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Identification of genetics and hormonal factors involved in Quercus robur root growth regulation in different cultivation system
AbstractUnderstanding the molecular processes and hormonal signals that govern root growth is of paramount importance for effective forest management. While Arabidopsis studies have shed light on the role of the primary root in root system development, the structure of root systems in trees is considerably more intricate, posing challenges to comprehend taproot growth in acorn-sown and nursery-cultivated seedlings. In this study, we investigated Quercus robur seedlings using rhizotrons, containers, and transplanted containers to rhizotrons, aiming to unravel the impact of forest nursery practices on processes governing taproot growth and root system development. Root samples were subjected to RNA-seq analysis to identify gene expression patterns and perform differential gene expression and phytohormone analysis. Among studied cultivation systems, differentially expressed genes (DEGs) exhibited significant diversity, where the number of co-occurring DEGs among cultivation systems was significantly smaller than the number of unique DEGs in different cultivation systems. Moreover, the results imply that container cultivation triggers the activation of several genes associated with linolenic acid and peptide synthesis in root growth. Upon transplantation from containers to rhizotrons, rapid enhancement in gene expression occurs, followed by gradual reduction as root growth progresses, ultimately reaching a similar expression pattern as observed in the taproot of rhizotron-cultivated seedlings. Phytohormone analysis revealed that taproot growth patterns under different cultivation systems are regulated by the interplay between auxin and cytokinin concentrations. Moreover, the diversification of hormone levels within the root zone and cultivation systems allows for taproot growth inhibition and prompt recovery in transplanted seedlings. Our study highlights the crucial role of hormone interactions during the early stages of taproot elongation, influencing root system formation across.
Low Temperature Enhances N-Metabolism in Paxillus involutus Mycelia In Vitro: Evidence From an Untargeted Metabolomic Study
ABSTRACTThis metabolomic study investigates, using GC MS/MS analysis, the molecular response of Paxillus involutus mycelia to prolonged low temperature (4°C) exposure. Alongside reduced growth, decreased overall nutrient levels, and increased oxidative stress indicators, analyses revealed a significant increase in nitrogen (N) concentration and enhanced N metabolism, particularly via the GS–GOGAT pathway, which was associated with elevated concentrations of numerous amino acids. In contrast, carbon (C) metabolism was not intensified but largely reprogrammed, with varying changes in carbohydrate abundance but higher levels of several stress‐related metabolites, such as trehalose and inositol family members, indicating activation of tolerance mechanisms, all with unchanged C (%). These changes suggest enhanced NH4+ uptake and a redirection of glycolysis‐derived C skeletons towards N‐compound biosynthesis. The lack of massive upregulation of typical anti‐stress compounds under low temperature exposure indicates either acclimatisation or mild stress. Mycelial restructuring, including increased dry mass (%) and accumulation of chitin precursors, implies cell wall remodelling and cold acclimatisation, supported by changes in membrane components. All these findings suggest that low temperatures may enhance N metabolism in ECM fungi even without additional carbon supply, potentially affecting symbiotic balance under climate change. Further studies are needed to validate these mechanisms and ecological implications.
Root anatomical adaptations of contrasting ectomycorrhizal exploration types in Pinus sylvestris and Quercus petraea across soil horizons
Abstract Aims The anatomical characteristics of ectomycorrhizal exploration types in response to soil variability remain insufficiently understood. We examined the root anatomy of contact and long-distance exploration types in Pinus sylvestris and Quercus petraea, species with distinct ecological needs, across different soil horizons. Methods The diameter of ectomycorrhizal roots, the root absorptive traits i.e. proportion of cortex and mantle area, the percentage stele in the diameter, and the weighted average diameter of vessels (Ra) in the ectomycorrhizas were measured within ectomycorrhizas collected from organic and mineral soils across the soil profile. Results The absorptive traits varied along soil horizons, in which water and nutrient availability changed inversely. The proportion of cortex was associated with exploration type, but was not specific to tree species. However, the ectomycorrhizal diameter and the percentage of mantle within the root forming contact exploration type of P. sylvestris showed no variation among soil horizons. In contrast, the soil horizon significantly influenced all root anatomical traits in the contact exploration type of Q. petraea by enhancing the contribution of the absorption area of the root area, mainly in the illuvial horizon, but reaching the smallest value in the organic horizon. The Ra and the cell wall thickness of the vessels were strongly dependent on tree species. With increasing soil depth, Ra in Q. petraea increased, and stele proportion in root diameter decreased. Conclusion The results suggest that water acquisition traits differ among tree species, but traits associated with nutrient absorption (proportion of cortex and mantle area) within specific soil horizons are closely related to the ectomycorrhizal exploration type.
