Involvement of soluble proteins in growth and metabolic adjustments of drought-stressed Calligonum mongolicum seedlings under nitrogen addition

Plant root mechanisms and their effects on carbon and nutrient accumulation in desert ecosystems under changes in land use and climate

Deserts represent key carbon reservoirs, yet as these systems are threatened this has implications for biodiversity and climate change. This review focuses on how these changes affect desert ecosystems, particularly plant root systems and their impact on carbon and mineral nutrient stocks. Desert plants have diverse root architectures shaped by water acquisition strategies, affecting plant biomass and overall carbon and nutrient stocks. Climate change can disrupt desert plant communities, with droughts impacting both shallow and deep-rooted plants as groundwater levels fluctuate. Vegetation management practices, like grazing, significantly influence plant communities, soil composition, root microorganisms, biomass, and nutrient stocks. Shallow-rooted plants are particularly susceptible to climate change and human interference. To safeguard desert ecosystems, understanding root architecture and deep soil layers is crucial. Implementing strategic management practices such as reducing grazing pressure, maintaining moderate harvesting levels, and adopting moderate fertilization can help preserve plant-soil systems. Employing socio-ecological approaches for community restoration enhances carbon and nutrient retention, limits desert expansion, and reduces CO2 emissions. This review underscores the importance of investigating belowground plant processes and their role in shaping desert landscapes, emphasizing the urgent need for a comprehensive understanding of desert ecosystems.

Potential role of root-associated bacterial communities in adjustments of desert plant physiology to osmotic stress

Plants possess the ability to adapt to osmotic stress by adjusting their physiology and morphology and by cooperating with their root-associated (rhizosphere and endosphere) microbial communities. However, the coordination of host self-regulation with root-associated microorganisms at the community level, especially for desert plants, remains unclear. This study investigated the morphophysiological responses of seedlings from the desert plant Alhagi sparsifolia Shap to osmotic stress, as well as the relationships between these adaptations and their root-associated bacterial communities. The results indicated that osmotic stress contributed to a reduction in height and increased levels of reactive oxygen species (ROS) and malondialdehyde (MDA). In response, A. sparsifolia exhibited a series of morphophysiological adjustments, including increased ratio of root to shoot biomass (R/S) and the number of root tip, enhanced vitality, high levels of peroxidase (POD), ascorbate peroxidase (APX), and glutathione (GSH), as well as osmolytes (proline, soluble protein, and soluble sugar) and modification in phytohormones (abscisic acid (ABA) and jasmonic acid (JA)). Additionally, osmotic stress resulted in alterations in the compositions and co-occurrence patterns of root-associated bacterial communities, but not α-diversity (Chao1). Specifically, the rhizosphere Actinobacteria phylum was significantly increased by osmotic stress. These shifts in root-associated bacterial communities were significantly correlated with the host's adaptation to osmotic stress. Overall, the findings revealed that osmotic stress, in addition to its impacts on plant physiology, resulted in a restructuring of root-associated microbial communities and suggested that the concomitant adjustment in plant microbiota may potentially contribute to the survival of desert plants under extreme environmental stress.

Patterns of salt transport and factors affecting typical shrub in desert-oases transition areas

Soil salinization and water deficits are considered the primary factors limiting economic development and environmental improvement in arid areas. However, there remains limited knowledge of the adaptability of typical shrubs to salinization of desert areas in arid zones. This study was conducted in a desert oasis transition zone (Tarim River, China), aiming to investigate: i) the spatial-temporal changes in soil salinity; ii) the interactions between the pedoenvironment vs typical shrub (Calligonum mongolicum). The van Genuchten soil salinity retention ensemble model (TVGSSREM-3D) was developed to simulate variations in soil water-salt transport in the desert-oasis zone and to accurately explain the main factors influencing Calligonum mongolicum desert-oases transition areas. The results showed that monthly average salinity ranged from 2.0 to 8.0 g kg-1, with a peak in August (9.17 g kg-1). The presence of human activities (Salt Drainage Canal) and the distribution of Calligonum mongolicum resulted in a clear spatial salinity zonation. Moreover, analysis of environmental indicators using the TVGSSREM-3D model revealed strong correlations between the distribution of salinity in Calligonum mongolicum desert-oases transition areas and groundwater depth (GD), minimum relative humidity (MRH), and water vapor pressure (WVP). These findings provide a scientific basis for stabilizing, restoring, and reconstructing the ecosystem of the oasis-desert transition zone.

