Populus Euphratica Research Articles

Populusene A, an Anti-inflammatory Diterpenoid with a Bicyclo[8,4,1]pentadecane Scaffold from Populus euphratica Resins.

Populusene A (1), an unprecedented carbon skeleton featuring a bicyclo[8.4.1]pentadecane nucleus and a bridgehead double bond (anti-Bredt system), and populusin A (2), a cembrane-type diterpenoid possessing an uncommon dioxatricyclo[6.6.1.12,5]hexadecane scaffold, were isolated from the exudates of Populus euphratica. Their structures were elucidated by spectroscopic, computational, and crystallographic methods. A plausible biosynthetic route for 1 and 2 was proposed. Compounds 1 and 2 were found to significantly inhibit the production of TNF-α and IL-6 and the expression of iNOS, COX-2, and p-NF-κB at 125 nM in RAW264.7 cells.

Phylogeography Reveals Geographic and Environmental Factors Driving Genetic Differentiation of Populus sect. Turanga in Northwest China.

Populus sect. Turanga (hereafter referred to as “Populus”), including Populus euphratica and Populus pruinosa, are the predominant tree species in desert riparian forests in northwestern China. These trees play key roles in maintaining ecosystem balance, curbing desertification, and protecting biodiversity. However, the distribution area of Populus forests has been severely diminished and degraded in recent years due to increased habitat destruction and human activity. Understanding the genetic diversity among Populus individuals and populations is essential for designing conservation strategies, but comprehensive studies of their genetic diversity in northwest China are lacking. Here, we assessed the population structures and genetic diversity of 1,620 samples from 85 natural populations of Populus (59 P. euphratica and 26 P. pruinosa populations) covering all of northwestern China using 120 single nucleotide polymorphism (SNP) markers. Analysis of population structure revealed significant differentiation between these two sister species and indicated that strong geographical distribution patterns, a geographical barrier, and environmental heterogeneity shaped the extant genetic patterns of Populus. Both P. euphratica and P. pruinosa populations in southern Xinjiang had higher genetic diversity than populations in other clades, perhaps contributing to local geographic structure and strong gene flow. Analysis of molecular variance (AMOVA) identified 15% variance among and 85% variance within subpopulations. Mantel tests suggested that the genetic variation among P. euphratica and P. pruinosa populations could be explained by both geographical and environmental distance. The genetic diversity of P. euphratica showed a significant negative correlation with latitude and longitude and a positive correlation with various environmental factors, such as precipitation of warmest quarter and driest month, temperature seasonality, and annual mean temperature. These findings provide insights into how the genetic differentiation of endangered Populus species was driven by geographical and environmental factors, which should be helpful for designing strategies to protect these genetic resources in the future.

Tree mortality and regeneration of Euphrates poplar riparian forests along the Tarim River, Northwest China

BackgroundTree mortality and regeneration (seedling and sapling recruitment) are essential components of forest dynamics in arid regions, especially where subjected to serious eco-hydrological problems. In recent decades, the mortality of the Euphrates poplar (Populus euphratica) along the Tarim River in Northwest China has increased. However, few studies have quantified the causes of mortality and regeneration in this azonal riparian forest type.MethodsThe present study describes the annual hydrological response of tree mortality and regeneration in forest gaps. A total of 60 canopy gaps were investigated in six replicate grid plots (50 m × 50 m) and the annual runoff and water consumption data during the period of 1955–2016 were collected from hydrological stations in the middle reaches of the Tarim River. We compared the regeneration density of seedlings and saplings within the canopy gap areas (CGAs), undercanopy areas (UCAs), and uncovered riverbank areas (RBAs) through detailed field investigation.ResultsOur study found that the mortality of young and middle-aged gap makers has increased remarkably over recent decades, particularly since the year 1996. The main results indicated that regional water scarcity was the primary limiting factor for long-term changes in tree mortality, as shown by a significant correlation between the diameter at breast height (DBH) of dead trees and the annual surface water. The average density (or regeneration rate) of seedlings and saplings was highest in the RBAs, intermediate in the CGAs, and lowest in the UCAs. Compared with the UCAs, the CGAs promote tree regeneration to some extent by providing favorable conditions for the survival and growth of seedlings and saplings, which would otherwise be suppressed in the understory. Furthermore, although the density of seedlings and saplings in the CGAs was not as high as in the RBAs, the survival rate was higher in the CGAs than in the RBAs.ConclusionForest canopy gaps in floodplain areas can play a decisive role in the long-term germination and regeneration of plant species. However, as a typical phreatophyte in this hyper-arid region, the ecosystem structure, functions and services of this fragile P. euphratica floodplain forests are threatened by a continuous decrease of water resources, due to excessive water use for agricultural irrigation, which has resulted in a severe reduction of intact poplar forests. Furthermore, the survival of seedlings and saplings is influenced by light availability and soil water at the regional scale. Our findings suggest that policymakers may need to reconsider the restoration and regeneration measures implemented in riparian P. euphratica forests to improve flood water efficiency and create canopy gaps. Our results provide with valuable reference information for the conservation and sustainable development of floodplain forest ecosystems.

