropical forest in Southwest China. We found that both evergreen and deciduous tree species at eCO 2 had higher leaf area-based photosynthetic rates and lower leaf stomatal conductance. Further, leaf mass-based photosynthetic rate was more enhanced in evergreen than in deciduous trees at eCO 2. Biomass of evergreen and deciduous species was significantly higher at eCO 2 , with large species-specific variation among the evergreen species. Leaf-specific hydraulic conductivity was more enhanced in deciduous tree species than that of evergreen tree species with eCO 2 , which was mainly driven by the increase of biomass at eCO 2. Interestingly, eCO 2 significantly strengthened the coordination of stem hydraulic conductivity with leaf-gas exchange, leaf phosphorus concentration, and plant biomass across evergreen and deciduous species. These results highlighted greater enhancement of photosynthesis and greater species-specific variation in biomass at eCO 2 for evergreen species compared to deciduous species, and stronger hydraulic-photosynthesis correlations at eCO 2 than at aCO 2 for tree species from subtropical forests. The present study provides important insights on the potential impacts of eCO 2 on plant eco-physiology, growth and forest succession in a subtropical forest under global climate change. [ABSTRACT FROM AUTHOR]

Karst and non-karst forests occur in the same region in south-west China, but the soil water and mineral nutrients availability are different between the forests. Our hypothesis was that the leaves of karst trees would be better adapted to dry, nutrient-poor conditions than those of trees in a nearby non-karst forest. We compared the gas exchange, anatomical characteristics and mineral nutrient concentrations in leaves from 21 tree species in a tropical karst forest and 19 species in a nearby non-karst forest in south-west China. We found that the leaves of karst trees had higher P concentrations, photosynthetic capacity and water use efficiency, and greater adaxial and abaxial epidermis thickness than leaves of non-karst forest trees. Evergreen and deciduous trees differed more significantly in leaf functional traits in the karst forest than in the non-karst forest. The leaf palisade : spongy mesophyll thickness ratio was positively correlated with stomatal conductance and negatively correlated with photosynthetic water use efficiency in the karst forest but not in the non-karst forest. Our findings indicate that karst forest trees are more conservative in water use, whereas soil P deficiency could be a major limiting factor for the growth of non-karst forest trees. Karst habitats cover extensive areas of south-west China; however, we know little about the adaptive mechanisms of plants there. We compared leaf functional traits between a karst forest and a nearby non-karst forest and found that karst trees had more conservative water use and higher leaf P concentrations. Our results show that trees in the karst forest are structurally and physiologically acclimated to the dry, nutrient-rich soil. [ABSTRACT FROM AUTHOR]

Abstract Knowledge of the long-term frequency and intensity of drought events in an area is crucial since drought has adverse effects on natural ecosystems, food security, economy, society, and civilization. We developed a 405-year long (1611–2015C.E.) tree-ring chronology of Pinus wallichiana (Blue pine) from the Dolpo area of the trans–Himalayan region in Nepal to reconstruct drought variability in this remote region. Correlation analysis revealed significant positive relationships with February–August precipitation, but negative correlations with temperature. High positive correlations with the self-calibrated Palmer drought severity index (scPDSI) confirmed that moisture availability during the early growing season and full growing season is the primary limiting factor for Blue pine tree growth in the trans–Himalayan region. We used a linear regression model between our tree-ring record and regional climate data to reconstruct a 319-year long (1697–2015C.E.) February–August scPDSI series. This reconstruction accounts for 39.4% of the total variance in actual scPDSI over the calibration period (1957–2015C.E.). The reconstruction showed that the area was under slightly dry conditions for most of the reconstructed period, with below normal scPDSI values. An extreme drought was observed in the year 1707. Also, the years 1705, 1706, 1784, 1786, 1809, 1810, 1813, 1821, 1849, 1858, 1861, 1909, 1967, 2006, and 2009 experienced severe drought conditions. Consecutive years with moderate drought were 1702–1706, 1783–1789, 1796–1798, 1812–1814, 1816–1827, 1846–1848, 1856–1864, 1873–1877, 1879–1882, 1899–1901, 1908–1911, and 1967–1968. Three historic mega-drought events that occurred in Asia were also captured in our reconstruction: Strange Parallels drought (1756–1768), the East India drought (1790–1796), and the late Victorian Great Drought (1876–1878). Very few wet years (1776–1979, 1989, 1991, and 2003) were observed during the reconstruction period. Power spectrum analysis revealed drought variability at frequencies of 2.0–2.5, 3.0, 12.0, and 128 years, suggesting that drought in the region might be linked to broad-scale atmospheric-oceanic variabilities such as the El Niño-Southern Oscillation (ENSO) and the Atlantic Multidecadal Oscillation (AMO). The results not only improve our understanding on regional drought variability, but are also helpful to make decisions on adaptation measures for protecting the marginal communities of the trans–Himalayan region from the anticipated adverse impacts of future droughts. Highlights • Radial growth of Pinus wallichiana is mainly limited by moisture availability. • February-August scPDSI during 1697–2015 C.E. was reconstructed for trans-Himalaya region • The trans-Himalayan region experienced prolonged drought during 19th and 20th century. • Drought variability in the trans-Himalayan regions has teleconnections with ENSO and AMO. [ABSTRACT FROM AUTHOR]

