Effect Of Nitrogen And Phosphorus Co-doped Carbon Quantum Dots On Photosynthesis Of Wheat Under Red-blue Light Cultivation Model

Due to excellent biocompatibility,water solubility and breakthrough in large-scale preparation methods,the application of CDs in agriculture has gradually entered people’s vision in recent years.In combination with vertical farming technology,the effect of CDs on wheat growth and development was explored by dissolving CDs in the wheat hydroponic nutrient solution.Firstly,we investigated the mechanism of the change in the optical properties of CDs induced by heteroatom P doping.Secondly,we explored the reasons for the impact of the difference in optical properties of CDs on wheat growth and development under suitable light conditions.The main findings are as follows:(1)Nitrogen doped CDs(N-CDs)and five kinds of nitrogen and phosphorus codoped CDs(CDs-P)were synthesized by one-step hydrothermal method by adopted citric acid and ethylenediamine as precursors and phosphoric acid as dopants.Optical property characterization revealed that introducing heteroatom P does not change the fluorescent emission site of CDs,but significantly affects the quantum yield(PLQY)of CDs.the introduction of heteroatom P,which replace the oxygen atom at the edge and the-COOH connected on the surface of CDs,will restore the conjugate structure between the edge and the nucleus,and suppresses the non-radiative transition of low energy level electrons.In addition,since the electronegativity of P is less than O,the electron donor conjugation effect of P maintained the integrality of π-conjugated structures in CDs,thus increasing the PLQY of CDs.(2)Light is one of the most important regulatory means in vertical farming.The experiment took white light as the control group(CK)and set up five different combinations of red,green,and blue light quality,namely,red light: blue light = 5:1(5R1B),red light: blue light: green light = 4:2:1(4R2B1G),red light: blue light = 3:3(3R3B),blue light: red light = 4:2(4B2R),and blue light: red light: green light = 4:2:1(4R2B1G).Compared with the blank control,5R1 B is the most favorable for the synthesis of photosynthetic pigments and the accumulation of soluble substances,and can significantly enhance the root activity of wheat,so the 5R1B treatment group is the most suitable light environment for wheat growth.(3)Under suitable light conditions,CDs with PLQY of 29.73% and CDs-P with PLQY of 41.82% were dissolved in the wheat hydroponic nutrient solution.We found that when the concentration of CDs and CDs-P were 100 mg/L,which could significantly enhance the photosynthesis of wheat and therefore promote the growth and development of wheat seedlings.During photosynthesis,CDs and CDs-P can activate photosystem II(PS II),improve the transfer efficiency of photosynthetic electrons and increase the activity of Rubisco enzyme,the content of photosynthetic pigments and the density of stomata,thereby enhancing the photosynthesis of plants.PLQY is a key influencing factor for CDs to promote plant photosynthesis as CDs with high PLQY possessed higher energy conversion efficiency and transfer efficiency of photo-generated electrons,thereby promoting wheat photosynthesis more effectively.