Drought resistance index screening and evaluation of lettuce under water deficit conditions on the basis of morphological and physiological differences

Introduction

Water is one of the important factors affecting the yield of leafy vegetables. Lettuce, as a widely planted vegetable, requires frequent irrigation due to its shallow taproot and high leaf evaporation rate. Therefore, screening drought-resistant genotypes is of great significance for lettuce production.

Methods

In the present study, significant variations were observed among 13 morphological and physiological traits of 42 lettuce genotypes under normal irrigation and water-deficient conditions.

Results

Frequency analysis showed that soluble protein (SP) was evenly distributed across six intervals. Principal component analysis (PCA) was conducted to transform the 13 indexes into four independent comprehensive indicators with a cumulative contribution ratio of 94.83%. The stepwise regression analysis showed that root surface area (RSA), root volume (RV), belowground dry weight (BDW), soluble sugar (SS), SP, and leaf relative water content (RWC) could be used to evaluate and predict the drought resistance of lettuce genotypes. Furthermore, the drought resistance ranks of the genotypes were similar according to the drought resistance comprehensive evaluation value (D value), comprehensive drought resistance coefficient (CDC), and weight drought resistance coefficient (WDC). The cluster analysis enabled the division of the 42 genotypes into five drought resistance groups; among them, variety Yidali151 was divided into group I as a strongly drought-resistant variety, group II included 6 drought-resistant genotypes, group III included 16 moderately drought-resistant genotypes, group IV included 12 drought-sensitive genotypes, and group V included 7 highly drought-sensitive genotypes. Moreover, a representative lettuce variety was selected from each of the five groups to verify its water resistance ability under water deficit conditions. In the drought-resistant variety, it was observed that stomatal density, superoxide anion (O2.-wfi2) production rate, and malondialdehyde (MDA) content exhibited a low increase rate, while catalase (CAT), superoxide dismutase (SOD), and that peroxidase (POD) activity exhibited a higher increase than in the drought-sensitive variety.

Discussion

In summary, the identified genotypes are important because their drought-resistant traits can be used in future drought-resistant lettuce breeding programs and water-efficient cultivation.

Phosphorous Supplementation Alleviates Drought-Induced Physio-Biochemical Damages in Calligonum mongolicum

Calligonum mongolicum is a phreatophyte playing an important role in sand dune fixation, but little is known about its responses to drought and P fertilization. In the present study, we performed a pot experiment to investigate the effects of P fertilization under drought or well-watered conditions on multiple morpho-physio-biochemical attributes of C. mongolicum seedlings. Drought stress leads to a higher production of hydrogen peroxide (H₂O₂) and malondialdehyde (MDA), leading to impaired growth and metabolism. However, C. mongolicum exhibited effective drought tolerance strategies, including a higher accumulation of soluble sugars, starch, soluble protein, proline, and significantly higheractivities of peroxidase (POD) and catalase (CAT) enzymes. P fertilization increased the productivity of drought-stressed seedlings by increasing their growth, assimilative shoots relative water content, photosynthetic pigments, osmolytes accumulation, mineral nutrition, N assimilation, and reduced lipid peroxidation. Our findings suggest the presence of soil high P depletion and C. mongolicum high P requirements during the initial growth stage. Thus, P can be utilized as a fertilizer to enhance the growth and productivity of Calligonum vegetation and to reduce the fragility of the hyper-arid desert of Taklamakan in the context of future climate change.

The roles of HD-ZIP proteins in plant abiotic stress tolerance

Homeodomain leucine zipper (HD-ZIP) proteins are plant-specific transcription factors that contain a homeodomain (HD) and a leucine zipper (LZ) domain. The highly conserved HD binds specifically to DNA and the LZ mediates homodimer or heterodimer formation. HD-ZIP transcription factors control plant growth, development, and responses to abiotic stress by regulating downstream target genes and hormone regulatory pathways. HD-ZIP proteins are divided into four subclasses (I-IV) according to their sequence conservation and function. The genome-wide identification and expression profile analysis of HD-ZIP proteins in model plants such as Arabidopsis (Arabidopsis thaliana) and rice (Oryza sativa) have improved our understanding of the functions of the different subclasses. In this review, we mainly summarize and discuss the roles of HD-ZIP proteins in plant response to abiotic stresses such as drought, salinity, low temperature, and harmful metals. HD-ZIP proteins mainly mediate plant stress tolerance by regulating the expression of downstream stress-related genes through abscisic acid (ABA) mediated signaling pathways, and also by regulating plant growth and development. This review provides a basis for understanding the roles of HD-ZIP proteins and potential targets for breeding abiotic stress tolerance in plants.

