Showing papers by "Lixin Wang published in 2020"

Causes and consequences of pronounced variation in the isotope composition of plant xylem water

Abstract: . Stable isotopologues of water are widely used to derive relative root water uptake (RWU) profiles and average RWU depth in lignified plants. Uniform isotope composition of plant xylem water ( δxyl ) along the stem length of woody plants is a central assumption of the isotope tracing approach which has never been properly evaluated. Here we evaluate whether strong variation in δxyl within woody plants exists using empirical field observations from French Guiana, northwestern China, and Germany. In addition, supported by a mechanistic plant hydraulic model, we test hypotheses on how variation in δxyl can develop through the effects of diurnal variation in RWU, sap flux density, diffusion, and various other soil and plant parameters on the δxyl of woody plants. The hydrogen and oxygen isotope composition of plant xylem water shows strong temporal (i.e., sub-daily) and spatial (i.e., along the stem) variation ranging up to 25.2 ‰ and 6.8 ‰ for δ2H and δ18O , respectively, greatly exceeding the measurement error range in all evaluated datasets. Model explorations predict that significant δxyl variation could arise from diurnal RWU fluctuations and vertical soil water heterogeneity. Moreover, significant differences in δxyl emerge between individuals that differ only in sap flux densities or are monitored at different times or heights. This work shows a complex pattern of δxyl transport in the soil–root–xylem system which can be related to the dynamics of RWU by plants. These dynamics complicate the assessment of RWU when using stable water isotopologues but also open new opportunities to study drought responses to environmental drivers. We propose including the monitoring of sap flow and soil matric potential for more robust estimates of average RWU depth and expansion of attainable insights in plant drought strategies and responses.

Quantifying the Controls on Evapotranspiration Partitioning in the Highest Alpine Meadow Ecosystem

Abstract: Quantifying the transpiration fraction of evapotranspiration (T/ET) is crucial for understanding plant functionality in ecosystem water cycles, land‐atmosphere interactions, and the global water budget. However, the controls and mechanisms underlying the temporal change of T/ET remain poorly understood in arid and semiarid areas, especially for remote regions with sparse observations such as the Tibetan Plateau (TP). In this study, we used combined high‐frequency laser spectroscopy and chamber methods to constrain estimates of T/ET for an alpine meadow ecosystem in the central TP. The three isotopic end members in ET (δET), soil evaporation (δE), and plant transpiration (δT) were directly determined by three newly customized chambers. Results showed that the seasonal variations of δET, δE, and δT were strongly affected by the precipitation isotope (R 2 = 0.53). The δO‐based T/ET agreed with that of δH. Isotope‐based T/ET ranged from 0.15 to 0.73 during the periods of observation, with an average of 0.43. This mean result was supported by T/ET derived from a two‐source model and eddy covariance observations. Our overarching finding is that at the seasonal timescale, surface soil water content (θ) dominated the change of T/ET, with leaf area index playing only a secondary role. Our study confirms the critical impact of soil water on the temporal change of T/ET in water‐limited regions such as the TP. This knowledge sheds light on diverse land‐surface processes, global hydrological cycles, and their modeling.

Sporadic activation of an oxidative stress–dependent NRF2-p53 signaling network in breast epithelial spheroids and premalignancies

Abstract: Breast and mammary epithelial cells experience different local environments during tissue development and tumorigenesis. Microenvironmental heterogeneity gives rise to distinct cell regulatory states whose identity and importance are just beginning to be appreciated. Cellular states diversify when clonal three-dimensional (3D) spheroids are cultured in basement membrane, and one such state is associated with stress tolerance and poor response to anticancer therapeutics. Here, we found that this state was jointly coordinated by the NRF2 and p53 pathways, which were costabilized by spontaneous oxidative stress within 3D cultures. Inhibition of NRF2 or p53 individually disrupted some of the transcripts defining the regulatory state but did not yield a notable phenotype in nontransformed breast epithelial cells. In contrast, combined perturbation prevented 3D growth in an oxidative stress-dependent manner. By integrating systems models of NRF2 and p53 signaling in a single oxidative stress network, we recapitulated these observations and made predictions about oxidative stress profiles during 3D growth. NRF2 and p53 signaling were similarly coordinated in normal breast epithelial tissue and hormone-negative ductal carcinoma in situ lesions but were uncoupled in triple-negative breast cancer (TNBC), a subtype in which p53 is usually mutated. Using the integrated model, we correlated the extent of this uncoupling in TNBC cell lines with the importance of NRF2 in the 3D growth of these cell lines and their predicted handling of oxidative stress. Our results point to an oxidative stress tolerance network that is important for single cells during glandular development and the early stages of breast cancer.