Litoribacter populi sp. nov., isolated from the soil of a Populus euphratica forest.

A Gram-stain-negative, rod-shaped, and orange-pigmented bacterium, designated XAAS-A1T, was isolated from the soil of a Populus euphratica forest. The main respiratory quinone of XAAS-A1T is MK-7, and the principal cellular fatty acids are iso-C15:0, C17:1 ω6c, Iso-C17:0 3OH, and summed feature 3 (C16:1ω6c and/or C16:1ω7c). The major polar lipids are phosphatidylethanolamine, phosphatidylcholine, and two unidentified lipids. The 16S rRNA gene sequence analysis indicated that XAAS-A1T belongs to the genus Litoribacter within the family Cyclobacteriaceae, having the highest sequence similarities to Litoribacter ruber KCTC 22899T (97.1%) and L. alkaliphilus KCTC 32217T (96.9%). XAAS-A1T has a DNA G + C content of 42.1mol%. The orthoANI and the digital DNA-DNA hybridization values were markedly lower than the recommended threshold values of 96% and 70%. Phenotypic and genotypic data suggest that XAAS-A1T represents a novel species of the genus Litoribacter, for which we propose the name Litoribacter populi sp. nov. and XAAS-A1T (= CCTCC AB 2017159T = KCTC 62045T) as the type strain.

Heterophylly Quantitative Trait Loci Respond to Salt Stress in the Desert Tree Populus euphratica.

Heterophylly, or leaf morphological changes along plant shoot axes, is an important indicator of plant eco-adaptation to heterogeneous microenvironments. Despite extensive studies on the genetic control of leaf shape, the genetic architecture of heterophylly remains elusive. To identify genes related to heterophylly and their associations with plant saline tolerance, we conducted a leaf shape mapping experiment using leaves from a natural population of Populus euphratica. We included 106 genotypes grown under salt stress and salt-free (control) conditions using clonal seedling replicates. We developed a shape tracking method to monitor and analyze the leaf shape using principal component (PC) analysis. PC1 explained 42.18% of the shape variation, indicating that shape variation is mainly determined by the leaf length. Using leaf length along shoot axes as a dynamic trait, we implemented a functional mapping-assisted genome-wide association study (GWAS) for heterophylly. We identified 171 and 134 significant quantitative trait loci (QTLs) in control and stressed plants, respectively, which were annotated as candidate genes for stress resistance, auxin, shape, and disease resistance. Functions of the stress resistance genes ABSCISIC ACIS-INSENSITIVE 5-like (ABI5), WRKY72, and MAPK3 were found to be related to many tolerance responses. The detection of AUXIN RESPONSE FACTOR17-LIKE (ARF17) suggests a balance between auxin-regulated leaf growth and stress resistance within the genome, which led to the development of heterophylly via evolution. Differentially expressed genes between control and stressed plants included several factors with similar functions affecting stress-mediated heterophylly, such as the stress-related genes ABC transporter C family member 2 (ABCC2) and ABC transporter F family member (ABCF), and the stomata-regulating and reactive oxygen species (ROS) signaling gene RESPIRATORY BURST OXIDASE HOMOLOG (RBOH). A comparison of the genetic architecture of control and salt-stressed plants revealed a potential link between heterophylly and saline tolerance in P. euphratica, which will provide new avenues for research on saline resistance-related genetic mechanisms.

