Effects Of Root-zone Oxygen Environment On Physiological And Biochemical Characteristics Of Tomato Seedlings

With the development of facility agriculture,soilless cultivation method has been increasingly favored by people because of its various advantages,but whether in the substrate cultivation or hydroponics hypoxia stress comes into appearance,due to the formation of the root mat or nutrient solution does not flow,and hypoxia stress has become one of the main limiting factors in crop production.Tomato has now become an important vegetable in the world,and it is also the main crop in soilless culture for its multiple merits.Therefore,it is of great significance to investigate the effects of oxygen concentration on the growth and physiological characteristics of tomato in nutrient solution culture,and to figure out the useful management measures and the relationship between oxygen concentration and production in soilless culture.To explore the influence of oxygen concentrations,especially the saturated oxygen concentration in root system on growth,photosynthetic characteristics and nitrogen metabolism of tomato seedling,the tomato cultivar 'Henan 4' were grown in nutrient solution under three dissolve oxygen(DO)concentrations,which are normoxia(7-8mg/L;Air treatment),saturate oxygen(14-17 mg/L);Oxygen treatment)and no aeration as control((6-0 mg/L).The results are as follows:1.With the increase of oxygen concentration,the growth of tomato seedlings was better.And compared with the control group,except for the average diameter of root,the biomass of tomato seedlings,plant height,stem diameter,root length,and the surface area,root volume,total root length,root branches and root tips were significantly increased in normoxia(T1)and saturation oxygen(T2).The relative growth rate of tomato Seedlings under different oxygen environment is T2>T1>CK,and the total dry weight in T1 and T2 increased by 24% and 74.86%,respectively,and the root length increased by 121.44% and154.32%,respectively.Under the condition of saturated oxygen,the root system developed and robust,and the growth of aboveground part was better,the relative growth rate was the highest,and the biomass accumulation was the highest.The relative growth rate and biomass were the highest,and the root was more flourishing and stronger under saturate oxygen treatment.Consequently,improving the oxygen concentration in rhizosphere can be beneficial to the growth of tomato.2.In the mid and late period of different treatments,the root activity of tomatoseedlings increased but the content of proline and MDA decreased significantly in normoxia T1 and saturation oxygen T2.At the end of treatments,the proline content of T1 and T2 reduced by 28.49% and 42.17%,respectively,and the content of MDA decreased by 47.47%and39.24%,respectively,which compared with CK.It showed that with the treatment time extended,the continuing lack of aeration easily caused the rhizosphere hypoxia stress on tomato seedlings,while increasing the rhizosphere oxygen concentration was beneficial to alleviate the damage caused by hypoxia,and to maintain a high root activity,thus promoting the growth of tomato.3.Increasing the oxygen content in the rhizosphere decreased the photosynthetic pigment content of the seedlings,and the saturation oxygen(T2)was significantly lower than that of the normoxia(CK),and the decrease was the largest.With the increase of treatment time,there was no significant difference between T1 and CK in the late period of treatments.Meanwhile,there was no significant effect of rhizosphere oxygen concentration on F0 and Fm of tomato seedling leaves.Fv/F0,Fv/Fm,?PS?,ETR(II)and q P of T1 and T2 were significantly increased in the early and late period of treatments,while q N decreased significantly.The results showed that the concentration of rhizosphere oxygen could alleviate the photoinhibition of seedlings,improve the utilization of solar energy,and maintain high photosynthetic performance.However,the photoinhibition of normoxia(CK)was serious,and the photosynthetic rate could be increased by increasing the content of photosynthetic pigment,so as to alleviate the hypoxia.4.In the late period of treatments,the nitrogen content of the shoots significantly increased under normoxia and saturates oxygen,but it had no significant impact on the nitrogen content of the roots.In the 12-day and 18-day of treatment,the nitrogen content of root in saturate oxygen concentration was significantly lower than that of CK.And the nitrogen accumulation in shoot,root and plant of tomato seedlings significantly increased under normoxia and saturate oxygen,but the content of free amino acid and the activity of NR reduced.And the plant nitrogen accumulation of saturated oxygen was highest among all the treatment and it showed rhizosphere aeration could improve the nitrogen utilization of root and increase the nitrogen accumulation of tomato seedlings.However,the seedlings under non-aeration had altered nitrogen metabolism and resulted in the increase in NR activity and free amino acid content,so as to improving the absorption and transformation of nitrogen to resist hypoxia.The results showed that increasing the rhizosphere oxygen concentration could significantly improve the root growth of tomato seedlings,increase the root activity,increase the utilization efficiency of light energy and increase the amount of nitrogen accumulation,thus promoting the growth and development of seedling plants.At thesaturated oxygen concentration,the growth rate of tomato seedlings was the highest,the biomass and nitrogen accumulation were the largest,while the seedlings under the untreated rhizosphere were deeply stressed,the seedlings grew slowly and the photosynthesis was enhanced.