Phenotypic, molecular, and symbiotic characterization of the rhizobial symbionts isolated from Acacia saligna grown in different regions in Morocco: a multivariate approach.

The introduced species Acacia saligna is a very promiscuous host as it can be efficiently nodulated with a wide range diversity of rhizobia taxa, including both fast and slow-growing strains. Fourteen nitrogen (N)-fixing bacteria were isolated from root nodules of wild Acacia saligna growing in distinct geographic locations in Morocco and were examined for their symbiotic efficiency and phenotypic properties. Multivariate tools, such as principal component analysis (PCA) and hierarchical clustering analysis (HCA), were used to study the correlation between phenotypic and symbiotic variables and discriminate and describe the similarities between different isolated bacteria with respect to all the phenotypic and symbiotic variables. Phenotypic characterization showed a variable response to extreme temperature, salinity and soil pH. At the plant level, the nodulation, nitrogen fixation, and the shoot and root dry weights were considered. The obtained results show that some of the tested isolates exhibit remarkable tolerances to the studied abiotic stresses while showing significant N2 fixation, indicating their usefulness as effective candidates for the inoculation of acacia trees. The PCA also allowed showing the isolates groups that present a similarity with evaluated phenotypic and symbiotic parameters. The genotypic identification of N2-fixing bacteria, carried out by the 16S rDNA approach, showed a variable genetic diversity among the 14 identified isolates, and their belonging to three different genera, namely Agrobacterium, Phyllobacterium and Rhizobium.

Community structure and diversity characteristics of rhizosphere and root endophytic bacterial community in different Acacia species.

Rhizosphere and endophytic microbiota significantly affect plant growth and development by influencing nutrient uptake and stress tolerance. Herein, root and rhizosphere soil of Acacia species were collected and analyzed to compare the structural differences of the rhizosphere and root endophytic bacterial communities. High-throughput 16S rRNA gene sequencing technology was employed to analyze the rhizosphere and root endophytic bacterial communities. A total of 4249 OTUs were identified following sequence analysis. The rhizosphere soil contained significantly more OTUs than the root soil. Principal component analysis (PCA) and hierarchical cluster analysis indicated that bacterial communities exhibited significant specificity in the rhizosphere and root soil of different Acacia species. The most dominant phylum in the rhizosphere soil was Acidobacteria, followed by Proteobacteria and Actinobacteria, whereas the dominant phylum in the root soil was Proteobacteria, followed by Actinobacteria and Acidobacteria. Among the various Acacia species, specific bacterial communities displayed different abundance. We systematically described the core bacteria in the rhizosphere and root endophytic bacterial communities and predicted their relevant functions. The type and abundance of specific bacteria were correlated with the nutrient absorption and metabolism of the Acacia species. This study addresses the complex host-microbe interactions and explores the rhizosphere and root bacterial community structure of different Acacia species. These results provide new insights into the role of rhizosphere and root endophytic bacterial communities on the growth and reproduction of Acacia, thus informing future efforts towards sustainable development and utilization of Acacia.

Influence of mycorrhiza and fly ash on the survival, growth and heavy metal accumulation in three Acacia species grown in Cu-Ni mine soil.

Acacia albida, Acacia luederitzii, and Acacia tortilis are dominant acacia species in Botswana and have the potential to rehabilitate the heavy metal degraded environment. To establish this claim, experiments to assess the influence of mycorrhizal inoculation and fly ash amendments on the survival, growth and heavy metal accumulation of these species in mine tailings were conducted. A two-factor (AM inoculation × fly ash) in CRD was done on each of the three Acacia species consisting of four treatments: control (no mycorrhizal, no fly ash coded as - AM/- FA), with mycorrhizal but no fly ash (+ AM/- FA), no mycorrhizal but with fly ash (- AM/+ FA), and with mycorrhizal and with fly ash (+ AM/+ FA). After 24 weeks, results showed that the survival and dry matter yield of all Acacia species were enhanced by 10% with fly ash amendments. However, mycorrhiza inoculation alone improved the survival of A. albida and A. luederitzii but reduced that of the A. tortilis in mine tailings. Fly ash amendments increased the pH of the mine tailings, reduced the availability of Cu, Ni, Pb, Mn and Zn and consequently reduced the concentration of these metals in shoots. On the other hand, it increased the availability of As in the mine tailings. In addition, mycorrhizal inoculation reduced the concentration of these metals in shoots regardless of fly ash amendments. Overall, combined mycorrhizal inoculation and fly ash amendment enhanced the establishment of A. luederitzii in heavy metal-contaminated soils by reducing the heavy metal availability and metal uptake, thus increasing the survival and dry matter yield of plants.

