LED红蓝光连续照射对高氮肥水培生菜AsA代谢网络的影响机理及节律效应

Hydroponics is a popular and promising cultivation technique for vegetable production in modern protected facilities (e.g. glasshouses and plant factory) worldwide with high productivity year-round. However, hydroponic leafy vegetables cultivated with nutrient solution containing high-level nitrate nitrogen usually have poor nutritional quality, e.g. lowered ascorbic acid (AsA) content and nitrate overaccumulation etc., with a higher yield due to their nitrophilous biological trait, which threats human health seriously and hinders large-scale application for hydroponics technique in horticulture. Semiconductor LED lights can emit narrow-width wavelength monochromatic lights that provide a tool to study the effects of light qualities on growth and nutritional quality of leafy vegetables cultivated hydroponically for practice. Our previous studies found that AsA content in hydroponic lettuce cultivated with high nitrogen nutrient solutions could be greatly increased after treatment by short-term continuous light (CL) with LED red & blue compound light (the invention patent was authorized),and the coumpoud light is superior to monochromatic light in efficacy. Up to date, no study was reported on the physiological mechniams and circadian rhythm of CL with red & blue coumpoud light for improvement of AsA accumulation in hydroponic lettuce. Therefore, the project wants to study and clarify the physiological mechanisms of CL with red & blue light in improving AsA accumulation in terms of the metablic network (synthesis, oxidation-reduction and decomposition, and AsA-GSH cycle processes) responsive site and cascades among metabolic processes as the breakthrough points. We will investigate the effects of CL of red & blue light on AsA accumulation and its metablic network, particularly to the contents of metabolites and key enzymatic activities on the network, then to examine the effects of CL light intensity, duration, leaf age and nitrate level and composition in nutrient solution on regulation efficiency. Ultimately, we will reveal the physiological responsive mechanisms of AsA metabolic network to CL under red light, blue light, and red plus blue light with various combinative ratios accompanied by relative influential factors, such as light quality, light intensity and circadian rhythm of CL, also hydroponic nitrogen supply regimes. Research data will improve our understanding on AsA accumulation regulation mechanisms under CL with various light qualities. More importantly, the results will provide scientific basis for establishment of CL quality improvement technology by light environmental control for hydroponic leafy vegetables in practice.

水培是现代设施蔬菜生产的国际主流技术，高产优势明显。叶菜是喜氮作物，高氮肥水培高产的同时叶菜品质低（AsA含量低等）的问题十分突出，既危害公众健康，也制约了水培技术的商业化应用。LED光源可发射纯单色光，为精准光环境调控设施水培叶菜品质研究与实践开辟了新途径。研究发现，LED红蓝光连续照射（CL）增加了高氮水培生菜中AsA含量（已授权发明专利），效果优于单色光且受光质组分调节。迄今，红蓝光CL促进水培叶菜AsA累积的代谢网络机理及昼夜节律效应未见报道。本项目以AsA代谢网络（合成、氧化还原分解和AsA-GSH循环）CL响应位点与联动机制为突破口，研究红蓝光CL对高氮水培生菜AsA代谢网络中各形态AsA含量和关键酶活性的影响及其与光质、光强、昼夜节律和氮营养的关系，揭示代谢网络响应CL的机理。研究结果将阐明水培叶菜AsA代谢的CL调控机理，为建立设施高氮水培叶菜CL品质提升技术提供科学依据。

高氮肥水培高产的同时叶菜品质低的问题十分突出，在弱光寡照的情况下尤为严重，表现为抗坏血酸（Ascorbic acid，AsA）和可溶性糖等营养物质含量低，硝酸盐过量累积，超标严重等方面。低品质叶菜不利于公众健康，也制约了水培技术的商业化应用。LED红蓝光连续光照（Continuous light, CL）可增加了高氮水培生菜中AsA和可溶性糖含量，降低硝酸盐含量，同时提高产量。LED红蓝光CL为精准光环境调控设施水培叶菜品质研究与实践开辟了新途径。然而，红蓝光CL促进水培叶菜AsA累积的代谢网络机理及昼夜节律效应未见报道。本项目研究目的是揭示红蓝光CL对高氮肥水培生菜AsA代谢网络影响的位点与机制，阐明CL 强度、昼夜节律与水培生菜AsA 代谢网络响应之间的关系。本项目以AsA代谢网络（合成、氧化还原分解和AsA-GSH循环）CL响应位点与联动机制为突破口，研究红蓝光CL对高氮水培生菜AsA代谢网络中各形态AsA含量和关键酶活性的影响及其与光质、光强、昼夜节律和氮营养的关系，揭示代谢网络响应CL的机理。项目4年执行期内，按计划安排执行了多个试验。研究表明，红蓝光CL对高氮肥水培生菜AsA含量有提升作用，对生菜AsA代谢网络影响受光质、光强、氮营养、昼夜节律和照射时长等因素的调控，响应的位点主要是AsA合成酶GalLDH与氧化还原酶MDHAR和DHAR，通过调控AsA合成途径和AsA氧化还原途径的机制来调增AsA含量。除提升AsA水平外，红蓝光CL还可显著提高生菜产量，并且这种增调效果随着CL光强以及红光比例的增加而增加。基于生菜产量和AsA累积机理，项目研究获得了一批LED红蓝光CL提高AsA含量的最佳效益的光质、光强、氮营养、昼夜节律和照射时长等指标参数。根据项目研究结果，构建出了设施高氮水培叶菜CL品质提升技术，即在生菜生长前期采取长期（9d之内）、较高光强（200、300μmol•m-2•s-1）和高红光比例（3R:1B）的CL以提升产量，而在采收前采取短期（24~48h）、高光强（300μmol•m-2•s-1）、高蓝光比例（1R:3B）的CL提高生菜AsA含量以实现生菜的优质高产。