High-resolution palaeoclimate proxy records have been lacking for the subtropical region of southwest China. To gain insights into hydroclimate variability in central Yunnan Province, we constructed a tree ring-width chronology of Tsuga dumosa from the Wuliang Mountain area. Correlation analysis shows that moisture availability is predominantly the limiting factor on radial growth, particularly during the spring-early summer season. Using a well-calibrated regression model (R2 = 0.36, p < 0.001), we reconstructed the March–June Standardized Precipitation-Evapotranspiration Index (SPEI) for the period from 1826 to 2020 CE. Eleven extreme drought years (1860, 1897, 1958, 1960, 1979, 1984, 1987, 2006, 2010, 2013, and 2019) were identified, with most of them confirmed by historical evidence. The reconstruction series shows inter-annual to inter-decadal variations and an increasing occurrence of severe dry or wet events in the recent past, particularly during the last 50 years. Our drought reconstruction series shows high frequency cycle of 2–8 years. Spatial correlations indicate that our drought reconstruction captures hydrological signals over a larger area. In line with this, the reconstructed dry periods exhibit broad consistency with other tree-ring based drought reconstructions conducted in nearby regions. Our findings demonstrate the potential of tree-ring proxies for hydroclimate reconstruction in the subtropical areas of southwest China and provide crucial information for evaluating long-term climate change in this region. • Radial growth of T. dumosa in central Yunnan is mainly limited by spring-early summer moisture availability. • The two-century SPEI reconstruction identified eleven extreme drought years that align with historical records. • There has been a notable increase in the occurrence of severe dry or wet events in recent decades. [ABSTRACT FROM AUTHOR]

• The growth of Abies spectabilis is mainly limited by low temperatures during the growing season. • Low spring moisture availability reduces Himalayan fir growth at low- to middle-elevations. • Growth rates of Himalayan silver fir trees were declining at low- to middle-elevations since 1980s. The impacts of rapid climate change in the Himalayan region on growth and sensitivity of tree species across their entire elevation distribution range are not well understood. This study investigates the growth and climate sensitivity of the endemic species Himalayan silver fir (Abies spectabilis , D.Don) along an elevation gradient in the sub-alpine belt in the Mt. Everest region. We developed tree ring-width chronologies, spanning 98 to 310 years, from six sites along an elevation gradient (3400–4100 m a.s.l.). The growth of Himalayan silver fir is primarily limited by low temperatures during the growing season and moisture availability during spring. Significant positive correlations were found between tree growth and mean, minimum and maximum temperatures for most parts of the vegetation period except spring. In contrast, significant positive correlations are apparent for precipitation, self-calibrated Palmer drought severity index (scPDSI), and standardized precipitation-evapotranspiration index (SPEI) during the spring season (March–May) at most of the elevations except for the upper treeline site. Thus, low summer temperatures are the primary limiting factor at all investigated elevations, while moisture supply during spring triggers growth variations at low- to mid-elevations. The long-term growth trends of A. spectabilis have decreased at low- to mid-elevation sites but increased at the treeline during the period 1981–2011. Warming and intensified moisture stress during spring could have negative effects on tree growth, potentially resulting in growth decline and forest dieback at middle and low elevations. These findings emphasize the importance of understanding the vulnerability of forests at middle and low elevations to future climate change. [ABSTRACT FROM AUTHOR]

