Precision nanobubble irrigation tailors plant physiology to drive sustainable lettuce growth with water savings

Under accelerating climate-driven water scarcity, improving irrigation efficiency for high-value leafy crops has become an urgent challenge for global food security. Nanobubbles (NBs), gas-filled cavities < 500 nm in diameter, have emerged as a promising irrigation technology capable of enhancing root-zone processes and early plant development with minimal additional water inputs. However, their effects in soil-based systems remain poorly resolved, particularly for leafy vegetables grown in water-stressed regions. Here, we systematically evaluate the influence of four gas types (O2, CO2, N2, and air), delivered as NBs at three dilution levels (100 %, 50 %, and 10 %; corresponding to >108 particles mL−1 at 100 %), on early-stage growth and water productivity (WP) in lettuce (Lactuca sativa, var. 'Little Gem') grown in a peat moss, coconut coir, and vermiculite mixture. Our results reveal that moderately diluted O2 NBs (10 %–50 %) accelerate germination, boost biomass accumulation, and improve water savings by up to ∼23 %. In contrast, high concentrations (100 %) of O2 NBs reduced overall performance and induced elongated but narrow leaf morphology, consistent with stress-related growth allocation. The use of CO2 NBs, particularly at higher concentrations, stimulates root expansion and leaf area development, while moderate N2 NBs concentration enhanced ammonium uptake and root elongation. Air NBs produce modest and variable effects, serving as a baseline but never outperforming pure gas NBs. Together, these results demonstrate that gas-specific NBs treatments can be strategically tuned to regulate distinct physiological pathways during early plant development, supporting the potential of NBs-based irrigation as a tool for water-efficient, climate-resilient leafy crop production.