Adaptation of resource acquisition and investment in resource acquiring tissues of Betula nana in response to climatic constraints
Comparative RNA sequencing-based transcriptome profiling of Quercur robur: specific sets of genes involved in taproot and lateral roots emergence
Abstract Root development is well recognized in model plants, with many studies focusing only on primary root growth or lateral root initiation. However, taproot vs lateral root development has rarely been explored using molecular tools, and even less is understood about how the molecular processes engaged in taproot elongation shape the emergence of lateral roots in trees in the time-dependent manner. We address how gene expression is associated with elongation of taproot and lateral root formation of Quercus robur L. In addition, we have analyzed how the exogenous application of hormones and inhibitors shapes the root architecture. We also revealed that lateral root formation and emergence corresponds to expression of genes at specific taproot length points. Therefore, our study suggests that the pattern of gene expression in the taproot tips is involved in the shaping of lateral root growth. In addition, we have shown that lateral roots are characterized by a set of genes that are distinct from those expressed in the taproot tips. Insights from this study contribute to better understanding root development in trees.
Drought legacy effects on fine-root-associated fungal communities are modulated by root interactions between tree species
With climate change, the frequency of severe droughts is predicted to increase globally, resulting in increased forest dieback. Although fine-root systems and their associated fungi are considered crucial for tree nutrient exchange after a drought period and consequently for tree recovery, post-drought dynamics remain poorly understood. We rewatered mature European beech and Norway spruce after a 5-year experimental summer drought to shed light on belowground recovery processes. Therefore, we tracked the fine-root parameters growth, vitality, and mycorrhization in monospecific rooting zones with intraspecific root contact and mixed rooting zones with interspecific root contact of both tree species during the first 3 months of recovery, and we analyzed compositions of their root-associated fungal communities by DNA- and RNA-ITS2 sequencing. During recovery, the fine-root parameters differed between both tree species, with only minor effects of the tree rooting zone. Root-associated fungal communities showed no significant response to irrigation within 3 months after drought release. The rooting zone was the dominating factor affecting the root-associated fungal diversity, the abundance of trophic modes, and the response of individual saprotrophic and ectomycorrhizal (ECM) species. Furthermore, an analysis of the most abundant fungal species revealed that for ECM fungi, drought tolerance was common and for saprotrophs, a facultative, root-associated lifestyle. These results suggest that tree species-specific fungal communities are stable despite previous long-term drought and are closely associated with tree species-specific response patterns related to root survival and recovery. Moreover, an association between saprotrophic fungi and roots might be a strategy to support fungal drought survival.
Climate legacy in seed and seedling traits of European beech populations
Tree species’ ability to persist within their current distribution ranges is determined by seed germination and seedling growth. Exploring variation in these traits in relation to climatic conditions helps to understand and predict tree population dynamics, and to support species management and conservation under future climate. We analyzed seeds and seedlings of 26 European beech populations from the northeastern boundary of the species range to test whether: 1) adaptation to climatic conditions is reflected in depth of dormancy and germination of seeds; 2) climatic characteristics of origin predictably affect seedling traits. The variation in seed dormancy and germination in a laboratory test, and seedling growth and morphology traits in a nursery common-garden test was examined. Populations originating from warmer and drier sites (mostly from the northern region), compared to those from the opposite end of climatic gradient, germinated later, with a lower success, and produced seedlings with shorter and tougher roots. They had deeper dormancy and poorer seed germination capacity, and are likely more vulnerable to environmental changes. The climatic conditions at the origin shape the intraspecific variation of seed germination and seedling traits, and may limit regeneration from seed and affect adaptation potential of beech to increasing temperatures and decreasing precipitation.
