Exudate Fractions Research Articles

Relationship between the Composition of Root Exsudates and the Efficiency of Interaction of Wheat Plants with Microorganisms

Plant roots secrete various organic substances into the rhizosphere, which are a source of nutrition for microorganisms and largely determine the nature of plant-microbe interactions. The composition of the main fractions of root exudates in ten modern varieties of wheat was determined: amino acids, organic acids and sugars. Reliable qualitative and quantitative differences between varieties for individual components of exudates were revealed, which determined the peculiarities of cultivar clustering on this trait. Relationships between exudation and the effectiveness of plant interaction with the growth-promoting rhizobacterium Pseudomonas fluorescens SPB2137 and the phytopathogenic fungus Fusarium culmorum 30 in laboratory systems, as well as with the resistance of varieties to diseases in the field, were found. The number of P. fluorescens SPB2137 in the root zone positively correlated with the amount of many amino acids, as well as maltose, secreted by the roots. The stimulating effect of rhizobacteria on root growth positively correlated with the amount of released glucose and melibiose. The relationship between the nature of root exudation and root colonization or the susceptibility of varieties to F. culmorum 30 was not found. The analysis of correlations between the incidence of wheat varieties in the field and the intensity of exudation of certain substances, as well as with the biocomposition index of amino acid exudation, was carried out. The role of root exudate components in the formation of effective plant-microbial systems is discussed.

Identification and Analysis of Antimicrobial Activities from a Model Moss Ceratodon purpureus.

The emergence of bacterial drug resistance is often viewed as the next great health crisis of our time. While more antimicrobial agents are urgently needed, very few new antibiotics are currently in the production pipeline. Here, we aim to identify and characterize novel antimicrobial natural products from a model dioicous moss, Ceratodon purpureus. We collected secreted moss exudate fractions from two C. purpureus strains, male R40 and female GG1. Exudates from the female C. purpureus strain GG1 did not exhibit inhibitory activity against any tested bacteria. However, exudates from the male moss strain R40 exhibited strong inhibitory properties against several species of Gram-positive bacteria, including Staphylococcus aureus and Enterococcus faecium, though they did not inhibit the growth of Gram-negative bacteria. Antibacterial activity levels in C. purpureus R40 exudates significantly increased over four weeks of moss cultivation in liquid culture. Size fractionation experiments indicated that the secreted bioactive compounds have a relatively low molecular weight of less than 1 kDa. Additionally, the R40 exudate compounds are thermostable and not sensitive to proteinase K treatment. Overall, our results suggest that the bioactive compounds present in C. purpureus R40 exudates can potentially add new options for treating infections caused by antibiotic-resistant Gram-positive bacteria.

Antimicrobial Activities of Secondary Metabolites from Model Mosses.

Plants synthetize a large spectrum of secondary metabolites with substantial structural and functional diversity, making them a rich reservoir of new biologically active compounds. Among different plant lineages, the evolutionarily ancient branch of non-vascular plants (Bryophytes) is of particular interest as these organisms produce many unique biologically active compounds with highly promising antibacterial properties. Here, we characterized antibacterial activity of metabolites produced by different ecotypes (strains) of the model mosses Physcomitrium patens and Sphagnum fallax. Ethanol and hexane moss extracts harbor moderate but unstable antibacterial activity, representing polar and non-polar intracellular moss metabolites, respectively. In contrast, high antibacterial activity that was relatively stable was detected in soluble exudate fractions of P. patens moss. Antibacterial activity levels in P. patens exudates significantly increased over four weeks of moss cultivation in liquid culture. Interestingly, secreted moss metabolites are only active against a number of Gram-positive, but not Gram-negative, bacteria. Size fractionation, thermostability and sensitivity to proteinase K assays indicated that the secreted bioactive compounds are relatively small (less than <10 kDa). Further analysis and molecular identification of antibacterial exudate components, combined with bioinformatic analysis of model moss genomes, will be instrumental in the identification of specific genes involved in the bioactive metabolite biosynthesis.

