Guobao Xu

Chinese Academy of Sciences | CAS · Northwest Institute of Eco-Environment and Resources

It is important to understand the history and dynamics of climate in a transitional region between areas with different atmospheric circulation patterns, where the vegetation and ecosystems are vulnerable to environmental change. We investigated variations in the long-term oxygen isotope composition (δ18O) in tree rings of Qinghai spruce (Picea cra...

The jet stream is an important dynamic driver of climate variability in the Northern Hemisphere mid-latitudes1–3. Modern variability in the position of summer jet stream latitude in the North Atlantic–European sector (EU JSL) promotes dipole patterns in air pressure, temperature, precipitation and drought between northwestern and southeastern Europ...

Climate warming, rising atmospheric CO2 concentration (Ca) and nitrogen (N) availability are exerting profound impacts on global forest ecosystems, particularly in high-altitude mountains. This study investigated the tree-growth dynamics of timberline Larix chinensis in the Taibai Mountain, central China, to explore its ecophysiological responses t...

Terrestrial vegetation growth is stimulated by rising atmospheric CO2 concentration, a warmer climate, and increased soil nutrient availability. However, as plants age, progressive nutrient limitation is known to occur, especially in mature forests where soil nitrogen is deficient. Yet the long-term growth response of mature trees to rising CO2 acc...

Understanding the impact of management upon post-drought tree growth recovery and drought legacy effects is among the fundamental challenges hindering the improvement of forest conservation strategies in the face of increasingly frequent, longer, and intensified extreme droughts under ongoing climate change. Yet surprisingly little is known to date...

Drought is the primary limiting factor for tree growth in water‐stressed regions through its effects on xylem development. In this study, we developed intra‐annual series of tree‐ring stable carbon (δ¹³C) and oxygen (δ¹⁸O) isotopes from Chinese pine (Pinus tabuliformis) to investigate the ecophysiological responses of trees to drought during the gr...

Recently, forests in the Tianshan Mountains have shown a marked decline in growth and an increased mortality rate because of the more frequent and severe effects of extreme drought, which threatens the ecosystem services they provide. To achieve forest conservation and sustainable development benefits, it is crucial to understand the post-drought r...

Climate warming may induce growth decline in warm-temperate areas subjected to seasonal soil moisture deficit, whereas increasing atmospheric CO 2 concentration (C a) is expected to enhance tree growth. An accurate understanding of tree growth and physiological processes responding to climate warming and increasing C a is critical. Here, we analyze...

Climate warming has profoundly altered the status of permafrost and has caused extensive permafrost degradation in the Northern Hemisphere. However, long-term observations investigating the hydrological dynamics of permafrost and its ecological effects on plant growth are lacking. Previous studies have reported tree-ring stable hydrogen isotope rat...

Stable hydrogen isotope ratios of wood lignin methoxy groups (δ²HLM values) of mid-latitude forests are increasingly applied to reconstruct δ²H patterns in precipitation of regional to sub-continental scales. To date, the knowledge about the effect of topographic factors on δ²HLM values is still scare, especially in the biogeographic boundary. We m...

Tree-ring intra-annual stable isotopes (δ13C and δ18O) are powerful tools for revealing plant ecophysiological responses to climatic extremes. We analyzed interannual and fine-scale intra-annual variability of tree-ring δ13C and δ18O in Pinus massoniana from southeastern China to explore environmental drivers and potential trade-offs between the ma...

Understanding the water-use strategy of human-planted species used in response to climate change is essential to optimize afforestation programs in dry regions. Since 2000, trees on the central Loess Plateau have experienced a shift from strengthening drought to weakening drought. In this study, we combined tree-ring δ13C and δ18O records from Pinu...

Permafrost is a potential mercury (Hg) pool released by thawing, which can raise the risk of Hg pollution under global warming. Tree rings are useful archives of environment-specific Hg exposure over long periods. We determined Hg concentrations in tree rings of two dominant tree species (Larix gmelinii and Pinus sylvestris) at permafrost sites in...

