BIOL 2335 Lecture Notes - Lecture 22: Nitrifying Bacteria, Nitrogen Fixation, Rhizobia
April 13, 2018
Biology 2335
Biogeochemistry I
Cycles of Matter
o Matter is recycled within ecosystem and between different ecosystems
▪ Law of Conservation of Mass
o Recycling in biosphere is done through biogeochemical cycles
Types of Biogeochemical Cycles
o Water Cycle
▪ Water is found in bodies of water (oceans, lake, ground water) and in atmosphere
(clouds and rain)
▪ Evaporation – change from liquid form to gas form at surface
▪ Transpiration – evaporation through levels of plants
▪ Condensation – change from gas to liquid (what clouds are)
▪ Precipitation – form of rain or snow where water falls back to earth
▪ Runoff – can go into water sources
• Seepage runoff going to ground water
• Root uptake transpiration or ocean
o Nutrient Cycle
▪ Carbon cycle
• Carbon dioxide in air photosynthesis glucose and then feeding
• Some carbon goes into food chain and other goes into deposition
o Deposition – when organisms die; can become fossil fuels over
time
• Respiration – carbon dioxide is given back to environment by breathing
• Volcanic activity can lead to more CO2
• CO2 in ocean will dissolve into water used by photosynthesis CO2
given off by organisms
▪ Nitrogen cycle
• Nitrogen is used to make proteins
• Nitrogen fixation ~ some bacteria turn N2 into useable forms of NO3-
and NO2-
o cyanobacteria
• N2 (atmospheric nitrogen) has to be converted into nitrates and nitrites
in order to be useable
• Denitrification ~ some bacteria convert nitrates into N2
▪ Phosphorous cycle
• Phosphorous is needed by living things to form DNA/ RNA
o Phosphorous groups
• Phosphorous does not enter atmosphere like C, O and N
o In living things or old rocks
• Phosphorous in water phytoplankton food chain sediments
land producers organisms decomposers
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Questions
Which of these factors are involved in nutrient cycles?
o Microbes
o Atmosphere
o Soil
o Volcanos
o Lakes
o NOT Chuck Norris
Which of these factors are important in carbon cycle?
o Decomposition
o Volcanic activity
o NOT Fixation by bacterial species
o Photosynthesis
Where do we commonly find nitrifying bacteria?
o In the soil
o NOT In Chuck Norris
o On the roots of plants
o In lakes and rivers
Energy declines while materials do not (nitrogen is still on the planet, just in different form)
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April 16, 2018
Some higher plants (clovers and soybeans) have formed facultative mutualism with bacteria called
Rhizobia, which infect root systems, causing nodules to form in which they live. Rhizobia can provide up
to 40 to 70% of soybean nitrogen. Humans now add synthetic nitrogen sources (fertilizers) to crops in
order to produce higher yields.
Based on your understanding of mutualisms, predict how mutualism might change when fertilizer is
added. Design an experiment to test whether synthetic fertilizer alters plant bacteria interactions. Which
components of Nitrogen cycle are altered?
Mutualisms – Although the Rhizobia were once able to provide nitrogen for the plants, they may
not be providing nearly as much nitrogen to the crops as the fertilizer. Since the plants are now
given nitrogen (not sure how much but if it is large amount), then the bacteria are now more like
parasites to the plants. They now take resources from the plants with no benefit to plants.
o Energy of the plants is not focused towards maintain mutualism mutualism would cost
more for the plants and they would not benefit as much
o With fertilizer - No mutualism
o Without fertilizer - Mutualism
Experiment – add nitrogen to the soil adding nitrogen should show less dependence on the
bacteria (plant energy is not focused on maintain mutualism)
o Nodules will begin to disappear on the roots over time
o Measure biomass of plants in soil without fertilizer (mutualism present), soil with
fertilizer (mutualism not present biomass should still be larger)
Nitrogen Cycle atmospheric nitrogen ends up building up in air if plants get rid of bacteria
o If bacteria continue to stay on plants’ roots, atmospheric nitrogen can still be converted
into usable nitrogen, but the plants will no longer need the nitrogen. Instead, nitrogen
may become very abundant in the soil, making it hard for other plants (that do not need
nitrogen at high levels) to grow in the environment
o Inorganic nitrogen (fertilizer) is increasing while atmospheric nitrogen fixation declines
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Document Summary
Cycles of matter: matter is recycled within ecosystem and between different ecosystems, law of conservation of mass, recycling in biosphere is done through biogeochemical cycles. In living things or old rocks: phosphorous in water phytoplankton food chain sediments land producers organisms decomposers. Which of these factors are involved in nutrient cycles: microbes, atmosphere, soil, volcanos, lakes, not chuck norris. Which of these factors are important in carbon cycle: decomposition, volcanic activity, not fixation by bacterial species, photosynthesis. In the soil: not in chuck norris, on the roots of plants. Energy declines while materials do not (nitrogen is still on the planet, just in different form) Some higher plants (clovers and soybeans) have formed facultative mutualism with bacteria called. Rhizobia, which infect root systems, causing nodules to form in which they live. Rhizobia can provide up to 40 to 70% of soybean nitrogen. Humans now add synthetic nitrogen sources (fertilizers) to crops in order to produce higher yields.
