Questions on nitrogen and phosphorus. (updated 3/30/14)
1. Why do we (and all biota) need phosphorus?
2. In what form(s) do plants obtain phosphorus?
3. What is the relationship between soil pH and phosphorus availability?
4. Why is phosphorus limiting in many areas of the tropics, but not in most
temperate zone ecosystems?
5. Why is phosphorus limiting in many freshwater ecosystems?
(why doesn’t it leak out of the soil?)
6. For the nitrogen cycle:
a) What's N fixation? Who does it, and what's the benefit?
Why, if this is so beneficial, don't more plant-microbe interactions do this?
b) What's the specific term for nitrogen mineralization?
c) What controls ammonia volatilization?
d) What forms of nitrogen can plants use (take up from the soil or from mycorrhizae)?
e) What's nitrification? Who does it? Under what environmental conditions will
it occur? What are the benefits to the organisms that do this?
f) What's denitrification? Who does it? What's required for this to occur?
What are the benefits to the organisms that do this?
g) How do plant activities contribute to nitrogen limitation? (name three).
h) What forms of nitrogen are volatile (gaseous)?
i) What's the most mobile, dissolved form of nitrogen (what form is most likely to leach from
soils)?
7. Why should conservation biologists care about the amounts and availability of nitrogen?
Questions from textbook, chpt 9 (some duplication with above, but that’s ok):
1.What are the relative magnitudes of atmospheric inputs and mineralization from dead organic
matter in supplying the annual nitrogen uptake by vegetation?
2. If Earth is bathed in di-nitrogen gas, why is the productivity of so many ecosystems limited
by availability of nitrogen? What is biological nitrogen fixation? What factors influence the
times and places where it occurs?
3. What determines the balance between nitrogen mineralization and nitrogen immobilization in
soils? (why does the microbe ‘throw away’ the nitrogen as ammonium?)
4. What factors determine the balance between plant uptake and microbial uptake of dissolved
organic and inorganic nitrogen in soils?
8. How do ammonium and nitrate differ in mobility in the soil? Why? How does this influence
plant uptake and susceptibility to leaching loss?
9. What is denitrification and what regulates it? What are the gases that can be produced, and
what are their roles in the atmosphere?
10. What is the main mechanism by which phosphorus enters ecosystems?
11. What factors control availability of phosphorus for plant uptake? Why is phosphorus
availability low in many tropical soils?
12. Why are mycorrhizae so important for plant acquisition of phosphorus?
13. What is the main pathway of phosphorus loss from terrestrial ecosystems?