This paper is to explore the effects of regulation of exogenous nitrogen on early root external morphology and internal structure of alfalfa.In order to simulate soil nutrient that could be absorbed by plants,the study was based on two nitrogen forms (nitrate nitrogen and ammonium nitrogen) and five nitrogen levels (0,105,210,315,420 mg · L-1).‘ Gannong No.3 ’ alfalfa was used as the experimental material by using sand culture supplied with different nutrient solutions,and observation of paraffin section and the photomicrography of roots.The results showed that under each level of two kinds of nitrogen forms,the root biomass,length,surface area and volume,average diameter were significantly higher than that of controls (P ＜0.05).With the levels of nitrogen increase,each root indexes were increased at the beginning and then decreased.When two kinks of nitrogen forms were 210 mg · L-1,the root growth and morphological indexes were maximum,and NH4+-N treatments were better than NO3--N.Root conduction tissue anatomy also showed the same trend as root morphology.When NH4+-N treatment was 210 mg · L-1,the root anatomy of conducting tissue (vascular area,xylem area,phloem area and the number of catheter) showed the best performance.The result showed that NH4+-N 210 mg · L-1 level can effectively promote roots outside morphogenesis,improve internal conducting tissue structure.%为探究外源氮调控对紫花苜蓿(Medicago sativaL.)生长早期根系外部形态及内部结构的影响,本研究模拟自然条件下土壤中可供植物吸收利用的不同浓度水平(0,105,210,315,420mg·L1)的2种氮素形态(NO3--N,NH+-N),以‘甘农3号’紫花苜蓿为材料,经营养液砂培,采用石蜡切片技术和根系扫描系统,展开试验研究.结果表明:2种氮形态各水平处理下根系生物量、总长度、表面积、体积、平均直径显著高于对照(P＜0.05),根系各指标均随氮素水平的增加呈先上升后下降的趋势,并在210 mg·L-1处理下达到最大值,NHg-N处理好于NO3-N.根系输导组织解剖结构也表现为相同的变化趋势,在NH4+-N 210 mg·L-1时根系维管束面积、木质部面积、韧皮部面积、导管数达到最大值.由此可见,210 mg·L1水平NH4+-N可有效促进其根系外部形态建成及改善其内部输导组织结构.
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