Foliar Spraying Zinc–Carbon Dot Nanofertilizer Promotes Yield and Quality of Lettuce (Lactuca sativa L.) through Leaf–Root Regulation

Abstract

Currently, the “invisible hunger” of micronutrient deficiencies is threatening human health worldwide. Herein, foliar spraying zinc–carbon dot nanofertilizers (Nano-ZCDs, 10 mg·L^–1) improved lettuce yield (62.3%) and quality, especially Zn content (41.2%). Primarily, Nano-ZCDs could take advantage of CDs as an artificial antenna to enhance photosynthesis and up-regulate the expression of zinc-regulated and iron-regulated transporter-like protein (ZIP) genes to facilitate nutrient uptake, resulting in increased photosynthetic pigments, giving rise to an increase in chlorophyll a by 59.1%, chlorophyll b by 32.2%, and carotenoid by 85.9%, and enhance the photosynthetic efficiency by 106.7%. Additionally, the improvement of photosynthesis by Nano-ZCDs promoted the secretion of low molecular compounds (decenoic acid, proline, adipic acid, medronic acid, 4-aminosalicylic acid, etc.) in roots and then recruited rhizosphere beneficial microorganisms (e.g., Pseudomonas and Penicillium). These microorganisms could activate phosphorus in soil and make a 22.0% increase in available phosphorus (AP) in rhizosphere soil, thus augmenting the P content (4.2%) in the shoot, which mitigates the antagonistic effect between Zn and P. Consequently, the application of Nano-ZCDs can be considered a promising strategy for agricultural development, particularly in the aim of tackling the challenge of micronutrient deficiencies in crop products.