root exudation
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Forests ◽  
2021 ◽  
Vol 12 (12) ◽  
pp. 1797
Author(s):  
Zuwang Li ◽  
Zhi Liu ◽  
Guoqiang Gao ◽  
Xinlei Yang ◽  
Jiacun Gu

Tree age has an important effect on the form and function of fine roots. Previous studies have focused on the variations in root morphological and chemical traits among tree ages, while less attention has been given to the physiological traits, impeding a full understanding of the relationship between root resource acquisition strategy and tree age. Here, we measured root morphological (diameter, specific root length, specific root area and tissue density), chemical (nitrogen concentration) and physiological (respiration and exudation rate) traits of young, middle-aged and mature trees of Fraxinus mandshurica in a temperate secondary forest in northeastern China. Our overall aim was to determine how root traits and related resource acquisition strategy change with tree age. The results showed that from young to mature trees, root diameter gradually increased, but specific root length, specific root area, root nitrogen concentration, respiration and exudation rates all decreased, and the significant differences were mainly found between young and mature trees. Pearson’s correlation analysis revealed that the relationships of root respiration and exudation rates to root morphological and chemical traits depended on tree age and the specific traits examined, but these correlations were all significant except for root tissue density when the data were pooled across all tree age classes. Principal component analysis (PCA) showed that the conservative traits represented by root diameter, and the acquisitive traits such as root respiration and exudation rates and related morphological and chemical traits, occupied two ends of the first axis, respectively, while root tissue density occupied one end of the second axis, partially confirming the conceptual framework of “root economics space”. Standardized major axis (SMA) analysis of root exudation and respiration rates showed that young trees allocated more root carbon flux to the formation of root exudation, compared to middle-aged and mature trees. Our findings suggest that root resource acquisition strategy in F. mandshurica appears to shift from an absorptive to conservative strategy associated with increasing tree age, which may have substantial consequences for individual growth and interspecific competition, as well as belowground carbon allocation in ecosystems.


2021 ◽  
Vol 12 ◽  
Author(s):  
Yuanhui Liu ◽  
Bin Ma ◽  
Wenfeng Chen ◽  
Klaus Schlaeppi ◽  
Matthias Erb ◽  
...  

Root-microbiome interactions are of central importance for plant performance and yield. A distinctive feature of legumes is that they engage in symbiosis with N2-fixing rhizobia. If and how the rhizobial symbiotic capacity modulates root-associated microbiomes are still not yet well understood. We determined root-associated microbiomes of soybean inoculated with wild type (WT) or a noeI mutant of Bradyrhizobium diazoefficiens USDA 110 by amplicon sequencing. UPLC-MS/MS was used to analyze root exudates. The noeI gene is responsible for fucose-methylation of Nod factor secreted by USDA 110 WT strain. Soybean roots inoculated with the noeI mutant showed a significant decrease in nodulation and root-flavonoid exudation compared to roots inoculated with WT strain. The noeI mutant-inoculated roots exhibited strong changes in microbiome assembly in the rhizosphere and rhizoplane, including reduced diversity, changed co-occurrence interactions and a substantial depletion of root microbes. Root exudates and soil physiochemical properties were significantly correlated with microbial community shift in the rhizosphere between different rhizobial treatments. These results illustrate that rhizobial symbiotic capacity dramatically alters root-associated microbiomes, in which root exudation and edaphic patterns play a vital role. This study has important implications for understanding the evolution of plant-microbiome interactions.


2021 ◽  
Vol 9 (12) ◽  
pp. 2456
Author(s):  
Ruixin Fu ◽  
Haichao Feng ◽  
Francisco Dini-Andreote ◽  
Zhen Wang ◽  
Chunbin Bo ◽  
...  

Plant hormones have been recently shown to exert an indirect influence on the recruitment of plant-associated microbiomes. However, it remains unclear the extent to which the disruption of the ethylene (ET) signaling pathway affects the assembly and functioning of plant-root microbiomes. In this study, the Never-ripe tomato mutant (Nr) was profiled for differences compared to the wild type (control). Tomato plants were subjected to root exudate profiling and the characterization of bacterial and fungal communities. Compared to the control, Nr revealed differences in the composition of root exudates, including lower amounts of esculetin, gallic acid, L-fucose, eicosapentaenoic acid, and higher amounts of β-aldehyde. Interestingly, Nr significantly differed in the composition and functioning of the rhizosphere bacterial community. We also identified the taxa that occurred at relatively higher abundances in Nr, including the genus Lysobacter, which displayed a significant negative correlation with changes in eicosapentaenoic acid and esculetin, and a significant positive correlation with changes in β-aldehyde. Taken together, our study provides evidence that a mutation in the ET receptor exerts predictable changes in the root-associated microbial taxa of tomato plants. These indirect effects can potentially be explored towards new strategies to engineer beneficial plant microbiomes via targeted changes in plant genetics and physiology.


2021 ◽  
Author(s):  
Yi Zhou ◽  
Yanli Wei ◽  
Zhongjuan Zhao ◽  
Jishun Li ◽  
Hongmei Li ◽  
...  