Resistant soil organic carbon is more vulnerable to priming by root exudate fractions than relatively active soil organic carbon

Resistant soil organic carbon is more vulnerable to priming by root exudate fractions than relatively active soil organic carbon

A Preliminary Study on Allelopathy and Potential Allelochemicals of Root Exudates from Solanum rostratum Dunal

Aims: In order to understand the role of allelopathy in invasion success, effects of root exudates from Solanum rostratum Dunal on germination and primary growth of wheat and cabbage seeds were studied by vitro bioassay. These results indicated the allelopathy of root exudates and would be helpful for understanding Solanum rostratum Dunal invasion. &#x0D; Study Design: The roots were washed clean for three times with distilled water before they were gathered in a big bucket. The container was filled with distilled water, enough to submerge the roots, and air was aerated constantly with an air pump. The water extract was collected per 24 hs and for four times totally. The water extract from Solanum rostratum was concentrated with a rotary evaporator at 40°C and deposited in a refrigerator at 4°C. All the root exudates were pooled around 1500 mL, and the fresh weight of Solanum rostratum used for exudates collection was 1208 g, the exudate concentration was then marked as 0.8g f w/mL.&#x0D; Place and Duration of Study: Solanum rostratum was grown in the greenhouse on April 15th, 2019, its seeds were collected from the invaded fields in Chaoyang city (Liaoning province, China).&#x0D; Methodology: Petri dish bioassay was applied to test the effects of root exudates of Solanum rostratum on the seeds of wheat and Chinese cabbage. For test of allelochemicals exudated through the root, The compounds in organic fraction of root exudates analysed by GC-MS.&#x0D; Results: These results indicated the allelopathy of root exudates and would be helpful for understanding Solanum rostratum Dunal invasion.&#x0D; Conclusion: Root exudates of Solanum rostratum contained some allelochemicals, which could inhibit the germination and radicle growth of wheat and Chinese cabbage, though the effects of root exudates on shoot growth are different, with a stimulation on Chinese cabbage while a inhibition on wheat. The difference indicated a selectivity of allelopathy effect of root exudates from Solanum rostratum Dunal.

Dynamic carbon flux network of a diverse marine microbial community

The functioning of microbial ecosystems has important consequences from global climate to human health, but quantitative mechanistic understanding remains elusive. The components of microbial ecosystems can now be observed at high resolution, but interactions still have to be inferred e.g., a time-series may show a bloom of bacteria X followed by virus Y suggesting they interact. Existing inference approaches are mostly empirical, like correlation networks, which are not mechanistically constrained and do not provide quantitative mass fluxes, and thus have limited utility. We developed an inference method, where a mechanistic model with hundreds of species and thousands of parameters is calibrated to time series data. The large scale, nonlinearity and feedbacks pose a challenging optimization problem, which is overcome using a novel procedure that mimics natural speciation or diversification e.g., stepwise increase of bacteria species. The method allows for curation using species-level information from e.g., physiological experiments or genome sequences. The product is a mass-balancing, mechanistically-constrained, quantitative representation of the ecosystem. We apply the method to characterize phytoplankton—heterotrophic bacteria interactions via dissolved organic matter in a marine system. The resulting model predicts quantitative fluxes for each interaction and time point (e.g., 0.16 µmolC/L/d of chrysolaminarin to Polaribacter on April 16, 2009). At the system level, the flux network shows a strong correlation between the abundance of bacteria species and their carbon flux during blooms, with copiotrophs being relatively more important than oligotrophs. However, oligotrophs, like SAR11, are unexpectedly high carbon processors for weeks into blooms, due to their higher biomass. The fraction of exudates (vs. grazing/death products) in the DOM pool decreases during blooms, and they are preferentially consumed by oligotrophs. In addition, functional similarity of phytoplankton i.e., what they produce, decouples their association with heterotrophs. The methodology is applicable to other microbial ecosystems, like human microbiome or wastewater treatment plants.

