Annals of botany最新文献

Background and aims: The global supply of phosphorus (P) is decreasing. At the same time, climate change is reducing the availability of water in most regions of the world. Insights into how decreasing P availability influences plant architecture are crucial to understanding its influence on plant functional properties, such as the root system's water uptake capacity.

Methods: In this study, we investigated the structural and functional responses of Zea mays to varying P fertilization levels focusing especially on the root system's conductance. A rhizotron experiment with soils ranging from severe P deficiency to sufficiency was conducted. We measured the architectural parameters of the whole plant and combined them with root hydraulic properties to simulate time-dependent root system conductance of growing plants under different P levels.

Key results: We observed changes in the root system architecture, characterized by decreasing crown root elongation and reduced axial root radii with declining P availability. Modelling revealed that only plants with optimal P availability sustained a high root system conductance, while all other P levels led to a significantly lower root system conductance, under both light and severe P deficiency.

Conclusion: We postulate that P deficiency decreases root system conductance, which could mitigate drought conditions through a more conservative water use strategy, but ultimately reduces biomass and impairs root development and overall water uptake capacity. Our results also highlight that the organization of the root system, rather than its overall size, is critical for estimating important root functions.

Background: Roots anchor plants in the ground, providing an interface for interactions with the environment and sensing potential stressors. At the same time, they contribute to acclimatization to stressful conditions through their growth plasticity. Root growth is a combination of cell division and cell elongation, ultimately shaping root system architecture depending on environmental stimuli. Root thermomorphogenesis refers to the altered root growth response under moderately elevated ambient temperatures, characterized, for example, by an increase in primary root growth during early seedling development. While the molecular regulation of shoot thermomorphogenesis is comparatively well understood, the gene- and hormone-regulatory networks underlying root growth responses to warm temperature have only begun to be uncovered in recent years.

Scope: In this article, we review the latest findings of how root growth, comprising cell division and elongation, is regulated by the phytohormones auxin, cytokinins and brassinosteroids at optimal temperatures. We then summarize our current understanding of root growth responses to warm temperatures during early seedling development and the key role of auxin in this process. Furthermore, we address the contributions of cell division versus cell elongation to root thermomorphogenesis, discuss whether the root is autonomous in sensing and reacting to increased temperatures, and provide an outlook of how root thermomorphogenesis research can be applied to crops.

Conclusions: Root growth is a complex process that is tightly regulated and strongly depends on environmental factors. During early seedling development, elevated ambient temperatures stimulate auxin signalling, which leads to an increase in both cell division and elongation, resulting in elongated primary roots. It appears that the root can autonomously sense and react to temperature changes at this stage. Root thermomorphogenesis seems to be conserved among many plants, including crops, but its ecophysiological relevance remains open to further research.

Background and aims: Root ecology has rapidly advanced as a key discipline for understanding plant adaptive strategies and ecosystem functioning. However, comprehensive assessments of its overarching framework remain limited. This study provides a global perspective by systematically analysing research power, intellectual bases and research frontiers in root ecology.

Methods: We analysed 35 371 articles from the Web of Science Core Collection using CiteSpace and VOSviewer within a customized bibliometric framework. Co-occurrence analyses based on publication volume, citation frequency and micro-citation labels revealed the spatiotemporal distribution of research power. Intellectual bases and research frontiers were identified through document co-citation and cluster analyses.

Key results: The results indicate a three-phase growth trajectory in root ecology research over the past decade. China (13 027 articles) and the USA (5679 articles) dominate global academic output. Frontiers in Plant Science (2721 articles) and Plant and Soil (1436 articles) are the leading journals in terms of publication volume. Key articles forming the intellectual base of this field were identified and interpreted, encompassing six major aspects, including method standardization and the root economics spectrum theory. The research frontiers were clustered into five core themes - abiotic stress, microbial symbiosis, ecological remediation, functional traits and physiological mechanisms - which were further subdivided into 19 specific research directions.

Conclusions: Root ecology is evolving from a primarily theoretical discipline towards practical applications. To support sustainable agriculture, ecological restoration and carbon neutrality, the development of global observation networks and multifactorial stress models should be further advanced.

Background and aims: The frequency of extreme precipitation events is predicted to increase owing to climate change, leading to soil waterlogging and crop yield losses, particularly in the case of susceptible species, such as barley (Hordeum vulgare). Aerenchyma formation is a key morphological adaptation to waterlogging stress and hypoxic conditions; however, its genetic regulation in barley remains largely unresolved. The aim of this study was to address this knowledge gap and characterize the transcriptional signatures associated with the waterlogging stress response and aerenchyma formation in barley roots.

Methods: Two barley cultivars (Franklin and Yerong) were subjected to waterlogging stress, followed by analysis of phenotypic traits, including root aerenchyma formation, and transcriptomic profiling of root tissue. Differential gene expression analysis and gene regulatory network construction were carried out using generated RNA-sequencing datasets.

