Evaluation of phosphorus sources in tomato plants inoculated with plant growth-promoting rhizobacteria

Tomatoes are agriculturally and gastronomically significant and serve as model organisms in scientific research. This study examined plant-phosphorus interactions, evaluated two P sources for fertilization, and analyzed the effects of rhizobacteria on plant growth. Phosphorus (P) is an essential yet limited nutrient for plants. Microbial inoculants formulated with plant growth-promoting rhizobacteria (PGPR) enhance plant health and growth and improve P solubility. Tomato seedlings were inoculated with the following PGPR strains capable of P solubilization: Paenibacillus spp. BSP 1.1, Arthrobacter enclensis JN24, and Arthrobacter pokkalii JLB4. Morphological and physiological analyses were used to assess nitrogen (N) and P intake and developmental differences among treatments. The P source, bacterial strain, and their interactions influenced plant development differently. Plants treated with phosphate rock exhibited a higher greenness index and root volume, whereas those with soluble phosphate had increased leaf area when inoculated with BSP and JLB4. Strain JLB4 specifically increased leaf area when combined with soluble phosphate. P concentration was lower in phosphate rock-treated plants, although deficiency symptoms were absent. N concentrations and growth-related variables were diminished in the early stages but improved to the end of the experiment. In conclusion, P demand was constant, but its availability increased with the effect of P solubilization throughout the experiment. Therefore, the addition of phosphate rock as a source of P in soilless agriculture may be a viable alternative for tomato cultivation.