Inhibition of Protease and Egg Hatching of Haemonchus contortus by Soybean Seed Exudates.

Gastrointestinal nematode infection of small ruminants causes losses in livestock production. Plant compounds show promises as alternatives to commercial anthelmintics that have been exerting selective pressures that lead to the development of drug-resistant parasites. Soybean (Glycine max) is an economical value crop, with a higher protein content compared to other legumes. The objective of this study was to evaluate whether the protease inhibitors exuded from the G. max mature seeds have anthelmintic activity against Haemonchus contortus. To obtain the soybean exudates (SEX), mature seeds were immersed in 100 mM sodium acetate buffer, pH 5.0, at 10 C, for 24 hr. Then the naturally released substances present in SEX were collected and exhaustively dialyzed (cutoff 12 kDa) against distilled water. The dialyzed seed exudates (SEXD) were heated at 100 C for 10 min and centrifuged (12,000 g, at 4 C for 15 min). The supernatant obtained was recovered and designated as the heat-treated exudate fraction (SEXDH). The protein content, protease inhibitor activity, and the effect of each fraction on H. contortus egg hatch rate were evaluated. The inhibition extent of SEX, SEXD, and SEXDH on H. contortus egg proteases was 31.1, 42.9, and 63.8%, respectively. Moreover, SEX, SEXD, and SEXDH inhibited the egg hatching with EC50 of 0.175, 0.175, and 0.241 mg ml-1, respectively. Among the commercial protease inhibitors tested, only EDTA and E-64 inhibited the H. contortus hatch rate (79.0 and 28.9%, respectively). We present evidence demonstrating that soybean exudate proteins can effectively inhibit H. contortus egg hatching. This bioactivity is displayed by thermostable proteins and provides evidence that protease inhibitors are a potential candidate for anthelmintic use.

Species-dependent eco-corona dictates the aggregation of black phosphorus nanosheets: the role of protein and calcium

Dispersion of BPNSs was stabilized by crop root exudate fractions &gt;3 kDa, resulted from ecological corona hindering their connections with other BPNSs and electrolyte (Ca2+).

The Beneficial Root-Colonizing Fungus Mortierella hyalina Promotes the Aerial Growth of Arabidopsis and Activates Calcium-Dependent Responses That Restrict Alternaria brassicae-Induced Disease Development in Roots.

The endophytic fungus Mortierella hyalina colonizes the roots of Arabidopsis thaliana and stimulates growth and biomass production of the aerial parts but not of roots. An exudate fraction from the fungus induces rapid and transient cytoplasmic Ca2+elevation in the roots. The Ca2+ response does not require the well-characterized (co)receptors BAK1, CERK1, and FLS2 for pathogen-associated molecular patterns, and the Ca2+ channels GLR-2.4, GLR-2.5, and GLR-3.3 or the vacuolar TWO PORE CHANNEL1, which might be involved in cytoplasmic Ca2+ elevation. We isolated an ethyl-methane-sulfonate-induced Arabidopsis mutant that is impaired in this Ca2+ response. The roots of the mutant are impaired in M. hyalina-mediated suppression of immune responses after Alternaria brassicae infection, i.e., jasmonate accumulation, generation of reactive oxygen species, as well as the activation of jasmonate-related defense genes. Furthermore, they are more colonized by M. hyalina than wild-type roots. We propose that the mutant gene product is involved in a Ca2+-dependent signaling pathway activated by M. hyalina to suppress immune responses in Arabidopsis roots.