The growth resilience of forests to extreme drought event has become an urgent topic in global change ecology because of exacerbated water constraints upon trees’ growth over the last few decades. Yet, surprisingly little is empirically known about the contribution of stand age, a key factor influencing forest structure and ecological processes, to...

The mechanistic pathways connecting ocean-atmosphere variability and terrestrial productivity are well-established theoretically, but remain challenging to quantify empirically. Such quantification will greatly improve the assessment and prediction of changes in terrestrial carbon sequestration in response to dynamically induced climatic extremes....

Mt. Everest (Qomolangma or Sagarmatha), the highest mount on Earth and located in the central Himalayas between China and Nepal, is characterized by highly concentrated glaciers and diverse landscapes, and is considered to be one of the most sensitive area to climate change. In this paper, we comprehensively synthesized the climate and environmenta...

Tree-ring chronologies underpin the majority of annually-resolved reconstructions of Common Era climate. However, they are derived using different datasets and techniques, the ramifications of which have hitherto been little explored. Here, we report the results of a double-blind experiment that yielded 15 Northern Hemisphere summer temperature rec...

Stable isotope in tree rings are effective proxies for the study of climate change and environmental evolution. Coupling analysis of stable isotope records of tree rings can reveal the spatiotemporal variation characteristics and interactions of carbon, water and nitrogen in forest ecosystems, and reflect the physiological effects of environmental...

Although stand age has been shown to strongly affect forest ecosystem processes, little is known about the role that forest stand age plays in tree radial growth processes. The knowledge on geographical patterns of the stand age effect on radial growth along climatic gradients is also scarce. Based on dendrological methods and tree-ring cores from...

Rising atmospheric CO 2 may enhance tree growth and mitigate drought impacts through CO 2 fertilization. However, multiple studies globally have found that rising CO 2 has not translated into greater tree growth despite increases in intrinsic water use efficiency (iWUE). The underlying mechanism discriminating between these two general responses to...

Rising atmospheric CO2 may enhance tree growth and mitigate drought impacts through CO2 fertilization. However, multiple studies globally have found that rising CO2 has not translated into greater tree growth despite increases in intrinsic water use efficiency (iWUE). The underlying mechanism discriminating between these two general responses to CO...

Understanding the spatial–temporal tree growth variability and its associative climatic response is fundamental in the assessment of forest vulnerability and the appraisal of forest risk under climate change. Based on 4219 tree-ring cores from 23 sample plots, this study demonstrates divergent radial growth dynamics of Qinghai spruce (Picea crassif...

Drought-related forest growth declines are observed globally in main forest types, especially with repeatedly hot droughts. Therefore, quantifying forest resilience and identifying the factors driving resilience in response to extreme drought with the consideration of atmospheric CO2 fertilization is crucial for the accurate assessment of forest dy...

Decline in snow mass threatens the regional economy that critically depends on meltwater. However, the economic scale of snow mass loss is hardly understood, and its role in the vulnerability of future economic development is unclear. We investigate the current reserves of snow cover and the value of its loss. The result showed that the total annua...

Intra-annual variability of tree-ring oxygen stable isotopes (δ18O) can record seasonal climate variability and a tree’s ecophysiological response to it. Variability of sub-annual tree-ring δ18O maxima and minima, which usually occur in different parts of the growing season, may exhibit different climatic signals and can help in understanding past...

Understanding varying climate responses in tree‐ring data across tree ages is important, but little is known about tree‐age effects on climate responses in tree‐ring stable isotopes. To detect whether age differences in tree‐ring δ¹³C and δ¹⁸O could lead to differing climate responses, we measured tree‐ring cellulose δ¹³C and δ¹⁸O (1901–2010) from...

Modes of climate variability affect global and regional climates on different spatio-temporal scales, and they have important impacts on human activities and ecosystems. As these modes are a useful tool for simplifying the understanding of the climate system, it is crucial that we gain improved knowledge of their long-term past evolution and intera...

