Zhijun Li

Dryland riparian forests depend on river-derived water in arid landscapes, but the relative associations of regional climate, local soil moisture, and biodiversity with ecosystem multifunctionality (EMF) remain uncertain. We analysed data from 516 plots in Populus euphratica forests across northwestern China. EMF was quantified from eight vegetation and soil attributes using averaging and multi-threshold approaches. We combined species richness, Rao’s quadratic entropy, community-weighted trait axes, climate principal components, and soil principal components in mixed-effects models, hierarchical partitioning and partial least-squares path models. EMF declined from near- to far-riparian plots, whereas soil water content did not differ significantly among distance bands. Hydroclimatic stress was negatively associated with EMF, especially in far-riparian plots and at higher thresholds, while soil moisture was positively associated mainly at low-to-intermediate thresholds. The relative explanatory contributions of biodiversity varied across riparian positions and predefined functional thresholds: RaoQ contributed most near rivers at lower thresholds, species richness was more important at intermediate and far positions, and community-weighted traits became prominent under selected high-threshold conditions. Species richness and community-weighted trait axes also changed with riparian distance, whereas RaoQ was comparatively stable. In the PLS-PMs, modelled direct abiotic associations were generally stronger than indirect associations involving biodiversity. Given the observational study design and correlational analyses, these findings indicate context-dependent associations among climate, soil moisture, biodiversity and ecosystem multifunctionality rather than causal relationships.

To reveal the variation patterns and differences in the adaptation strategies of leaf functional traits between male and female Populus euphratica in an arid desert environment, this study evaluated the effects of sex, developmental stage, and their interaction on 31 leaf traits using variance partitioning and trait network analysis. Furthermore, we analyzed the topological characteristics of the trait networks across two dimensions: developmental stage and vertical canopy gradient. The results indicated that sex moderately explained the variation in leaf nutrient characteristics (N and K) and physiological resistance indicators (Pro). Meanwhile, developmental stage largely accounted for variations in traits such as leaf dry weight, leaf width, specific leaf area, and photosynthetic physiology. The interaction between sex and developmental stage significantly influenced leaf anatomical structures and water-use strategies. Leaf trait network analysis revealed that during development, the male network exhibited higher connectivity and shorter average path lengths, with its core traits shifting from photosynthetic physiological indicators to nutrient and water transport characteristics; female plants exhibited higher network modularity during key developmental stages, with core nodes concentrated on leaf area, biomass, and structural traits. Along the vertical canopy gradient, the male leaf trait network showed pronounced topological reorganization in the mid-to-upper layers, suggesting a stronger capacity to respond to environmental fluctuations. Conversely, the core hubs of the female leaf trait network shifted from morphogenesis toward a synergy between structure and metabolism, which may be associated with maintaining system stability at different canopy heights. These findings suggest that female and male P. euphratica may adopt “conservative” and “acquisitive” ecological adaptation strategies, respectively, potentially leading to differentiated patterns of trait variation and coordination. This study provides a theoretical basis for understanding the potential ecological adaptation mechanisms and evolutionary strategies underlying sexual dimorphism in desert plants.

Plant AT-rich sequence and zinc-binding (PLATZ) proteins are a class of plant-specific transcription factors that have been identified and functionally characterised in multiple species. However, the PLATZ gene family has not yet been systematically characterised in Populus euphratica. In this study, 19 PePLATZ genes were identified and classified into five subgroups. The analyses of gene structure, conserved motifs and protein domains indicated that the PLATZ family is highly conserved during evolution. Meanwhile, promoter cis-acting element profiling suggested their potential roles in stress-responsive transcriptional regulation. Transcriptomic and qRT-PCR analyses showed that PePLATZ1, PePLATZ6, PePLATZ8, PePLATZ14 and PePLATZ19 were highly expressed in the roots, stems and leaves of P. euphratica and were strongly induced by drought stress. PePLATZ8 localised to the nucleus and lacked transactivation activity but acted as a transcriptional repressor in planta. Transgenic poplar lines overexpressing PePLATZ8 exhibited significantly enhanced drought tolerance. Furthermore, after drought treatment, PePLATZ8-overexpressing plants accumulated high levels of H₂O₂ and exhibited significantly increased total superoxide dismutase activity, which likely contributed to improved drought tolerance. Together, the above findings deepen our understanding of the structure–function relationships of PePLATZ proteins and identify PePLATZ8 as a promising candidate gene for the molecular breeding of drought-resistant poplar germplasm.

