Nitrogen & Phosphorus Cycles: Always Recycle! Part 2 - Crash Course Ecology #9

Introduction

• Organisms often struggle to access vital nutrients like nitrogen and phosphorus, which are abundant but not available in usable forms.

• Humans face similar challenges when needing resources that are plentiful but inaccessible.

Importance of Nitrogen and Phosphorus

• Elements cycle through Earth, with organisms requiring numerous elements to survive.

• Essential elements for life include:

  • Oxygen, Carbon, Hydrogen

  • Nitrogen (3%) and Phosphorus (1%) are vital for DNA, RNA, and proteins.

• Despite their small percentage in body composition, these elements are crucial.

Nitrogen Cycle

The Challenge of Nitrogen

• Nitrogen gas (N2) comprises 78% of the atmosphere but is found in a triple-bonded state, making it difficult for plants to use directly.

• Plants require different nitrogen forms: nitrates, nitrites, and ammonium.

Role of Nitrogen-Fixing Bacteria

• Nitrogen-fixing bacteria convert atmospheric N2 into usable forms (ammonia, then ammonium when mixed with water).

• Bacteria can be found in soil and water or symbiotically in legume root nodules (e.g., soybeans, clover).

• Enzyme Involvement:

  • Nitrogenase is vital for breaking nitrogen's triple bond; it's the only enzyme capable of this.

• Organic nitrogen enters food chains as animals consume plants and decomposers break down organic matter, releasing nitrogen back into the ecosystem.

The Decomposition and Denitrification Phases

• Organic nitrogen is eventually processed by denitrifying bacteria that convert nitrogen oxides back into N2, releasing it into the atmosphere.

• This process closes the nitrogen cycle, showcasing the collaboration between organisms and nature.

Phosphorus Cycle

Characteristics of Phosphorus

• Unlike nitrogen, phosphorus does not exist in the atmosphere; it is abundant in Earth's lithosphere through rocks, particularly sedimentary ones.

• Phosphorus is often locked in rock form until weathering and erosion dissolve phosphates into the water, making them available to plants.

Flow Through Ecosystems

Phosphates are rapidly absorbed by plants, which use them for growth and development. When animals eat these plants, they consume the phosphorus and incorporate it into their own bodies. After animals die or excrete waste, decomposers break down the organic matter, returning phosphorus to the soil where it can be used again by plants.

Phosphorus can stay in aquatic environments for extremely long periods, with some estimates suggesting it can exist there for up to 100,000 years before being utilized or transformed. Eventually, through geological processes, phosphorus is processed in such a way that it accumulates in sediments and contributes to sediment buildup. Over time, these sediments can harden and transform back into rock, completing the phosphorus

• Phosphorus cycle can involve long residence times in aquatic environments (up to 100,000 years).

• Eventually, phosphorus enters a decomposed state, reinforces sediment buildup, and becomes rock again.

Human Intervention in Nutrient Cycles

• Humans have developed synthetic fertilizers containing nitrogen and phosphorus to enhance food production.

• The impact of these fertilizers on ecosystems can be detrimental, leading to pollution and environmental degradation.

• The history of synthetic nitrogen and phosphorus usage in agriculture ties back to historical figures like Fritz Haber.

Conclusion

• Nitrogen and phosphorus are abundant yet limited in availability, creating a need for biological processes and human interventions.

• Understanding nutrient cycles is essential for evaluating human behavior and its ecological effects.