To better understand long-term drought variations in the central Himalaya, we developed new tree-ring width chronologies of Himalayan spruce ( Picea smithiana (Wall.) Boiss.) from three sites in the north-western Nepal. The local site chronologies showed high cross correlations and similar growth-climate responses to regional spring drought variability. We thus combined all site chronologies into a regional composite (RC) standard chronology that spans 516 years (1498–2013 CE). The RC chronology showed significant positive (negative) correlations with spring (March–May) precipitation (temperature) variability. Meanwhile, RC chronology showed the highest correlation with spring self-calibrating Palmer drought severity index (scPDSI, r = 0.652, p < 0.001), indicating that radial growth of P. smithiana is strongly limited by spring moisture availability. Using RC chronology, we reconstructed the spring drought variability for the period 1725–2013, which explained 42.5% variance of the actual scPDSI during the calibration period 1957–2012. Our reconstructed spring drought variability in the central Himalaya showed consistent wet-dry episodes with other regional drought and precipitation reconstructions from the Himalaya and nearby regions. Spectral peaks and spatial correlation analysis indicate that spring drought variability in the central Himalaya may be linked to large scale climatic drivers, mainly Atlantic Multidecadal Oscillation activities due to sea surface temperatures variation in the Atlantic Ocean. Our reconstruction revealed a continuous shift toward drier conditions in the central Himalaya since early 1980s that coincide with continental-scale warming and reduced spring precipitation in the central Himalaya. [ABSTRACT FROM AUTHOR]

Tropical lianas deploy most of their leaves towards the top of the forest canopy, whereas trees exhibit a more stratified crown. Forest canopies are often exposed to hot and windy conditions, and how lianas cope with the extremely high transpirational demands under these environments remains unknown., We investigated stem hydraulic properties, leaf drought tolerance, diurnal changes in leaf and stem water potentials (Ψleaf and Ψstem), stomatal conductance ( gs), photosynthetic rate, sap flow and stem native percentage loss of conductivity ( PLC) for four liana species in a tropical forest in southwest China. Five co-occurring tree species were also selected for comparison., Lianas reached maximal transpiration at a relatively lower vapour pressure deficit (<1 kPa) than did co-occurring trees, suggesting vigorous photosynthesis during the morning. However, liana gs declined markedly over the day, with low gs at midday and afternoon. Lianas generally had higher stem sapwood-specific conductivity and maximum sap flux density but were less tolerant to drought-induced cavitation than were evergreen trees. Both lianas and trees lost leaf turgor in the top canopy at midday, but lianas lost leaf turgor earlier (∼2 h) than trees., Seven of eight species exhibited midday increases in PLC when xylem tensions were released to −0·3 to −0·5 MPa for PLC measurements. On average, lianas experienced high PLC (35·9%), along with a greater degree of disequilibrium between leaf and stem water potentials than trees (ΔΨstem-leaf: 1·37 MPa vs. 0·75 MPa) during the day. Earlier stomatal closure and efficient water transport may help lianas maintain higher Ψstem than trees despite having similar Ψleaf., Our results provide evidence that physiological regulation and efficient water transport mediate daily water relations in tropical lianas and may explain how lianas operate efficiently in tropical seasonal forests. Further studies involving a broader range of species are needed to confirm our findings. [ABSTRACT FROM AUTHOR]

