Biochemical and pharmaceutical traits of L. plants treated with plant growth-promoting bacteria and elevated CO.

The present research aimed to understand the influence of plant growth-promoting bacteria (PGPB) on various biochemical, nutritional, and pharmaceutical characteristics of plants grown under elevated carbon dioxide (eCO). To achieve this objective, a pot experiment was carried out, consisting of two treatments, namely: (i) biofertilization (Bf) by a PGPB strain ( sp.) and (ii) two different air CO levels, including ambient CO (aCO) and eCO concentrations (410 and 710 μmol CO mol, respectively). The improvement in the photosynthesis rate of eCO and Bf-treated plants can explain the increase in the production of carbohydrate. This is evidenced by a substantial rise, reaching up to + 75% and 25% in the total sugar and starch content in plants subjected to eCO treatment, respectively. Additionally, eCO-treated plants exhibited a remarkable 102% increase in soluble sugar synthesis, while plants subjected to Bf treatment showed a notable increase of 66%. Such modifications could be the main factor affecting plants carbon and nitrogen metabolism. Although the level of certain amino acids (such as glycine, tyrosine, and phenylalanine) in plants exhibited significant increases in response to eCO and Bf, the levels of other amino acids demonstrated enhancements in plants grown under eCO (e.g., histidine) or under treatments containing Bf (e.g., alanine and ornithine). Improvements in primary metabolites led to more benefits in plants treated with Bf and CO by boosting secondary metabolites accumulation, including phenolics (+ 27-100%), flavonoids (+ 30-92%), and essential oils (up to + 296%), as well as improved antioxidant capacity (FRAP). This remarkable effectiveness was evident in the significant increase in the biomass production, highlighting the synergistic impact of the treatments. Therefore, the interaction of Bf and eCO not only induced plant biomass accumulation but also improved the nutritional and pharmaceutical value of plants.