Two Dominant Herbaceous Species Have Different Plastic Responses to N Addition in a Desert Steppe

Nitrogen (N) deposition rates are increasing in the temperate steppe due to human activities. Understanding the plastic responses of plant dominant species to increased N deposition through the lens of multiple traits is crucial for species selection in the process of vegetation restoration. Here, we measured leaf morphological, physiological, and anatomical traits of two dominant species (Stipa glareosa and Peganum harmala) after 3-year N addition (0, 1, 3, and 6 g N m-2 year-1, designated N0, N1, N3, and N6, respectively) in desert steppe of Inner Mongolia. We separately calculated the phenotypic plasticity index (PI) of each trait under different N treatments and the mean phenotypic plasticity index (MPI) of per species. The results showed that N addition increased the leaf N content (LNC) in both species. N6 increased the contents of soluble protein and proline, and decreased the superoxide dismutase (SOD) and the peroxidase (POD) activities of S. glareosa, while increased POD and catalase (CAT) activities of P. harmala. N6 increased the palisade tissue thickness (PT), leaf thickness (LT), and palisade-spongy tissue ratio (PT/ST) and decreased the spongy tissue-leaf thickness ratio (ST/LT) of S. glareosa. Furthermore, we found higher physiological plasticity but lower morphological and anatomical plasticity in both species, with greater anatomical plasticity and MPI in S. glareosa than P. harmala. Overall, multi-traits comparison reveals that two dominant desert-steppe species differ in their plastic responses to N addition. The higher plasticity of S. glareosa provides some insight into why S. glareosa has a broad distribution in a desert steppe.

Genome-wide identification of HD-ZIP transcription factors in maize and their regulatory roles in promoting drought tolerance

Drought is the main limiting factor of maize productivity, therefore improving drought tolerance in maize has potential practical importance. Cloning and functional verification of drought-tolerant genes is of great importance to understand molecular mechanisms under drought stress. Here, we employed a bioinformatic pipeline to identify 42 ZmHDZ drought responsive genes using previously reported maize transcriptomic datasets. The coding sequences, exon-intron structure and domain organization of all the 42 genes were identified. Phylogenetic analysis revealed evolutionary conservation of members of the ZmHDZ genes in maize. Several regulatory elements associated with drought tolerance were identified in the promoter regions of ZmHDZ genes, indicating the implication of these genes in plant response to drought stress. 42 ZmHDZ genes were distributed unevenly on 10 chromosomes, and 24 pairs of gene duplications were the segmental duplication. The expression of several ZmHDZ genes was upregulated under drought stress, and ZmHDZ9 overexpressing transgenic plants exhibited higher SOD and POD activities and higher accumulation of soluble proteins under drought stress which resulted in enhanced developed phenotype and improved resistance. The present study provides evidence for the evolutionary conservation of HD-ZIP transcription factors homologs in maize. The results further provide a comprehensive insight into the roles of ZmHDZ genes in regulating drought stress tolerance in maize.

Phytoremediation of secondary saline soil by halophytes with the enhancement of γ-polyglutamic acid

Soil salinization has severely affected the quality of tillage land in China, and most greenhouse soils in Shanghai suburb suffer from secondary salinization with high salinity levels dominated by Ca²⁺, Mg²⁺ and NO₃^-. In this work, a sandy loam soil (Calcaric Fluvisols) contaminated by the above ions was selected as research object, and the binding conditions and abilities of γ-polyglutamic acid (γ-PGA) to water-soluble Ca²⁺ and Mg²⁺ in the soil were examined, and then pot experiments were conducted to remove Ca²⁺, Mg²⁺ and NO₃^- by two halophytes (Sedum aizoon L., Sesbania cannabina Pers.) integrated with γ-PGA application. The results showed that under the conditions of adding 1000 mg L^-1γ-PGA (pH 7) and 25 °C, the binding efficiencies of Ca²⁺ and Mg²⁺ were 51.59% and 68.03%, respectively. Compared with Sesbania cannabina Pers., Sedum aizoon L. displayed better remediation performance for the soil with γ-PGA application in pot experiments, and the removal efficiencies of Ca²⁺, Mg²⁺ and NO₃^- reached 93.25%, 94.78% and 84.26% after applying 1000 mg L^-1γ-PGA for 56 d, respectively. Moreover, γ-PGA application could mitigate salt stress and promote plant growth, and activate antioxidant defense systems. Compared with the control, 1000 mg L^-1γ-PGA application significantly increased plant height and fresh weight of Sedum aizoon L., and the removal efficiencies of Ca²⁺, Mg²⁺ and NO₃^- increased by 45.48%, 82.62% and 69.91%, respectively. In the future, more in-depth mechanism of joint effect and field-scale investigation need to be further studied.