Seasonal Variation Characteristics of Chlorophyll and Spectrum in Leaves of Populus euphratica Under Water Stress

Seasonal Variation Characteristics of Chlorophyll and Spectrum in Leaves of Populus euphratica Under Water Stress

RESULTS OF FOREST PATHOLOGICAL SURVEY OF TUGAI FORESTS IN THE FLOODPLAIN OF THE SYRDARYA AND ILE RIVERS

This article presents the results of a reconnaissance and detailed forest pathological survey of tugai forests of the floodplain of the Syrdarya and Ile rivers. The studies were carried out at KSU “Otyrar forestry” along the floodplain of the Syrdarya River and KSU “Bakanas forestry” along the floodplain of the Ile River. The reconnaissance surveillance was carried out by an overground visual method from May to September 2021. Also, detailed surveys of the infestation and degree of damage to trees and shrubs by insect pests were carried out. According to the survey results, the sanitary condition of tugai forests is satisfactory. At the same time, the average degree of damage by leaf-gnawing and gall-forming pests of Populus diversifolia and Eleagnus angustifolia is more than 50%, which confirms the need for forest pathological monitoring.

Poplar trees in Israel's desert regions: Relicts of Roman and Byzantine settlement

The Euphrates poplar (Populus euphratica), can be found in the arid regions of the Negev highlands, the Judean desert, and the northern Arava in a number of clustered populations located near permanent water sources. The trees' distribution in the desert regions is not continuous, being disconnected from its major area of distribution along the Jordan River, where its distribution is uninterrupted. It is unclear how and when this disjunctive distribution occurred, and what were the initial ecological conditions for this poplar's original establishment and success. In this article we present a study of the current distribution of these trees within an arid environment, and of their various traditional uses. A strong relationship is demonstrated between the present location of the trees and settlements from the Roman and Byzantine periods (between the 1st century BCE to 7th century CE). Euphrates poplars are abundant today near early Christian monasteries, which could have been the main factor responsible for their present-day distribution.

Responses of two dominant desert plant species to the changes in groundwater depth in hinterland natural oasis, Tarim Basin.

Groundwater is increasingly becoming a permanent and steady water source for the growth and reproduction of desert plant species due to the frequent channel cutoff events in arid inland river basins. Although it is widely acknowledged that the accessibility of groundwater has a significant impact on plant species maintaining their ecological function, little is known about the water use strategies of desert plant species to the groundwater availability in Daryaboyi Oasis, Central Tarim Basin. This study initially determined the desirable and stressing groundwater depths based on ecological and morphological parameters including UAV‐based fractional vegetation cover (FVC) images and plant growth status. Then, leaf δ13C values of small‐ and big‐sized plants were analyzed to reveal the water use strategies of two dominant woody species (Populus euphratica and Tamarix ramosissima) in response to the groundwater depth gradient. The changes in FVC and growth status of plants suggested that the actual groundwater depth should be kept at an appropriate range of about 2.1–4.3 m, and the minimum groundwater depth should be less than 7 m. This will ensure the protection of riparian woody plants at a normal growth state and guarantee the coexistence of both plant types. Under a desirable groundwater condition, water alternation (i.e., flooding and rising groundwater depth) was the main factor influencing the variation of plant water use efficiency. The obtained results indicated that big‐sized plants are more salt‐tolerant than small ones, and T. ramosissima has strong salt palatability than P. euphratica. With increasing groundwater depth, P. euphratica continuously decreases its growth status to maintain hydraulic efficiency in drought condition, while T. ramosissima mainly increases its water use efficiency first and decreases its growth status after then. Besides, in a drought condition, T. ramosissima has strong adaptability than P. euphratica. This study will be informative for ecological restoration and sustainable management of Daryaboyi Oasis and provides reference materials for future research programs.

