氮循环 · The Nitrogen Cycle
背景知识 / Building Background
氮是地球上生命的关键元素，是所有氨基酸的组成部分。在植物中，大部分氮用于叶绿素的合成——光合作用和植物生长的核心物质。鱼菜共生中的氮循环与传统农业中的氮循环本质上没有太大差异。
Nitrogen is crucial for life on Earth and is a component in all amino acids. In plants, much of the nitrogen is used in chlorophyll — essential for photosynthesis and plant growth. The nitrogen cycle in aquaponics isn't much different from traditional agriculture.
氮循环三态转化 / Three Forms of the Nitrogen Cycle
阶段一 / Stage 1: NH₃ 氨氮 · Ammonia
来源于鱼的排泄物和有机物分解。是氮循环的起始物质。
Found in both fish waste and decaying organic matter. Essential to the contribution of the Nitrogen Cycle. NH₃ is toxic to fish at high levels.
阶段二 / Stage 2: NO₂ 亚硝酸盐 · Nitrite
第一组硝化细菌将氨氮转化为亚硝酸盐。亚硝酸盐对鱼类有毒，需密切监测。理想水平：0 ppm。
Nitrifying bacteria (Group A) convert ammonia into nitrite — an essential form of nitrogen. Nitrite is toxic to fish and should be monitored closely. Ideal level: 0 ppm.
阶段三 / Stage 3: NO₃ 硝酸盐 · Nitrate
第二组硝化细菌将亚硝酸盐转化为硝酸盐。仅在高浓度（>160 ppm）时对鱼有毒。被植物吸收用于生长，从水中移除。
Nitrifying bacteria (Group B) convert nitrite into nitrate — the final step. Nitrate is primarily used for fertilizers because it is soluble. Only toxic to fish at high levels (>160 ppm). Plants absorb and remove nitrate from the water.
氮循环总览 / Cycle Overview
Fish Waste/Organic Matter → NH₃ Ammonia → (Bacteria A) → NO₂ Nitrite → (Bacteria B) → NO₃ Nitrate → Plant Uptake → Clean Water
硝化细菌关键环境 / Key Conditions for Nitrifying Bacteria
富含氧气 · 无紫外线光照 · 温暖温度 · 充足表面积
Rich in oxygen · No UV light · Warm temperatures · Sufficient surface area
讨论 / Discussion
大多数肥料由 N、P、K 构成——但这是植物所需的所有元素吗？还缺少哪些？
Most fertilizers contain N, P, K — but are these the only elements plants need? What else is essential?
元素周期表探索 · The Periodic Table of Elements
教学目标 / Objective
研究元素周期表，寻找 ECO-Cycle 和户外花园中出现的元素名称，搜索植物生长所需的重要元素。
Study the periodic table and search for elements found in the ECO-Cycle and outdoor garden. Identify essential elements for plant growth.
所需材料 / Materials
- 元素周期表 / Periodic Table of Elements
- 氮循环图表 / Nitrogen Cycle Chart
延展学习 / Swimming Deeper
选择一个元素深入研究：撰写关于该元素重要性的短文；探讨如果没有这个元素我们能否生存；研究其在自然界中的循环路径。
Adopt an element: write an essay about its importance; could we survive without it? Research its cycling in nature.
本模块覆盖的 NGSS 标准 / Covered NGSS Standards
- HS-LS1-6: Construct explanations for how carbon, hydrogen, and oxygen form larger molecules
- HS-LS2-3: Construct explanations for cycling of matter and flow of energy
- HS-LS2-5: Develop a model illustrating the role of photosynthesis in the carbon cycle
- HS-PS1-1: Use the periodic table to predict properties of elements