Increased human pressures on the alpine ecosystem along the Qinghai-Tibet Railway

Abstract: Construction of the Qinghai-Tibet Railway (QTR) increased the links between inland China and the Qinghai-Tibet Plateau (QTP). The QTR accelerated surrounding tourism, boosted the local economy and led to rapid development of livestock raising. To assess how distance from the railway and different regions has influenced the impact of the QTR on the alpine ecosystem, human footprint maps were produced to indicate human pressures, and the normalized difference vegetation index (NDVI), an index of vegetation greenness, was used to characterize the growth of alpine vegetation. The construction and operation of the QTR have increased human pressures, while the establishment of nature reserves has effectively reduced human pressures. The QTR contributes significantly to the increased human pressures in the Tibetan region compared with the Qinghai region and exerts negative impacts on alpine vegetation. Although the warmer and wetter climate trend has proven beneficial in enhancing alpine vegetation greenness, the declining trend of alpine vegetation has been stronger in regions with more intensive human pressures, especially in the grazing areas and the tourist areas around Lhasa. These results suggest that the impact of the QTR on alpine vegetation in Tibet is greater than that in Qinghai and that the spatial extent of the indirect impact of the QTR in Tibet is confined to approximately 30 km from the railway. These results will provide guidance and a theoretical basis for the protection of the alpine environment on the QTP under intensified anthropogenic influence.

Upstream of gene expression: what is the role of microtubules in cold signalling?

Abstract: Cold stress is a major abiotic stress, restricting plant growth and development. Therefore, gene expression in response to cold stress and during cold acclimation has been studied intensively, including the ICE-CBF-COR pathway, as well as the modulation of this cascade by secondary messengers, for instance mitogen-activated protein kinase (MAPK) cascades. In contrast, the early events of cold perception and cold adaption have received far less attention. This is partially due to the fact that cold is a physical signal, which requires the conceptual framework to be adjusted. In this review, we address the role of microtubules in cold sensing, and propose a model whereby microtubules, while not being part of signalling itself, act as modulators of cold sensitivity. The purpose of this model is to derive implications for future experiments that will help to provide a more complete understanding of cold adaptation.

Satellite observed positive impacts of fog on vegetation

Abstract: State Key Laboratory of Remote Sensing Science, Institute of Remote Sensing and Digital Earth, Chinese Academy of Sciences, Beijing, China University of Chinese Academy of Sciences, Beijing, China Department of Earth Sciences, Indiana University-Purdue University Indianapolis (IUPUI), Indianapolis, IN, USA Key Laboratory of Oasis Eco-Agriculture, Xinjiang Production and Construction Group, Shihezi University, Shihezi, China Gobabeb – Namib Research Institute, Walvis Bay, Namibia

Satellite Solar-Induced Chlorophyll Fluorescence Reveals Heat Stress Impacts on Wheat Yield in India

Abstract: With continued global warming, the frequency and severity of heat wave events increased over the past decades, threatening both regional and global food security in the future. There are growing interests to study the impacts of drought on crop. However, studies on the impacts of heat stress on crop photosynthesis and yield are still lacking. To fill this knowledge gap, we used both statistical models and satellite solar-induced chlorophyll fluorescence (SIF) data to assess the impacts of heat stress on wheat yield in a major wheat growing region, the Indo-Gangetic Plains (IGP), India. The statistical model showed that the relationships between different accumulated degree days (ADD) and reported wheat yield were significantly negative. The results confirmed that heat stress affected wheat yield across this region. Building on such information, satellite SIF observations were used to further explore the physiological basis of heat stress impacts on wheat yield. Our results showed that SIF had strong negative correlations with ADDs and was capable of monitoring heat stress. The SIF results also indicated that heat stress caused yield loss by directly impacting the photosynthetic capacity in wheat. Overall, our findings demonstrated that SIF as an effective proxy for photosynthetic activity would improve our understanding of the impacts of heat stress on wheat yield.