Assessment of Poplar Looper (Apocheima cinerarius Erschoff) Infestation on Euphrates (Populus euphratica) Using Time-Series MODIS NDVI Data Based on the Wavelet Transform and Discriminant Analysis

Poplar looper (Apocheima cinerarius Erschoff) is a destructive insect infesting Euphrates or desert poplars (Populus euphratica) in Xinjiang, China. Since the late 1950s, it has been plaguing desert poplars in the Tarim Basin in Xinjiang and caused widespread damages. This paper presents an approach to the detection of poplar looper infestations on desert poplars and the assessment of the severity of the infestations using time-series MODIS NDVI data via the wavelet transform and discriminant analysis, using the middle and lower reaches of the Yerqiang River as a case study. We first applied the wavelet transform to the NDVI time series data in the period of 2009–2014 for the study area, which decomposed the data into a representation that shows detailed NDVI changes and trends as a function of time. This representation captures both intra- and inter-annual changes in the data, some of which characterise transient events. The decomposed components were then used to filter out details of the changes to create a smoothed NDVI time series that represent the phenology of healthy desert poplars. Next the subset of the original NDVI time series spanning the time period when the pest was active was extracted and added to the smoothed time series to generate a blended time series. The wavelet transform was applied again to decompose the blended time series to enhance and identify the changes in the data that may represent the signals of the pest infestations. Based on the amplitude of the enhanced pest infestation signals, a predictive model was developed via discriminant analysis to detect the pest infestation and assess its severity. The predictive model achieved a severity classification accuracy of 91.7% and 94.37% accuracy in detecting the time of the outbreak. The methodology presented in this paper provides a fast, precise, and practical method for monitoring pest outbreak in dense desert poplar forests, which can be used to support the surveillance and control of poplar looper infestations on desert poplars. It is of great significance to the conservation of the desert ecological environment.

Drought adaptability of phreatophytes: insight from vertical root distribution in drylands of China

Abstract Aims The vertical distribution of plant roots is a comprehensive result of plant adaptation to the environment. Limited knowledge on fine vertical root distributions and complex interactions between roots and environmental variables hinders our ability to reliably predict climatic impacts on vegetation dynamics. This study attempts to understand the drought adaptability of plants in arid areas from the perspective of the relationship between vertical root distribution and surroundings. Methods By analyzing root profiles compiled from published studies, the root vertical profiles of two typical phreatophytes, Tamarix ramosissima and Populus euphratica, and their relationships with environmental factors were investigated. A conceptual model was adopted to link the parameter distribution frequency with plant drought adaptability. Important Findings The strong hydrotropism (groundwater-dependent) and flexible water-use strategy of T. ramosissima and P. euphratica help both species survive in hyperarid climates. The differences in the developmental environments between T. ramosissima and P. euphratica can be explained well by the different distribution characteristics of root profiles. That is, higher root plasticity helps T. ramosissima develop a more efficient water-use strategy and therefore survive in more diverse climatic and soil conditions than P. euphratica. We conclude that the higher variation in root profile characteristics of phreatophytes can have greater root adaptability to the surroundings and thus wider hydrological niches and stronger ecological resilience. The inadequacy of models in describing root plasticity limits the accuracy of predicting the future response of vegetation to climate change, which calls for developing process-based dynamic root schemes in Earth system models.

Variations in water use strategies of sand-binding vegetation along a precipitation gradient in sandy regions, northern China

Water is the most important factor limiting the growth of sand-binding vegetation (SBV) in desert ecosystems. This study explored the water sources and water use strategies of SBV under a natural precipitation gradient. Six typical SBV species were selected, comprising three tree species, Pinus sylvestris, Haloxylon ammodendron and Populus euphratica, and three shrub species, Artemesia ordosica, Caragana korshinshii and Tmarix ramosissima. The stable isotope values (δD, δ18O) of xylem water and potential water sources (precipitation, soil water, and groundwater) of these species under a precipitation gradient in the sandy regions of northern China were measured. In addition, the relative contributions of the different potential water sources to water use by SBV were analyzed using the MixSIAR model. The results indicated that the Local Meteoric Water Lines (LMWLs) of the six SBV species were located on the right side of the Global Meteoric Water Line (GMWL), with the degree of deviation gradually increasing with a decrease in precipitation. The results showed that T. ramosissima, H. ammodendron and P. euphratica mainly used groundwater (GW), whereas P. sylvestris, A. ordosica and C. korshinshii mainly used soil water. Among those species using soil water, P. sylvestris and A. ordosica mainly used shallow soil water (20–80 cm). P. sylvestris and C. korshinshii showed the highest soil water utilization rate of 14%, whereas P. euphratica showed the lowest soil water utilization rate of 2%. The different SBV species showed significantly different soil water utilization rates due to the influence of plant root distribution (p < 0.001). Among the six SBV species, trees showed a higher GW utilization rate compared to shrubs at 65.74% and 47.29%, respectively, whereas shrubs showed a higher deep soil water utilization rate (140–200 cm) compared to trees at 65.74% and 47.29%, respectively. The precipitation utilization rates amongst the six SBV species were highest in spring, followed by autumn and summer. The utilization of GW by SBV will be intensified in the future due to climate change. However, the stability of T. ramosissima may pose a threat due to its low utilization rate of GW.