Significance of Arbuscular Mycorrhizal Fungi for Acacia: A Review.

Microbes play a vital role in ecosystem stability. Here, microbes-Acacia association is discussed with particular reference to Arbuscular Mycorrhizal Fungi (AMF) which help in the establishment of crop-plants, especially in arid and semi-arid areas. The association helps to restore the structural composition of soil from the hazardous impact of agrochemicals, increase resistance against various pathogenic attack as well as several abiotic stresses. Further, a comparative account of microbes found in the rhizosphere of Acacia is illustrated. Among these, Rhizobia, Acetobacter, Bradyrhizobium, Bacillus, Pseudomonas and Trichoderma were described in detail. All these microbes can be regarded as Plant Growth Promoting Rhizospheric Microbes (PGPM), some of PGPM are Phosphate Solubilizing Microbe (PSM). Both of them help AMF for infecting mycorrhizal hyphae inside the plant cell. Overall, microbes can be used as biofertilizers along with other organic compounds, that can compensate for the nutrient's availability.

Diversity of arbuscular mycorrhizal fungi associated with acacia trees in southwestern Saudi Arabia.

Acacia species produce extensive, deep root systems with a capacity to develop mycorrhizal symbioses that facilitate plant nutrition via enhanced soil nutrient absorption. This study aimed to evaluate the mycorrhizal status and the diversity of arbuscular mycorrhizal fungi (AMF) associated with acacia trees in southwestern Saudi Arabia. The mycorrhizal status varied greatly between species. The highest values of AMF root colonization and spore density were observed in the roots and in the rhizospheric soil of Acacia negrii. DNA was extracted from plant roots and the AMF large subunit ribosomal DNA (LSU rDNA) was amplified by a nested polymerase chain reaction. A total of 274 LSU rDNA cloned fragments from roots of the three acacia trees were sequenced. Phylogenetic analysis revealed a high AMF diversity, especially in Acacia tortilis. On the basis of LSU rDNA sequences, AMF was grouped into five genera: Glomus, Claroideoglomus, Acaulospora, Gigaspora, and Scutellospora. The genus Glomus fungi were the dominant colonizers of all three acacia species, while the genus Scutellospora fungi were found only in A. tortilis roots. The high AMF-acacia diversity suggests that AMF plays an important role in the sustainability of acacia species in the arid environment.

Botryosphaeriaceae associated with Acacia heterophylla (La Réunion) and Acacia koa (Hawaii).

Acacia koa and A. heterophylla are commonly occurring native trees on the Hawaiian Islands and La Réunion, respectively. A recent phylogenetic study suggested that A. heterophylla renders A. koa paraphyletic, and that the former likely arose from the Hawaiian Islands around 1.4 million years ago. An intriguing question is whether their microbiota is similar, although they occur naturally in two very distant geographical locations. In this study, we compared the fungi in the Botryosphaeriaceae isolated from natural populations of A. koa and A. heterophylla. These fungi were chosen because they commonly occur on woody plants and some are important pathogens. They are also known to have been moved globally on asymptomatic plant materials. Isolates were identified based on comparisons of DNA sequence data for the rDNA-ITS, TEF1-α and ß-tubulin loci. Ten Botryosphaeriaceae species were identified, of which four species were specific to A. koa from the Hawaiian Islands and five to A. heterophylla in La Réunion. Only one species, Neofusicoccumparvum, which is known to have a wide global distribution, was common to both hosts. The overall results of this study suggest that although A. koa and A.heterophylla share a recent evolutionary history, they have established independent microbiota, at least in terms of the Botryosphaeriaceae.

In Colombia the Eurasian fungus Amanita muscaria is expanding its range into native, tropical Quercus humboldtii forests.