Key results: Performed analyses identified genes transcriptionally responsive to 24 and 72 h of waterlogging in both cultivars and highlighted metabolic adaptations, regulation of reactive oxygen species signalling and management of stress responses as key elements of the waterlogging response in barley roots. Large intra-individual variation was observed for root aerenchyma formation. This variation was exploited to identify 81 candidate aerenchyma-associated genes and ascertain pathways involved in aerenchyma formation. Furthermore, network analyses suggested that the DNA damage response gene DRT100 and the cell wall-modifying genes XTH16 and XTH15 are regulatory hub genes in aerenchyma formation.

Conclusions: This study provides new insights into transcriptional signatures associated with waterlogging responses and aerenchyma formation in barley roots. The identified candidate aerenchyma-associated genes offer new targets for future research and breeding efforts aimed at enhancing waterlogging tolerance in this crop species.

Background and aims: Understanding the relationship of root traits and crop performance under varying environmental conditions facilitates the exploitation of root characteristics in breeding and variety testing to maintain crop yields under climate change. Therefore, we (1) evaluated differences in root length and surface area between ten winter wheat varieties grown at 11 sites in Europe covering a large pedoclimatic gradient, (2) quantified differences in root response to soil, climate and management conditions between varieties, and (3) evaluated variety-specific relationships of grain yield and root length and surface area under diverse environmental conditions.

Methods: At each site, we sampled the roots to 1 m soil depth after harvest and determined various root traits by scanning and image analysis. The impacts of soil, climate and management on roots and yield of the ten varieties were analysed by means of multivariate mixed models.

Key results: Root length averaged 1.4 m root piece-1, 5007 m root m-2 soil, and 5300 m root m-2 soil and root surface area 0.039 m2 root piece-1, 40 m2 root m-2 soil, and 43 m2 root m-2 soil in 0.00-0.15 m, 0.15-0.50 m, 0.50-1.00 m soil depth, respectively. The variation in both traits was 10 times higher between sites than varieties, the latter ranging by a factor of 2 within sites. Irrespective of variety, temperature was a major driver of subsoil root traits, suggesting that warmer climates promoted root growth in deeper soil layers. Other soil and climate variables affected root length and/or root surface area of individual varieties, highlighting different degrees of root plasticity. The varieties displayed distinctly different relationships between yield and root traits under varying pedoclimatic conditions, highlighting genetic differences in yield response to environmentally driven root plasticity.

Conclusions: These findings suggest that breeding efforts should target flexible root-yield relationships in the subsoil to maintain crop performance under climate change.

Background and aims: The whole-plant economics spectrum describes coordination between organ-level traits that together determine resource-use strategies and is relevant for understanding plant responses to environmental change. Although coordination between organs has been explored previously across species, it remains unclear whether patterns observed across species hold within species. In addition, the key driving forces underlying this coordination warrant clarification.

Methods: In this study, we used univariate (regression analysis) and multivariate (principal components analysis and network analysis) analyses to investigate the environmental drivers of intraspecific trait variation and, consequently, trait covariation, focusing on leaf and fine root traits. We sampled 60 individuals of Schima superba, a widespread evergreen tree, across five elevations in a subtropical forest in China, measuring traits associated with resource use and capture, including photosynthesis, specific root length and root diameter.

Key results: Leaf and root traits were significantly correlated within species, forming a whole-plant economics spectrum. We found that plants at low and high elevations had more resource-acquisitive traits than at intermediate elevation. Notably, leaf and root traits, in addition to a composite variable that contained both, varied non-linearly with elevation. Leaf trait variation was driven primarily by temperature, whereas root trait variation and a composite variable containing leaf and root traits were most strongly influenced by temperature and plant-available soil phosphorus.

Conclusions: Our findings show that the coordinated responses of individual traits to climate and soil properties underlie intraspecific variation in whole-plant resource-use strategies across environmental gradients. These findings are contrary to recent studies that have found evidence of decoupling between above- and below-ground traits, which suggests that there is selection for coordination among traits in S. superba. Thus, our study enhances our understanding of the key drivers and the ecological significance of environmentally driven intraspecific trait variation.

Background and aims: Deep roots may help plants adapt to climate change by allowing them to access deeper soil layers where water is still available, reducing water stress and increasing nitrogen (N) uptake. Water stress significantly affects yield during later developmental stages, but methods are lacking for phenotyping for deep rooting under field conditions and at maturity.

Methods: Over 3 years, we used minirhizotron root imaging in the RadiMax semi-field facility to compare deep rooting in winter wheat genotypes grown in field soil to 2.7 m depth. We related this to deep soil uptake of water and N using isotopic tracers injected into the soil at 1.6-1.8 m depth. Carbon isotope discrimination was used to evaluate water stress levels.

Key results: Deep rooting was positively correlated with uptake of deep-placed N and water, and uptake of deep-placed N was three times higher in the genotype with deepest roots compared with the shallowest. Deep rooting was negatively correlated with water stress, measured using carbon isotope discrimination. This correlation was strongest in 2023, a dry year, highlighting the role of deep roots in mitigating water stress. Some genotypes had consistently deeper or shallower roots over the three experimental years, and there were strong correlations of isotopic measurements between genotypes across years.