In arid and semiarid regions, riparian forests are crucial for maintaining ecological biodiversity and sustainability, and supporting social and economic development. For the typical arid and semiarid ecosystem, streamflow variability is thought to be the dominant factor influencing the vulnerability and evolution of the riparian forests, which oft...

Stable carbon isotope ratios (δ13C) are widely used as climate proxies for assessing and predicting climatic information at an annual resolution. However, the detailed information in the isotopes that results from intra-annual climate scenarios and is associated with mineral accumulation remains unclear. Combined with investigations of elements and...

To improve our understanding of climate variability in the Tibetan Plateau (TP) and its sensitivity to external forcings, recent temperature changes need to be placed in a long-term historical context. Here, we present two tree-ring based temperature reconstructions: a 1003-year (1000–2002 CE) annual temperature reconstruction for the northeastern...

Conifer forests in semi-arid regions are fragile and sensitive to climate change. As the climate changes, more frequent drought and higher temperatures may reduce conifer stem growth in these regions, but moistening and lengthening of the growing season may improve tree growth conditions. The relative influences of specific climate parameters on coni...

Plain Language Summary During the past 50 years, the northeastern Qinghai‐Tibetan Plateau region experienced alpine glacial retreat, increased desertification, and a reduction of river and lake levels. Understanding the region's background hydroclimate variation is critically important to assess current and future water‐management policies in this...

Mercury (Hg) is a potent neurotoxin in low concentrations and can be transported over a long distance in the atmosphere. Due to Hg accumulation, plant tissues could be used as a low-cost and efficient biological indicator. A significant linear relationship was found between Hg value and organic carbon content in soil, and the highest Hg concentrati...

Leaf stable isotope compositions (δ13C and δ15N) are influenced by various abiotic and biotic factors. Qinghai spruce (Picea crassifolia Kom.) as one of the dominant tree species in Qilian Mountains plays a key role in the ecological stability of arid region in the northwest of China. However, our knowledge of the relative importance of multiple fa...

Drought occurrence and duration in central Asia are of important socioeconomic, ecological, and geophysical significance and have received increasing research attention in recent years. Understanding long-term drought trends and their driving forces require reliable records of past drought variability with broad spatial representativeness. Here, we...

Intrinsic water-use efficiency (iWUE) is affected by the balance of photosynthetic rate, stomatal conductance, and climate, along with many other exogenous factors, such as the CO2 concentration in the atmosphere (CO2atm), nutrients, and water holding capacity of the soil. The relative contributions of CO2atm and climate to iWUE are still incomplet...

Stable isotopes in tree-ring cellulose provide important data in ecological, archaeological, and paleoenvironmental researches, thereby, the demand for stable isotope analyses is increasing rapidly. Simultaneous measurement of cellulose δ¹³C and δ¹⁸O values from tree rings would reduce the cost of isotopic commodities and improve the analytical eff...

Rising atmospheric CO2 (Ca) can increase tree radial growth by increasing intrinsic water-use efficiency (iWUE). However, the effects of age on the response remain unknown, particularly for forests in remote areas such as China's Tianshan Mountains. Here, we assessed age-dependent growth trends of Picea schrenkiana using tree-ring data from low and...

The thermal and moisture balance of permafrost regions has been altered by global warming, profoundly influencing vegetation dynamics and forest carbon cycling. To understand the spatial and temporal characteristics and driving forces responsible for changes in moisture conditions in the permafrost region of the Greater and Lesser Hinggan Mountains...

Ongoing climate changes posed significant threats to forest growth, structure and ecological functions. However, in our field survey in the east Qilian Mountains, we found that growth condition of Qinghai spruce under climate changes was better in anthropogenic management forest than disturbance-free stands. Accordingly, we suggested a hypothesis t...

Drought occurrence and duration in central Asia are of important socioeconomic, ecological, and geophysical significance and have received increasing research attention in recent years. Understanding long-term drought trends and their driving forces requires reliable records of past drought variability with broad spatial representativeness. Here, w...

