Effects Of CO₂ Enrichment And LED Light Recipes On Physiological Characteristics Of Cucumber Seedlings

At present,the CO₂ concentration in the atmosphere is rapidly increasing.And in the process of facility cultivation,there are problems such as shortage of CO₂ concentration and insufficient light environment due to the relatively closed environment and the effect of light transmittance of covering.In this experiment,in order to optimize the light and air conditions of greenhouse for cultivating robust cucumber seedlings,the cucumber variety’Jinyou No.35’was used as the test material,and a split-plot experimental design was adopted.The main plot was CO₂ treatment.Divided into 2 levels of atmospheric CO₂ concentration(≈400μmol·mol^-1)and enriched CO₂ concentration(≈800μmol·mol^-1).The split-plot factor was the light recipes treatment.Divided into 3 light recipes of white light（W）,red and blue light（RB=7:3）,red and blue light plus UV-A(RBU=7:3+20μmol·m^-2·s^-1).There were six treatments in the experiment.Effects of CO₂ enrichment and LED light recipes on the morphology,photosynthetic properties,carbon metabolism,nitrogen metabolism and antioxidants of cucumber seedlings were studied.The aim of this study was to investigate the effects of CO₂enrichment and LED light recipes on cucumber seedlings and to provide a theoretical basis for precise environmental regulation of intensive seedling production of cucumber in greenhouse.The main results were as follows:1.CO₂ enrichment reduced the plant height under the RB and RBU treatments,but increased stem thickness,leaf area and dry and fresh weight of seedlings.It is conducive to the accumulation of dry matter.2.CO₂ enrichment significantly increased the content of photosynthetic pigments and the activity of key enzymes for photosynthetic carbon assimilation under the RB and RBU treatments.Increasing the electron transfer rate（ETR）of cucumber seedling leaves,thus improving the photosynthetic performance of seedlings,and thus increasing the content of non-structural carbohydrates in cucumber seedling leaves to provide more carbon sources for seedling growth.3.CO₂ enrichment and RBU treatment facilitate the accumulation of non-structural carbohydrates in cucumber seedlings,increase the activities of sucrose synthase,sucrose phosphate synthase and leaf transforming enzymes,and promote sucrose metabolism,thus maintaining the"source-library"balance;CO₂ enrichment and RBU treatment also significantly increased the content of glycolytic-tricarboxylic acid cycle intermediates and the activity of key enzymes in the leaves of cucumber seedlings,thus promoting the rate of sugar metabolism in cucumber seedlings and providing sufficient energy for other metabolic activities and seedling growth.4.CO₂ enrichment inhibited the reduction of nitrate nitrogen under the RBU treatment,but increased the activity of key enzymes for nitrogen assimilation,thus enhancing the process of nitrogen assimilation in cucumber seedlings,promoting the synthesis of nitrogenous substances such as proteins and chlorophyll,and providing enzymes or proteins needed for other metabolic pathways.5.CO₂ enrichment and RBU treatment significantly increased the activity of antioxidant enzymes such as SOD,POD,CAT and APX and the content of osmoregulatory substances,thus reducing the content of MDA and ROS under the RBU treatment and slowing down the oxidative damage caused by the addition of UV-A to cucumber seedlings.