Assessment of the current status of the turanga forests in the south-east of Kazakhstan

Data reflecting the current state of Turanga forests in the South-East of Kazakhstan (within the Almaty region) is presented based on the analysis of forest management (as of 01.01.2020) and field surveys by authors in the period 2015-2020. It was found that stunted, understocked stands, which are mainly mature and over-mature in terms of age composition dominate. By the species composition of the stand is prevailed by pure plantings or with a slight admixture of Elaeagnus oxycarpa. Natural regeneration in the form of creeping-rooted specimens was observed only in some small areas, which characterizes the plantings as unstable. Rare, relict and endemic species of trees and shrubs are noted in the composition of the flora of the Turanga forests, their phytocoenotic indexes and practical significance are evaluated. Turanga woodlands need special protection, because these forests have a great environment-forming, soil-fixing, and reclamation value, i.e., they generally stabilize the ecological situation in the floodplains of rivers in arid regions. The main factors of anthropogenic impact on the Turanga forests of the region are shown: changes of the hydrological regime in the Ili River valley, recreation (increasing the road and path network, trampling the soil, setting up campfires), as well as grazing. Proposals are made to improve the protection of these relict forests and an analysis of ways to preserve individual floral elements based on clonal micropropagation methods is given. Key words: Populus pruinosa, Populus diversifolia, bonitet, age-class composition, endemic, relict, abundance, plant community. &nbsp;

Different sexual impacts of dioecious Populus euphratica on microbial communities and nitrogen cycle processes in natural forests

Plant-soil microbe interactions are determined by plant characters. Sexual dimorphism in root development, nitrogen (N) assimilation and resource allocation have been studied in different environments. However, how dioecious plants affect soil microbial communities in natural forests, particularly in low precipitation regions, is still poorly known. In this study, natural Populus euphratica forests were investigated in three arid regions. We hypothesized that males and females impose sex-specific impacts on physiochemical traits of soil, microbial communities and N-cycling processes. We discovered only little sex effect on most physiochemical traits, and bacterial and fungal communities in top soil (0–20 cm) in the three studied forests. However, the sex effect was greater in deep soil. Compared with fungi, the structure and composition of bacterial communities were affected more by plant sex in the rhizosphere and bulk soil. Sex indirectly affected N-cycling processes through a negative impact on the soil water content. Expressions of AOA, AOB, nifH, nirS and nirK in the rhizosphere soil were significantly affected by sex, forest site and their interactions. Proteobacteria, Actinobacteria and Firmicutes in the rhizosphere and bulk soils of P. euphratica males showed more significant effects on ammoxidation, N fixation, denitrification and protease activities when compared to females. The results suggest that sexual differences in shaping bacterial communities and affecting N-cycling processes are greater when the soil becomes drier. Thus, low precipitation causes intense sex differences in the nitrogen uptake and use efficiency. Our study highlights the importance of sexual effects on shaping specific microbial communities and N-cycling processes.

