Inoculation of Plant Growth Promoting Bacteria on Yield, Stomatal Conductance and Chlorophyll Index of Corn under Potassium Deficiency

Potassium is one of essential elements for plants and it is the most abundant nutrient on soil surface which is important factor on plant growth and development. Factors such as potassium fixation, erosion, run-off and leaching cause reduction in available potassium of soil. Microorganisms especially bacteria play important role in changing unavailable potassium to available form. Hence, such bacteria can be used for increasing available potassium in soil and consequently production and quality of crops. The K- releasing bacteria can be employed as a biofertilizer to provide plant nutrients in a sustainable approach.
In this study, 10 bacterial isolates including Enterobacter sp. S16-3, Azotobacter chroococcum 14SP2-1, Pseudomonas sp. 34A-2, Pseudomonas Az-48, Psudomonas Az-8, S11-2 and 36A-2L provided from soil biology laboratory, department of soil science, University of Tabriz, Bacillus sp. 44-1 provided from soil biology laboratory of Gorgan University of Agricultural Sciences and Natural Resources, and S19-1 S14-3 isolated from Potabarvar biofertilizer produced by Green Biotech Company were used as a potassium biofertilizer. For this purpose, bacterial inoculant prepared in bagasse and perlite carrier was used to inoculate the disinfected seeds of corn (single cross 704). In this research, bacterial treatments were compared with chemical fertilizer treatments including K50 and K100, in these treatments based on soil test, 50% and 100% of fertilizer recommendation were used (equal to 0.115 g and 0.23 g potassium sulfate per pot, respectively). The experiment was conducted based on completely randomized design with three replications. Duration of this study was about 2 months. Parameters measured during growth were stem diameter, height, chlorophyll index and stomatal conductance and after harvesting, wet and dry weight of root, shoot wet and dry weight, total wet and dry weight.
The results showed that expect root dry weight, total wet weight and stem diameter, all parameters were significantly affected by the treatments. The highest plant height was observed for fertilizer treatment 50% (100.8 cm) with an increase of 3.5% compared to the negative control. As to bacterial isolates, highest height was measured in Bacillus sp. 44-1 (98.6 cm). Plant height and stem diameters are indicators of vegetative growth, these parameters can thus increase when plant can use soil nutrients more than others. Enterobacter sp. S16-3 had the maximum stem diameter and the lowest height. It can be due to decreased potassium nutrition and auxin and gibberellin transferred from root. The chlorophyll index and stomatal conductance were equal to 9.567 and 0.097, respectively, which were related to A. chroococcum 14SP2-1. These are the factors of photosynthesis parameters. Increase of these factors may be attributed to the hormone balance effects such as cytokinin which can expand root growth and absorbance of nutrients. A. chroococcum is one of plant growth promoting rhizobacteria which can provide more phytohormones and cause improved plant growth. Therefore, photosynthesis activities can be better. The highest wet weight (265.6 g) and shoot dry weight (44.4 g) were found at fertilizer treatments 50% and then 100% fertilizer recommendation, but in regards to bacterial isolates, A. chroococcum 14SP2-1 and Pseudomonas Az-8 had higher values as compared with the control. The maximum root dry weight was observed in Pseudomonas Az-48 (187.2 g). However, the lowest root weight was obtained at 50% fertilizer recommendation. Hence, this can be explained by the root developing types. The highest total dry weight was measured in Enterobacter sp. S16-3 (63.68 g) and Pseudomonas Az-8 and after these bacterial isolates, fertilizer treatments had better condition. Consequently, these bacteria had another effects on plants such phytohormones productions and enzymatic activities that chemical fertilizer did not have such influences. The highest average of shoot potassium content was observed at 100% fertilizer recommendation (1077.3 mg/plant).
The results showed that fertilizer treatments K50 and K100 had better conditions and pots with chemical fertilizer grew more than others in most plants. But some bacterial isolates showed comparable results relative to K50 and K100. These bacteria can affect plants with directly and indirectly mechanisms. Bacterial treatments such as A. chroococcum 14SP2-1 and Pseudomonas Az-8 improved growth parameters through solubilizing potassium and producing phytohormones. Hence, these isolates can be considered for further studies particularly under field condition.