Studies On Factors Concerned In Nutrient Media Aeration Improving Growth As Well As Yield In Cucumber

Normally,Plants were planted in soil,and the proportion of solid,liquid as well as gas in soil directly impacted on the growth of plants and the absorbtion of roots.Especially for the protected cultivation,the interchange of gases between the soil and the surrounding air was overwhelmingly limited resulting from soil compaction,smaller aeration porosity or other factors frequently.[O₂]in soil reduced gradually companied with the increase of[CO₂],and the interaction of them boosted gases' harm on the plants seriously.Up to date the researches on the theoretics and practical technology for improving rhizosphere gas environments of the solid-cuitivation(soil and matrix,etc.) was yet few.In this experiment,the air was firstly introduced into the roots system space,and the effect of the different aeration manners on the gas environment,physical and chemical properties of cultivation matrix were studied in cucumber employing the matrix-ventilation-cultivation mode.Furthermore,the growth and development of plants,leaf photosynthesis,root physiological metabolism and root anatomy, especaiUy the relationship between nitrogen metabolism together with nutrition absorption in roots and concentrations of O₂/CO₂ in rhizosphere were explored and analyzed for ascertaining the best manner of matrix ventilation and clarify the physiology machanism that matrix-ventilation-cultivation improved the rhizosphere environment and the absorption of roots,particularly increased the yield and quality of cucumber production in greenhouse.The main results were as follows:1.The comparison of growth and yield in cucumber for the different aeration manners, the results showed that gas exchange rates of matrix was the fastest in D1 treatment,and O₂ concentrations were the highest,and CO₂ concentrations were lowest in matrix.But the effects of matrix ventilation was the best in G1 treatment,because it had vigorous growth of plant and the highest yield,and the outflow rate of xylem sap,root activity and nitrate reductase activity were higher.Therefore,the gas concentrations in matrix must be within the appropriate scope which was benefit to the plant growth.In this study,the most appropriate concentrations of O₂ and CO₂ in matrix were respectively in the range of 18.25～17.55%and 0.82～1.11%.Moreover,gas stress in rhizosphere has a reversible character to some extent. For the recovering ventilation after 15 days,non-ventilation treatment markly accelerated growth,and growth potential was increased more clearly with the prolonging of recovering time.2.The comparison of physical and chemical properties of cultivation matrix in cucumber for the different aeration manners,the results showed that matrix enzyme activities,contents of available N and available P in G1 treatment were higher,and compared to CK,contents of available N and available P respectively increased by 17.53%and 24.97%.However,matrix enzyme activities,contents of available N and available P significantly reduced in non-ventilation treatment(F1),compared to CK,contents of available N and available P respectively decreased by 10.56%and 21.32%.Correlation analysis results showed that the correlation between the matrix ventilation and matrix enzyme activities was not significant, but the correlation between the matrix ventilation and nutrients and pH of matrix was significant.Therefore,matrix aeration significantly increased available nutrition contents, which benefited roots to absorb and use them.3.The comparison of nutrition absorption in cucumber roots for the different aeration manners,the results showed that the accumulation of nutrient elements,ion concentrations of xylem sap,flow rate of xylem sap,roots activities,activities of Ca²⁺-ATPase and Mg²⁺-ATPase were higher in G1 treatment,but those decreased significantly in F1 treatment compared with CK.Effect of matrix ventilation on ion concentrations of xylem sap followed by K⁺＞NO₃^-＞PO₄^3-＞Ca²⁺ and Mg²⁺.Correlation analysis results showed that[K⁺],[NO₃^-],[Ca²⁺]and[Mg²⁺]in xylem sap were a significant negative correlation with[CO₂]in the matrix,but those were a significant positive correlation with the[O₂]in matrix.The correlation between[PO₄^3-]and[O₂]and[CO₂]in the matrix was no significant.Therefore, matrix aeration significantly promoted nutrition absorption and transport.4.The comparison of defensive function in cucumber roots for the different aeration manners,the results showed that contents of O₂^·,MDA and autotoxin substances in cucumber roots were lower,and activities of catalase(CAT) and superoxide dismutase(SOD) were also lower in G1 treatment.However,contents of