The importance of cuticular permeance in assessing plant water-use strategies.

Abstract: Accurate understanding of plant responses to water stress is increasingly important for quantification of ecosystem carbon and water cycling under future climates. Plant water-use strategies can be characterized across a spectrum of water stress responses, from tight stomatal control (isohydric) to distinctly less stomatal control (anisohydric). A recent and popular classification method of plant water-use strategies utilizes the regression slope of predawn and midday leaf water potentials, σ, to reflect the coupling of soil water availability (predawn leaf water potential) and stomatal dynamics (daily decline in leaf water potential). This type of classification is important in predicting ecosystem drought response and resiliency. However, it fails to explain the relative stomatal responses to drought of Acer sacharrum and Quercus alba, improperly ranking them on the spectrum of isohydricity. We argue this inconsistency may be in part due to the cuticular conductance of different species. We used empirical and modeling evidence to show that plants with more permeable cuticles are more often classified as anisohydric; the σ values of those species were very well correlated with measured cuticular permeance. Furthermore, we found that midday leaf water potential in species with more permeable cuticles would continue to decrease as soils become drier, but not in those with less permeable cuticles. We devised a diagnostic parameter, Γ, to identify circumstances where the impact of cuticular conductance could cause species misclassification. The results suggest that cuticular conductance needs to be considered to better understand plant water-use strategies and to accurately predict forest responses to water stress under future climate scenarios.

No-till is challenged: Complementary management is crucial to improve its environmental benefits under a changing climate

Abstract: Tillage is the most common agricultural practice dating back to the origin of agriculture. In recent decades, no-tillage (NT) has been introduced to improve soil and water quality. However, changes in soil properties resulting from long-term NT can increase losses of dissolved phosphorus, nitrate and some classes of pesticides, and NT effect on nitrous oxide (N2O) emission remains controversial. Complementary management that enhances the overall environmental benefits of NT is therefore crucial. By incorporating cover crops, nutrient cycling and nutrient use efficiency in NT fields could be improved given the nutrient supplying capacity of some cover crops. Cover crops could also offset the need for occasional tillage of NT cropland, an operation whose effect is only temporary in reducing, for example, soil compaction associated with NT management. When used in combination with NT, cover crop termination methods, using agrochemicals, should be carefully considered to prevent further jeopardy to water quality. Compared to herbicides, the use of roller crimping could potentially result in production cost saving while minimizing soil disturbance and export of agrochemicals. Future research should focus on various combinations of cover crop traits (e.g., decomposition rate) and management (e.g., timing of cover crop termination) that account for site- and cash crop-specific requirements.

Water sources of major plant species along a strong climatic gradient in the inland Heihe River Basin

Abstract: Knowledge on vegetation water sources is crucial to understand the ecohydrological processes and ecological management of arid and semi-arid ecosystems. The identification and quantification of plant water uptake from precipitation, soil and groundwater remain challenging along large climatic gradient. Stable oxygen isotope compositions of xylem water, soil water and groundwater were analyzed to assess seasonal and spatial patterns of water uptake of 11 major plant species along the Heihe River Basin. In the upper reaches, soil water recharged by precipitation was the main plant water source, and plants extracted water from the shallow soil water in wet season while used more deep soil water in dry season. In the middle reaches of desert-oasis ecotone, the water sources of shrubs shifted between soil moisture and groundwater depending on variations of precipitation and groundwater level, while shrubs at Gobi relied on deep soil water and shallow soil water after rainfall. In the lower reaches, the driest part of the region, groundwater and deep soil water were main water sources for the riparian plants. Groundwater was stable water source for shrubs growing on the planted shrubland, and soil water was stable water sources for shrubs growing at Gobi. Our results also revealed that water use strategies of the same species were plastic under different groundwater level and precipitation. This study identified water use patterns of different plant species along a climatic gradient and provided scientific implication for water management of different ecosystems of the arid and semi-arid ecosystems.

Triple isotope variations of monthly tap water in China.