Validation of the Chemotaxis of Plant Parasitic Nematodes Toward Host Root Exudates

Plant parasitic nematodes (PPN) are microscopic soil herbivores that cause damage to many economic crops. For the last century, it has been proposed that chemotaxis is the primary means by which PPN locate host plant roots. The identities and modes of action of chemoattractants that deliver host-specific messages to PPN, however, are still elusive. In this study, a unique multidimensional agar-based motility assay was developed to assess the impacts of root exudates on the short-range motility and orientation of PPN. Three PPN (Rotylenchulus reniformis, Meloidogyne incognita and Heterodera glycines) and root exudates from their respective host and non-host plants (cotton, soybean, and peanut) were used to validate the assay. As predicted, R. reniformis and M. incognita were attracted to root exudates of cotton and soybean (hosts), but not to the exudates of peanut (non-host). Likewise, H. glycines was attracted to soybean (host) root exudates. These results underpinned the intrinsic roles of root exudates in conveying the host specificity of PPN. In particular, PPN selectively identified and targeted to hydrophilic, but not hydrophobic, fractions of root exudates, indicating that groundwater should be an effective matrix for chemotaxis associated with PPN and their host plant interactions.

Bioassay-guided isolation of a novel chemoattractant for Ralstonia solanacearum in tomato root exudates

Tomato root exudates were analyzed using a bioassay to detect the chemoattractant for Ralstonia solanacearum. An activated charcoal-adsorbed fraction of root exudates from tomato cultivar Oogata-fukuju had chemoattractant activity for R. solanacearum strain MAFF 730138. The active component, purified using a Sep-Pak C18 cartridge, an activated charcoal column, diol-modified silica gel, and NH2-modified silica gel, is a new hydrophobic attractant. The final purified fraction produced a single peak in a diol-modified silica gel HPLC analysis.

A New Phenol Glycoside from Root Exudates of Peperomia pellucida L. HBK. and its Role in Plant Invasion

Peperomia pellucida is an annual, shallow-rooted, succulent, delicate, glabrous herb. It is a native weed species of tropical North and South America, and it is now pantropic in distribution and abundant in India as an invasive aggressive colonizer. Medicinal properties of the plant have been well documented but no work has been done to find out the reason behind its invasive aggressive nature. The objective of our present work was to study the allelopathic activity of allelochemicals released by root exudates of P. pellucida which may play an important role in invasive and aggressive properties of the plant. Root exudates of P. pellucida were collected in root exudates trapping system. Main compound was isolated from methanol fraction of root exudates of P. pellucida, purified by thin layer and column chromatography and finally subjected to mass spectra, infrared, and nuclear magnetic resonance (both 1H and 13C) for complete structural elucidation. In vitro allelopathic activities of the compound were studied by rice, wheat and mustard seed bioassays. A new phenol glycocide [(6-(4-hydroxyphenoxy)-tetrahydro-2H-pyran-2, 3, 4, 5-tetraol); C11H14O7; Mol. Wt. 258] has been isolated and purified from root exudates of P. pellucida. This pure compound exhibited significant allelopathic activities on rice, wheat and mustard seeds in vitro bioassay experiment. This compound showed maximum inhibitory activity on rice, than in wheat and mustard bioassays. Peperomia pellucida released a phenol glycoside through root exudates into rhizophere which may act as a major allelopathic agent and may be responsible for its invasive and aggressive nature.

Growth factor and pro-inflammatory cytokine contents in platelet-rich plasma (PRP), plasma rich in growth factors (PRGF), advanced platelet-rich fibrin (A-PRF), and concentrated growth factors (CGF)

