Root Growth Patterns in Relation to Nitrogen Availability

氮是植物需要量最大的矿物元素，其有效性在很大程度上决定了自然和栽培生态系统的生产力。植物可获得的氮的两种矿物形式是铵和硝。在野外条件下，由于方法的限制，人们对铵和硝作为氮源的相对重要性知之甚少。氮没有长寿命的放射性同位素。使用稳定同位素15n（测量植物从土壤吸收的最常用方法）有很大的缺点。建议的研究将开发利用甲胺（铵的化学类似物）和氯酸盐（硝酸盐的化学类似物）研究植物氮吸收的新领域方法。这些类似物有几个优点。它们在土壤中不易代谢。它们可以在低浓度下使用，因为它们具有长寿命的放射性形式，14c -甲胺和36cl -氯酸盐。此外，使用放射性形式可以将铵从硝酸盐吸收中分离出来。目的是设计一种程序，只使用少量的放射性化合物，并确保几乎没有放射性物质留在现场。利用这些技术进行的田间试验将了解铵和硝可利用性的季节和空间变化。番茄根系在土壤中的分布应该表明根系是否发育特殊的分支模式以优化铵态氮或硝态氮的吸收。番茄突变体对铵态或硝态氮的吸收能力下降，或根系分枝模式不寻常。这些突变体与普通番茄氮素积累的差异应反映出植物生理机制和根系形态对土壤铵态氮吸收的相对重要性。这项研究汇集了创新的技术和独特的遗传物质，以检查氮获取在现实条件下。这一信息将促进品种和农业实践的发展，提高氮肥的利用效率。由于氮肥的生产消耗了现代农业总能量投入的1/3到1/2，提高氮肥效率将大大降低农业的能量需求。

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.