Abstract: Tap water isotopic compositions could potentially record information on local climate and water management practices. A new water isotope tracer 17O-excess became available in recent years providing additional information of the various hydrological processes. Detailed data records of tap water 17O-excess have not been reported. In this report, monthly tap water samples (n = 652) were collected from December 2014 to November 2015 from 92 collection sites across China. The isotopic composition (δ2H, δ18O, and δ17O) of tap water was analyzed by a Triple Water Vapor Isotope Analyzer (T-WVIA) based on Off-Axis Integrated Cavity Output Spectroscopy (OA-ICOS) technique and two second-order isotopic variables (d-excess and 17O-excess) were calculated. The geographic location information of the 92 collection sites including latitude, longitude, and elevation were also provided in this dataset. This report presents national-scale tap water isotope dataset at monthly time scale. Researchers and water resource managers who focus on the tap water issues could use them to probe the water source and water management strategies at large spatial scales. Machine-accessible metadata file describing the reported data: https://doi.org/10.6084/m9.figshare.12923681

The hidden costs of desert development.

Abstract: Economic benefits and ecological restoration are the leading drivers of desert development through man-made oasis expansion. However, the sustainability of oasis expansion in combating desertification while promoting economic growth remains unclear, though such knowledge is critical for future desert development across the globe. To address this knowledge gap, a comprehensive assessment integrating meteorological, groundwater and remote-sensing data as well as groundwater simulation datasets was conducted to evaluate the spatial-temporal changes in the desert-oasis ecotone of northwest China over the past six decades. Desert development causes a rapid decline in the surrounding groundwater table, increases pollution in soil and groundwater and is associated with an increased frequency of strong sandstorms. Desert development seems to have improved the environment and promoted the economy, but there is a huge cost for the overexploitation of water resources and the transfer of pollution from surface to underground, which could cause deserts to degrade further.

Responses of secondary wind dispersal to environmental characteristics and diaspore morphology of seven Calligonum species

Abstract: Secondary diaspore dispersal by wind, that is, wind‐driven movement along the ground surface (GS), is important for the structure and dynamics of plant populations and communities. However, how wind velocity (WV), GS, and diaspore morphology influence diaspore secondary dispersal by wind are unclear. We used a wind tunnel and video camera to measure the threshold of WV (TWV) and diaspore velocities (DV) of secondary diaspore dispersal. Diaspores of seven Calligonum species with different appendages (wings, bristles, membranous balloon, and wings + thorns) were used to determine the TWV and DV under variable wind speed (4, 6, 8, and 10 m s‐¹) and four GSs (cement, sand, loam, and gravel). GS and diaspore morphological traits explained 37.1 and 18% of diaspore TWV, respectively. Meanwhile, WV, GS, and diaspore morphological traits explained 62.4, 13.6, and 3.2% of DV, respectively. An increasing trend was shown for TWV, and a decreasing trend was shown for DV in the order of cement, sand, loam, and gravel surfaces. Spherical and light diaspores had low TWV and high DV, whereas winged and heavy diaspores had high TWV and low DV. Our results indicated that adaptive features of diaspore appendages might be the result of selection for primary dispersal or secondary dispersal. The mechanism of diaspore secondary dispersal is important for understanding the recovery of degraded sand dunes and providing theoretical support for restoration practices.

Assessing Temperate Forest Growth and Climate Sensitivity in Response to a Long‐Term Whole‐Watershed Acidification Experiment

Abstract: Acid deposition is a major biogeochemical driver in forest ecosystems, but the impacts of long‐term changes in deposition on forest productivity remain unclear. Using a combination of tree ring and forest inventory data, we examined tree growth and climate sensitivity in response to 26 years of whole‐watershed ammonium sulfate ((NH4)2SO4) additions at the Fernow Experimental Forest (West Virginia, USA). Linear mixed effects models revealed species‐specific responses to both treatment and hydroclimate variables. When controlling for environmental covariates, growth of northern red oak (Quercus rubra), red maple (Acer rubrum), and tulip poplar (Liriodendron tulipifera) was greater (40%, 52%, and 42%, respectively) in the control watershed compared to the treated watershed, but there was no difference in black cherry (Prunus serotina). Stem growth was generally positively associated with growing season water availability and spring temperature and negatively associated with vapor pressure deficit. Sensitivity of northern red oak, red maple, and tulip poplar growth to water availability was greater in the control watershed, suggesting that acidification treatment has altered tree response to climate. Results indicate that chronic acid deposition may reduce both forest growth and climate sensitivity, with potentially significant implications for forest carbon and water cycling in deposition‐affected regions.

