Abstract:Increased frequency of droughts and degraded edaphic conditions decreases the success of many reforestation efforts in the Pacific Northwest. Microbial endophyte consortia have been demonstrated to contribute to plant growth promotion and protection from abiotic and biotic stresses – specifically drought conditions – across a number of food crops but for limited tree species. Our research aimed to investigate the potential to improve establishment of economically and ecologically important conifers through a s… Show more
“…The increased chlorophyll level (greenness) in the needles after inoculation with Paenibacillus sp. s37 is in agreement with reports showing that other bacterial inoculants can increase chlorophyll levels ( Xie et al, 2009 ; Aghai et al, 2019 ) and the photosynthetic rate in other plants ( Xie et al, 2009 ). It would be interesting if future studies on strain s37 could link the impact on growth with the effects on photosynthesis and on carbohydrate levels in shoot tissue, to determine if increased photosynthesis leads to improved vigor via carbohydrate accumulation.…”
Section: Discussionsupporting
confidence: 92%
“…The effects of PGPR on plant growth are frequently determined by measuring plant biomass, but their effects may even be revealed by measuring constituents or processes underlying plant growth, e.g., chlorophyll levels. Chlorophyll levels are central for plant growth and have previously been reported to increase after inoculation with PGPR in other plants, including conifers ( Xie et al, 2009 ; Aghai et al, 2019 ). In the case of A. nordmanniana , the chlorophyll level is also an important measure as greenness is a crucial quality trait for the growers.…”
Abies nordmanniana
is used for Christmas tree production but poor seed germination and slow growth represent challenges for the growers. We addressed the plant growth promoting potential of root-associated bacteria isolated from
A. nordmanniana
. Laboratory screenings of a bacterial strain collection yielded several
Bacillus
and
Paenibacillus
strains that improved seed germination and produced indole-3-acetic acid. The impact of three of these strains on seed germination, plant growth and growth-related physiological parameters was then determined in greenhouse and field trials after seed inoculation, and their persistence was assessed by 16S rRNA gene-targeted bacterial community analysis. Two strains showed distinct and significant effects.
Bacillus
sp. s50 enhanced seed germination in the greenhouse but did not promote shoot or root growth. In accordance, this strain did not increase the level of soluble hexoses needed for plant growth but increased the level of storage carbohydrates. Moreover, strain s50 increased glutathione reductase and glutathione-S-transferase activities in the plant, which may indicate induction of systemic resistance during the early phase of plant development, as the strain showed poor persistence in the root samples (rhizosphere soil plus root tissue).
Paenibacillus
sp. s37 increased plant root growth, especially by inducing secondary root formation, under in greenhouse conditions, where it showed high persistence in the root samples. Under these conditions, it further it increased the level of soluble carbohydrates in shoots, and the levels of starch and non-structural carbohydrates in roots, stem and shoots. Moreover, it increased the chlorophyll level in the field trial. These findings indicate that this strain improves plant growth and vigor through effects on photosynthesis and plant carbohydrate reservoirs. The current results show that the two strains s37 and s50 could be considered for growth promotion programs of
A. nordmanniana
in greenhouse nurseries, and even under field conditions.
“…The increased chlorophyll level (greenness) in the needles after inoculation with Paenibacillus sp. s37 is in agreement with reports showing that other bacterial inoculants can increase chlorophyll levels ( Xie et al, 2009 ; Aghai et al, 2019 ) and the photosynthetic rate in other plants ( Xie et al, 2009 ). It would be interesting if future studies on strain s37 could link the impact on growth with the effects on photosynthesis and on carbohydrate levels in shoot tissue, to determine if increased photosynthesis leads to improved vigor via carbohydrate accumulation.…”
Section: Discussionsupporting
confidence: 92%
“…The effects of PGPR on plant growth are frequently determined by measuring plant biomass, but their effects may even be revealed by measuring constituents or processes underlying plant growth, e.g., chlorophyll levels. Chlorophyll levels are central for plant growth and have previously been reported to increase after inoculation with PGPR in other plants, including conifers ( Xie et al, 2009 ; Aghai et al, 2019 ). In the case of A. nordmanniana , the chlorophyll level is also an important measure as greenness is a crucial quality trait for the growers.…”
Abies nordmanniana
is used for Christmas tree production but poor seed germination and slow growth represent challenges for the growers. We addressed the plant growth promoting potential of root-associated bacteria isolated from
A. nordmanniana
. Laboratory screenings of a bacterial strain collection yielded several
Bacillus
and
Paenibacillus
strains that improved seed germination and produced indole-3-acetic acid. The impact of three of these strains on seed germination, plant growth and growth-related physiological parameters was then determined in greenhouse and field trials after seed inoculation, and their persistence was assessed by 16S rRNA gene-targeted bacterial community analysis. Two strains showed distinct and significant effects.
Bacillus
sp. s50 enhanced seed germination in the greenhouse but did not promote shoot or root growth. In accordance, this strain did not increase the level of soluble hexoses needed for plant growth but increased the level of storage carbohydrates. Moreover, strain s50 increased glutathione reductase and glutathione-S-transferase activities in the plant, which may indicate induction of systemic resistance during the early phase of plant development, as the strain showed poor persistence in the root samples (rhizosphere soil plus root tissue).
