Effects of plant growth promoting bacteria (PGPB) rhizo-inoculation on soil physico-chemical, bacterial community structure and root colonization of rice (Oryza sativa l. var. faro 44) grown in ferruginous ultisol conditions

Abstract

Ferruginicity is a special condition when soil became rich in iron. This condition is characterized by high pH and reduced bioavailability of  plant limiting nutrients. Unfortunately, this type of soil covered 30% of arable lands in Nigeria. This research aimed at using a native plant  growth promoting bacteria (Bacillus cereus strain GGBSU-1, Klebsiella variicola strain AUH-KAM-9 and Proteus mirabilis strain  TL14-1) with phosphate solubilizing capabilities to remediate iron toxicity and improve soil nutrients, as well as soil micro-biota  colonization. Soil physico-chemical properties before rhizo-inoculation (FA), after 16 weeks of rhizoinoculation with the PGPB into the  rhizoid of a growing rice seedling (FB) and after 16 weeks of natural attenuation (FC) were analyzed. Phosphate solubilizing capacity of  the PGPB was investigated using a developed Pikovskaya’s growth medium. The results showed that FA is rich in iron and deficient in  bioavailable phosphorus and nitrogen (200.67 mg/kg, 8.01 mg/kg and 0.20%) respectively, as against the FB soil which showed moderate  iron and increased soil nutrients (51.22 mg/kg, 20.21 mg/kg and 0.33%). The presence of acidic exudates, which was indicated by a red  litmus paper at the rhizosphere in FB signifies the iron chelation capacity of the PGPBs resulting in iron remediation and soil nutrient  improvement. Furthermore, the significant increase in microbial population in the FB soil as against the FA and FC corresponds with the  SEM results at the root epidermis. Furthermore, other nitrogen-fixing bacteria such as Bacillus subtilis were observed to be active and  motile in the FB. This indicated the effectiveness of PGPB with PSB capacities in iron remediation and soil nutrient enhancement.