New isotope-based evapotranspiration partitioning method using the Keeling plot slope and direct measured parameters

Abstract: . To better quantify water and energy cycles, numerous efforts to partition evapotranspiration (ET) into evaporation (E) and transpiration (T) have been made over the recent half century. Various methods such as direct measurements, analytical models and satellite-based estimations have been used to separate ET across the field scale to the global scale. One of the analytical methods, isotopic approach, has been often applied in terrestrial ecosystem ET partitioning. The isotopic composition of ET (δET) is a crucial parameter in the traditional isotope-based ET partition model, which however has considerable uncertainty. Here we proposed a new method relying on Keeling plot slope (k), and relying on the direct measurements of atmospheric vapor concentration (Cv) and isotopic composition of atmospheric vapor (δv), to avoid the direct use of δET. Mathematical derivation of the new method was provided, and field observations were used to evaluate the new method. The T/ET results based on the new method agreed well with those using the traditional isotopic method. The new method eliminates the high sensitivity contribution parameter δET. In addition, the new method utilized directly measured values and regressive slope of Keeling plot instead of using the interpolated Keeling plot intercept. Our study shows an analytical framework to estimate T/ET based on the Keeling plot slope and direct-measured parameters. The new method potentially reduces the uncertainty of isotope-based ET partition approach.

Single-cell Bottlenecks and Dead-ends During Glioma Premalignancy

Abstract: Cancer evolves from premalignant clones that accumulate mutations and adopt unusual cell states to achieve transformation. Tracking a cancer cell-of-origin through the cell-state alterations of premalignancy could provide clues for early-detection and cancer-prevention strategies. Previously we pinpointed the oligodendrocyte precursor cell (OPC) as a cell-of-origin for glioma. However, the early adaptations and cell-state changes of mutant OPCs during premalignancy are unknown. Using a genetically engineered mouse model (GEMM) of inducible Nf1–Trp53 loss in OPCs, we acutely isolated labeled mutant OPCs by laser-capture microdissection and determined gene-expression changes in two ways: global changes in gene expression were measured by differential analysis of wild-type and mutant OPCs after bulk RNA sequencing; cell-to-cell state variations were identified by a fluctuation analysis, called stochastic profiling, which uses RNA-sequencing measurements from random pools of 10 mutant cells. We chose two time points for the analysis. At 12 days after Nf1–Trp53 deletion, while bulk differences were mostly limited to increases in mitotic hallmarks and decreases in ribosome biosynthesis, stochastic profiling of mutant OPCs revealed a spectrum of stem-progenitor, proneural, and mesenchymal states as potential starting points for gliomagenesis. At 90 days after Nf1–Trp53 deletion, while bulk sequencing detected very few differentially expressed transcripts, stochastic profiling revealed multiple cell states that are absent from glial tumors, suggesting that they marked dead-ends for gliomagenesis. In parallel, we identified cells without dead-end markers but abundantly expressing key effectors of nonsense-mediated decay and homology-dependent DNA repair. This suggests that resolution of replication stress may pose a considerable bottleneck for glioma initiation in premalignant mutant OPCs. Statement of significance In situ heterogeneity profiling of cell states in a mouse model of glioma uncovers regulatory confusion in a glioma cell-of-origin and defines a state of replication stress that precedes tumor initiation.