Conclusions: Our findings show strong relationships between deep rooting and deep root functions, which indicate that deep rooting is a desirable trait that should be targeted. The significant genotypic variation observed, which can be phenotyped for even under field conditions, indicates that deep rooting is a trait that can be incorporated into breeding programmes. Furthermore, the methods used in this study are effective and should be developed for further application.

Background: Understanding how annual weather variation, including droughts, affects plant roots and rhizosphere prokaryote dynamics in different years is essential for predicting plant responses to climate fluctuations. This study aimed to investigate the effects of alternating dry and moist years on maize root gene expression and rhizosphere prokaryote composition, and to reveal interactions between the two.

Methods: Zea mays B73 wild-type (WT) and a root hair-deficient mutant (rth3) were grown on two substrates during a 3-year field experiment with alternating precipitation, designated as dry, moist and dry. Root gene expression was analysed between the two dry years and the moist year, supported by superoxide dismutase activity. The rhizosphere was analysed by measuring the enzyme kinetic parameters β-glucosidase, acid phosphatase, leucine aminopeptidase and N-acetylglucosaminidase, accompanied by the 16S rRNA-based and 1-aminocyclopropane-1-carboxylate deaminase (acdS+)-based microbial community.

Key results: Year was the main driver of root gene expression and the 16S rRNA-based microbial community, with a distinct pattern of drought-responsive genes between dry years and the moist year. Substrate was the main driver of the acdS+-based microbial community and influenced root gene expression and the 16S rRNA-based microbial community, indicating interactive effects between maize roots and rhizosphere prokaryotes. The effect of year and substrate on enzyme kinetics was enzyme-specific. Root hair presence had a marginal effect.

Conclusions: This study highlights the role of annual weather variation in shaping root gene expression, rhizosphere prokaryotes and enzyme kinetics and underlines the role of substrate in structuring acdS+-based microbial communities. Our results suggest that plant-microbe interactions are highly sensitive to precipitation variability and might be influenced by repeated maize planting. They emphasize the importance of precipitation history in shaping plant-microbe interactions, which can serve as a basis for drought resilience strategies in agriculture.

Background and aims: Plants have evolved various root adaptive traits to enhance their ability to access soil water in stressful conditions. Although root mucilage has been suggested to facilitate root water uptake in drying soils, its impact during combined edaphic and atmospheric stress remains unknown. We hypothesized that mucilage decreases the saturated soil hydraulic conductivity, and consequently, a genotype with high mucilage production will exhibit lower maximum soil-plant hydraulic conductance and restrict transpiration at relatively low vapour pressure deficit (VPD). On the contrary, in drying soil, mucilage attenuates the gradients in matric potential at the root-soil interface and thus facilitates root water uptake, especially at high VPD.

Methods: We compared two cowpea genotypes with contrasting mucilage production rates and subjected them to three consecutively increasing levels of VPD (1.04, 1.8 and 2.8 kPa) while the soil was left to dry out. We measured the transpiration rate and soil and leaf water potentials and estimated canopy and plant hydraulic conductance during soil drying.

Key results: In wet soil conditions, the high-mucilage genotype restricted transpiration rate at lower VPD (1.46 kPa) compared with the low-mucilage genotype (1.58 kPa). Likewise, the initial slope of transpiration rate in response to VPD (the maximum conductance) was significantly lower in the high- compared with the low-mucilage genotype. During soil drying, the transpiration rate declined earlier in the low- compared with the high-mucilage genotype, supporting the hypothesis that mucilage helps to maintain the hydraulic continuity between roots and soil at lower water potentials in the high-mucilage genotype.

Conclusions: Root mucilage is a promising trait that reduces water use in wet soil conditions, thereby conserving soil moisture for critical phases (e.g. flowering and grain filling), both on a daily basis (increasing VPD) and on a seasonal time scale (soil drying).

Background and aims: There is growing interest in the production of ancient grains including emmer, einkorn and spelt, particularly in low-input systems. Differences in their root systems and how these affect water and nitrogen uptake are not well known, but can offer important insights into the effects of plant breeding on resource use and root physiology, which can inform breeding of future crops.

Methods: In this study, we used imaging in minirhizotron tubes to evaluate root development in emmer, einkorn, spelt and modern wheat growing under field conditions, taking images to 2.2 m soil depth. We evaluated water stress in the different species using carbon isotope discrimination and used a nitrogen tracer to compare N uptake over time.

Key results: The results show that modern wheats have deeper and more efficient root systems. Modern wheats showed less water stress in late developmental stages due to their deeper roots which allow access to deep soil water, and can therefore sustain high grain yields. They were also able to translocate N more efficiently to the grain. The results contradict previous hypotheses that modern wheat has shallow rooting systems due to high inputs, showing that where more nutrient resources are available, deeper roots have become important for water uptake to support higher yields.

Conclusions: This is the first field study of roots of ancient and modern wheats, where we clearly see that there are substantial differences between the root systems. These results help to explain how past selection for yield has affected below-ground crop physiology.