Paenibacillus
sp. s37 increased plant root growth, especially by inducing secondary root formation, under in greenhouse conditions, where it showed high persistence in the root samples. Under these conditions, it further it increased the level of soluble carbohydrates in shoots, and the levels of starch and non-structural carbohydrates in roots, stem and shoots. Moreover, it increased the chlorophyll level in the field trial. These findings indicate that this strain improves plant growth and vigor through effects on photosynthesis and plant carbohydrate reservoirs. The current results show that the two strains s37 and s50 could be considered for growth promotion programs of
A. nordmanniana
in greenhouse nurseries, and even under field conditions.
“…Several studies have proven the advantages of consortia over single strain inoculation in several agronomic crops (reviewed in the study by Compant et al ., 2019). Multiple strains in endophyte consortia have also been shown to promote plant growth and to mitigate abiotic stresses in tree species (Aghai et al ., 2019). For many years, microbial strains have been combined in a non‐targeted manner on a trial and error basis obtaining variable results.…”
Section: Improving the Performance Of Endophytes In Promoting Plant Growth And Healthmentioning
The plant endosphere is colonized by complex microbial communities and microorganisms, which colonize the plant interior at least part of their lifetime and are termed endophytes. Their functions range from mutualism to pathogenicity. All plant organs and tissues are generally colonized by bacterial endophytes and their diversity and composition depend on the plant, the plant organ and its physiological conditions, the plant growth stage as well as on the environment. Plant-associated microorganisms, and in particular endophytes, have lately received high attention, because of the increasing awareness of the importance of host-associated microbiota for the functioning and performance of their host. Some endophyte functions are known from mostly lab assays, genome prediction and few metagenome analyses; however, we have limited understanding on in planta activities, particularly considering the diversity of micro-environments and the dynamics of conditions. In our review, we present recent findings on endosphere environments, their physiological conditions and endophyte colonization. Furthermore, we discuss microbial functions, the interaction between endophytes and plants as well as methodological limitations of endophyte research. We also provide an outlook on needs of future research to improve our understanding on the role of microbiota colonizing the endosphere on plant traits and ecosystem functioning.
“…There is a strong and steadily increasing interest in microbial endophytes of plants (Rho et al, 2017) and how they could be harnessed to improve sustainability in agriculture, forestry and bioenergy production (Busby et al, 2017;Doty, 2017). Endophytes from plants in high stress environments have strong impacts on plant stress tolerance (Timmusk et al, 1999;Rodriguez et al, 2004;Aghai et al, 2019). While shifts in microbiome composition has been observed to be cultivar/species-specific and possibly linked to plant physiology (Perez-Jaramillo et al, 2018;Liu et al, 2019), plants can select their microbiome (Jones et al, 2019), and under abiotic stress conditions such as in drought, they have a different microbiome (Xu et al, 2018;Cheng et al, 2019).…”
Section: Introductionmentioning
confidence: 99%
“…Poplar (Populus) and willow (Salix) trees of the Salicaceae have a wide global distribution, both in native riparian forests across the Northern Hemisphere and in planted forests, accounting for more than 95 million hectares globally (fao.org). Native poplar trees have a diverse microbiota, many with the ability to fix dinitrogen gas, solubilize phosphate, and promote plant growth and health especially under abiotic stresses such as drought and nutrient limitation (Doty et al, 2005Xin et al, 2009;Khan et al, 2012Khan et al, , 2015Khan et al, , 2016Kandel et al, 2015Kandel et al, , 2017Doty, 2016;Aghai et al, 2019). Beneficial microbiota have been isolated from hybrid poplar trees grown in contaminated sites, in field sites, or in tissue culture (Moore et al, 2006;Ulrich et al, 2008;Barac et al, 2009;Scherling et al, 2009;Taghavi et al, 2009).…”
Plant-associated microbial communities play a central role in the plant response to biotic and abiotic stimuli, improving plant fitness under challenging growing conditions. Many studies have focused on the characterization of changes in abundance and composition of root-associated microbial communities as a consequence of the plant response to abiotic factors such as altered soil nutrients and drought. However, changes in composition in response to abiotic factors are still poorly understood concerning the endophytic community associated to the phyllosphere, the above-ground plant tissues. In the present study, we applied high-throughput 16S rDNA gene sequencing of the phyllosphere endophytic bacterial communities colonizing wild Populus trichocarpa (black cottonwood) plants growing in native, nutrient-limited environments characterized by hot-dry (xeric) riparian zones (Yakima River, WA), riparian zones with mid hot-dry (Tieton and Teanaway Rivers, WA) and moist (mesic) climates (Snoqualmie, Skykomish and Skagit Rivers, WA). From sequencing data, 587 Amplicon Sequence Variants (ASV) were identified. Surprisingly, our data show that a core microbiome could be found in phyllosphere-associated endophytic communities in trees growing on opposite sides of the Cascades Mountain Range. Considering only taxa appearing in at least 90% of all samples within each climatic zone, the core microbiome was dominated only by two ASVs affiliated Pseudomonadaceae and two ASVs of the Enterobacteriaceae family. Alpha-diversity measures indicated that plants colonizing hot-dry environments showed a lower diversity than those from mid hot-dry and moist climates. Beta-diversity measures showed that bacterial composition was significantly different across sampling sites. Accordingly, we found that specific ASV affiliated to Pseudomonadaceae and Enterobacteriaceae were significantly more abundant in the phyllosphere endophytic community colonizing plants adapted to the xeric environment. In summary, this study highlights that sampling site is the major driver of variation and that only a few ASV showed a distribution that significantly correlated to climate variables.
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