Lecture 20 - Terminology

Ecosystem services

The direct and indirect benefits that ecosystems provide humans

Microbes as chemical engineers

Decompose organic matter, drive biogeochemical cycles, and perform bioremediation

Microbes as biological regulators

Control population dynamics

Microbes as ecosystem engineers

Physically modify environments

Climate regulation

Microbes regulate atmospheric CO₂ through fixation and respiration

Carbon fixation

Conversion of CO₂ into organic matter via photosynthesis

Respiration

Conversion of organic matter into CO₂

Bioremediation

Use of microbes to degrade pollutants

Contaminants degraded

Hydrocarbons, oil, heavy metals, pesticides, dyes

Water purification

Microbes filter contaminants in soil and water systems

Disease and pest regulation

Microbes stimulate plant defenses; Produce biopesticides; Target specific pests

Provisioning services

Products from ecosystems (food, water, fuel, pharmaceuticals)

Microbial cellulose

Environmentally friendly fiber

Supporting services

Processes that maintain ecosystems

Include (for supporting services)

Soil formation; Water cycling; Primary production; Nutrient cycling

Cultural services

Non-material benefits (aesthetic, spiritual, recreational, educational)

Biogeochemistry

Study of how chemical elements flow through living systems and the environment

Redfield ratio

C-N-P = 106-16-1 (average elemental ratio in ecosystems)

Organic molecules

Carbon-based molecules containing hydrogen

DNA/RNA

Genetic material made of sugar-phosphate backbone and nitrogen bases

Proteins

Made of amino acids with nitrogen; cysteine contains sulfur

Disulfide bonds

Bonds formed between cysteine residues

Phospholipids

Membrane components containing carbon and phosphate

Trace elements

Required in small amounts

EX trace elements

Iron (Fe)- Used in enzymes and cytochromes; Silica- Used in diatom shells; Cobalt-Used in vitamins (e.g., B12)

Liebig’s Law of the Minimum

Growth is limited by the nutrient in shortest supply

Limiting nutrient

The nutrient that restricts growth

Marine phytoplankton

Limited by nitrogen compounds

Freshwater phytoplankton

Limited by phosphorus compounds

Iron limitation

Can limit 25–50% of ocean productivity

Heterotroph limitation

Limited by organic carbon

Carbon fixation

CO₂ → organic carbon

Carbon respiration

Organic carbon → CO₂

Fast Carbon Cycle

Occurs over days–years; Driven by- Photosynthesis, Respiration

Slow Carbon Cycle

Occurs over millions of years; Involves rocks, ocean, and atmosphere; Calcium carbonate (CaCO₃)- Formed by marine organisms; Limestone formation- From deposited shells Fossil fuels- Formed from buried organic matter

Microbial Role

Responsible for ~50% of global carbon fixation; Drive carbon recycling

Anthropogenic Impact

Fossil fuel burning- Releases excess CO₂; Disrupts natural carbon balance

Dinitrogen gas (N₂)

Atmospheric nitrogen, not usable by most organisms

Nitrogen fixation

N₂ → NH₃ (ammonia)

Nitrification

NH₃ → NO₂⁻ → NO₃⁻

Denitrification

NO₃⁻ → N₂

Nitrogen fixation

Anaerobic

Nitrification

Aerobic

Denitrification

Anaerobic

Nitrogen Fixation

Converts nitrogen gas into usable forms

(nitrogen Fixation) Done by

Microbes; Lightning; Haber-Bosch process

Diazotrophs

Nitrogen-fixing organisms

Heterocysts

Specialized cells for nitrogen fixation

Temporal separation

Photosynthesis (day), N-fixation (night)

Leghemoglobin

Binds oxygen in root nodules

Ammonia oxidation

NH₃ → NO₂⁻

Nitrite oxidation

NO₂⁻ → NO₃⁻

Denitrification

Converts nitrate back to nitrogen gas; Produces N₂O (nitrous oxide); Occurs in low oxygen environments

Microbial Role in Nitrogen Cycle

Carry out all major steps; Provide biologically available nitrogen; Remove excess fertilizers

(Phosphorus Cycle) Orthophosphate

Bioavailable form of phosphorus

(Phosphorus Cycle) Weathering

Releases phosphorus from rocks

(Phosphorus Cycle) Phosphorus limitation

No microbial process creates new phosphorus

(Phosphorus Cycle) Microbial loop and viral shunt

Keep phosphorus cycling

Microbial Loop

Microbes recycle nutrients from organic matter; Keeps nutrients in ecosystem

Viral Shunt

Viruses lyse cells; Release nutrients back into environment

Lytic infection

Virus destroys host cell

Lysogenic infection

Virus integrates into host genome

Holistic Importance

Prevents nutrient loss; Maintains life on Earth

Anthropogenic nitrogen sources

Fertilizers, fossil fuels, agriculture

AI environmental cost

High energy use; CO₂ emissions; Resource extraction (e,g, lithium)