Abstract Background The microbiome in plant-soil systems has a significant influence in promoting plant growth. The extent of selectivity that the plant exerts on the microbiome in the continuum of internal plant tissues is not well understood. This study analysed the root microbiome of a legume, Melilotus officinalis (L.) Pall., sweet clover, and focused on dynamic shifts in the microbial community structure through the niches of bulk soil, rhizosphere, periderm, phloem and xylem, and further examined the effects of environmental factors, root exudates and root cell wall development on the microbiome assemblages in different root compartments.ResultsYoung and mature plants were sampled at 24 field sites and the microbial communities in different niches from bulk soil and rhizosphere through to root compartments were analysed by 16S rRNA gene sequencing. The microbiome composition changed from periderm to phloem to a greater extent than across other boundaries (0.95 vs 0.71 based Bray–Curtis distance). Variation in microbiome composition was associated with geographic distance and soil properties for the bulk soil, rhizosphere and periderm niches. The composition of root exudate compounds were correlated with the rhizosphere microbiome assemblages in mature and young plants. The endophyte communities that occupied the phloem and xylem were most conserved and were independent of growing environments and root exudation. Symbiotic rhizobia able to nodulate M. officinalis were prominent colonisers of the periderm (~15%) and xylem (~6.2%), but were only a minor component in other soil-related niches (0.1%-2.5%). In xylem tissues, endophyte diversity was correlated with the total cell wall and lignin content across the sampled sites (r=0.29-0.62). Conclusions Our results demonstrate that selection of microbiome constituents occurs at different boundaries through bulk soil, rhizosphere, periderm, phloem and xylem, and is especially strong across the periderm boundary. The conserved endophyte community in the innermost tissues (phloem and xylem) was identified, and will be advantageous to the development of specific beneficial microbial inoculants.


2021 ◽  
Author(s):  
Zhihui Wen ◽  
Philip J. White ◽  
Jianbo Shen ◽  
Hans Lambers

2021 ◽  
Author(s):  
Peng Wang ◽  
Lucas Dantes Lopez ◽  
Sophie Alvarez ◽  
Martha Lopez-Guerrero ◽  
Karin van Dijk ◽  
...  

Root exudates are important for shaping root-associated microbiomes. However, studies on a wider range of metabolites in exudates are required for a comprehensive understanding about their influence on microbial communities. We identified maize inbred lines that differ in exudate concentrations of DIMBOA and GABA using a semi-hydroponic system. These lines were grown in the field to determine the changes in microbial diversity and gene expression due to varying concentrations of DIMBOA and GABA in exudates using 16S rRNA amplicon sequencing and metatranscriptomics. Results showed individual and interaction effects of DIMBOA and GABA on the rhizosphere and root endosphere beta-diversity, most strongly at the V10 growth stage. The main bacterial families affected by both compounds were Ktedonobacteraceae and Xanthomonadaceae. Higher concentrations of DIMBOA in exudates affected the rhizosphere metatranscriptome, enriching for KEGG pathways associated with plant disease. This study validated the use of natural variation within plant species as a powerful approach for understanding the role of root exudates on microbiome selection. We also showed that a semi-hydroponic system can be used to identify maize genotypes that differ in GABA and DIMBOA exudate concentrations under field conditions. The impact of GABA exudation on root-associated microbiomes was shown for the first time.


2021 ◽  
Author(s):  
Valerie A Seitz ◽  
Bridget B McGivern ◽  
Mikayla A Borton ◽  
Jacqueline M. Chaparro ◽  
Rebecca A Daly ◽  
...  

Root exudation is one of the primary processes that mediate interactions between plant roots, microorganisms, and the soil matrix. Previous research has shown that plant root exudate profiles vary between species and genotypes which can likely support different microbial associations. Here, utilizing distinct sorghum genotypes as a model system, we characterized the chemical heterogeneity between root exudates and the effects of that variability on soil microbial membership and metabolisms. Distinct exudate chemical profiles were quantified and used to formulate synthetic root exudate treatments, a High Organic acid Treatment (HOT) and a High Sugar Treatment (HST). Root exudate treatments were added to laboratory soil reactors and 16S rRNA gene profiling illustrated distinct microbial membership in response to HST or HOT amendments. Alpha and beta diversity metrics were significantly different between treatments, (Shannon’s, p < 0.0001, mrpp = 0.01, respectively). Exometabolite production was highest in the HST, with increased production of key organic acids, non-proteinogenic amino acids, and three plant growth-promoting phytohormones (benzoic acid, salicylic acid, indole-3-acetic acid), suggesting plant-derived sugars fuel microbial carbon metabolism and contribute to phytohormone production. Linking the metabolic capacity of metagenome-assembled genomes in the HST to the exometabolite patterns, we identified potential plant growth-promoting microorganisms that could produce these phytohormones. Our findings emphasize the tractability of high-resolution multi-omics tools to investigate soil microbiomes, opening the possibility of manipulating native microbial communities to improve specific soil microbial functions and enhance crop production.


2021 ◽  
Author(s):  
Carla de la Fuente Canto ◽  
Marcel Nahim Diouf ◽  
Papa Mamadou Sitor Ndour ◽  
Marilyne Debieu ◽  
Alexandre Grondin ◽  
...  

The rhizosheath, the layer of soil that adheres strongly to roots, influences water and nutrients acquisition. Pearl millet is a cereal crop that plays a major role for food security in arid regions of sub Saharan Africa and India. We previously showed that root-adhering soil mass is a heritable trait in pearl millet and that it correlates with changes in rhizosphere microbiota structure and functions. Here, we studied the correlation between root-adhering soil mass and root hair development, root architecture, and symbiosis with arbuscular mycorrhizal fungi and we analysed the genetic control of this trait using genome wide association (GWAS) combined with bulk segregant analysis and gene expression studies. Root-adhering soil mass was weakly correlated only to root hairs traits in pearl millet. Twelve QTLs for rhizosheath formation were identified by GWAS and bulk segregant analysis on a biparental population further validated five of these QTLs. Combining genetics with a comparison of global gene expression in the root tip of contrasted inbred lines revealed candidate genes that might control rhizosheath formation in pearl millet. Our study indicates that rhizosheath formation is under complex genetic control in pearl millet and suggests that it is mainly regulated by root exudation.


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