BackgroundThe development of platelet-rich fibrin (PRF) drastically simplified the preparation procedure of platelet-concentrated biomaterials, such as platelet-rich plasma (PRP), and facilitated their clinical application. PRF’s clinical effectiveness has often been demonstrated in pre-clinical and clinical studies; however, it is still controversial whether growth factors are significantly concentrated in PRF preparations to facilitate wound healing and tissue regeneration. To address this matter, we performed a comparative study of growth factor contents in PRP and its derivatives, such as advanced PRF (A-PRF) and concentrated growth factors (CGF).MethodsPRP and its derivatives were prepared from the same peripheral blood samples collected from healthy donors. A-PRF and CGF preparations were homogenized and centrifuged to produce extracts. Platelet and white blood cell counts in A-PRF and CGF preparations were determined by subtracting those counts in red blood cell fractions, supernatant acellular serum fractions, and A-PRF/CGF exudate fractions from those counts of whole blood samples. Concentrations of growth factors (TGF-β1, PDGF-BB, VEGF) and pro-inflammatory cytokines (IL-1β, IL-6) were determined using ELISA kits.ResultsCompared to PRP preparations, both A-PRF and CGF extracts contained compatible or higher levels of platelets and platelet-derived growth factors. In a cell proliferation assay, both A-PRF and CGF extracts significantly stimulated the proliferation of human periosteal cells without significant reduction at higher doses.ConclusionsThese data clearly demonstrate that both A-PRF and CGF preparations contain significant amounts of growth factors capable of stimulating periosteal cell proliferation, suggesting that A-PRF and CGF preparations function not only as a scaffolding material but also as a reservoir to deliver certain growth factors at the site of application.

Fractionation and some physicochemical properties of almond gum (Amygdalus communis L.) exudates

Compositions of both soluble and insoluble fractions of gum exudates from the trunk and branches of sweet almond tree (Amygdalus communis L.) were investigated. Monosaccharide analysis by HPLC indicated the presence of galactose and arabinose as the main sugars. FTIR spectra showed no significant differences between the functional groups of the whole gum and those of its fractions. Furthermore, only the intensity of OH and amide bond in the insoluble fraction was found to be higher than those of the soluble fraction and whole gum. XRD analysis revealed the amorphous structures of the whole gum and its fractions. Higher crystallinity index and crystalline size were observed in the insoluble fraction than in either the whole gum or the soluble fraction. TGA analysis revealed that the thermal decomposition of almond gum and its fractions occurred at around 250–260 °C. Finally, GPC analysis showed that the insoluble fraction had a higher molecular weight than did the whole gum or its soluble fraction.

Drying of mucilage causes water repellency in the rhizosphere of maize: measurements and modelling

Although maize roots have been extensively studied, there is limited information on the effect of root exudates on the hydraulic properties of maize rhizosphere. Recent experiments suggested that the mucilaginous fraction of root exudates may cause water repellency of the rhizosphere. Our objectives were: 1) to investigate whether maize rhizosphere turns hydrophobic after drying and subsequent rewetting; 2) to test whether maize mucilage is hydrophobic; and 3) to find a quantitative relation between rhizosphere rewetting, particle size, soil matric potential and mucilage concentration. Maize plants were grown in aluminum containers filled with a sandy soil. When the plants were 3-weeks-old, the soil was let dry and then it was irrigated. The soil water content during irrigation was imaged using neutron radiography. In a parallel experiment, ten maize plants were grown in sandy soil for 5 weeks. Mucilage was collected from young brace roots growing above the soil. Mucilage was placed on glass slides and let dry. The contact angle was measured with the sessile drop method for varying mucilage concentration. Additionally, capillary rise experiments were performed in soils of varying particle size mixed with maize mucilage. We then used a pore-network model in which mucilage was randomly distributed in a cubic lattice. The general idea was that rewetting of a pore is impeded when the concentration of mucilage on the pore surface (g cm−2) is higher than a given threshold value. The threshold value depended on soil matric potential, pore radius and contract angle. Then, we randomly distributed mucilage in the pore network and we calculated the percolation of water across a cubic lattice for varying soil particle size, mucilage concentration and matric potential. Our results showed that: 1) the rhizosphere of maize stayed temporarily dry after irrigation; 2) mucilage became water repellent after drying. Mucilage contact angle increased with mucilage surface concentration (gram of dry mucilage per surface area); 3) Water could easily cross the rhizosphere when the mucilage concentration was below a given threshold. In contrast, above a critical mucilage concentration water could not flow through the rhizosphere. The critical mucilage concentration decreased with increasing particle size and decreasing matric potential. These results show the importance of mucilage exudation for the water fluxes across the root-soil interface. Our percolation model predicts at what mucilage concentration the rhizosphere turns hydrophobic depending on soil texture and matric potential. Further studies are needed to extend these results to varying soil conditions and to upscale them to the entire root system.