O₂^·,MDA and autotoxin substances in cucumber roots were significantly increased in F1 treatment,especially contents of benzoic acid and p-hydroxybenzoic acid were 2～7 times of CK,and activities of catalase(CAT) and superoxide dismutase(SOD) in roots were the trend of the dropping after the first rising. Therefore,matrix aeration significantly reduced contents of hazardous substances in roots.5.The comparison of contents of carbohydrate and hormone in cucumber roots,the root dry weight,soluble sugar content,glucose content,sucrose content,fructose content were higher,but starch contents werelower,and the contents of ZT,GA and IAA in xylem sap and roots were higher in G1 treatment,but ABA content was lower.However,the root dry weight significantly decreased in non-ventilation treatment(F1),and starch content,soluble sugar content,glucose content,fructose content were the trend of the dropping after the first rising, and sucrose content was lower,and the contents of ZT,GA and IAA in xylem sap and roots were lower,but ABA content was higher.It showed that matrix aeration promoted carbohydrates accumulation and the synthesis and transport of hormone in roots.6.The absorption of root system was the main sources of nitrogen in the plant.The effects of matrix ventilation on the abaorption,transportion and metabolism of nitrogen in the root system of cucmber were discussed deeply.The results showed that contents of ammonium,nitrate,free amino acids and soluble protein in cucumber roots were higher in G1 treatment.Contents of ammonium,nitrate and free amino acids in cucumber roots were the trend of the dropping after the first rising in F1 treatment,but contents of soluble protein was lower11.03%than that of the control.Activities of nitrate reductase,nitrite reductase, aspartate aminotransferase,alanine aminotransferase,glutamine synthetase in roots were higher in G1 treatment.Activities enzyme of F1 treatments had a significant reduction at the end of treatment,especially activities of glutamine synthetase was lower 33.33%than that of the control.Matrix ventilation made the relative contents of certain amino acid changed in roots,but effect it on the components of amino acids was little.Therefore,matrix aeration significantly promoted nitrogen metabolism and protein synthesis in roots,which might be one of the main reasons to promote the growth and development of plant.7.The comparison of carbohydrate contents and photosynthesis in cucumber leaves for the different aeration manners,the results showed that contents of starch and soluble sugar in leaves of G1 treatments had no significant differences compared with CK,but contents of the soluble protein and free amino acids significantly increased.However,contents of starch, soluble sugar and free amino acids in leaves of F1 treatment were the trend of the dropping after the first rising,and contents of soluble protein were 10.72%lower than those of the control.Net photosynthetic rate,stomatal conductance,transpiration rate were higher in leaves of G1 treatment,but the concentrations of intercellular carbon dioxide were the highest in leaves of F1 treatment.Maximal fluorescence yield,PSâ…¡photochemical efficiency and performance index were higher in leaves of G1 treatment,but original fluorescence was the highest in F1 treatment.Therefore,qualities and photosynthetic abilities of leaves in cucumber were indirectly affected by matrix ventilation.8.The comparison of cells of the epidermis,cortex,endothelial and stele in roots tip of cucumber for ventilation treatment(G1) and non-ventilation treatment(F1),the results showed that the metabolic characteristics of active cells were observed in roots tip of ventilation treatment such as cells with regular,nuclei integrity,dense cytoplasm,a large of mitochondria with the integral structure and well-developed cristae,and starch grains were only found in the cells of epidermis and cortical with a smaller number.However, non-ventilation treatment greatly affected organelle of cells of the epidermis,cortex, endothelial in roots tip of cucumber,and affected stele cells lightly,and the cytoplasm also contained some highly dense deposits.Non-ventilation treatment(F1 treatment) made plastids swell,the number of plastid increase,starch grains in plastid increase markly,especially the largest number in the epidermis and the cortex,less number in the endothelial and stele cells. The number of mitochondria was small.Mitochondria appeared highly translucent,and its membrane structure was severely damaged.Cells were irregular and scattered,and nuclei was also irregular,karyoplasm was sparse,nucleolus was loose,nuclear membrane were partly vague.Vacuole was large and its inclusions were rich.