Drought stress is a major constraint in jujube production. Although abscisic acid (ABA) and cytokinin exert opposing effects on plant growth, recent findings revealed that their combined application enhanced drought tolerance in jujube; however, the underlying mechanism remains elusive. In this study, three exogenous treatments were applied to sour jujube seedlings under drought stress: 5 mg L^-1 ABA, a cytokinin mixture of 50 mg L^-1 6-benzylaminopurine (6-BA) and 100 mg L^-1 kinetin (KT), and a combined ABA and cytokinins solution. Transcriptomic and metabolomic analyses were integrated to elucidate how ABA and cytokinins jointly modulate drought responses. The results showed that ABA induced stem thickening, enhanced osmotic regulation and antioxidant capacity, upregulated the expression of cytochrome P450 84A1-like (CYP84A1) involved in lignin biosynthesis, and downregulated cinnamyl alcohol dehydrogenase (CAD). In contrast, cytokinins promoted stem elongation by upregulating elongation factor 2 and L-lactate dehydrogenase B, downregulating anthocyanin synthase (ANS) and peroxidase, and altering galactose/starch metabolism, thereby prioritizing growth at the expense of stress tolerance. The combined treatment reconciled these opposing effects, enhancing stress defense without compromising cytokinin-mediated growth advantage, inducing 3018 differential genes and 285 metabolites. The phenylpropanoid biosynthesis pathway was identified as central to ABA-cytokinin crosstalk, with upregulation of two CADs contributing to drought resistance and four genes encoding CAD, peroxidase, and cinnamate 4-hydroxylase (C4H) playing a critical role in this crosstalk. Additionally, beta-glucosidase 18 (BGLU18) was identified as a candidate gene correlated with 13 phenylpropanoids. Our findings reveal the molecular link between the phenylpropanoid pathway and ABA-cytokinin crosstalk in jujube drought tolerance.

Afforestation plays an important role in controlling soil erosion and nutrient loss on the Loess Plateau in China. However, previous studies on soil nutrient changes have mainly focused on the effects of tree species, whereas little is known about how changes in shrubs and herbs caused by afforestation drive soil nutrient changes. In this study, we examined the variation characteristics of understory vegetation and soil nutrients for different vegetation types. The results showed that compared to abandoned farmland, plantations significantly increased soil organic carbon and total nitrogen but had no significant effect on total phosphorus. Robinia pseudoacacia L. forests were more effective than Pinus tabuliformis Carr. forests in increasing soil nutrient content. In addition, herbaceous vegetation in the R. pseudoacacia forest better explained the soil nutrient variation, and herb abundance was the best explanatory variable; however, shrub vegetation contributed more to soil nutrient variation in the P. tabuliformis forest, and shrub abundance contributed the most. Accordingly, we determined that understory plant abundance, rather than species richness, may be the most important factor driving soil nutrient changes. Specifically, herb abundance in the R. pseudoacacia forest may drive soil nutrient changes mainly by regulating herb biomass and litter biomass. By contrast, shrub abundance in the P. tabuliformis forest indirectly affected soil organic carbon mainly by altering shrub biomass. Furthermore, although the phylogenetic relationships had less effect on soil nutrients than species composition, they also made important contributions. Therefore, the phylogenetic relationships should also be considered in addition to species composition when assessing the impact of vegetation on soil properties in the future.

The plant-specific Lateral Organ Boundaries Domain (LBD) transcription factors (TFs) are critical regulators of the expression of genes related to tissue development and stress responses. Sour jujube (Ziziphus jujuba var. spinosa), a stress-tolerant rootstock for jujube cultivation, remains understudied in terms of its LBD gene family. In this study, a genome-wide analysis of the sour jujube genome was performed and 37 ZjLBD genes were identified. These genes were phylogenetically classified into two classes and six subgroups based on evolutionary relationships with Arabidopsis and poplar. These genes were unevenly distributed across 11 chromosomes, with 15 segmental duplication events detected. Upstream TFs of ZjLBDs were predicted and grouped into six interactive networks, revealing that the functions of ZjLBDs may be enriched in stress response, hormone signaling, and tissue development. RNA-seq data demonstrated tissue-specific expression patterns of ZjLBDs, with limited genes highly expressed in fruit. The ZjLBD23 may regulate the development of flowers and white mature fruits, while ZjLBD11, ZjLBD13, ZjLBD22 and ZjLBD28 may be involved in lateral root formation. Analysis of the cis-acting elements, homology relationships and abiotic stress-induced expression levels suggested functional divergence: ZjLBD13, ZjLBD19 and ZjLBD28 may contribute to extreme cold resistance, ZjLBD11, ZjLBD14, ZjLBD33 and ZjLBD35 may be associated with drought tolerance, and ZjLBD9, ZjLBD13 and ZjLBD22 with salt stress adaptation. This study provides critical insights into the biological roles of ZjLBDs and lays a foundation for breeding sour jujube varieties with enhanced stress resilience.

Drought is a decisive abiotic constraint limiting the growth and yield of jujube, its alleviation is orchestrated by a complex hormonal network that governs the tree’s drought-resistance responses. Based on preliminary evidence that abscisic acid (ABA) and cytokinin play coordinated roles in drought adaptation, this study aimed to clarify their individual and combined effects on regulating drought resistance in sour jujube. Phenotypic responses, anatomical alterations, endogenous hormone profiles, and the expression levels of genes involved in the zeatin biosynthesis pathway after exogenous hormone spraying under drought stress were comprehensively analyzed. The results demonstrated that ABA and cytokinin significantly modulated drought adaptation of sour jujube across multiple aspects. Compared with the control group, ABA spraying xylem vessels number in leaf veins and roots, shortened stem internodes, and elevated the content of salicylic acid (SA), thereby enhancing drought resistance. In contrast, spraying cytokinin treatment increased drought sensitivity, expanded root xylem vessel diameter, and induced a slender stem and increased auxin content. Combined application of ABA and cytokinin was found to further increase vessel number and diameter in leaves and roots, improve branching density, and significantly increase SA, ABA, and jasmonic acid (JA) levels compared with single application of ABA and cytokinin. These factors may collectively enhance the drought resistance of sour jujube. Through weighted gene co-expression network analysis (WGCNA), candidate genes such as CGLD27 , GNAT10 , and LOC107415885 were obtained. Further analysis found that, both ABA and cytokinin inhibited zeatin biosynthesis, while accelerated trans-zeatin metabolism and delayed cis-zeatin turnover. Spraying of cytokinin enhanced isopentenyladenine degradation, which may reduce resistance, whereas downregulation of ZjZOG1 , ZjZOG2 , and ZjZOG3 may promote resilience. These findings provide a preliminary mechanistic framework for the role of ABA and cytokinin in drought adaptation of sour jujube.