To meet a global demand for timber, tree plantations were established in South America during the first half of the 20th century. Extensive plantings of non-native species now are found in Brazil, Chile, Argentina, and Uruguay. In Colombia, miscellaneous plantations were established in the 1950s, during a period of intensive local logging, when policies to limit deforestation in native Quercus humboldtii forests were established. One unforeseen consequence of planting non-native trees was the simultaneous introduction and subsequent persistence of ectomycorrhizal fungi. We sought to document the origins and spread of the introduced Amanita muscaria found in Colombian plantations of the Mexican species Pinus patula, North American species P. taeda, and Australian species Acacia melanoxylon and Eucalyptus globulus. In Colombia, Amanita muscaria is establishing a novel association with native Q. humboldtii and has spread to local Q. humboldtii forests. According to a Bayesian phylogeny and haplotype analysis based on the nuclear rDNA internal transcribed spacer region ITS1-5.8-ITS2 (ITS barcode), A. muscaria individuals found in four exotic plant species, and those colonizing Q. humboldtii roots, have a Eurasian origin and belong to two Eurasian haplotypes. This is the first time the spread of an introduced mutualist fungus into native Colombian Q. humboldtii forests is reported. To arrest its spread, we suggest the use of local inocula made up of native fungi, instead of inocula of introduced fungi.

Rhizobial inoculation in black wattle plantation (Acacia mearnsii De Wild.) in production systems of southern Brazil.

Black wattle (Acacia mearnsii De Wild.) is a tree legume native to southeast Australia, but present in all continents. Today it covers about 142,400 ha in Brazil, with plantations concentrated in the southern region of the country. Black wattle may form nodules and establish rhizobial symbiosis capable of fixing N2, but rhizobial inoculation is not done in commercial plantations. About 40 kg ha-1 of urea is applied during seedling transplantation. In this review, evidences by which rhizobial inoculation affects monoculture, mixed cultivation, and agroforestry black wattle production systems were searched in literature. Previous measurements in cultivated forests have indicated that biological nitrogen fixation in black wattle may provide up to 200 kg of N ha-1 year-1 to the soil. Therefore, rhizobia inoculation may bring several opportunities to improve black wattle production systems. Black wattle is not a very selective partner in the rhizobial symbiosis, but the genus Bradyrhizobium dominates the rhizobial diversity of black wattle nodules. Investigation on rhizobial diversity in soils where the crop is cultivated may represent an opportunity to find more effective rhizobia strains for inoculants. The successful history of biological nitrogen fixation in grain legumes must inspire the history of tree legumes. Microbiology applied to forestry must overcome challenges on the lack of trained professionals and the development of new application technologies.

A leguminous species exploiting alpha- and beta-rhizobia for adaptation to ultramafic and volcano-sedimentary soils: an endemic Acacia spirorbis model from New Caledonia.

Acacia spirorbis subsp. spirorbis Labill. is a widespread tree legume endemic to New Caledonia that grows in ultramafic (UF) and volcano-sedimentary (VS) soils. The aim of this study was to assess the symbiotic promiscuity of A. spirorbis with nodulating and nitrogen-fixing rhizobia in harsh edaphic conditions. Forty bacterial strains were isolated from root nodules and characterized through (i) multilocus sequence analyses, (ii) symbiotic efficiency and (iii) tolerance to metals. Notably, 32.5% of the rhizobia belonged to the Paraburkholderia genus and were only found in UF soils. The remaining 67.5%, isolated from both UF and VS soils, belonged to the Bradyrhizobium genus. Strains of the Paraburkholderia genus showed significantly higher nitrogen-fixing capacities than those of Bradyrhizobium genus. Strains of the two genera isolated from UF soils showed high metal tolerance and the respective genes occurred in 50% of strains. This is the first report of both alpha- and beta-rhizobia strains associated to an Acacia species adapted to UF and VS soils. Our findings suggest that A. spirorbis is an adaptive plant that establishes symbioses with whatever rhizobia is present in the soil, thus enabling the colonization of contrasted ecosystems.

The ability of a host plant to associate with different symbiotic partners affects ectomycorrhizal functioning.

