氮是一种重要的营养成分，它是蛋白质和核酸的结构元素的组成，并对酶的活性有重要作用（高，2011）。因此，植物需要比其他营养物质更多的氮，但氮需要更多的能源获取和利用（Gutschick，1981）。豆类可以作为生物固氮细菌由于其共生菌。豆科植物产生高含量的土壤，如此看来，豆类能增加作物生产低含量的环境（辛克莱& vadez，2002）。然而，尽管生物固氮，在大多数非热带生态系统植物生长是有限的氮含量（Vitousek & Howarth，1991）。因此，对土壤n-deficit豆类优势可能无法像过去想象中的大。
方法，如相对生长率（RGR），净同化率（NAR），叶面积比（LAR）和比叶面积（SLA），用于分析植物生长条件。RGR意味着工厂质量每重量每时间的增加，使用分析增长率的内在变化。NAR的变化最为依赖的光合速率变化（该公司，1989）。SLA是每单位叶重和叶面积大，单位重量意味着植物叶面积（poorter & Van der Werf，1998）。
在生长对氮反应缺乏种间差异的研究，本研究旨在探讨在玉米的变化（Zea mays），大麦（Hordeum vulgare）、豌豆（Pisum sativum）不同含氮量的环境下。新梢生长、叶面积、根系生长、生长速率的计算来衡量NAR，在两个氮水平的可用性的植物生长的LAR和SLA。
Growth responses to nutrients vary greatly in different plant species, which may lead to species distribution by fertility gradients (Taub, 2002). For example, relative growth rates (RGR) of different plant species increased in the high-nutrient treatment by varying coefficient of variance; species with higher RGR in fertile conditions had their RGR most depressed in the low-nutrient treatment (Shipley & Keddy, 1988; Meziane & Shipley, 1999). Growth responses to nitrogen are also different among different plant species. When low nitrogen is available, C4 species, including maize, had higher radiation use efficiency than C3 species (Sinclair & Vadez, 2002). Despite the significance of interspecific variations in ecology, there are relatively few studies exploring the variation between species in growth responses to nutrients.
Nitrogen is an important nutrient content, which is the composition of protein and structural element of nucleic acids, and plays a vital role in enzymatic activity (Marschner, 2011). Therefore, plants require more nitrogen than other nutrients, but nitrogen needs more energy to obtain and utilize (Gutschick, 1981). Legumes can be regarded as biological nitrogen fixers owing to its symbiotic bacteria. Legumes generate high N-content soil, so it seems that legumes are able to increase crop production in low N-content environments (Sinclair & Vadez, 2002). However, despite biological N fixation, plant growth in most non-tropical ecosystems is limited to N content (Vitousek & Howarth, 1991). Therefore, advantages of legumes on N-deficit soils may be not as huge as past thought.
Methods, like Relative Growth Rates (RGR), Net Assimilation Rate (NAR), Leaf Area Ratio (LAR) and Specific Leaf Area (SLA), are used to analyze the growth condition of plants. RGR means the increase in plant mass per weight per time, using to analyze the inherent variation in growth rate. NAR variation depends most on variation in the photosynthesis rate (Konings, 1989). SLA is leaf area per unit leaf weight, and LAR means leaf area per unit plant weight (Poorter & Van der Werf, 1998).
Lack of studies on interspecific variation in growth responses to nitrogen, this research aims to study the variation among corn (Zea mays), barley (Hordeum vulgare) and field peas (Pisum sativum) under different N-content environments. Shoot growth, leaf area, root growth, RGR, NAR, LAR and SLA are calculated to measure the plant growth at two levels of nitrogen availability.