| environ. |
organic nitrogen Essential nutrient of the food supply of plants and the diets of animals. Animals obtain it in nitrogen-containing compounds, particularly aminoacids. Although the atmosphere is nearly 80% gaseous nitrogen, very few organisms have the ability to use it in this form. The higher plants normally obtain it from the soil after microorganisms have converted the nitrogen into ammonia or nitrates, which they can then absorb. This conversion of nitrogen, known as nitrogen fixation, is essential for the formation of amino acids which, in turn, are the building blocks of proteins (动植物食品供给的基本养分。动物获取含氮化合物，特别氨基酸。虽然空气含有接近80%的气体氮，但很少有生物有能力以此形式使用它。通常在微生物已将氮转化成氨水或硝酸盐后，高等植物从土壤中获得它并能吸收。氮的这种转换，称为固氮，对形成氨基酸即蛋白质的构件，起着至关重要的作用。) |
