【作者】 李剑峰；

【导师】 孙吉雄； 安渊；

【作者基本信息】 甘肃农业大学 ， 草业科学， 2007， 硕士

【摘要】 紫花苜蓿为豆科苜蓿属多年生牧草,具有生长迅速、饲草产量高、蛋白质含量高、抗逆性强,适应范围广,适口性好等特点,素有“牧草之王”的美誉,在世界各地被广泛栽培利用。但要在占世界面积40%的酸性富铁土壤上种植推广苜蓿,就必须研究和解决该区域限制其生长发育的酸,铁胁迫问题。通常该方面的研究以实地酸壤栽培为主,模拟实际生产中遇到的多重胁迫环境,但无法具体的探究酸,铁胁迫各因子对植株的单独影响,因此无法确定对紫花苜蓿造成伤害的主要胁迫因素,难以就不同生产条件下的具体情况提出相应的对策。本论文通过分离典型南方酸性土壤中的铁胁迫和酸胁迫因子,对苜蓿幼苗进行不同pH值环境下的酸胁迫实验和两种酸度环境结合不同Fe²⁺浓度处理的铁胁迫实验,探讨紫花苜蓿对于各酸度的耐受极限、胁迫表现,以及在不同酸度下对Fe²⁺耐受差异和受害表现。并得到以下结论:1.紫花苜蓿幼苗在不同pH值环境条件下的生长表现有明显的差异,在环境pH值在5-6的区间内表现为生长受到促进。在pH值为5的环境下,紫花苜蓿出苗速度加快,出苗率增大,叶片新生速率加快,根瘤数目显著增加,生物量显著增加,生理指标亦优于对照（pH=7）的水平;说明单就环境酸度而言,pH值为5的弱酸环境最适于苜蓿的生长发育。2.pH=4的环境酸度是苜蓿幼苗能够耐受的酸度极限。在此酸度环境下,苜蓿植株虽表现出一定的酸害症状,但植株的根系活力,光能转化效率,以及生物量的积累尚能维持在与对照差异不大的水平上,可以维持正常生长。在撤除胁迫后酸害症状可逐渐消失,并恢复到较好的生长状态。当环境pH值低于该水平时,植株不能耐受。同时通过分析也表明,pH=4.5的酸度环境并未达到苜蓿酸的耐受极限,而这一pH水平也是大多数酸壤地区土壤的平均酸度,在这一酸度下进行Fe²⁺胁迫实验,既可以较好的模拟实际生产中的酸壤环境,又可以确保苜蓿幼苗不会因无法耐受环境酸度而过度的干扰Fe²⁺的胁迫或营养效应。3.酸环境结合Fe²⁺胁迫实验证明,苜蓿幼苗对Fe²⁺浓度的反应在pH=4.5的环境下比在pH=6的环境下更为敏感;在pH=4.5的环境下,10mg/kg的Fe²⁺施入量即表现出显著的营养作用,而在100mg/kg的处理浓度下达到耐受极限。在pH=6的环境下,50mg/kg的Fe²⁺处理表现出良好的营养作用,而在150mg/kg的浓度下达到耐受极限。4.紫花苜蓿幼苗在酸胁迫和Fe²⁺胁迫下有些生理或形态指标仅对单一的胁迫因子敏感。如出苗率、株高、新生叶片数目和叶绿素含量等指标变化仅对环境的酸度敏感;而根瘤数目、叶绿素荧光特性（Fv/Fm）（Fv/Fo）、和根系活力指标仅对Fe²⁺浓度变化敏感;也有一部分指标由两种胁迫因子共同作用,如地下生物量、植株存活率和质膜透性等指标在低Fe²⁺浓度下,酸胁迫的影响效果比较明显,随着Fe²⁺离子浓度的增大而酸胁迫的作用逐渐减弱。更多还原

【Abstract】 Alfalfa （Medicago sativa） is a kind of perennial forage grass of leguminosae, growth rapidly, yield is high and rich in protein content, the ability of tolerance are strongly, adaption broad, palatableness is good, usually be named "king of the foragegrass". Is widely cultivated in world. But if we want to promote it acidic and iron-rich soil which are 40% of whole area in world, we should face the stress factor that reduce yield of alfalfa in acid and iron-rich soil. Traditional research primarily use sour soil cultivation.Be in the very good simulation of real environment.But it’s unable to concretely inquired the effective of single stress factor on alfalfa respectively, therefore it’s unable to determine dominate factor causes the damage, and difficult to proposes the corresponding countermeasure and find the special details in the different regions.In this experiment, separation acid and iron-rich soil to research the iron stress and acid stress respectively simulates solely forces of factor, carries on the single factor to the alfalfa seedling the different acidity to experimental two level of acidity environment combine different Fe²⁺ density. To discussion alfalfa regarding various limit for acidity tolerance, forces the performance, as well as and suffers injury the performance under the different acidity to the Fe²⁺ tolerance difference.Following is the conclusion:1.Alfalfas has the difference for the different acid treatment germination responded, between pH5-6 for the growth receives the promotion, under the pH=5 environment, germination be speed up, the new born rate of leaves are speed up, the nodule number and biomass remarkable increased, the physiological target basically is in surpasses the comparison （pH=7）; Explained the pH=5 environment most is suitable for the alfalfa germination and growth, have a difference with others results.2.pH=4 is the lowest acidity of alfalfa, in this environment, the alfalfa show the symptom causes by acid, but the difference of vigorous of roots , photosynthesis efficiency,the biomass accumulation comparison are not obviously,and may maintain the normal growth. After the removal forces of acid, the symptom in acid will be possible gradually to vanish, restores to the better growth condition. When the pH value is lower than this level, the plant couldn’t tolerant.3.The environment of pH4.5 not achieved the limit of alfalfa; this pH value also is the majority sour soil area average acidity. Fe²⁺ experiment in this pH value, then by better simulation objective sour soil environment, also may guarantee alfalfa living, without excessively disturbance the effect of Fe²⁺.Dual forces the experimental means that alfalfa more sensitive in pH4.5 to the Fe²⁺ than in pH6, executes in10mg/kg inputs displays the remarkable nutrition function; the durable limit is 100mg/kg treatment density.50mg/kg Fe²⁺ treatment displays the good nutrition function under pH6, and the limited is the 150mg/kg density4.The acid and the iron forces have own sensitive physiology or the shape target. such as the rate of germination, newborn leaves and leaf blade number and chlorophyll content main factor is the acidity; The nodule number, the chlorophyll fluorescence characteristic （Fv/Fm） （Fv/Fo）,and the root vigor is more sensitive to the Fe²⁺; some part of targets sensitive with two kind factors together, as under-ground biomass, plant survival rate and protoplasmic membrane penetrability under the low Fe²⁺ density, the function which the acidity forces quite is obvious, with the increases of Fe²⁺ concentration the relationship of acidity wreaked gradually.更多还原