Abstract
Lodgepole pine, a prominent Pinaceae tree species native to western North America, is well-known for its ability to thrive in highly disturbed and degraded areas. One such area is the Sub-Boreal Pine-Spruce xeric-cold (SBPSxc) region in British Columbia, Canada, which is characterized by weakly-developed, parched soils that lack an organic forest floor and essential plant-available nutrients. We hypothesized that plant growth-promoting bacteria could play a significant role in sustaining the growth of lodgepole pine trees in the SBPSxc region. Testing this hypothesis, we evaluated plant growth-promoting abilities of six endophytic bacterial strains previously isolated from lodgepole pine trees growing in this region. These bacterial strains significantly enhanced the length and biomass of their natural host (lodgepole pine) as well as a foreign host (hybrid white spruce) in a 540-day long greenhouse trial. This growth stimulation could be linked to the diverse plant growth-promoting (PGP) abilities detected in these strains using in vitro assays for inorganic/organic phosphate-solubilization, siderophore production IAA production, ACC deaminase activity, lytic enzymes (chitinase, β-1,3-glucanase, protease, and cellulase) activity, ammonia production and catalase activity. ACC deaminase activity was also detected in vivo for all strains using ethylene-sensitive plants–canola and tomato. Notably, strains belonging to the Burkholderiaceae family (HP-S1r, LP-R1r and LP-R2r) showed the greatest potential in all PGP assays and enhanced pine and spruce seedling length and biomass by up to 1.5-fold and 4-fold, respectively. Therefore, such bacterial strains with multifarious PGP abilities could be crucial for survival and growth of lodgepole pine trees in the SBPSxc region and could potentially be utilized as bioinoculant for Pinaceae trees in highly disturbed and nutrient-poor ecosystems.
Highlights
Boreal ecosystems across the northern hemisphere are home to a wide variety of coniferous trees, mainly belonging to the Pinaceae family such as spruce, pine, fir and cedar
Our main motive was to investigate the plant growth-promoting (PGP) abilities of endophytic bacterial strains isolated from lodgepole pine trees growing in a nutrient-poor, disturbed ecosystem in the Sub-Boreal Pine-Spruce xeric-cold (SBPSxc) region in British Columbia (BC)
When the six endophytic bacterial strains were analyzed for their potential to enhance tree growth via inoculation studies with their original host and a foreign host, it was observed that all strains were effective in significantly increasing the length (30–60%) and biomass (125–302%) of both tree hosts, 540 days after inoculation (Figs 1 and 2)
Summary
Boreal ecosystems across the northern hemisphere are home to a wide variety of coniferous trees, mainly belonging to the Pinaceae family such as spruce, pine, fir and cedar. Soils in this region are sandy (often gravelly) in texture since they develop from granitic rocks and have thin or no organic forest floor with slow mineralization rates [4] Soils in this region typically have poor physico-chemical health with high carbon to nutrient ratio, low cation exchange capacity, acidic pH, limited organic matter, high bulk density and minimal amounts of plant-available macro- and micro-nutrients [5]. This region is frequently disturbed by wildfires, logging activity and attack of pests such as the mountain pine beetle, pine blister rust, pine gall rust and pine root collar weevil [3]. Despite such highly disturbed and extreme climatic and edaphic conditions, lodgepole pine (Pinus contorta var. latifolia)–a prominent member of the Pinaceae family found ubiquitously in Western North America– thrives in the SBPSxc region
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