Auxin plays a crucial role in plant growth and development via concentration gradient regulation, with auxin response factors (ARFs) as key transcription factors in its signalling pathway. However, comprehensive identification and characterisation of ARF genes in Salicaceae remain limited. This study performed a genome-wide analysis of ARF genes in three Salicaceae species (Populus euphratica Oliv., Populus pruinosa, and Salix sinopurpurea), aiming to clarify their physicochemical properties, evolutionary relationships, and functional relevance. A total of 34 ARF genes were identified in each species, all being nucleus-localised hydrophilic unstable proteins clustered into six phylogenetic subgroups. Their promoters contain numerous cis-acting elements responsive to light, phytohormones, and stresses. Transcriptome and qRT-PCR data showed significant up-regulation of PeARF18 in ovate/broad-ovate leaves of P. euphratica compared to linear/lanceolate leaves. This study provides preliminary insights into the characterisation and potential role of the Salicaceae ARF gene family, laying a foundation for further functional exploration of PeARF18 in P. euphratica leaf shape development.

Populus euphratica Oliv. serves as a keystone species in desert riparian ecosystems. Owing to its pronounced tolerance to drought and salinity, as well as its robust reproductive capacity, it has become a pioneer species in desert oases. The xyloglucan endotransglucosylase (XET)/hydrolase (XTH) gene family plays a critical role in the remodeling of plant cell walls; however, its potential biological functions in poplar remain poorly understood. In this study, we identified the XTH gene family in P. euphratica and conducted a preliminary functional analysis. A total of 33 PeXTH genes were identified, which were unevenly distributed across the chromosomes, with the highest density observed on chromosome 6. Conserved domain analysis indicated that most members contain the typical GH16 domain associated with xyloglucan endotransglucosylase activity. Phylogenetic analysis classified them into four distinct subgroups, exhibiting evolutionary conservation with the model dicot plant of Arabidopsis thaliana. Notably, the promoter analysis revealed an abundance of ABA-responsive and stress-related cis-elements, suggesting their potential involvement in response to multiple stresses. Under drought stress, PeXTH7 (PeuTF07G00088.1) exhibited a distinct expression pattern, with transcript levels significantly increasing with persistent treatment. RT-qPCR results confirmed that PeXTH7 is highly expressed in both roots and leaves. Furthermore, subcellular localization assays demonstrated that the PeXTH7 protein localizes to the secretory pathway and the cell wall, implying a role in cell wall dynamic remodeling through the regulation of xyloglucan metabolism. The PeXTH7-overexpressing transgenic lines exhibited a significant increase in root length compared to the wild-type controls. As the first systematic analysis of the XTH gene family in P. euphratica, this study fills an important knowledge gap and provides new insights into the adaptive mechanisms of desert tree species.

Improving plant water use efficiency (WUE) and drought tolerance by modulating stomatal activity constitutes a promising strategy for mitigating the impacts of water scarcity. SnRK2, a key component of the abscisic acid (ABA) signaling pathway, plays a critical role in modulating stomatal behavior under abiotic stress. However, the functional role of SnRK2 in regulating stomatal movement to enhance WUE and drought tolerance in Populus euphratica remains to be characterized. In this study, 11 PeSnRK2 genes were identified in the P. euphratica genome, each comprising 9–14 exons and exhibiting an uneven distribution across seven chromosomes. Subcellular localization predictions indicated that these proteins are predominantly localized in the Cytoplasm and Cytoskeleton. Phylogenetic analysis grouped the PeSnRK2 genes into three distinct subfamilies, and conserved gene structures were observed within each clade. Analysis of cis-acting regulatory elements suggested that PeSnRK2 genes were involved in hormonal signaling and stress response pathways. Further transcriptomic data also indicated substantial alterations in PeSnRK2 expression due to polyethylene glycol (PEG) and abscisic acid (ABA) treatment. Finally, qRT-PCR and subcellular localization showed that PeSnRK2.6 is highly induced by ABA and functions in both nucleus and cytoplasm. This first characterization in a desert woody species bridged gaps in SnRK2 evolution and function.