Stable isotopes in tree rings are increasingly used as proxies for climatic and ecophysiologi-cal changes. However, uncertainties remain about the strength and consistency of their response to environmental variation at different temporal (i.e. seasonal to inter-decadal) scales. We developed 5 yr of intra-seasonal and 62 yr of early-and late-wood d...

Due to the lack of available long-term climatic records, data related to past autumn precipitation variability throughout Northwest China, especially high-frequency variation, remains limited. In this study, it was found that inter-annual changes in Qinghai spruce radial growth were significantly and negatively (p < 0.05) correlated to inter-annual...

Global warming will significantly increase transpirational water demand, which could dramatically affect plant physiology and carbon and water budgets. Tree ring δ18O is a potential index of the leaf-to-air vapor-pressure deficit (VPD) and therefore has great potential for long-term climatic reconstruction. Here we developed δ18O chronologies of tw...

Owing to a lack of available long-term climatic records, data related to past climatic variability throughout the Tibetan Plateau remains limited. In this study, we found that Qilian juniper tree growth was significantly and positively correlated (p < 0.001) to yearly mean temperatures in the northeastern margin of the Tibetan Plateau. We developed...

Alpine forest population dynamics are sensitive to climate change. Response patterns are complex, and it is still unclear as to whether or not population dynamics are species-dependent. In this study, population dynamic patterns for alpine timberline Qilian juniper and Qinghai spruce tree species in the mid Qilian Mountains were determined from app...

Tree-ring width chronologies are important records of climate change. Mounting evidence suggests that tree-ring climate response is elevation dependent. In this study, even-aged Qinghai spruce (Picea crassifolia Kom.) chronologies from six sites along a consistent slope in the Qilian Mountains region were selected to investigate altitudinal variabi...

Central Asian droughts have drastically and significantly affected agriculture and water resource management in these arid and semi-arid areas. Based on tree-ring δ18O from native, dominant Schrenk spruce (Picea schrenkiana Fisch. et Mey.), we developed a 300-year (1710 to 2010) standard precipitation-evaporation index (SPEI) reconstruction from Ja...

Rising atmospheric CO2 concentration (Ca) is expected to accelerate tree growth by enhancing photosynthesis and increasing intrinsic water-use efficiency (iWUE). However, the extent of this effect on long-term iWUE and its interactions with climate remains unclear in trees along an elevation gradient. Therefore, we investigated the variation in the...

temperature Abstract. Recent studies have detected the amplitude of spring plant phenology in whole Tibet Plateau and growing season by remote sensing technology. However, few studies have examined that how the plant phenology has changed in the past decade. At the regional scale, we investigated the phenological variations in five regions (Dingri,...

We developed an annual tree-ring δ18O chronology from Larix sibirica in the eastern Tianshan Mountains of northwestern China. Climatic response revealed that tree-ring δ18O was significantly positively correlated with the mean and maximum July–August temperatures, whereas the July precipitation and relative humidity were significantly negatively co...

Pollution from urban centers and fossil fuel combustion can decrease forest growth and interfere with physiological processes. To evaluate whether tree growth and the carbon isotope ratio (delta C-13) and nitrogen isotope ratio (delta N-15) in tree rings can serve as proxies for air pollution, this study compared these indices for poplar (Populus c...

The rising atmospheric CO2 concentration (Ca) has increased tree growth and intrinsic water-use efficiency (iWUE). However, the magnitude of this effect on long-term iWUE and whether this increase could stimulate the growth of riparian forests in extremely arid regions remain poorly understood. We investigated the relationship between growth [ring...

We measured the annual variation in the stable isotopes of oxygen (delta O-18) and hydrogen (delta D) in tree rings of Abies georgei on the Batang-Litang Plateau of western China. Although correlations between tree-ring delta O-18 and delta D are relatively weak in semi-arid regions, we found a strong correlation between the delta O-18 and delta D...