土壤缺氮是造成我国黄土高原冷凉地区农业低产的主要原因.为了筛选耐低氮苦荞基因型及适宜鉴定指标,采用苗期水培方式,测定9个不同基因型苦荞在不同氮水平下的农艺性状、生理特性及植株氮素利用等指标,采用隶属函数法计算各指标耐低氮指数,通过主成分分析与聚类分析评价各基因型苦荞综合耐低氮能力.结果表明,低氮胁迫下,苦荞地上部生长受抑制程度大于根系,株高、茎粗、叶面积、地上部干重、根系体积、根系表面积及根系平均直径均呈下降趋势,主根长和根冠比呈上升趋势;根系活力、根系硝酸还原酶(NR)活性及可溶性蛋白含量有所下降,而根系超氧化物歧化酶(SOD)、过氧化物酶(POD)活性、丙二醛(MDA)、可溶性糖及游离脯氨酸含量有所升高;叶片叶绿素含量、Fm和Fv/Fm降低,而Fo升高;植株全氮含量及氮积累量降低,而由于植株氮积累量降幅明显大于生物量降幅,导致氮利用效率显著升高.将25个单项指标转化为4个相互独立的综合指标(累计贡献率达87.44%),并将9个苦荞基因型划分为耐低氮型、中间型和不耐低氮型.为了预测苦荞基因型的耐低氮能力,将D值作因变量,各指标耐低氮指数作自变量进行逐步回归分析,建立最优回归方程,筛选出株高、茎粗、叶面积、根冠比、叶绿素含量、Fm、根系超氧化物歧化酶(SOD)活性及氮利用效率8项对苦荞耐低氮能力有显著影响的指标,并且9个苦荞基因型的苗期耐低氮能力预测值Y与D值显著相关(R2=0.998,P<0.01),表明这8个指标可用于耐低氮苦荞基因型的快速鉴定.%Nitrogen (N) deficiency is a major problem for agricultural production in the cold area of Loess Plateau. In this study, multiple indices of seedlings, including agronomic traits, physiological characteristics, and N utilization parameters, were meas-ured in a hydroponics experiment with nine F. tararicum genotypes. The low-N tolerance was assessed by calculating subordinate function values, and making the comprehensive evaluation after principal component and clustering analyses. Under low-N stress, the restraint degree was greater for shoots than for roots. Compared with normal-N supply, low-N stress resulted in decreases of plant height, stem diameter, leaf area, shoot dry weight, root average diameter, root volume and root surface area and increases of main root length and root-to-shoot ratio. In addition, the root activity, nitrate reductase (NR) activity and soluble protein content decreased under low-N stress, whereas the activities of superoxide dismutase (SOD) and peroxidase (POD) as well as the contents of malonaldehyde (MDA), soluble sugar and free proline increased. The photosynthesis-related indices also changed under low-N stress, showing the decreases of leaf chlorophyll content, Fm and Fv/Fm and the increase of Fo. The plant N content and plant N accumulation decreased under low-N condition, however, the plant N utilization efficiency showed obvious increase, owing to the greater decline of N accumulation than that of plant biomass. The 25 single indices were converted into four independent com-prehensive 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.
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