• Our approach successfully removed the effect of insect outbreak on the tree-ring width chronology. • The approach improved growth-climate relationships, especially for summer (June-September) temperatures. • 313-year-long summer temperature reconstruction showed a wiggly trend before the 1980 s before experiencing a rapid warming trend. • The insect outbreaks can result in biased climate prediction, especially in cold periods. Insect outbreaks are proven to harm trees, reducing their biomass accumulation due to the defoliation of leaves during the growing season. Various defoliators are responsible for the formation of extremely narrow tree rings in different tree species. In climate reconstructions based on tree-ring width, such narrow rings are often considered as noise, because their formation is not entirely caused by climatic conditions. Thus, the impact of defoliators should be removed (nullified) for unbiased climate reconstructions. This study mainly describes a statistical approach to disentangle the effects of Larch budmoth(LBM) (Zeiraphera diniana) and climate for an unbiased temperature reconstruction in the Bai-Ma mountain area in Southwest China using Larix potaninii. After applying our new approach, growth-climate relationships improved significantly (p < 0.05), especially with minimum temperature during the growing season (June-September). The resulting temperature reconstruction (BTmin) covers the period 1712–2020 CE (313 years). Our final temperature reconstruction for the Bai-Ma area showed a wiggly trend from 1712 to 1980, with some cool periods (1791–1853 and 1888–1930) and warm episodes (1724–1745, 1854–1887, 1950–1967). During the recent 50 years, BTmin reveal an alarming warming trend of up to 0.4 °C per decade. We also observed a strong coherency of BTmin with regional temperature series. Furthermore, we detected a differential effect of various climate modes, with the most substantial impact of the Atlantic Multidecadal Oscillation (AMO) on BTmin (p < 0.01). Interestingly, the Pacific Decadal Oscillation (PDO) showed a coupled effect along with AMO on BTmin. As revealed in this study, removing the LBM effect improved the chronology's climate sensitivity, leading to a more robust transfer function and in terms of insect infestations unbiased climate reconstructions. Thus, it is recommended to check ring-width data for any periodicity potentially related to insect outbreaks and correct the original data before using tree-ring chronologies for climate reconstruction. [ABSTRACT FROM AUTHOR]

The pseudobulb is a storage organ for water and nutrients that plays a crucial role in the growth and survival of epiphytic orchids. However, the role of water and metabolites in pseudobulb during adaptation to environmental stress are rarely detected through control experiments. In the present study, water-related physiological traits and metabolite changes in the pseudobulbs at the flowering stage and full leaf expansion stage for Pleione aurita were investigated after drought stress and recovery treatments. We found that the composition of non-structural carbohydrates (starch vs. soluble sugar) varied over the lifetime of pseudobulbs, and older pseudobulbs stored more water, whereas younger pseudobulbs stored more dry matter. When plants were subjected to drought stress and subsequent recovery, multiple metabolites in the pseudobulbs including non-structural carbohydrates, flavonoids, phenolic acids, as well as amino acids and their derivatives responded positively to these water level fluctuations. For those metabolites that differently accumulated in both stress and recovery processes, old pseudobulbs contained a higher number of these key metabolites than did the connected younger pseudobulbs. In addition, young and old pseudobulbs use different metabolic pathways to both respond and recover to drought. These results indicate that orchid pseudobulbs cope with water level fluctuations by mobilizing metabolite reserves and that pseudobulbs of different ages exhibit different physiological and metabolic responses to drought stress. These findings broadens our understanding of the role pseudobulbs play in the survival of orchids growing in epiphytic habitats. • Multiple metabolites in pseudobulb responded positively to water level fluctuations. • Old pseudobulb donated more key metabolites than its connected young pseudobulb. • Pseudobulbs of different ages use different metabolic pathways when respond and recover to drought. [ABSTRACT FROM AUTHOR]

Cardiac myxoma (CM) is an important etiology of stroke in young adults, but studies on CM-related ischemic stroke (CM-IS) are limited and conflicting. Hence, we investigated clinical characterizations, risk factors of CM-IS, and short-term survival after surgical resection. We performed a retrospective analysis of data from all CM patients at three referral management centers and conducted follow-up examination. Among 414 CM patients, 402 were recruited for further analysis, including 54 patients with CM-IS and 348 patients with CM without stroke (Non-stroke). In the acute phase, patients presented with NIHSS 3 (interquartile range: 0–10) and clinical presentation comprising neurological, cardiac and constitutional symptoms. Multivariate analysis showed that the factors associated with an increased risk of CM-IS were tumor width < 30 mm [OR = 2.652, 95% CI: 1.061–6.627, P = 0.037], tumors with high-mobility (OR = 2.700, 95% CI: 1.357–5.371, P = 0.005), thrombus on the tumor surface (OR = 1.856, 95% CI: 1.003–3.434, P = 0.049), and lower B-type natriuretic peptide (BNP) levels (OR = 0.995, 95% CI: 0.989–0.999, P = 0.047). The overall three-year survival rate was 95.7% (95% CI: 94.9–96.5) in CM-IS patients who underwent surgery. CM-IS patients had mild or moderate neurologic deficits with various presentations at disease onset. Narrower tumor width, tumors with high-mobility, thrombus on the tumor surface, and lower BNP levels are potential predictors of CM-IS development. Surgical removal of CM is safe and efficacious in patients with CM-IS. [Display omitted] • This is a retrospective, multicenter, case-control study in patients with cardiac myxoma-related ischemic stroke (CM-IS). patients with CM-IS have mild-to-moderate neurologic deficits at the onset of the disease. • Narrower tumor width, tumors with high-mobility, thrombus on the tumor surface, and lower BNP levels are potential predictors of CM-IS development. • Prolonged symptoms to operation time (SOT) is a potential predictor of CM-IS recurrence. • Surgical removal of cardiac myxoma is safe, efficacious, and definitive in patients with CM-IS. [ABSTRACT FROM AUTHOR]