The arabinogalactan of dried mango exudate and its co-extraction during pectin recovery from mango peel

Hot-acid extraction of the peel of fully ripe ‘Nam Dokmai’ (NDM) and ‘Maha Chanok’ (MHC) mangoes yielded pectins (PNDM, PMHC) being comparatively poor in uronic acids (38–47 g hg−1) in favor of the neutral sugars (23 g hg−1), chiefly galactose. Beyond the high-molecular-weight fraction, they displayed a characteristic, almost monodisperse fraction with a peak molecular weight of 18,200–19,100 relative to dextrans. In order to examine the hypothesized co-extraction of non-pectin polymers, the pectin PNDM and the exudate of mature-green ‘Nam Dokmai’ fruit (SAPNDM) were characterized regarding composition and molecular properties both before and after fractionation. By fractionation of PNDM on a weak anion exchanger, the high-molecular-weight pectin was largely separated from this characteristic fraction, which was composed of arabinogalactans. Likewise, the almost monodisperse molecular weight distribution of the dried fruit exudate SAPNDM with a peak molecular weight of 22,400 was shown to be caused by arabinogalactans being the main component (77.6 g hg−1) with a molar ratio of 82/10/4/4 for the major carbohydrate residues galactose, arabinose, rhamnose, and glucuronic acid. Fractionation of SAPNDM by size exclusion chromatography (SEC) and rechromatography (HPSEC) confirmed the high molecular uniformity of these arabinogalactans. The occurrence of hydroxyproline-rich proteins (≤0.2 g hg−1) in these exudate fractions may indicate small percentages of arabinogalactan-proteins. Co-extraction of residual fruit exudate may thus be considerable in pectin recovery from mango peel. Options for obtaining both pure pectins (galacturonic acid, 94 mol hmol−1) and arabinogalactans from this source were discussed.

Profiling of secondary metabolites in root exudates of Arabidopsis thaliana

To explore the chemical composition of root exudates of the model plant Arabidopsis thaliana a workflow for nontargeted metabolite profiling of the semipolar fraction of root exudates was developed. It comprises hydroponic plant cultivation and sampling of root exudates under sterile conditions, sample preparation by solid-phase extraction and analysis by reversed-phase UPLC/ESI-QTOFMS. Following the established workflow, root exudates of six-week-old plants were profiled and a set of reproducibly occurring molecular features was compiled. To structurally elucidate the corresponding metabolites, accurate mass tandem mass spectrometry and on-line hydrogen/deuterium exchange were applied. Currently, a total of 103 compounds were detected and annotated by elemental composition of which more than 90 were structurally characterized or classified. Among them, 42 compounds were rigorously identified using an authenticated standard. The compounds identified so far include nucleosides, deoxynucleosides, aromatic amino acids, anabolites and catabolites of glucosinolates, dipeptides, indolics, salicylic and jasmonic acid catabolites, coumarins, mono-, di- and trilignols, hydroxycinnamic acid derivatives and oxylipins and exemplify the high chemical diversity of plant root exudates.

Research on Allelochemicals with Material Properties Exuded by Submerged Freshwater Macrophyte &lt;i&gt;Elodea nuttallii&lt;/i&gt;

Elodea nuttalliiis well-known for its successful invasion to Europe and Asia. In addition to its high growth rate and nutrient storage capacity, chemical defense was recently found to play an important role in excluding other aquatic organisms. To reveal the chemical nature of its allelopathic effects on cyanobacterial development, extraction of plant exudates with different solvents and eluted procedures followed by 72h bioassays withMicrocystis aeruginosawas conducted. The results showed that the fraction eluted with methanol exhibited the strongest inhibitory effects, which indicated that the anti-cyanobacterial active allelochemicals released byE.nuttalliiwas hydrophilic. Then ten phenolic acids were identified in the purified methanol fraction ofElodeaexudates by GC-MS analysis. Quantification of the four phenolic acids therein showed the release contents were lower than 10μg/L whenE.nuttalliiwas cultivated at 10g FW/L, which increased with the increasing culture density. When the culture density was 100g FW/L, the detected contents of vanillic acid, protocatechuic acid, ferulic acid and caffeic acid inE.nuttalliiculture water were 23.41μg/L, 17.56 μg/L, 12.31 μg/L and 18.93μg/L, respectively. These results were helpful to understand the allelopathy mechanisms ofE.nuttalliiin aquatic ecosystems and useful in control of harmful cyanobacterial blooms.

