Sustaining the growth of Pinaceae trees under nutrient-limited edaphic conditions via plant-beneficial bacteria - PubMed (original) (raw)

Sustaining the growth of Pinaceae trees under nutrient-limited edaphic conditions via plant-beneficial bacteria

Akshit Puri et al. PLoS One. 2020.

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.

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Conflict of interest statement

The authors have declared that no competing interests exist.

Figures

Fig 1

Mean values of (a) length and (b) biomass of 540-day old lodgepole pine seedlings subjected to six bacteria-inoculated (Caballeronia sordidicola HP-S1r, Pseudomonas frederiksbergensis HP-N1r, Phyllobacterium myrsinacearum HP-R1r, Pseudomonas mandelii LP-S1r, Paraburkholderia phytofirmans LP-R1r and Caballeronia udeis LP-R2r) and one non-inoculated control treatments. Error bars represent standard errors of the mean (n = 10 seedlings per treatment) and bars with different letters are significantly different (P < 0.05).

Fig 2

Mean values of (a) length and (b) biomass of 540-day old hybrid white spruce seedlings subjected to six bacteria-inoculated (Caballeronia sordidicola HP-S1r, Pseudomonas frederiksbergensis HP-N1r, Phyllobacterium myrsinacearum HP-R1r, Pseudomonas mandelii LP-S1r, Paraburkholderia phytofirmans LP-R1r and Caballeronia udeis LP-R2r) and one non-inoculated control treatments. Error bars represent standard errors of the mean (n = 10 seedlings per treatment) and bars with different letters are significantly different (P < 0.05).

Fig 3

Population density of each of the six bacterial strains (Caballeronia sordidicola HP-S1r, Pseudomonas frederiksbergensis HP-N1r, Phyllobacterium myrsinacearum HP-R1r, Pseudomonas mandelii LP-S1r, Paraburkholderia phytofirmans LP-R1r and Caballeronia udeis LP-R2r) inside the endophytic tissues (needle, stem and root) and in the rhizosphere of (a) lodgepole pine and (b) hybrid white spruce seedlings evaluated 540 days after inoculation. For clarity of presentation, the data was log-transformed. Error bars represent standard errors of the mean (n = 5 seedlings per treatment for endophytic colonization and 5 seedlings per treatment for rhizospheric colonization).

Fig 4

Correlation of bacterial population sizes (x-axis) with length and biomass (y-axis) of (a) lodgepole pine and (b) hybrid white spruce seedlings. For this correlation, the population sizes in the rhizosphere and internal tissues were aggerated for each strain (Caballeronia sordidicola HP-S1r, Pseudomonas frederiksbergensis HP-N1r, Phyllobacterium myrsinacearum HP-R1r, Pseudomonas mandelii LP-S1r, Paraburkholderia phytofirmans LP-R1r and Caballeronia udeis LP-R2r). Population size, length and biomass variables were analyzed 540 days after the inoculation of pine and spruce.

Fig 5

Primary root length of (a), (b) canola and (c), (d) tomato seedlings subjected to six bacteria-inoculated (Caballeronia sordidicola HP-S1r, Pseudomonas frederiksbergensis HP-N1r, Phyllobacterium myrsinacearum HP-R1r, Pseudomonas mandelii LP-S1r, Paraburkholderia phytofirmans LP-R1r and Caballeronia udeis LP-R2r) and one non-inoculated control treatments. Seedlings were evaluated five days after germination in the gnotobiotic root elongation assay to evaluate in situ ACC deaminase activity. Error bars represent standard errors of the mean (n = 7 seedlings per treatment) and bars with different letters are significantly different (P < 0.05).

Fig 6

Correlation of in vitro ACC deaminase activity (x-axis) with primary root length (y-axis) of (a) canola and (b) tomato seedlings. The in vitro ACC deaminase activity was measured as the amount of α-ketobutyrate produced per mg protein in an hour. The primary root length of canola and tomato enhanced by each bacterial strain (Caballeronia sordidicola HP-S1r, Pseudomonas frederiksbergensis HP-N1r, Phyllobacterium myrsinacearum HP-R1r, Pseudomonas mandelii LP-S1r, Paraburkholderia phytofirmans LP-R1r and Caballeronia udeis LP-R2r)reflects the in vivo ACC deaminase activity.

References

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Sustaining the growth of Pinaceae trees under nutrient-limited edaphic conditions via plant-beneficial bacteria - PubMed (original) (raw)