The Effect of Microbial Endophyte Consortia on Pseudotsuga menziesii and Thuja plicata Survival, Growth, and Physiology Across Edaphic Gradients

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 series of in situ field trials and ex situ simulations. Microbial endophyte consortia from Salicaceae, previously shown to confer drought tolerance, and conifer endophyte strains with potentially symbiotic traits were selected for trials with Douglas-fir ( Pseudotsuga menziesii ) and western redcedar ( Thuja plicata ). Reductive experimentation was used to subject seedlings to a spectrum of simulated drought levels or presence/absence of fertilizer, testing hypotheses that endophyte consortia impart improved drought resistance and growth promotion, respectively. Inoculation from Salicaceae consortia significantly ( p ≤ 0.05) improved survival among seedlings of both species subject to increasing drought stress, with T. plicata seedlings surviving at twofold higher rates in extreme drought conditions. Both species demonstrated improved growth 540 days after inoculation of seed with conifer derived consortia. In the carefully controlled greenhouse experiments with both species, seedling Fv/Fm and SPAD values remained significantly ( p ≤ 0.05) more stable in inoculated treatment groups as stress increased. Our findings confirm that multi-strain consortia may be applied as seed or field amendment to conifers, and the approach is efficient in garnering a positive growth response and can mitigate abiotic stressors.

Identification of Root-Associated Bacteria That Influence Plant Physiology, Increase Seed Germination, or Promote Growth of the Christmas Tree Species Abies nordmanniana

“…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.…”

“…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.…”

The plant endosphere world – bacterial life within plants

“…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.…”

Influences of Climate on Phyllosphere Endophytic Bacterial Communities of Wild Poplar

“…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).…”

“…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).…”