Developing microbial inoculants for sustainable spinach cultivation: Soil and endophytic community insights

Abstract

Spinach (Spinacia oleracea L.), a widely consumed leafy vegetable, often faces growth challenges in nutrient-poor sandy loam soils. To address this, rhizospheric and endophytic bacteria capable of thriving in nitrogen-free and phosphate-solubilizing growth media were isolated and tested individually and in combination to develop a microbial consortium for sustainable spinach cultivation. Experiments were conducted at Jagannath Kishore College, Purulia, using control sandy loam soil from the college premises (CP). Plants grown in CP exhibited poor biometric performance, indicating that limitations in intrinsic soil properties affected both plant growth and microbial activity. To overcome these limitations, the soil was amended with water hyacinth compost and chicken manure (OCM). The amendment ratio was optimized prior to inoculation via response surface methodology (RSM) and central composite design (CCD), with leaf area as the key response variable. The inoculum consisted of Bacillus, Pseudomonas, and Flavobacterium species, which were selected for their complementary functional traits and synergistic biotic interactions. Application of bacterial inoculants to OCM produced the OCM+MI treatment. The OCM+MI, characterized by low bulk density and high nutrient content, clearly improved plant growth. The treatment produced an average leaf area of 238.07 cm², representing a statistically significant approximately 12.3% increase over the organic amendment alone (OCM, 212 cm²). This increase highlights the bio-stimulant value of the microbial consortium beyond the baseline fertilization effect of the compost. 16S rRNA sequencing identified Bacillus, Pseudomonas, Microbispora rosea, and Paenibacillus as dominant generalist taxa in OCM+MI. These taxa fostered community stability through high evenness, increased richness, low dominance, and balanced turnovernestedness patterns. Lysinibacillus emerged as a core taxon. Endophytic communities (BP) had lower diversity and were led by a specialist Flavobacterium. Functional profiling via Tax4Fun predicted the metabolic potential, suggesting an enrichment of amino acid metabolism and ABC transporters in the inoculated soil. The resulting consortium, blending generalist and specialist taxa, validated effectively in amended soil-offering a stable, low-input path to better productivity and ecosystem resilience. The developed consortium offers a ready-to-use, low-cost biofertilizer for organic and conventional spinach production in nutrient-poor soils.