Lecture 10: Notes, etc.

Nutrient Cycling in Terrestrial Ecosystems

Elements necessary for life

C, H, O

  • We don’t consider these “nutrients” or “nutrient cycles”
  • They are closely connected with energy flows
  • (You will hear people talk about “carbon cycling” in an ecosystem, but C does not typically cycle the way nutrients do)
  • N and P: most commonly limiting to growth
  • The focus of most nutrient cycling resaerch
  • Also cause problems in downstream aquatic ecosystems if they are lost from terrestrial ecosystems

Macronutrients: Ca, K, Mg, S
Micronutrients: Fe, Mn, and others
“N fixation”: biological conversion of atmospheric N2 gas into biologically reactive forms of N: primarily NH3

  • This is an energy-consuming reaction. It requires ATP

Cyanobacteria = blue-green algae

  • N fixers in both aquatic and terrestrial ecosystems
  • Live in water column, or form films on surfaces, or in soils or sediments, or in decaying logs

In terrestrial systems

  • When “free-living” bacteria, in which case it is called non-symbiotic N fixation
  • Can be bacteria living in symbiosis with plant roots, requiring anaerobic conditions, called symbiotic N fixation

Root nodules of plants seal out the oxygen. The N-fixing bacteria live in these nodules in a mutualistic symbiosis with the plant.
Some N-Fixing Plants: Red alder, black locust, some herbaceous plants, legumes (i.e. beans and peanuts). We also wondered if rice was one: maybe this article will answer the question?

Please add more, and also notes on the readings on N saturation

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