• The evolution of lignified xylem allowed for the efficient transport of water under tension, but also exposed the vascular network to the risk of gas emboli and the spread of gas between xylem conduits, thus impeding sap transport to the leaves. A well-known hypothesis proposes that the safety of xylem (its ability to resist embolism formation and spread) should trade off against xylem efficiency (its capacity to transport water). • We tested this safety-efficiency hypothesis in branch xylem across 335 angiosperm and 89 gymnosperm species. Safety was considered at three levels: the xylem water potentials where 12%, 50% and 88% of maximal conductivity are lost. • Although correlations between safety and efficiency were weak (r² < 0.086), no species had high efficiency and high safety, supporting the idea for a safety-efficiency tradeoff. However, many species had low efficiency and low safety. Species with low efficiency and low safety were weakly associated (r² < 0.02 in most cases) with higher wood density, lower leaf- to sapwood- area and shorter stature. • There appears to be no persuasive explanation for the considerable number of species with both low efficiency and low safety. These species represent a real challenge for understanding the evolution of xylem. [ABSTRACT FROM AUTHOR]

Lianas exhibit peak abundance in tropical forests with strong seasonal droughts, the eco-physiological mechanisms associated with lianas coping with water deficits are poorly understood., We examined soil water partitioning, sap flow, and canopy eco-physiological properties for 99 individuals of 15 liana and 34 co-occurring tree species in three tropical forests that differed in soil water availability., In the dry season, lianas used a higher proportion of deep soil water in the karst forest ( KF; an area with severe seasonal soil water deficit ( SSWD)) and in the tropical seasonal forest ( TSF, moderate SSWD), permitting them to maintain a comparable leaf water status than trees in the TSF or a better status than trees in the KF. Lianas exhibited strong stomatal control to maximize carbon fixation while minimizing dry season water loss. During the dry period, lianas significantly decreased water consumption in the TSF and the KF. Additionally, lianas had a much higher maximum photosynthetic rates and sap flux density in the wet season and a lower proportional decline in photosynthesis in the dry season compared with those of trees. , Our results indicated that access to deep soil water and strong physiological adjustments in the dry season together with active wet-season photosynthesis may explain the high abundance of lianas in seasonally dry forests. [ABSTRACT FROM AUTHOR]

• Tree growth in the Karnali river catchment was sensitive to moisture availability. • March–July streamflow was reconstructed for Karnali River Basin since 1628 CE. • An increasing frequency of extreme events was found during the recent decades. • Streamflow variability of the Karnali river is mainly linked with ENSO and PDO. The Karnali River is one of the major transboundary rivers of the Nepalese central Himalaya and a major tributary of the Ganges River. In order to investigate regional historical hydroclimate variability, we compiled eleven tree ring-width chronologies based on 354 exactly dated tree cores from five coniferous species for the Karnali River catchment. The chronologies were moisture-sensitive and the composite chronology was significantly correlated with spring-to-early summer (March–July) (R = 0.67, P < 0.001) discharge at the Chisapani gauging station. The robust calibration (R2 = 0.45, 1962–2010) enabled us to reconstruct March–July streamflow variability of Karnali River Basin (KRB) over the past four centuries. The streamflow reconstruction showed prolonged pluvial periods during 1650–1661, 1711–1718, 1723–1731, 1824–1831, 1877–1889, 1924–1931, and 1971–1981, while prolonged low-flow periods occurred during 1639–1649, 1689–1710, 1753–1769, 1777–1784, 1803–1823, 1867–1876, 1942–1959, and 1963–1970. Our reconstructed March–July streamflow series correlated positively with the seasonally averaged drought index and precipitation in the central-west Himalayan region and vicinities. The streamflow reconstruction revealed an increasing frequency of extreme low-flow and pluvial events in the central-west Himalayan region, especially during the past century. We found short (2.1–3.3, 6.2–6.3, and 8.5–8.7 years) to medium (12.2–12.5 years) periodicities in the reconstructed streamflow series, implying teleconnections with broad-scale climate modes like the El Niño-Southern Oscillation (ENSO) and the Pacific Decadal Oscillation (PDO). Our Karnali River streamflow reconstruction represents an update of regional hydroclimate variability, which may serve as a useful reference for water resource management and appropriate water-use policies in the context of current and future climate change. [ABSTRACT FROM AUTHOR]

