In agricultural ecosystems P. polymyxa can promote plant growth through three mechanisms. The first mechanism is production of hormones like cytokinins, auxins, ethylene and gibberellins.
These compounds increase root expansion and plant growth. The second mechanism is production of antibiotics and promoting immunity of rhizosphere. Heulin et al. (1994) observed that antagonistic activity of P. polymyxa decreased the activity of two plant pathogenic fungis (Gaeumannomyces graminis var. tritici and Fusarium oxysporum) .
The third mechanism is the bacterium's nitrogen fixing ability that can produce a form of nitrogen (ammonia NH3) that is usable by plants from atmospheric N2.
In addition, soil fluctuation and porosity is improved due to organic compounds released from P. polymyxa into the soil.