Root Morphology And Nitrogen Adsorption Of Oriental Melon Seedling In Response To High CO₂ Stress In Rhizosphere

In modern agricultural production,on the one hand,soil compaction,water accumulation or flooding caused by improper cultivation and management,as well as root system and rhizosphere microbial respiration and other factors will result in lower oxygen concentration and higher CO₂ concentration in plant root system gas environment.On the other hand,the increase of greenhouse gas concentration in the atmosphere will indirectly lead to the increase of CO₂ concentration in the soil.Excessive CO₂ concentration in the rhizosphere environment will also affect the normal growth and development of plants.In this experiment,the oriental melon ‘Rainbow NO.7'as material,the oriental melon seedings were ventilated by the rhizosphere CO₂ automatic control system under aerosol cultivation conditions.The three rhizosphere CO₂ concentrations were set in this experiment: Normal atmospheric CO₂ concentration,0.5% CO₂ and 1% CO₂,were used to investigate the root morphology,root tip cell ultrastructure,nitrogen absorption and related gene expression in response to high concentrations of CO₂ in the rhizosphere.The main results of the test are as follows:1.Long-term high concentration CO₂ treatment significantly inhibited the growth and development of oriental melon seedlings,reduced the accumulation of plant biomass,and weakened root vitality.On the 15 th day of treatment,compared with the control,the longest root length was reduced by 16.57% at 0.5% CO₂ and 27.06% at 1% CO₂.Root volume was reduced by 14.78% at 0.5% CO₂ and 34.66% at 1% CO₂.Plant height and stem diameter were significantly inhibited,and the higher the concentration of CO₂ in rhizosphere treatment,the higher the degree of inhibition of various growth indicators.2.Long-term treatment with high concentration of rhizosphere CO₂ inhibited the normal growth of root morphology.The root morphology scanning images showed that the roots growing in the normal rhizosphere gas environment were long and thick.Under the treatment of rhizosphere CO₂ concentration of 0.5%,the roots was shorter than that under the treatment of 1% CO₂,but thicker than that under the treatment of 1% CO₂.Under the treatment of 1% CO₂ concentration in the rhizosphere,the roots were slender and grew weakly.Through the analysis of root morphological parameters,on the 15 th day of treatment,compared with the control,the number of root tips was reduced by 24.70% under 0.5% CO₂ treatment,and 40.17% under 1% CO₂ treatment.The total root length was reduced by 27.36% under 0.5% CO₂ treatment and 33.28% under 1% CO₂ treatment.The total root area,projected area and total root tips decreased.The proportion of fine roots?nutrient uptake active roots?with root diameter of 0.0-0.5 mm was also inhibited.The higher the concentration of rhizosphere CO₂ treatment is,the more the number of coarse roots will take up,that is,the higher concentration of CO₂ in the rhizosphere will affect the absorption of nutrients by plants through affecting root morphology.3.By observing the ultrastructure of root tip cells,we found that under the treatment of high concentration of rhizosphere CO₂,the root tip cells showed premature aging,fewer organelles,fewer mitochondria,and fewer contents.The higher the CO₂ concentration of rhizosphere,the higher the aging phenomenon of apical cells.4.The rhizosphere high concentrations of CO₂ in oriental melon seedling root nitrogen metabolism and its gene expression: the influence of the first close at the early stage of ventilation treatment,root in the content of total nitrogen,nitrate nitrogen and ammonium nitrogen content,NR activity and GS activity showed a control group was increased,then decreased with the extension of time all present a downward trend.The relative expression levels of Cm NR and Cm GS of genes related to nitrogen metabolism enzymes were significantly down-regulated.The relative expression level of CmNRT2.4,CmNRT2.5 was also down-regulated in roots with high nitrate transport affinity.These results indicated that the high concentration of CO₂ in rhizosphere could affect the nitrogen absorption of thin rhizosphere melon seedlings at the transcriptional level.