Some plants that associate with ectomycorrhizal (ECM) fungi are also able to simultaneously establish symbiosis with other types of partners. The presence of alternative partners that may provide similar benefits may affect ECM functioning. Here we compared potential leucine-aminopeptidase (LA) and acid phosphatase (AP) enzyme activity (involved in N and P cycling, respectively) in ECM fungi of three hosts planted under the same conditions but differing in the type of partners: Pinus (ECM fungi only), Eucalyptus (ECM and arbuscular mycorrhizal -AM- fungi) and Acacia (ECM, AM fungi and rhizobial bacteria). We found that the ECM community on Acacia and Eucalyptus had higher potential AP activity than the Pinus community. The ECM community in Acacia also showed increased potential LA activity compared to Pinus. Morphotypes present in more than one host showed higher potential AP and LA activity when colonizing Acacia than when colonizing another host. Our results suggest that competition with AM fungi and rhizobial bacteria could promote increased ECM activity in Eucalyptus and Acacia. Alternatively, other host-related differences such as ECM community composition could also play a role. We found evidence for ECM physiological plasticity when colonizing different hosts, which might be key for adaptation to future climate scenarios.

Ten new species of Calonectria from Indonesia and Vietnam.

Vietnam and Indonesia have rapidly growing and extensive plantation forestry programs, especially of Acacia spp. and Eucalyptus spp. As these plantations expand, the threat from pests and diseases also increases. Calonectria species are among those pathogens causing diseases of trees in plantations and nurseries in these countries. Extensive surveys were conducted across plantations and nurseries of Vietnam and parts of Indonesia, where a large number of Calonectria isolates were retrieved from diseased leaves and soils associated with symptomatic trees. The aim of this study was to identify and resolve the phylogenetic relationships among these isolates using DNA sequence comparisons of four gene regions as well as morphological characters. From a collection of 165 isolates, the study revealed five known and 10 undescribed species. The relatively high diversity of Calonectria species found in this study supports the view that many more species in this genus remain to be discovered in other areas of Southeast Asia.

The Functional Potential of the Rhizospheric Microbiome of an Invasive Tree Species, Acacia dealbata.

Plant-microbe interactions mediate both the invasiveness of introduced plant species and the impacts that they have in invaded ecosystems. Although the phylogenetic composition of the rhizospheric microbiome of Acacia dealbata (an invasive Australian tree species) has been investigated, little is known about the functional potential of the constituents of these altered microbial communities. We used shotgun DNA sequencing to better understand the link between bacterial community composition and functional capacity in the rhizospheric microbiomes associated with invasive A. dealbata populations in South Africa. Our analysis showed that several genes associated with plant growth-promoting (PGP) traits were significantly overrepresented in the rhizospheric metagenomes compared to neighbouring bulk soils collected away from A. dealbata stands. The majority of these genes are involved in the metabolism of nitrogen, carbohydrates and vitamins, and in various membrane transport systems. Overrepresented genes were linked to a limited number of bacterial taxa, mostly Bradyrhizobium species, the preferred N-fixing rhizobial symbiont of Australian acacias. Overall, these findings suggest that A. dealbata enriches rhizosphere soils with potentially beneficial microbial taxa, and that members of the genus Bradyrhizobium may play an integral role in mediating PGP processes that may influence the success of this invader when colonizing novel environments.

Arbuscular Mycorrhizal Fungi Favor the Initial Growth of Acacia mangium, Sorghum bicolor, and Urochloa brizantha in Soil Contaminated with Zn, Cu, Pb, and Cd.

This study evaluated the effect of inoculation with a mixture of spores of arbuscular mycorrhizal fungi (AMF) (Glomus macrocarpum, Paraglomus occultum, and Glomus sp.) on the initial establishment of Acacia mangium, Sorghum bicolor, and Urochloa brizantha in soil contaminated with heavy metals. The experiment was conducted in a greenhouse, in plastic pots containing 1.8 kg of soil, which presented 7200, 1140, 480, and 72 mg of Zn, Cu, Pb, and Cd, respectively. The chlorophyll content (SPAD index) of inoculated plants of A. mangium and U. brizantha was higher than those of non-inoculated plants (p < 0.05). No differences were detected for the concentration of heavy metals in plant shoots, whether the plant was inoculated or not. However, inoculated plants had greater root length (S. bicolor and U. brizantha) (p < 0.05) and greater plant height (A. mangium) (p < 0.05). The present results demonstrate that the beneficial effects of AMF on plant growth and the alleviation of contaminants are imperative factors for the rehabilitation of soils contaminated with heavy metals.

