| In agricultural production, watering soil improperly, soil compaction or stagnant water, floods, soil microbial activities and root respiration enable root-zone O2 concentration insufficient, and make root-zone CO2 concentration increased massively, thereby affecting normal growth and development of plants. The study is the use of melon varieties called ’Rainbow 7’as test materials. By the aeroponics culture automatic control system, the effects of root-zone different CO2 concentration (2000μL·L-1,3000μL·L-1,4000μL·L-1 and 5000μL·L-1) on root growth and root nitrogen metabolism of melon seedlings were studied during vegetative growth periods. The main results show that:1. Root-zone high CO2 concentration inhibited the growth of melon seedlings. In the treatment 5 days, the height, stem diameter and root length of root-zone CO2 concentration at 4000μL·L-1 and 5000μL·L-1 was significantly lower than the control treatment. From treatment 10d the stem diameter, root length and root volume of root-zone CO2 concentration higher than 2000μL·L-1 compared with the control treatment were significantly inhibited, and the higher CO2 concentration the greater the degree of inhibition.2. The total root absorption area and active absorption area in root and root activity with root-zone high CO2 concentration were higher than that the 370 μL·L-1 (control) at the initial stage of treatment, and they were decreased with treatment time progressed. In treatment with 5d and root-zone CO2 concentration at 2000μL·L-1 the total root absorption area and active absorption area and root activity in root were significantly higher than the control, and then they began to decline rapidly. In treatment with 10d, the total root absorption area and active absorption area in root with root-zone high CO2 concentration were significantly lower than the control. However, in treatment with 15d, root activity was significantly lower than the control. With the extension of treatment time and the CO2 concentration increased, the difference became larger.3. The xylem sap content, xylem sap conductivity and pH with root-zone CO2 concentration at 2000μL·L-1 in treatment with 25d were significantly reduced, and they were decreased with the elevated root-zone CO2 concentration over the treatment time. The Xylem sap content with CO2 concentration at 2000μL·L-1,3000μL·L-1 4000μL·L-1 and 5000μL·L-1 compared to the 370μL·L-1 (control) were decreased by 21.02%,25.88%,43.13% and 48.79% (P<0.05).4. The content of NH1+-N, NO3--N and the total nitrogen content in root with root-zone CO2 concentration more than 2000μL·L-1 were higher than that the 370μL·L-1 (control) at the initial stage of treatment, and they were decreased with treatment time progressed. In treatment with 5d,the content of NH4+-N、NO3--N and the total nitrogen content in root and xylem sap were significantly higher than the control, and then they began to decline rapidly. In treatment with 15d, they were significantly lower than the control.5. With the elevated root-zone CO2 concentration, the activity of nitrate reductase (NR), glutamate synthase (GOGAT) and other nitrogen metabolism-related enzyme activity and plasma membrane H+-ATPase activity in root were in the same trend. All of them were higher than the control in treatment with 5d and root-zone CO2 concentration more than 2000μL·L-1,and glutamine synthetase (GS) and vacuolar membrane H+-ATPase activity were higher than root-zone CO2 concentration more than 4000μL·L-1 and 3000μL·L-1. And then all of them were significantly lower than the control in treatment with 15d. The aspartate transaminase (GOT) and glutamic pyruvic transaminase (GPT) activity and soluble protein content in root with root-zone CO2 concentration more than 2000μL·L-1 were lower than that the 370 uL·L-1 (control), and with the extension of treatment time and the CO2 concentration increased, the difference became larger.6. The nitrogen content, nitrogen metabolism related enzyme activity and soluble protein content in xylem sap of melon with root-zone CO2 concentration at 2000μL·L-1 in treatment with 25d were lower than that the 370 μL·L-1 (control), and the difference between 2000μL·L-1 and 3000μL·L-1(CO2 concentration) were not significant and the difference between 4000μL·L-1 nd 5000μL·L-1 were also not significant. The content of the major part amino acid in xylem sap were decreased with the elevated root-zone CO2 concentration over the treatment time. It was concluded that the uptake of nitrogen, assimilation, amino acid synthesis and transporation were inhibited in root when the root-zone CO2 concentration reached 2000μL·L-1 in of melon, which resulted the decrease of the ability of nitrogen metabolism and the level of plant nitrogen cycle. |
PDF Full Text Request