Enhancing plant productivity by nature-based solutions: exploring plant growth promoting bacteria (PGPB) application on sterilized and non-sterilized Technosol for urban farming

Climate change and urbanization are exacerbating environmental challenges, especially in the Mediterranean region, where soil degradation threats agriculture. Technosols—artificial soils created from organic and mineral waste—offer potential for urban greening and land restoration, but limit plant growth because of nutrient scarcity. This study investigates the use of Plant Growth-Promoting Bacteria (PGPB) to enhance lettuce growth in Technosols. Plant growth performance was tested in sterile and non-sterile Technosols. Sterilized soil experiments isolated the plant-consortium relationship, avoiding interference from native microbes. Three PGPB inocula were tested: a Technosol-derived consortium (P3), halotolerant Bacillus amyloliquefaciens (RHFS18), and a combination of both (P4). In sterile Technosols, the P3 strain improved leaf traits, water content, and photosynthetic performance. However, under non-sterile conditions, the benefits due to plant-PGPB relationships were reduced due to competition of PGPB and native microbiome, leading to increased oxidative stress in plants. The P3 treatment demonstrated higher specific leaf area with minimal root infection, while RHFS18 delayed leaf aging, improved water retention, and enhanced photosynthetic efficiency. These findings highlighted the importance of soil context in optimizing the use of PGPB, offering a Nature- Based Solution for enhancing urban greening and agricultural productivity, utilizing plant-microbe interactions to address nutrient deficiencies in Technosols.