Effects Of Root-zone CO₂ Enrichment On Carbon And Nitrogen Metabolism In Oriental Melon Seedling Leaves

Melons?Cucumis melo L.?are very sensitive to changes in the root-zone gas environment.The root-zone gas mainly composed of O₂ and CO₂.O₂ deficiency and CO₂enrichment in the root-zone caused by poor soil aeration are one of main factors affecting the yield and quality of the plant.It's important to improve its yield and quality of melons production by regulating the root-zone gas environment.There are many studies about effects of low root-zone O₂ on plant growth,development,yield,and root nutrient uptake and few systematic studies about the changes of carbon and nitrogen metabolism during the vegetative stage of oriental melon may be rarely reported in relation to root-zone CO₂ enrichment.In this study,the oriental melon cultivar of‘Caihong 7'was chosen as experimental smaples.By the aeroponics culture automatic control system developed by our research group,the effects of different root-zone CO₂ concentration(380?L·L^-1,1000?L·L^-1,and 5000?L·L^-1)on seedling growth,leaves photosynthesis,sugar metabolism,nitrogen absorption metabolism,carbon and nitrogen content and accumulation,and the influence of C/N ratio were studied.The effects of root-zone CO₂ enrichment on the vegetative growth,carbon and nitrogen balance of oriental melon were discussed.It provides a theoretical basis to improve the root-zone gas environment for the facilities cultivation.The main results show that:1.The long term 1000?L·L^-1 and 5000?L·L^-1 root-zone CO₂ treatment significantly inhibited the seedling growth and the accumulation of biomass in various parts of the oriental melon.The results showed that 1000?L·L^-11 CO₂ concentration in the treatment 15 days,the height and stem diameter,aboveground and underground part of fresh and dry weight were significantly lower than the control.And 5000?L·L^-11 CO₂ treatment in the treatment 5 days,the plant height,stem diameter and underground part of fresh and dry weight of the oriental melon were significantly decreased compared with the control.But the aboveground fresh and dry weight began to significant decreased in the treatment 10 days.Additionally,5000?L·L^-1CO₂ treatment inhibited the oriental melon seedling growth were more significant than 1000?L·L^-11 CO₂ treatment.2.The contents of leaves photosynthesis pigments,photosynthesis and accumulation of photosynthetic products were affected under the root-zone CO₂ concentration of 1000?L·L^-1or 5000?L·L^-11 CO₂ treatment.The chlorophyll content?chlorophyll a,chlorophyll b,chlorophyll?a+b??,net photosynthetic rate?P_n?,stomatal conductance?G_s?,intercellular CO₂concentration?C_i?and transpiration rate?T_r?of leaves were significantly decreased by treatment time,but the stomatal limitation value?L_s?was increased compared with the control.The restrain effect was the highest when CO₂ concentration reached 5000?L·L^-1.1000?L·L^-1and 5000?L·L^-11 CO₂ treatment significantly reduced the xylem sap contents and the soluble sugar contents of xylem sap on the 15 and 10 days,respectively.The higher CO₂concentration in root-zone,the more decrease of the xylem sap contents and the soluble sugar contents of xylem sap.Treatments with 1000?L·L^-1 and 5000?L·L^-11 CO₂,the contents of the xylem sap.Treatments with 1000?L·L^-1 and 5000?L·L^-11 CO₂,the contents of fructose,glucose and sucrose in leaves increased and then dropped compared with the control.3.The activity of SPS in leaves treated with 1000?L·L^-11 and 5000?L·L^-1 root-zone CO₂was significantly higher than the control at 10 and 5 days,respectively.The activity of SS in leaves treated with 1000?L·L^-11 CO₂ was basically the same as the control and there was no significant difference in that.But,5000?L·L^-11 CO₂ treatment of the SS activity increased first and then dropped,and at 15 days significantly lower than the control.The root-zone enrichment caused the activities of AI and NI in leaves to decreased first and then increase.4.The contents of NH₄⁺-N?NO₃^--N at 1000?L·L^-1 CO₂ concentration and the activities of NR?GS?GOGAT and GDH were all gradually increased and the differences were smaller than control.But the contents of NH₄⁺-N?NO₃^--N at 5000?L·L^-1 CO₂ concentration and the activities of NR?GS?GOGAT and GDH were all increased first and then dropped.And that are all significantly higher than the control at treatment 5 days.While the treating time was prolonged,nitrogen absorption and metabolism in leaves were all significantly inhibited.With the root-zone CO₂ concentration increased,the inhibition of nitrogen metabolism became larger.1000?L·L^-11 and 5000?L·L^-11 CO₂ treatment significantly reduced the soluble protein contents in leaves and there was reduced greatly at 5000?L·L^-11 CO₂ concentration.5.With the treatment at 1000?L·L^-11 CO₂ and 5000?L·L^-11 CO₂ concentration,the accumulation of carbon and nitrogen in root,stem and leaves of oriental melon were significantly reduced.The coordination degree of carbon and nitrogen metabolism can be directly reflected by C/N ratio.The C/N ratio was gradually declined in root,ans inversely in leaves.6.The 1000?L·L^-11 and 5000?L·L^-11 CO₂ treatments showed that the root carbon contents of oriental melon was increased and then decreased to a stable trend.At 5 days,root carbon contents of 1000?L·L^-11 and 5000?L·L^-11 were all higher than the control.And there was no obvious change in different treatments at 25 days.The root nitrogen content was increased and then dropped at 5000?L·L^-1 CO₂ treatment compared with the control.It increased at1000?L·L^-1 CO₂ treatment.On the treatment 5 days,the carbon contents of oriental melon leaves treated with 5000?L·L^-1 CO₂ was significantly lower than control,but there was no significant differences in 1000?L·L^-11 CO₂ treatment.As processing time went,the differences in carbon contents between treatments were not significant.The nitrogen contents of the leaves were significantly reduced when the 1000?L·L^-11 and 5000?L·L^-11 CO₂ treatment at 10days.