Nutrient Cycles and Organism Adaptations

TOLERANCE

• Long exposure to toxins can cause organisms to evolve tolerance.

  • Example: Mangroves have developed salt tolerance.

  • Certain plants can tolerate high levels of toxic metals.

HYPERACCUMULATION

• Some plants can neutralize toxins by storing them in vacuoles.

  • Examples: Mangroves and metal hyperaccumulators.

  • This ability is utilized in bioremediation to remove pollutants from the environment.

ENERGY TRANSFER VS. NUTRIENT CYCLES

• Life requires a continuous input of new energy.

• Nutrients, in contrast, are cycled repeatedly within ecosystems.

NUTRIENT BUDGETS

• Nutrient cycles have budgets that include:

  • Input

  • Transformations

  • Output

• Nutrient cycles involve several compartments:

  1. Atmospheric gases

  2. Organic pool

  3. Available nutrients

  4. Rocks and soil

CARBON CYCLE

• Carbon is the backbone of life and forms key structural molecules.

  • Carbon dioxide (CO₂) is fixed from the atmosphere via the process of photosynthesis.

  • Carbon is released back into the atmosphere through respiration and decomposition.

  • Carbon can be stored long-term as biomass, such as in peat, coal, oil, and natural gas.

CARBON METHANE

• In low-oxygen conditions, organic matter decomposes slowly, producing carbon in the forms of CO₂ or CH₄ (methane).

  • Sources of Methane:

  • Bacteria

  • Fossil fuel combustion

  • Some flatulent autotrophs

CARBON ANTHROPOGENIC EFFECTS

• Human activities, such as the use of fossil fuels and changes in land cover, have led to a significant increase in atmospheric CO₂ levels.

NITROGEN CYCLE

• Nitrogen is essential for the formation of all proteins.

  • Limiting Factor: Often limits plant growth.

  • Plants can absorb nitrogen in the following forms:

  • Nitrate (NO₃⁻)

  • Ammonium (NH₄⁺)

  • Atmospheric nitrogen (N₂) is generally not directly usable by most organisms.

NITROGEN: FIXATION

• The atmosphere contains 78% nitrogen (N₂), which is very stable and unusable by most organisms.

• Nitrogen fixation is the conversion of atmospheric nitrogen into biologically usable forms, such as ammonium (NH₄⁺) or nitrate (NO₃⁻).

  • Nitrogen can be fixed through several mechanisms:

  • By bacteria (either free-living or in symbiosis with plants).

  • By lightning, through atmospheric oxidation.

  • Industrially, which has allowed agriculture to move beyond reliance on manure-based fertilization.

NITROGEN FIXATION BY LEGUMES

• Legume root nodules serve as hosts for Rhizobium and Bradyrhizobium bacteria.

• The process of nitrogen fixation is energy-intensive but provides advantages to plants in nitrogen-poor soils by supplying usable nitrogen.

PHOSPHORUS CYCLE

• Phosphorus is essential for ATP and other key biomolecules.

  • It often limits growth in aquatic systems, such as lakes.

  • Excess phosphorus can lead to eutrophication, resulting in harmful algal blooms and oxygen depletion.

  • Most phosphorus resides in marine sediments.

  • There is no atmospheric phosphorus cycle.

  • Phosphorus moves primarily from land to ocean sediments, cycling through various organisms along the way.

PHOSPHORUS FROM OCEAN

• Animals, especially birds, function as biovectors by transporting phosphorus across ecosystems.

• Migratory fish moving from ocean to freshwater also help transfer phosphorus back to terrestrial environments.

SULPHUR CYCLE

• Sulphur is essential for proteins and other biomolecules.

  • Volcanoes release sulphur gases into the atmosphere.

  • Some bacteria also produce sulphur as a byproduct of their metabolism.

SULPHUR: ACID RAIN

• 78% of global SO₂ emissions stem from human activities, including:

  • Burning fossil fuels

  • Smelting sulphide-rich ores

  • In the atmosphere, SO₂ converts into sulfuric acid, leading to acid rain.

SOIL

• Soil is the foundation of terrestrial ecosystems and consists of:

  • Minerals (rock fragments)

  • Nutrients

  • Organic matter

  • Water

  • Gases

  • Living organisms

• Soil provides physical support for plants and ecosystems.

• Hosts diverse life, including roots, bacteria, protists, invertebrates, and earthworms.

SOIL STRUCTURE

• Clay soils drain poorly due to the presence of fine particles.

• Sandy soils drain well but dry out quickly.

• Organic matter (humus) enhances soil tilth by improving water and nutrient retention.

NUTRIENTS

• Nutrients are essential substances that organisms require for health and growth.

• Principle of Limiting Factors: The growth of an organism or ecosystem is limited by the nutrient that is in the shortest supply, even when other nutrients are plentiful.

• Nutrients such as phosphorus and nitrogen are crucial for the growth of aquatic plants and algae.

  • When these nutrients are limited in the environment, they become limiting factors, meaning ecosystem productivity depends on their availability.

• Excess phosphorus and nitrogen entering aquatic ecosystems (often due to agricultural runoff, wastewater discharge, or other human actions) can cause nutrient enrichment or eutrophication.

  • This leads to excessive algal growth, resulting in harmful algal blooms that can deplete oxygen levels in water, adversely affecting aquatic life.

MACRONUTRIENTS

• Macronutrients are elements that organisms need in relatively large quantities.

  • Primary Macronutrients:

  • Carbon (C)

  • Oxygen (O)

  • Hydrogen (H)

  • These elements form the backbone of organic molecules such as carbohydrates, proteins, and lipids, and are typically abundant as they are derived from water, air (CO₂), and organic compounds.

  • Other macronutrients, often termed mineral nutrients, include:

  • Nitrogen (N)

  • Phosphorus (P)

  • Sulfur (S)

  • Calcium (Ca)

  • Magnesium (Mg)

  • Potassium (K)

  • These are vital for biological processes such as protein synthesis, energy transfer, enzyme function, and structural roles.

  • Among these, mineral nutrients are often limited in availability, particularly nitrogen and phosphorus, which can constrain plant growth in both terrestrial and aquatic ecosystems.

MICRONUTRIENTS

• Micronutrients are nutrients required in very small amounts, including:

  • Iron

  • Manganese

  • Boron

  • Zinc

  • Chlorine

  • Sodium

  • Copper

  • Nickel

  • Molybdenum

• Deficiencies in micronutrients can lead to health issues; for instance, low copper levels may cause physical issues like root or stem breakage.

IMPORTANCE

• Macronutrients are critical components of vital molecules, such as nitrogen's role in proteins and phosphorus in cellular membranes (phospholipids).

• Micronutrients, despite being required in small amounts, play crucial roles in biological functions; for example, iron is essential for hemoglobin.

TOXICITY

• Some essential micronutrients can exhibit toxicity at high concentrations.

  • Examples: Excessive nickel and copper can stunt growth.

  • Toxicity levels can vary depending on the organism, highlighting the importance of balance in nutrient availability and regulation.