Novel Keeling-plot-based methods to estimate the isotopic composition of ambient water vapor

Abstract: . The Keeling plot approach, a general method to identify the isotopic composition of source atmospheric CO2 and water vapor (i.e., evapotranspiration), has been widely used in terrestrial ecosystems. The isotopic composition of ambient water vapor ( δa ), an important source of atmospheric water vapor, is not able to be estimated to date using the Keeling plot approach. Here we proposed two new methods to estimate δa using the Keeling plots: one using an intersection point method and another relying on the intermediate value theorem. As the actual δa value was difficult to measure directly, we used two indirect approaches to validate our new methods. First, we performed external vapor tracking using the Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) model to facilitate explaining the variations of δa . The trajectory vapor origin results were consistent with the expectations of the δa values estimated by these two methods. Second, regression analysis was used to evaluate the relationship between δa values estimated from these two independent methods, and they are in strong agreement. This study provides an analytical framework to estimate δa using existing facilities and provides important insights into the traditional Keeling plot approach by showing (a) a possibility to calculate the proportion of evapotranspiration fluxes to total atmospheric vapor using the same instrumental setup for the traditional Keeling plot investigations and (b) perspectives on the estimation of isotope composition of ambient CO2 ( δa13C ).

Educational modules and research surveys on critical cybersecurity topics

Abstract: Cybersecurity comprised all the technologies and practices that protect data as well as computer and network systems. In this article, we develop four course modules on critical cybersecurity topic...

Diurnal variation in the isotope composition of plant xylem water biases the depth of root-water uptake estimates

Abstract: . 1. Stable isotopologues of water are a widely used tool to derive the depth of root water uptake (RWU) in lignified plants. Uniform isotope composition of plant xylem water (i-H2O-xyl) along the stem length is a central assumption, which has never been properly evaluated. 2. We studied the effects of diurnal variation in RWU, sap flux density and various other soil and plant parameters on i-H2O-xyl within a plant using a mechanistic plant hydraulic model and empirical field observations from French Guiana and northwestern China. 3. Our model predicts significant i-H2O-xyl variation arising from diurnal RWU fluctuations and vertical soil water heterogeneity. Moreover, significant differences in i-H2O-xyl emerge between individuals with different sap flux densities. In line with model predictions, field data show excessive i-H2O-xyl variation during the day or along stem length ranging up to 25.2 ‰ in δ2H and 6.8 ‰ in δ18O, largely exceeding the measurement error range. 4. Our work show that the fundamental assumption of uniform i-H2O-xyl is violated both theoretically and empirically and therefore a real danger exists of significant biases when using stable water isotopologues to assess RWU. We propose to include monitoring of sap flow and soil water potential for more robust RWU depth estimates.

Infrared heater warming system markedly reduces dew formation: An overlooked factor in arid ecosystems

Abstract: Dew plays a vital role in ecosystem processes in arid and semi-arid regions and is expected to be affected by climate warming. Infrared heater warming systems have been widely used to simulate climate warming effects on ecosystem. However, how this warming system affects dew formation has been long ignored and rarely addressed. In a typical alpine grassland ecosystem on the Northeast of the Tibetan Plateau, we measured dew amount and duration by artificial condensing surfaces, leaf wetness sensors and in situ dew formation on plants from 2012 to 2017. We also measured plant traits related to dew conditions. The results showed that (1) warming reduced the dew amount by 41.6%-91.1% depending on the measurement method, and reduced dew duration by 32.1 days compared to the ambient condition. (2) Different plant functional groups differed in dew formation. (3) Under the infrared warming treatment, the dew amount decreased with plant height, while under the ambient conditions, the dew amount showed the opposite trend. We concluded that warming with an infrared heater system greatly reduces dew formation, and if ignored, it may lead to overestimation of the effects of climate warming on ecosystem processes in climate change simulation studies.

Efficient Algorithm for Multi-Constrained Opportunistic Wireless Scheduling

Abstract: The onset of wireless networks globally has thrust researchers in academia and industry to solve problems related to this ever-growing field. In this paper, we study the multi-constrained opportunistic wireless scheduling problem in cognitive radio networks. Given a collection of secondary user communication links, the channel state of each link is unknown due to the unpredictable primary users’ activities, but can be estimated by exploring the channel state transitions and channel state feedback. A scheduling algorithm is used to decide a subset of links to transmit each time with both interference-free constraints and power budget constraints. The objective of this paper is to design a scheduling algorithm to optimize the average reward over a long time horizon. Current existing approaches cannot satisfyingly provide solutions for the wireless opportunistic scheduling problem when considering multiple constraints. In this work, we adopt the paradigm of the restless multi-armed bandit and propose a fast and simple approximation algorithm. The performance of the proposed algorithm is verified with a small approximation bound for the multi-constrained wireless opportunistic wireless scheduling problem.