| The Manihot esculenta Crantz is mainly cultivated in tropical and subtropical zones,and is the perennial shrub as the member of Manihot genus of Euphorbiaceae family.This shrub is deemed as one of three major tuber crops.In China,the Manihot esculenta Crantz is not only recognized as the major raw material for starch industry and biomass energy,but also as the effective and valid supplementary crop for maintaining food security.Nitrogen is perceived as the primary element during the cultivation and nurture of Manihot esculenta Crantz.Adding the application of nitrogenous fertilizer to a certain extent shall increase the yield of Manihot esculenta Crantz.However,the excessive fertilization shall waste the resources and give rise to a series of nitrogen pollution issues.For this reason,the effective resolution of the mentioned issues is to sufficiently exert the nitrogen nutrition potential of crop itself and carry out the genetic improvement25 varieties of Manihot esculenta Crantz are selected as the research materials.The nitrogen efficiency of these 25 materials are classified in accordance with each material's yield and relative nitrogen accumulation through carrying out 2-year field experiment.Select the representative variety from both the high nitrogen efficiency varieties and low nitrogen efficiency varieties.On that basis,the high nitrogen efficiency mechanism of Manihot esculenta Crantz is further analyzed from the perspective of nitrogen absorption and utilization.The analysis of absorption is mainly carried out from the perspective of nitrogen accumulation characteristics,root morphology difference,root architecture and nitrate nitrogen absorption kinetics.The illustration of the utilization is implemented from the perspective of dry matter accumulation characteristic,photosynthetic characteristics and nitrogen metabolism assimilation enzyme.Finally the genetic expression of Manihot esculenta Crantz shoot under two factors(variety and disposition)is measured through adopting the RNA-Seq technology.The biological function and metabolic pathways of these differential genes are delved into on the basis of the biological information.The possible molecular pathways of high nitrogen efficiency genotype in the course of absorption and utilization of nitrogen element is acquired.The research conclusion is specifically acquired as follow:].Nitrogen Efficiency Evaluation of cassava.The nitrogen absorption(nitrogen accumulation)and nitrogen utilization efficiency of 25 selected Manihot esculenta Crantz varieties are significantly different from the perspective of variety,nitrogen disposition and interaction.Hence the variety with high nitrogen efficiency can be selected.The overall Manihot esculenta Crantz varieties are classified into four categories in accordance with index of the low nitrogen disposition yield and relative nitrogen accumulation(low nitrogen/high nitrogen).Compare the two-year results after the classification,and select the variety with stable yield trait as the candidate variety.Eventually the SC 10 is selected as the high nitrogen efficiency variety,and SC205 is selected as the low nitrogen efficiency variety.As the path analysis result indicates,the absorption efficiency and nitrogen utilization efficiency of Manihot esculenta Crantz positively contribute to the increase of dry weight of the whole plant.Additionally,as the absorption rate raises,the contribution rate increases.It is demonstrated that in the dry matter growing course,the absorption efficiency of nitrogen element exerts larger influence than the utilization efficiency of nitrogen element.2.Mechanism of Different Nitrogen Absorption of cassava with Different Nitrogen Efficiency(1)The high nitrogen efficiency and low nitrogen efficiency cassava are differents from each other in the nitrogen accumulation of each cultivation period.Commonly the accumulation of SC10 in each period is higher than that of SC205.The periodical nitrogen accumulations indicate that,the nitrogen element accumulations of SC 10 in the period between seedling and formative periods and between formative and swelling periods(0-80 days after the seedlings emerge)are remarkably higher than that of SC205.However,in the period between formative to swelling periods(80-160 days after seedlings emerge),these two types of Manihot esculenta Crantz are not significantly different in the accumulation of nitrogen.Under the low nitrogen disposition,these two types of Manihot esculenta Crantz are not significantly different in the accumulation in the period between swelling to mature periods(160-250 days after seedling emerge).All these data indicate that these two types of Manihot esculenta Crantz are different in nitrogen accumulation before the formative period and are less different after the formative period(2)In the seedling stage,the total root length,root superficial area and root volume of high nitrogen efficiency variety SC 10 are basically higher than those of low nitrogen efficiency variety SC205.However,the fine root ratios of two types are basically