Analysis on water use efficiency of Populus euphratica forest ecosystem in arid area

Water use efficiency (WUE, the ratio of gross primary productivity (GPP) to evapotranspiration (ET)) reflects the coupled relationship between water loss and carbon gain in the process of plant photosynthetic carbon assimilation. As a dominant tree species in arid area, Populus euphratica plays an important ecological role in slowing desertification. Here, continuous observations of carbon, water, and energy fluxes were carried out in Populus euphratica forest with eddy covariance (EC) technique in 2018. We systematically explained the variation characteristics of energy fluxes and WUE at different time scales, and explored the main controlling factors of WUE in drought-stressed environment based on the synchronous meteorological data. Results showed that the carbon exchange of the Populus euphratica forest ecosystem occurred mainly during the growing seasons (April–October). During this period, the entire ecosystem appeared as a carbon sink with the potential to sequester atmospheric carbon dioxide. The average daily WUE was 2.2 g C/kg H2O, which was lower than other temperate forests (2.57–6.07 g C/kg H2O) but higher than grassland, wetland, and cropland. We also concluded that an increase in carbon dioxide concentration (CCO2) and air relative humidity (RH) could promote the increase of WUE. Nevertheless, WUE was negatively correlated with air temperature (Ta), photosynthetically active radiation (PAR), and normalized difference vegetation index (NDVI). Additionally, WUE increased under moderate soil water content (SWC), but decreased due to the continuously rising SWC. WUE was more strongly affected by factors affecting water consumption than carbon uptake. Under the conditions of high temperature, strong radiation and low humidity in the summer, the growth rate of ET was much larger than that of GPP. This study not only contributes to our understanding of the carbon, water, and energy dynamics of the Populus euphratica forest ecosystem but also provides an important reference for ecological conservation and ecological restoration in arid regions.

Evapotranspiration partitioning for multiple ecosystems within a dryland watershed: Seasonal variations and controlling factors

Partitioning of evapotranspiration (ET) into evaporation (E) and transpiration (T) is challenging but important to better understand the mechanisms of water loss from the ground surface to the atmosphere, especially in semiarid and arid regions. In this study, the underlying water use efficiency (uWUE) method is compared with hydrometric and remote sensing-based ET partitioning methods. The uWUE method is considered to be a promising method for partitioning ET, and can also be used to obtain temporal continuous data with fine spatial representation. Thus, the uWUE method was used to partition ET in six typical ecosystems in the Heihe River basin (HRB), which is the second largest endorheic river basin in western China. During 2008–2016, the daily average contributions of T to ET (T/ET) were 0.53, 0.52, 0.59, 0.37, 0.56, and 0.59 in the alpine meadow, Qinghai spruce, maize, desert, Tamarix, and Populus euphratica–Tamarix ecosystems, respectively. The T/ET ratio exhibited obvious seasonal variations in alpine meadow, maize, Tamarix, and Populus euphratica–Tamarix ecosystems. The ET partitioning results were related to air temperature in all ecosystems, especially in areas with sufficient precipitation or irrigation water supply. The vapor pressure deficit was also a main controlling factor in the upper- and middle-reach ecosystems, especially in the Qinghai spruce ecosystem. Groundwater and/or soil moisture made high relative contributions (RCs, %) to the T/ET ratio of the riparian forest in the lower reaches. Additionally, the leaf area index also made a high RC to the T/ET ratio of deciduous vegetation. Determining the quantitative contribution of T to ET in the HRB is beneficial for water resource management to guide the rational allocation and efficient use of water resources.

Effect of the competition mechanism of between co-dominant species on the ecological characteristics of Populus euphratica under a water gradient in a desert oasis

The relationship between the growth characteristics of vegetation and factors that limit the protection of relevant populations and communities needs to be clarified. To gain a deeper understanding of the mechanism that couples groundwater factors with the growth of Populus euphratica in a desert ecosystem, as well as to explore the effect of its competitive relationship with Tamarix chinensis under the restrictive conditions of self-development and community succession, we established 11 typical sample plots in the Daliyaboyi Oasis in the Taklimakan Desert. In the current study, we evaluated the competitive relationship between these two dominant species under a groundwater gradient to illustrate the effect of the competition between groundwater factors and restrictive conditions on the plasticity of the ecological characteristics of P. euphratica via redundancy analysis. The results showed that groundwater depth and pH were the main variables that controlled growth and development of P. euphratica. Spatial heterogeneity of the water environment caused changes in the morphological and physiological characteristics of P. euphratica. Groundwater factors induced competition between P. euphratica and T. chinensis. Such a stress relationship prompts P. euphratica to reduce its own population density as well as photosynthetic and metabolic rates to ensure its survival and remain as a dominant species. Our results support the hypothesis that competition does not produce a single elimination effect and that complex symbiotic mechanisms may reduce the severity of low-density population competition to ensure the coexistence of species.

