Characterization of salt-tolerant diazotrophs with plant growth-promoting potential isolated from soda industry-affected technosoils

Soils developed due to anthropogenic activities are known as technosoils. Microorganisms retrieved from such habitats are naturally adapted to extreme environments. Strains displaying plant growth-promoting abilities can play a vital role in improving degraded soil performance. The utilization of diazotrophs as natural nitrogen sources is particularly important as it reduces the reliance on synthetic nitrogen fertilizers.

To investigate this further, bacteria were isolated from the rhizosphere of wheat (Triticum aestivum L.), Salicornia europaea (L.), aster (Tripolium pannonicum subsp. tripolium (L.) Greuter), and maize (Zea mays L.) cultivated in the technosoils of Inowrocław, central Poland, influenced by the soda lime repository. A total of eleven bacteria were selected based on the presence of the nifH gene. The isolates were also tested for other growth-promoting traits, as well as biocontrol properties and antibiotic sensitivity. Finally, a germination test was performed on wheat seeds grown under nitrogen (N absence) and salt stress (150 mM NaCl) conditions.

Isolates Azo12 and W4ii, identified as Agrobacterium sp. and Azotobacter chroococcum, respectively, significantly promoted the growth of seedling roots and leaves under salt stress compared to seedlings without bacteria (P < 0.001). Agrobacterium sp. (Azo12), Sphingobium fuliginis (Azo7), and Variovorax paradoxus (Azo11) significantly increased seedling growth under nitrogen stress compared to control seedlings (P < 0.05).

Studies revealed that technosoils developed by the soda industry are an unexplored source of various salt-tolerant nitrogen-fixing bacteria with significant potential to be further explored for producing biostimulants for sustainable agriculture.