Root Growth Patterns in Relation to Nitrogen Availability

氮是植物生长所需的矿物元素， 最大的数量和它的可用性决定了一个大的 扩大自然和人工生产力 生态系统 氮的两种矿物形式， 植物是铵和硝酸盐。 关于这一点，我们知之甚少。 铵态氮和硝酸盐氮的相对重要性 在实地条件下，部分原因是 局限性。 氮没有长寿命的放射性同位素。 使用 稳定同位素15 N--最常用的测量方法 植物从土壤中吸收具有主要的缺点。 拟议的研究将开发新的实地方法， 研究植物氮吸收利用甲胺， 铵的化学类似物，和氯酸盐，一种用于 硝酸盐 这些类似物具有若干优点。 他们不是 容易在土壤中代谢。 可用于低 因为它们具有长寿命的放射性形式， 14 C-甲胺和36 Cl-氯酸盐。 此外，使用 放射性形式可以将铵与硝酸盐吸收分离。 我们的目标是设计一个程序，只使用小 大量的放射性化合物，并确保几乎没有 放射性物质留在现场。 使用这些技术的实地实验将获得 铵的可用性的季节和空间变化， 硝酸盐 番茄根系在土壤中的分布 应该表明根是否发展出特殊的分枝模式 以优化铵或硝酸盐的吸收。 番茄 吸收铵的能力减弱的突变体， 硝酸盐或不寻常的根分枝模式已被隔离。 这些突变体氮素积累的差异， 在正常番茄中，这应该反映出 植物生理机制和根系形态对铵或 从土壤中吸收硝酸盐。 这项研究汇集了创新技术， 独特的遗传物质来检查氮的获取， 现实条件。 这一信息将刺激 发展品种和农业实践， 氮肥利用率。 因为 生产氮肥的费用从1/3到1/2， 现代农业的总能量投入， 肥料效率将大大减少能源 农业的要求。

Nitrogen is the mineral element that plants require in greatest quantity and its availability determines to a large extent the productivity of both natural and cultivated ecosystems. The two mineral forms of nitrogen accessible to plants are ammonium and nitrate. Little is known abut the relative importance of ammonium and nitrate as nitrogen sources under field conditions, in part, because of the methodological limitations. Nitrogen has no long-lived radioisotope. Use of the stable isotope 15N-the most common approach for measuring plant absorption from soils-has major disadvantages. The proposed research shall develop new field methods for studying plant nitrogen absorption utilizing methylamine, a chemical analog for ammonium, and chlorate, a chemical analog for nitrate. These analogs have several advantages. They are not readily metabolized in the soil. They can be used at low concentrations because they have long-lived, radioactive forms, 14C-methylamine and 36Cl-chlorate. Moreover, use of the radioactive forms can separate ammonium from nitrate absorption. The objective is to design a procedure which uses only small amounts of radioactive compounds and ensures that virtually no radioactive material is left in the field. Field experiments using these techniques will access seasonal and spatial changes in the availability of ammonium and nitrate. The distribution of tomato roots through the soil should indicate whether roots develop special branching patterns to optimize the absorption of ammonium or nitrate. Tomato mutants that have diminished abilities to absorb ammonium or nitrate or unusual root branching patterns have been isolated. Differences among the nitrogen accumulation in these mutants and that in normal tomatoes should reflect the relative importance of plant physiological mechanisms and root morphology on ammonium or nitrate absorption from soils. This research brings together innovative techniques and unique genetic material to examine nitrogen acquisition under realistic conditions. This information should stimulate the development of cultivars and agricultural practices that increase the efficiency of nitrogen fertilizer use. Because the production of nitrogen fertilizer expends from 1/3 to 1/2 of the total energy inputs in modern agriculture, increased nitrogen fertilizer efficiency would dramatically reduce the energy requirements of agriculture.