• The subtropical forest has a high water conservation capacity. • High spatial-temporal differentiations in water use of co-occurring canopy trees. • Trees of similar ages showed interspecific competition for water under drought. • Large and middle-sized trees depended on water from both shallow and deep soil layers. • Seedlings relied on soil water from shallow depths all the time. Southern China houses the largest subtropical broadleaf forest in the world, with abundant rainfall brought by the Pacific and Indian monsoons. As the intensity and frequency of drought are increasing, understanding the water use patterns of co-occurring trees is a key issue for predicting the response of these subtropical forests. The water uptake depths and water use-related leaf traits of three dominant canopy tree species at different ages (DBH) were investigated in a subtropical forest (2018–2019). We found that the δ 2H and δ 18O of various water pools, such as fog, soil, stream, lake, and groundwater, plotted almost entirely on the local meteoric water lines (2018: y = 8.2x +11.5; 2019: y = 8.1x +10.4). This result suggested that water bodies within the forest experienced minor evaporation. An interspecific partitioning of water acquisition was detected among tree species of similar ages in 2018 (a regular year), but they tapped soil water from similar depths after experiencing drought event in 2019. Most large (DBH > 50 cm) and middle-sized (15 cm < DBH < 30 cm) trees switched their major water sources from shallow (2018) to deep (2019) soil layers, whereas the seedlings (DBH < 2 cm) relied on shallow soil water during the study periods. The water use patterns of different trees were related to the leaf-level intrinsic water use efficiency (WUE i) and specific leaf area (SLA). The spatial-temporal differentiation of water use in regular years can facilitate plant co-existence among the canopy trees, but the interspecific competition for similar water sources in drought years may increase the risk of tree dieback in the subtropical forests. These fingdings provide a mechanistic explanation for the high diversity of subtropical forests in China from the perspective of differentiation in plant water use. [ABSTRACT FROM AUTHOR]

The Himalayan region has already witnessed profound climate changes detectable in the cryosphere and the hydrological cycle, already resulting in drastic socio-economic impacts. We developed a 619-yea-long tree-ring-width chronology from the central Nepal Himalaya, spanning the period 1399–2017 CE. However, due to low replication of the early part of the chronology, only the section after 1600 CE was used for climate reconstruction. Proxy climate relationships indicate that temperature conditions during spring (March–May) are the main forcing factor for tree growth of Tsuga dumosa at the study site. We developed a robust climate reconstruction model and reconstructed spring temperatures for the period 1600–2017 CE. Our reconstruction showed cooler conditions during 1658–1681 CE, 1705–1722 CE, 1753–1773 CE, 1796–1874 CE, 1900–1936 CE, and 1973 CE. Periods with comparably warmer conditions occurred in 1600–1625 CE, 1633–1657 CE, 1682–1704 CE, 1740–1752 CE, 1779–1795 CE, 1936–1945 CE, 1956–1972 CE, and at the beginning of the 21st century. Tropical volcanic eruptions showed only a sporadic impact on the reconstructed temperature. Also, no consistent temperature trend was evident since 1600 CE. Our temperature reconstruction showed positive teleconnections with March–May averaged gridded temperature data for far west Nepal and adjacent areas in Northwest India and on the Southwest Tibetan plateau. We found spectral periodicities of 2.75–4 and 40–65 years frequencies in our temperature reconstruction, indicating that past climate variability in central Nepal might have been influenced by large-scale climate modes, like the Atlantic Multi-decadal Oscillation, the North Atlantic Oscillation, and the El Niño-Southern Oscillation. [ABSTRACT FROM AUTHOR]