A gene that underwent adaptive evolution, LAC2 (LACCASE), in Populus euphratica improves drought tolerance by improving water transport capacity

Drought severely limits plant development and growth; accordingly, plants have evolved strategies to prevent water loss and adapt to water deficit conditions. However, experimental cases that corroborate these evolutionary processes are limited. The LACCASEs (LACs) family is involved in various plant development and growth processes. Here, we performed an evolutionary analysis of LACs from Populus euphratica and characterized the functions of LACs in Arabidopsis and poplar. The results showed that in PeuLACs, multiple gene duplications led to apparent functional redundancy as the result of various selective pressures. Among them, PeuLAC2 underwent strong positive selection. Heterologous expression analyses showed that the overexpression of PeuLAC2 alters the xylem structure of plants, including thickening the secondary cell wall (SCW) and increasing the fiber cell length and stem tensile strength. Altogether, these changes improve the water transport capacity of plants. The analysis of the physiological experimental results showed that PeuLAC2-OE lines exhibited a stronger antioxidant response and greater drought tolerance than WT. Three genes screened by transcriptome analysis, NAC025, BG1, and UGT, that are associated with SCW synthesis and drought stress were all upregulated in the PeuLAC2-OE lines, implying that the overexpression of PeuLAC2 thickened the SCW, improved the water transport capacity of the plant, and further enhanced its drought tolerance. Our study highlights that genes that have undergone adaptive evolution may participate in the development of adaptive traits in P. euphratica and that PeuLAC2 could be a candidate gene for molecular genetic breeding in trees.

Bioinformatic analysis of chromatin organization and biased expression of duplicated genes between two poplars with a common whole-genome duplication

The nonrandom three-dimensional organization of chromatin plays an important role in the regulation of gene expression. However, it remains unclear whether this organization is conserved and whether it is involved in regulating gene expression during speciation after whole-genome duplication (WGD) in plants. In this study, high-resolution interaction maps were generated using high-throughput chromatin conformation capture (Hi-C) techniques for two poplar species, Populus euphratica and Populus alba var. pyramidalis, which diverged ~14 Mya after a common WGD. We examined the similarities and differences in the hierarchical chromatin organization between the two species, including A/B compartment regions and topologically associating domains (TADs), as well as in their DNA methylation and gene expression patterns. We found that chromatin status was strongly associated with epigenetic modifications and gene transcriptional activity, yet the conservation of hierarchical chromatin organization across the two species was low. The divergence of gene expression between WGD-derived paralogs was associated with the strength of chromatin interactions, and colocalized paralogs exhibited strong similarities in epigenetic modifications and expression levels. Thus, the spatial localization of duplicated genes is highly correlated with biased expression during the diploidization process. This study provides new insights into the evolution of chromatin organization and transcriptional regulation during the speciation process of poplars after WGD.

Physiological changes of three woody plants exposed to progressive salt stress

The saline character of water imposes restrictions on plant growth and survival in the Taklamakan Desert, China. Experiments were conducted on woody plant species, Tamarix ramosissima, Populus euphratica, and Haloxylon ammodendron grown under different levels of salinity to elucidate their adaptation to a saline environment. H. ammodendron accumulated large amounts of Na+ and Cl- in leaves. P. euphratica restricted redundant Na+ and Cl- transport to the shoots treated with lower NaCl concentrations. Na+ in leaves of T. ramosissima accumulated significantly only under higher NaCl concentrations (&ge; 200 mM NaCl). The analyzed plants' exposure to high saline concentrations induced oxidative stress as evidenced by the increase of H2O2 and malondialdehyde and changes in photosynthetic pigments, gas-exchange characteristics, and antioxidant enzyme activities. T. ramosissima and H. ammodendron exhibited a greater ability to adapt to saline-induced oxidative stress due to more efficient antioxidant enzyme system to prevent oxidative damage.