Ectomycorrhizal Communities Associated with the Legume Acacia spirorbis Growing on Contrasted Edaphic Constraints in New Caledonia.

This study aims to characterize the ectomycorrhizal (ECM) communities associated with Acacia spirorbis, a legume tree widely spread in New Caledonia that spontaneously grows on contrasted edaphic constraints, i.e. calcareous, ferralitic and volcano-sedimentary soils. Soil geochemical parameters and diversity of ECM communities were assessed in 12 sites representative of the three mains categories of soils. The ectomycorrhizal status of Acacia spirorbis was confirmed in all studied soils, with a fungal community dominated at 92% by Basidiomycota, mostly represented by/tomentella-thelephora (27.6%), /boletus (15.8%), /sebacina (10.5%), /russula-lactarius (10.5%) and /pisolithus-scleroderma (7.9%) lineages. The diversity and the proportion of the ECM lineages were similar for the ferralitic and volcano-sedimentary soils but significantly different for the calcareous soils. These differences in the distribution of the ECM communities were statistically correlated with pH, Ca, P and Al in the calcareous soils and with Co in the ferralitic soils. Altogether, these data suggest a high capacity of A. spirorbis to form ECM symbioses with a large spectrum of fungi regardless the soil categories with contrasted edaphic parameters.

Symbiotic N2-Fixer Community Composition, but Not Diversity, Shifts in Nodules of a Single Host Legume Across a 2-Million-Year Dune Chronosequence.

Long-term soil age gradients are useful model systems to study how changes in nutrient limitation shape communities of plant root mutualists because they represent strong natural gradients of nutrient availability, particularly of nitrogen (N) and phosphorus (P). Here, we investigated changes in the dinitrogen (N2)-fixing bacterial community composition and diversity in nodules of a single host legume (Acacia rostellifera) across the Jurien Bay chronosequence, a retrogressive 2 million-year-old sequence of coastal dunes representing an exceptionally strong natural soil fertility gradient. We collected nodules from plants grown in soils from five chronosequence stages ranging from very young (10s of years; associated with strong N limitation for plant growth) to very old (> 2,000,000 years; associated with strong P limitation), and sequenced the nifH gene in root nodules to determine the composition and diversity of N2-fixing bacterial symbionts. A total of 335 unique nifH gene operational taxonomic units (OTUs) were identified. Community composition of N2-fixing bacteria within nodules, but not diversity, changed with increasing soil age. These changes were attributed to pedogenesis-driven shifts in edaphic conditions, specifically pH, exchangeable manganese, resin-extractable phosphate, nitrate and nitrification rate. A large number of common N2-fixing bacteria genera (e.g. Bradyrhizobium, Ensifer, Mesorhizobium and Rhizobium) belonging to the Rhizobiaceae family (α-proteobacteria) comprised 70% of all raw sequences and were present in all nodules. However, the oldest soils, which show some of the lowest soil P availability ever recorded, harboured the largest proportion of unclassified OTUs, suggesting a unique set of N2-fixing bacteria adapted to extreme P limitation. Our results show that N2-fixing bacterial composition varies strongly during long-term ecosystem development, even within the same host, and therefore rhizobia show strong edaphic preferences.

