Foliar Nanoparticles Improve Growth, Photosynthetic Performance, and Mineral Nutrition in Field-Grown Jalapeño Pepper Under Severe Water Limitation

Severe water limitation constrains crop productivity through coordinated effects on growth, photosynthetic performance, and mineral nutrition. This study evaluated whether foliar nanoparticle (NP)-based formulations and commercial biostimulants could improve the physiological and productive performance of field-grown jalapeño pepper (Capsicum annuum L.) receiving 50% of the reference irrigation volume. Treatments included ZnO NPs, SiO2 NPs, ZnO + SiO2 NPs, Nano ZnMo, Osmoplant, and Codasil, together with well-watered and water-limited controls. Severe water limitation markedly reduced stem and fruit biomass, aboveground biomass, and fruit yield, despite relatively stable instantaneous gas exchange. Foliar treatments induced distinct responses. ZnO NPs produced the strongest productive recovery, restoring fruit dry biomass to well-watered levels and increasing fruit yield by 72.8% relative to the water-limited control. Codasil maximized net photosynthesis, photochemical quenching, and electron transport rate, whereas Osmoplant produced the highest water-use and intrinsic water-use efficiencies. ZnO + SiO2 NPs maximized carboxylation efficiency, while Nano ZnMo partially restored Fe and maintained a distinctive mineral profile. Correlation and principal component analysis (PCA) showed that productivity was primarily associated with coordinated gas exchange and photochemical traits. Finally, the ZnO NP-based formulation showed the greatest improvement in fruit yield among the evaluated foliar treatments under water-limited conditions, highlighting its potential for sustaining jalapeño pepper productivity.