章节大纲

  • 常规

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  • 氮循环

    Close-up of green bean pods growing on a climbing plant in a garden.

    What can bean plants do that most other plants can't?
    ::豆类植物能做什么? 其他植物不能做什么?

    No, they don't grow giant stalks to the clouds. Bean plants and other legumes (plants that have their seeds in pods) can use the nitrogen in the air to grow. It takes the help of special bacteria friends in the soil , and this relationship is unique to the legumes.
    ::豆类植物和其他豆类植物(其种子在豆类中的植物)可以使用空气中的氮来生长。这需要土壤中特殊的细菌朋友的帮助,而这种关系是豆类中独有的。

    The Nitrogen Cycle
    ::氮循环

    Like water and carbon, nitrogen is also repeatedly recycled through the . This process is called the nitrogen cycle . Nitrogen is one of the most common elements in living organisms . It is important for creating both proteins and nucleic acids , like . The air that we breathe is mostly nitrogen gas (N 2 ), but, unfortunately, animals and plants cannot use the nitrogen when it is a gas. In fact, plants often die from a lack of nitrogen even through they are surrounded by plenty of nitrogen gas. Nitrogen gas (N 2 ) has two nitrogen atoms connected by a very strong triple bond. Most plants and animals cannot use the nitrogen in nitrogen gas because they cannot break that triple bond.
    ::氮是活生物体中最常见的元素之一,对于产生蛋白质和核酸非常重要,例如。我们呼吸的空气主要是氮气(N2),但不幸的是,当氮气是气体时,动物和植物不能使用氮。事实上,植物往往因氮缺乏而死亡,即使它们周围有大量的氮气。氮气(N2)与两个氮原子相连,一个非常强的三联。大多数植物和动物无法在氮气中使用氮气,因为它们无法打破三联。

    In order for plants to make use of nitrogen, it must be transformed into molecules they can use. This can be accomplished several different ways ( Figure ).
    ::为使植物能够使用氮,必须将其转化为可以使用的分子。 这可以通过几种不同的方式实现(图 )。

    • Lightning: When lightning strikes, nitrogen gas is transformed into nitrate (NO 3 - ) that plants can use.
      ::闪电:当闪电袭击时,氮气转化为硝酸盐(NO3-),植物可以使用。
    • Nitrogen fixation : Special nitrogen-fixing bacteria can also transform nitrogen gas into useful forms. These bacteria live in the roots of plants in the pea family . They turn the nitrogen gas into ammonium (NH 4 + ) (a process called ammonification). In water environments, bacteria in the water can also fix nitrogen gas into ammonium. Ammonium can be used by aquatic plants as a source of nitrogen.
      ::氮固化:特殊的氮固化细菌也可以将氮气转化为有用的形式。这些细菌存在于豆类家庭植物的根部,它们将氮气转化为氮气(NH4+)(一个称为火化的过程)。在水环境中,水中的细菌也可以将氮气固定在氮气中。水生植物可以使用作为氮的来源。
    • Nitrogen also is released to the environment by decaying organisms or decaying wastes. These wastes release nitrogen in the form of ammonium.
      ::氮也通过衰变生物或衰变废物释放到环境中,这些废物以铵的形式释放氮。

    Ammonium in the soil can be turned into nitrate by a two-step process completed by two different types of bacteria. In the form of nitrate, nitrogen can be used by plants through the process of assimilation . It is then passed along to animals when they eat the plants.
    ::通过由两种不同类型的细菌完成的两步过程,土壤中的可以变成硝酸盐,用硝酸盐的形式,植物可以通过同化过程使用氮,然后在动物食用植物时将氮传给动物。

    Sending Nitrogen back to the Atmosphere
    ::将氮送回大气层

    Turning nitrate back into nitrogen gas, the process of denitrification , happens through the work of denitrifying bacteria. These bacteria often live in swamps and lakes. They take in the nitrate and release it back to the atmosphere as nitrogen gas.
    ::硝酸盐又变成氮气,即脱硝过程,通过脱硝细菌的工作发生,这些细菌往往生活在沼泽地和湖泊中,它们吸收硝酸盐,作为氮气释放到大气中。

    Just like the , human activities impact the nitrogen cycle. These human activities include the burning of fossil fuels , which release nitrogen oxide gasses into the atmosphere. Releasing nitrogen oxide back into the atmosphere leads to problems like acid rain .
    ::正如人类活动影响氮循环一样,人类活动也影响氮循环。这些人类活动包括燃烧化石燃料,这些燃料将氮氧化气体释放到大气中。 将氮氧化物释放回大气会导致酸雨等问题。

    Flowchart illustrating the nitrogen cycle, including processes like denitrification and assimilation.

    The nitrogen cycle includes assimilation, when plants absorb nitrogen; nitrogen-fixing bacteria that make the nitrogen available to plants in the form of nitrates; decomposers that transform nitrogen in dead organisms into ammonium; nitrifying bacteria that turn ammonium into nitrates; and denitrifying bacteria that turn nitrates into gaseous nitrogen.
    ::氮循环包括:植物吸收氮时的同化;以硝酸盐形式向植物提供氮的固氮细菌;将死亡生物中的氮转化为铵的分解器;将氨转化为硝酸盐的硝化细菌;将硝酸盐转化为气态氮的脱硝细菌。

    Summary
    ::摘要

    • Gaseous nitrogen is converted into forms that can be used by plants during the process of nitrogen fixation.
      ::气氮被转换成植物在固氮过程中可以使用的形态。
    • Denitrifying bacteria turn nitrate back into gaseous nitrogen.
      ::脱硝细菌将硝酸盐转化为气态氮。

    Review
    ::回顾

    1. How do living organisms use nitrogen?
      ::活生物体如何使用氮?
    2. What is nitrogen fixation? Describe how it happens.
      ::什么是固氮?描述它是如何发生的。
    3. How is nitrate in the soil converted back to nitrogen gas?
      ::土壤中的硝酸盐是如何转化为氮气的?
    4. How does acid rain form?
      ::酸雨是如何形成的?