Effect Of High CO₂ In Root-zone On Carbon Absorption And Assimilation Of Oriental Melon Seedling

In agricultural production,bad conditions such as soil compaction or stagnant water often occur,which greatly increases the CO₂ in the soil,thereby affecting the growth and development of plants.Melon is a plant that is sensitive to root-zone gas.In facility cultivation,CO₂ in the soil is often increased,which affects melon growth and development.Previous studies have shown that CO₂ can be absorbed by roots and transported in plants.Although this subject has conducted a lot of research on the changes of plant growth and nutrient absorption and metabolism under high root-zone CO₂,it is still unclear how the root-zone CO₂ enters the melon root and its distribution in the plant.In this experiment,the oriental melon"Yumeiren"was used as the test material,and two different concentrations of0.2%and 1%root-zone ¹³CO₂ treatment were set through stable isotope tracing technology（0.2%is the root-zone conventional CO₂ concentration,1%is the root-zone high CO₂concentration）,to locate and quantify the distrib ution of carbon absorbed by roos in the system,explore the effects of different concentrations of root-zone CO₂ on the absorption of CO₂ by melon root,and provide a theoretical basis for the efficient absorption and utilization of rhizosphere carbon by melon root.At the same time,through aerosol cultivation,the root-zone CO₂ automatic control system developed by this research group is used to treat melon seedlings with two different concentrations of 0.5%and 1%root-zone high CO₂（the control treatment is 0.2%,the root-zone regular CO₂ concentration）,to study the effects of different root-zone high CO₂ on the growth and development of oriental melon seedlings,leaf photosynthesis,leaf photosynthetic carbon assimilation related e nzyme activities and gene expression,and to clarify the mechanism of different root-zone high CO₂ concentrations affecting melon carbon assimilation.The main results are as follows:1.In the ¹³CO₂ stable isotope tracing test,root-zone ¹³CO₂ at 0.2%and 1%concentration detected ¹³C in P1（melon root system）at 0.5h.1%¹³CO₂ treated in P2（count the first and second leaves and the first and second stems from bottom to top）detected ¹³C at 0.5h,0.2%¹³CO₂ treated in P2detected ¹³C within 1.5h.0.2%and 1%¹³CO₂ treated in P3（remaining stems and leaves）detected ¹³C at 1.5h.Theδ¹³C value is the largest at the time of treatment for 5h,which is P1>P2>P3,and 1%¹³CO₂ treatment is higher than 0.2%¹³CO₂ treatment.It shows that the root of melon can absorb CO₂ and transport it to the above-ground part,and the higher the concentration of CO₂ in the root-zone within a certain range,the more CO₂absorbed by the root,and the faster the upward transportation speed.2.During treatment with different root-zone ¹³CO₂ concentrations,the distribution of ¹³C in the roots,stems and leaves of the 1%¹³CO₂ treatment was significantly higher than that of the0.2%¹³CO₂ treatment.However,as the processing time increases,the total amount of ¹³C for0.2%¹³CO₂ treatment was increasing,and the total amount of ¹³C for 1%¹³CO₂ treatment was decreasing.It shows that the absorption of carbon by roots is affected by the concentration of CO₂ in the root-zone and the treatment time.3.During different root-zone ¹³CO₂ concentration treatments,the distribution ratio of ¹³C in roots and stems of 0.2%¹³CO₂ treatment was significantly higher than that of 1%treatment.On the contrary,in leaves,the distribution ratio of ¹³C in 1%¹³CO₂ treatment was significantly higher than that of 0.2%treatment.It shows that the concentration of CO₂ in the root-zone affects the distribution of carbon absorbed by the roots in the roots,stems and leaves of the melon.4.During different root-zone ¹³CO₂ concentration treatments,the carbon accumulation in roots,stems and leaves of 0.2%¹³CO₂ treatment were significantly higher than that of 1%¹³CO₂ treatment.The amount of carbon accumulation in a plant is the most intuitive manifestation of the amount of carbon fixation.It shows that the treatment with high CO₂ in the root-zone inhibited the carbon fixation of melon seedlings,thereby affecting the carbon assimilation of melon5.During treatment with different root-zone high CO₂ concentration,0.5%and 1%root-zone high CO₂ treatment 9 days later,the activities of carbon assimilation-related enzymes such as Rubisco,RCA,FBPase,FBA,SBPase and TK were significantly reduced compared with the control.After treatment with 0.5%and 1%root-zone high CO₂ for 9 days,the expression of Cm Rubisco、Cm RCA、Cm SBPase、Cm FBPase、Cm FBA、Cm PRK of carbon assimilation-related genes was significantly lower than that of the control.After 12 days of treatment,the expression of Cm PGK gene was significantly lower than that of the control.At9～12 days,the expression of Cm TK gene was significantly lower than that of the control.It shows that treatment with high concentration of CO₂ of 0.5%and above in the root-zone inhibited photosynthetic carbon assimilation-related enzyme activity and gene expression in melon after 9 days,thereby inhibiting the carbon assimilation in melon seedlings.