Plant phloem sterol content: forms, putative functions, and implications for phloem-feeding insects

All eukaryotes contain sterols, which serve as structural components in cell membranes, and as precursors for important hormones. Plant vegetative tissues are known to contain mixtures of sterols, but very little is known about the sterol composition of phloem. Plants are food for many animals, but plant-feeding arthropods (including phloem-feeding insets) are unique among animals in that they have lost the ability to synthesize sterols, and must therefore acquire these essential nutrients from their food, or via endosymbionts. Our paper starts by providing a very brief overview of variation in plant sterol content, and how different sterols can affect insect herbivores, including those specializing on phloem. We then describe an experiment, where we bulk collected phloem sap exudate from bean and tobacco, and analyzed its sterol content. This approach revealed two significant observations concerning phloem sterols. First, the phloem exudate from each plant was found to contain sterols in three different fractions – free sterols, sterols conjugated to lipids (acylated), and sterols conjugated to carbohydrates (glycosylated). Second, for both plants, cholesterol was identified as the dominant sterol in each phloem exudate fraction; the remaining sterols in each fraction were a mixture of common phytosterols. We discuss our phloem exudate sterol profiles in a plant physiology/biochemistry context, and how it relates to the nutritional physiology/ecology of phloem-feeding insects. We close by proposing important next steps that will advance our knowledge concerning plant phloem sterol biology, and how phloem-sterol content might affect phloem-feeding insects.

Prokaryotes in salt marsh sediments of Ria de Aveiro: Effects of halophyte vegetation on abundance and diversity

The aim of this study was to investigate the influence of monospecific colonization of sediment stands by Spartina maritima or Halimione portulacoides on benthic prokaryote assemblages in a salt marsh located in Ria de Aveiro (Portugal). The distribution of Bacteria, Archaea and sulfate-reducing bacteria (SRB) in sediments with monospecific plant stands and in unvegetated sediments was characterized by Fluorescence In Situ Hybridization (FISH). Total prokaryote abundance (0.4 × 109–1.7 × 109 cells gdw−1) was highest in sediments from the surface layer. The domain Bacteria comprised approximately 40% of total prokaryote communities with the highest percentages occurring in the surface layer. Archaeal cells corresponded to an average of 25% of total prokaryote population, with higher abundance in the vegetation banks, and displaying homogeneous vertical distribution. The relative abundance of SRB represented approximately 3% of total 4′, 6-diamidino-2-phenylindole dihydrochloride (DAPI) stained cells at unvegetated sediment and H. portulacoides stand and 7% at S. maritima stand. Headspace solid-phase microextraction (HS-SPME) combined with Comprehensive Two-Dimensional Gas Chromatography–Time-of-Flight Mass Spectrometry (GC × GC–ToFMS) was used to analyse the volatile and semi-volatile fraction of root exudates. A total of 171 compounds were identified and Principal Component Analysis showed a clear separation between the chemical composition (volatile and semi-volatile organic compounds) of the exudates of the two plants.The patterns of vertical distribution and differences in the proportion of SRB and Archaea in the prokaryote communities developing in sediments colonized by Spartina maritima or Halimione portulacoides suggest the existence of plant-specific interactions between halophyte vegetation and estuarine sediment bacteria in Ria de Aveiro salt marshes, exerted via sediment lithology and root-derived exudates.