Study Guide:Barnes; CH 19


Concept: Nutrient Cycling


6 macronutrients: N, Ca, P, K, Mg, S

micronutrients: Fe, Zn, Bo, Mn, Cu, NiÖ

essential for plant growth


1.  What nutrients are most commonly limiting in what kinds of ecosystems?


N is most commonly limiting in boreal, temperate and some tropical forests: only certain organisms can fix N.  The atmosphere is mostly N; why is N ever limiting?  N2 gas is not available to plants. 


P is most commonly limiting in wet tropical forests.  High rainfall, high temperature, and old soils mean that most of the available nutrients have already been weathered.  Ultisols, Oxisols


2.  Describe three sources of nutrients to forest ecosystems.  Which nutrients are supplied by each source?


a.  Atmospheric deposition (wet and dry):  S: pollution from burning of fossil fuels containing S (SO4)

N in NOx: automobile emissions. 


b.  N fixation


c.  Mineral weathering:  all the ones in rocks: Ca, Mg, K, (major in rocks) S, P (small amounts)

3.  Compare wet and dry deposition (differences in particle size, distance that particles are transported, etc.)

Larger particles come down in wet deposition; only small particles are transported a long way in the air. 


4.  How do legumes add N to soil?


Only bacteria can do it.  Plants form associations with these bacteria (rhizobium for legumes, Frankia for alder, myrica); the bacteria fix N, the plant supplies the bacterium with energy in the form of carbohydrate.


5.  Describe the 2 mechanisms by which nutrients move towards root surfaces.


Diffusion: ions move from high to low concentration by random movement.

Mass flow:  water moves towards the root driven by transpiration


6. Explain the relationship between mycorrhizae and plants.


Symbiosis between a fungus and a plant.  It canít fix N.  The fungus can explore the soil and take up nutrients.  The plant provides C to the fungus.


7.  What is nutrient-use-efficiency?  How does it vary with climate?


Most common definition: Crop yield/fertilizer applied. 

In your textbook: Leaf production/leaf nutrient content.

The graphs illustrate N limitation, except in tropical forests, where P seems to control litter production.



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