Mangrove endophyte promotes reforestation tree (Acacia polyphylla) growth

ABSTRACT Mangroves are ecosystems located in the transition zone between land and sea that serve as a potential source of biotechnological resources. Brazil's extensive coast contains one of the largest mangrove forests in the world (encompassing an area of 25,000 km2 along all the coast). Endophytic bacteria were isolated from the following three plant species: Rhizophora mangle, Laguncularia racemosa and Avicennia nitida. A large number of these isolates, 115 in total, were evaluated for their ability to fix nitrogen and solubilize phosphorous. Bacteria that tested positive for both of these tests were examined further to determine their level of indole acetic acid production. Two strains with high indole acetic acid production were selected for use as inoculants for reforestation trees, and then the growth of the plants was evaluated under field conditions. The bacterium Pseudomonas fluorescens (strain MCR1.10) had a low phosphorus solubilization index, while this index was higher in the other strain used, Enterobacter sp. (strain MCR1.48). We used the reforestation tree Acacia polyphylla. The results indicate that inoculation with the MCR1.48 endophyte increases Acacia polyphylla shoot dry mass, demonstrating that this strain effectively promotes the plant's growth and fitness, which can be used in the seedling production of this tree. Therefore, we successfully screened the biotechnological potential of endophyte isolates from mangrove, with a focus on plant growth promotion, and selected a strain able to provide limited nutrients and hormones for in plant growth.

Mangrove endophyte promotes reforestation tree (Acacia polyphylla) growth.

Mangroves are ecosystems located in the transition zone between land and sea that serve as a potential source of biotechnological resources. Brazil's extensive coast contains one of the largest mangrove forests in the world (encompassing an area of 25,000km2 along all the coast). Endophytic bacteria were isolated from the following three plant species: Rhizophora mangle, Laguncularia racemosa and Avicennia nitida. A large number of these isolates, 115 in total, were evaluated for their ability to fix nitrogen and solubilize phosphorous. Bacteria that tested positive for both of these tests were examined further to determine their level of indole acetic acid production. Two strains with high indole acetic acid production were selected for use as inoculants for reforestation trees, and then the growth of the plants was evaluated under field conditions. The bacterium Pseudomonas fluorescens (strain MCR1.10) had a low phosphorus solubilization index, while this index was higher in the other strain used, Enterobacter sp. (strain MCR1.48). We used the reforestation tree Acacia polyphylla. The results indicate that inoculation with the MCR1.48 endophyte increases Acacia polyphylla shoot dry mass, demonstrating that this strain effectively promotes the plant's growth and fitness, which can be used in the seedling production of this tree. Therefore, we successfully screened the biotechnological potential of endophyte isolates from mangrove, with a focus on plant growth promotion, and selected a strain able to provide limited nutrients and hormones for in plant growth.

Tannic extract potential as natural wood preservative of Acacia mearnsii.

High toxicity of the preservatives most frequently used in wood treatment and the resulting risks of handling pose a threat to small producers and to the environment. In an attempt to mitigate these problems, the present study was conducted with the objective of evaluating the preservative effect of tannic extract on biodeterioration of Acacia mearnsii wood. For this purpose, untreated and preserved specimens, some with tannin extract and some with a preservative mixture based on CCB (Chromated Copper Borate), were submitted to accelerated rotting trials with the fungus that causes white rot (Pycnoporus sanguineus) for 16 weeks. The evaluations were made with a basis on weight loss and chemical components analysis, and they showed that the natural resistance of Acacia wood is moderate when exposed to the white rot fungus. The tannin concentrations showed similar effects to those of the CBB mixture in all evaluations, i.e., they significantly increased the biological resistance of the material, which started to be classified as very resistant to the fungus. Overall, the results suggest that tannin can be considered as a potential natural preservative product.

Tannic extract potential as natural wood preservative of Acacia mearnsii

ABSTRACT High toxicity of the preservatives most frequently used in wood treatment and the resulting risks of handling pose a threat to small producers and to the environment. In an attempt to mitigate these problems, the present study was conducted with the objective of evaluating the preservative effect of tannic extract on biodeterioration of Acacia mearnsii wood. For this purpose, untreated and preserved specimens, some with tannin extract and some with a preservative mixture based on CCB (Chromated Copper Borate), were submitted to accelerated rotting trials with the fungus that causes white rot (Pycnoporus sanguineus) for 16 weeks. The evaluations were made with a basis on weight loss and chemical components analysis, and they showed that the natural resistance of Acacia wood is moderate when exposed to the white rot fungus. The tannin concentrations showed similar effects to those of the CBB mixture in all evaluations, i.e., they significantly increased the biological resistance of the material, which started to be classified as very resistant to the fungus. Overall, the results suggest that tannin can be considered as a potential natural preservative product.