Regenerating oak trees with different techniques has long-lasting legacy effects on root development, stem growth and plant physiology
Abstract Regeneration methods can have legacy effects on tree physiology and growth via differential root development and affect forest climate sensitivity. However, there are few studies providing a long-term perspective on how forest regeneration techniques affect root development and physiology of established seedlings that have grown into trees. This study investigates leaf carbon (C), oxygen (O) and nitrogen (N) isotope composition (δ13C, δ18O, δ15N) and stem growth in ⁓20-year-old oak (Quercus robur L.) trees regenerated in two stands by three methods: direct acorn sowing in the field, bare-root planting preceded by root pruning and containerized planting with the root plug intact. Leaf isotopic values were measured three times during summer, together with tree-ring δ13C. Ground penetrating radar analyses indicated that acorn sowing resulted in deep root systems compared shallower root systems of bare-root and containerized trees. Higher annual basal area increment was observed in acorn-sown oaks than in bare-root or containerized oaks. Leaf δ13C, δ18O and δ15N values varied among regeneration origins. Trees with deeper root systems consistently showed lower leaf δ18O values, regardless of the season, which suggests higher uptake of water from deep soil horizons and better leaf hydration. In contrast, oaks with shallower root systems exhibited higher leaf δ18O values, which were positively related with δ13C. More negative leaf δ15N values in shallow-rooted oaks pointed to higher water stress. A lack of correlation between N concentration and intrinsic water-use efficiency (iWUE) for containerized trees suggests that variability in stomatal conductance rates governed iWUE in these shallow-rooted oaks. The lack of correlation between leaf and tree-ring δ13C supports that leaf physiological processes do not necessarily explain latewood isotopic composition. We conclude that regeneration techniques have long-lasting, carry-over effects on root development, plant physiology and tree growth. The findings underscore the importance of considering tree regeneration origin and root distribution when assessing the impact of climate change on tree performance and forest vigor.
Gymnosperms demonstrate patterns of fine‐root trait coordination consistent with the global root economics space
Abstract Gymnosperms encompass a diverse group of mostly woody plants with high ecological and economic value, yet little is known about the scope and organization of fine‐root trait diversity among gymnosperms due to the undersampling of most gymnosperm families and the dominance of angiosperm groups in recent syntheses. New and existing data were compiled for morphological traits (root diameter, length, tissue density, specific root length [SRL] and specific root area [SRA]), the architectural trait branching ratio, root nitrogen content [N] and mycorrhizal colonization. We used phylogenetic least squares regression and principal component analysis to determine trait–trait relationships and coordination across 66 species, representing 11 of the 12 extant gymnosperm families from boreal, temperate, subtropical and tropical biomes. Finally, we compared the relationship between family divergence time and mean trait values to determine whether evolutionary history structured variation in fine‐root traits within the gymnosperm phylogeny. Wide variation in gymnosperm root traits could be largely captured by two primary axes of variation defined by SRL and diameter, and root tissue density and root nitrogen, respectively. However, individual root length and SRA each had significant correlations with traits defining both main axes of variation. Neither mycorrhizal colonization nor root branching ratio were closely related to other traits. We did not observe a directional evolution of mean trait values from older to more recently diverged gymnosperm families. Synthesis. Despite their unique evolutionary history, gymnosperms display a root economic space similar to that identified in angiosperms, likely reflecting common constraints on plants adapting to diverse environments in both groups. These findings provide greater confidence that patterns observed in broad syntheses justly capture patterns of trait diversity among multiple, distinct lineages. Additionally, independence between root architecture and other traits may support greater diversity in below‐ground resource acquisition strategies. Unlike angiosperms, there were no clear trends towards increasingly thin roots over evolutionary time, possibly because of lower diversification rates or unique biogeographic history among gymnosperms, though additional observations are needed to more richly test evolutionary trends among gymnosperms.