not remarkably different.As the relevant analysis indicates,the nitrogen absorption of the entire plant of Manihot esculenta Crantz is significantly positively correlated with the total root length nitrogen absorption and the root unit length nitrogen absorption of Manihot esculenta Crantz.The further analysis indicates that the nitrogen absorption of root unit length contributes more than that of total root length(3)It is acquirable through the root canal experiment that,during the whole cultivation stages,the root length density of high nitrogen efficiency variety SC 10 n the superficial layer(35cm of soil depth),deep layer(65cm of soil depth)is higher than that of low nitrogen efficiency variety SC205.As the observation result through the casement window approves the root of high nitrogen efficiency variety SC10 is much deeper and higher distributed in the deep layer soil than that of low nitrogen efficiency variety SC205.The root system of low nitrogen efficiency variety SC205 is basically concentrated in the superficial layer of soil(4)According to the NO3 absorption kinetics experiment towards root system under two-week low nitrogen disposition,high nitrogen efficiency Manihot esculenta Crantz has lower Km value and Vm value whereas the low nitrogen efficiency Manihot esculenta Crantz has higher Km value and Vm value,which indicates that the high nitrogen efficiency Manihot esculenta Crantz is more adaptable in the external environment with less nitrogen.3.Mechanism of Different Nitrogen Utilization of Manihot esculenta Crantz with Different Nitrogen Efficiency(1)The dry weight of high nitrogen efficiency Manihot esculenta Crantz during the whole cultivation stages is significantly higher than that of low nitrogen efficiency Manihot esculenta Crantz under the same nitrogen disposition.The synthetic intensity data of dry matter indicates that this intensity reaches the highest in the period from formative period to the swelling period(80-160 days after seedlings emerge).The synthetic intensity of dry matter of high nitrogen efficiency variety SC 10 among the entire cultivation periods is higher than that of low nitrogen efficiency variety SC205.Hence it is demonstrated that the SC10 is better than SC205 in the synthetic of dry matter.(2)The high nitrogen efficiency variety SC 10 has larger LAI(leaf area index)in each cultivation stages.However,in view of the Pn value(net photosynthetic rate),these two types are not significantly different.SCI 0's Gs(stomatal conductance),Ci(intercellular carbon dioxide)and Tm(transpiration rate)are either higher or lower than those of SC205.For Fv/Fm and Y(?),high nitrogen efficiency variety SC 10 is higher than low nitrogen efficiency variety SC205.As the relevant analysis indicates,the LAI has always been significantly positively correlated with dry weight among the entire cultivation periods,whereas the Pn value is merely significantly positively correlated with dry weight in the formative period of root tuber.As the path analysis indicates,LAI exerts larger contribution on the dry weight increase than Pn value.(3)Different varieties are significantly different in NP,GS,GOGAT and GDH of leaf.The high nitrogen efficiency variety is higher than low nitrogen efficiency variety,which indicates that the high nitrogen efficiency variety has higher N03 absorption rate.The relevant and path analysis indicate that,among the relations between Manihot esculenta Crantz and four enzymes,the NR enzyme of SC10 contributes the most to the Nitrogen absorption.The GOGAT of SC205 exerts greatest contribution to the nitrogen absorption.This result demonstrates that cassava in different types have different enzymes for disposing the nitrogen absorption.4.Different Expressed Genes on Leaves of cassava with Different Nitrogen EfficiencyThe transcriptomic information of two types and two disposed leaves is acquired through adopting the RNA-Seq technology.Through genetic assembling and splicing,SC10N1,SC10N0,SC205N1 and SC205N0 have respective 27096,26945,27598 and 24928 genetic expressions.The differential expressions of SC 10 and SC205 under NO disposition are analyzed through adopting the DGE methods,and accordingly 68 and 1307 differential expressions respectively for SC10 and SC205 are acquired,which indicates that the SC 10 is less affected by the NO disposition.In view of the Go analysis,the up-regulated genes of SC205 are significantly concentrated in the wake of oxidation-reduction process.The down-regulated genes are concentrated in lipid metabolism and photosynthetic system,which demonstrates that SC205 photosystem is greatly damaged.In view of the KEGG enrichment analysis,the up-regulated genes of SC 10 under the NO disposition are enriched in the flavonoid metabolic pathways.Such pathway is bound by the pigment and antioxidant activity However,the down-regulated genes of SC205 under the NO disposition are enriched in photosynthesis and antenna proteins,further indicating that the photosystem of SC205 is damaged. |
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