| In order to screen the high-efficient genotypes and evaluation indexes for Fagopyrum tararicum to low nitrogen(N)stress and reveal the physiological response mechanism,we did the following study: From May to June in 2016,we researched the effects of low-N stress on the growth and development of 9 different F.tararicum cultivars;Based on this,we made a comprehensive evaluation of low nitrogen tolerance of F.tararicum and a screening of Low-N tolerance genotypes and suitable identifying indexes.From June to July in 2016,we made different degrees of low-N stress to low-N tolerant and N sensitive cultivars,and discussed the effects of low-N stress on growth and development;By this,we could reveal the response mechanism of F.tararicum to low-N stress.Between June and October in 2017,we studied the effects of N fertilizer on root growth and yield characteristics of F.tararicum by pot experiment;Then we deeply studied the physiological response mechanism and found the optimum N rate of F.tararicum.The main results are as follows:1.Under low-N stress,the restraint degree was greater for shoots than for roots.Compared with normal-N supply,the plant height,stem diameter,leaf area,shoot dry weight,root diameter,root volume and root area of F.tararicum were declined,root/shoot ratio and main root length were increased;Low-N stress could make leaf chlorophyll content,Fm Fv/Fm,root activity,nitrate reductase(NR)activity and soluble protein content significantly decreased,but make Fo,root superoxide dismutase(SOD)activity,peroxidase(POD)activity,malonaldehyde(MDA)content,soluble sugar content and free proline content increased;Plant N content and plant N uptake significantly decreased under low-N stress,while plant N utilization efficiency increased.The study has shown that the different F.tararicum cultivars to low-N stress were significantly different.Under low N environment,low-N tolerant cultivars had the obvious advantages of growth not only because the less influence of low N pressure to agronomic character?photosynthesis and root activity,but also because the higher root protective enzyme activity,osmotic adjustment substances contents,plant N contents and plant N uptake.2.The 25 single indices were converted into four independent comprehensive indices(accumulative contribution of 87.44%),with which the nine F.tararicum genotypes were classified into high-,medium-and low-tolerance groups.An optimal equation was also set up to evaluate and predict low-N tolerance of F.tararicum genotypes through stepwise regression with D value as the dependent variable and low-N tolerance index as the independent variable.Finally,eight indices,plant height,stem diameter,leaf area,root-shoot ratio,chlorophyll content,Fm,root activity and plant N utilization efficiency,were selected due to their significant impacts on low-N tolerance.These indices are recommended in quick by screening low-N tolerant F.tararicum genotypes.3.Under different N supply levels,there was a big difference between 3 F.tararicum cultivars on root growth,N using and yields;The optimum N application rate of the three cultivars was 100 mg/kg level.Compared to the normal-N treatment,N high-efficiency cultivars had more smaller range of changes on plant N content,plant N accumulation,and plant N utilization efficiency.All these advantages owed to the excellent root configuration and root physiological characteristics;And the advantages promoted the absorption and assimilation of nitrogen for roots,improved the efficiency of dry weight transport from root to shoot,and got more higher production. |
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