Abscisic acid (ABA) is a key phytohormone involved in regulating plant growth and responses to environmental stress. As receptors of ABA, pyrabactin resistance 1 (PYR)/PYR1-like (PYL) proteins play a central role in initiating ABA signal transduction. In this study, a total of 30 PopPYL genes were identified and classified into three sub-families (PYL I–III) in the pan-genome of 17 Populus species, through phylogenetic analysis. Among these subfamilies, the PYL I subfamily was the largest, comprising 21 members, whereas PYL III was the smallest, with only four members. To elucidate the evolutionary dynamics of these genes, we conducted synteny and Ka/Ks analyses. Results indicated that most PopPYL genes had undergone purifying selection (Ka/Ks < 1), while a few were subject to positive selection (Ka/Ks > 1). Promoter analysis revealed 258 cis-regulatory elements in the PYL genes of Populus euphratica (EUP) and Populus pruinosa (PRU), including 127 elements responsive to abiotic stress and 33 ABA-related elements. Furthermore, six structural variations (SVs) were detected in PYL_EUP genes and significantly influenced gene expression levels (p < 0.05). To further explore the functional roles of PYL genes, we analyzed tissue-specific expression profiles of 17 PYL_EUP genes under drought stress conditions. PYL6_EUP was predominantly expressed in roots, PYL17_EUP exhibited leaf-specific expression, and PYL1_EUP showed elevated expression in stems. These findings suggest that the drought response of PYL_EUP genes is tissue-specific. Overall, this study highlights the utility of pan-genomics in elucidating gene family evolution and suggests that PYL_EUP genes contribute to the regulation of drought stress responses in EUP, offering valuable genetic resources for functional characterization of PYL genes.

DNA methylation, mediated by DNA methyltransferases (DMTs) and demethylases (DMLs), is an important epigenetic modification that maintains genomic stability and regulates gene expression in plant growth, development, and stress responses. However, a comprehensive characterization of these gene families in Populus sect. Turanga remains lacking. In this study, eight PeDMT and two PeDML genes were identified in Populus euphratica, and six PpDMT and three PpDML genes in Populus pruinosa. Phylogenetic analysis revealed that DMTs and DMLs could be classified into four and three subfamilies, respectively. The analysis of cis-acting elements indicated that the promoter regions of both DMTs and DMLs were enriched with elements responsive to growth and development, light, phytohormones, and stress. Collinearity analysis detected three segmentally duplicated gene pairs (PeDMT5/8, PeDML1/2, and PpDML2/3), suggesting potential functional diversification. Transcriptome profiling showed that several PeDMTs and PeDMLs exhibited leaf shape- and developmental stage-specific expression patterns, with PeDML1 highly expressed during early stages and in broad-ovate leaves. Whole-genome bisulfite sequencing revealed corresponding decreases in DNA methylation levels, suggesting that active demethylation may contribute to heteromorphic leaf formation. Overall, this study provides significant insights for exploring the functions and expression regulation of plant DMTs and DMLs and will contribute to future research unraveling the molecular mechanisms of epigenetic regulation in P. euphratica.

The distinctive leaf and twig heteromorphism in Euphrates poplar (Populus euphratica Oliv.) reflects its adaptive strategies to cope with arid environments across ontogenetic stages. In the key distribution area of P. euphratica forests in China, we sampled P. euphratica twigs (which grow in the current year) at different age classes (1-, 3-, 5-, 8-, and 11-year-old trees), then analyzed their morphological traits, biomass allocation, as well as allometric relationships. Results revealed significant ontogenetic shifts: seedlings prioritized vertical growth by lengthening stems (32.06 ± 10.28 cm in 1-year-olds) and increasing stem biomass allocation (0.36 ± 0.14 g), while subadult trees developed shorter stems (6.80 ± 2.42 cm in 11-year-olds) with increasesd petiole length (2.997 ± 0.63 cm) and lamina biomass (1.035 ± 0.406 g). Variance partitioning showed that 93%–99% of the trait variation originated from age and individual differences. Standardized major axis analysis demonstrated a consistent “diminishing returns” allometry in biomass allocation (lamina–stem slope = 0.737, lamina–petiole slope = 0.827), with age-modulated intercepts reflecting developmental adjustments. These patterns revealed an evolutionary trade-off strategy where subadult trees optimized photosynthetic efficiency through compact architecture and enhanced hydraulic safety, while seedlings prioritized vertical space occupation. Our findings revealed that heteromorphic twigs play a pivotal role in modular trait coordination, providing mechanistic insights into P. euphratica’s adaptation to extreme aridity throughout its lifespan.